How to run more current through fuse? - Page 1
Forum section: electronics / projects

author: NotABagel
author_rank: Contributor
timestamp: October 10, 2015, 09:21:55 pm
content: So I'm building a vehicle to compete in the Power Racing Series -http://www.powerracingseries.org/, a race that restricts the current you can run via a slow car fuse. It is a well known fact that everyone runs more power than rated through their fuse. I want to be competitive this year, but I don't have any formal education in electronics. How can I run more amperage through a fuse? I was thinking dry ice to keep it from burning, and to allow the condensation to take load off the fuse. What sort of electronic trickery can I use to get more power through, besides pushing more current through in bursts.Here are the fuses that the race requires.36v = 40A Fuse (Digikey #F3089-ND)28.8v = 50A Fuse (Digikey #F3090-ND)24v = 60A Fuse (Digikey #F3091-ND)12v = 125A Fuse (Digikey #F1879-ND)Thanks for the help : )

author: 10101
author_rank: Contributor
timestamp: October 10, 2015, 09:37:48 pm
content: Liquid nitrogen would be even better !

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 10, 2015, 09:45:30 pm
content: What about a "smart" battery module that starts at a low voltage, but then switches to a higher voltage when given a command? Then have the inverter only send the command when the vehicle is going above a certain speed.And then there are the counterfeit fuses that blow well above their marked values. This could be a place where it's actually useful.

author: Kalvin
author_rank: Super Contributor
timestamp: October 10, 2015, 10:09:08 pm
content: I guess that the engineers at volkswagen would come up with something like this: Take two 12V batteries connected in parallel, and you will get 125A fuse. At the race the batteries will be connected in series giving you 24V @ 125A. When inspected, the batteries are connected again in parallel. Cheating? No, unless you get caught.

author: NotABagel
author_rank: Contributor
timestamp: October 10, 2015, 11:27:57 pm
content: Thanks for the suggestions, though here's the thing: I don't want to cheat. The rules for the race permit you to run what you can through the fuse they supply. If you change the voltage, that's not allowed. If you swap out the fuse you are given, that's also not allowed. If you can figure out how to trick the fuse, that's lauded. MIT said they used dithering to crank up the current, though I don't really know what they mean by that.

author: Monkeh
author_rank: Super Contributor
timestamp: October 10, 2015, 11:33:59 pm
content: Quote from: NotABagel on October 10, 2015, 11:27:57 pmQuoteSo yes, you want to cheat.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 11, 2015, 12:18:33 am
content: If you make a thermal model of the fuse (the time curves are provided in the datasheet), you can estimate the internal temperature of it, and control current flow so as to stay just below the melting threshold.Tim

author: retrolefty
author_rank: Super Contributor
timestamp: October 11, 2015, 12:32:59 am
content: Quote from: T3sl4co1l on October 11, 2015, 12:18:33 amfor this idea. It doesn't 'cheat', but rather uses technology knowledge and application to help run closer to a physical (rules) limitation.VW should hire you.

author: nctnico
author_rank: Super Contributor
timestamp: October 11, 2015, 12:42:32 am
content: I'd concentrate on getting as much power from that 1440W into the wheels by keeping the controller and motor in their optimum efficiency at racing speeds. Maybe look at aerodynamics as well to streamline the body.Fuses have datasheets with graphs showing which current they can endure without blowing. Have a 'turbo mode' on the motor controller to output short burts (when leaving corners for example) but stay within the fuse's limit. Speaking of corners... if the car has good handling you can go through corners quicker which means losing less power.

author: Someone
author_rank: Super Contributor
timestamp: October 11, 2015, 01:27:28 am
content: Quote from: nctnico on October 11, 2015, 12:42:32 amThis is where all the energy goes, trying to squeeze a few percent in other areas when there are factors of 2x or greater available in aerodynamics is a poor investment of time and effort.

author: fivefish
author_rank: Frequent Contributor
timestamp: October 11, 2015, 02:29:35 am
content: My experience is a fuse usually blows on that initial power surge (inrush current). If you can ramp up the load current slowly instead of applying it instantaneously, the fuse may be able to hander higher currents and not blow up instantly?

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: October 11, 2015, 03:21:28 am
content: just go for the this:Quote

author: Rerouter
author_rank: Super Contributor
timestamp: October 11, 2015, 03:54:40 am
content: Yeah i agree a themal model in a power controller could let you get some nice gains here and there, been sitting on the starting line for 15 minutes?, pull away at 2000W for a few seconds then have the controller back throttle as it starts to get too close to the curve limits,You reduced your throttle to 40% going around a corner for a few seconds?, pull away at 130% for a second and a half,The dithering stuff is another way you could abuse it a little, using PWM to get an average / RMS voltage of say 36V, but actually be supplying peaks of 48V (maximum unlicensed voltage), with trails of 24V to get higher tourque,

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 11, 2015, 04:04:01 am
content: Quote from: EvilGeniusSkis on October 11, 2015, 03:21:28 amStick a boost converter inside the battery module. Have it start at 36V and boost it as high as maybe 200V if the inverter calls for it. Basically a scaled down version of what's done in modern Toyota hybrids.

author: eas
author_rank: Frequent Contributor
timestamp: October 11, 2015, 04:51:38 am
content: Quote from: T3sl4co1l on October 11, 2015, 12:18:33 amGo further. Look at a real-world sample of the fuses. How optimistic or pessimistic is the datasheet? Is there enough variation that it would be worthwhile coming up with a way to non-destructively test the fuse you are given and set your tuning parameters to run as close to the limit as possible?

author: mrpackethead
author_rank: Super Contributor
timestamp: October 11, 2015, 05:00:00 am
content: (1) accurately measure the fuse temp, so you know what its doing.. and then feed that back into your control system.(2) Store power down stream of the fuse, ( supercaps ) so, you can draw a bit more, when you need it... This woudl let you run the system at an average of 100%, ( ie, when you throttle off, your caps charge up )...

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 11, 2015, 05:12:29 am
content: Quote from: mrpackethead on October 11, 2015, 05:00:00 amYes, that was exactly my first thought.Exactly WHERE in the circuit do they require the fuse?

author: mrpackethead
author_rank: Super Contributor
timestamp: October 11, 2015, 05:24:59 am
content: Quote from: Richard Crowley on October 11, 2015, 05:12:29 amA lot of depends..

author: Ian.M
author_rank: Super Contributor
timestamp: October 11, 2015, 05:31:43 am
content: Rules: "Finally, there are no capacitor banks for providing additional vehicle power permitted. That’s just too unsafe. Even for us."So any energy storage cant be a capacitor bank. 50K RPM vacuum magnetic bearing flywheel energy storage system, maybe?

author: nbritton
author_rank: Frequent Contributor
timestamp: October 11, 2015, 06:22:37 am
content: The best advise I can give you is to hire a 80 lb petite girl to drive your toy car. Also I would implement a negative feedback current limiting circuit using an arduino that computes an exponentially weighted moving average of the current going through the fuse, that way you can always be at the maximum temperature rating of the fuse.

author: ConKbot
author_rank: Super Contributor
timestamp: October 11, 2015, 06:54:08 am
content: First, my instinct would be to go for a 36 volt system, lower I^2R loses in everything, lighter wiring.Second, if you can afford lithium ion, go for it, lighter, and a 36v pack (10s) will be 41-41v charged and should be above 36v for half the discharge. A 36v lead acid pack will be 38.5v fully charged, maybe a sight edge in the beginning. Try to find cheap rc airplane packs?Definitely heatsink the fuse, use an aluminum block for the fuse holderand have it make good contact with the broad leads. You're not gonna let it get hot, so the aluminum shouldn't be an issue, just use noalox or equivalent on the contact area.Try to keep your average power at 100 percent. Do you can draw more than 100 percent for short durations like others said. I've worked with motor controllers which let you set an I^2t product, so you can get more torque peak without burning stuff out. Integrate/filter your current draw and use that in determining maximum "throttle"on the motor controller.And for that last push, a "go baby go" button button which dumps some inverted duster cans on the fuse. Maybe some fabric gauze to help retain the liquid and keep it from just skittering off of it because of leidenfrost effect. If your motor controller can't handle a peak like that, then a contactor bypass too.If you really want to get into it, dissect the fuse, take measurements on where to drill holes, or mill slots so the coolant can get right to the fuseable link.Oh and if you're doing all of this to defeat the fuse functioning, make sure your wires can handle itmaybe a second higher rated fuse in series in case your tricks work too well :p

author: Someone
author_rank: Super Contributor
timestamp: October 11, 2015, 07:08:27 am
content: Quote from: wilfred on October 11, 2015, 02:47:34 amI didnt go through the rules extensively but is there anything about driving position? They want the vehicle too look substantially as original but skinny tires (solid rubber industrial trolley wheels?) and a prone position dont seem to be an issue:https://en.wikipedia.org/wiki/Prone_bicycleon top ofhttp://www.modifiedpowerwheels.com/forum/topic.asp?TOPIC_ID=5020Aerodynamic drag is substantial above 10km/h, but as mentioned above practice and a vehicle that handles well are also important!Quote from: mrpackethead on October 11, 2015, 05:00:00 amKnowing a close temperature and the voltage across the fuse you could run it right on the thermal limit.

author: Someone
author_rank: Super Contributor
timestamp: October 11, 2015, 07:13:36 am
content: Found an appropriate video, go hard or go home:

author: Rerouter
author_rank: Super Contributor
timestamp: October 11, 2015, 07:55:16 am
content: OK, yeah, the rules at no point say its not allowed for your inverters output to be greater than 36V, just that the RMS may not be higher than 36V, which means for acceleration you could switch to a higher voltage at a lower ratio to get more acceleration, while when holding level can return to a normal direct voltage output for normal operation,

author: SeanB
author_rank: Super Contributor
timestamp: October 11, 2015, 08:10:28 am
content: Put the fuse in an exposed holder, with mounting lugs with a very large thermal mass, and blow air over the fuse to keep it as cool as possible, and remove any heat it generates from internal resistance so it will handle a higher current before blowing. If you look at the fuse ratings, you will see a derating for ambient temperature, so keeping it as cool as possible and removing heat from it as efficiently as possible ( if a blade fuse make a holder with parallel copper jaws that clamp the fuse ends firmly, with a machines set of fins on them to allow cooling air to flow from a dedicated fan) so you can go further up the current curve.Then measure the temperature rise directly at the fuse, and use that to back off current draw as the fuse heats up. You will need a model of how much the measuring point reads compared to the element inside as to actual melting point of the fuse material.

author: ErikTheNorwegian
author_rank: Frequent Contributor
timestamp: October 11, 2015, 08:28:19 am
content: Interesting, this tread reminded me off some experiences i had years ago. The fuse in a device blew, Even the curent was under the limit. After some tests, i found out, running hot, the fuse blew faster under vibration. So hanging the fuse holder into a shock absorbert case solved the problem and we could enjoy a couple of hundred milliamps more before it blew.http://m.rs-online.com/h5/mobile/uk/catalog?url=%2Fweb%2Fp%2Frail-mount-fuse-holders%2F0354385A%2F

author: Rerouter
author_rank: Super Contributor
timestamp: October 11, 2015, 08:37:31 am
content: In the rules, the holder part number is specified,http://www.digikey.com/product-detail/en/04980900ZXT/F3094-ND/553455But that in its own looks like it should be very easy to add a thermocouple that is in contact via mounting pressure, equally having a low gauge wire coming away from the fuse block to the kill switch would increase the thermal mass of the fuse allowing you just a little more, without obviously doing everything you can to abuse the fuse,

author: ErikTheNorwegian
author_rank: Frequent Contributor
timestamp: October 11, 2015, 08:40:23 am
content: Mount the fuse on a rubber damping plate...or add anti vibration ontoo the fuse holder.http://www.antivibrationmagic.ca/index.php?page=info#Fuses

author: Ian.M
author_rank: Super Contributor
timestamp: October 11, 2015, 09:03:33 am
content: The fuse rules state: "We will be using the LittelFuse MIDI 498 series of fuses. The fuse holder they use is Digi-Key P/N F3094-ND". It does NOT actually prescribe the use of a F3094-ND holder. Even if the use of that holder is enforced, if your fuse cooling scheme is sufficiently outrageous (but safe) the "7.2.3 | The “I Ain’t Even Mad” Clause" is likely to get you out of trouble. Cryogenics or discharging volatile fluids would be likely to raise safety concerns.I'd have a couple of options that can easily be swapped in - A forced air cooled heatsinked custom fuse holder, a F3094-ND holder with provision to immerse it in a bath of Fluorinert under partial vacuum (pump it down after each fuse inspection or change) to implement heatpipe cooling, and a F3094-ND holder with heavy cables and good airflow.I suspect that the fuse temperature can be sensed to sufficient accuracy by measuring its resistance. i.e. accurately measure the voltage drop across it and the current through it. If the controller adaptively manages the fuse temperature, even if the judges force you to swap to an unmodified F3094-ND holder, you'll still be better off than any competitor without active fuse temperature management.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 11, 2015, 10:05:48 am
content: Quote from: nbritton on October 11, 2015, 06:22:37 amOn second thought, a feedback current limiting circuit using a temperature probe on the fuse would be easier to implement. To set the device you would drive around a test track and using a potentiometer slowly inch up the value until you blow the fuse, then back off the potentiometer and replace the fuse. This has everything to do with heat, the fuse blows not because too much current is flowing through it, but because the current is causing the metal in the fuse to melt.Furthermore, the rules do not state that you have to use the F3094-ND fuse holder, they simply recommend that part number for the people who don't know what fuse holder to get. I further recommend making a fuse holder from a block of copper or aluminum, so that the holder can act as a heat sink. Furthermore, the rules do not state that you can't use a fan to actively cool the fuse. In fact, you could even liquid cool the fuse by submersing it in water, plain old water has very high thermal capacity. A block of dry ice might work.I'm assuming you're using DC motors, but if you used AC motors you could go with three phase power. The rules don't say that you can't use a three phase motor. I wonder if they would give you one fuse for each phase or just fuse one of the three phases? Ether-way you will have three time the power.In the rule book it says motors must be 12-36 volts RMS maximum, so you could boost the 36V up to 144V through the fuse and then buck it back down 36V at the motor. 1440W / 36V = 40A veruse 1440W / 144V = 10A

author: Zero999
author_rank: Super Contributor
timestamp: October 11, 2015, 10:37:49 am
content: The rules clearly state "No vehicle may have a total peak power consumption of greater than 1440 watts." which implies that this figure can't even be exceeded during acceleration so cooling the fuse to stop it blowing won't be any good, if they disqualify you because you're exceeding the power limit.Reducing weight and good aerodynamics would help but the rules state "The vehicle may not exceed 62” long by 36” wide." which will make that difficult to achieve, unless you get a dwarf driver.

author: mikerj
author_rank: Super Contributor
timestamp: October 11, 2015, 11:04:10 am
content: Quote from: Hero999 on October 11, 2015, 10:37:49 amDepends at what point this power consumption is measured. If it's at the primary energy storage device, then you are free to draw 1440 watts from it all day long (or for as long as it lasts) but downstream you could have secondary energy storage that permits higher peak power to be delivered to the motor for short periods. Capacitor banks are apparently out, but NiCd could be usable, or a kinetic storage device.Basic liquid cooling with e.g. deionised water would probably be sufficient to raise the current handling of the fuse by a fair bit, i.e. immerse the entire fuse and connections in the coolant.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 11, 2015, 11:07:53 am
content: Quote from: nbritton on October 11, 2015, 10:05:48 amThis is potentially as good as the [open loop] model, but is still missing things: the ambient near the fuse (or even on the fuse body, or at the terminals) is not the fusible element's temperature.Ideally, one would combine both for a very accurate system. A thermal model of the element-to-thermometer path is what's missing here.Perhaps, the thermometer-to-ambient path still remains in the model, but rather than being purely open loop (i.e., where current is used to calculate element temp, and body temp, down to ambient), that node's state is 'informed' by real measurements: its value is the sum of external (as measured, but perhaps noisy or systematically inaccurate) input, and of the estimated (modeled) value.This is something like a Kalman filter, implemented in analog (or DSP just as well, but in such simple terms that either would do). A full expression of that would require a few more stages (including accounting for the confidence level of the measured data; which could be done in analog terms with a 'fading' circuit controlled by some measure of noise, perhaps). Even without the full functionality, it's an interesting method.Regarding peak power: without a logging instrument thrown on each battery, it's a preposterous claim! One supposes the fuse acts as their monitor; so in that case, "peak" means over a period of [thermal time constant], which is hardly the electrical meaning of 'peak'! And, in that case, gaming the fuse is not only desired, but encouraged, so it would seem!Tim

author: Rerouter
author_rank: Super Contributor
timestamp: October 11, 2015, 11:11:23 am
content: I'm still going to have to say that actively monitoring the temperature of the fuse to allow yourself a higher peak current would fit quite nicely under the "I Aint even mad" exception, he is not giving himself much of an advantage, just stretching it to go as far as he can,obviously he exceededs that mark and he will blow a fuse, using the recommended fuse holder may win him some benefit of the doubt with the judges as he will not be trying to bypass the protection of the fuse, just run the knife edge,

author: NotABagel
author_rank: Contributor
timestamp: October 11, 2015, 11:25:09 am
content: Quote from: nctnico on October 11, 2015, 12:42:32 amThat leads into a second question: What motor should I get to maximize efficiency? I was looking at converting alternators to brushless motors, as several teams had success with that, but I don't really know how efficient that will be.Aerodynamics isn't really important for the race. The track is very twisty, so you won't get up to very high speeds, and since you have to use a body from a power wheels car, you can't really play with aerodynamics much.

author: Psi
author_rank: Super Contributor
timestamp: October 11, 2015, 11:27:34 am
content: Quote from: T3sl4co1l on October 11, 2015, 12:18:33 amHave two fuses of the same type in series with the load.Fuse 1 is the official unmodified fuse for the rules.Fuse 2 is the same part number but has been modified to have a temp probe mounted hard up against the fuse wire.You can then monitor the temp of fuse2 in real time and keep under the blow temp.

author: NotABagel
author_rank: Contributor
timestamp: October 11, 2015, 11:30:13 am
content: QuoteSo yes, you want to cheat.I talked to one of the race organizers, who told me that if you can run more current through, you have earned the right to run more current through. Also, everyone is pretty open about the fuse trickery. For these reasons. I consider messing with the fuse to be aboveboard.

author: NotABagel
author_rank: Contributor
timestamp: October 11, 2015, 11:36:54 am
content: Quote from: Rerouter on October 11, 2015, 03:54:40 amHow do I realistically do this? I have no electronic engineering knowlege, but I do have a teacher with an electronic engineering degree. How much work would this entail?

author: NotABagel
author_rank: Contributor
timestamp: October 11, 2015, 11:51:02 am
content: Quote from: NiHaoMike on October 11, 2015, 04:04:01 amHow could I convert this back to DC for powering the motor?

author: Rerouter
author_rank: Super Contributor
timestamp: October 11, 2015, 12:24:13 pm
content: I've rethought it and you can avoid the 24V stage, just relying on the bulk 48V PWM'd to get your torque,For your controller you would have a standard PWM h bridge controller controlling the motor, however you can add a boost converter to the input of this stage, the stored energy would be low so you could have it respond fairly quicklyAt low speed or while accelerating, or even when someone presses a boost button, You ramp up the voltage, scale back the h-bridge ratio (To keep within there voltage rules) and gain more torque for the same input power, then when cruising switch off the boost converter and the freewheeling diode will allow the power to flow through to the motors at the normal battery voltage, (yes there will be a small efficiency loss)Tie this in with a thermal fold back from measuring the fuse temperature and / or resistance and you should have a nice number of gains that abide by there rules from how you have so far described it, you can make it as simple as that an op amp proportionally scales back the pwm ratio as the temperature of the fuse exceeds X degrees, it prevents the vehicle from going full limp, and prevents you from ever blowing the fuse outside of a genuine fault condition.This however would make electronic breaking harder to recharge from, but can still be done if neccesary,

author: Kalvin
author_rank: Super Contributor
timestamp: October 11, 2015, 12:38:19 pm
content: After watching the promotional movie on the site's front page, I would also pay attention to driving skills. Although you had a powerful car but you couldn't drive it efficiently you can still lose to less powerful car with a better driver and with less total weight. Then, I would look at the mechanical parts too. Maybe two separate motors, one for each back wheels instead of one (Frankly, I do not know how the drivetrain is implemented on these small cars) so that the wheels can get optimal torque at the curves. If you can select the tyres, select something that has as little rolling friction as possible and use high tyre pressure. Check the bearings. Think about the whole instead of concentrating on the fuse and maximum current only. Nice and very interesting project!

author: Fungus
author_rank: Super Contributor
timestamp: October 11, 2015, 12:52:06 pm
content: For those who haven't read them yet (including the OP, apparently) here are the rules:http://www.powerracingseries.org/rules(please read before continuing)Section "2.7.1 Fuses" says:Quote36V x 40A = 1440W28.8V x 50A = 1440W24V x 60A = 1440W12V x 125A = 1500WIf the peak power consumption isn't allowed to be more than 1440W than how will any sort of fuse fiddling help? The supplied fuses can already handle that.So mostly you're limited to:a) Building a lightweight car and finding the smallest driver possible. (VERY important)b) Learning to drive well (even more important than 'a')...last of all, the electronics:c) You can make sure you're drawing 1440WALLthe time, ie. you need to be drawing 1440W even when you're braking and storing it somewhere ready for a power boost coming out of the curves. Rule 2.5 says "no capacitor banks" so this will be difficult.You couldmaybespin up a flywheel with a motor during the 'storage' moments then use the same motor as a generator during the 'boost' moments. There's a lot of electronics knowledge needed to do that properly though.In short, electronics 'cheating' is going to be difficult.And: You can earn just as many points by building funny cars and dressing up, so...Quote from: Rerouter on October 11, 2015, 12:24:13 pmHint: Try reading the actual rules. Messing with the fuse won't help because Watts are also limited.(though I'm not sure how they can monitor the Watts when you're out on the track)Quote from: Kalvin on October 11, 2015, 12:38:19 pmThis.

author: Kalvin
author_rank: Super Contributor
timestamp: October 11, 2015, 12:58:36 pm
content: How about the different fuse types 125A vs 40A. I have a hunch that the 125A is more tolerant to overloading and abuse than the 40A fuse.

author: Fungus
author_rank: Super Contributor
timestamp: October 11, 2015, 01:02:28 pm
content: Quote from: Kalvin on October 11, 2015, 12:58:36 pmMaybe, but then you have to work at 12V which makes everything else worse.Me? I'd go for the higher voltages.

author: Rerouter
author_rank: Super Contributor
timestamp: October 11, 2015, 01:07:30 pm
content: For the motors, I have done some reading, and alternator motors get most of there power at higher RPM's, so if your going slow through a weaving course, using hobby motors may get you an advantage,Edit: Or much better, see if you can find brushless cordless drills that have dud batteries or cosmetic damage, 2 of those motors would give you the best of all worlds, or even just see if they sell the motors as a spare part,

author: Kalvin
author_rank: Super Contributor
timestamp: October 11, 2015, 01:14:48 pm
content: Can you use some sort of fuel cell onboard? If you run the battery at the maximum current 100% of the time and use the unused power to convert water into hydrogen and feed the hydrogen into a fuel cell to give you some extra boost.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 11, 2015, 01:38:42 pm
content: Quote from: Kalvin on October 11, 2015, 01:14:48 pmI don't even know where to begin telling you what's wrong with this.Unless it was intentional. "Sufficiently developed satire is indistinguishable from the thing it aims to criticize."Tim

author: NotABagel
author_rank: Contributor
timestamp: October 11, 2015, 01:43:30 pm
content: Quote from: Richard Crowley on October 11, 2015, 05:12:29 amUnfortunately, the rules expressly prohibit capacitor banks. It's too dangerous for even Power Wheels Racing.

author: DanielS
author_rank: Frequent Contributor
timestamp: October 11, 2015, 01:54:09 pm
content: I'm guessing the "no capacitor" rule means no major energy storage devices of any sort allowed downstream from the fuse, electrical, chemical, thermal or electromechanical. Most of these would likely get ruled out as either too dangerous or self-out themselves as simply too bulky to compete.Since fuses and batteries are not exact devices, the competition should be using calibrated and sealed power metering devices to enforce the 1440W (5s rolling average) limit.

author: NotABagel
author_rank: Contributor
timestamp: October 11, 2015, 02:02:43 pm
content: Quote from: Rerouter on October 11, 2015, 01:07:30 pmWell, my initial plan was to have two drill motors that power the kart through chain drive. Unfortunately, the Ryobi drill motors I used simply didn't have enough startup torque to get the kart moving. If I were to actually use drill motors again, I'd have to use a big reduction gearbox, as the lowest gear for the drill wasn't low enough.

author: Fungus
author_rank: Super Contributor
timestamp: October 11, 2015, 02:22:50 pm
content: Quote from: NotABagel on October 11, 2015, 02:02:43 pmA big reduction gearbox will compromise your top speed.A proper gearbox with two or three selectable gears will help a lot (more than any messing around with electronics). One very low gear to get away from the line. Two gears for the race (straights/corners).

author: NotABagel
author_rank: Contributor
timestamp: October 11, 2015, 03:07:16 pm
content: Quote from: Fungus on October 11, 2015, 02:22:50 pmWhere could I get a gearbox for that purpose?

author: Fungus
author_rank: Super Contributor
timestamp: October 11, 2015, 03:09:56 pm
content: Quote from: NotABagel on October 11, 2015, 03:07:16 pmWhen I was a kid I had one of these:Gotta love that gear shifter...IIRC you have to freewheel or pedal backwards during shifting so you might need a "clutch" button to make the motor go slowly backwards while you shift.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 11, 2015, 03:20:02 pm
content: Could you make it into a hybrid as in like a hybrid bicycle?

author: Fungus
author_rank: Super Contributor
timestamp: October 11, 2015, 03:38:41 pm
content: Quote from: NiHaoMike on October 11, 2015, 03:20:02 pmThe rules don't actually mention pedals, but.... I'm guessing "not". It would be a MASSIVE advantage but nobody in the video seems to be doing it.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 11, 2015, 04:09:44 pm
content: Quote from: Fungus on October 11, 2015, 02:22:50 pmHow do diesel-electric railroad locomotives do it? The don't have gearboxes, do they? The use direct-drive electric motors on the wheels, IIRC. And yet they can pull many tons of dead-weight from a standing start. And pull it along at pretty good speeds when it gets going on the open road.

author: Fungus
author_rank: Super Contributor
timestamp: October 11, 2015, 04:16:27 pm
content: Quote from: Richard Crowley on October 11, 2015, 04:09:44 pmNope, but they can dump MASSIVE current into the motor to get it moving. This guy has a fuse.(Also: They're not in a race...)

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 11, 2015, 04:17:25 pm
content: They don't have UNLIMITED current available. They have a power budget, also.Their race is economic and much more real than hobby toys.Wikipedia says that they used tapped series-connected electric motors on the wheels.Sort of an electronic "gear-shifting". To get more torque at low speeds (and start-up), but then better performance at high speed.I don't suppose any competitors are winding their own motors for competitive advantage.

author: mikerj
author_rank: Super Contributor
timestamp: October 11, 2015, 05:16:05 pm
content: Quote from: NotABagel on October 11, 2015, 02:02:43 pmHang on, you are permitted to use up to 1440 Watts and you're checking out ways to exceed this by fuse cooling and yet you are considering tiny little cordless drill motors?1440 watts is just about 2 brake horse power, you'd need quite a few cordless drill motors to reach that. You should be looking at motors for e.g. mobility scooters.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 11, 2015, 05:57:02 pm
content: Quote from: Fungus on October 11, 2015, 03:38:41 pmYeah. Petal power could get you bursts of like 900 Watts for short periods of time and maybe 450W of continuous power.

author: NotABagel
author_rank: Contributor
timestamp: October 11, 2015, 06:18:00 pm
content: Quote from: mikerj on October 11, 2015, 05:16:05 pmThat was my initial idea. Because of my own incompetence, I had grossly underestimated the power I would need. I'm now going back to the drawing board, having used a 1kw brushed scooter motor to a certain degree of success last year.

author: IanB
author_rank: Super Contributor
timestamp: October 11, 2015, 07:12:28 pm
content: Quote from: Richard Crowley on October 11, 2015, 04:09:44 pmQuote from: Richard Crowley on October 11, 2015, 04:17:25 pmAs you note, DC electric trains used series-wound motors with tapped resistor banks for current limiting when moving away from a standstill and often had a "weak-field" setting for running at maximum speed. This kind of thing could be done electronically to match the torque and speed of the motor to the instantaneous load, but such an approach has been rendered obsolete by modern variable frequency drives and brushless motors.In fact, brushless motors are capable of tremendous power to weight ratios. In the radio controlled hobby arena, I believe motors weighing a few ounces can produce power outputs of a kilowatt or more.If one were trying to maximize the performance of an electric vehicle brushless motors and modern electronic control would seem to be the ultimate solution (although cost may be a constraint if funds are limited). Depending on the vehicle speed and the accelerator position the motor could be driven at the optimum point on the performance map at all times.

author: nctnico
author_rank: Super Contributor
timestamp: October 11, 2015, 07:18:07 pm
content: A motor with a 'switchable' number of poles will also help. It is basically an electrical gear box.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 11, 2015, 09:29:33 pm
content: Quote from: NotABagel on October 11, 2015, 06:18:00 pmA 1000W motor is still not enough power to continuously max out a 1440W fuse. You want the fuse junction to always be at its maximum temperature so you're going to need perhaps a 2000W motor and a current limiting feedback circuit connected to a temperature sensor that is directly on the fuse.Since you're limited to a $500 budget I'd say skip the voltage boost/buck and DC/AC converters and go straight for a 36V DC motor. A quick search of the internet found a 1000W scooter motor for $129, get two of them to double the power to 2000W:http://www.monsterscooterparts.com/36-volt-1000-watt-motor-mounting-bracket-11-tooth-8mm-05t-chain-sprocket-my1020.htmlhttp://www.monsterscooterparts.com/36v70mowichs.html

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 12, 2015, 12:28:49 am
content: People are getting really hung up on the 1440W figure.This doesn't appear to be a solid rule (and should probably just be stricken altogether).They don't monitor or measure the power. The only way they verify is whether the fuse survives or not.The fuse can let through considerably more than 1440W in all configurations, for a useful duration. This is the only hard limit, a matter of physics (of the fuse element).Tim

author: Joule Thief
author_rank: Regular Contributor
timestamp: October 12, 2015, 04:19:52 am
content: Just a quick thought - does the fuse element need to be left within the manufacturer's housing or can the element be removed and surrounded by a more thermally conductive material?

author: ErikTheNorwegian
author_rank: Frequent Contributor
timestamp: October 12, 2015, 11:06:30 am
content: Just add a coupple of BATTERISERS, that ought to fix your problem!!

author: Fungus
author_rank: Super Contributor
timestamp: October 12, 2015, 11:12:16 am
content: Quote from: T3sl4co1l on October 12, 2015, 12:28:49 amNone of the rules are "solid" but I'm not sure how you can bend this one so far that the judges let you off.a) Liquid nitrogen on the fuse? Would probably be disallowed for safety reasons.b) I can't think of a 'b'Besides, you'll get far more speed from good car mechanics, weight reduction and skillful driving well than you will from sneaking another 100W past the fuse.Quote from: Joule Thief on October 12, 2015, 04:19:52 amFrom the rules (whichhavebeen linked to):"2.7.1 FusesNo vehicle may have a total peak power consumption of greater than 1440 watts. Current-limiting fuses will be issued to the teams on race day by the Sanctioning Body. We will be using the LittelFuse MIDI 498 series of fuses. The fuse holder they use is Digi-Key P/N F3094-ND....If you blow a fuse during a race, you have to go to the timing and scoring booth and beg us for another. On race day we are the only source of permitted fuses, so don’t expect to get away with tampering."It seems like they take the "fuse" part of the rules very seriously.Plus: If it was my team I wouldn't like race success to depend on keeping a fuse within a few degrees of blowing. Murphy's law says that on race day you'll get issued with the one fuse that will blow...

author: Tim F
author_rank: Regular Contributor
timestamp: October 12, 2015, 11:47:24 am
content: Quote from: Kalvin on October 11, 2015, 12:58:36 pmNo matter which voltage/fuse combination you choose you'd have to overload the fuse by the same % of it's nominal rating to achieve the same % increase in power output. What makes you think that the 125A fuse will be able to tolerate a higher % of it's nominal rating before it pops?My 2c:I^2*R losses will be higher in the 125A fuse - think about it, the fusible element is thicker so it's going to take more power (=heat) to blow it, so the I^2*R loss in the 125A fuse has to be worse for the same system power output compared to the lower current fuses.Therefore if you are overloading the 125A fuse by a given % you generate more excess heat than the same % overload on the 40A fuse. If you consider the fuse holder to also be acting as a heatsink, then it's going to run cooler with the 40A fuse than the 125A, therefore the rating of the 40A is going to be boosted more by the cooling effect of the fuse holder - long term of course, the fuse holder isn't going to help you much for a 10 second overload.

author: crispy_tofu
author_rank: Super Contributor
timestamp: October 12, 2015, 11:53:11 am
content: Quote from: ErikTheNorwegian on October 12, 2015, 11:06:30 amYep, and a few of those 'free energy' overunity thingos too!

author: Fungus
author_rank: Super Contributor
timestamp: October 12, 2015, 11:55:24 am
content: Quote from: crispy_tofu on October 12, 2015, 11:53:11 amYou're thinking too small.Add a device to harvest energy from the other drivers - make them all goslowerwhile you get your free boost!

author: NotABagel
author_rank: Contributor
timestamp: October 12, 2015, 12:07:33 pm
content: Quote from: Fungus on October 12, 2015, 11:12:16 amYou have to understand: EVERYONE plays with their fuse, and rather openly. If I want to be competitive, I will have to too.

author: Fungus
author_rank: Super Contributor
timestamp: October 12, 2015, 12:10:42 pm
content: Quote from: NotABagel on October 12, 2015, 12:07:33 pmSo...what do they do? Tell us!This the sort of info you should be posting if you want real help. It's all a bit one-sided so far.

author: Rerouter
author_rank: Super Contributor
timestamp: October 12, 2015, 12:42:02 pm
content: Sorry Op, but sometimes these threads get hung up on a detail and run away from you, like we see now.Are you planning to go with 2 motors, or 4?, I suppose 2, but could be wrong, and yeah my thoughts where off on the drill motors, they tend to top out at 250W continuous, so not quite suitable,something closer would be these guys,http://www.ebay.com.au/itm/36-Volt-350-Watt-Unite-Motor-Gear-Reduction-Razor-Dirt-Quad-Scooter-36V-350W-TA-/321875637433?hash=item4af14874b9you can find them for even cheaper, if you had one per tire, then at full throttle you would be just under at 1400W consumption, but throw in a boost converter and you can go way higher for bursts, 48V would get you to about 2500W for however long you where safe to do so, but you can scale that in your controller to prevent instantly popping the fuse,

author: DanielS
author_rank: Frequent Contributor
timestamp: October 12, 2015, 02:20:48 pm
content: My thought process regarding which voltage/fuse to pick stops at I2R wiring losses: the reduced wiring, Rdson, other losses and weight at 28-36V free up about as much continuous power budget as you might be able to get out of a reasonable repeatable overload on 12V/125A.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 12, 2015, 06:43:33 pm
content: Quote from: Tim F on October 12, 2015, 11:47:24 amNot only that, but you would need like 0000 AWG wire to manage 167A. With 36V you can use 6 AWG. The rules say you can't spend more than $500 total.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 12, 2015, 06:54:44 pm
content: Quote from: Rerouter on October 12, 2015, 12:42:02 pmPer the rules, the voltage at the motor can't be higher than 36V RMS and also there is a $500 budget limit:Quote

author: SeanB
author_rank: Super Contributor
timestamp: October 12, 2015, 07:21:52 pm
content: 72V supply and the fuse on the battery bank, then a buck converter to supply 36.0V to the motor terminals, using sense feedback to the buck converter at the terminals.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 12, 2015, 07:30:45 pm
content: Quote from: SeanB on October 12, 2015, 07:21:52 pmMy interpretation of the rules are that the power supply also can't exceed 36V. The wording verbatim is: "All power supplies must range from 12-36 volts RMS maximum input to the motors."Furthermore it says: "Before each race, track officials will test the voltage to the motor of each vehicle." what test point are they measuring???

author: DanielS
author_rank: Frequent Contributor
timestamp: October 12, 2015, 11:56:53 pm
content: Quote from: SeanB on October 12, 2015, 07:21:52 pmOn top of the 36V maximum voltage in the rules, you have the 1440W limit from the battery and I bet the safety rules also prohibit running fuses beyond their nominal breaking voltage.So you would get disqualified for obviously intending to draw twice as much battery power than permitted, exceeding the voltage rating of provided fuses and exceeding the maximum voltage rating allowed on the track.The reason for 36V as the limit is likely to practically eliminate electrocution hazards, so I doubt anything higher at any point in the drive train and support systems will be tolerated.

author: NotABagel
author_rank: Contributor
timestamp: October 12, 2015, 11:57:38 pm
content: Quote from: nbritton on October 12, 2015, 07:30:45 pmThis correct. The rules around voltage requirements are pretty strict, and they look at the motor terminals for voltage. Most other teams were simply pushing extra current through their fuses in bursts, but I want to go further.

author: Fungus
author_rank: Super Contributor
timestamp: October 13, 2015, 06:32:28 am
content: Quote from: SeanB on October 12, 2015, 07:21:52 pmDo you think they'd hand out a fuse without measuring anything? In that case everybody would just ask for the 125 amp fuse.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 13, 2015, 08:22:20 am
content: Quote from: NotABagel on October 10, 2015, 11:27:57 pmdesign a fuse holder in practical sized watertight box enclosure. you have sealed door for easy fuse replacement. put water in it...your fuse will become a nice water heater for the duration of your racing... you can make a "digikey fuse flavored" coffee then to enjoy the winning... edit: ps: dont forget the pressure relieve valve you dont wanna blow your fuse holder due to excessive steam pressure... ymmv..

author: TheRevva
author_rank: Regular Contributor
timestamp: October 13, 2015, 09:16:09 am
content: I only read a couple of pages of this thread, and I have to admit that it was all 'intriguing' to say the least...Many of the comments dealt with various methods to keep the fuse from getting hot enough to actually melt.Immersion in liquid nitrogen was one, fairly logical, method to keep things nice and cool....However...Is there any aspect of the rules that state you're not allowed to 'immerse' the entire fuse (holder and all) into a nice bath of ... say... good old LEAD.Imagine a small pot / kettle full of molten lead. The race inspector first 'verifies' that you have the 'correct' fuse and possibly even the correct fuse holder too. Once it has 'passed' that inspection, you immerse the ENTIRE fuse + holder into the bath of molten lead (making sure the molten lead forms a nice connection to BOTH sides of the fuse). You wouldn't even need to retain the lead in a molten state... (In fact, it'd possibly be wise to HELP it solidify)It'd probably qualify for the "I am not mad but..." clause, and I'm pretty confident that with a large enough 'bath' of lead that just happens to be in direct contact with BOTH of the fuse connections, the fuse would be fairly unlikely to blow... Hell, even if it DID manage to melt the fuse, the surrounding 'lead bath' would still happily allow a few THOUSAND Amps!!! <Grins>(I'd strongly recommend installing an 'additional' fuse of appropriate rating for basic safety though).Then there's the next suggestion....Does it actually SAY in the rules that you cannot connect both the SUPPLY feed _AND_ the load from the motor onto the SAME side of the fuse? (i.e. The fuse is actually NOT pat of the circuit)In that case, I would SERIOUSLY doubt the fuse would blow even if you were drawing several MEGA AMPS. (If the fuse DOES somehow manage to go open circuit though, you'd have some SERIOUS issues and might require the fire department rather urgently)

author: Fungus
author_rank: Super Contributor
timestamp: October 13, 2015, 01:33:09 pm
content: Quote from: Mechatrommer on October 13, 2015, 08:22:20 amReally? You'd base your chance of race success on something as random as that?

author: Fungus
author_rank: Super Contributor
timestamp: October 13, 2015, 01:45:34 pm
content: Quote from: TheRevva on October 13, 2015, 09:16:09 amThey banned capacitor banks on safety grounds so it's a safe bet they wouldn't allow that.Quote from: TheRevva on October 13, 2015, 09:16:09 amHow is that different from just soldering a wire across the fuse holder? Do you really think they'd allow that?Quote from: TheRevva on October 13, 2015, 09:16:09 amReally?

author: DanielS
author_rank: Frequent Contributor
timestamp: October 13, 2015, 05:59:55 pm
content: Quote from: TheRevva on October 13, 2015, 09:16:09 amThe rules would not require the use of official-provided fuses if they could so casually be bypassed. There is no point in specifying a fuse if it is not required to be in-circuit where it is intended to be: between the source and whatever is connected downstream.

author: Kalvin
author_rank: Super Contributor
timestamp: October 13, 2015, 07:43:39 pm
content: Energy density 12V battery vs 36V battery. How large a volume is needed for the battery/batteries? Those cars are pretty small. What is the total energy required during the race?There are 1500W 12V DC/AC inverters available, compact in size too. Maybe a 12V DC/DC-converter driving the motor(s) would be okay too. I am not sure about the I2R losses here if the converter is placed close to the battery. And there is still current advantage for the 12V over other voltages, should there be higher power loss using 12V power supply and which may compensate the losses. And, if the 125A fuse is more tolerant to overload, this could provide some opportunities.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 14, 2015, 05:12:46 am
content: Quote from: Fungus on October 13, 2015, 01:33:09 pmno its not random, its thermodynamics law and used in millions of kettle, unless you take it for granted without proper testing and math. my uneducated guess, you can double your system wattage with this method. anyway, its your choice on more advanced technological features that maybe cost weight and money and err reliability (read as randomness or murphy's law)... this is "hack" thread afterall. i was about to give another nasty but better non random hack but its strictly speaking illegal if found out by the organizer. learnt from the ghetto..

author: Fungus
author_rank: Super Contributor
timestamp: October 14, 2015, 05:48:51 am
content: Quote from: Mechatrommer on October 14, 2015, 05:12:46 ama) Kettle elements aren't made of stuff which is near melting point at 100 degrees C. Small hotspots are OK.b) Kettles aren't bashed around much.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 14, 2015, 06:17:06 am
content: Quote from: Fungus on October 14, 2015, 05:48:51 amso does fuse element. except kettle element will take all the power when energized. whereas fuse element only take excessive wattage when you start beyond the rated wattage. meaning while you are under the specifed 1440W, there is no heating going on, no coffee for youQuote from: Fungus on October 14, 2015, 05:48:51 amthats why the watertight and pressure relieve valve suggestion. the OP's job is to ensure 2 things though that i dont need to feed:1) the fuse is immersed in water all the time, that probably means near full water before closing down the fuse holder door.2) the water can get into the fuse enclosure into the fuse element... suggesting an assumption that the "organizer's approved fuse" is not watertight. well YMMV...and 3) its the OP's job to make the whole water heater thing is bash proof...edit: water heater thing in automobile have been around for decades, its called radiator... YMMV..

author: Ian.M
author_rank: Super Contributor
timestamp: October 14, 2015, 09:48:50 am
content: From a safety viewpoint, I cant see the judges permitting a fuse cooling system that could discharge steam or boiling water. I thought I was pushing it to suggest a fully sealed Fluorinert heat-pipe system, which would have to be very carefully engineered not to discharge coolant.Also, once you get high enough temperatures at the surface of the fuse's internal element, any leakage into the fuse body will result in a tiny amount of water flashing to steam which will blow the s--t out of the fuse, rupturing the body and severely stressing the element. You really don't want a cooling system that vastly increases the probability of fuse failure when you hit the throttle several corners intop the race!

author: langwadt
author_rank: Super Contributor
timestamp: October 14, 2015, 04:25:07 pm
content: Quote from: NotABagel on October 12, 2015, 11:57:38 pmif you are not allowed any storage after the fuse there isn't much to gain other than trying to get as close to blowing as possible.I imagine measuring the current through and voltage across the fuse to calculate the resistance and thus the temperature.Then have the motor controller pull as much current as needed while keeping the fuse wire temperature below some safe level

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 14, 2015, 06:47:36 pm
content: Quote from: Ian.M on October 14, 2015, 09:48:50 ampoint the steam relieve valve drain downward to the road? i'm pretty sure the fuse compartment is somewhere far away from the driver's seat regardless of where you point the drain, heat from the motor should be more of the concern, no?. then whats the contigency plan if indeed through murphy's law, the fuse blows up from inside during the race? i dont see much difference in safety point of view to the "harmful if inhaled, and care should be taken to avoid contact with eyes and skin" Fluorinerthttps://en.wikipedia.org/wiki/Fluorinerthow about lets push it further... a very carefully engineered and sized sealed container not to discharge steam? perharps an aluminium sealed box with fins and door and a body temperature controlled 12W fan? 5mm aluminium thickness and M16 bolt nut door retainer should be more than safe enough in case steam do indeed develops from inside.. edit: whatever the system will be like, i hope that can fit in the $500 budget..

author: Fungus
author_rank: Super Contributor
timestamp: October 14, 2015, 07:00:18 pm
content: Quote from: langwadt on October 14, 2015, 04:25:07 pmIt doesn't say that, it just says "no capacitor banks".Quote from: Mechatrommer on October 14, 2015, 06:47:36 pmWhat would it get you? 5% extra? Just build a better car, it will be easier.

author: langwadt
author_rank: Super Contributor
timestamp: October 14, 2015, 07:31:48 pm
content: Quote from: Fungus on October 14, 2015, 07:00:18 pmthere is not a lot of other ways to store a appreciable amount of electric energy

author: Fungus
author_rank: Super Contributor
timestamp: October 14, 2015, 07:49:04 pm
content: Quote from: langwadt on October 14, 2015, 07:31:48 pmThere's not a lot of ways to cheat a fuse either.I say keep it simple: Put in a fuse temperature sensor and a MOSFET. Apply PWM if the fuse is getting too hot.An inductor to smooth the PWM pluscurrent sensorwould help too - that way you're not relying on the motor to keep the fuse alive.

author: AMS
author_rank: Contributor
timestamp: October 14, 2015, 07:54:44 pm
content: How about using a peltier cell to cool the fuse done when needed. You can control it via micro controller or even a simple threshold switch circuit. I have used peltier cells before to cool stuff down and it certainly works very well all you need is the cell, supply, heat sink and potentially a fan (on the heatsink).

author: Fungus
author_rank: Super Contributor
timestamp: October 14, 2015, 08:01:43 pm
content: Quote from: AMS on October 14, 2015, 07:54:44 pmThey need a lot of amps...(but I guess you could cool a big chunk of metal when you're braking and the amps aren't needed for the motor...)

author: AMS
author_rank: Contributor
timestamp: October 14, 2015, 08:28:43 pm
content: Quote from: Fungus on October 14, 2015, 08:01:43 pmExactly, he cannot store charge in capacitors but I assume there is no ban on storing thermal energy (or in this case lack of thermal energy). when the motor is under the max allowed current the rest can be used to cool stuff (sealed cooling system or simply as you pointed out a chunk of metal).

author: DanielS
author_rank: Frequent Contributor
timestamp: October 14, 2015, 09:07:54 pm
content: Quote from: Fungus on October 14, 2015, 07:00:18 pmI bet they would not allow a stack of secondary AGM, lithium, NiMH or other cells for "local" storage downstream from the fuse either. The ban on capacitor banks is likely intended to mean that once the fuse is removed or blown, there won't be any significant amount of energy left in the system, presumably for safety reasons.

author: Fungus
author_rank: Super Contributor
timestamp: October 14, 2015, 09:09:59 pm
content: Quote from: AMS on October 14, 2015, 08:28:43 pmI wonder if the Peltier in reverse would generate useful amounts of current from the heatsink. Use it to store power...

author: Fungus
author_rank: Super Contributor
timestamp: October 14, 2015, 09:11:08 pm
content: Quote from: DanielS on October 14, 2015, 09:07:54 pmMaybe. There's very specific instructions about kill switches.

author: mikerj
author_rank: Super Contributor
timestamp: October 14, 2015, 09:48:37 pm
content: Quote from: Fungus on October 14, 2015, 07:49:04 pmYou can cool it as much as possible to raise the rupture current, and that's what many suggestions have been about (be it water, dry ice, flourinert heat pipe etc.).The actual amount of heat emitted by the fuse is pretty low, it's (cold) resistance is just 1.4 milliohms which gives 2.2 watts at 40 amps, though that will increase as it heats so keeping it cool is clearly a good thing.You pit every 15 minutes, so a water cooled solution could presumably be drained/refilled during that period if you don't want to add a radiator/pump etc. 250 millilitres of water would be raised by less than 2 Celsius, no chance of spitting boiling water anywhere.

author: Fungus
author_rank: Super Contributor
timestamp: October 14, 2015, 11:36:02 pm
content: Quote from: mikerj on October 14, 2015, 09:48:37 pmDry ice is probably better/cleaner/safer.Or maybe an adaptedCO2 pipe freezer.

author: IanB
author_rank: Super Contributor
timestamp: October 15, 2015, 07:33:10 am
content: The whole trend of this thread (get more current through the fuse) seems to be missing other aspects that may be more important.Just because you can get 1440 W to the motor doesn't mean the motor can put 1440 W down on the road. I would venture that far more is to be gained by making efficient use of that 1440 W than by trying to squeeze a few more watts past the fuse. What about gearing and/or electronic control systems? What about AC motors with VFD? Are there no other outlets for creativity other than the maximum supply current?

author: Fungus
author_rank: Super Contributor
timestamp: October 15, 2015, 12:16:28 pm
content: Quote from: IanB on October 15, 2015, 07:33:10 amYep.Quote from: IanB on October 15, 2015, 07:33:10 amI think the OP was after a quick+magic fuse trick from the geniuses here.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 15, 2015, 01:51:24 pm
content: Quote from: IanB on October 15, 2015, 07:33:10 amthere are.. thermodynamics, aerodynamics, mechanical structure and material constructions, energy loss and friction analysis, weight analysis, the usual electronics system and controls, stability, aesthetics and ergonomics, risk management, costing etc. ones can pick, to lump all in one "lets make $500 electric race car" thread or make them into smaller separated threads... we already have 8 pages for a fuse...

author: mikerj
author_rank: Super Contributor
timestamp: October 15, 2015, 04:58:33 pm
content: Quote from: IanB on October 15, 2015, 07:33:10 amWhat would prevent you putting more than 1440 watts down to the road? We aren't talking about some kind of 1000bhp tarmac rippling monster here. Assuming the tyres are rubber rather than Teflon, there should be no problem.

author: Fungus
author_rank: Super Contributor
timestamp: October 15, 2015, 05:00:54 pm
content: Quote from: mikerj on October 15, 2015, 04:58:33 pmFriction.

author: mikerj
author_rank: Super Contributor
timestamp: October 15, 2015, 05:22:25 pm
content: Quote from: Fungus on October 15, 2015, 05:00:54 pmYou need to clarify your meaning. Too much friction in the drivetrain is limiting the power available at the wheels, or not enough friction at the tyre/road interface causing traction issues?Traction is most unlikely to be a problem with such low power. 1440 watts is almost half what a 50cc moped makes and you don't tend to see them burning up tyres.Friction in the drivetrain is a consideration for sure, but simple electric vehicles only require the most basic of drive systems, e.g. toothed rubber belt or bicycle chain and sprockets (both of which are highly efficient) so there is limited scope to get this badly wrong.

author: Fungus
author_rank: Super Contributor
timestamp: October 15, 2015, 05:38:37 pm
content: Quote from: mikerj on October 15, 2015, 05:22:25 pmNot easy to clarify because we don't know what 'drivetrain' is.Or 'wheels'... wheels have rolling resistance as well as traction.It's easy to lose energy due to friction in both of those things.(Anybody who's pushed a car knows that it doesn't roll for very long....)

author: max_torque
author_rank: Super Contributor
timestamp: October 15, 2015, 06:22:17 pm
content: A few point that spring to mind:1) overall drivetrain efficiency will be the major factor. Things like converted claw pole alternators etc struggle to be over 65% efficient (a massive penalty). A decent brushless motor is more like 95% efficient!. You mechanical drive needs to be robust, efficient and allow a good spread of torque. A high speed brushless motor with a washing machine PolyV or toothed belt reduction (possibly multistage if you can't package the necessary diameter is efficient, cheap and robust!2) Assuming that battery energy storage isn't limited, the trade off is to get within the the cost requirements. Specific energy of battery systems varies hugely!3) Assuming total battery power ISN'T monitored and that the limit is just an unmodified Fuse, during off throttle times, you need to use some battery power to actively cool the fuse! High speed forced air cooling (think dyson air blade fan etc!) accurately targeted to blow the fuse down will make a huge difference to the fuses average temperature (and hence average current capacity). Using ambient air is safe so shouldn't cause to many issues with scrutineer! Obviously, when you use full throttle, that cooling system needs to turn off / down to allow the traction system the full power capacity of the fuse. A basic track model would allow you to optimise these factors fairly easily. (assumption that the fuse cooler must be powered from downstream of the fuse, ie all the vehicle power comes via the fuse). As the fuse in question is plastic clad, you will have to indirectly cool it, by using a suitable custom fuse folder, that has a very low thermal impedance (clamp both sides of the fuses tangs, as close as possible to the plastic centre bit!)4) Depending on the rotors iron loses and the de-mag capability of the motors magnets, you can seriously overspeed the motor to get a wide vehicle speed range (using Field weakening techniques) and apply a massive current at low speed to get high torque (phase current x phase voltage < 1440w, so at low rpm, when Bemf is tiny, phase current can be massive!)5) F=MA. low mass, low friction, low drag will win the day!6) A fuse testing rig would be easy to build, using a suitable transformer (you need high current, not high volts to test it) so you can carry out a parametric study to identify the best techniques to maximise fuse thermal capability. The regs limit the max cost of the finished vehicle, and NOT the cost of the R&D effort to optimise that vehicle!