Electric Go-kart motor controller circuit - Page 1
Forum section: electronics / beginners

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: July 21, 2017, 10:17:13 pm
content: I am building a small, tame/slowish, electric go-kart for my 9yr old son.For the motor, I plan to use a "gs electric" b4cpm-085t motor (from a treadmill), 2.5 hp, 6700 rpm, 18 amps, 130 v dc.So far, the only motor controllers I have used in circuits are LM293 based, ...so for very small/tiny motors.This circuit will not need to max out the motor, but I do want enough power and rpm's to at least move the fairly lightweight go-kart with my 60 lb son at a fairly slow rate of speed.I have reviewed a few h bridge designs on line, but I suspect this community would be the best to point me in the right direction.I welcome thoughts or schematic designs...ps: I am flexible as to how many volt's I supply. I could do anywhere from 12v Lead acid, or multiple in series, or some high powered higher voltage battery technology (I welcome thoughts on that also)pss: In my limited experience, I have built some power supply circuits using voltage rectified, filtered, regulated mains (non SPMS). I have also done a variety of pwm circuits (via PIC microcontrollers and 555's, etc)

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 21, 2017, 10:54:15 pm
content: How did you select that motor? It seems particularly ill-suited for your target application.The horse-power, speed and voltage don't seem very appropriate.Stepping up 12 or 24 volts to something that the motor can use will waste a lot of power which will make design much more complex.When people re-purpose large motors like that it is common practice to recycle the motor power/control circuit along with it.Designing and building a high-power motor control is rather a higher-end project.

author: BrianHG
author_rank: Super Contributor
timestamp: July 21, 2017, 11:53:49 pm
content: A 60lb son running a 2.5hp motor, he'll fly away...Anyways, if you are using the motor just because you have one, and I don't believe you are looking for the most efficient possible design, just something with some go, running the 130v motor at only 24v or 36v, geared down for the wheels should get you up to a few to 10 miles per hour or so even going up-hill. Again, efficiency will be not horrible, but, don't expect the optimum 82% possible from the motor.Based on knowledge working with 2 old treadmill motors, if you decide to keep using the mini-ribbed flat belt with the pulley they typically have, the drive RPM running at 5v thru 36v, you can expect a really smooth quiet functionality. Any higher voltage would be too much for a 60lb child unless you are making a racing cart and your child wears appropriate helmet and pads safety gear while your go-cart has re-enforced crash cage and seat-belt. Yes, at the higher voltages closer to 100v, your motor will get close to 80% efficiency, but your power electronics will need to improve to handle the voltage range and haveserioussafeties in it's design.As for speed control, I would go the PIC route using the PWM driving a single N-channel-mosfet running from a 24v, or 36v battery setup. I would use an ADC input to read your throttle so you can create a custom curve of throttle position VS PWM % drive + a few outputs to drive a few LEDs to display throttle position. You can get more complex by monitoring battery voltage and compensating...Warning, the treadmill motor, if it is a good high quality one, will sink a ton of current as you begin from a stopped position. They do generate a lot of torque and you should program you PIC accordingly. IE softly engage the throttle...

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: July 24, 2017, 03:10:19 am
content: Quote from: Richard Crowley on July 21, 2017, 10:54:15 pmI was given this motor by a friend, so I thought this might be a decent application for it.I am curious, what type of motor would you recommend, and could you send a link or two?

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 24, 2017, 05:01:29 am
content: There are several good videos on YouTube about using DC treadmill motors. It would probably be helpful to watch half a dozen of the better ones.If I wanted to build something like that I would start with the DC electric motor conversion kits for bicycles. They are more likely to have controller electronics designed to be operated from rechargeable batteries.

author: Zero999
author_rank: Super Contributor
timestamp: July 24, 2017, 03:43:20 pm
content: As far as shock risk is concerned: anything up to 120VDC as relatively tame, compared to the mains, which being AC is more likely to cause ventricular fibrillation: DC is far less likely to cause electrocution, than AC of the same voltage. There is some risk, so voltages over 60VDC need to be insulated from the user, but not to the same extent as mains: basic insulation is all that's required. The main hazards with batteries are: the power can't be disconnected, so it's permanently live and fire: both due to the high short circuit current and the gases produced by the batteries themselves. A fuse or circuit breaker is a must and it needs to be rated to for DC, with the appropriate voltage and breaking capacity.Yes, 2.5hp is huge for a child. I do agree with the comments about making sure they have a crash helmet and padded clothing. The weight for the vehicle should also be taken into account because it could crush them, if it rolls over, hence the need for a roll cage, if it can go fast enough for that to happen. Note that, if it's top heavy, then it doesn't have to go very fast to flip over.There should be some other safety device to stop the motor, other than transistors, which have a tendency to fail short circuit, causing the motor to jam on at full speed. There should be an emergency stop button and cutting power to the motor, so the car needs to be restarted, if the break is pressed hard, is also a good idea.

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: July 24, 2017, 04:18:23 pm
content: Quote from: Hero999 on July 24, 2017, 03:43:20 pmThank you for the helpful notes on Safety.Do you have any recommended for the schematics? (aka: transisiters which could handle the load, etc) Note: I have several heat sinks and fans I could use for the cooling. (ps: I can start with 12v on the source to keep things slow for the first iteration)

author: Zero999
author_rank: Super Contributor
timestamp: July 24, 2017, 06:06:47 pm
content: Quote from: mikeinfodoc on July 24, 2017, 04:18:23 pmDo you want this to reverse or does it only need to go forward?To go forwards only. All you need is a PWM circuit (plenty can be found using a search engine) a MOSFET with a suitable and current rating and as low on resistance as possible and a diode in reverse parallel with the motor. The motor can have a higher supply voltage, than the PWM circuit.Here's one of the simplest PWM controllers there is. The lamp needs to be replaced with the motor and flyback diode, which can have a higher supply voltage than the 555 timer. Unfortunately this circuit probably won't be able to charge/discharge the MOSFET's gate capacitance fast enough for it to switch with low enough losses. A MOSFET driver IC, such as the TC4427 or MC34152, can be placed in between the 555 timer and the MOSFET's gate.A big disadvantage of the above circuit is it can't go down to 0% duty cycle (fully off) or 100% (fully on) so isn't practical for a go kart. This following circuit will go all the way to 0% and up to 100% but the 1k resistor makes it weaker than the 555 circuit so you definitely do need a MOSFET driver.http://ww1.microchip.com/downloads/en/DeviceDoc/21422c.pdfhttps://www.onsemi.com/pub/Collateral/MC34152-D.PDFTo go backwards, as well as forwards, then you need an h-bridge. The only sensible way to do this is to use an IC, either for everything or just to drive the MOSFETs. An h-bridge controller IC will shift the low voltage signals up to switch the high side MOSFETs and prevent both MOSFETs on one side from turning on simultaneously and short circuiting the supply. Here was some examples:https://www.intersil.com/content/dam/Intersil/documents/an93/an9324.pdfhttp://www.ti.com/lit/ds/snvs725g/snvs725g.pdfhttp://www.nxp.com/docs/en/data-sheet/MC33883.pdfhttp://www.mskennedy.com/sites/default/files/4227re-1.pdfhttp://datasheet.octopart.com/MD7120K6-G-Supertex-datasheet-11966372.pdf

author: oldway
author_rank: Super Contributor
timestamp: July 24, 2017, 07:45:38 pm
content: If the goal is only to make a kart for your 9 year old son and not to make a project in power electronics, I believe you have not chosen the right solution.For me, the right solution is the simplest one.I share the finding that the electric motor you have is too powerful.Therefore, it is not necessary to supply it with 130V.My solution would be to use 2 batteries in series to provide 24V.The motor would be powered with only 24V.The circuit would be very simple because it would not use electronics, barely 2 relays.An on / off relay and a relay to bypass the start resistor.The accelerator pedal would operate 2 microswitches at 2 different positions of the accelerator.At start-up, a resistor is in series with the motor to limit the current and therefore the torque at start-up.If the child pushes more on the accelerator, a second microswitch feeds a relay that short circuits the resistance, thus providing a greater torque.With 24V, the motor speed is limited to about 2000 rpm, which is a safety factor.The speed would be controlled by alternating the traction / freewheel sequences by pressing and releasing the accelerator pedal.

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: July 27, 2017, 03:20:01 am
content: It appears the MC33883 has a 1Amp peak.http://www.nxp.com/docs/en/data-sheet/MC33883.pdfThe TI is pretty low also (1.2Amp with 5Amp peak)http://www.ti.com/lit/ds/snvs725g/snvs725g.pdfThe MSK looks like it can do 20Ampshttp://www.mskennedy.com/sites/default/files/4227re-1.pdfI assume that is because the nxp and ti (and supertex and intersil) do NOT have the mosfet's inside/integrated;whereas the MSK DOES (mosfets built into the chip), right?So the msk would mean less components in the circuit... (which could be good for novices like me)Have you used the msk before?

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2017, 09:00:25 am
content: Quote from: mikeinfodoc on July 27, 2017, 03:20:01 amThe MC33883 and LM5113 are not designed to drive the motor directly. They're MOSFET gate drivers. The current specification determines how fast, they can charge and discharge a MOSFET's gate-source capacitance.You're right, MSK4227 doesn't need as many components, as the other ICs I suggested. To be honest, this isn't really a project for a novice.No, I've not used any of the aforementioned ICs before. I haven't attempted such a project. The last h-bridge project I did was much lower power.

author: oldway
author_rank: Super Contributor
timestamp: July 27, 2017, 09:43:03 am
content: QuoteI think the first problem to solve is the voltage, type and capacity of the battery....With lead acid technology, you go nowhere.What's the armature resistance of your motor ?

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 27, 2017, 01:58:30 pm
content: Did you see this?https://www.eevblog.com/forum/chat/ebay-pwm-speed-controller-60-amps-for-less-than-gbp-10-!/

author: voltsandjolts
author_rank: Unknown
timestamp: July 27, 2017, 02:35:53 pm
content: Try searching ebay for Bafang BBS01 (250W/350W) or BBS02 (500W/750W). They are intended for bicycle conversion and include the motor driver, just need a 36V or 48V li-ion battery.They can be used with a thumb throttle (supplied) or twist throttle.IMHO 250W is more than enough for a 9 year old but you could use a more powerful motor and program it for reduced power. Search for programming cable on ebay, free software available.

author: schmitt trigger
author_rank: Super Contributor
timestamp: July 27, 2017, 03:21:03 pm
content: A 2.5HP, 130 volt motor will only produce the full 2.5HP at its rated voltage, 130 volt.For 24 volt operation, it will be 2.5*24/130 = 0.46HP.

author: oldway
author_rank: Super Contributor
timestamp: July 27, 2017, 04:47:23 pm
content: Quote from: schmitt trigger on July 27, 2017, 03:21:03 pmIt is 343W, it is quite enough for a kid ....It is the reason why I suggested to use 24V and with such a reduced power, it is possible not even to use any controller at all.A power resistor of 1 R or 1.5R (made with inox wire) at start-up to limit current would be enough....But the Ebay controller seems to be even cheaper....if it worksNB: it seems that there is no current limitation, maesure the armature resistance, perhaps you will have to had a power resistor in serie to limit current in acceptable values.

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: July 28, 2017, 02:38:09 am
content: Quote from: Richard Crowley on July 27, 2017, 01:58:30 pmThank you for the idea of just buying one.If I do that, perhaps I should go more robustWhat do you think of this one?https://www.amazon.com/Governor-Adjustable-Reversible-Digital-Tachometer/dp/B01MXR4T32/ref=sr_1_8?ie=UTF8&qid=1501208441&sr=8-8&keywords=pwm+motor+speed+controller

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: July 28, 2017, 03:06:58 am
content: Quote from: oldway on July 27, 2017, 09:43:03 amAny thoughts about this li-ion 24v ?https://www.amazon.com/GreenWorks-29842-G24-Battery-24V/dp/B00MYXFPNIand chargerhttps://www.amazon.com/GreenWorks-29862-G24-Battery-Charger/dp/B00MYXFPBA/Also, the armature resistance I measure was around 5 Ohms. (it varied a little as I measures the shaft in various positions/rotations)

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: July 28, 2017, 03:17:59 am
content: Quote from: Hero999 on July 27, 2017, 09:00:25 amWell that is probably true. :-) I might press the easy button and simply buy one (see amazon link from my earlier post); however that takes the fun out of it.So I might go ahead and try a few PWM motor controller circuit builds and check heat/performance/etc. (before installing on go-kart)If I use the MSK4227, I think it has a max of 20Amps. So I would likely want to measure the motor current draw at full_load/stalled (aka: vice clamps preventing motor shaft movement) to see if the motor would exceed 20Amps at 24V. if so, I could go with less source voltage.Does that sound reasonable/sane?

author: oldway
author_rank: Super Contributor
timestamp: July 28, 2017, 10:41:53 am
content: QuoteIt seems not possible for a 18A motor.... Perhaps 0.5 Ohm ?

author: Zero999
author_rank: Super Contributor
timestamp: July 28, 2017, 12:21:06 pm
content: Quote from: oldway on July 28, 2017, 10:41:53 amPerhaps the meter's output voltage/current is too low to break the oxide layer on the commutator, so the resistance reading is higher than expected?

author: oldway
author_rank: Super Contributor
timestamp: July 28, 2017, 12:40:20 pm
content: The collector of a motor which has already been used is covered with a black layer of graphite / copper mixture which does not oxidize.There is therefore normally no oxide layer on the collector even if the motor has not been used for a while..

author: BrianHG
author_rank: Super Contributor
timestamp: July 28, 2017, 03:25:08 pm
content: Quote from: mikeinfodoc on July 28, 2017, 03:17:59 amJust as safety, if you are supporting reverse on your cart, when switching directions, full throttle, you will easily exceed 20 amps, but this would be momentary and if your driver has current limitation capabilities, you can get away with it. I still like your 60amp unit. It offers a good safety range as I think that 20 amps at the wrong time may peak or excessively heat up on a hot day.As for your 2Ah battery, click on the 4Ah version. It is only 10$ more if you wand double capacity. Link:https://www.amazon.com/dp/B00MYXFPD8/ref=twister_B01MG93D2S?_encoding=UTF8&psc=1