Toggle switch for small aircraft charging system in case of failure - Page 1
Forum section: electronics / projects

author: ITman496
author_rank: Regular Contributor
timestamp: April 16, 2020, 05:27:52 am
content: Hello!I'm trying to figure out the best way to have a toggle switch to temporarily disable the charging system of a small 440CC engine.The charging system is a shunt regulator on a single phase stator and permanent magnets on the flywheel. It's a 4 wire regulator.The theory, as far as I can tell for how it works, is the regulator directly dumps into the battery after passing through the rectifying diodes in the regulator, and the regulator has SCRs connected across the stator winding BEFORE the rectifying diodes, and it will intermittently shunt the current of the stator winding to short them out when the voltage at the battery starts to rise too high. As load increases, it shorts them less, and as load decreases, it shorts them more often, until zero load where theoretically it's holding the winding shorted as to not charge anything.My question is this. I'm building an airplane, and I know from past experience with friends with dirtbikes/motorcycles/atvs/snowmobiles, which all have this charging system, that regulators commonly fail, and their failure mode is to start just pumping power into the 12V system, overcharging the battery, boiling it over, and frying whatever is on the 12V system if it cant take voltages north of 17V or however high it decides to go.My ability to disconnect the regulator has two benefits.One, on the ground, I can easily turn it on and off and see, hey, I'm charging when its on, and not when its off, due to the voltage dropping from 13 something to 12 something and then rising back up again.Two, if the regulator fails, I can turn it off and just cruise home on battery. The capacity of the battery is such that it can run the aircraft even with the backup electric fuel pump switched on for around 2-3 hours. It's oversized for the demand because I need the CCA for the starter motor. It's a big boy. But when the aircraft is flying, normally, the only electrical demand is the flight computer, which draws 1.5 amps. The fuel pump is mechanical (crank case pressure pulse driven) and the backup draws 1.6 Amps.If I can't turn a failed charging system off, then my issue is under my seat, in my wooden airplane, is a battery that's having up to 130W (I have no idea what the overcharge curve of an AGM lead acid battery is. How does the current absorption work as you go over the limit?) being shoved into it. This turns an OK turn and head back for home situation into a land ASAP situation, which is far more annoying. Also, I'd rather like to not find out just how high the unregulated voltages can go, and fry my flight computer.So what I am asking here is... How can I disconnect the charging system safely while not damaging it due to the aforementioned testing idea.So far I've devised 3 methods.A: Disconnect positive wire from regulator from battery, let it do whatever.Pros:Simple, the wire for it even passes right where the switch would be located.Cons:Nothing to sink the rectified voltage from the stator into. Voltage skyrockets, I've heard upwards of 100V p2p can be sourced from those stator winding at high RPMs!B: Short stator winding on engine with toggle switch, cut it off at the source.Pros:As this is how the regulator works anyway, it shouldn't harm anything, right?Cons:Unnecessary parasitic load on the engine. It won't be 130W, as while the stator can supply a relatively constant amperage across the rpm range, the voltage will rise and fall with rpm, and if you short it out, you reduce the voltage across it and the back EMF winds up reducing the resistance on the motor. I think. That's what I read, anyway. The idea being that if your regulator on your motorcycle shorts the winding out, its not putting the full load of the electrical system on the engine, just a little bit. (The numbers I saw were that a 400w charging system on a motorcycle will experience 60W of heat generation when the regulator is completely nullifying the output due to the battery being fully charged) But the switch that shorts it will still have to flow considerable current. How much does a stator winding supply at short circuit?C: Run one stator winding wire through the switch before it goes into the regulator input.Pros:Completely open circuits the stator, removing its ability to generate any load at all, can't overcharge the battery, can't load down the engine, can't get hot.Cons:Open circuit voltage of the winding can skyrocket north of 100V on some engines at high speed, or so I've read. Is this bad? Does the winding care? The other catch I can think of is when you reconnect the winding back to the regulator input. If you are unlucky, you'll close the switch contacts right at the highest peak voltage, exposing the regulator/rectifier to incredibly high voltages, blowing it out.D: Do nothing. I'm overthinking this problem. Get rid of the switch and just move on.Does anyone have any experience with any of this?

author: ITman496
author_rank: Regular Contributor
timestamp: April 16, 2020, 05:36:11 am
content: Embedded here is an example circuit of how the system works that I found on google. The example is 3phase, however, and mine is single phase, but you get the idea.EDIT: However I would like to note that my regulator does not get an ignition circuit power source. Fed from its own output. Also, it is old, and this is an old design, so the regulation is likely not an IC, but a zener that triggers the SCRs when the voltage is too high. It is not.. very exact regulation.

author: Nusa
author_rank: Super Contributor
timestamp: April 16, 2020, 07:23:15 am
content: In general, the answer would be A. As for cons, what do you think will happen in the zero-load case? And how is that a problem?However, if you've already got a proper fuse or circuit breaker panel, the answer may be D. You can pull the breaker or pull the fuse to kill the circuit.If it's not a fused circuit, it should be, like everything else electrical in an aircraft. You can't afford to have the wire itself be the weakest link.

author: ITman496
author_rank: Regular Contributor
timestamp: April 16, 2020, 08:14:55 am
content: My worry for A is that with nothing to sink the load into, the voltage coming out of the regulator will spike to whatever the p2p voltage of the stator winding is. Which may be above the rating of certain components in the regulator. I've seen evidence of this when friends have ran ATV's without batteries in them. It tends to melt the wiring harness from the surging voltages shooting through, the lights tend to run a lot brighter and pulse at idle.It does have a breaker, but that will not really help because the issue is it not regulating. When a regulator fails, its typical failure mode is to simply do nothing. Which leaves the stator to dump freely through the rectifying diodes and charge and charge and charge the battery until it boils over and there's nothing left. The charging current will never exceed the usual current you'd see through the circuit, it just will never stop.Unless anyone has a better idea, I'm going to simply put a toggle switch that is normally always switched on that links the output of the regulator to the battery. I'll then put a red flip cover on it so it can't be disturbed and is actively held down, conducting. If the computer sees the voltage rise above 15 or so volts, it will throw an alarm, and if I determine its overcharging, I'll pull the cover up and flip the switch to isolate the rectifier. Then I'll go and land and replace the unit, since at that point its already broken and it doesn't matter if it breaks more.

author: Nusa
author_rank: Super Contributor
timestamp: April 16, 2020, 09:01:16 am
content: If you don't have a complete circuit, there is no load. It's current that melts things, not voltage. So your anecdote about the ATV isn't terribly relevant. Yes, the charging circuit needs the battery to act like a capacitor and smooth the voltage, so no surprise the voltages are too high and pulsing. Visible pulsing at idle is simply because the frequency of the AC being converted to DC is very low when engine speed is low. It pulses at high speeds too, but it gets too fast to see with the human eye.Most aircraft-type breakers are also intended to be used as switches, in which caseyou've already got what you're asking for. If you have a different kind of DC breaker, then never mind. I never said the breaker/fuse should pop in this instance, merely that one should be present for safety reasons.

author: David Hess
author_rank: Super Contributor
timestamp: April 16, 2020, 11:37:48 am
content: Quote from: ITman496 on April 16, 2020, 08:14:55 amThe rectifier diodes can be driven into reverse breakdown and damaged if the output is left open.There used to be kits to convert car alternators to 120 volts which could work to power hand tools which used universal motors. But the result was often a failure of one of the rectifiers in the alternator due to high voltage.

author: ITman496
author_rank: Regular Contributor
timestamp: April 16, 2020, 12:48:36 pm
content: My breaks unfortunately are pop up only and push to reset type, I can not pull them manually. Everything that matters has to also have a switch. But that's besides the point.That's interesting David! It makes sense though, those windings can sure put out a lot if you let them! I had no idea that was ever a thing. I guess I know why it continues to not be one..

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 16, 2020, 01:55:49 pm
content: What does the generator AC voltage do when presented with a capacitive or inductive load? What does the waveform look like on a scope?Quote from: ITman496 on April 16, 2020, 05:27:52 amHave you considered using a LiFePO4 or NiMH battery instead? Weight really matters on aircraft, hence why lead acid is rarely used in those applications.Quote from: ITman496 on April 16, 2020, 08:14:55 amWhat about have the switch redirect the generator to a dummy load?

author: ITman496
author_rank: Regular Contributor
timestamp: April 16, 2020, 02:09:35 pm
content: Quote from: NiHaoMike on April 16, 2020, 01:55:49 pmI'll have to get back to you on that as I am soon to get the engine running but not quite yet.Presumably whatever a permanent magnet ac motor, single phase would do when presented with that, which I'm not sure. A little outside my area..Quote from: NiHaoMike on April 16, 2020, 01:55:49 pmI was actually considering a LiFePO4, but I could not get definitive answers on how they would cope with the charging system of a small engine like this. I heard that they do not appreciate the large pulses of single phase charging systems, and much prefer the 3 phase ones. Also, this regulator overcharging issue would go from thats annoying to catastrophic with one of those, so this issue is even more important. Finally I'd need to get a new, more expensive regulator because lead acid ones float too high for the LiFePO4 cells. Not done any research into NiMH cells, however. I kind of forgot they existed..The thing that swung me to lead acid was simply cost and at the end of the day, a couple pounds difference at this scale. It's no car battery, that's for sure, only a little AGM. The cost and charging system retrofit savings made it worth it.Quote from: NiHaoMike on April 16, 2020, 01:55:49 pmI was thinking about that, too. Just have to find one, I suppose. Maybe a chunky aluminum finned power resistor bolted on the other side of the floor into the air stream? Or perhaps an incandescent light?

author: BradC
author_rank: Super Contributor
timestamp: April 16, 2020, 02:57:43 pm
content: Quote from: ITman496 on April 16, 2020, 08:14:55 amYou are asking for a way to disconnect the charging circuit in the case of rectifier/regulator failure, and you are worried about damaging the regulator?I'd be more concerned about an unrestrained stator generating enough voltage to cause insulation breakdown in the windings.I'm with Mike. Switch it over to a dummy load small enough to be viable and big enough to prevent huge inductive spikes. A couple of well calculated high power resistors somewhere in the prop airflow should do the job and weigh bugger all.

author: ITman496
author_rank: Regular Contributor
timestamp: April 16, 2020, 03:12:59 pm
content: Quote from: BradC on April 16, 2020, 02:57:43 pmAgreed. Also, the reason for the disconnect without damaging the regulator was to allow me to disconnect it on demand, on the preflight run-up of the engine on the ground before takeoff to test to make sure its working. But in retrospect, that's kind of dumb because I can see that its working by the voltage rise on the system. If the battery is 13V or higher, it HAS to be working.I'll instead use a SPDT switch and route the positive output of the regulator to a power resistor pack under the aircraft to take the edge off the pulses.

author: richard.cs
author_rank: Super Contributor
timestamp: April 16, 2020, 04:05:52 pm
content: Personally I would go for a shorting switch before the rectifier. Output voltage remains low so prevents diode or insulation damage and the load on the engine will be much lower than with a resistor connected. This kind of stator is usually designed to have high output voltage compared to the load and high series inductance so they behave pretty much as a current source (it's a nice trick - open circuit voltage and impedance both scale linearly with RPM so it's constant current independent of revs). They're specifically designed to be regulated by shorting so it does them no harm. Yes there's the I2R loss in the winding, but that current won't be a great deal higher than the normal charging condition.Using a load resistor draws more power from the engine (a shorted stator looks largely reactive) and gives you the problem of needing to safely dissipate that power somewhere without a fire risk.There is one advantage to an opening series switch though - it protects you from shorted regulator or rectifier discharging your battery which is a failure mode that hasn't been discussed. An optimal solution is probably a DPDT switch with one pole wired to open the battery connection and the other wired to short the stator. You need it to be break before make or (perhaps better) have a shunt zener on the rectifier output to soak up the voltage transient during switching.

author: David Hess
author_rank: Super Contributor
timestamp: April 16, 2020, 04:37:02 pm
content: Quote from: ITman496 on April 16, 2020, 12:48:36 pmBack then there were fewer options. The flux-switched inverters available back then only put out a square wave and not a modified sine waves and they were pretty heavy compared to just modifying an alternator. Today we have cheap and powerful high frequency inverters.What I might do is use a switch to open the output but also include a big power zener diode to limit the voltage to 24 volts or something. Big stud mount power zener diodes used to be available but no longer. That leaves a more complex power shunt regulator although it is possible to configure a common voltage regulator like an LM317 as a shunt regulator by shorting its output; use an LM338 instead for higher power capability although I am not sure it will be high enough.

author: ITman496
author_rank: Regular Contributor
timestamp: April 16, 2020, 05:37:54 pm
content: Quote from: richard.cs on April 16, 2020, 04:05:52 pmInteresting. I'll have to raid the parts pile and see if I can find anything like that, I know I have a few stud mount components.Right now the plan is to use a dual throw switch to redirect the regulator output to a ~50W 10 Ohm power resistor mounted under the plane on the bottom skin in the air stream for cooling. Just enough to take the edge off the high spikes, and assuming this switch is only thrown in regulator failure, it should.. be okay? The idea is that it only has to last until I get back home and not damage the stator in the process.I do like your idea to have it short the stator instead though. The only annoying thing with that is that I now have to route a very noisy high frequency AC line through to the middle of my plane, past all the guts and electronics, to the switch. I suppose I could use a relay up front, but now we're getting very complicated again and I'm trying to avoid that.Quote from: David Hess on April 16, 2020, 04:37:02 pmI went on ebay and they seem to be.. not awfully expensive?

author: richard.cs
author_rank: Super Contributor
timestamp: April 16, 2020, 07:29:08 pm
content: If you route the stator in on twisted pair then the noise shouldn't really be to much of a problem. The AC is low frequency, and whilst it will have switching harmonics from the regulator the energy is quite limited - it's impulses when the SCRs turn on and the repetition rate and therefore the overall energy content will be low. I'd expect it to mess with poorly shielded audio but not to have enough high frequency content to cause radio problems - SCRs are just not very fast devices.You could put the short circuit after the rectifier. It'll obviously stress the rectifier diodes a bit more but the current won't be much different to charging a dead battery. That would allow you to have a simple changeover switch with alternator output on the moving contact, battery one side and short circuit the other. You would need it to be an ordinary break-before-make switch and a permanently connected Zener, or better a TVS diode (basically a pulse rated Zener) on the alternator output to clamp the voltage for a few tens of milliseconds as the switch moves. This is exactly the same as your proposed load dump, just with a zero Ohm dump resistor. The power resistor would get you slightly lower (perhaps 20%, dependent on engine revs and chosen resistor value) rectifier currents when dumping at the expense of increased engine load. With or without a power resistor, a Zener or TVS to cover the switchover is required - 10 ms of switching time is forever as far as insulation breakdown and the semiconductors are concerned. Thinking about it a bit more this is probably the approach I would take, with a zero-Ohm dump. It's simpler than switching both output and stator, and the rectifier should cope just fine.PS: you can replicate the behaviour of a high power Zener with a low power Zener and a big transistor, though at >100 W it might not be that sensible. If you really want a load dump then it should probably be a resistor.

author: ITman496
author_rank: Regular Contributor
timestamp: April 16, 2020, 07:56:09 pm
content: Quote from: richard.cs on April 16, 2020, 07:29:08 pmSee now, this is why I'm glad I came here. You know exactly what you're talking about.How high are the currents going to be do you think, when it comes to the shorting the regulator output? The "lighting coil" as it is called is stated to have a rating of 120W. So presumably a normal current of 10A or so. I assume it will short circuit higher, though? I want to make sure my wiring and my switch are up to snuff, so to speak. Would hate to have it melt down! I'm also a little worried about the DC current but it's pulsed anyway so in theory that means I can use the AC ratings on the switch..Now the question is, what TVS diode to use. Do they come in mounts that are easy to deal with? I assume thermals are irrelevant because its a pulsed load. I've never worked with TVS diodes before.. What voltage would be good? Presumably I want the reverse standoff voltage to be somewhere in the 18-24V range so it never tries to conduct while the system is running normally?

author: richard.cs
author_rank: Super Contributor
timestamp: April 16, 2020, 08:54:54 pm
content: The way it normally works is that the stator is approximately constant current. As it's designed for use with a battery that current will probably be slightly more than the expected maximum load current of a lightbulb or two to allow for charging, and the short-circuit current might be 20% more or so than the normal current.As a very rough guide a typical 12V system might make 20 V or so at tickover (and not manage full charge current) and 100 V or so at max rpm. If it were designed for 10 A output it might have a 9 Ohm or so stator reactance at whatever frequency corresponds to max RPM, so with 14 V across the battery you get a current of around (100-14)/9 = 9.6 A. At half revs the open circuit voltage will be half so 50 V, but the frequency is also halved so the reactance is halved and the current is similar: (50-14)/4.5 = 8 A, so the output current is fairly flat with rpm until low revs where the battery voltage becomes significant. Calculating the short circuit current of this example, at max rpm it's (100-0)/9 = 11 A and half revs is the same, (50-0)/4.5 = 11 A.This is a simplification which ignores a few points, e.g. that at low revs when the reactance is low the resistance becomes significant, eddy current losses in the core, etc. but it makes the basic point that short circuit current is usually only modestly more than the normal running current. If you're unsure of the rated current then it would be fairly simple to measure the short circuit current with a suitably rated meter.TVS diodes are normally rated in slightly silly units, peak power for a some particular test waveform. This is a little annoying, but basically corresponds to an amount of energy that they can absorb, better datasheets give this in Joules in addition to the peak power though it can be estimated from power specifications. The event is assumed to be adiabatic, so fast that no energy is dissipated from the TVS, it just gets hot according the the energy dissipated and its own heat capacity.As a rough guide a mechanical switch might take 10 milliseconds to change over. Note, you will definitely want a switch with a snap action, not a cheap slide switch or whatever, to make this reliably fast. If your TVS voltage were 20 V say (this is the voltage at which they're rated not to leak much) and it's many-hundreds-of-amps clamping voltage were 28 V (normally you only get these two points, and maybe a zener voltage at a few milliamps) then we could guess that at 10 A it might drop around 25 V. 10 A * 25 V = 250 Watts, 250 W * 0.01 seconds = 2.5 Joules, so now you have an energy spec to aim for.You can get them in leaded, diode-like packages. A common current waveform (due to the near-constant voltage the power waveform is similar) specified is 1 us rising exponential, 1000 us falling. Let's approximate it to a simple sawtooth 1 ms wide. A TVS rated to 1000 W with this waveform is really rated to about 0.5*1000*0.001 = 0.5 Joules, so you probably want a 5 kW rated TVS for your 2.5 Joules. Looking at a random manufacturer's datasheet for a 5 kW 15-20 V part:https://www.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_5kp_datasheet.pdf.pdfI shall pick out 5KP16A. It's rated to leak near-zero-current at 16 V, behaves as a poorly specified Zener around 19 V, and clamps to 26 V at 200 A. This particular one is 9 mm long so could be soldered across the back of the switch or anywhere else convenient.I'm not recommending that specific part, though it's probably fine for your needs, more trying to explain the selection process.

author: SkyMaster
author_rank: Frequent Contributor
timestamp: April 16, 2020, 10:23:42 pm
content: Quote from: ITman496 on April 16, 2020, 05:27:52 amIsn't the alternator Field that you want to disconnect (or is it short to ground?) in order to disable the alternator?In a light aircraft, the alternator switch is switching the Field of the alternator; there is no switching done on the output of the alternator.Now, with a 440 cc engine, what is your aircraft?

author: Nusa
author_rank: Super Contributor
timestamp: April 16, 2020, 10:52:37 pm
content: Quote from: SkyMaster on April 16, 2020, 10:23:42 pmThat would be true if he had a modern alternator with field coils. He's got permanent magnets on the flywheel to create the field. Sometimes called a magneto, even today. Although in aircraft that term usually refers to units dedicated to firing the spark plugs.

author: ITman496
author_rank: Regular Contributor
timestamp: April 16, 2020, 11:00:50 pm
content: Quote from: richard.cs on April 16, 2020, 08:54:54 pmThank you again so, so SO much for not only the advice, but the education. People like you are why I love the internet so much. I feel a lot better about this. I will do a bit of research and figure out what TVS I need.A question, can I parallel them or is that a bad idea? I figure if I get one like you listed, putting two in wouldn't hurt?Quote from: SkyMaster on April 16, 2020, 10:23:42 pmIt's an ultralight! More specifically, a Minimax 1100/1030R hybrid, with a kawasaki 440A 2 stroke engine!I unfortunately can't just disconnect the field winding, as much as I wish I could, as it is not a field winding driven alternator, but a permanent magnet on the flywheel moving past a single phase coil. Can't turn that off no matter how hard you try.

author: richard.cs
author_rank: Super Contributor
timestamp: April 17, 2020, 08:21:28 am
content: Quote from: ITman496 on April 16, 2020, 11:00:50 pmYes, you can parallel them but they won't really share the dissipation very well and you should assume one (random which but probably the same each time) will absorb all of the energy. If you want multiples as a backup and each can individually cope with the expected energy then this is fine. If instead you want to increase the energy absorption ability it's better to make aseriesstring of lower voltage ones.As a side-note the usual failure mode for semiconductors at low to moderate overloads is short-circuit. They overheat and re-diffuse into a single conductive lump of silicon. As very high currents bond wires can blow open like fuses, but that wouldn't be expected on TVS diodes which are made for huge peak currents and certainly not in your application.

author: ITman496
author_rank: Regular Contributor
timestamp: April 17, 2020, 08:34:05 am
content: Fascinating! I really had no idea about the mechanical aspect of a silicon meltdown but it makes a lot of sense the way you explained it.I will put two in parallel just for the sake of it since they are small, and I got a 5 pack.Do you think this setup is testable or will it damage the regulator to short it out like this? I suppose it probably won't because, well.. Looking at the schematic I found before, it uses the SCRs to short the stator winding through the bridge rectifier anyway. So they should be used to this treatment.

author: richard.cs
author_rank: Super Contributor
timestamp: April 17, 2020, 08:59:24 am
content: It should do no harm to test it, from the stator's perspective it's the same as normal regulation, and the rectifiers will see only a modest current.You're doing the project I've wanted to do for a long time, but the rules here are very different which makes it much more difficult, plus there's the question of space. Got any photos?

author: ITman496
author_rank: Regular Contributor
timestamp: April 17, 2020, 09:52:42 am
content: Quote from: richard.cs on April 17, 2020, 08:59:24 amSure do! Keep in mind its a little rough still because I inherited the built from someone else and am going over it. The fabric will be coming off next week and replaced and repainted with new stuff. Also, these photos are in no particular chronological order, covering the span of 2 years. Hence the different looking engine, different instrument panel, windshield, no windshield.. etc. The First picture is the most current.Ignore the electronics in the food container. That's just temporary engine datalogging for testing stuff while I continue to build the actual electronics.Keep in mind that I did not have the ailerons/flaps installed for the photo because they were still strapped to a trailer at the time

author: fcb
author_rank: Super Contributor
timestamp: April 17, 2020, 11:27:09 am
content: I would just have a warning alarm that monitors the battery for prolonged over and under voltage, if the warning goes off I'd land and investigate/disconnect the alternator belt/wiring - I guess you fly with a small tool-pouch!

author: floobydust
author_rank: Super Contributor
timestamp: April 17, 2020, 06:38:38 pm
content: I think it's important to look at the root cause of the regulator SCR's failing. For what you are trying to do, the added wires, switch and complexity I think would lower reliability maybe worse than the voltage regulator's alone. I see a main output circuit breaker anyway on airplanes to fuse/disconnect the output winding which seems best.Having a TVS diode or snubber or diode-clamp at the winding will prevent large voltage spikes from stressing the regulator. Some older designs had almost nothing for surge protection. Not sure of your part number. I looked at a Rotax/Ducati RV12 andwas not impressed, they are terriblebad solder joints and connections, nothing for surge protection. Also I've seen a huge capacitor 22,000uF 40V added to Rotax 912/914 engines, so it's possible ignition noise and spikes are high. Heat is also the other enemy, so located away from the engine in a place of cool airflow. Vibration is not good for them either.Never short the output of a PM generator (dynamo). It will just load the engine and burn up the stator winding. Whoever said the short-circuit current is small is out to lunch. I have seen Kawasaki voltage regulators fail shorted and the engine was loaded and the stator (oil immersed in the crankcase) burned up as a black tar covered piece of carbon.Example schematics of PM generator voltage regulator- Kubota, Yanmar Tractor RS1105https://www.eevblog.com/forum/projects/ac-generatoralternator-charger-rs1105-replacement/msg1256470/#msg1256470Just a note, a vehicle has a few grounds- the battery (-ve) connects to the engine block but also it's important to have a thick wire braid from engine block to chassis, where the regulator, nav, radio stuff is. If you instead ground the chassis at the battery, there is a surge (at the engine block) during cranking that can raise havoc - like your USB troubles it can damage some electronics connected to the block.

author: SkyMaster
author_rank: Frequent Contributor
timestamp: April 17, 2020, 07:15:32 pm
content: Quote from: ITman496 on April 17, 2020, 09:52:42 amWhen looking at your instrument panel, a Glass Cockpit no less, it is not possible to imagine that this is for a Minimax.FBW CTRLS... Fly-by-wireElectric trims, on all three axis; wow.Your project looks like a lot of fun.What is the EFIS you are using? It this your own creation?

author: richard.cs
author_rank: Super Contributor
timestamp: April 17, 2020, 07:22:53 pm
content: If his regulator is of the type he described then it is a current source, designed to be shorted. That's what the SCRs do in normal operation, and the stator has deliberately high leakage inductance so to make everything behave. This was the normal design on engines of this era (I read 80s on wiki). In fact this type predates regulation at all and battery overcharging at sustained high revs was normal.Therearedesigns meant for use with modern regulators that have low inductance and act like voltage sources, the regulator for one of those is essentially a buck converter. This type shouldn't be shorted but you're unlikely to find that type of stator on an 80s engine.If there's any doubt the two types can be distinguished by measurement.

author: floobydust
author_rank: Super Contributor
timestamp: April 17, 2020, 07:55:09 pm
content: I've never seen or encountered a constant-current dynamo. I guess they would be on a moped or small engine, where do you see them used?I see the regulator uses SCR's as a switchable rectifier diodes, doing cycle-by-cycle control, not shunt regulation.KZ440A service manual gives 75VAC at 4,000RPM with no load on the dynamo - but this is a 4-stroke bike and OP said he has a 2-stroke engine. Anyhow, some idea of the open-circuit voltage.

author: ITman496
author_rank: Regular Contributor
timestamp: April 17, 2020, 08:14:38 pm
content: @richard.cs and @floobydustAt this point I'm leaning towards it being the shortable coil style, but I could be wrong! The points you brought up about crummy regulators is also an interesting point.The solder looks okay at least, but I can not check any further as it is epoxy potted and I can not get it out without likely destroying it.Identifying marks are sparse, but I can see: "2" "TYMPANIUM CORP" "620403" "4990"Googling reveals this similar product with some semblance of spec sheet. What do you think?https://www.classicbritishspares.com/products/tympanium-regulatorsAlso, what measurements can I do to test as you suggested, richard?@skymasterHahahaha yeah, right? I love it.The fly by wire controls are a backup system I decided on to raise the travel limits of the trim motors and raise the speed so god forbid something happens to the teleflex control cables, I can fly the plane home via the trim motors.It is tremendous fun!!The EFIS is my own creation, running on a pi 3b+ (well a 3b, i got a b+ to swap in though for more performance) running on processing 3. Which is why it looks like garbage. The screen is a 10.1" 1200nit brightness non touch with a glass multitouch overlay stuck on top.Still tidying the wiring on the switches on the right! I had connectors on it to remove them (glad I did since I had to twice to shuffle things around)Here is a custom board I made to run power for everything. On it is an arduino to listen to the rotary encoder and backup mfd hardware buttons, and to run the power supplies. On startup it listens to the power switch, turns 12v and 5v on (for the pi and 12v lcd) and the pi raises a gpio high while the software is running. Then when I flip the power switch on the panel down, it lowers a gpio to the pi and the pi sees that and shuts itself down, eventually powering down and the gpio its holding high drops, which signals to the arduino its safe to cut power.

author: richard.cs
author_rank: Super Contributor
timestamp: April 17, 2020, 08:16:42 pm
content: @Floobydust, the schematic you just posted is simplified (missing the SCR gate drive) but shows the SCRs as shunt regulators. With the SCRs off you just have a rectifier bridge. With them on one SCR and one bottom diode will conduct at any time, shorting the stator. The top diodes prevent any current flowing backwards from the battery into the short under this condition. The SCRs are not in series with the output so are not acting as switchable rectifiers.The 3phase version in the second post is similar only with the SCRs inverted so it's the top diodes that conduct when shunting the winding.Knowing the specified open circuit voltage is useful, not only in itself but the shear fact they specify it means that it is measurable without damaging the stator insulation. Transients from opening disconnecting the battery whilst running could still be many kV and trash the insulation though.The other common constant-current dynamo is the bog standard 3W pedal bike dymano. It's roughly a 0.5A current source which is how it (usually) avoids blowing tungsten lamps at high speeds. Modern ones with rare earth magnets are better, giving higher open-circuit volts per rpm so both lighting at lower speeds and being closer to constant current (because Voc>>Vload).

author: richard.cs
author_rank: Super Contributor
timestamp: April 17, 2020, 08:33:21 pm
content: @ITman496, the simplest measurement is short circuit current (without rectifier or regulator), measure it at idle and then even if it's not a shuntable type you shouldn't break anything with a brief test. A shuntable one will have Isc perhaps 1.1*Inominal, whereas for a low impedance one it might be 5-10*Inominal and may well stall the engine. Don't remove it under power unless you have a TVS fitted because you'll get a huge voltage spike - stop the engine instead to stop the test (actually I'm not sure I'd switch a short *in* with the engine running and no TVs either because switch bounce will make spikes).If you don't fancy that then measure the resistance and inductance of the winding (one of the cheap component testers will do), and then measure the frequency and open circuit voltage at tickover. You can then calculate how it behaves at any speed or even put it into SPICE. I have done this to fully (well, mostly) model one when designing regulators. That then allows you to see what the current will be shorted or with any given load (resistor, battery, etc.), at any rpm, which it kind of cool.

author: ITman496
author_rank: Regular Contributor
timestamp: April 17, 2020, 10:28:36 pm
content: This is a picture of the unit that I found online.I will take those measurements when I can! And good point about the test. I'm not gonna do it until I have the TVS diodes in place anyway.I've never done a spice model before but I'd certainly love to try. When I get those measurements I'll do my best!

author: floobydust
author_rank: Super Contributor
timestamp: April 17, 2020, 11:22:51 pm
content: The Tymphanium is series, and old Kawasaki is shunt-type. I find there are many types of dynamo regulators, series and shunt, SCR or MOSFET i.e.https://www.shindengen.com/products/electro/motorcycle/regThe series-type is only two diodes, not four. I just can't get over the waste in a shunt reg or why use more parts.

author: ITman496
author_rank: Regular Contributor
timestamp: April 17, 2020, 11:32:23 pm
content: Quote from: floobydust on April 17, 2020, 11:22:51 pmThat page was extremely helpful to explain how my system works. Thank you!

author: richard.cs
author_rank: Super Contributor
timestamp: April 17, 2020, 11:39:00 pm
content: Quote from: ITman496 on April 17, 2020, 10:28:36 pmAttached is a spice model I made a while back for a small bicycle hub dynamo, based on published measurements. It has the constant-current characteristic discussed, but at much lower output power. In this model I got fancy and used a modulator block to simulate the voltage and frequency change with road speed, but you can also put it in as an equation and have something like voltage=rpm*const1*sin(const2*rpm*time), from memory I started using the modulator because the simulation ran faster.In this model there are some sources on the left performing simple calculations with V1 as a speed input, and then A1 turns it into a speed dependent voltage and frequency which represents the open circuit voltage. E3 just allows this to float and not be 0V referenced which is useful when it's used in a more complex simulation. L1 represents the inductance of the stator, and R2 the resistance. R1 represents the iron loss in the dynamo but doesn't affect the result very much. That's it for the stuff in the dotted box modelling the dynamo.Outside the box is a resistor which is switched between 0.1 Ohms, 1 Ohms and 10 Ohms. The waveform plot shows the current in that resistor. Between 0 and 1 second the model has the bike moving at 5 mph, then at 10, then at 20 mph. The cyan line is current into 10 Ohms, red into 1 ohm and blue into 0.1 ohms. Of particular note is that 1) as the bike speed and therefore dynamo rpm varies 4:1 the current only varies 1.3:1, and 2) as the load varies 100:1, the current varies only 1.6:1 at low speed and 1.2:1 at high speed (where L1 dominates much more over R2).Obviously this is not what you've got, but this type of model can be modified to suit your particular dynamo. There are two constants to tweak that set frequency(rpm) and voltage(rpm), and then put your measured resistance and inductance into R2 and L1. You then have a model that's a reasonable approximation and you can then connect things to the outputs like rectifiers, batteries, short circuits and see what kind of behaviour to expect.

author: ITman496
author_rank: Regular Contributor
timestamp: April 17, 2020, 11:54:08 pm
content: Wow, that is fancy. Is spice free? I've never actually used it before. I have an LCR meter, a decent handheld one, and a scope, so I'll be able to get the measurements pretty easily when I do get the engine running (Hopefully in a few days)When you were looking into aircraft, did you have any particular model in mind? I've seen a few minimaxes flying around in england, though I believe they are called the 88 instead of 1100. I saw a picture of an english spec one on another forum that looked pretty sweet!

author: richard.cs
author_rank: Super Contributor
timestamp: April 18, 2020, 11:40:04 am
content: There are lots of implementations of SPICE, some free, some not. That one is LTspice which is free to use and very powerful, but has a slightly odd user interface.Aircraft-wise it's been years since I looked at it properly, but at the time I thought it would be cool to make a modern version of one of the early aircraft, which after all were very much man-in-a-shed technology. Something like a Blériot XI or Fokker Eindecker perhaps.Notin any way a historically accurate replica, but more using it as an inspiration for the basic airframe and then tweaking it to use a more modern construction and engine.Did you ever see the scrapheap challenge / junkyard wars "flight of the century" special? There's a very poor quality rip on youtube:When I looked into it it basically seemed that for the UK there are not really any simplified rules for small aircraft, either for construction or flying them,* and it looked to be a massive regulatory pain-in-the-arse (I do remember finding French rules interesting, under 250 kg is/was basically a free-for-all). Combined with leaving university and switching from "lots of time, no money" to "money for project, no time" it just got dropped. Ten years ago or so there was almost no-one building them in the UK, or at least not people who put stuff online. Perhaps that's changed now and I should revisit it, find some forums and see how other people are doing it and especially how they're dealing with the regulatory side.Of course then there's the problem of finding space in a suburban house...*It was a long time ago so memory is a bit fuzzy here. I would be pleased to be proved wrong.edit: the forum seems to insist on embedding a youtube preview when I put a link in, and I can't seem to get rid of it even if I remove the URL tags. It doesn't appear in the preview of my post though. Unless that's my browser doing it?

author: ITman496
author_rank: Regular Contributor
timestamp: April 18, 2020, 06:32:31 pm
content: I have no idea how it works in the UK, but I would certainly check into it! There are certainly small aircraft flying around, people seemed to have found a way.I know mine was designed to be built in about a 1 bay garage. 2 would be better, but you can make the dream work in a single bay.I used to be ADDICTED to junkyard wars. That show inspired a lot of what I learned and became today!The usa ultralight class of aircraft (less then 255lbs) is also a free-for-all, including no license or anything needed. I wish it was 250kg!!! I'd have about twice the horsepower and twice the engine strokes. But alas.

author: richard.cs
author_rank: Super Contributor
timestamp: April 18, 2020, 10:30:30 pm
content: Quote from: ITman496 on April 18, 2020, 06:32:31 pmIt surely doesn't fit in a single garage once complete? Unless the wings are removable?QuoteIt looks like I would need a private pilots license to fly something like what you've built in the UK, unless it can be made <70kg in which case it falls into a catagory meant for self propelled hang gliders. This wasn't possible until 2017 when this catagory had to take off on foot but now they seem to be allowing slightly more conventional aircraft within the mass and stall speed limits.Construction wise it looks like it's a submit plans before beginning kind of job with multiple inspections throughout the build.

author: ITman496
author_rank: Regular Contributor
timestamp: April 18, 2020, 11:55:47 pm
content: The wings come right off with just 3 pins! Big pins, but.. still actually quite fast!Some quick googling seems to suggest your microlight license is still significantly cheaper, at 4000 pounds, vs 15k for a normal ppl?One thing I know I saw on the forums was that the blueprints for the plane had to be approved in the UK. Luckily, the minimax has been already approved so I think you can just say hey I'm making one of these and they go oh ok we've seen those before and approved them already. I'm sure there are other models just like that.

author: richard.cs
author_rank: Super Contributor
timestamp: April 19, 2020, 12:29:08 am
content: It looks like a pre approved design helps but there's still a lot of faff, lodging plans beforehand, logging the whole build, every item that goes into it and where it came from, inspection at the end, a series of formal test flights, etc. It also looks like they want a full assessment for even minor deviations from an approved design.It's clearly possible and I'm sure people do it, but it's nothing like the US ultralight class. For me it pushes it from "fun, cool project" to "pain in the arse" which is quite sad really.If you're interested the whole UK process is in a document called CAP 659.Maybe I should learn French.

author: SkyMaster
author_rank: Frequent Contributor
timestamp: April 19, 2020, 12:41:24 am
content: Quote from: richard.cs on April 19, 2020, 12:29:08 amThe United States ultralight category (Part 103) is for very small ultralight with an empty weight of less than 254 lbs, max speed of 55 kts, etc.But, you could buy an already flying aircraftOn the other hands, all those regulations are there for a good reason; safety.

author: SkyMaster
author_rank: Frequent Contributor
timestamp: April 19, 2020, 01:10:18 am
content: Quote from: ITman496 on April 17, 2020, 08:14:38 pmVery impressive.Your Instrument Panel would fit right in a BD-5, or even a BD-5J.

author: ITman496
author_rank: Regular Contributor
timestamp: April 19, 2020, 01:26:50 am
content: Quote from: richard.cs on April 19, 2020, 12:29:08 amYeah, that is quite depressing. Reasonable, but depressing. I'm honestly shocked that the FAA of all groups in the usa allows ultralights to exist still.Quote from: SkyMaster on April 19, 2020, 01:10:18 amOh thank you very much! I know the bd-5 and bd-10 were two things that super inspired me to want to make my own airplane. Too bad the bd-10 was a failure.I'll be sure to start a thread on the electronics of the aircraft once I get more progress! It's going to be quite the system, with a bunch of modules talking over CAN bus!

author: SkyMaster
author_rank: Frequent Contributor
timestamp: April 19, 2020, 02:54:07 am
content: Quote from: ITman496 on April 19, 2020, 01:26:50 amJohn Bede was a genius. Among other things he designed the BD-1, which became the Grumman American AA-1. Instead of using rivets, the skin is glued to the inner structure. I never flew the AA-1, but flew the GA-7 were Grumman American took the same approach; smooth skin everywhere, no rivets.Unfortunately, except for the BD-4 none of Bede design were commercial success.I saw a BD-10 in a museum in Toronto, I was surprise how relatively small it was.

author: ITman496
author_rank: Regular Contributor
timestamp: April 19, 2020, 04:12:30 am
content: That is fascinating!! I know another plane I wanted to make which would have a similar appearance was the Velocity, specifically the v-twin. Because fiberglass.I didn't know there was a museum with a BD-10 in it in toronto. That's only 8 hours from me, maybe when this whole covid thing blows over I'll go over and find it!

author: richard.cs
author_rank: Super Contributor
timestamp: April 19, 2020, 04:54:10 pm
content: Quote from: ITman496 on April 19, 2020, 01:26:50 amWhat I did find looking at things (far too late last night/this morning tbh) is that as a result of a change in 2017 the UK almost has an unregulated category again, but a very restrictive one. Under 70 kg and under 20 kt stall speed is now in the same category as paramotors, with no requirements other than insurance. I'm currently mulling over whether modern materials allow any kind of conventional design in a 70 kg mass budget. I suspect you need so much wing area to meet the 20 kt stall speed requirement that it eats up most of the budget straight away.

author: ITman496
author_rank: Regular Contributor
timestamp: April 19, 2020, 09:50:40 pm
content: Oof, that is not a lot of weight! I suspect you're squarely in the territory of those paramotors but instead of a backpack its a gokart kind of thing.Do they actually check? I know with the FAA they have their limits but nobody actually comes and weighs the airplane.

author: richard.cs
author_rank: Super Contributor
timestamp: April 20, 2020, 08:24:01 am
content: Quote from: ITman496 on April 19, 2020, 09:50:40 pmIt's intended for paramotors with gokarts (people here call them trikes). It came about in response to various disabled people wanting an exemption to use a trike because they were unable to footlaunch. You may well be right that it's all that can be done in 70 kg but when I get some time maybe I'll run through some design calculations.The question of enforcement is an interesting one. I mean if I were to buildanythingand fly it at low altitude over private land it seems highly unlikely anyone would either notice or care however big it were. Not that I or anyone I know owns a plot that big. However if I made something that looked like a microlight but didn't have paperwork, registration numbers, etc. and took it anywhere where I might encounter someone who knows the rules then it is likely to at least get questions, and if the response is "it's under 70kg" then that's going to raise interest if it's not a paramotor simply because that's hard to do (if it's even possible).

author: richard.cs
author_rank: Super Contributor
timestamp: April 20, 2020, 05:04:49 pm
content: After a bit of hunting around online it looks like non-paramotor, <70kg designs are quite possible after all. The Whing Ding II is 55 kg and that's with 1970s materials.Some photos:https://mayaultralight.com/portfolio/11-wdii-build/Plans were freely available on yahoo groups before it died, but not captured by the wayback machine as they were in a members area. Found them for a few dollars anyway so whatever. There's also the bloop which comes in at 81 kg.http://m-sandlin.info/bloop/bloop.htm.Sorry, I seem to have hijacked your thread a little...

author: ITman496
author_rank: Regular Contributor
timestamp: April 20, 2020, 06:03:28 pm
content: Yeah, thats fair. I know a lot of ultralights operate slightly "fat" in that nobody really cares if its 5-10lbs over the limit. Especially because simply having dew on the wings from sitting outside can push you over the limit. That's why they stopped weighing them at the oshkosh meetup (so I heard) because depending on the humidity, you might violate the weight restriction. Not cool!But 70kg.. that's like.. a whole 100lbs less then my plane. I don't know how I'd lose that much weight off of it! Unless you become jet man and become part of the structure of the airplane. Do carbon fiber pants count as part of the aircraft if they form the tail boom?Oh I don't mind! I'm happy to talk airplanes at all. Besides, the thread is pretty much concluded anyway. I may make an actual project thread for it eventually if anyone cared about it! I know the plane as a whole isn't strictly.. electronic.I like those two designs! They are extremely creative. Its amazing how light you can make a flying machine that can carry a person. It truly is.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 21, 2020, 12:06:10 am
content: I wonder how feasible it would be to couple a BLDC motor/generator to the engine and connect it to a smart inverter in order to make it a hybrid. Would the weight savings from downsizing the engine be enough to offset the added weight of the electric drive system? (What's the ratio of cruising power to takeoff power?)

author: ITman496
author_rank: Regular Contributor
timestamp: April 21, 2020, 12:50:10 am
content: I've pondered about that but batteries sure do weigh a lot compared to gasoline. And the less powerful aircraft engines don't seem to weigh much less than the more powerful ones, at least at this size range, not on a linear scale..

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 21, 2020, 02:00:53 pm
content: The batteries would only need to supply a substantial amount of power during the seconds it takes for the plane to takeoff and climb. At least in the R/C world, even miniature jet engines have been mostly rendered obsolete by BLDC motors.What batteries are not good for is range, hence why the hybrid arrangement.

author: SkyMaster
author_rank: Frequent Contributor
timestamp: April 21, 2020, 04:12:35 pm
content: Quote from: NiHaoMike on April 21, 2020, 12:06:10 amFor low power aircraft (typically all piston powered light aircraft) the take off power is 100% power, cruise is 75% power, climb is 100% power.If the aircraft is climbing from sea level to 10,000 ft, at a vertical speed of 500 ft per minute; this will be 100% power for 20 minutes.

author: richard.cs
author_rank: Super Contributor
timestamp: April 21, 2020, 04:19:33 pm
content: Quote from: SkyMaster on April 21, 2020, 04:12:35 pmSo such a system would allow a 1/3 smaller engine (ignoring charging power). I suspect that it's not a sufficient saving on engine mass to balance out the motor and batteries. Might be better off using a much smaller motor and battery as an electric supercharger. Hmmm, I wonder if an RC ducted fan would be good in that role.

author: ITman496
author_rank: Regular Contributor
timestamp: April 21, 2020, 06:27:29 pm
content: I don't think an EDF can do that, as they don't have tremendously good static pressure, which is the one key trait a super/turbo charger needs. They do have viable electric turbos, however! They are essentially the compressor turbine and housing of a turbo, driven by a very powerful BLDC. Can make a couple PSI boost on the average engine, enough to add a kick.Pardon the uh.. american-ness, but this does show what it can do.On another note, I got the TVS diodes in today! I'm gonna put them into the aircraft now.

author: richard.cs
author_rank: Super Contributor
timestamp: April 22, 2020, 08:38:26 am
content: Looks goodAnd good point about EDF suitability, that was a silly suggestion.

author: ITman496
author_rank: Regular Contributor
timestamp: April 23, 2020, 02:08:27 am
content: Its fine! Air systems like that are very counter-intuitive. Axial compressors are very difficult at small scales.

author: richard.cs
author_rank: Super Contributor
timestamp: April 27, 2020, 08:31:06 am
content: As a thought more related to your original question, you said you had a large, and presumably therefore also heavy, lead acid starting battery. Have you considered options for reducing that weight, smaller batteries that can still manage the starting current, lithium rather than lead, etc.? Is it used for much other than starting (do you actually need capacity or just peak current)?

author: ITman496
author_rank: Regular Contributor
timestamp: April 29, 2020, 07:48:01 am
content: I have considered a lithium battery but to save some money I am sticking with lead acid for now. Can always change, though! The issue is that my regulator will likely be set for a lead acid float voltage that is too high for the lifepo4 powersport battery packs. So I'd need to get a regulator rated for lithium. Then I need to get a lithium that is a good quality. All said and done, both would add up to likely 3-400 dollars for not junk parts. Or, I can spend 70 dollars on a good lead acid battery and use my existing parts and be okay. For now, just keeping it simple.....says the person who just did all this stuff with the disconnect.

author: ITman496
author_rank: Regular Contributor
timestamp: May 15, 2020, 07:33:31 am
content: Just to update. Engine tested at high power with no serious mishaps. Charging system working! Switch shunt not tested but.. here's hoping!And yes, the person (my friend) walking around and near the propeller while its spinning will get a talking to about safety distances and the axis at which a thrown propeller blade will likely travel! I was too distracted monitoring the engine to realize just how close he got at the time.

author: SkyMaster
author_rank: Frequent Contributor
timestamp: May 15, 2020, 03:07:39 pm
content: Quote from: ITman496 on May 15, 2020, 07:33:31 amYour friend was very busy too, devices in both hands; measuring the engine temperature and filming the action. It seems that he walked around the spinning propeller with considerable distance when he switched side. Don't be too hard on him, but make sure he has less task to do next time

author: ITman496
author_rank: Regular Contributor
timestamp: May 15, 2020, 03:52:21 pm
content: He did great! Was extremely helpful strapping the plane down, too. Mostly just putting that statement out there pre-emptively for when people do freak out about being near a prop!