Honda GX 35 Power for Nuvinci Developers Kit

Discussion in 'Electrical' started by bigoilbob, Oct 11, 2011.

  1. bigoilbob

    bigoilbob Member

    Help, please. Can't believe that this does not exist somewhere. I have a Honda GX35 hooked up to a Nuvinci Developers Kit, through a Staton 18.75/1 gearbox. As some of you might know, the actuator requires as much as 4 amps at ~12 volts, to shift with, and probably has an average power consumption between 10-20 watts. I now have a Shimano dyno hub in front, on a 16" wheel, with circuitry to change the 6 volt AC output to 12 volt DC, and to charge a little 12 volt battery. But the hub is only good for ~3 watts, which will leave me short of power.

    Here's the question. What is the best way to generate 20-30 watts (a little more for lights would be nice) of 12 volt DC power from my engine or drive train? I have a chain that will be turning when the bike is moving, at ~0 -200 feet/minute. I also have the engine, but don't know how to get on it. The ideal would be a Wonderful Creations type setup, sized for my desired wattage, but that is not a product.

    I know that someone has done this already.

    Thanks in advance.

  2. loquin

    loquin Active Member

    You could get a second output shaft setup for staton's gearbox, (you can upgrade the existing gearbox, I believe, with a new cover and internal shaft. Check with Staton - he refers to this as his 'Tri-Hybrid' gearbox.) Then use the new output shaft to drive a small permanent magnet (PM) dc motor, operated as a generator. The gearing between output shaft and motor shaft should be set so as to provide max PM motor RPM at max engine RPM. The middle shaft on Staton's gearbox spins at about 1600 RPM with an input of 7800 RPM (Max for the GX35) so if your generator has a max RPM of 4200, you would need a 2.6 to 1 speed increase.

    The two photos below are from Staton's site; the second photo shows an electric drive motor (250 watts or greater) which could be used to push the bike in addition to, or instead of, the gas motor. What I'm suggesting is that you use this shaft and smaller motor strictly as a generator. (If you do go with this approach, get the smaller, 1/2 inch shaft, as it will be easier to find small sprockets/pulleys in a smaller shaft size.)

    Depending on the 'generator' speed, it might be better to extend the primary shaft on the gearbox, instead of using the middle shaft. This means that the aux. shaft would be driven directly at 7800 RPM max, rather than the apx. 1600 RPM of the mid-shaft. This means that for a 4300 RPM generator, you would reduce the speed by 1.8:1, instead of increasing speed by 2.6:1. However, you would probably need to use a belt (A 1/4 inch V-Belt or a 5mm synchronous belt instead of a #25 chain, as driving a chain directly at 7800 RPM may cause problems. At the lower RPMs at the mid-shaft, you could drive a chain directly...)

    Most small DC motors operate in the 3000 to 10000 RPM range. Your motor should have a rated power near the output you're looking for, at as close to the output shaft RPM as possible. A 1/25th HP motor would easily provide 20-30 watts of electrical power.

    The motor should be totally enclosed (if not, you'll have to provide a weather-resistant shroud for it,) and be rated for continuous duty. You will need a regulator between generator and battery/load, and if at all possible it should be a switching-type regulator. (linear regulators waste too much power.)

    You might want to look at a nominal 24/28V motor (at full speed of your engine,) and add a small solar power battery charge controller as the regulator. This motor, at Surplus Sales, might be just the ticket. (Solar charge regulators are efficient, they allow input voltages over a wide range (as "12V" solar panels can put out up to 30 volts) , and they have the lead-acid battery charger circuitry built-in. I've seen some that are in the 15 dollar range, for a 60 watt controller.) And, the wiring is extremely simple for these things... see below.

    Another advantage in using a 24V motor, with a switching-type regulator (or solar charge regulator,) is that the engine RPM wouldn't have to be at near maximum RPMs for you to be producing enough voltage to charge the battery - the solar regulator allows voltage between 11 volts and 30 volts to go to the load and/or be charging the battery. So, you can charge over half the RPM range of the engine.

    Attached Files:

    Last edited: Oct 14, 2011
  3. bigoilbob

    bigoilbob Member

    Just what I might need, Lou

    I'm going to do some final testing (after I finish my final strengthening of my engine/gearbox mount) to see if I need this power. But I'm 99% sure I do.

    Many thanks for really reading my post and for responding in such a complete manner. I know this took significant effort, but such posts help the tone of the whole forum. The only way I can pay you back is to post a good build thread once I have a few more test runs under my belt. I already have a few pix/videos. I don't have nearly your build expertise but I think it might inspire a few smiles and "why nots?!".

    Thx again;

    Bob D.
  4. bigoilbob

    bigoilbob Member

    Charging System Update

    Hello Lou;

    Your charging system specs were so right on that I used them whole cloth. Staton converted my drive to Tri-Hybrid for a good price, and I got the rest of the equipment. I then mounted, and wired it. I tested the motor/gen with pulleys that gave me 3000-3200 r/m at the motor, and it seemed to put out 18-19 volts easily. Then I tried it, and no charging. All fine mechanically. I thought my controller was bad and sent off for a new one. Delayed a couple of months for cold weather, but I got prepped to install the new controller today.

    But for fun I checked motor/gen voltage again, and it was ~ 4 volts! Motor/gen looks and sound ok, and I am pretty sure I am not slipping in the drive system. I checked the brush cap screws - ok. Could my permanent mags be weak? Any ideas?

    The system you described works so well mechanically and seems so right sized for me that I would really like to make it work.

    Thanks in advance;

    Bob D.
  5. loquin

    loquin Active Member

    How much current is being pulled at that 4 volt output?

    A DC permanent magnet motor used as a generator can be considered to be a 'perfect' voltage source, in series with an internal resistance.

    To measure the value of this internal resistance, you need to add a known test resistance as a load. Pick up a 10 ohm resistor to use as the load. Since it isn't going to be used very long, a 2 watt resistor should be fine. Measure the resistance, log it, add the resistor as the only load on the generator, spin the generator up to full speed, then measure/log the voltage across the resistor.

    To calculate the internal resistance, first calculate the current from the generator into the load:

    I = E/R where I is current, E is the voltage across the load, and R is the load resistance.

    The internal resistance equals the voltage across the internal resistor divided by the current through it. Which would be the perfect voltage (Ep) minus the load voltage (E), divided by the current (I):

    Ri = (Ep - E)/I where Ri is the internal resistance and Ep is the perfect voltage.

    If you wanted, you could combine the first two equations, and get

    Ri = (Ep-E)/E/R = R(Ep-E)/E

    As an example, lets assume that when you added the 10 ohm resistor, you saw that the voltage dropped from 19V to 16V.

    Your current through the 10 ohm resistor is then

    I = E/R, = 16/10 = 1.6A.

    So, the internal resistance would be

    Ri = (19-16)/1.6 = 3/1.6 = 1.875 Ohm.

    If the actual internal generator resistance is greater, the current that the generator can supply is lower. In your case, where the voltage drops to about 4 volts, this means that either you are pulling excessive current, and/or the generator has excessive internal resistance.

    Attached Files:

  6. loquin

    loquin Active Member

    And, once you know the internal resistance, you can calculate how much current your generator can provide before the output voltage drops below a given point.

    Assuming that we use the values from the above example (19V, 1.875 Ohm) and we would like to know the max current we can draw when the output is at 12 volts.

    Well, 19V - 12V is 7 volts, and the current needed to drop that 7 volts across the internal resistor would be:

    I = E/R = 7/1.875 = 1.86 amps.
  7. bigoilbob

    bigoilbob Member

    Thanks Lou, but moot now

    Moot because the ~4 volts was across an open circuit, i.e. no current. That's how I tested it initially when I was getting ~19 volts, so that's apples/apples.

    I punted and bought a new motor (~$31). I am going to test the controller by running an external ~13 volt power source thru it to see if I can charge up my partially discharged battery. If not, I have a new controller. Then, I will replace my motor/gen when I get the new one, and try it all out together.

    Since my motor/gen is unsprung (except for the rear tire) might I be beating the magnetism out of it? I ride on paved roads, but it still gets shook some.

    Thanks for the electrical fact family refresher. They always come in handy, and I have an old resistor that can handle the power around here somewhere..

    Bob D.
  8. BigBlue

    BigBlue Active Member


    I am also using the Staton gearbox for my build, but I am just using a motor. I've thought of different ways to mount a stator onto the gearbox. I would like to use a 1:1 drive off the main drive as loquin suggested. Here's a crude mock-up with Microsoft Paint that I came up with. Mount a 50cc stator to the outside of the gearbox. I've found several with the back plates between $25 and $35 on Ebay. I've seen several on Ebay with the flywheel 4-3/8" in diameter. Of course, as loquin suggested, have the drive shaft extended. With the stator, I would have to have the end tapered and threaded. I am going to contact Staton and see if he'll be up to the job.

    Here's my idea:

    If your idea doesn't pan - maybe try something different.

    Good Luck,

    AKA: BigBlue

    Attached Files:

  9. loquin

    loquin Active Member

    Ideally, the stator should bolt to the clutch mount on the motor, and have a plate on the other side, drilled/tapped, where the clutch would then mount. You would need to add spacers/stator housing that is as thick as the stator.

    By putting the stator between the engine and the clutch, you have full time electric generation.
    Last edited: Feb 3, 2012
  10. BigBlue

    BigBlue Active Member


    thanks for the idea. Something like this:

    Staton didn't want to take on my idea due to high cost. He suggested a local machine shop. His shop - his prerogative.

    I think with non-shaft drive engines, like the Subaru-Robin, Tanaka, and Mitsubishi a double clutch would be necessary. A clutch to shaft, stator, then another clutch to gearbox. The Honda GHX50 would work better since it has a shaft.

    Again, thanks for getting to think out of my box. An idea for the future project!

    AKA: BigBlue

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  11. bigoilbob

    bigoilbob Member

    Recommend Lou's original idea

    I had my Staton gearbox converted to tri-hybrid for ~$40, including shipping. Dave drilled the hole for me and I just had to wrench it together. My intermediate shaft turns at 1100-1600 r/m, perfect for motor/gen PTO.

    Just to update, my motor/gen was apparently bad. Four volts are useless, no matter the current. The new one (~$30 delivered) puts out the good volts. And the controller also worked. It blinks like it should when hooked up to the battery, while being charged from my motor/gen. The weather got cold so I could not test the whole system (motor/gen, controller, battery, and Nuvinci auto shifter as electric load) while riding, but I'm guessing it's ok. I'm also guessing there's enough extra power for a 12v light in front. I'll hang the bike off and check it out with the hyperterminal from my wife's netbook and my Radioshack voltmeter first.

    We need to fully appreciate the practicality of Lou's thinking. This is a system that is affordable, balanced, and available to anyone using a Staton gearbox. I could have Mickey Moused around for months otherwise. There are lots of builds that could easily be retrofitted. I did it, so believe me, you could too!

    Best to all;

    Bob D.
  12. BigBlue

    BigBlue Active Member


    look forward to pictures and an update.

    AKA: BigBlue
  13. bigoilbob

    bigoilbob Member

    Charging system, lesson learned


    I have recently used up 2 of these little motors, as generators.

    They work well for a few hours, giving me plenty of power to shift my Nuvinci 171 CVP with the auto shift from the Developer's Kit. But then, voltage drops away. I took apart my first one, and it seems that my brushes wore down. Suppose I could replace them, but I don't want that much frequent maintenance. I am still thanking Loquin because he got me pointed in the right direction, and only pointed out this product without touting it.

    Here is the advice from the folks I'm going to try now, along with the product..

    I hope it works. I will have to get a belt and mount to fit, but that's achievable. Also a bridge circuit, but that's cheap from Radio Shack. Any advice/user experience would be appreciated.
  14. loquin

    loquin Active Member

    re the surplus center motors: what sort of voltage regulator circuitry did you use, b.o.b ?

    That motor is 1/25th HP, and at 28 volts, you can only pull apx. 1 amp from it. If you are over-drawing on the current, this would cause the brushes to wear down very quickly.

    Ideally, you would want to use a switching-type regulator, as this is the most efficient means of getting your battery charged (you don't waste a lot of the available power in heating up a resistor.) Nor do you want to just feed the voltage directly to the battery, as the high voltage difference between battery (14.4) and generator (28) will pull excess current from the generator to drag down the voltage.

    motorscooter type regulators are going to pull down the voltage on the generator as well; they are designed to work with a 12V alternator/generator that has beefier wiring (and brushes, if it's a generator) that'll support 60-100 watts of power at that voltage.
  15. bigoilbob

    bigoilbob Member

    My voltage regulator

    Hello Loquin;

    Here's what I ended up with. If I screwed up the attachment I will see when I post and reattach.

    I tried the smaller one you pointed me to, but two of them failed. My currently installed regulator seems to be working ok. I don't know my charging amperage, but I had enough amperage to both charge the tiny motorcycle battery to a charging voltage of ~14.5 volts, and send ~2.5 amps at over 12 volts to my transmission shift control. I know that amperage because I can measure it on my wife's netbook using hyperterminal. That amperage might be higher when running (not just hung off stationery) because I am shifting under load. I charge up even while running, and with using the battery for downshifting to a stop (the mid drive gearbox PTO is stopped then). The voltage regulator was never hot, and seems to be well below it's rating, so if I had an overloading problem I think it would have been from the motor/gen. FYI, I took it apart and saw no burning of varnish or anything like that. Just worn brushes.

    Bob D.

    Attached Files: