2200W Electric conversion

[nedfunnell]

I did the first part of my conversion today, mounting the motor. I'm doing this as simply as I can because I live in an apartment for the summer and hardly have any tools to work with. By day I am a welding engineering intern, but at home all I've got is a cordless drill, a dremel, and hand tools. We'll see how it goes. This is a 36v motor, but I will be running the first generation of this bike at 24v so that it will be tamer and because that fits the batteries I have. (My third battery is weak..er). I'll keep you posted.

 

[nedfunnell]

Chain on. It's #40 roller chain which is much too wide for the bike sprocket, but it's what I have around, and matches the #40 sprocket I have for the motor.

Gallery: http://www.majhost.com/cgi-bin/gallery.cgi?f=206454

 

[duivendyk]

Do you have any info on this motor,motor type,no load rpm, & max current ? What is the reduction to the chainwheel.If you run a 36V motor at 24 V the efficiency can take a quite a beating (depends on motor type)

 

[nedfunnell]

I don't know the model of the motor, I got it on ebay as a mystery motor, and the brand on nameplate was scratched off. Nonetheless, it does 2500 RPM at 36v. The ratio to the chainwheel is 4.2:1, which should give me 31mph max is lowest gear at 24v. Not sure on the current draw, but the controller I have that I will be using when I eventually step up to 36v will take 225A, and is current limited to that. The rated power is 3 HP (~2200W), which at stock voltage would be 62A. The stall current will be higher, naturally.

 

[fetor56]

I'm the first to admit i know little about e-bikes,but it will be interesting to see your final setup(with batteries/controller,etc).
Wonder how it'll perform....weight would have to be an issue.

 

[duivendyk]

That would seem to make sense, with about a 1:1 ratio to the rear.If the motor was say 80% efficient at 36 V, (input 36V at 60A) ,output power 1700 W,power dissipation 500W,speed 2000rpm.At 24V and 60A with 1450 W input and about the same 500W loss,speed 1100 rpm,the efficiency becomes 950/1440= 0.66, or 66 % and a 14% reduction.The output power at 950 W (1.3 hp),is say reduced by 43%.At lower voltages(speed) the efficiency decreases rapidly.Of course normally the power requirements will go down also (at least when you're not climbing hills) so the actual efficiency won't go down as much than when at full power.What can be said is that running at low speed and high current,like climbing a long hill at low speed can overload(overheat) a motor because of inherently poor efficiency.Controllers usually limit the input and not the motor current.So it is possible to fry the motor at low speed because of excessive current,like climbing a hill slowly. It turns out that it is actually more energy efficient to charge up the hill at full speed than crawling up it,intending to spare the motor!

 

[nedfunnell]

Version 0.9 is done, but I can't go for a test ride because it's raining out. Aside from the pains of biking in the rain, it would be less than ideal for the electrics. I mounted the batteries with a long bolt through the rack and a crude bracket I made from polycarbonate and some machine screws. The motor control is a simple contactor, which should be fine for running it at 12v- the theoretical max speed with this setup (in low gear) is 15mph- so I can just pedal it up to something close to that and hit it. I'll trial-and-error down from there to see if I can get away with switching on at lower speeds. This is just a R&D build, really, for when I eventually get prius batteries and wire in my golf cart controller. I'm starting to question the wisdom of building this onto a rickety old bike- perhaps the final revision with all the goodies will wind up on a dirtbike or supermoto frame. That's a little bit more conspicuous, though. One problem I ran into was that the contactors I have are 24v/36v coils, and would not throw at 12v. I put a 7.4v LiPo I had for my RC car in series to get 19.4v, which throws the contactor reliably. I'll let some pictures do the explaining:

 

[nedfunnell]

It rides. I took it out this afternoon and I've been troubleshooting. Yes, it runs the pedals. I need to have my feet elsewhere while the motor is running. Annoying. I will put pegs on it eventually. It was tame enough at 12v that I switched it over to 24v immediately. Not a bad ride, gets up to speed pretty quickly. The batteries are the limit, I think- performance will get better after they 'wake up' from their long storage period. Predictably, I have been having chain trouble. I just took the front derailleur off, which is no loss as neither chain should be shifting on the front chainring anyway. That should help, as it was impinging on the heavy chain a bit. Power chain tension is an issue- as you can see, nothing is keeping the motor from sliding backwards except for the U-bolt pressure. That threw the chain once. The rear chain got garbled up in the front derailleur once in an epic fashion. After I got that fixed, the front chain slipped onto the middle chainring and was hard to get off due to the front derailleur. Hopefully, now that that is off, I shouldn't have too much trouble with it.

Now that I'm at 24v, I don't need that lipo booster for the contactor anymore. I ditched it and wired in a safety switch, which you'll see below.
Pics:

 

[nedfunnell]

I didn't get to successfully ride it in the improved configuration yet, without the derailleur. When I took it back out, the front chain was loose, which would cause both chains to derail even if I just pedalled. The motor mounting system I have now is no good at keeping the chain tension, as the motor will move back with nothing to stop it. I kick-rolled the bike along to my destination and watched the fireworks. I was showing it to a friend after the show and did a wheel-up power on test to demonstrate. This promptly broke the rear chain. Whoops. I'll have to put that back on tomorrow and see how it goes. This motor really belongs on a heavier-duty frame.

 

[duivendyk]

For sure,unless you limit the motor current you'll be zapping chains galore.It's not just the frame either,those dinky rear chains won't cut it,plus you need a narrower chain in the front ,a sturdy chain tensioner would not hurt either,IMO