So, how much power can a P2-A give?

[Mathurin]

http://www.users.bigpond.com/solarbbq/P2-A.htm

I've been toying with the idea of a bike with twin 36V P2-A motors, running both off a single 36V 50A controller. After playing around with the curves a bit I've determined this should be able to give satisfactory torque/power. For power comparison, climbing a hill at 25km/h it should be pretty much like a 408 running 72V/35A. I mostly want hill assist and shots of grunt at near-stall for crossing snowbanks and such.

Also both the twin P2-A's and a 4X clyte run in 7kg, but the weight & power distribution are preferable with the twin motors. I'm hoping to get maybe ~500g off each motor, so the weight for both would be ~6kg. Also removing half of the freewheel bearings ought let it coast even better (that, or lock up the motor always engaged.)

Thing is this would make nearly 4X more heat in each motor vs. stock, and I don't really know how much it can take. Apparently people have run these at 48v 16A no problem, I'm thinking using a sensor between the two brushes to sound a buzzer or something at maybe 80c or so would be non-optional.

I remember on the old V seeing some brushed motor with a chunk blown off the commutator from pushing it too far. This motor is sold as 36V 16A, I don't know what kinda amps would be too much for the brushes/commutator? My idea was to use one 36v 50A controller so that if a wheel gets bogged down it should get a kick to keep it going. Would something like 48v/35A , or 36V25A X2 be preferable?

From the pics on Brett's site, the motor is in a casing that is inside the hub, and it seems quite possible to make it holy on each side of it so as to ventilate the motor in the hub. Since it runs at 10:1 reduction, at 25 km/h it would be running 2000 RPM. I don't really know what material to use or how to make them hold on the windings, but it seems I could fit in fins of some kind to get more air circulation.

How much do you suppose can be gotten out of a 36V P2-A?

 

[Jeremy Harris]

I've just done a "quick and dirty" comparison on the ebikes.ca simulator, using a Goldenmotor as an example to see the sort of difference in current draw you might expect by just changing the controller to a 50A version, with it's inherent lower voltage drop and higher current limit.

The 20A controller on 36V maxes out at about 570 watts, which is around 15.8 amps. The 50A controller on 36V maxes out at a tiny bit more, about 580 watts or 16.1 amps. I guess this is pretty much what would be expected, as to get the motor to take more current means upping the voltage.

I don't know the figures for the P2 motor, but would guess that just changing the controller for a higher current one won't make a huge difference at 36V, unless the present controller is actively hitting it's internal current limit in normal use.

Jeremy

 

[fechter]

It's hard to predict how much a commutator can take without actually frying one. You also have limitations on the motor windings. My Zappy motor has taken waaay more than I though it would handle, but the brushed Vego motors were prone to having the commutator segments come unglued when they were overvolted.

I think in most cases you can run double the rating without commutator problems.

I did a Google image search on "fried commutator" and was surprised to see two of my pictures on the first page. What does that tell you?

 

[Jozzer]

That you have a limited sense of mechanical sympathy? :wink:

 

[Mathurin]

Ok, double the rating in most cases, good that would be ~32A, stands to reason 25A per ought to be safe-ish for the commutator.

So now I have a question about how they deal with momentary abuse. My idea of using a single 50A controller for the two motors is mainly for weight savings, also this works out like a limited slip differential witch could be a major plus for winter, but take this scenario: I'm about to come off a snowbank, full throttle, pushing hard weight back on the bars to keep the bike horizontal and going forwards at <19km/h, front wheel not touching the ground. Front wheel quickly spins up to no-load, rear motor sucks ~49 amps, ~3X rated current, for less then a second before both wheels comes back on level earth. Commutator blows chunks?

Or what if I push my luck and try feeding them 60 amps, and then same as above happens. Nearly 4X rated current.

Just for fun I made an edumacated guess of how much power these things would give if unlimited, based on graphs on Brett White's site and comparing with other motors and such, etc. Gets me a max Pout ~700w @ ~176RPM - 22km/h, ~45%Eff, ~39.8Nm & ~45.2A. Also, at stall >80Nm, 90.4A. Wish I knew the resistance tho, P=V^2/R and so on.

 

[fechter]

For a few seconds, you can really pound them. It's the temperature rise that causes failure in most cases. My old brushed Vego motor was taking near 100A on takeoff, but the commutator failed on a long hill at around 50A. The motor was rated for around 30A.

 

[solarbbq2003]

think i'd better say something here,
I tried p2a on 48v 20amp controller went really fast on slight downhill grade, on uphill grade it got hot, really really hot,
couldn't touch it for ages, bad news on opening motor, windings pretty nice blackish colour, all got very hot,
good news nylon gears not effected by high temp was very surprising, not a good motor to overamp!!!
Can go up one voltage from 24v to 36 , or 36 to 48v , on the different versions but cant overamp really, other thing is my previous workman in china and his rather criminal family stole alot of my stock including all the remaining p2a motors, so probably wont sell anymore