24s , low amps, low efficiency?

[cbr shadow]

I'm using 88.8v nominal but I want to start out with the very conservative controller settings (30A, very low block time). Is high voltage and low amps generally a bad idea? I know high voltage = high top speed, but without the high amps I dont think I'll reach its full potential, right? Am I causing extr heat by having such high voltage with such low amps? How does the 20mph efficiency of my setup compare to say a 36v setup with 30amps @ 20mph?
I do plan on bringing the settings up once I know the bike is reliable with the current settings, but for the time being I want to make sure I'm not making a recipe for a very hot motor at low speeds.

 

[neptronix]

depends on the winding of your motor.

If you don't give it enough amps and it can't reach it's maximum speed, you're going to see low efficiency because the motor can't reach it's ideal 70-80% unloaded speed.

ebikes.ca simulator should be helpful here:

http://ebikes.ca/simulator/

 

[cbr shadow]

I'll take another look at the bike simulator. I forgot to mention my setup.

KMX Trike
- Crystalyte HS3540 mounted in 20" wheel
- 24S 3P (88.8V nominal, 15AH) Turnigy Lipo
- Lyen 18FET controller (Light settings so far.. 30A continuous)

 

[neptronix]

Oh, 20" wheel and trike? your load is going to be rather low due to the smaller wheel and good aerodynamics. Your controller can easily push double the amps. No need to be so conservative

 

[cbr shadow]

Thanks maybe I'll bring the amps up a bit then. Is it just a big waste to have the amps so low as far as efficiency goes? I took the trike around a few blocks in my area that have big hills and I noticed the motor was just starting to get hot. These were pretty steep and long hills though, so maybe it doesn't have as much to do with efficiency as it does with the big load that was on it.
I'm wondering if I'm better off powering up the hills full throttle, or just going up slowly.

 

[neptronix]

It depends..
Starving a motor for amps can definitely produce some heat. But too high of a load produces heat as well.

I think you are doing the former.. because when you hit a hill and aren't pushing enough amps, the motor bogs down pretty bad, and runs outside of it's efficiency zone. It may want 40-50 amps but you're only giving it 30A.

You will have to experiment, but my vote is for higher amps. Install a temp sensor if you don't have one already.

Thanks maybe I'll bring the amps up a bit then. Is it just a big waste to have the amps so low as far as efficiency goes? I took the trike around a few blocks in my area that have big hills and I noticed the motor was just starting to get hot. These were pretty steep and long hills though, so maybe it doesn't have as much to do with efficiency as it does with the big load that was on it.
I'm wondering if I'm better off powering up the hills full throttle, or just going up slowly.

 

[dogman dan]

I agree. I was about to say choose a winding that will reach it's efficient speed on less amps, but you got a tiny wheel and a motor that will take the amps provided the load is not crazy high, like ski slope steep hills.

I would try 40 amps at least, and see how the motor heating goes.