[peggus]

I have an inductor in my motor loop to help the poor curtis out. It got rid of the starting issues I had. I use an iron core inductor though, not air core, less EMI that way.

In theory a well designed inductor should also improve the motor efficiency. The forklift type motors aren't exactly designed for high frequency ripple. The solid steel motor case at 90 degrees to the B field is the optimum design for maximizing ripple losses. Reduced ripple current also reduces IIR losses.

Now, I have no idea if the gain in efficiency is meaningful, it would make an interesting experiment though, If only someone had a dyno setup.......

 

[peggus]

deleted duplicate message

 

[peggus]

Yes, you're about right, if I recall correctly I designed the inductor for ~50uH. I used an iron core made of very thin laminations, I only needed 4 turns of 3/0 cable so IIR losses should be minimal. It's a heavy chunk of metal but it beats suddenly loosing power when making a left turn on a busy road.

14m of 2/0 wire has only 3mOhm of resistance according to my calculations, at 250A (~rated cont motor current) that's just 200W of losses out 20kW to propel the car, 1% significant but not that much.

I seem to recall that you guys measured about ~10% lower motor efficiency than the manufacturer stated, I wonder how much of that can be attributed to iron losses from ripple current.

Of course, if I had a half way decent controller I would have never bothered adding an inductor.

Sure...with an emphasis on "well-designed", though.

...Anyway, while you are technically correct that there are some iron losses in the motor housing, and that adding external inductance will reduce those particular losses, the unfortunate reality is that you will be adding far more in losses from cable resistance.

 

[peggus]

There's a huge amount of dc bias here, though, so you really need to use a core with an air gap (preferably a distributed one) otherwise it is just going to saturate. Powdered iron or MPP are good choices.

I used an 1/8" airgap, the core saturates at 500A

Sure, at 250A the I²R loss in the 14m of cable isn't too bad - and the AC losses are probably negligible - but at 400A (the example datum I used before) the conduction loss will be 480W. That exceeds the conduction loss of the IGBTs in the Soliton1 (~0.9V at that current).

Sure, but how much time do you spend at 400A.

It's been awhile since I did that test, but at 200A - the current the WarP 9 is rated to carry for 1 hour - the efficiency was the same as what NetGain claims, or about 85%. It was at much higher currents that the efficiency plummeted. I don't recall the exact number, but at 1000A and 105V (1900 RPM on our dyno) the efficiency was closer to 60%.

Ah, thanks, very interesting.