[PocoEV]

Converted an old lead sled..... it came with a 1990s vintage 9" GE 21Hp motor (5BT1346B50 Series) with a Auburn Scientific 700 amp Grizzly controller. Conversion brings in 43 CALB 100AH LiFePO4 watched over by Orion BMS. Vehicle weight is at 2500 pounds.

Car runs great in the flats but limiting myself to 2C current draw.... I can only get to 25MPH when climbing 500 ft over a steep 1 mile (10% grade). Drawing 200 amps continuous for the 3 minute climb raises average cell temps about 2 degrees C.

I'm a newbie to DC motor torque curves...see attached. Should I increase current to 3C or 4C for this limited 2-3 minute duration? I have not found any posts talking about current draw when climbing a hill?

Or is this "old GE motor" tired and needs to be replaced? Would a HPEVS AC-51 provide me better performance in this hill climb challenge?

Thanks for helping in my education....

 

[PZigouras]

Both my cars have 9" GE motors, and I have to say that hill climbing should never be a problem. These are tough little motors... they do get hot when climbing, but they take the heat very well.

At 200 amps, you are putting out less than 30 kW, which is about right for 25 mph on a 10% grade. We have a 12% grade bridge near my house, and I have hit 70+ kW to maintain 40 mph over it.

I really can't compare amps (since I have a 320 volt pack), but my guess is that you will need almost 400 amps to hold 40 mph on that grade. 400 amps is a lot for a 9-inch motor, and I would not hold that for more than a few seconds.

Keep in mind that the efficiency of a DC motor will drop tremendously when under high loads -- resulting in even more heat. In contrast, a typical AC motor is most efficient at 95 to 120% of its load rating... which would probably be ideal for hill climbing.

I have to add that the 9" GE motor in my daily driver is forced-cooled by two 180 cfm electric fans (I had the internal mechanical fan removed before installing the motor). This may be part of the reason why the motor lasted so long... this is the start of my 6th year with it.

From what I've been told, the stock GE internal fans have very poor flow numbers -- at any RPM.

 

[PocoEV]

Excellent to hear my numbers "sound right"... I have been very cautious with drawing more than that "2C continuous" from the CALB batteries.

Help me to understand your words around 400amps for 40MPH... you said "400 amps is a lot for a 9-inch motor, and you would not hold that for more than a few seconds" but earlier in the post you mentioned "These are tough little motors... they do get hot when climbing". This is a mile long 10% grade taking about 2.5 minutes at 25MPH to climb. What recommendations do you suggest? I would love to be able to use your words of "hill climbing should never be a problem". Right now I'm frustrated....

I am running the motor at 138VDC instead of the 108VDC shown in the torque curve. Also, I installed fan forced air. It's a 250CFM fan ported directly into the brushes. I thought fan forced air would be important with the higher voltage.

THANKS for any suggestions.

 

[dcb]

sounds like what was suggested in the other thread, you can experiment with bumping up the max current a bit at a time, just keep an eye on motor temp and battery current (and motor current if you have to manually back off on motor temp to make more current available on demand). Your foot controls motor current, until the rpm gets high enough to limit current. Current is the big heat source for the motor (or the batteries) so you might have to drive by ammeter when you aren't putting your foot into it.

 

[PZigouras]

I would say that the longest I have ever held 400 amps is about 30 seconds. At that point, the internal temp of the motor (according to the sensor on my field coils) rose from 190 F to 260 F. Keep in mind that class H insulation is rated for around 355 F.

Also, keep in mind that I have 360 CFM of airflow.

I am curious to find out how long these motors can hold 400 amps before the internal temp hits the insulation's limits. But I don't have enough of a hillclimb here to find out.

Excellent to hear my numbers "sound right"... I have been very cautious with drawing more than that "2C continuous" from the CALB batteries.

Help me to understand your words around 400amps for 40MPH... you said "400 amps is a lot for a 9-inch motor, and you would not hold that for more than a few seconds" but earlier in the post you mentioned "These are tough little motors... they do get hot when climbing". This is a mile long 10% grade taking about 2.5 minutes at 25MPH to climb. What recommendations do you suggest? I would love to be able to use your words of "hill climbing should never be a problem". Right now I'm frustrated....

I am running the motor at 138VDC instead of the 108VDC shown in the torque curve. Also, I installed fan forced air. It's a 250CFM fan ported directly into the brushes. I thought fan forced air would be important with the higher voltage.

THANKS for any suggestions.

 

[kennybobby]

@PZ, Just ride your foot on the brakes while climbing the hill--that will give you some extra load to see what happens