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Curtis B.
Curtis B., Other
Category: Electric Vehicles
Satisfied Customers: 28074
Experience:  Worked on fleet of various electric vehicles, golf carts, scissor lifts and electric booms.
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My 2000 modified gem has sudden loss of speed and power.

Customer Question

My 2000 modified gem has sudden loss of speed and power.
Previous ran 30mph and 21mph uphill.
3.5hp and T1 control.
Turf switch is ok.
Battery volts ok @ 90%.
Seems to roll free in garage.
Submitted: 1 year ago.
Category: Electric Vehicles
Expert:  Curtis B. replied 1 year ago.

Battery voltage steady when driving? All batteries check same voltage?

Expert:  Curtis B. replied 1 year ago.

Typical power loss is battery or cable. and it only takes one!

Customer: replied 1 year ago.
Batteries are all 12.7volts
If you think battery cable problem is likely I'll check under load, but my battery meter stays at 90-100 while driving. I also plan on checking current.
Just so you know. I'm an industrial electronic tech.
Only had the Gem for a week or two.
Do yo know what the voltage should read on high side of throttle pot? says 5vdc. I have 3.7.
Expert:  Curtis B. replied 1 year ago.

I would check batteries and cables first! A fully charged battery would be well over 13 volts. 12.7 sounds to me, to be on the low side!

Expert:  Curtis B. replied 1 year ago.

the 3.7 volts on the throttle is low, but not sure where it gets it's voltage.

Customer: replied 1 year ago.
Thank you, ***** ***** for something simple. The three pot connections come from the GE-T1 controller. See previous link.
It lists it as 5v nominal. Yet it also states that >4.5v ,to control, from throttle will set "over voltage" code. ??
If I know that 3.7v is low. (for sure) I will continue in that direction. Checking continuity from control to pot. And worst case, bad 5v regulator in control.
I do need Gem car or GE-T1 specific information, which I have not yet found online.
Customer: replied 1 year ago.
I checked battery voltage after a short run.
I don't yet suspect battery problem as in the week it worked, I could get many miles before going down to 85%.
And loss of performance was sudden. One day backing out of garage, it was a slug.
Not discounting your suggestion. I will check voltage under load with another meter.
In a pinch I will connect a voltage data logger during a run.
Expert:  Curtis B. replied 1 year ago.

OK, let me know the result

Customer: replied 1 year ago.
Meanwhile, I really need to know proper voltage to throttle pot.
Expert:  Curtis B. replied 1 year ago.

Input voltage to the pot, has to be 5 volts or more, for it to have variable output. Then the output can't be over the 4.5 V or it sets the code. Is the 3.7 output or input?

Customer: replied 1 year ago.
Input to the pot is 3.7volts. Output varies nicely from zero to 3.7.If you agree that input is low, that would be the problem. As I would only have ~75% throttle.Can you quote a source for that information, or experience tells you it's always a 5v source?I jut don't want to waste time on a dead end.The fix will be wiring from control to pot or internal repair to control.
I can repair the control if it can be opened and has thru-board components. I would not attempt to repair surface mount board unless it was junk.I have been in poor health, so this may drag on. I can't work most days.
Expert:  Curtis B. replied 1 year ago.

I have no experience on the voltage requirement, only by what manual states.

Customer: replied 1 year ago.
Ok, thanks
That's all I know too.
It seems too simple.
I'll find a way to check it right at the control.
Expert:  Curtis B. replied 1 year ago.

Just remove the wire, and see what actual output is.

Customer: replied 1 year ago.
3.7v right at the control.
Goes to 4.7 open circuit when disconnecting 5k pot.
Expert:  Curtis B. replied 1 year ago.

Sill questionable. Have you tried new wire.

Customer: replied 1 year ago.
The wire is fine. I checked multiple ways. The 5v supply seems "soft" 5k pulls it down.
The 5v supply to the "PY" plug that goes to speedometer is fine.I have ways to test car operation with a separate isolated 5v supply. It is not without risks however.I need someone who knows for sure if low voltage on pin "9" indicates bad control.
I've asked on a Gem car forum. Still waiting for an answer.
Don't know who to call.
Expert:  Curtis B. replied 1 year ago.

Ok, thanks for reply.