I just had to add something to this.

LAst year I was living in Atlanta working for a general aviation company. We were "cleaning" house and I was tasked to moving the heavier things like aircraft windshields and the like that the "girls" I was working with wouldn't move.

I remebered throwing out (recycling) two 160 pound electric motors from our massive air compressor system that ran all of the air tools in the hanger. I have no idea what the specs where on them but I'm sure they could have worked on an EV.

Just think of it. If I had been into EV's back then I would have saved myself $300 easily not to mention all of the 28V batteries I recycled as well. hell I even threw out a controller!!!!!!

Next time you see an avation company or heck even drive down to your local FOB see if they have any of these thing collecting dust? I'm sure since they have to track their spending they will be more than willing to just give them to you for free.

Also would a electric motor from a generator work? After hurricane Katrina hit my town there is bound to be a few old generators lying around?

Sounds like you've got the ideal situation with your landlord being an electronics teacher.

Schematic time...

OK, now you're talking. I have some questions.
1. Are the the coils of the contactor solenoids intended to operate at 36 - 48V?

2. Are you connecting the 12V battery ground and the 36V battery grounds together? Or is only one connected to the body (I assume atleast the 12V gnd is or you'd have to rewire the rest of the car).

3. The controller looks as if it regulates only the negative connection to the motor. If the negative side of the battery is always connected to ground (once the neg contactor is closed) and the positive is always connected to the motor (once the positive contactor is closed), then there is a risk of any short (e.g. dropping a wrench) between ground and the negative motor connections throwing the motor into full power (serious lurch).

Nope he did but it looks just like this one but baby blue......

https://www.austinev.org/evalbum/991

Yes - they're out of the forklift. It only had 1 pack (no 12

Brelandt: he's got a CitiCar/ComutaCar! Awesome. He's basically driving what I'm building. I probably would have bought one of those if there were any around here.

Yes.

Well, yes isolating the ground should greatly reduce such a risk. BTW contactors sometimes do stick.

4th question:
If so, you may be able to further mitigate accidental lurches the way Jerry does with that latching relay, though in your case, you'd may need to use a DPDT relay. Let me think about that.

If I understand Jerry's setup, his pot box latching relay prevents the pack +ve contactor from closing if the ignition is switched on while the go pedal is pressed.

His approach is sort of equivalent to forcing you to depress the clutch before starting a manual, or pressing the brake to shift out of park.

I omitted that precaution.

Right again. It does make sense to omit that interlock if you're the only one who will drive it. Some people (like my mother) have a tendency to step on the gas pedal when turning on a car - that can be bad since there's no engine that must first be started. I believe the interlock is required (in the US) of EV manufacturers but I don't think it applies here.

OK, so back to the ground issue. Your shematic shows the negative connections to the contactor coils with a "chassis ground" symbol but there is no place where that ground actually connects to the negative side of the 36V. I assume those connections go to the point just after the shunt.

I would put a small fuse (1A or less)) on the + side of both the voltmeter and the ammeter. It's just a precaution and won't affect their accuracy.