72v Gem jump pack

Any Gem dealers on forum?
Could you use a portable battery pack to test operation?
A few mile range. 35lb
Not easy to make a small pack able to supply 150a surge.
I have all the pieces of the puzzle. Only need a reason to put it together.


Dave I could see wanting one. Do I need one? I’m sure on the next gem I go to buy I could use one and would be kicking my self with out one.

Every car I have ever bought that was Dead! Had way more wrong with it then the owner said. If you could hook up this jumper pack and then you would be able to tell for sure what is wrong with the car

If you want I’m sure I could get the local gem car mechanic to buy one

That’s the encouragement I’m looking for. What about charging?
Most people that need one will have a 72v charger. Right?
Or does it need a built in maintainer?
I can do cheap and dirty. Throw the cells in the box. Or have it hi tech with charger, bms, and Bluetooth.
In theory, I can throw one together for $350.
To make it worth building more $500 Or $750 with hi tech goodies.
What would it be worth?
Maybe adding an inverter for 120vac for added value.
72vdc may run power tools as is.

How about a bigger audience? Sell it as an auxiliary gas tank to alleviate range anxiety.

A little closer. 6s module. Now need to do the same with 6X more cells.MVC-009FMVC-010FMVC-008F
I believe it will do 100 amps for a short time. 150a pulse, but voltage may drop too far.
Could you drive your car and keep it under 100 amps in a pinch?


Well the good news is that It’s done. :slight_smile:MVC-017F

Much more time and effort than initially thought.

Test #2 went well. Too cold for a long ride. About 1 mile hitting 125 amps, uphill.
Never hit turtle mode. I think it had a few miles left, but didn’t want to get stuck in the cold and snow.
Too much voltage at 33s. Dropping back to 32s which is 88 volt max.
That means car will start down to 2.1 volts per cell. Should keep running below that. Seems a good compromise, and I have a 32s bluetooth cell monitor.

Grant, take a look at the end plates. I have good sources for HDPE but no router.
Do you know a guy?
Other that the plates, there is no machining needed.
Mike, what kind of a strapper did you get?

More devilish details…34 balance wires. Sad that it is no more work to build a real pack.:persevere:

I forgot how nice the BT bms is.
Using all 32 cells.
An led on each balance wire to show balancing. That’s what the bms-24 needs.


I luv this bms!
Still blinky blinky balancing away.
Mike, you need one. :slight_smile:
Cut back one cell.

After tear down and neater wiring through bms.MVC-009FMVC-008F

Inverter/generator, we don’t need no stinkin generator. :sunglasses:
This ran my Milwaukee heat gun, (Gem defroster?), and my Milwaukee sawzall. :slight_smile:At only 86 vdc too.
I can easily make a 110vdc module.
Anything with brushes!
Possibly smps devices. At your own risk. Smps wallwarts work. That opens it up to tvs etc.MVC-011FMVC-012F

You’ve got some skills. Really cool pack. Love the creativity.

Thank you,
I’m looking for creative uses for these 11ah cells. Large quantity available.
This project ballooned beyond practical cost, but the cells themselves are not expensive.

As Gem dealers are not exactly beating my door down, a portable power pack kit might be more useful.

It’s deffinatly somthing I hate to admit I could use and should have.

I have bought a “Few” gems with Bad Battery’s.
That have turned out to have had more wrong with them then just “Bad Battery’s”

Sometimes I think owners purposely sell the cars with dead batteries so it masks what is truly wrong with the car. Example you can’t find out what’s wrong with the car when you can’t drive it

I’m trying to come up with other uses for it, as I do not see much demand.
To make the 11ah cells more useful and affordable, I may make 6 packs with shunt balancers.
More of a kit! The final assemble takes too much time.
6 packs are about 12v. Max of 16. 5=80v max.
Needs to do more than test a Gem.
Either way, I need to get you something to test.