GEM Car Lithium Conversion - DIY batteries are awesome for cars!

[Watts Happening]

We picked up a GEM car a couple years back for cruising around town and trying to get grandpa out for some fun while he still can. It had relatively new batteries when we got it so I reluctantly used those for a while, but whenever we let grandpa use it, he'd forget things due to beginning stages of dementia and end up with completely dead batteries etc. Now we're to the point that it barely goes a mile or two and the time has come for a change.

Originally (6) flooded lead acid batteries creating a 72v nominal car, removed them in favor of a 24s 100ah pack with JK BMS. Two batteries were originally under the hood with four more under the seats with a total weight of 525 pounds. Replacement lithium setup weighs 110lbs with box and BMS and the entire setup fits comfortably under the hood. Now we'll have quite a bit of extra storage under the seat and a pretty serious weight savings.

While I'm at it we're bumping the top speed from 25mph to 35mph, technically not legal but it's insanity that the car is/was allowed to be operated on streets with a 35mph speed limit or below, yet only allowed to go 25mph. They're a blast to cruise around town, I highly suggest them to anyone. Totally street legal in most states.

 

[Danke]

While I'm at it we're bumping the top speed from 25mph to 35mph, technically not legal but it's insanity that the car is/was allowed to be operated on streets with a 35mph speed limit or below, yet only allowed to go 25mph.

Reported.

 

[Watts Happening]

Reported.

What I meant was, only for off-highway use, of course..

 

[millsan1]

Looks awesome. I did a conversion on my electric sxs. But I had to go with 8 48 volt 16s batteries because of amp draw. Motor on my sxs can pull 450+ amps on hard acceleration, uphill, etc.

Any idea what this machine pulls?

Cruising flat, I pull about 100 amps.

Thanks

 

[Watts Happening]

Looks awesome. I did a conversion on my electric sxs. But I had to go with 8 48 volt 16s batteries because of amp draw. Motor on my sxs can pull 450+ amps on hard acceleration, uphill, etc.

Any idea what this machine pulls?

Cruising flat, I pull about 100 amps.

Thanks

Controller is listed as a max of 350 amps, the biggest BMS I could find was the JK BMS that is rated for 200a constant and spike to 350a which I think will suit us just fine. Hell, just dropping the extra 400 pounds will help with the amp draw in some regards, as will the extra voltage.

 

[millsan1]

Holy crap. I just configured one and it came to $42k. Granted that's about every option, but wow

 

[millsan1]

Controller is listed as a max of 350 amps, the biggest BMS I could find was the JK BMS that is rated for 200a constant and spike to 350a which I think will suit us just fine. Hell, just dropping the extra 400 pounds will help with the amp draw in some regards, as will the extra voltage.

Just looked. Yeah, 7 hp motor on this, mine is like 30, so that would be a big difference. Plus mine is 2000 lbs empty, 800 lbs heavier.

Still a very cool thing. I want to try and get my sxs registered as an LSV, but in reality, there are no cops around my area, so I can use it as such without much worry. My top speed, downhill, with a tailwind is 23.

 

[Watts Happening]

Just looked. Yeah, 7 hp motor on this, mine is like 30, so that would be a big difference. Plus mine is 2000 lbs empty, 800 lbs heavier.

Still a very cool thing. I want to try and get my sxs registered as an LSV, but in reality, there are no cops around my area, so I can use it as such without much worry. My top speed, downhill, with a tailwind is 23.

Ours is old, I think it's a 4hp motor, but honestly I don't see why it would need any more, it zips around just fine, without 'good' traction it'll spin the tires. 25mph is no problem, the 35 will be nice just to have a bit of headroom, sucks being so limited. We often use it at our vacation house in a very small town, about 2 minutes from one side to the other haha.

 

[millsan1]

Ours is old, I think it's a 4hp motor, but honestly I don't see why it would need any more, it zips around just fine, without 'good' traction it'll spin the tires. 25mph is no problem, the 35 will be nice just to have a bit of headroom, sucks being so limited. We often use it at our vacation house in a very small town, about 2 minutes from one side to the other haha.

Yeah, no disrespect intended. I didn't mean it in a measuring contest way. Mine is a big slow hunting tool, yours is a cool sleek road tool. Two different things, both great

 

[Gromike2]

As far as top speed, I like my ebikes to be able to go 35mph. Not that I go that fast, but sometimes I appreciate the speed to avoid being crushed.

It seems that you figured out how to fix a GEM. Kinda like a diamond in the rough. I'll have to look for one. There were quite a few of them around here a few years ago. Don't see them on the road anymore, so I assume they're sitting somewhere not too far away.

 

[Minimoose]

As far as top speed, I like my ebikes to be able to go 35mph. Not that I go that fast, but sometimes I appreciate the speed to avoid being crushed.

It seems that you figured out how to fix a GEM. Kinda like a diamond in the rough. I'll have to look for one. There were quite a few of them around here a few years ago. Don't see them on the road anymore, so I assume they're sitting somewhere not too far away.

Probably with dead batteries!

 

[JWLV]

My brother had a GEM many, many years ago. It felt like luxury golf cart, but it was definitely fun to drive and great to get around the neighborhood.
I can't remember if they need to be registered, licensed, and insured or are they more like golf carts? It certainly would be a fun project car if an old used one can be picked up for cheap.

 

[Gromike2]

Probably with dead batteries!

...and that's what I'm looking for, dead flooded lead acid batteries, low mileage, and a low price.
But it seems that people think their GEMS are gems. I found something at auction. Not a GEM, but maybe a gem. Hope to buy at under $400 for a NEV with a good drivetrain and lead acid batteries. That would be a win for me .

 

[Watts Happening]

Alright... I need some grading here @timselectric or another smarter-than-me individual on the forum.. As I started wiring in the BMS today I realized I'm an idiot and had laid the cells out as though it was only two rows and not three.... Well the box had to come back apart and this is the best I could come up with to reach 24s. Thoughts on the bus bar layout, any better way to accomplish it without making jumper wires? Red cap system positive, black cap negative obviously. I wish they were both on the outside but this was the best that came to my mind at the time. Kinda/sorta played a game of snake.

 

[Watts Happening]

Nothin, huh?

 

[fromport]

Nothin, huh?

Could this be a solution:


yellow = negative
red = positive.
Probably have to buy a few new longer connections

 

[UpNorthMan]

Where would you like the plus and minus ends to be?

 

[Watts Happening]

Where would you like the plus and minus ends to be?

Truth be told I don’t think I care, just wanting to make sure I’m going lazily doing anything stupid.

The first iteration isn’t always the best haha!

 

[UpNorthMan]

I do like the way fromport has separated the positive/negative from each other. Also, that they are on the "outside" of the pack. This can reduce the chance of shorting out the batteries when installing the cables.

It can also be slightly modified if you want the posts closer for running cables.

 

[mikewired]

We picked up a GEM car a couple years back for cruising around town and trying to get grandpa out for some fun while he still can. It had relatively new batteries when we got it so I reluctantly used those for a while, but whenever we let grandpa use it, he'd forget things due to beginning stages of dementia and end up with completely dead batteries etc. Now we're to the point that it barely goes a mile or two and the time has come for a change.

Originally (6) flooded lead acid batteries creating a 72v nominal car, removed them in favor of a 24s 100ah pack with JK BMS. Two batteries were originally under the hood with four more under the seats with a total weight of 525 pounds. Replacement lithium setup weighs 110lbs with box and BMS and the entire setup fits comfortably under the hood. Now we'll have quite a bit of extra storage under the seat and a pretty serious weight savings.

While I'm at it we're bumping the top speed from 25mph to 35mph, technically not legal but it's insanity that the car is/was allowed to be operated on streets with a 35mph speed limit or below, yet only allowed to go 25mph. They're a blast to cruise around town, I highly suggest them to anyone. Totally street legal in most states.


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How is the factory battery gauge working with the Li batt? Are you using the onboard charger?