GEM eL XD Truck - Upgrades - Lithium, R4F Motor, On-Board Solar Charging, 72v to 110v Inverter, Lights

I currently have a 2011 GEM eL XD with the Max Box (one of the last made by Chrysler).
Like this:

Actually I just sold my first GEM which was a 2011 eL (not heavier duty XD) from later in the year under the Polaris name. With new batteries, tires & wheels, upholstery and a few other things I sold it for $4,800.

I started our love affair with GEM soon after self-installing a 60 panel 20.1 kWp solar array with Suniva panels and Solar Edge inverters in 2016. It’s funny how having that solar array makes a guy want to start swapping out everything for battery power… Switched to Ego outdoor equipment last spring and just ordered a Robomow Rs630.

Now, I am looking to do a variety of upgrades on the GEM

  • Lithium battery conversion
  • 7.5 hp Ride-4-Fun motor that has been sitting in a box for about a year
  • On-board solar charging using a spare 340w 72 cell 37.8v panel on the roof rack
  • On-board 72v to 110v Inverter to create a rolling power supply
  • LED lighting and maybe some RGBW just for fun

The combination of the Panel + Battery + Inverter by definition should qualify the system for the same federal tax credit I used when I installed the solar array & equipment in 2016. The system would be able to collect, store, and supply energy to my home. As my GEM is currently charged from the large array in my yard, I would almost say that it already qualifies but I felt that was a stretch. 2019 is the last year for the full 30% tax credit before the phase out begins.

Lithium Battery Conversion
The GEM I just sold went out with an almost brand new set of DEKA group 31 Industrial AGM batteries at a cost of about $1,700 that I installed. My “new” GEM that I bought at auction last year for $2,800. year came with a mismatched set of flooded lead acid batteries. When I tested them with a multimeter I found that 3 of them are okay, 2 of them are internally reverse polarity which I did not even know was possible, and one shows zero volts which means it is toast.

So I started battery shopping! I had looked at the solution offered by the now defunct company Lithium Boost with a bank of chargers paired to 22 individual Calb cells. Then I stumbled upon the idea of utilizing Chevrolet Volt modules with BMS which seems to be a fairly popular approach on this forum. I found an eBay seller selling volt packs but he seemed sketchy. I am glad I found this GEM forum and in particular @Inwo & @grantwest. David had a couple of compelling options:

  • Using 50 of his green 3.2v nominal cells in 2p25s to create a 120ah+ pack (BMS not needed)
  • A portion of Chevy Bolt battery unit that he had to break down to create a 20s 160 ah 12kw pack.
    I saw the video Grant had with a split pack and a Chargery BMS. I ended up opting for the 20s Bolt pack split in half & stacked to fit in the back half of the battery tray. It would fit lengthwise with small modification but I wanted to save room up front under the seat for other equipment such as the inverter, solar MPPT boost charger, etc. David is assembling it with a 24s Bluetooth BMS. I wanted a BMS and more power (like Tim Taylor). I think the cells are LG and the Bolt has only been out for a couple of years, so these are newer tech as well. Sure, it costs more but with David it’s a bargain at any price. :money_mouth_face:

David is already working on the Bolt pack


Not David but interesting info on the Bolt battery

More on other aspects of my GEM upgrade coming soon.

Mechanically complete stacked 10s Bolt modules.
20s 160ah 12kwh
Wiring next week.

Thanks for your detailed post your gonna love the range on that battery. That’s just like Tyson’s Bolt pack:

Are you putting those in the front? Or under the seat. If they go In front you will have to stager them for space. I have found they fit but with Centimeters to spare. I just finished the front install let me know if you have questions the front is tight.

It’s a thing of beauty David. Thanks for the progress updates.

Pretty sure he said they were gonna go under the back so he will not have to stagger like your battery tyson

@Tyson_Davis, your install is pretty slick!

In my GEM truck there is one large battery tray that had more than enough room to hold all 6 of the original group 31 batteries clustered right next to each other with room to spare. The battery tray measures 22.5" wide X 31.75" long with at least 14" of height clearance. The front half of the tray is directly under the seat and extends back under the truck bed.

Either way would work but I decided to go with the split & stacked configuration for the following reasons:

  • Save space toward the front of the tray for other electronics that I plan to install where they will be best protected by the seat
  • Keep center of gravity low and in the middle lengthwise
  • Grant’s video as referenced above
  • Split & stacked like firewood, another popular source of stored energy… really this is the modern classic approach
  • Should be easy to install because the underside of the truck bed is hollow with an access door on the top as well
  • I plan to enclose the battery itself and the attached BMS in some sort of water resistant box. Perhaps something as simple as a plastic bin with a rubber seal will work so I can still show people that nifty battery pack.

This particular bin is 19.70"L x 15.75"W x 11.02"H according to the listing. On Amazon, the Q&A section said interior bottom is 19 x 15. At the top 20.5 x 16 and 10.5 deep. Presumably the split and stacked configuration would be 17" long X 14" wide X 10" high. @Inwo, please verify actual assembled dimensions including “feet”. It may be best to mount the BMS on the original end plate.

This is the long answer to a simple question and @grantwest gave a slightly more concise answer while I was typing this. This is my thought process.

I ended up deciding to go with the Chargery BMS24s like the one in the video instead of the IC GoGoGo BMS. I lose Bluetooth and add some complexity, but pick up additional data such as live amperage, SOC, and temperature monitoring on a dedicated display. David had both options in house, which should be no surprise. I plan to use just the on board Delta-Q charger. To reprogram my Delta-Q charger, David says:

I could add the separate Chargery charging unit later on if I wanted to.


While I’m thinking of it:
Chargery does a poor job of isolating the case from electronics. I’ve learned the hard way to isolate the case from Gem frame. As the frame of the Gem is not connected to the traction battery, the frame can be at high potential in relation to battery B- and B+.
Grant uses velcro which is good electrical insulation, but also thermal. (not ideal)

The shunt must also be prevented from inadvertent contact with anything conductive.
Lead to the lcd must be routed away from any power wiring.

Looks like I will have to go one size bigger on the bin to the 60 qt. size. 23.60"L x 17.75"W x 11.22"H In the specs, 21.5 by 18.5 and 10" deep internal as measured in Amazon Q&A. Depending on the taper it may fit snugly widthwise or with room to spare lengthwise.

Based on what you advised about the need to isolate the BMS from the frame or battery, I will instead mount the BMS to the inside of the bin instead of to the battery. I plan to bolt through the aluminum angle foot, through the bin and through the aluminum tray. I will take care to mount the shunt on something non, conductive. Does the shunt get hot?

I may use liquid tight conduit to run the LCD wire and separate runs of conduit for other items. I do not expect a perfectly waterproof result, more like IP65. I have seen battery packs shrink wrapped and enclosed so I do not think there will be any thermal concerns, might actually help in cold weather. I will have the temp probe. If it is a problem I could add liquid cooling (kidding).

The feet can be shortened, but it’s extra length you need.
Lcd wire is shielded. No need to run in conduit. Tie it tight to frame opposite other conductors.
Thermal issues are unlikely.
The added feet may need help in a crash. Added gussets or straps? Your call.

I am all for over-building to make it robust, sturdy, and safe. Without looking at it in person it is hard to say but maybe use some threaded rod to catch the upper and lower feet. Obviously, I trust your judgement and welcome any suggestions or additions you think might help.

MVC-002F MVC-003F

Charging & balancing already I see, and in a pretty tight range from highest to lowest with a differential of 0.017v.

I have been reading a bit about lead acid vs lithium. A perfect lead acid pack in a GEM would produce about 76v then start declining rapidly versus this lithium pack which would in theory stay around 80v for most of a reasonable discharge cycle to about 80% depth of discharge.

Grant had said

Doctor, do you concur? Actually, what I am asking is do these numbers represent generally accepted conservative minimum and maximum to prolong battery life. That is a primary goal. Of course, the higher voltage at 80v + has performance advantages that I am looking forward to as well.

This is probably a big rookie question, but when I get to 80% DOD, for example, does the BMS have a way to shut down or limit the battery pack to prevent damage and prolong life? If so, is there a “limp home” mode to go a bit more to avoid getting stranded? If not is there a way to make it closer to fool proof? Of course, I would try to be careful and keep an eye on it and the large capacity offers quite a bit of margin for error. On the top end, the Chargery BMS and the Delta-Q charger should prevent over charge.

Or another scenario; because I plan to hook up a 72vdc to 110vac inverter, is there a way I could interrupt the connection to said inverter if the pack voltage goes below 70v? Really, regardless of the reason for the battery drain (motor, heater, lights, inverter) it seems it would be good to have some kind of protection.

Here is an inverter under consideration
It is about $250 from China. There are some others on eBay and one for over 1k on Amazon.

Product description

HuiKe pure sine wave inverters represent the most technologically advanced,
lightweight, compact and diverse inverters on the market to help ensure the
widest use of applications. For over a decade, the HuiKe ’ Power has
consistently delivered the broadest range of sizes to accommodate virtually
every power requirement. Advantages of a pure sine inverter: -Equipment
runs more efficiently -Motors run cooler -Cleaner power -Ideal for power tool
chargers, laser printers, electric shavers, microwaves, variable speed motors, TV’s, medical equipment.

Intelligent LCD automatically detects faults and provides modification suggestions.

Full Power, True Pure Sine Wave, No electromagnetic Interference

About Description:
inverter input: 12V/24V/48V/60V/72VDC
DC input range: 10V-15V/21V-30V/42V-58V/50V-70V/70V-90V
Inverter output:AC110+/-5%
Output frequency: 60Hz
Ouput waveform: Pure Sine Wave
Continous power: 2500W
PEAK power: 5000W
Inverter Best efficiency: Aprox 92%~97.2%
No Load Current Draw:less than 0.3
Low Voltage Alarm:10+/-0.5V, 20.5+/-1V, 44+/-1V, 55.5+/-1V, 62+/-3V
Low Voltage Shut Down: 9.5+/-0.5V, 19.5+/-1V, 42+/-1V, 55.5+/-1V, 62+/-1V
Over Voltage Shut Down:15.5V+/-0.5V
Thermal shutdown: 60+ degrees
Cooling Ways: Cooling Fan will run when the temperature is over 50 degree
AC output: 2 BS socket
Voltage input meter: yes
Power out put meter: yes
LCD display
Over Thermal :Shut Off Output Automatically
Fuses: Short Circuit
Start:Soft Start
Protection:Overload, Short Circuit, Overtemp, Reverse Polarity, Under/Over Voltage
Machine Size(mm): 390185150MM
Net Weight(kgs): 5.5kg aprox.

I found this online calculator to be useful.
It does not have 72v but you can just use 36v & divide Amps DC by two.

I am aiming to create a 20 Amp 110 VAC supply and slightly oversizing the inverter for headroom.

This is about 34 Amps DC (67.47 / 2 = 33.74). Is this unreasonable? Too much? For comparison, what does the motor draw through the controller?

This is an example supplying 1,000 watts. How long will it last?

  • 1,000 watts equates to 15.35 Amps DC @ 72v (even less amperage at 80v)
  • 160ah / 15.35 Amps = 10.42 hours theoretical max runtime
  • 10.42 X 0.80 = 8.33 hours assuming a safe 80% depth of discharge
  • 1,000 watts for 8 hours, 500 watts for 16 hours, and so on

Please point out any flaws in the math.

I also found another thread about this idea with @Old_Houseboater @LA-GEM4s @Big_Dee @LithiumGods

Maybe customize with this guy?

Solar & Battery Hybrid Inverter?

I may miss some things in a long post. You seem to have a good understanding of requirements.

The bms has relay driver outputs if you want to use them. One more thing to go wrong and get you stranded. Imo
The Gem will limp before battery damage from pack low voltage. No protection from a single cell going low without a lvc relay.
Bms has alarms if you want to connect them.
The controller can be spoofed to raise lvc if desired. Test without it first.
A good inverter may have low voltage protection. Lvc

There are other bms options that can interrupt power using internal Mosfets. Hobby priced 24s limited to 300a. I use one in my 22s E4. It has LCD + by.
Truck will exceed 300a on occasion and trip. Requiring reset.
A brand new version is out. 20s 400a. Very inexpensive. I can give you the link. Not to late to switch. All power goes through Mosfets, for total control of anything connected without a relay.
20s means that it will not work if you decide to add cells for hotrod performance.