Just purchased 2002 e825-4 where to start rejuvenation?

The latest from another employee at the local CartMart/GEM Authorized Dealer was that early on the recall was implemented using a potted circuit board with wire harness attached. Later he said they started using the 3rd party 72V:12V converter(SurePower?) along with a relay and other parts and it required splicing into the existing wire harness.

Therefore he said it was likely my GEM already had the recall bulletin implemented and there was nothing further he could do without Polaris instructing him directly.

I still have a big question as to why the GEM service bulletin instruction manual shows the potted converter being removed and calls it “old style converter” and I wonder how my pretty complete documentation received from the previous owner has no mention of recall service.

But it sounds like a dead end trying to get them to replace the unit. My next step is to see if I can gain access to the connection at the 72V input wires(2 wires on far right side of converter/vehicle) to see what is causing the periodic loss of connectivity and subsequent resetting of the speed controller while driving.

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dougl, can you tell me what the complete circuit is so I can fab a replacement.

Also can you provide what the output is when the temperature is in range. I can see that the voltage to the sensor (blue wire) assembly is 5V. I tested adding several resistors to lower the voltage hoping to simulate the output at what I was hoping was room temp by adding 1Meg resistors which dropped the voltage ~ 0.5V each. I tested adding 1, 2, 3, then 4 of the 1Meg resistors in series to drop the voltage down to ~3V but that didn’t work. I guess I could have kept going, but I stopped at 3… Just trying to make my own override until I get the complete circuit .

In the mean time I did order a replacement from the Zivan folks for $65 total on 10/20/2020.

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@rocket90703 are you talking about the battery temperature probe for the Zivan? You’ll want to scroll back to my sections on that because I post that it’s only a capacitor and an active temp sensor part. You should be able to look up the specs to see if you can simulate that with some 1% resistors.

In my case, I’d thought the active component failed but instead I believe it was the capacitor. I state this because I put on a new active part and it still didn’t work so I grabbed a physically similar sized capacitor from and old circuit board and then it worked again. YMMV


Hi dougl,
Got my 2001 Gem recall done early in 2021 by Polaris dealer in NC. Does anyone know what it should look like when completed? I took photos and there are two connectors hanging loose, two ground wires loose and a pin from wire plug that is pulled out.

Thanks for all of your great information.

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does everything work? ie lights and all 12V things(test them all).

Stock converter also had ‘extra’ wires but they were/are labelled radio or something like that. Did you contact Polaris and ask them what the extra wires were for? I mean they just did the conversion and should have labelled the wires along with taping the ends up to protect them from weather.

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Here’s what the update looked like on our e825 after Polaris did recall. I don’t see any loose connections.

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I did not notice the wires until I took the cover off. It didn’t work at all with their first attempt. Was told it was related to the charger upgrade. I was reading through all your posts related to the recall when I posted. It was suggested that I move my questions to a new thread.

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It looks like all the problems related to this GEM instant throttle disconnects were due to poor 72V input to the 12V converter. I would drive down the street and hit a bump, or not, and throttle/acceleration would stop which sent everyone in the vehicle forward in their seats. I just pulled my foot from the pedal and re-engaged throttle and it would be back accelerating. I thought it was the throttle pedal and replaced the switch, tested the POT and cleaned the connectors but that had little effect. Later I put the GEM on blocks and found I could trigger the throttle cut-out by wiggling the wire harness leading to the 12V converter and thought it might be a broken/intermittent 12V wire to the speed controller.

I put off digging into this because I thought I had to remove not only the top dashboard(easy) but also the lower dash and frame. I felt silly when I figured out the lower dash cover just needs 4 easy to access crews removed and it pulls out after angled and 2 thick tabs are pulled from the firewall area. SOOO easy. Once I pulled the 72V power connector from the converter it was obvious the problem was the whole 12V power was dropping out due to so little metal-to-metal contact in the connector sockets. I filed down 2 thick upholstery staples to act as pin removal tool and cleaned out the sealant, sprayed contact cleaner on connectors and pins and worked them a bunch of times to further clean the contacts and reassembled. Worked great the last 3 times I had the GEM out before I found out my battery charger had failed.

The connector was full of sealant…


Update on the adventure with our 2002 GEM e825.
After fixing the VERY annoying intermittent power issues due to the 72V-12V converter input power connections being full of sealant and became flaky, The Zivan battery charger cooling fan had failed and so did the charger. Over the past 2 years, one of the cells of battery module 0 failed so I had to place a bumper block across it which turned the 22S Nissan Leaf Gen4 battery pack into a 21S battery pack. At 4V/cell that means top charge is 84V.

Luckily had picked up 3 new 42V,2A Segway scooter chargers from a neighbor who was going to throw them away. Two of these in parallel gives me 84V 2A which is good enough to charge my battery pack.

I had creat a connector while commercial connectors came from China and wired it up to a XT60 connector. I also brought 72V through the back of the dashboard glovebox on an XT60 connector plus AUX/Radio 12V on an XT30 connector. After charging with the dual 42V,2A noticed a few cells getting to 4.1V and a few at 3.8V so I FINALLY found a small converter with adjustments for constant voltage(CV) and constant current(CC) with a output range of 10-120VDC. Setting that to 86V 500mA I let that run until all battery modules were triggering their balance circuit voltage of 4.05V.

I ran the GEM around for 4 days and noticed a battery cell voltage deviation of only .06V. Put back on the 84V 2A charger over night and it still only showed a cell voltage deviation of .05V with top cell voltage of 4.01V and low of 3.96V. I really should have done this balance charge 2 years ago and I would not be surprised if not doing it was the cause of cell 0 in module 0 failing. Over 4 days of use, 3 days maintained a charge indication of 100% charged and on the 4th day I saw cell voltages ~3.7V so probably good for another 2 or 3 days before I’d see the low 3.3V max min I go with this pack.

I also now have the wireless battery head unit in the glovebox where it used to be at home just inside the door so I never knew how it was running while running around. I hope to 3D print a new glovebox lid, with a sun visor, so I can see the display while driving or atleast when stopped. Darn 2002 drives like a tank with only 105 lbs of lithium batteries under the back seat instead of 268 lbs(4 Pb batt.) and I left 2 dead batteries up front.

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Using the adjustable CV/CC DC-DC converter set to 86V/500mA and one of the 42V segway scooter power supplies, I balanced the cells to within .03V and after running the pack/cells down to 3.7xV and 3.65V(2 recharge cycles) they remain with highest to lowest cell voltage difference of 0.3V so boy I wish I’d balanced these when I first installed them…

Regarding charging, each Nisson Leaf Gen 4 module is 4S2P 14.6V 116.6Ah. and I have 5.5 modules but with one cell in module 0 failed and bipassed. So instead of a 22S2P pack I have an operational 21S2P battery pack and as others have mentioned, longevity means not charging over 4V per cell.
4V x 21 = 84V and two 42V Segway scooter chargers( 2A models ) will charge this pack to 82.95V( 3.95V ea ) over night. A recent charge from 3.65V cell level took in 5.5KWh of charge and the stock battery indicator was showing 60% SoC so really the sweet spot for stock operation seems to be a 21S configuration. I also see close to 30MPH going up slight inclines with stock T1 controller settings.

Not a rocket, not a slug and will slip the tires slightly on starting down to 80% SoC. The 2002 suspension is a tank so that might be on the list to tackle next. And if/when I sell it I will probably need to put a regular charger onboard as opposed to my dual Segway 3D printed adapter and XT60 dash connector setup.

Then again, another hack could be to debox the two chargers, mount them on a plate and cover while wiring them up to the GEM 120VAC power cable for stock-like power connectivity. Then connect the dash charge LED(s) to one or both of the Segway charger LEDs. Maybe eventually.

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What bms are you using?

Not sure you would call it a BMS as it stands. They are wireless modules made specifically for the Gen 4 Leaf battery module so one board has connections for the 4 cells of each battery module. It does top balancing to a couple of Amps max and I was given the source firmware to the MSP430 driving the boards so I can set the balance threshold voltage. Each module gets a Vehicle ID and a Module ID which is messaged to the head unit which displays the information. Unfortunately I don’t ahve the source for the head unit but it does display Max and Min battery cell voltages on the first display. Sub displays show battery voltages per module, icons displaying color to show voltage varisations, showing temp variations and showing what cells are being balanced if there are any.

A pic of the module is on this thread post: Nissan Leaf Gen 4 battery conversion - #3 by dougl

The developer used this system on an EV he used to race and was suposed to be coming up with a new head unit and updated battery modules with more accurate ADC’s and better wireless connectivitiy/noise handling. But I’ve not heard from him since Covid stuff started in early 2020.

It’s nice that each each battery module only has 6 wires( 4 cells ) and they are on a connector harness with ring lugs so easy to remove. I"ve designed a 3D printed case for the BMS module which mounts on each battery module.

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I’m sorry, I remember now. It seems that the bms is not doing it’s job, if you need to keep balancing and lost a cell.
Losing a cell is the best scenario, when looking on what might have been! Not everyone has been so lucky.

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I never did a proper balance on these modules. The developer told me to charge the pack and then put a constant 500mA on them until all were triggering the balance circuits. I did not have a PS which could reach the charge voltage and thought I was close with being a couple of tenths of a volt off.

I was wrong as a couple of tenths is a big enough variation when you get down to 3.5V and under load that one now-dead cell probably went well below 3.0V. I should have used the power supply I had which could do CV/CC and put it on part of the pack over 3 or 4 days rotating to other parts of the pack to bring them all up to the same balance charge. I fsck’ed up by not thinking it was important to get them all within a couple of hundredths of a volt.

Top it off, I did not keep the head unit with me on the GEM. It was powered off 12VDC at my front door so it would not only get spotty wireless reception with the battery modules it wasn’t something I could quickly look at to see high and low battery levels.

I finally got off my ass and pulled 12V into the glove box and put my ~BMS head unit there. Eventually I will design and 3D print a new cover which will hold the BMS head unit so it doesn’t need the big box it’s currently in and I can monitor it while driving.

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A real bms will protect even if cells are out of whack.
How is the charger and load connected to bms. If they are not, then what you have is a battery monitor.
Not that there is anything wrong with that, but a good production bms with 450a amp mosfets is less than $200.
You can use both if your plans is helping the developer. The bms will protect battery while he gets the bugs out.

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There are facilities for communications over CAN bus to a charger but I don’t have such a charger nor any knowledge of the CAN bus APIs. That was the plan once he came out with the upgraded system but from what I’m gathering he may have stopped work on the upgrade.

So ya, it’s mostly a battery monitor but could keep the system balanced if the charger were to do a constant current top charge up to ~4.00V/cell. I currently have the balance charge level set to 3.97V and the Segway chargers do drop the current as the cells reach 3.8-3.9V from what I’ve observed on the WATT Meter monitoring the AC input so if any battery cell gets out of whack it should start to reflect on cells getting more charge and the balance circuits should keep them from getting too high and hopefully keep cells from getting too low. Besides, it’s now very easy for me to see the high and low battery cell voltages and know what’s going on.

The better solution would have been to get a real charger or have spent the couple hundred to get the Zivan reprogrammed and purchased a BMS with the battery protection capabilities you mention. ie being able to shut down if things get out of hand but better, address cells getting out of whack in a controlled manner.

After you posted about a BMS vendor/model I looked it up on Aliexpress and was amazed at what you can now get for a couple hundred bills.

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Finally got around to pulling off the front disc brakes wheel spacer and seeing if it will work on the rear with the old Prius wheels and tires. It does!

See the GEM “cookie cutters” on the Prius waiting for a call to KPBS for donation.

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A part of me just died inside.

Goodbye pizza cutters. Gone too soon. You were something that could only be seemingly loved by Captain Furillio, but only if you had your brushed aluminum skullcap on.

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If anyone wants to show up with a set of 4 tires/wheels to put on this thing so it can be towed up the flatbed they can have the “pizza cutters”…

I also have 4 hubcaps with 3 of them in pretty good shape. I think one I tried to use a lug wrench on the fake lug nuts when I first got the vehicle. LOL

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I also have 4 hubcaps with 3 of them in pretty good shape.

I think it is a rule that you must have one messed up hubcap on these things.

I think one I tried to use a lug wrench on the fake lug nuts when I first got the vehicle.

This is funny. When I got mine one of the hubcaps was installed over the valve stem so I popped it off to straighten it out. That’s when I saw the wheel only had 3 real lug nuts holding it on. I put the hubcap back on just so my OCD would think there were actually 4.