Vampiric drain on 99 Gem e4 with leaf lithium upgrade

So I came back after 5 weeks and my 99 Gem E4 with a 20s leaf lithium upgrade was completely dead. The GFI tripped on my charging plug and the car was left disconnected for about 5 weeks. I have a chargery BMS24 managing it. Obviously something on board drained the battery while it was unplugged. Any ideas on what could be causing the drain? Could the the chargery BMS draw that much? I have an onboard deltaQ programmed for lithium charging. The deltaQ interconnect wire is connected to the chargery BMS 24 that manages overcharging and balancing. Balancing is only done during charging.

The only relay I have installed is tied to 110v charging plug that disables the Gem from running while plugged in. This shouldn’t be a problem since the relay is energized only when the Gem is plugged in.

Anyone have any ideas what the vampire could be?

Thanks in advance,

Don’t know about the 99. The 12v dc-dc converter draws standby current on the newer Gems.
The BMS and led circuit to charger is only a few ma. Should take 6Mo. to drain battery.
1/2 amp will drain battery in 5 weeks.
I wonder if surepower converter lists idle current?

Surepower lists 8ma max.
That is 6ah drain in 5 weeks.
Must be something else on.
Or possible self discharge.

Thanks I looked that up also. I suspect it’s self discharge. :slightly_frowning_face:

It’s a mystery to me. I can check my Tomberlin pack one day after sitting for weeks, then the next day it’s near dead.
Join the club. Most of us have let batteries go dead.:persevere:

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Man nothing sucks like coming to a Dead, pack.
I suspect the ShurePower DC to DC converter.
99’s have the circuit board DC to DC converter. I’m not sure what the draw on the orignal DC to DC converters

Good point! That could be the source of the mysterious drain. I don’t have anything sensitive enough to measure the standby mA drain. I think I’m just going to make sure it’s not plugged into a GFI outlet when I leave it for a prolonged period of time.


I think your best bet is to install a Kill Switch like the 05 and up cars have under the dash. That way when your not near the car and your not sure of the 110v power source if the kill switch is thrown your not at risk of leaving or having the car un plugged for weeks. If the main power switch is thrown then your good to go for MONTHS not Weeks.

I know your car has a main power switch but having it under the rear seat is a Pain

Would that be a 72 DCV disconnect or just a kill switch for the 12v system? I would prefer to have a charger hooked up to the system until I make sure that it’s not a self discharge issue.

What I need is a kill switch that kills anything after between the charger and the remained of the GEM/Controller. The only thing on the circuit would be batteries, charger and BMS 24(already wired to each cell). I could setup a storage “off board” option with a separate connector when I leave it for weeks. An easier solution may be to isolate the DC-DC converter with a switch under the dash. I suspect the 72v source is at the controller. It would be a simple task to interrupt the positive lead through a 12v 30A switch.

I would run the delta q charge wires directly to the battery so if you used the 72 volt disconnect you can have any and all draw removed from your battery and still charge. It’s kinda stupid how a factory gem disconnect doesn’t allow you to charge the car with the disconnect off.

A 12v disconnect would be interesting.

What did your Lead cells draw down to?

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Pull the fuse from 72 to 12 converter (F13) on my drawings.

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The cells are lithium and dropped down to 14v.

I think I would use another master cut off for a second 72v line for charging from the delta Q. Otherwise you have a constantly energized wire going into the charger and no way to shut it down in an emergency. Easier to just shut down the 12v system.

Can you send me or post the fuse box drawing? I think I could easily tap into the fuse box and replace the existing fuse with an inline fuse to a switch and back to the fuse box.

Happy to send you what ever I have that would help. My docs are for a 2008 eS. I have a schematic and a mechanical view of the front of the fuse panel - not sure it will be very helpful. The fuse holder is a high voltage DC

The entire 20 cell pack went down to 14 volts ?

What did you do? Did you have a way of bringing the cells back up?

Yes the whole pack.

Unfortunately not my first rodeo. In the past I would use a 12v charger for 4 cells at a time x 5 and get them high enough till the DeltaQ would kick in and balance out with the BMS. Since then I bought a 72v 2A charger for such emergencies. It’s slow but much easier.

Thanks, I don’t think it’s the same, though. I looked up the wiring diagram for the early gem cars and 72 V feeds directly into the DC converter then 12v into the the fuse box.

Thought that might be the case. Lot of changes in design from 99 to 08 - best I can tell . Surprised the converter is not fused somewhere. Something must be pulling your batteries down. Doubt self discharge would pull them down to 14 vdc total. Am interested what you did or plan to do to bring them back up??

Just got my motor back from the rebuild shop. Will install it today and see it this puppy will run. Hope to document all normal voltages, wave forms, and currents for future references as part of shake down. Will look at the standby current for the 72/12 converter (Sure). Batteries are stock (vintage 2012) for now but switching them to C-Max/Volt/Leaf when they play out. I have a 25 ah /88 vdc C-Max stack & BMS to play with. Trying to come up to speed on the technology.

Good luck. :slight_smile: