Switched to Big Battery 72 volt Falcons

GEM Forum
1

I Switched to Big Battery 72 volt Falcons 2x kit in my 2005 GEM. Runs great but the Charge gauge seems to be off. When It is fully charged it only shows half. I have a range of over 30 miles. Any idea what the issue is?

2

Have you tried resetting your SOC meter(the battery gauge) since you installed your new battery?

You should charge your battery fully, then reset your display so that it shows full.

It also may be due to how/what you are charging your new batteries with. If you are doing this outside of the normal car wiring and pre PSDM module then it cannot keep track of the energy coming back into the pack and is really messing with the SOC function.

Does Big Battery have a solution?

3

Are you using the oem Gem charger? A charger connected to battery will not work in a Gem.

Maybe they don’t build batteries for Gems.

5

Thanks for the response. I am using an external charger from Big Battery for LIFEPO4 batteries. The existing charger will work (I think)

6

That’s a big question.

7

Thank you. I will check with them today. How do I reset the SOC display?

8

Here you go, follow Mike’s directions here, they should be good for gems with T3, T4 or T5 controllers. 05s had T3s

9

Thank you for your help. It is much appreciated!

10

But this is the point. The way Big Battery is charging this battery system (being two batteries) is not the correct way to include the stock Gem SOC meter.

Is there a dedicated charge plug on this battery?
Or are you pulling the main plug out and plugging the charger into that connection.
Are you charging the second battery also?

What you will find is that you will be resetting the SOC meter every time you charge the car.

Not knowing too much about the internal works of BB i hesitate to take a guess and be wrong. You will need to ask BB if it is Ok to charge the batteries via the OUTPUT connection to the car. and can you charge BOTH batteries at the same time with your present BB charger.

Finally- is your old charger still mounted in the car?

11

Thanks for your response. There are two 72-volt batteries in parallel hooked up via a parallel bus bar to which the Big Battery charger is also connected. Yes, the old charger is still in the GEM. It will charge the batteries but to be safe, I use the BB charger

12

And each battery has a 175 Powerpole connector which is also connected to the parallel bus bar

13

Thsts a big problem.

14

Yeah, I am thinking about just installing aftermarket state of charge meter and calling it good

15

As far as I know, there are two things that need to happen to get the SOC meter to count up(add bars) correctly on it’s own.

  1. You need to inject your charge current on the correct side of the sensor(shunt). Where you have it now is not the correct side. The B- connection needs to be on the other side of the shunt.

  2. You need to put the car into charge mode via the interlock circuit. This hobbles the car so you don’t drive away with the car plugged in. It appears you are not doing this either(guessing). Your BB charger probably does not have the needed hookup for interlock sensing so you will probably need to switch that manually. I have seen other guys do this with a simple switch.

As you noted, your onboard charger will charge your new Lifepo4 batteries, but not correctly. If your charger is the stock DQ from 2005 it is most likely not one that can be programmed for alternate profiles.

16

Thank you for the informative response