BiPolar disorder and dueling BMS

GEM Forum
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1

Second time this has happened. New Lithium battery pack and BMS showing 95% full. 2012 GEM E2 cart speedo/dash battery indicator has fallen from 95% down to 50% after sitting unused for a month. It appears that there is an ‘expectation’ of a parasitic drain on the battery by the Original BMS on the GEM, that isn’t reflected by the actual BMS on the battery (that talks to my bluetooth phone). Is this a quirk or a problem? I got stuck in limp mode when the original meter showed very very low and the actual BMS on the battery still had lots left (45%). I could go into the programming with the turn signal and adjust the indicator . . . OR just plug it in and charge everything back to 100%. Where’s the fun in that??

OK, embarass me with what I’m missing. Don’t hold back!

Gem Dandy.

2

Several things going on here:
First, It might be important to list which lithium pack you have installed. (Sure, I suppose I can look back at your history and possibly find it, But I am lazy).

95% down to 50% after sitting unused for a month.

That is odd. I don’t think I have seen a Square Display SOC drop while in storage. Usually it has to be powered up for it to count its beans.
When did you observe this drop"

  • At KeyON? It will show full bars during a boot/display test, then drop to actual when done.
  • Full when leaving driveway, but after two stop signs it dropped to one bar.

There seems to be an occasional peek at PackV and bars can be taken away if the SOC sees a huge V drop while driving. Maybe it saw this and did a peek at KeyON and self adjusted. There is still much that is unknown how the SOC does it’s calculations.

We might want to look at how you are putting your car into sleep mode. If you leave the Master Battery Disconnect ON then your DC Converter is still active and consuming power(even tho your Key is OFF).

Best practice is to shut that off unless you are charging. When done charging, shut it off afterwards. If you are going away for a while, Shut off the output FETs via the APP. Shut off all 3. CHG, DIS, and BAL.

I got stuck in limp mode when the original meter showed very very low and the actual BMS on the battery still had lots left (45%).

Also odd. I was not aware the SOC did this on the 2012 cars. (2016+ yes).
Were there any other active lights on your display? The only two I know of that would force a limp home are the Turtle and the Temp.

You said your APP was reporting SOC @45%. Did you happen to note the Voltages? How low was it? (especially under load?)

It might be a good idea to clamp a voltmeter directly on your controller (so you can see it while driving) then comparing it to what you see on your app. You will be looking for a radical difference in Pack V (between controller and pack). There are a handful of connections between the front and back that (if loose) can cause a drop when under load.

What motor is in this car? When was the last time it was serviced? Perhaps it is borderline time for a look

It appears that there is an ‘expectation’ of a parasitic drain on the battery by the Original BMS on the GEM,

There was no BMS on the Gen2 cars. The batteries were more/less left to their own. When they changed the body style in 2016, is when they added all the fancy (BMC, VMC, Dash) boxes showed up and started talking to each other.

3

On a 2012? What BMS?

4

Given more time to think . . . Let me rephrase that.
WHY DO THE BMS AND THE SOC DISAGREE? More to the point, which one is lying?
The battery is one of Lithium God’s DiLithium 220aH extended range (Two 36V packs in series with a JK BMS (Bluetooth phone connection).

Here’s what’s new: last night I plugged it in. BMS on the battery showed 94%, the SOC on the speedo began charging by showing 54%. Now after 4 hours, the phone-bluetooth BMS reports 100% full, and the cart’s SOC on the dash is showing 76%.

Looks like I should go into the settings and manually turn-signal the battery level back to show 100%. Right?

One thing you mentioned is that the motor might need servicing, it’s a 5hp GE that’s only been dusted out. What do I do?

5

If you have the JK BMS app then you know that the BMS is connected to and looking at ALL cells in the battery pack. The SoC indicator only knows about the battery pack voltage(sum of all cells/modules in series) and knows how many coulombs(electrical current flow) have moved in and out of the battery. The SoC (State of Charge) indicators can be smart-ish by looking at when there’s lots of energy moving into the battery and watch the battery voltage so when the battery voltage peaks and current stops or slows flowing INTO the battery then it can set itself to a 100% setting. For the SoC, it counts the coulombs/current flowing out and has stored some value which after that number it drops the display by 10%, one bar, etc.

The BMS looks at all the cells and their voltages and while I don’t know how its SoC indicator gets that value, what I look at is the cell voltages. 4.0V is fully charged, 3.3V is less than 20% charged and time to get back on the charger. 3.2 or less is time to cut the battery from the GEM and tow the vehicle home becasue that’s too low for a lithium cell.

6

Yes, Now that your battery has been fully charged you can nudge the Dash display back up to 100%.

WHY DO THE BMS AND THE SOC DISAGREE? More to the point, which one is lying?

Not sure how it got confused- I can only guess without more input.

  • What position was your MainBatt switch when you left it? (On/Off?)
  • What was BMS FETs Status?
  • Was the SOC Display accurate after the battery upgrade?

Lying is such a strong word. I’d say the one ‘not accurate’ was the dash display since it is coupled with the power source in limited ways. For the record, SOC is very difficult to calculate and most of the time it is a best guess anyway. A more accurate condition is looking at cell V. I have not studied LG’s DiLithium packs enough to know the CellV voltage curves.

What is more of a concern to me is that your car went into a low power condition (limp mode?)

  • Did you notice any lights?

Now that your pack is charged back up-

  • Does it perform normally now?

motor might need servicing, it’s a 5hp GE that’s only been dusted out. What do I do?

Depending on your abilities you might want to pull the motor out and inspect the brushes. A GE5 has 4 brushes. If one of them loses contact you lose 1/2 of your motor. Remove the band cover on the end and give them a quick look. Make sure they are free to slide in their holders.
Be aware that the brushes are more fragile than they appear. They are quite fragile and can chip/crack/break quite easily.

7

Why are you shouting? I have tinnitus Its not nice for you to do that.

8

The gauge and bms calc remaining power very differently. Different things will effect the way they calculate soc. Jk has recently updated the app and the BMS to more accurately calculate SOC. I would start with updating the app. Need to see what version bms you have and if it can work with new app for better accuracy.