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My Roadster 2.5 keep balancing cycle again, and again for 4 days

nicky _cwt

Member
Sep 22, 2019
38
5
Hong Kong
Hope somebody can show me some lights on my issues.

Background: I had a roadster 2.5 previously but sold. Recently I brought another 2.5 from a car dealer. I know the car dealer only charge the car once a month for the pass 6 month. I check the CAC and it seems ok at 133. I got the car last Friday and put it on charge around 6:00pm. I check Sat night around 9:00pm and at that time charging was done but the car still under balancing (in my previous experience, balancing only take 1 to 2 hours after charging completed. The balance cycle took much longer than I expected). At that time ideal range was at 245KM.

I checked the balancing status on Sunday night again, the ideal mileage increased to 249KM, and the car still doing started another balancing cycle itself (I did not top up). I checked Monday night again, the ideal mileage increased to 251KM, and the car started another balancing cycle. I check today and the ideal mileage increased to 253KM, and it started another balancing cycle again.

I think the battery was out of balance (as the car dealer did not know how to take care the car) before I brought it. It may need to go for longer balancing cycles before the battery reach a balanced It is the 4th days since I plugged in the car for a standard mode charging, and the car is still under balancing cycles again and again and again.

Should I concern about this, or it is normal? Should I disconnect the cable now or let it runs another balancing cycle until it stop. I just worry it will go for balancing cycles continuously and eventually damage the battery.

Hope you guys can give me some guidance. Thanks in advance,

Nicky
 

ML Auto

Member
Mar 8, 2014
721
737
SW Florida
Check the min and max brick voltages in the service menu to see how far out of balance it is. As long as the range keeps increasing, you are OK. Some of the cars I have in storage that I charge every 6 months sometimes take a week to balance.
 

markwj

Moderator, Asia Pacific
Apr 10, 2011
4,604
1,219
Hong Kong
I'll reply by eMail, but based on what you sent me this seems normal. The pack is just slightly out of balance.

The balancing process is very slow, using very small resistors. It can take several days of being connected before balancing completes.
 

nicky _cwt

Member
Sep 22, 2019
38
5
Hong Kong
Thanks for the replies

I checked the min/max was 53% to 59% (before charging), 83% to 87%. (2 days after charging done) , and now is 85% to 87%. It seems the balancing is keep improving.

The ideal mileage increased to 256KM (compared to original at 245KM).

I think this is the reason why Tesla suggested us to always plug-in the car.
 
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markwj

Moderator, Asia Pacific
Apr 10, 2011
4,604
1,219
Hong Kong
You may know this already, but anyway here are some explanatory notes on balancing that I left in another thread:

Fundamentally, the car only has the ability to charge all the bricks, or discharge them on an individual basis (aka 'balancing'). The way balancing works is that you charge the car until it stops charging (max brick at target voltage) and leave it that way. Don't unplug or turn off the power. The car will then go through its 'balancing' process (that you can monitor on the balancing screen in the diagnostics on that little VDS - the screen with a bunch of 1's and 0's. If you look at that screen on your car, you should be able to clearly see the faulty brick (the odd one out).

For example, let's say you have 98 bricks at 3.9V and 1 brick at 3.1V. The car will then start bleeding power from each of those high 98 bricks, using comparatively small switchable resistors on each brick. Say after 24 hours, those 98 bricks are now at 3.8V (and the 3.1V brick is unchanged). So, now the car charges and brings back those 98 bricks to the limit of 3.9V but also brings up the one low brick to 3.2V. Repeat the process for several days, and the battery would slowly come back into balance.
(the voltage numbers above are not the actual limits, but just used for demonstration purposes)

The MIN% is the SOC of the brick with the lowest voltage. It controls how far the car can be driven (until MIN% is 0).

The MAX% is the SOC of the brick with the highest voltage. It controls how much the car can be charged (until MAX% is the limit).

On the balancing display, a '1' means it is discharging that brick, and a '0' means it is not. A display of all 1's and one 0 on the VDS would indicate the car is discharging all the bricks except one, in order to try to balance the pack. The car is trying to bring down all the other bricks to the same voltage as the lowest one. Balancing only occurs after the car has completed a charge, so all 0's when charging is expected.
 

ML Auto

Member
Mar 8, 2014
721
737
SW Florida
Thanks for the replies

I checked the min/max was 53% to 59% (before charging), 83% to 87%. (2 days after charging done) , and now is 85% to 87%. It seems the balancing is keep improving.

The ideal mileage increased to 256KM (compared to original at 245KM).

I think this is the reason why Tesla suggested us to always plug-in the car.


Looks like it is almost done balancing. Good news.

If you drive the car a lot you dont have to keep it plugged in daily, just when it needs a charge. It will balance after its done charging.

If you dont drive it for months, you can save some wear and tear on the contactors by just charging it before you use it, and then keeping it plugged in as you are doing now to allow it to balance.

I dont have much faith in the reliability of the Chinese made contactors inside the ESS, which would be outrageously expensive for you to replace if they fail. So I charge only as needed.
 

nicky _cwt

Member
Sep 22, 2019
38
5
Hong Kong
Mark: Thanks a lot for the information. It really help me to understand the balancing cycle.
ML: I only use the car around 2 times (usually driving short distance during weekend) and I charge it roughly every 10 days. I am also avoid having additional charging cycles, as I worry about having additional charging cycles would reduce the PEM life.
 

jason.tv

Member
Feb 13, 2020
410
379
Florida
Mark: Thanks a lot for the information. It really help me to understand the balancing cycle.
ML: I only use the car around 2 times (usually driving short distance during weekend) and I charge it roughly every 10 days. I am also avoid having additional charging cycles, as I worry about having additional charging cycles would reduce the PEM life.

I don't think this has any issue; I thought about doing this as well then if you charge once every 10 days your car only turns on / charges 36 times throughout the year instead of 365 times to top off daily charge reducing how many times the pem is turned on or other components of the car reducing life of the car. Even The LCD VDM Screen can prob last 40 years; if it fails Grubermotors.com has or is creating a new lcd screen board that works ever better than the original.

But this does not matter; there is a battery / charging guide that comes with the car that says keep the car plugged in daily to exhaust daily cycles; assuming this is the build up of heat that can still accumulate inside the battery (even when the car is sleeping), When energy moves inside batteries from the anode back to the cathode or cathode back to the anode whatever the negative loss of charge causes heat in which should be exhausted on a daily basis.

This instruction sheet also is useful for people or at this time there was no ovms to monitor if your battery or cars ambient temperature or ideal temp to go to sleep; most roadster owners don't realize their car might not go to sleep and pem / coolant pump can run 24/7; this is another reason to exhaust or keep your car plugged in daily so it exhausts that heat from the battery. Still till this day we have roadster owners question why their car is not going to sleep.

I have it set now so when the first radiator heat exhaust cycle is done from the front after 2 minutes of charging I stop charging and my car goes to sleep all within a 6-7 minute time frame from start to finish; so that's my daily charging cycle as my car does not lose any range from the night before, maybe 1 mile here and there.
 
Last edited:

nicky _cwt

Member
Sep 22, 2019
38
5
Hong Kong
I don't think this has any issue; I thought about doing this as well then if you charge once every 10 days your car only turns on / charges 36 times throughout the year instead of 365 times to top off daily charge reducing how many times the pem is turned on or other components of the car reducing life of the car. Even The LCD VDM Screen can prob last 40 years; if it fails Grubermotors.com has or is creating a new lcd screen board that works ever better than the original.

But this does not matter; there is a battery / charging guide that comes with the car that says keep the car plugged in daily to exhaust daily cycles; assuming this is the build up of heat that can still accumulate inside the battery (even when the car is sleeping), When energy moves inside batteries from the anode back to the cathode or cathode back to the anode whatever the negative loss of charge causes heat in which should be exhausted on a daily basis.

This instruction sheet also is useful for people or at this time there was no ovms to monitor if your battery or cars ambient temperature or ideal temp to go to sleep; most roadster owners don't realize their car might not go to sleep and pem / coolant pump can run 24/7; this is another reason to exhaust or keep your car plugged in daily so it exhausts that heat from the battery. Still till this day we have roadster owners question why their car is not going to sleep.

I have it set now so when the first radiator heat exhaust cycle is done from the front after 2 minutes of charging I stop charging and my car goes to sleep all within a 6-7 minute time frame from start to finish; so that's my daily charging cycle as my car does not lose any range from the night before, maybe 1 mile here and there.


Jason: I had OVMS on my first roadster (was sold) and not yet install OVMS on my second roadster, so I can not monitor the battery temp. I will do the tricks you suggested for battery cooling cycle. Thanks for the advice.

You day time running light really looks gorgeous, it really stand out from the crowd.
 

slcasner

Active Member
Feb 20, 2011
1,190
795
Sunnyvale, CA
But this does not matter; there is a battery / charging guide that comes with the car that says keep the car plugged in daily to exhaust daily cycles; assuming this is the build up of heat that can still accumulate inside the battery (even when the car is sleeping), When energy moves inside batteries from the anode back to the cathode or cathode back to the anode whatever the negative loss of charge causes heat in which should be exhausted on a daily basis.
But in my experience charging the battery does not exhaust the heat. The battery temperature is often left above the threshold where the coolant pump is running constantly. And I'm talking about a standard charge, not a range charge. So I finally took the step to implement @ML Auto's mod to install a switch to force the A/C to cool the battery.
 

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