How To Balance Battery?

[Pantera Dude]

It appears to me that there is no consensus on how to balance the battery? I've read on the forum that it should be done by charging in range mode and I've also read that it just happens by charging in standard mode? If you see no loss in ideal miles over time, could your battery be out of balance? Or would there be a certain number of miles lost at which balancing in range mode should be attempted? I assume if you attempt to rebalance by charging in range mode and see no change, that would mean that your battery was in balance all along?

 

[strider]

The fastest way to balance is to drive it down to 20-30% capacity, do a range mode charge, let it sit for a few hours still plugged in, and then unplug and let it sit for a couple days. Then go back to standard mode charges. You should not do this often but it will bring a badly out of balance pack back into balance. You can also just keep doing standard mode charges and it will balance the pack if left to sit plugged in after charging for an hour or more before driving each time but it will take longer. The reason is that it is easier for the system to calculate the differences between bricks at 100% than it can at 90% so it can balance quicker.

Some additional info: If you use the VMSParser app ( VMS Log Parser for Tesla Roadster ) and run it w/ the "-b" option you'll get output like this:

timestamp, brickahmin, brickahave, bricknumber
11/10/2010 16:14:16, 156, 156, 73
11/11/2010 16:14:15, 156, 156, 73
11/12/2010 16:14:14, 157, 157, 70
11/13/2010 16:14:14, 157, 157, 70
11/14/2010 16:14:13, 157, 157, 70
11/15/2010 16:14:13, 157, 157, 44
11/16/2010 16:14:12, 157, 157, 44
11/17/2010 16:14:12, 157, 157, 44
11/18/2010 16:14:12, 157, 157, 44
11/19/2010 16:14:12, 157, 157, 44
11/20/2010 16:14:12, 157, 157, 44
11/21/2010 16:14:10, 157, 158, 44
11/22/2010 16:14:09, 157, 158, 87
11/23/2010 16:14:09, 158, 158, 91
11/24/2010 16:14:08, 158, 158, 45
11/25/2010 16:14:08, 158, 158, 45
11/26/2010 16:14:07, 158, 159, 45
11/27/2010 16:14:06, 158, 159, 45
11/28/2010 16:14:06, 158, 159, 45
11/29/2010 16:14:06, 158, 159, 45
11/30/2010 16:14:05, 158, 159, 45
12/01/2010 16:14:05, 158, 159, 45
12/02/2010 16:14:05, 158, 159, 45
12/03/2010 16:14:05, 158, 159, 45
12/04/2010 16:14:05, 158, 159, 45
12/05/2010 16:14:05, 158, 159, 45
12/06/2010 16:14:04, 158, 159, 45
12/07/2010 16:14:04, 159, 159, 45
12/08/2010 16:14:03, 159, 159, 45
12/09/2010 16:14:03, 159, 159, 45
12/10/2010 16:14:01, 159, 159, 45
12/11/2010 16:14:01, 159, 159, 45
12/12/2010 16:14:01, 159, 159, 45
12/13/2010 16:14:00, 159, 159, 45
12/14/2010 16:14:00, 159, 159, 45
12/15/2010 16:13:59, 159, 159, 0
12/16/2010 16:13:59, 159, 159, 89
12/17/2010 16:14:59, 159, 159, 89
12/18/2010 16:14:58, 159, 159, 89
12/19/2010 16:14:58, 159, 159, 89
12/20/2010 16:14:56, 159, 159, 89
12/21/2010 16:14:56, 159, 159, 89

In addition to the lowest brick # (last number on the right) it will give you the difference between the average brick's amp-hours and the lowest brick's amp-hours. If those numbers diverge (looking at my data, the largest difference I've had is 4) then that's a clue that you may have a bad brick and Tesla should take a look. I don't know what that number is, maybe 5 is ok, maybe not. It's also recovered and my latest data has a delta of 2. So as long as the lowest brick number is changing and the delta between average and lowest isn't getting steadily wider then you're ok.

update: Just saw your Ideal Miles post. At 183 in Standard your battery is in great health. I'd just leave it in Standard and drive!

 

[Pantera Dude]

Sounds good, thanks!

 

[brianman]

do a range mode charge, let it sit for a few hours

I thought this was one of the worst things you could do for battery lifetime?

 

[strider]

I thought this was one of the worst things you could do for battery lifetime?

That's why I said you should not do it often. Yes, it is hard on the battery to sit at high SOC, but it is the fastest way to bring it into balance. There have been instances of Roadsters that had been sitting in storage mode (holds battery at 50% SOC) for long periods and the packs had become quite unbalanced. Driving w/ a highly unbalanced pack is hard on the batteries too as you're running the lower cells extra low compared to higher cells so in that case (way off-balance pack) it is best to get the pack in balance as quickly as possible.

 

[Alan]

I thought this was one of the worst things you could do for battery lifetime?

Correct, but as Strider says above "You should not do this very often" Driving with a battery pack out of balance does not make sense so
its something to do if out of balance.

I charge at work each week day and not at home. This means that the pack is fully charged (standard mode) just before I leave for home. The advantage is that the pack spends most of its life in the 40 to 60% state of charge (& also I dont pay for the electricity . At the weekends though I charge in standard mode & leave the car overnight to give it a chance to do balancing.

Now at 23,000 miles with 187 ideal after a standard charge from 13A, its more like 184 from a 30A charge.