[Oeva-list] Is my lead-acid battery pack dead?

[Graunke, Gary]

Tim,

Clearly you have some thermal runaway with at least some of the batteries. This will cause a CV/CC charger to overcharge the rest of the pack, if it doesn't have a time, thermal, or AH limit to also shut it off. Of course, monitoring individual battery (or even cell) voltages to slow down/shut off the charger would also help--this is a requirement for all but flooded cells. It looks like it is a good idea for them as well! 

I had this with some old hawkers that I ran for a while. Some batteries will actually drop in voltage and then heat up while charging. This may prevent your pack from reaching the CV point. 

Usually for many reasons a few batteries will suffer reduced AH, and thus greater depth-of-discharge (DOD) as well as more overcharging. This is self-reinforcing, so those batteries will die first. But with a good BMS/charger, they won't take out the rest of the pack. 

As a rule, a good lead pack of adequate size and power (30% of vehicle weight is batteries) can get about 15000 miles, if you keep the usual DOD to 50%, don't leave them sitting uncharged, etc. But most of us don't get it right the first time, and do worse. (Sometimes we do much worse in the case total lack of battery management. Unfortunately, there are commercial products out there with no BMS, and the manufacturer has no clue about caring for batteries and even gives customers bad advice!).  

Now might be a good time to look at the packtracker data (does it follow charging as well?). Getting your battery management system to work with aging batteries is a good exercise *before* you buy a new pack. If it can handle unmatched batteries, it will do fine with a shiny new pack of fairly equal batteries (except perhaps for manufacturing defects/variances).

If you have more detailed data, that would be worth looking at. It's also interesting to note how many KWH your pack was, and your usual miles driven (or KWH consumed) between charges.

The batteries are pretty much the only maintenance item on an EV. But it is easy to ignore them. With a good BMS, you can check on them once in a good while. Not only will it extend the life of all the batteries, it will alert you when the first battery dies (or just loses enough capacity to limit your range) and prevent it from taking out the rest of the pack.

Gary

-----Original Message-----
From: oeva-list-bounces at oeva.org [mailto:oeva-list-bounces at oeva.org] On Behalf Of Tim Kutscha
Sent: Tuesday, December 30, 2008 8:47 PM
To: oeva-list at oeva.org
Subject: [Oeva-list] Is my lead-acid battery pack dead?

Hi All,

  I think I finally killed my first battery pack and would like to hear from
some folks who have been around awhile to confirm if this is true.  Here's
what I've got:

- 8600 miles driven
- typically plugged in twice a day to initiate a charge sequence
- 18 8-v flooded golf cart batteries (USBattery 8VGCHC) (144V pack)
- Zivan NG3 charger

The Zivan charger does bulk charging up to 171.6 volts and then holds that
voltage until the current comes down.  Recently, I've found that the pack
never gets above 170 volts during bulk charge even though the pack is
"boiling" rather vigorously.  Each battery is sitting around 9.4-9.5V during
bulk charge. I wake up in the morning now and find that its 40 degrees outside
but the pack is at 80 degrees due to heat generation from bulk charge.

I've also heard that the Zivan chargers tend to kill battery packs due to over charging.

Does anyone have any thoughts on this?  I can still drive around and get to work
but I bet my batteries are going quickly.

Cheers,
Tim

P.S. Anyone interested in a pile of limited capacity 8V flooded batteries for cheap
  in case I need a new pack?  They all seem to have aged equally.


      
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