DIY Electric Car Forums banner

Re: [EVDL] How much does OCV 1 hr after charge and voltage at full charge change for

486 Views 0 Replies 1 Participant Last post by  EVDL List
Re: [EVDL] How much does OCV 1 hr after charge and voltage at full charge change for

Steve Powers wrote:
> old 6V flooded Golf Cart batts... 5-7 years old. Not cycled much...
> 1-2k miles on them... in an EV that was sitting...
> am charging them now. I used a very slow charge
> rate, about 3 Amps...

If they were all sitting at 6v or more, that's good. They weren't dead,
there are no shorted cells, and so should take a charge normally. But
it's going to take a while to get them "broken in" again, to find out
how good they really are. Sort of like a person that gets up from a long
stay in the hospital; it will take a little exercise to get back in shape.

I'd raise the charging current to 5 amps, and keep charging until the
voltage stops rising. This may take a while. They will gas and fizz a
lot. When you finish, you'll need to add water. This is called an
equalizing charge.

If you check the voltage on each battery just before you turn off that 5
amp charge, it would be around 7.5 volts for a good battery. These may
only be at 7.2v or so.

If the batteries are old and sulfated, you may have trouble getting them
up to even 7.0v at 5 amps. You may need to increase the current as high
as 10 amps to get them to fully charge, at least for the first few
recovery cycles.

Be careful during the first few discharges. Don't try to see how fast or
how far you can go! They are likely to have higher internal resistance
and lower amphour capacity on these first cycles, but improve noticeably
with each subsequent charge/discharge cycle.

> So, when do I stop? How do I know I am getting a full charge without
> overcharging them?

These are floodeds; it's OK, even necessary to overcharge them. You just
need to replace the water used during the equalization.

> I don't want to undercharge them either. I am watching for
> gassing and keeping the charge rate very low.

No; you WANT them to gas!

> the best way. Should I cycle them under heavy EV load or use
> something like a 100 W bulb, which will be very very slow?

Modest loads are best. Testing is faster, and it gives you a better idea
how they will perform in an EV. They are designed for a 75 amps nominal
load, so anything in the 25-100 amp range is reasonable.

It's possible that they have grid corrosion, and will have adequate
amphour capacity for low-current applications, but not good enough for
high-current EV use. It's also possible that they're sulfated, and so
have lost amphour capacity, but still have a low enough internal
resistance to be fine in an EV if you don't mind half the range. Testing
will tell the story.

Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart | That's how the light gets in -- Leonard Cohen

| REPLYING: address your message to [email protected] only.
| Multiple-address or CCed messages may be rejected.