Re: Mixing Batteries

Lone Haranguer wrote:
Mickey wrote:
Bob Giddings wrote:

Well, here's what I did. I charged both the new ones and the old
ones up overnight. Then I let them rest an hour while I had some
coffee and caught up on the news. Then I measured the voltage.
The new ones got to 12.65V. The old ones got to 12.55 V. The
new ones started from 12.5V. The old ones started from much
lower, 12.3V, but I didn't think that should make much difference
over a 14 hour time span. If it does, even better.

According the charge charts I consulted, 12.5 V is still 90% of
capacity. Too good to throw away, no matter how old they are.
Amazing for batteries I bought in February 2001.

Bob

Bob, am afraid this subject isn't really your strong suit. ;-)

While the voltage measurement will tell you whether the low reading battery will draw down the higher reading battery, it tells you nothing about capacity. While the chart may tell you you have 90% capacity remaining, it doesn't tell you what that capacity is. Bet you are assuming it is 90% of battery's rated capacity and that isn't the case necessarily. The older battery could be down say to 50% of capacity and the voltage reading of 90% would equal 45Ahr not 90Ahr if it was rated at 100Ahr when new.

Mickey

Reminds me of the time I bought a new battery for my tractor at a farm store. Even after charging it lacked the pep to turn the engine over.
So I took it back and told the sales clerk it was defective. He whips out his handy-dandy pocket meter and shows me the battery is putting out 6 volts.
I pointed out that 4 "D" cells in series would also produce 6 volts but wouldn't turn over my tractor's engine. He got sort of a glazed look in his eyes and
said if it produced 6 volts it was a good battery. So I went to the shelf and got a hydrometer and showed him the battery had 2 cells that were dead.

He got the manager's permission to replace the battery but was still pondering his new knowledge when I left.
LZ

Yep, need to think of voltage as pressure. Tells you nothing about vol/capacity. Like thinking a bicycle tire inflated to 65psi is the same amount needed to fill a truck tire that also carries 65psi.

Mickey
.

Relevant Pages

  • Re: Sealed Lead Acid Battery Tester Strategy?
    ... > I'm using the right stopping voltage for my tester as "stop discharge" point. ... > the full capacity of the battery. ...
    (sci.electronics.design)
  • RE: [POWER] battery calibration parameters from sysfs
    ... Isn't the standard thing here to handle this voltage to ... capacity mapping in userspace if we're just extrapolating ... and must be ignored by userspace. ... battery will change over time. ...
    (Linux-Kernel)
  • Re: LEAD ACID BATTERY
    ... Its rated as 13AH battery over 20AH. ... If you have a lead acid battery with a capacity of 13AH (ampere ... what's called the "cutoff voltage"; usually 5.25V for a 6V battery. ... the battery, the rate of discharge is specified as C/10 or C/20, ...
    (sci.electronics.design)
  • Re: Digital Multimeter : General / Basic questions (DC amps/volts)
    ... with voltage on the vertical axis, then a battery curve tends ... 10 amps - for your first current measurement. ...
    (sci.electronics.basics)
  • Re: Battery capacity -- Next Day
    ... remaining capacity of zero. ... I have been using battery voltage under load to determine the ...
    (sci.chem.electrochem.battery)
Loading