WBH wrote:
"Wayne.B" wrote in message
...
| On Wed, 24 Oct 2007 21:59:21 -0700, Richard Lane
| wrote:
| I have 2x SRM27 (85Ah) flooded batteries approximately 5 yrs old on my
| sailboat. I wish to test their remaining Ah capacity by applying a fixed
| current load and monitoring the terminal voltage over time.
| Question: I believe the Interstate table of voltage vs state of charge
| is open circuit voltage, if this is true then I would have to interrupt
| the discharge periodically in order to measure the o/c voltage then
| resume the load until I have achieved 1/2 remaining Ah.
| Does anyone have a more direct test of remaining Ah capacity?
| Dick
|
| Battery capacity in Amp-Hours is usually spec'd at the 20 hour rate,
| e.g., a 100 AH battery should be measured with a 5 amp discharge
| current, and your 170 AH bank should be measured at a rate of 8.5
| amps.
|
| First step is to build a load that will draw about 8.5 amps. Some
| combination of 12 volt bulbs will work.
|
| Next step is to fully charge the batteries and leave them with no load
| attached for 24 hours. The open circuit voltage at the batteries
| should measure about 12.6 volts.
|
| Now attach your 8.5 amp load and measure the time it takes for the
| voltage to decrease to 11.6 volts (approximately 50% discharged).
|
| Your effective A-H capacity is the time in hours x 8.5 x 2, e.g., if
| it took 7.6 hours to reach 11.6 volts your capacity is 7.6 x 8.5 x 2.
|
|
|

I presume you do not mean 11.6V at open circuit Voltage, because I'd
consider the battery completely empty at 11.6V (after stabelizing).
wbh


No, I think Wayne B meant 11.6 v on load as he did not specifically
mention disconnecting the load prior to measuring the voltage. I have
asked him privately where he got the loaded voltage to state of charge data.
Dick