agm capacity test
I've installed 2 8d deka intimidators in my fiver. Closing in on 15 cycles. Would like to do a baseline test so I will have something to compare to in the future. What would be the proper way to prefo...
Forum Discussion
My test is to first make sure the batts are full.
Then I get the 20hour rate by dividing the rated capacity by 20, so EG 300AH would be 15amps. Reduce the est full capacity for really cold temps, but getting the temp correction right is dodgy since some of that is supposed to be internal battery temp, not ambient.
Now I need a 15amp load to run for 10 hours to get the batts down to 50%. This is not so easy but you can get "close enough"
A. turn on a bunch of lights till the monitor says 15a. As battery voltage falls lights dim and amps fall, so keep turning on more lights to keep amps up near 15.
B. using an inverter with enough 120v load to make it draw 15a. now amps will slowly rise as battery voltage drops. So start with say 14a and let it get to 16a by the ten hour point to average 15.
When to stop? You might hit 50% at nine hours, indicating your batts are not at rated capacity, but at 90% of that. Now you need that monitor to show what AH you are down.
If you go to half the rated AH and stop you might be at 40% if the batts are not up to rated AH, so you don't want to overshoot. (with Wets you can spot check the SG to see 50% that way too) so you have to stop "early" and wait a bit to see what the voltage does. it will come back up but you don't want it to come back over 12.2 or whatever it is for AGMs at 50%. If it does, start up again and try later, till you get it right.
If you do this test a few times you get a good "feel" for when you are close to 50% by how fast the voltage comes back up after stopping. also you can tell by the loaded voltage as it falls. eg, at the 20 hr rate , when voltage falls to about 11.5 you are there with Wets--it might be higher with AGMs.
Once you are at 50% (estimated) then take your AH amount that you are down, times two, and that's your capacity. Compare that with the time it took wrt the ten hours for a cross-check.
Then I get the 20hour rate by dividing the rated capacity by 20, so EG 300AH would be 15amps. Reduce the est full capacity for really cold temps, but getting the temp correction right is dodgy since some of that is supposed to be internal battery temp, not ambient.
Now I need a 15amp load to run for 10 hours to get the batts down to 50%. This is not so easy but you can get "close enough"
A. turn on a bunch of lights till the monitor says 15a. As battery voltage falls lights dim and amps fall, so keep turning on more lights to keep amps up near 15.
B. using an inverter with enough 120v load to make it draw 15a. now amps will slowly rise as battery voltage drops. So start with say 14a and let it get to 16a by the ten hour point to average 15.
When to stop? You might hit 50% at nine hours, indicating your batts are not at rated capacity, but at 90% of that. Now you need that monitor to show what AH you are down.
If you go to half the rated AH and stop you might be at 40% if the batts are not up to rated AH, so you don't want to overshoot. (with Wets you can spot check the SG to see 50% that way too) so you have to stop "early" and wait a bit to see what the voltage does. it will come back up but you don't want it to come back over 12.2 or whatever it is for AGMs at 50%. If it does, start up again and try later, till you get it right.
If you do this test a few times you get a good "feel" for when you are close to 50% by how fast the voltage comes back up after stopping. also you can tell by the loaded voltage as it falls. eg, at the 20 hr rate , when voltage falls to about 11.5 you are there with Wets--it might be higher with AGMs.
Once you are at 50% (estimated) then take your AH amount that you are down, times two, and that's your capacity. Compare that with the time it took wrt the ten hours for a cross-check.
