Calculating AH usage Based on SOC

Note the capacity of the battery below, in lieu of the 20hr rate (~100ah), they used the 125hr rate !!

red31 wrote:

Gjac wrote:

red31 wrote:
your 230 ah is based on a constant 11.5 a load for 20 hrs.
Used intermittently and at lower load yields a higher capacity.
SoC based on voltage is not that accurate either.

Your simple calc works for me to determine your ave usage in that type weather.
round it up by some factor!

By higher capacity do you mean more than 230 AH's with lower amp draws?

Yes, pianotuner's example misses the other side, ie when low load (amp) are used the capacity is in excess of 100%

One calculator suggests a 4.6 amp load for 60 hrs yields a 60 hr capacity of 276 ah or 120% of the 20hr capacity.

Thanks for posting this, this is very interesting and I did not know this. I dry camped with a friend with 4 6 v GC batteries and he had to recharge every day because of higher amp draws(residential refer) were as my 2 batteries last 6-7 days before they reach 50%.

smkettner wrote:

Gjac wrote:
If I dry camp for x days and my SOC is at say 50%, can I then assume that I have 115 AH's left?

Most people recharge at 12.0 to 12.2 volts. Do you expect to run them flat dead?

Down 50% is fine. Lower than 50% is harder on the battery. Lower than 20% is VERY hard on the battery. Are you expecting to go to 0%?

200+ watts of solar and your worries could be over.

I have never gone below 50% so no I would never expect to run them flat dead just to 50%. I just wanted to understand if my calculation was correct, assuming 7 days in a row had the same temperature range similar low amp draws each day(water pump,refer and a few lights).

Gjac wrote:

red31 wrote:
your 230 ah is based on a constant 11.5 a load for 20 hrs.
Used intermittently and at lower load yields a higher capacity.
SoC based on voltage is not that accurate either.

Your simple calc works for me to determine your ave usage in that type weather.
round it up by some factor!

By higher capacity do you mean more than 230 AH's with lower amp draws?

Yes, pianotuner's example misses the other side, ie when low load (amp) are used the capacity is in excess of 100%

One calculator suggests a 4.6 amp load for 60 hrs yields a 60 hr capacity of 276 ah or 120% of the 20hr capacity.

Hi,

Yet another reason why capacity is hard to measure.

scrubjaysnest wrote:
What this is saying is you might if you don't exceed the C/20 rate; or 230/20 = 11.5 amps. But then these are ball park figures and change as battery temperature goes up or down. Check this site on SOC info:Solar Homestead or here Battery FAQ's

Gjac wrote:
If I dry camp for x days and my SOC is at say 50%, can I then assume that I have 115 AH's left?

Most people recharge at 12.0 to 12.2 volts. Do you expect to run them flat dead?

Down 50% is fine. Lower than 50% is harder on the battery. Lower than 20% is VERY hard on the battery. Are you expecting to go to 0%?

200+ watts of solar and your worries could be over.

pianotuna wrote:
Hi,

If you use a high draw appliance the "apparent" capacity of the battery bank becomes much lower.



So a 5 amp load on a 100 amp-hour bank drained to 0% state of charge will last for 20 hours--but a 10 amp load reduces total by 15% less.

You might get a "rule of thumb" for your own bank and camping style but it may be a rough guess.

Gjac wrote:

pianotuna wrote:
Gjac,

Look up peukert law.

If you want long battery life 50% is as deep as you want to go, so it is time to recharge.

The gas valve on the fridge may use more than 16 amp-hours per day. Mine uses about 29 amp-hours per day.

Don, wouldn't my simple calculation include the peukert effect? Am I missing something basic with this simple calculation?

What this is saying is you might if you don't exceed the C/20 rate; or 230/20 = 11.5 amps. But then these are ball park figures and change as battery temperature goes up or down. Check this site on SOC info:Solar Homestead or here Battery FAQ's

red31 wrote:
your 230 ah is based on a constant 11.5 a load for 20 hrs.
Used intermittently and at lower load yields a higher capacity.
SoC based on voltage is not that accurate either.

Your simple calc works for me to determine your ave usage in that type weather.
round it up by some factor!

By higher capacity do you mean more than 230 AH's with lower amp draws?

Hi,

If you use a high draw appliance the "apparent" capacity of the battery bank becomes much lower.



So a 5 amp load on a 100 amp-hour bank drained to 0% state of charge will last for 20 hours--but a 10 amp load reduces total by 15% less.

You might get a "rule of thumb" for your own bank and camping style but it may be a rough guess.

Gjac wrote:

pianotuna wrote:
Gjac,

Look up peukert law.

If you want long battery life 50% is as deep as you want to go, so it is time to recharge.

The gas valve on the fridge may use more than 16 amp-hours per day. Mine uses about 29 amp-hours per day.

Don, wouldn't my simple calculation include the peukert effect? Am I missing something basic with this simple calculation?

Gjac wrote:
If I dry camp for x days and my SOC is at say 50%, can I then assume that I have 115 AH's left?

In theory yes, not in reality. Your voltage will suffer after 50%