State of charge

[S_Davis]

How accurate is using resting voltage as a indicator of state of charge?

[MEXICOWANDERER]

That is a primary charging voltage. -- time limited. When proven good, the battery reaches full charge then loses it's surface charge the voltage algorithm can be used.

[S_Davis]

pianotuna wrote:

S Davis wrote:

MEXICOWANDERER wrote:
Resize this......

A flooded battery can irreversibly sulfate it's way to death but show resting voltage as being "normal" full charge. Read nothing more or nothing less in your replies thank you 🙂

What causes this to happen?

Not being fully charged, often from too low a charging voltage.

Oh ok, my charger is charging at 14.75 Volts so that should not be an issue.

[pianotuna]

S Davis wrote:

MEXICOWANDERER wrote:
Resize this......

A flooded battery can irreversibly sulfate it's way to death but show resting voltage as being "normal" full charge. Read nothing more or nothing less in your replies thank you 🙂

What causes this to happen?

Not being fully charged, often from too low a charging voltage.

[S_Davis]

MEXICOWANDERER wrote:
Resize this......

A flooded battery can irreversibly sulfate it's way to death but show resting voltage as being "normal" full charge. Read nothing more or nothing less in your replies thank you 🙂

What causes this to happen?

[MEXICOWANDERER]

Resize this......

A flooded battery can irreversibly sulfate it's way to death but show resting voltage as being "normal" full charge. Read nothing more or nothing less in your replies thank you 🙂

[S_Davis]

So this ARB 50 quart frig is pretty efficient, it ran for 96 hours in 70-80 degree temperatures set to 34 degrees and pulled the two Trojans T105s down to 12.68 volts. So less than 10%. I let them rest for about 24 hours before checking the voltage.

[RJsfishin]

I use a loaded test, tv and 1 lite on, 11.9v time io recharge.

[time2roll]

S Davis wrote:
I am using a pair of Trojan T105s to power a ARB 50 quart frig, I leave for three days with them fully charged. They don’t seem to be being drawn down much, they started fully charged at 12.86 volts and only went down to 12.68 volts.

No harm at this measurement.

[pianotuna]

Better to turn on a 1 amp load for 10 minutes.

[BFL13]

The 15 min disconnect trick sounds about right to me. If you note how much it goes up in the first 15 min, you can just count that in right off without disconnecting.

[profdant139]

For whatever it's worth, I have found that if I disconnect the battery from everything for about 15 minutes, I get a fairly accurate measurement of resting charge. It's not as accurate as letting it sit for 24 hr., but I usually do this "quick rest" method when we are camping. So I can't disconnect it for 24 hr.

I developed the "15 minute test" by disconnecting the battery and taking readings with my voltmeter every three minutes. For the first 15 min. after disconnecting, the voltage kept going up. But the curve flattened out after 15 min. and stayed pretty constant for quite a while.

If anyone has different information, I would be very interested in hearing about it!

[S_Davis]

I am using a pair of Trojan T105s to power a ARB 50 quart frig, I leave for three days with them fully charged. They don’t seem to be being drawn down much, they started fully charged at12.86 volts and only went down to 12.68 volts.

[time2roll]

S Davis wrote:
How accurate is using resting voltage as a indicator of state of charge?

Close enough for RV use. I would speculate you are within 5% to 10%.

Are you wondering when to start the generator? Or how long to run it?

[pianotuna]

It is possible to compile a chart for loaded vs at rest. But it may be more trouble than it is worth. True "at rest" is 24 hours with no charging and no draws.