Performing a Temperature Corrected Specific Gravity test with a hydrometer

[chrisski]

What Hydrometer do you use for a specific gravity test? Do you do the temperature correction of .004 per 10 degrees F? Also, what do you consider fully charged for your battery bank since you’d expect a new one to be 100%, but at several years old, perhaps not?

I ask because with the Deka Hydrometer with the floating glass ampule I was recommended, the highest reading on that is 1.280, but to be 100% on my battery with temperature compensation for 80 F where I subtract .008 from each reading, I would need to read 1.285, but that is above what this hydrometer reads.
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This is the first time since I’ve installed the batteries that I did a check with a hydrometer.

I did a specific gravity test, and when I compensated for temperature, I got a charge rate of 96% after sitting in the sun with no load on the battery.

The temp compensated specific gravity of 1.270. Battery Temp was 61 degrees. With 1.277 being 100% and 1.258 being 90%.

Not sure if 96% fully charged is good or not. I also suspect the Deka Hydrometer I used is not accurate enough to get me to 100%. The highest reading was 1.280, so to be fully charged to 100%, I would need to read 1.285.

 

[snoobler]

These days, it's about readability for me. I'll sacrifice precision to be able to read the damn things.

I apply temperature corrections to SG based on the battery spec. Some manufacturer's use charts, others use a formula. They're all pretty close.

You will find it challenging to get your trojans to the specified 1.277 without a very long absorption time. 1.265-1.270 is more typical.

SG readings can be flighty. They basically need to be taken about 2 hours after floating with negligible load/charge on them., and you need to suck and expel the electrolyte 2-3 times before you take a reading.

If you're comfortable you're getting to nearly 100%, you're good. Some resources show ranges of SoC for a given SG, so it's pretty much a ±5% accuracy thing.

If you ever see an instance where one of the cells is notably lower, that's a definite trigger for equalization.

 

[chrisski]

If you ever see an instance where one of the cells is notably lower, that's a definite trigger for equalization

Based off Trojan.s recommendation of > .03, I do not have imbalanced cells, I have .003. They range from a high of 1.272 to a low of 1.269 with most cells right at 1.270. I do wonder if Trojan has a misprint and it is supposed to read .003.

I did notice Trojan recommend equalizing for one to two hours after 30 days, and I have not done that and the batteries have been in the Rv now for about 2 months, but only about 2 weeks of heavy use. So, based off this I will equalize once I’m done with this trip.

You will find it challenging to get your trojans to the specified 1.277 without a very long absorption time. 1.265-1.270 is more typical.

I’m beginning to understand about getting to 1.277 being difficult. I’m happy my new batteries are at the upper end of what you typically see.

SG readings can be flighty. They basically need to be taken about 2 hours after floating with negligible load/charge on them., and you need to suck and expel the electrolyte 2-3 times before you take a reading.

Appears I did the specific gravity test correctly. It had been on float charge for several hours and I did such and expel the electrolyte three times. I also shut the batttery power switch off, and whenI do that, the only thing that is on the circuit is the battery monitor. Seemed off to me that the battery monitor’s instructions had it set up prior to any master off switch, but I set up like Victron recommended.

If you're comfortable you're getting to nearly 100%, you're good. Some resources show ranges of SoC for a given SG, so it's pretty much a ±5% accuracy thing.

I’m pretty comfortable with the SOC for the battery. If I had to make a guess at how good the hydrometer is, I would say +/- 5% is good. A specific gravity reading of 96% is close enough for me, at least as I watch it over the next few days and am will contuinue after the batteries have received a good deep charging after the other three show up and start using the trailer. I’m by myself right now, and I only use about 2% of the battery bank overnight (12-20 ah), and when the other three are here, the power rises to between 18%-28% (110-150 ah).

As always, I appreciate your replies as I tweak this system.

 

[snoobler]

Probably not a typo. Other manufacturers indicate .03 too.

It appears you have everything well in hand. I would be happy if I got your results.

 

[Zil]

I just went to the tool room and found my hydrometer from East Penn, the makers of Deka. The highest float reading is 1310 the lowest is 1090. it has a built in thermometer with an add / subtract scales from 0-20 / 0-20. All numbers are specific gravity.