Which AGM batteries for solar?

[Alloy]

Using a decent BM / SoC meter, a given bank's at-rest voltages can be mapped to SoC%.

But the table changes as the bank wears out, so best is leaving the BM in place.

Some people just use voltage while not at rest, consider it "good enough", but that's very inaccurate.

A basic cheap coulometer is in between.

I was wondering which method the author of the post was using to reach 60% as there is no reliable way to test the SOC Of AGMwhen in use.

 

[luthj]

Well, there is a reliable well to test SOC when in use, but it requires two different sized loads (say 10 and 30A), and an accurate volt meter. Then you can determine the batteries internal resistance via the equation R = Delta V / Delta I. This would then be compared to a series of readings taken at 100%, 80, 50, 30% SOC. The smartgauge battery monitor does something similar, which makes it more accurate that coulomb counters over partial cycles.

 

[Alloy]

Flooded lead acid caps are designed to vent. No need to loosen or remove, even during equalize (unless the MFG specifically states so).

There are catalytic recombinant caps which do a good job at reducing water loss. These are similar to whats inside a sealed lead battery, just without the pressure generating valve.

I also agree that a pair of GC2 deep cycle batteries is hard to beat.

2nd paragraph under Preperation

Corrective Equalization & Instructions

The frequency of corrective equalizations will vary by system due to factors such as operating temperature, frequency of cycling and depth of discharge. Loss of capacity, imbalance and low specific gravity readings are indicators. Running ...

support.rollsbattery.com

 

[john61ct]

I was wondering which method the author of the post was using to reach 60% as there is no reliable way to test the SOC Of AGMwhen in use.

I just gave you multiple methods to do exactly that, some more reliable than others.

Even if only say 4% accurate, that is fine for guiding usage patterns.

For lead, a Merlin SmartGauge is best of all, does not need the frequent recalibration of the coulomb-counting BMs either.

 

[john61ct]

Sure loosening your caps while equalizing is fine, thought you meant all the time.

But if you think they maybe aren't venting properly that should be checked and fixed, since lots of bubbling and offgassing is normal and healthy for towards the end of regular daily cycling anyway.

With solar charging voltage should often go quite a bit higher than the normal Absorb/CV vendor spec, e.g. 14.8 rather than 14.4V at a high initial charge rate in Bulk, AHT could be 6+ hours.

 

[Alloy]

Sorry, by "in use" I mean being used in the vehicle. How does one get a consistent amp load (also considering ghost loads) as the voltage drops while in use?

I've had 2 AGM banks and both were PINA to determine SOC. I'd go Lithium before I ever went with AGM again. Maybe a smart guage would have been useful. With FLA I can pop 3-4 caps an test the SG.

 

[john61ct]

Even a hydrometer isn't accurate without resting.

SmartGauge is the **most** accurate BM for any lead. While high amps are flowing that accuracy is just reduced by a few percent.

Adding a coulometer for cross-referencing might help while under a heavy load, but even on its own, still lots better than just a voltmeter.

Top choice would be SmartGauge + Xantrex LinkPro, or Victron BMV close after.

None of these are paying attention to the gross voltage reading, so sag under load is irrelevant.

For Lithium delete the SmartGauge, get a BMS that counts coulombs as a cross-ref for a proper BM.

100% SoC is always via endAmps, and LVC 0% by voltage taking sag into account.