Minimum charge rate for an AGM?

[Soundhound]

Having lost two Hawker AGMs to thermal runaway I'm looking for advice on the next purchase. I have available 15A of solar charging capacity here in Spain. Not much it seems from other threads here. I would like to put in the highest capacity AGM possible but what I have found here so far on minimum rate doesn't settle the matter for me. I also need as high a discharge rate as possible.
Not many datasheets specify minimum/optimum charge rates.
Any ideas?

[Wy_White_Wolf]

This will vary by manufacturer. When looking at AGMs request that specification.

WWW

[littleharbor]

Lead acid batteries need to be recharged in a timely manner. The longer they sit in a discharged state the more sulphation you can expect. If you don't have a way to equalize them, as in AGM batteries. you are going to be replacing them prematurely. Why don't you get more panels and a bigger controller? Less expensive than replacing batteries.

[PNjunction]

I'd try to fix what caused those pure-lead hawkers to go into thermal runaway in the first place, so a bit more info is needed.

Generally, with the pure-lead agm's, (Odyssey, Enerys, Hawker), if you take them down to 80% DOD, they usually want to see 0.4C minimum current! This high rate is mostly due to getting you back in shape for the next cycle / shift, (get to absorb quickly) so you don't walk down the capacity with premature sulfation.

But, if you DID have the time to fully charge them with about 16-20 hours of so available, then .05C is the minimum from an efficiency standpoint. 0.10C is my personal minimum with the pure-leads. This 16-20 hour timeframe of course implies the use of an AC charger.

Fortunately, with pure-leads, you can hit them very hard, which makes them good for solar, IF you have enough solar current to take advantage of it. I can hit my pure-leads with up to about 1C (!) IF you have the absorb voltage set accurately, AND if the controller is doing temperature-compensation!

That being said, can you provide more info on your setup so we can find out why those two went thermal:
1) What model are they? Armasafe's perhaps? Or cast-off ups-style models?
2) Did you get them new or used?
3) Did you run them in series / parallel and charge each of them up *individually* at first before putting them into a series/parallel arrangment?
4) Is your charger / controller employing temperature-compensation (not just temp protection - different thing), and what was the absorb voltage you set them to?
5) What was your DOD and solar charge times like? Were you able to get them fully charged often?

These questions will help prevent any replacements from suffering the same fate.