I've been checking online and for deep cycle agm batteries it seems the max current draw, unless otherwise stated in technical docs, is the ah rating of the battery. So a 100ah would be safe to draw at 100amps. I ask because I'm looking at carbon pile load testers and for the 500 and 1000 amp models they recommend taking the ah rating of the battery and multiply by 3 and that's the amp load you put on it. Essentially I'm playing around with used AGM batteries (UPS) and wondering which carbon load tester would be best suited.
AGM Battery and Carbon Pile Load Tester
tessel on 02/08/2022 - 18:54
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No, just check general health and only used for general lights etc. I only mention it because carbon pile are meant to be the better way to check health of battery and they recommend 3 times the AH rating. Was just looking for best ways to check health of ups AGM batteries as the top end load testers are pricey but the bottom end are cheap and do about 100 amp load, which I'm thinking is fine for a rough health check of the battery.
Conductance testers have replaced carbon pile for a quick check. If you want an accurate measure setup a constant current load to run the battery down over 20hrs. I use a BT100 conductance tester.
Yeah, unfortunately I need to find one that works with batteries that don't have CCA specs etc, like UPS batteries. I bought one and it has no test option for AH only batteries but I do see some that do.
There are formulas and tables to estimate CCA from AH. Works fine if are testing lots of the same AH battery. Because all you really need is how well an unknown battery compares to a battery of the same size you know as good. Pretty sure one of the euro standards that they do support converts to AH pretty well. Also as per your original question don't try and pull more than the rated max discharge current as you will cause damage.
I don't think those formulas are reliable at least from my research but I haven't looked at all the different battery standards like you mention. Yes, definitely not going over max discharge current. Obviously best way is as you said 20 hour discharge. I have seen some digital battery testers that do have AH input and will probably grab one.
@tessel: Formulas are not reliable but it is all relative. The ones with ah probably use the same formula internally. Only accurate way is 20 hour method. Anything else is an approximation so just pick a number say 7 X AH and call that CCA. You will be accurate within ten percent and repeatable within 2%. Repeatable is all that matters. Just trying to save you spending money for no benefit in the ozbargain way.
@racer1234: And I appreciate the help. I'll definitely see if I can get one of the battery standards working on the digital battery tester I have.
What result are you after here? Are you hoping to weld with the batteries, or something else that would smash the current?
If you are just trying to check battery performance, to see if they are past it or not, I’d be inclined to just wire them up with a load and see how they go, assuming you aren’t trying to test hundreds.