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AGM VRLA Batteries and Constant-Voltage charging.

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paulca:
So I got a new battery for my motorbike.

It's an 8.6Ah AGM VRLA battery.  The manual that came with it was rubbish.  It just said to charge at 10% capacity for 8-10hours before use.

Reading on the Yusa website (my battery is actually a Lucas though), they say you should not use a constant current charger with this battery type.

The charge type matters less to me as the battery has gone straight to constant voltage (absorbsion) anyway.  I'm just curious as to how exactly a charger is meant to charge them from flat if they can take a huge amount of current at, say 10.5V and retain a constant voltage.

Anyway, I put it on my car battery charger for an hour and it went from 2 Amps to 1 Amp in under a minute.  I moved it to my bench supply to check on it and so far the current at 14.40V has gone UP from 275mA to 285mA and is still slowly rising.

Should I worry, just leave it for another few hours or back it off to float at 13.8V for a while before fitting to the bike on Saturday?

Benta:
For AGM batteries, you need constant voltage charge with current limiting. For an 8.6 Ah battery, I'd set the current limit at 1/10 capacity (~1 A). The battery will probably accept more, but unless you're in a hurry there's no need to.

paulca:
I'm not sure how you can have constant current AND constant voltage, but anyway.

On 14.40V the current fell back to 265mA and didn't move for an hour, so I took that (and a quick read on battery university) to mean it was fully charged.  I dropped it back to a float voltage of 13.5V (based on BU) and it seemed to stablise at 50mA after about 15 minutes.

I have taken it off the charger and will now let it rest.

I'll check it's fully charged; by checking it's voltage after 24 hours is still above 13V, ideally 13.1V and 13V after 48hours.

Of course this poor thing is about to be stuck in a bike outside, sit idle for weeks at a time, often in sub zero temps and then have 14.40V applied to it while getting cooked by the engine next door for an hour, for the rest of it's life!  I might as well baby it now.

Benta:

--- Quote from: paulca on August 14, 2018, 05:50:07 pm ---I'm not sure how you can have constant current AND constant voltage, but anyway.

--- End quote ---

I never said "constant current", I said "current limiting". The point is, that if you just apply constant voltage, you'll have a heck of a lot of current going into the battery if it is discharged. Limiting current until it's properly formated is just a precaution.

paulca:

--- Quote from: Benta on August 14, 2018, 06:29:03 pm ---
--- Quote from: paulca on August 14, 2018, 05:50:07 pm ---I'm not sure how you can have constant current AND constant voltage, but anyway.

--- End quote ---

I never said "constant current", I said "current limiting". The point is, that if you just apply constant voltage, you'll have a heck of a lot of current going into the battery if it is discharged. Limiting current until it's properly formated is just a precaution.

--- End quote ---

But how do you limit current without changing the voltage?

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