Quote:
Originally Posted by red-beard
AGM need a smart charger. 20% of the Amp-hr rating in Amps until the battery reaches 14.4V. Then constant 14.4V with diminishing current until current is near 0. Then drop voltage to ~13.8V and hold.
I'll post a diagram tomorrow.
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I have a schumaker 'smart charger' that came with the most basic instructions (how to hook it up, no explanation of any settings). I didn't trust it so used my voltmeter to graph what it actually does. Turns out what it does is mostly as perfect as my understanding allows. I wish they'd described the heuristics and given me graphs but now I'm happy with it. With fully discharged battery I've been able to bootstrap at autodetected 6v, then unplug and it will continue with battery as 12v. Key is it has a 'force charge' button. I think its surprisingly sophisticated and well designed but I couldn't appreciate it until I mapped its behavior with a multimeter. Is a case where product is pretty great but instructions keep everything mysterious.
I'm asking next bit because I want to understand.
How can a charger apply 14.4v to a battery "with diminishing current"? If voltage is constant isn't the amount current up to whatever the battery accepts? Can't control them both.
Translating what you wrote to voltage control:
To charge AGM:
1) maintain voltage to battery so that current is 20% of battery's ah rating - until voltage reaches 14.4v.
2) Maintain 14.4v until current drops to nothing.
3) Maintain at 13.8v (which really means no current until battery's internal false voltage drops to 13.8v)
Yes?