Peter VanDerWal wrote:
> Since it's for standby use, not frequent deep cycles, I'm
> wondering what is the best way to float charge AGMs?
> Do I need a three stage charger or can I just use a constant
> voltage power supply with current limit? If so, what's the
> best voltage for long life, 13.56V? or do AGMs need a higher
> float voltage?
Best bet is to check the datasheet/manufacturer's recommendations for your specific battery. The standard approach is to use a plain constant voltage charger, ideally with a temperature compensated voltage. The current limit is generally not critical; for many gels and AGMs a maximum charge current of 0.3-0.4 of the C/20 rating is recommended. The specific float voltage recommendation will vary from one manufacturer to another.
Longest life will probably result from not leaving the battery on float continuously, but rather charging it fully and then having the charger turn off and restart to top the battery up at regular intervals or after a discharge. Some automatic (not necessarily 3-stage) chargers will do this for you, or you can add this capability to a simple constant voltage charger (e.g. use a timer to limit its runtime to 24-48hrs at a time, and another to restart it once a month or automatically after any outage).
Cheers,
Roger.
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