[RE-wrenches] AGM battery charging, more details

[Hugh]

Thanks, Larry for the detailed response
>
>
>Generally, the manufacturers charge recommendations should be followed.

Yes but the issue I have is to know when and how to switch from 
absorption to float.  The Tristar has its own decision process but is 
it correct?  And if not then are the settings suitable.

>  If you take away the red paint, I believe the Rolls AGM is the 
>Fullriver DC series battery. We started selling Fullriver last year 
>and I was surprised to find the very high absorb voltage 
>recommendation. For the DC400-6 (415AH) in cycle use they recommend 
>charging at 29 to 29.8 volts and float at 27.6 @25C! That is the 
>highest AGM voltage settings I have seen from any manufacturer.

That's my worry.

>
>My thinking about AGM's is that the float voltage and transition 
>current are much more important factors than absorb voltage and 
>current.

Transition current is not in the vocabulary of the Tristar 
controller.  I am not aware of a product that has this feature aside 
from maybe some inverters.   I have read in an Outback manual that 
you should program the absorb time based on charge current 
measurements, but the logic of this depends on the battery being 
'flat' to the same degree at the start of each charge - whereas wind 
and solar charging is not like that.

>For most AGM's, initial charge current is almost unlimited. However, 
>Fullriver recommends current limiting and constant voltage for the 
>bulk/absorb cycle. Their current limit is .15 to .35*C20 rate. BTW, 
>make sure to adjust the temp. comp to 3mV/C/C for float. That is 
>lower than most.

Tristar default is 5 mV/C/C but can be modified by RS232 lead and 
software intervention.

>
>Equipment in a 24 volt system should be fine up to 32 to 33 volts. 
>Check the specs.

It's not me that has the problem it's the telemetry engineers.  I 
assume they read the manual.  But reduced temp comp helps.

>
>What I said about equalizing was that I had done it twice to my 
>personal AGM battery bank. After the battery is fully charged (<0.2A 
>per 100ah at C20) I put each battery, not each string, on a current 
>controlled charger. The current setting is .05*C20.

That is 5 amps for a 100Ah battery?  Does this not make them gas?

>I don't use voltage regulation when I do this. Once the battery 
>reaches 2.58 V/Cell, I charge for about 4 more hours always 
>monitoring battery temperature. I use this process to recover AGM 
>battery capacity and it has been mostly successful with all 
>brands. No more puzzle.

Thanks - AGMs are a puzzle to me but you make it sound pretty simple. 
I do still have an issue with controlling the charge rate using 
existing technology on an opportunity charging system where the 
battery may be in any state of charge when the wind starts blowing, 
or sun starts to shine.

best wishes,
-- 
Hugh Piggott

Scoraig
http://www.scoraigwind.co.uk