Hello Hugh,
Generally, the manufacturers charge recommendations should be followed. 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.
My thinking about AGM's is that the float voltage and transition current are much more important factors than absorb voltage and current. 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.
Equipment in a 24 volt system should be fine up to 32 to 33 volts. Check the specs.
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@C20) I put each battery, not each string, on a current controlled charger. The current setting is .05*C20. 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.
Larry
Starlight Solar Power Systems
-------- Original Message --------
Subject: [RE-wrenches] AGM set-points for 'opportunity charging'
From: Hugh <h...@scoraigwind.co.uk>
Date: Fri, April 22, 2011 11:49 pm
To: RE-wrenches <re-wrenches@lists.re-wrenches.org>
At 14:19 -0700 21/4/11, Starlight Solar, Larry Crutcher wrote:I disagree about AGM life. I have heard others say this about AGM's but it has not been our experience. I personally have a 900AH bank that is 6 years old and shows little signs of aging. I have equalized the batteries twice to keep the capacity up(each one individually, constant current, unregulated voltage) We only sell and install battery based systems at our retail store and about 50% of sales are AGM batteries. We have found that they have similar life to flooded batteries but with great benefits.I am curious about AGM battery charging set-points. I may be using Rolls AGM batteries for a telemetry application (unattended) with wind and PV inputs. This will be 'opportunity charging'. I wonder what set points I should use for absorption and float? Is it safe to set absorption to 29 volts (temperature compensated)? I may not be able to set it this high since the voltage will exceed 30 in cold weather and this may interfere with equipment. But will the batteries like that voltage? Float would be lower of course. But in my experience the Tristar flits between the two settings in a slightly random fashion.I am also puzzled by the above statement where Larry charges each battery string at constant current, unregulated voltage. I wonder what current is suitable?thanks
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