Todd:
Here’s the long story. First the bulk charge brings the bank to an 80% charging
level. The charger will maintain current level until the bulk set point has
been reached. Then, the charger will switch to the absorption timer.
The absorb mode takes care of the remaining 20% of the capacity, and is a
function of time and current. This needs to be programmed, or at least checked,
by the installer. To me this is the most important charge rate because as you
see if this is not correct the batteries really don’t have any chance of a long
life.
Most folks think that the absorption mode is some function of sensing by the
Charge Controller or Inverter/Charger. it is not. The absorb mode is governed
only by what ever the installer or the factory programs. Like I said earlier
the typical default setting is always way too short.
So what usually happens is the charger goes through the bulk charge, then
switches to absorb, holds it there for a too brief period, then goes to float.
The batteries never get full charged so they begin to hard sulfate and the
usual scenario goes like this; after a few years the customer calls and says
the batteries are bad because they’re loosing capacity
In the absorb mode the current levels start decreasing as the internal
resistance in the battery increases. I assume over the time of the absorption
charge that 50% of the maximum charge current will be available (this is
factored into the equation).
t = 0.42* C/1
Where:
t = Absorption Charge Time
C = 20hr Rated Capacity
I = Charging Current
0.42 = (20%/50%) + 5%.
5% is added due to losses
Some Inverter/Chargers will only let you set an absorb time by telling it the
AH capacity of the battery bank. If this is too short just tell the inverter
that bank is larger and the time will go up.
Also some of the cheaper Inv/Chargers don’t let you select absorb volts either
except by type, I always select Wet Cell even if I have AGMs which ups the
voltage a small amount.
Gel cell batteries are another matter all together and can be over charged and
cooked easily.
Tom Duffy
Systems Design Engineer
t...@thesolar.biz
575-539-2111 X 301
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From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of
toddc...@finestplanet.com
Sent: Wednesday, June 30, 2010 10:29 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Interstate UL-16 HC problem
"proper absorb times (do the math)"
Can you talk more about this please.
Todd
Sent from Finest Planet WebMail.
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