[RE-wrenches] Interstate UL-16 HC problem

[The Office of Tom Duffy]

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



     tom at thesolar.biz

       575-539-2111 X 301

Although no trees were killed in the sending of this message, a large number of electrons were terribly inconvenienced.

 

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From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of toddcory at 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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