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nate
Navigator

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240 Posts
Initially Posted - 04/04/2004 :  23:21:38  Show Profile
I was talking with a guy this weekend and he mentioned that using different types of batteries is not a good idea. I have a traditional (flooded) starting battery and a brand new 86amp hour gel that I purchased at WM. The o/b alternator charges the starting battery and I have a solar cell hooked up to the gel. I also have a battery isolator. Am I correct in assuming the battery isolator prevents discharge problems between the two batteries? Can anyone explain why different types of batteries should not be used together? Thanks!!
Nate Adams
C25 #5695 WK/SR/Trad
"Heeling Properties"
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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts
Response Posted - 04/04/2004 :  23:37:06  Show Profile
Whenever two batteries are connected in parallel to the same circuit, current will flow from the battery with the higher voltage to the battery with the lower voltage, until the two batteries equalize. This current flow does no useful work and results in partially discharging a battery that would otherwise be fully charged. If the two batteries are not identical in age, condition, type, and manufacturer, they may not equalize at exactly the same voltage, which will put a strain on the charging system, and could result in one or the other battery being overcharged.
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nate
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240 Posts
Response Posted - 04/04/2004 :  23:42:59  Show Profile
Larry,
I understand your explanation regarding the voltage in the two batteries trying to equalize, but isn't that what the battery isolator prevents?
Edited by - nate on 04/04/2004 23:44:15
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Dkn420
Captain

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USA
298 Posts
Response Posted - 04/05/2004 :  00:23:26  Show Profile
Nate: I'm just studying the use of two batteries...but I think what you need it a "battery combiner". It is described on page 120 of the Don Casey book, "Sailboat Electrics Simplified", and also West Marine has a discussion in that regard on their web site and you can also "Google" or "Yahoo" the term "battery combiner" and get plenty of information about adding a second battery and dealing with charging both and protecting both batteries....Dan #727
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RichardG
Admiral

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USA
990 Posts
Response Posted - 04/05/2004 :  00:36:44  Show Profile
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">two batteries are connected in parallel to the same circuit<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

With an Off/A/Both/B Switch, is switching to "Both" the only way two batteries can be connected in parallel to the same circuit (thus equalizing)?

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">current will flow from the battery with the higher voltage to the battery with the lower voltage, until the two batteries equalize.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

How quickly does the equalization occur? Is it instantaneous or does it take some time (e.g. when switching from "Off" to "B", for a very short moment it is on "Both")?

Also, does a battery isolator make a parallel circuit (thus equalization) impossible?
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.