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Old 27-09-2008, 15:06   #1
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Switching batteries while engine running

The question is will it damage my alternator?? My battery switch is the typical OFF, 1, BOTH, 2 in which going from 1 to BOTH there is no disconnect from Bat 1. Then I move it to BAt 2 to charge that battery bank. The alternator will always see a battery...but there maybe a momentary change in voltage. I called Balmar and they did not ans the question....referred me to their dual bat isolator. I still want to know if there will be damage to the alternator. Thanks for your help
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Old 27-09-2008, 15:08   #2
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Battery switches are make before break switches. As long as you don't turn it off all the way you should be OK going from 1 to all to 2.
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Old 27-09-2008, 16:34   #3
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Since you are always seeing voltage on your meter when switching banks, sounds like you have a 'make before break' switch. In other words, the current battery bank is not switched off before the new battery bank is on line. If you have that type, switch you can switch at will, just don't turn it off with the engine above idle.

One way to be sure that you don't damage the alternator is only switch between batteries with the engine at IDLE. If you switch at higher rpm, the alternator can produce enough juice to fry itself.

The change in voltage probably results because of different loads from the batteries because of different size, charge and/or condition of the different banks.

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Old 27-09-2008, 17:03   #4
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The reason Blamer probably did not answer your question is that even if the switch is make before break it may not do that. Your best solution with your current set up is to leave the switch on both and don't change it while the engine is running unless you "have" to change it. Do you feel lucky today? Do ya?
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Old 28-09-2008, 19:36   #5
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We anchor on 2, start on 1 and switch to all after start.

No problems.
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Old 28-09-2008, 20:00   #6
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Put a Zap-Stop diode on the alternator and quit fretting about the small stuff.
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Old 28-09-2008, 21:11   #7
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Originally Posted by Ex-Calif View Post
We anchor on 2, start on 1 and switch to all after start.

No problems.
I'm really tempted to do just this but read (can't remember where) that it is not good to parrallel dissimilar batteries....i.e. a starter battery and a deep cycle bat.
You have been doing this with no problems?
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Old 28-09-2008, 21:47   #8
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All are (3) batteries are the same. Delco Voyager Marine M24s. They are not strictly a "starting" battery or a deep cycle. I reckon the specs are about

RC = 90
CCA = 400
CA = 620
AH = 70

It's hard to get any straight answer on CCA to AH conversion (they are different measurements) so the 70 ah is an educated guess.

If I were mixing batteries and/or had multiple charging systems I would probably have a battery combiner/charger.

What you really don't want to do is accidentally switch to off - don't ask me how my partner knows...

What I don't understand is why there isn't a guard on this switch so it takes 2 hands to go to off.
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