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Old 16-11-2009, 09:46   #1
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Why Do I Have an Isolator with Only One Battery Bank?

Hi all,
I have been having some issues with my motor not charging the batteries. I don't have a separate starter and house bank, the engine starts from the house batteries. The back up is the generator which has a separate start battery and can charge the house bank. Anyway, I didn't design it, but its what is there.

I have a thing labelled "Battery Isolator" from Sure Power Industries. It has an alternator terminal, a positive terminal and a negative terminal. The 'isolator' initially failed because the terminals were so corroded it was not passing charge to the batteries. I cleaned this all up and we were getting good charging current to the battery - 30 amps. Then we weren't again. On inspection the positive wire from this isolator had cooked and the first inch or so of it was burnt. The wire is fairly thin, maybe about 1mm in diameter of twisted copper. This device itself looks pretty old and nasty.
I removed the isolator from the circuit, attaching the alternator cable direct to the battery cable. I get a charging current.

My issue is that at full speed the alternator produces a fairly high current, did this isolator do something to protect the batteries in some way? I am a bit worried that without this 'isolator' that I may be overcharging, or was its job to prevent current leakage back through the alternator?

Any insight would be appreciated.

cheers
JMB
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Old 16-11-2009, 10:02   #2
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An isolator is basically a set of one-way valves that allow alternator current to flow to the batteries, but not from battery to battery when the alternator is not producing.
It does a bit of a protection job by lowering the voltage as it flows thru the Diodes (valves)
Your alternator regulator is there to protect the batteries from overcharging.
Google "battery isolator wiring diagram" and you should find loads of info. Good luck
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Old 16-11-2009, 10:04   #3
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the current won't harm the batteries unless the voltage is to high. Without more than one positive terminal I can only assume the isolator is more of a blocking diode, like you would use with a solar panel.
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Old 16-11-2009, 10:27   #4
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Hello JMB,
A battery isolator would have three POSITIVE terminals ...... one POSITIVE terminal would connect to your alternator, a second POSITIVE terminal would connect to one battery bank (house bank) and the third POSITIVE terminal would connect to a second battery bank (a cranking or perhaps, in your case, the generator battery). There is NO negative terminal on the battery isolator! To connect one of the terminals to ground would result in a dead short with some pretty nasty results. If the isolator has been connected with one terminal to ground I would use a multitester to check and see if one or both of the diodes have been burned out (islolators are rated according to the size of diodes used inside ..... 30amp, 50amp, 100 amp, etc.).
Good Luck, Bill A.
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Old 16-11-2009, 10:51   #5
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Hello JMB,
A battery isolator would have three POSITIVE terminals ...... one POSITIVE terminal would connect to your alternator, a second POSITIVE terminal would connect to one battery bank (house bank) and the third POSITIVE terminal would connect to a second battery bank (a cranking or perhaps, in your case, the generator battery).
Bill,
agreed, that this is normally what is called an isolator, however this thing is labelled as I said, and has a (very faded) wiring diagram as I describe, hence the question. I don't know what its doing there either, nor can I find any similar products.
cheers
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Old 16-11-2009, 11:14   #6
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the current won't harm the batteries unless the voltage is to high. Without more than one positive terminal I can only assume the isolator is more of a blocking diode, like you would use with a solar panel.
I'm getting 13.9 - 14v at 1500 revs which I guess is about right. So still wondering what the thing was doing, if anything.
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Old 16-11-2009, 11:31   #7
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Call or E-mail Surepower and ask them what this thinghy is....

Sure Power Industries
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Old 16-11-2009, 12:53   #8
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Remove it.
The reason for a isolator is to charge 2 battery banks while not combining them. It uses diodes. There is no reason for it on a one battery system. Just adds resistance to the circuit, and the diodes take some juice I believe, so you lose some of that product your alt is producing.
On my boat, there was only one circuit as well. Not a good system imo. So I have rewired it for a start as well as a hous bank, totally isolated from each other. But of course I have to charge both, even though the start battery uses very little current to start the perkins. I started another thread on this topic yesterday.
I believe I will be going with a balmar duocharge to do that. It is a better concept than a diode system.
Either way, for your problem, are you sure your running the engine enough to charge the bank fully? How old are your batteries, what is the cable size, is there corrosion on the terminals, are they topped off with water... lots of reasons your batts are not charging properly. But first get rid of any power robbing links that get in the way. Then go step by step .
Hope that helps
bob
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Old 16-11-2009, 12:55   #9
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Call or E-mail Surepower and ask them what this thinghy is....
Haha, they don't know either. I've sent them a photo as they don't believe what I was telling them.

http://lh6.ggpht.com/__vBgUvd0cIk/Sw...tery_gizmo.jpg

http://lh3.ggpht.com/__vBgUvd0cIk/Sw...izmo_label.jpg

Check it out...
JMB
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Old 16-11-2009, 13:02   #10
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You are correct. A battery isolator is nothing more than a high current diode with a heat sink. There is a few tenths of a volt drop across an isolator. For some its a big concern, for others its no concern.

You could probably use a dedicated house battery isolated from your start battery but that's a whole different topic.
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Old 16-11-2009, 14:55   #11
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OK, solved!

It has been identified as a battery isolator which was a) unnecessary and b) wired up incorrectly. Just one of those things that you discover and say "What were they thinking of when they did that?!"
Thanks for all the feedback and help.
cheers
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Old 16-11-2009, 16:20   #12
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The isolater has a 0.6v voltage drop across it. If your alternator has an internal regulator, the isolater would drop the voltage at the battery to 13.4 volts, keeping the batteries from getting a proper charge, and removing would improve your charging system.

If you have an external regulator, the voltage sensing wire usually comes from the battery side of the isolator, and the alternator output voltage will be boosted up to 14.6 volts to maintain 14 volts at the battery. Removal of the isolator should not cause a problem with this system.
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