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post #1 of 7 Old 05-12-2007 Thread Starter
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Electrical Nightmare

So after my post the other day about having a C240 that wouldn't turn over, I did get it to crank around and determined my troubles were electrical.

I pulled my starter battery off the circut, and discovered it only puts out like 11.5 volts - a constant drain. I discovered I have not one but two battery isolator dials which were both in the "Both" position. (They're some old generic one, with three positions - Off, 1, or Both. Off disables each set [ starter or house ] directly and on enables it. Both should cross it over). I also had an Isolator which ran between the positive side of my alternator and my two separated banks. The gentleman at fisheries supply suggested that those isolators drop a significant amount of voltage and I should install a relay switch instead. He drew a little diagram for me as to how to disconnect the isolator and install a relay.

However his diagram didn't include the little negative wire the switch requires. So I disconnected my alternator line and put it directly on my house bank. I disconnected my positives and ran them through the relay. I connected the negative line on the relay directly to the house bank.

1.5 days later I still don't seem to have a charged starter battery. And my house bank doesn't seem to be able to turn my starter over, either.

I'm having some trouble figuring out why this thing is rigged up the way it is, and how it's rigged. Can anyone explain why I would have two isolator switches? To me it doesn't make much sense. And what would be preventing my reefer charge from getting to my starter battery?

So far as I know, it all worked before. But since both of my isolators have always been in the "Both" position (I can't say I knew what they were or what they did) I suspect I could have been starting my batteries from the house bank the whole time.

Is the way I have my isolator rigged proper? I guess the positive on the alternator must also be connected to my reefer charge?

What else do I need to look for?
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post #2 of 7 Old 05-12-2007
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My recommendation is that you consult a knowledgeable marine electrician. I know that sucks, but I think it will save you heartaches in the end.

It's not possible to diagnose your problem(s) from a distance for several reasons, including your misuse of terms. Battery switches are not "isolators", and I think you're referring to battery switches.

Battery isolators are diode-based devices which, indeed, have a voltage drop across them. This may or may not be related to your problem(s), but based on your description it's hard to tell.

Save yourself some time and, ultimately, expense: get a knowledgeable marine electrician to look at your setup.

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post #3 of 7 Old 05-12-2007 Thread Starter
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I certainly could use a diagram of my system so I know what the hell goes where.

So, the switches I'm refering to are big round dials which separate the battery bank(s) - you can turn them on or off, or turn them to both which is supposedly an emergency crossover to let you start your engine by drawing extra power from your house bank.

It looks almost identical to this one.

They call it a battery selector/changeover/isolator switch.
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post #4 of 7 Old 05-12-2007 Thread Starter
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To attempt to make sure I'm charging my starter battery, I disconnected everything from it and tested the lines. I've found one 10 guage wire which I was able to trace back to my battery charger, putting out 14.8 volts or so (positive). One 0 gauge positive outputting no power (goes to starter I assume), one 8 gauge wire I was able to trace back as the one that I removed from the old battery isolator and is now on the relay.

I disconnected everything but the battery charger from the starter battery. (And left the negative line to my starter on). I'll leave it like this for a while and see if the voltage of my starter battery increases (it was 12.5 but some how didn't have enough juice to turn over my motor).

Then I'll reconnect everything except for the line going to my relay switch, and see if I can get enough power from it to start it. If that works, I'll just debug from there and try to diagram how the rest of my electrical system is set up.

In the mean time, I'm looking for an experienced marine electrician in the Seattle Area. But I need to get my boat running again this weekend.
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post #5 of 7 Old 05-12-2007
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They call it a battery selector/changeover/isolator switch.

Well, maybe "they" do, but using that windy term for a switch is confusing. It's a battery switch, period. It switches between bank 1, 2 or bank 1 and 2 in combo (useful when you have a low starter bank).

A battery isolator is, as said, a device that keeps one bank from charging another if they are connected and one bank holds less charge. Its purpose is to keep a bad or low bank from draining a properly charged one, which would give you two half-charged banks and few amps for starting.

A battery combiner is the counterpart: it equalizes charge between banks *during charging* via shore power or alternator, and ensures a equal charge is attained. Once a preset voltage is reached, each bank acts independently.

Both to a degree supplement and circumvent the battery switch and both can be thought of as "patrolled gates" for current either leaving or entering separate battery banks.
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post #6 of 7 Old 05-12-2007
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Let's see if we can simplify this for you.
1. Connect a wire (the #10 red should be good) from your battery charger (+) terminal to the + terminal on your house bank.
2. Connect a wire (#10 black) from your battery charger (-)terminal to the(-) terminal on your house bank.
3. Connect a wire from your battery's (-) terminal to the engine block.
4. Connect a wire from your battery's (+)terminal to your start selenoid.
5. Ensure your alternator is wired to charge a battery or it will fry.
Go to westmarine.com to see how to connect the selector switches. The above should get you going in the mean time.
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post #7 of 7 Old 05-12-2007
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It sounds like someone either installed "more stuff" at some point or removed some batteries, so what you have left is just "more stuff that can get in the way".

If you have one house battery (or house battery bank) and one starter battery, there is no need for two battery switches, and no need for a battery "isolator".

A traditional "isolator" is in fact just a special diode, an electronic device that allows power to flow in only one direction. The problem is, it also cuts about 1/2 volt from that power, so unless other steps are taken, it also ensures you will never have properly charged batteries. By now these are obsolete and just should not be used.

Similarly, calling a battery switch an "isolator" is just wrong. I mean, a fire axe also would isolate batteries, that doesn't mean I would sell it as one.

What you probably should have, for your two batteries, is either one manual battery switch (A-B-Both-Off) or one battery combiner, like the West Marine (aka Yandina) automatic combiner. The combiner is more expensive and in theory less reliable, but it automatically connects your house bank after the engine has been running for 30 seconds, and isolates it after the engine is shut.

Either one will do, and the combiner also has instructions and options for manual switching, for emergency starting from the house bank, and so on.

Blue Seas Systems has a good simple diagram at http://bluesea.com/files/images/products/7650.jpg

Which actually shows more than you need.

If you just erase the black-and-yellow gizmo at the bottom (which is an optional extra) you have a nice picture of how to wire up a basic two battery system. The only thing I would say it omits, is that these days each battery is expected to have a high capacity FUSE mounted directly on the battery positive post. Most older boats don't have one, so don't let that stop you.

That switch in the picture is also "special", but if you image it says "1-2-Both-Off" the setup is the same, you just wire one battery up as #1 positive, the other as #2 positive, and the common post is what goes out to the starter, switch panel, etc.

While you are exploring, check that the terminals are all clean, replace what cables you may need to. It pays to charge each battery while it is disconnected, and then test it, to make sure the batteries are good/bad and that the problem isn't from something else (like a bad alternator diode) draining one battery.

Last edited by hellosailor; 05-12-2007 at 09:08 PM.
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