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Old 17-06-2015, 21:10   #1
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House / Start Battery Separation Techniques - Best Practice?

I came across this the other day and was somewhat intrigued by the method to separate house and start batteries. I hadn't seen this method used before (but that isn't unusual in itself ). I understand this may have appeared in a VDO publication but I am not sure of that claim.

Is this something that is routinely used elsewhere and what do the collective CF electrical whizzes think of it?

Please excuse the second rate drawing, I did it in a hurry so please overlook the shortcomings of the drawing and look only at the underlying principle. For instance the battery selector switch is really a "1, 2, both, off make before break" switch rather than what is actually drawn.

Comments anyone...
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Old 17-06-2015, 21:21   #2
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Re: House / Start Battery Separation Techniques - Best Practice?

The house bank is always on and cannot be switched off. So that seems like a negative.

What is the supposed advantage of this configuration?
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Old 17-06-2015, 21:40   #3
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Re: House / Start Battery Separation Techniques - Best Practice?

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Originally Posted by transmitterdan View Post
The house bank is always on and cannot be switched off. So that seems like a negative.

What is the supposed advantage of this configuration?
Yes but I think the drawing may not be complete in the detail of each circuit, more a description how to keep separate House and Start.

I'm not sure of the advantages (or disadvantages) but presumably someone thinks it is better

I'm hoping for more clarity after the collective CF input

For instance, I would think the lack of Volt and Amp meter on the Start bank is a negative and I yet to see any advantage of the setup.
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Old 17-06-2015, 22:13   #4
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Re: House / Start Battery Separation Techniques - Best Practice?

I think I read somewhere that the advantage of a negative shutoff switch is that it is then nearly impossible to have a sneak leak that causes galvanic corrosion. But I can't remember whence this idea got into my subconscious grey matter. Also, with the switch in the off position then shorting the battery positive to ground will not cause a fire which could be considered an advantage.
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Old 17-06-2015, 23:01   #5
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Re: House / Start Battery Separation Techniques - Best Practice?

Seems to me that if the main negative bus was wired to the selector switch/alt/starter ground you'd have something useful. With it wired as drawn, looks like all that's needed at the selector switch position is an on/off switch...
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Old 17-06-2015, 23:36   #6
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Re: House / Start Battery Separation Techniques - Best Practice?

you always switch the pos, not the neg.
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Old 18-06-2015, 00:42   #7
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Re: House / Start Battery Separation Techniques - Best Practice?

I have separated my starting and house systems because I have a steel boat and have experienced electrolysis problems with the underwater hull. I am not sure whether or not the corrosion was related to either of the electrical systems but it appeared to be a wise precaution to try to isolate both of them from the hull.

This turned out to be a little more involved than I thought. The house system was fairly simple as all that was required was to isolate it from the cranking system. The cranking system isolation required a flexible coupling on the propshaft, and mounting the Morse controls on an alloy plate insulated from the steel hull in the cockpit.

I do not have any permanent arrangement to connect the house batteries into the engine charging system using a couple of jumper cables instead on the rare occasions I need to use the engine alternator to charge house batteries. I use a stainless steel push bike spoke as a variable resister to keep from overloading the alternator.

I also have two starter motors fitted to the engine and two alternators and two cranking batteries. Call me paranoid if you will but when you really need the engine to crank to get you out of a bind you don't need to find out that it won't because you forgot to switch the isolation switch and the fridge, TV and all the other loads have pulled all the batteries down.

From a corrosion viewpoint it appears that we might be better off to have positive rather than negative earth systems on boats.
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Old 18-06-2015, 10:11   #8
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Re: House / Start Battery Separation Techniques - Best Practice?

Quote:
Originally Posted by transmitterdan View Post
The house bank is always on and cannot be switched off. So that seems like a negative.

What is the supposed advantage of this configuration?
The house Main Dist Panel is always supplied with + POS,but the Neg side of various house loads would be connected to Main NEG Buss,which is supplied with swxd Neg.?
So house bank is NOT always on? or am I missing something?
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Old 18-06-2015, 10:16   #9
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Re: House / Start Battery Separation Techniques - Best Practice?

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Originally Posted by jimbunyard View Post
Seems to me that if the main negative bus was wired to the selector switch/alt/starter ground you'd have something useful. With it wired as drawn, looks like all that's needed at the selector switch position is an on/off switch...
Not sure about that. See my answer to Transmitterdam. I could be missing something. / Len
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Old 18-06-2015, 10:17   #10
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Re: House / Start Battery Separation Techniques - Best Practice?

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you always switch the pos, not the neg.
Is that a Rule or just the way it's usually done? / Len
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Old 18-06-2015, 11:03   #11
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Re: House / Start Battery Separation Techniques - Best Practice?

I have separate batteries, in fact I call them house and reserve, because only the house is used. The alternator wire is hooked directly to the house, the engine is started from the house thru the switch, and the other battery is just there for contingency. There is an ACR between them.

Very well document here by Maine Sail:

1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com
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Old 18-06-2015, 11:13   #12
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Re: House / Start Battery Separation Techniques - Best Practice?

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Originally Posted by SVTatia View Post
I have separate batteries, in fact I call them house and reserve, because only the house is used. The alternator wire is hooked directly to the house, the engine is started from the house thru the switch, and the other battery is just there for contingency. There is an ACR between them.

Very well document here by Maine Sail:

1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com
Everyone attempting to wire a boat's batteries should read & understand this link./ Len
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Old 18-06-2015, 12:59   #13
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Re: House / Start Battery Separation Techniques - Best Practice?

My personal view is that 'best pratice' should not include the use of selector switches at all. House and start systems should be kept entirly seperate and each should have its own isolation switch (or or breaker) outside the engine room or other high fire risk area. Even better is to have a separate battery and circuit feeding the essential nav systems to prevent 'dirty' supply from pumps and machinery causing interference. This is particularly important wher a high power inverter is fitted. Charging is then through an external regulator and diode or loss-less splitter. This applies to anything for bluewater or any boat bigger than 26ft.
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Old 18-06-2015, 20:45   #14
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Re: House / Start Battery Separation Techniques - Best Practice?

I'd get rid of the amp meeter, 1-2-off switch. Add your engine ground to bussbar and off the hull. It's not a car. Plus many more changes.

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Old 18-06-2015, 20:48   #15
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Re: House / Start Battery Separation Techniques - Best Practice?

12 volt boat electrical book. Several great ones out there. Great place to start

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