Isolator switches and split charging

markleuty

markleuty

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Hi

My boat currently has two battery banks which are controlled by a 1/2/both switch, plus 2 isolator switches, one for the positive and one for the negative cables.

I am planning to changing to split charging (using either diodes or the Sterling Alternator battery charger, although that is not a point for discussion in this particular thread /forums/images/graemlins/grin.gif).

My question is do I really need an isolator switch for the negative cable. If not, then I could just rewire it so that I had a switch for House and one for Engine and then lose the 1/2/both switch completely.

Would this work or am I missing something?

Thanks

Mark
 
You miss:
a) the fact you will have to manage two switches
b) the fact that in excluding one bank and inserting thile <he other you might leave a running alternator without batteries to charge and this could damage the alternator (for this reason in the rotary switch positions are: 0, 1, 2, both: in this sequence is very hard to disconnect all banks while charging.
Cheers
 
Yes, it will work fine. You don't need an isolator in the negative lead to the batteries. And it's a great idea to get rid of your 1/2/Both switch - these things have no place on a boat today.

Having 2 simple on/off isolators is by far the easiest solution, and I have this set-up on my boat. I turn them both on when I arrive at the boat, and turn them both off when I leave it.

As an alternative to a diode splitter, you might consider a VSR (voltage sensitive relay). No voltage drop, as well as simplified wiring. Most VSRs now have a "parallel facility" which connects both banks together if needed for engine starting.
 
We have two switches, one for each battery. Normal practice is to have both on when engine running, and only one on when at anchor, alternating which one each day. In the marina, both off. No switch in the negative. Radio bypasses switches to one battery only. (so radio can't be isolated in error).
 
[ QUOTE ]
Presumably I'm missing something here

[/ QUOTE ] Look back at Clyde Wanderers diagram on http://www.ybw.com/forums/showflat.php?Cat=0&Board=pbo&Number=1686517 and the criticisms of it and you see what you missed.

I must admit though that although I might not adopt his circuit I can see nothing seriously wrong with it apart from what IIRC even he agreed was an unnecessary services isolator switch

It actually has the merit that he can select the services battery to supply the domestic services, close the starter battery isolation switch and leave them like that, supplying domestic services from the domestics battery and engine electrics from the stater battery with no further switching necessary. You can't do that with the conventional wiring of a 1,2, both, off switch alone.

(I think that might be the first bit of praise for his circuit that he has received!)

BTW I notice that you are located in Woking. If you do not already know about it you should check out the Guildford Coastal Cruising Club. They meet Tuesday evenings at the Rowing club, just down the road from the theatre. Google will find a website. Until he died earlier this year I crewed regularly for one of the founders.
 
[ QUOTE ]
(I think that might be the first bit of praise for his circuit that he has received!)

[/ QUOTE ]

I do not think anyone criticised the circuit, just that it was over complicated, but it's his boat and his choice.


Brian
 
If you're used to the boat the way it is,and are comfortable with the electrical opreation, consider the charging and output circuits separately: If you add a splitter/intelligent charging system, you can ignore any other switches from a charging point of view. Keeping the "1-2-both" switch will allow you to decide which battery is 'sacrificed' for the domestics, and will also give you the advantage of easy paralleling for engine start if needed. The negative isolator is good, and normally the only way to really isolate the system. I'm not sure where the positive isolator fits, as it must effectively be in series with the 1-2-both switch.
 
Sorry Mark, I wasent trying to be funny, and as VicS says have a look at the diagram.
BTW I always tell any guests on my boat that I am open to constructive criticism especially if they are of the knowledgeable type, as I am fairly new to sailing, (this is my second season) and always looking for ways of improving things.
One of the reasons for settling on the final diagram was to keep cable runs as short as possible, and to be able to use either bank seperatly for starting engine, while been able to isolate the start batt in the event of having to use the service bank to start engine, without the chance of start batt pulling down the service bank.
Also I can isolate the service bank and use start batt to run services, (only advisable after engine has been started).
With what I have read about all the charge regulaters, ie, sterling, driftgate etc, is that you still have to fit a split charge unit as well, so I reckon if I dont get too much volt drop using the X-Split then I shouldent have to fit any other gadgets.
But I have been given a Nasa Clipper BM1 moniter for a Christmas pressie, and am wondering if I fit it according to the instructions, will the fact that the Neg cables from both banks been connected together effect the moniter readings, as the shunt is on the neg side of services batt in the instructions. Any thoughts?
Mark have a look at the Driftgate X-Split unit for a really low volt loss splitter system at £90 odd, this is the one I bought so cant say yet what its performance is like, as it was only fitted last week.
They have a choice to buy one that was not properly finnished while been potted, (the black compound which seals it all up) and had to be finnished by hand and have some small joint lines in the sealing, they still come with the three year warranty, and cost 15% less. Cheers, C_W.
Thanks VicS for the wee vote of confidence /forums/images/graemlins/smile.gif
 
[ QUOTE ]
One of the reasons for settling on the final diagram was to keep cable runs as short as possible, and to be able to use either bank seperatly for starting engine, while been able to isolate the start batt in the event of having to use the service bank to start engine, without the chance of start batt pulling down the service bank.

[/ QUOTE ]The point halcyon and I were making was that you could achieve this much more simply. You'd have saved a lot of money on components and cable; you'd have an easier and more robust system. But, as halcyon said, it's your boat and your choice. The really strange thing is that you should go out and buy all the bits before asking the forum for advice on your circuit. /forums/images/graemlins/confused.gif
 
Thank you all for your advice!

My big question about whether an isolator switch was necessary on the negative cables has been answered along with many others.

Also, thanks VicS for pointing out about the Guildford Cruising Club. I'd vaguely heard of it before and will look it up.

Cheers

Mark
 
[ QUOTE ]
The really strange thing is that you should go out and buy all the bits before asking the forum for advice on your circuit

[/ QUOTE ] That's a bit harsh, unless you have a much better memory than I have.
CW did ask for advice back in August before adding the second battery. On the recent occasion, which I gave the link for, he volunteered his circuit diagram for consideration by someone else asking for advice.
 
[ QUOTE ]
That's a bit harsh, unless you have a much better memory than I have. CW did ask for advice back in August before adding the second battery. On the recent occasion, which I gave the link for, he volunteered his circuit diagram for consideration by someone else asking for advice.

[/ QUOTE ]My memory's lousy, Vic! But I did look back at the post you linked to, and he actually wrote "Here is the diagram I have settled on. Anyone see any problems with it?" - isn't that asking for advice?
 
[ QUOTE ]

But I have been given a Nasa Clipper BM1 moniter for a Christmas pressie, and am wondering if I fit it according to the instructions, will the fact that the Neg cables from both banks been connected together effect the moniter readings, as the shunt is on the neg side of services batt in the instructions. Any thoughts?


[/ QUOTE ]

This is exactly what I was wondering.... If anybody has any ideas on this it would be great to hear them..

Mark
 
It makes no matter to the output to the instrument, as the positive is probably selected from a 1/2/off/both switch. Make sure your engine start negative does NOT go through the shunt.

I've got a similar installation, but with a different instrument make.

Have a read of my reply to a similar question here - last item.
 
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