Battery - Domestic vs starter

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viva

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The boat is new to me and I was just doing a test to check that my rotary battery switch is "make before break" I had the cabin lights on and the battery switch on "2" . Fine. I switched to "BOTH" and the cabin lights stayed on. Fine. I swiched to "1" and the cabin lights were still on! Surely this isn't right ? Before I start doing a wiring diagram for the boat and tracing the wires can anyone explain why this should be other than the boat/batteries being incorrectly wired?
 
That is exactly what my switch does. I posted on another thread about my plotter turning off when using the windlass and it was explained but I did not really understand how my boat must be wired.
 
viva said:
The boat is new to me and I was just doing a test to check that my rotary battery switch is "make before break" I had the cabin lights on and the battery switch on "2" . Fine. I switched to "BOTH" and the cabin lights stayed on. Fine. I swiched to "1" and the cabin lights were still on! Surely this isn't right ? Before I start doing a wiring diagram for the boat and tracing the wires can anyone explain why this should be other than the boat/batteries being incorrectly wired?
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That's the way almost all 1-2-Both switches are wired.

Your boat has a single electrical system. Everything - lights, instruments, radio, engine (including starter) and anything else you have fitted - runs from the same supply.

All the battery selector switch does is change whether that single supply comes from one battery, the other battery, or both batteries.

In other words, you don't have a dedicated starter battery. You have a battery which (in normal use) is only connected up when the engine is running. When the engine goes off that battery is disconnected, so that if you run the other one flat you still have electrical power in reserve for starting the engine again.

So ... when your battery switch was at "2", battery number 2 was keeping your lights one. When you changed to "Both", the other battery joined in, and when you switched to "1", battery number 1 ran the lights on its own.
 
For me, the 1-2-both switch is a safety measure, to ensure I can't accidentally run the starter battery down.

I've wired Jissel so the engine systems powered by the starter battery while everything else is wired directly (via an isolator) to the domestic battery. The 0-1-2-both switch is wired 0 - engine bat. - domestic bat - both, purely to give additional options for starting. Charging from the alternator is wired directly to the starter battery, with a relay to charge the domestic battery.

The only way I can run the domestics from the starting battery is by switching to both, which is what I want, as I'm unlikely to do it accidentally.
 
JumbleDuck said:
..... You have a battery which (in normal use) is only connected up when the engine is running. When the engine goes off that battery is disconnected, so that if you run the other one flat you still have electrical power in reserve for starting the engine again. .....
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JD, I understand all your post (actually, it is one of the clearest explanations I have read) apart from the bit above. Are you saying that when the engine goes off the battery is disconnected automatically ? Sorry for being a bit thick ;)
 
Storyline said:
JD, I understand all your post (actually, it is one of the clearest explanations I have read) apart from the bit above. Are you saying that when the engine goes off the battery is disconnected automatically ? Sorry for being a bit thick ;)
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the engine will charge both batteries via a splitter diode

if you have the battery switch in either 1 or 2 position you are drawing power from either battery 1 or 2

when you stop the engine it will stop charging battery 1 and 2

if your switch is set to battery 1 then you will draw power from battery 1 until its flat, but battery 2 will be charged and "in reserve" so to speak so you can restart your engine - and charge battery 1 up again.

try not to have the switch set to both and run them flat.

as I suggested in my previous post on another thread a good upgrade would be to fit separate banks for domestic and starting. You could then do away with the 1 2 Both Off isolator as the starter battery would always be isolated from the domestic circuit.
 
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Storyline said:
JD, I understand all your post (actually, it is one of the clearest explanations I have read) apart from the bit above. Are you saying that when the engine goes off the battery is disconnected automatically ? Sorry for being a bit thick ;)
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Sloppy writing on my part. I would have been better to write "... when the engine goes off that battery can be disconnected with the switch ..." In other words, it's something you do rather than something which just happens.
 
JumbleDuck said:
Maybe. Traditional installations don't bother with that, and use the connection/disconnection of batteries with the 1-2-Both switch to control charging as well.
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agreed, which makes it all the more important that the user understands what is happening, it may well be that manual input is required to enable both batteries to charge - but without inspecting the boat we wont know for sure.
 
Many thanks for the input. But a subsidiary question please - when I checked the voltage of the batteries with the solar panel connected only one of the batteries appears to be charging one is at 14.6v and the other at 12.75v. When I switched the battery switch to "BOTH" the charge was equalised and both batteries read about 14v. When I have had the shore power connected both batteries appeared to be charging??
 
viva said:
Many thanks for the input. But a subsidiary question please - when I checked the voltage of the batteries with the solar panel connected only one of the batteries appears to be charging one is at 14.6v and the other at 12.75v. When I switched the battery switch to "BOTH" the charge was equalised and both batteries read about 14v. When I have had the shore power connected both batteries appeared to be charging??
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All perfectly normal. The solar panel is pushing 14.6V into the battery to which it is connected while the other floats happily at 12.75V. When you put the switch to "Both" you connect them together, so the solar panel is trying to charge them both. It does, but loses a bit of voltage as the current taken from it increases. Your battery charger has two outlets, one for each battery.
 
Marsupial said:
agreed, which makes it all the more important that the user understands what is happening, it may well be that manual input is required to enable both batteries to charge - but without inspecting the boat we wont know for sure.
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There is no way of stopping both batteries charging with the switch at "Both", however it has been set up. Well, unless someone has installed a "Fry My Alternator" switch to disconnect the alternator altogether, but that seems unlikely.
 
One of the advantages of everything - starter, alternator, domestics - being connected to the output of a Off-1-Both-2 switch is that even if you do turn it to Off while the engine is running, as long as the domestics are taking some current, all will be well. Not that I am recommending doing so, you understand.
 
JumbleDuck said:
There is no way of stopping both batteries charging with the switch at "Both", however it has been set up. Well, unless someone has installed a "Fry My Alternator" switch to disconnect the alternator altogether, but that seems unlikely.
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yes but IF there is a splitter diode then both batteries would be charged even if the switch was set to 1 or 2 or both so the user does not have to worry about the switch position to enable engine charging of both batteries. The 1 2 off both switch is there to manage output and "save" a battery not charging input, the splitter ensure each battery is isolated from the other for charging so the position of the switch is of no consequence.

If there is no splitter diode then the user has to remember to combine the batteries to make sure both are charged.

It appears that there is no splitter diode on the OP system so its all manual
 
Marsupial said:
If there is no splitter diode then the user has to remember to combine the batteries to make sure both are charged.

It appears that there is no splitter diode on the OP system so its all manual
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Indeed. But the neat thing about the classic 1-2-both arrangement is that you charge whatever battery you used to start the engine unless you do something deliberately daft.

At some point (it's been "next year" for four years) I plan to combine my two current batteries, add a stater battery and wire 'em all together with a BEP VSR cluster. I may even add the Adverc which has been sitting in my workshop for ages, though I'm not sure there is much point as I have a 14.4V alternator anyway. For the moment, though, the 1-2-Both is simple and reliable.
 
This is a bit o/t but is there any advantage to having the battery selector switch set to Both while motoring, provided you are aware that the starting current from the engine battery needs to be replaced. Our system is, start on bat1, motor for 10 minutes then switch to 2.

Edit: the only downside to this is that if we are lucky enough to be able to sail straight away then bat2 does not get a chance to be charged. I cannot see a way around this because we cannot go to both too soon or bat2 would pinch power from bat1 if 2 was a bit run down. Sounds a bit convoluted but i hope you see what I mean.
 
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Storyline said:
This is a bit o/t but is there any advantage to having the battery selector switch set to Both while motoring, provided you are aware that the starting current from the engine battery needs to be replaced. Our system is, start on bat1, motor for 10 minutes then switch to 2.
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I always start and run on both, then switch to a single battery for domestic use. As I have two identical 65Ah batteries (no room for bigger) I tend to alternate between them on trips, so if I have been using 1 for domestic one weekend I'll use 2 for domestic the next. Seventeen separate people will now tell me why I shouldn't do that.
 
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