I'm installing a second battery as a house battery to run the auto pilot etc. I will run both batteries through a
four position switch. I will continue to use the keyed isolating switch.
All switches are on the positive side.
The negative goes straight from the terminal to the engine block.
The batteries are side by side. If I join the neg ot the second battery to the neg terminal of the first battery
and hook both the positives to the battery switch, when I put the switch on BOTH, am I still on 12v or is it
now 24v.

Sam, what you describe would be batteries in parallel so it will always be 12 volt.
Cheers, Bob

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UncleBob said..
Sam, what you describe would be batteries in parallel so it will always be 12 volt.
Cheers, Bob

spot on

OK, thanks guys. I know electricity flows like water but some aspects of this medium confuses me.

Sam, I find it hard to believe there is anyone that knows less about electrics than me, in fact my eyes glaze over with confusion at most of the details.
I think the idea behind the BOTH position is to temporarily provide extra starting oomph if you run down your start battery for some reason, not to be on BOTH as your preferred default normal running setting, but im no expert.
I suggest you keep the batteries separate, ie run the negative of of the new battery to the negative busbar, then the positive of the new second battery to the autopilot (with a fuse, & switch inline, creating a separate circuit. That way you can run your autopilot along with your other things at the same time & not worry about your batteries being in parallel.
The reasoning is when you are in the BOTH position, if one of your batteries decides to kark it, before it does so it will drag your newer better battery into the grave with it. Im more than happy to be corrected.

Like I said I know less than the average person about electrics & will no doubt be asking a few questions when I re-do my electrics next year.

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BlueMoon said..
Sam, I find it hard to believe there is anyone that knows less about electrics than me, in fact my eyes glaze over with confusion at most of the details.
I think the idea behind the BOTH position is to temporarily provide extra starting oomph if you run down your start battery for some reason, not to be on BOTH as your preferred default normal running setting, but im no expert.
I suggest you keep the batteries separate, ie run the negative of of the new battery to the negative busbar, then the positive of the new second battery to the autopilot (with a fuse, & switch inline, creating a separate circuit. That way you can run your autopilot along with your other things at the same time & not worry about your batteries being in parallel.
The reasoning is when you are in the BOTH position, if one of your batteries decides to kark it, before it does so it will drag your newer better battery into the grave with it. Im more than happy to be corrected.

Like I said I know less than the average person about electrics & will no doubt be asking a few questions when I re-do my electrics next year.

Hi both batteries need a charging source, the 1 2 both switch provides that when the engine is running, then switched to the required battery when not running. An alternative is a voltage sensing relay that will combine the batteries when the voltage of the primary battery reaches a set voltage. Battery combiners and eco chargers do much the same thing, the beauty of these is that one cannot forget to switch the batteries to separate them, making the system somewhat mistake proof.
Cheers

Thanks Offy. But doesn't that diagram mean that the house battery is always supplying power to the system
and can't be turned off??. I don't really like that.
Also......if one pos lead from switch to battery is shorter than the other one does that mean the battery it's attached
to gets charged first (when the switch is on BOTH) because electricity always takes the path of least resistance.??.

Theoretically yes but they will balance unless there is a huge distance between batteries and switch.
To completely shut down, put another red key on dist side but if it's going to a switch panel, turning all switches off is the same. I have mine wired to a switch panel so I can leave the fridge switch on...

On the house battery side, I have 2 batteries permanenfly joined in parallel and they balance pretty well.
with 2 batts, I can go out for 3 days without the need to set up portable panels or run the engine. They are charged with a smart charger from shore power so I leave the pen with them fully charged. So in reality, my red key is always generally off and so when engine is running, it only charges the start batt and I cant forget to turn it to off.
The start batt is just like the one in your car, only charges when engine is running but if for some reason its flat just turn the red key on and join the second batt to it And if house batts are flat, run the engine and join them all together. sounds complicated but cheap and simple.
there are many ways to do this, depends on what you have, how your batts are charged if at all when the Engine isn't running, what you want to power and your memory! My main positI've lead is connected to the battery terminal with a big butterfly nut so I can spin it off in no time if theres a massive short circuit and the circuit breakers on the panel haven't done their job ( which has never happened).

Thanks Offy. Yes I understand how your system works. I'm on a swing mooring so I do not
have the advantage of shore power. I do however have a small charging solar panel that
seems to work well. When I bought my new battery (Battery World) I was given another small
charging panel as a 'Christmas Present" so now I can put a trickle into each batt. while
on the mooring........that'll do me.

Perfect.

A "Duo" solar battery charger like this one are fantastic to keep the batteries separate while you trickle charge them on the mooring.
You could then join them with a keyed switch while motoring if you like, ....or it might be possible to put the alternator charge in via the solar controller so you don't have to remember to turn the iso' key off when you turn the motor off?
www.lightinthebox.com/en/p/epsolar-dual-battery-solar-charge-controller-12v-24v-duo-battery-charger-db-10a_p2916541.html?currency=AUD&litb_from=&adword_mt=&adword_ct=84539756114&adword_kw=&adword_pos=1o2&adword_pl=&adword_net=g&adword_tar=&adw_src_id=1810908567_303095234_21769258874_pla-78632005516&gclid=CK2w8sOl18kCFYKWvAodl5EPzA

Sorry link moved to www.arb.com.au

I bought one of these a couple of years ago
www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

That looks great HG.....what does it do.???

It looks like it might be an automatic red key. The problem is that it seems to join them again when charging, always. I find that if my start battery is low, I leave the key off so that the alternator is devoted to only charging the start battery and not forced to charge to whole lot. When I happy the engine battery has enough,I'll join them But at least the engine batt has a bit of a head start As they will begin to balance. Depends on the situation but if one of your house batteries are stuffed then having them joined will only deplete the engine battery also. I like to keep them manually separated if need be.

Right Offy. My 4 position battery switch will allow me to choose which battery I can charge, won't it.??
When I fit it that is.

depends which batt has the positive from alternator.. From your panels, same but you could have two panels ( connect to individual batts) and select 1, 2 or off

For $380.00 you could purchase the lazy sailors battery switch and VSR , just set and forget.

Electrics is easy remember Kirchhoff's current law states "the sum of currents flowing into that node is equal to the sum of currents flowing out of that node"!!

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southace said..
For $380.00 you could purchase the lazy sailors battery switch and VSR , just set and forget.

That looks like it would be a good set up.

OK guys update time. Fitted the second battery yesterday. no problem fitting the 4 way battery switch.
everything works as it should. Each batt. has its own small solar charging panel. Many thanks for the input from you all.