Battery question

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Swanrad2

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Morning,

We are intending to spend a lot more time on board next summer and so have bought a leisure battery to add to the two Bosch battery battery (diesel engine start, charged from alternator and small solar panel trickle charger) which has always been sufficient for our limited draw. I am electrically, erm, inexperienced. I have the usual 1-2-both switch.

Is there any downside to moving the two Bosch to, say, position 1 on the main switch and the leisure battery to the other position. This, with my limited understanding, would mean I am starting the engine with 24V and running instruments off the leisure at 12V and running the system on 'both' all of the time? Is it better to remove one of the Bosch's, if for example there is a downside with starting the engine with 24V?

Boat electrics are on my list of things to learn, but this winter I am mostly doing Diesel engines - that's enough for one year.
 
You can't mix 12V and 24V systems on a 0-1-2-B switch. It will go...

bang.gif
 
Last edited:
It would be very unusual for an engine starter to require two batteries in parallel, which I assume is what you have, unless of course the Bosch ones are only 6 volt. The simplest arrangement is to have a smallish (dependent upon your engine size) automotive battery to start and one, two or more leisure or deep cycle type batteries for the domestic. I have my starter on position 1 and domestics on position 2.

In your case there are arguments that combining one Bosch and your new leisure together as the domestic bank may lead to premature failure of the new one. I have combined an old and new leisure type in one bank without problems but yours is a slightly different ccase.
 
You do not start the engine with 24 volts. You need to learn at least some some basic electrics - the difference between batteries in series and parallel. When you use two batteries for one bank you normally connect them in parallel to give still 12 volts, but more capacity. You do not put 24v on one side of the switch and 12v on the other.

Unless one of the batteries is failing, probably better to use all three rather than throw one out.

How you use your existing batteries will depend on what type the Bosch ones are: leisure or starting. Leisure batteries are meant to be good for domestic use - lighting, fridge etc, but not really intended to start engines. Start batteries the reverse. I'm sure someone else will have a diagram they can post to show how to connect 3 batteries and a 0-1-2 switch.
 
jwilson said:
I'm sure someone else will have a diagram they can post to show how to connect 3 batteries and a 0-1-2 switch.
Click to expand...

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615

These come from this topic that I developed:

Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

In the UK skippers tend to route their alternator output to the reserve (start) battery. In the US we prefer to route it to the house (leisure) bank because it more likely to be drawn down more from use.

Your boat, your choice.

Good luck.
 
jwilson said:
You do not start the engine with 24 volts.
Click to expand...


ahhh not really correct! A RCS dolphin engine does start on 24 v to give forward propulsion, to go astern you stop it and restart it backwards on 12 v! the switching gear is pretty heavy, but works. I had one in a deben 4 tonner and it never failed, until it ran out of fuel. Oh & they still make them!
 
jant said:
ahhh not really correct! A RCS dolphin engine does start on 24 v to give forward propulsion, to go astern you stop it and restart it backwards on 12 v! the switching gear is pretty heavy, but works. I had one in a deben 4 tonner and it never failed, until it ran out of fuel. Oh & they still make them!
Click to expand...

the exception to prove the rule!!
 
jant said:
ahhh not really correct! A RCS dolphin engine does start on 24 v to give forward propulsion, to go astern you stop it and restart it backwards on 12 v! the switching gear is pretty heavy, but works. I had one in a deben 4 tonner and it never failed, until it ran out of fuel. Oh & they still make them!
Click to expand...

Not sure about the 24 volts bit there: have started a RCA Dolphin with the stop-to-reverse type system and there was only one 12 volt battery on board. I'm 99.99% certain the reversing switch just feeds the dynastart with 12v pos/neg reversed.

There are boats with 24 volt systems, usually on much bigger engines. Once had to move an ex-Admiralty pinnace with an 8-cyl diesel and a 24 volt battery bank, rather flat. Eventually got it going with a third 12 volt battery added in series to give 36 volts, once the engine had run for a minute stopped it and reverted to 24 volts.
 
ah yes, I may be mistaken, but i think that may be the later version with the gearbox? the one i had restarted the engine backwards! of course i may be completely wrong & may now need to go into the garage to find the manual!i definitely had 2 battery, and the switch gear took up most of the aft locker. One really neat thing about the engine though was it's lightness. with it's alloy construction i could uncouple from the shaft and lift it out one handed within 30 mins & for 12 hp engine that's pretty good! :ambivalence:
 
One of the Watermotor engines (Sea Panther ???) had 24volt starting, using a 12 volt starter motor! IIRC later models had glow plugs an were started on 12v......... Something like that any way
 
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