12v to 24v, custom switch?

[dougcpdx]

I've got a sailboat that has both 12v and 24v systems. Nearly all systems are 12v. The 24v battery bank is used to power my anchor windlass and my inverter.

Currently I have two battery chargers and two alternators to charge each of the systems. I'm about to repower and I'd like to go with just a 12v alternator. I'm looking for a custom switch that will allow me to treat my 24v bank as two 12v banks for charging, then put them in series when I need the anchor windlass or inverter.

I understand that some truck manufacturers have done this to crank a 24v starter on a truck that otherwise runs off 12v. The switch is solenoid-driven and is called a series/parallel switch. But that's all I know about it. Since I'd need 24v for minutes or hours at a time the solenoid switch sounds like a bad idea, but maybe a manual equivalent exists.

I drew myself a diagram and it seems like I would need two switches (NC) for +12, one switch (NC) to connect the middle ground, and two more switches (NO) to put the batteries in series and hook up the 24v load. All would need to be capable of high amperage and they would need to be break-before-make to prevent dangerous high amperage shorts and arcing.

Has anyone ever seen such a switch?

 

[Silvertip]

Re: 12v to 24v, custom switch?

Does this help? Common setup for 12/24 volt trolling motors. Switch needs to be rated for the windlass load but you could use a lesser switch and simply use it to switch a "contactor" which is a fancy name for a solid state relay (or a standard relay if you wish).

 

[bruceb58]

Re: 12v to 24v, custom switch?

If you use the previous diagram, you will have to be very careful that the two charging systems do not use common grounds.

 

[dougcpdx]

Re: 12v to 24v, custom switch?

Wow, I appreciate you guys being so comfortable with the graphics. Here's what I had in mind though....

 

[dougcpdx]

Re: 12v to 24v, custom switch?

Something tells me displaying my picture might be tougher than building the switch I'm looking for...

 

[dougcpdx]

Re: 12v to 24v, custom switch?

One more try...

 

[dougcpdx]

Re: 12v to 24v, custom switch?

I give up. In words then...

Picture two 12v batteries. One is hardwired to ground. The other has a switched ground. Label this switch NC1. Each battery is connected to a 12v charging source via switches labelled NC2 and NC3. Now add a switch between the positive terminal of the hardwired battery and the negative terminal of the switched ground battery. This switch is labelled NO1. The positive terminal of this battery is connected to a 24v load via switch NO2. Now. If switches NC1 thru NC3 are opened and then switches NO1 and NO2 are closed I have a 24v battery for my anchor windlass.

To go back to 12v charging I open NO1 and NO2 and then close NC1 thru NC3.

Does anyone know of a manual multi-pole switch out there that implements that function?

 

[Silvertip]

Re: 12v to 24v, custom switch?

And if you forget to set them properly what happens? Use one switch if at all possible. Bruce is correct. If you have a dual output on-board charger (2 sets of +/- 12V) the outputs need to be isolated. Most newer chargers are configured that way.