safely running a 12 and 24v system

[colvic987]

I am trying to get some information to be able to control a 12v and 24v system, using three batteries and being able to charge them up simultaneously.

the 12v system is for the boat electrics and the eberspacher heater is a 24v system, it is on a friends boat, and he uses 2 switches to switch the 12 and 24v systems,but it is not failsafe, and if he switches the wrong way then a short will be introduced to the system.

any battery boffins know how to solve this problem of being able to use just one switch and to introduce a failsafe system..

 

[William_H]

Presumably you have essentially a 12v system and you need 24v for the heater.
Then you have lift the positive terminal of one battery away from the 12v bus and make it the 24v bus. At the same time you have to lift the negative terminal of that battery away from the earth and connect it to the 12v bus.
(bus meaning the main sort of rail of power available for services)

So you need 2 switches known as changeover switches. That is a contact which connects to one of 2 contacts. And you need this twice. In very low current switches you can get a switch with double pole double throw ie 6 terminals (or 2 of the above described switches in one block.
However I think you will find it difficult to find a switch capable of carrying the high current. ie thecurrent required to run the heater on start and the high current possible when recharging the battery.
You really need min. 20 amp rating switch I think.

Now if you can find high current swiches but you need 2 then you may be able to cobble up a bar to connect the levers of the switches together so they both operate at once.

I once made a gang of 4 switches that has steel levers by drilling a hole side ways through the end of the lever and soldering a piece of welding rod through them all. if they are plastic lever switches you might be able to glue a u shaped channel cross bar across the tips of the levers.

If all that fails then look for relays like a horn or headlight relay for a car which is rated at 20 amps and has the single pole double throw ie 3 contact terminals plus 2 coil terminals. If you can find a high current relay with 2 sets of switches ie double pole double throw so much the better.
The relay or relays are operated off 12 v bus with a small switch at a convenient place to provide 12v to one end of each coil and an earth -ve to the other end of each coil.

So I hope this description might give you some ideas. I am sorry but it is all about the hardware you can find and me not being in UK can't tell you specific parts to buy. don't forget to fit fuses at the battery positive and also one at the 12v bus which gets switched to the battery negative. good luck olewill

 

[VicS]

Take a look at this thread. There may be some ideas there you could use. In your case though you will not need swiches or solenoids to carry starter motor currents.

http://www.ybw.com/forums/showflat.php?Cat=&Board=pbo&Number=1525525

IIRC there was also some discussion about it on the Westerly owners association forum

http://westerly-owners.co.uk/woabb/index.php

 

[ccscott49]

I would use a 12v to 24v DC converter, then you have no switiching problems atall.

A few of the marine leccy companies do them.

 

[William_H]

Converters 24 down to 12 are very common ( I have got one somewhere here in the junk) but you may have difficulty finding a 12 to 24. Of course my experience is very limited so do a search by all means. olewill