24v electrics from a 12v system

[changeman]

I have an appliance that requires 24v but my sail boat runs at 12v using 2 batteries.
How can I deliver 24v to one appliance only and charge the batteries from a 12v alternator/wind charger?
I don't mind buying a third battery but what other kit do I nneed and how do I wire it?

 

[silverseal]

My brothers elderly Kingfisher 30 has a Ford Watermota diesel, which has no glow plugs, and uses 24 volts via 12 volt starter, to scare the living daylights out of the engine so it starts. I have to say it works very well and starts instantly! So it charges 12 volt and starts 24 volts, using a simple heavy duty relay system, which works in 24 volt mode (series) for starting, but automatically reverts to 12 volt (parallel)for charging.

I have the wiring diagram which I gave to a fellow yottie so that he could wire in 24 volt bow thruster on a 12 volt system. Obviously an extra battery is needed.

PM me if you want a copy of the wiring

 

[MacW]

you could always buy a 12v to 24v converter from Alfatronix =


www.alfatronix.co.uk.

Cost would depend on loadings capability.


pete

 

[dick_james]

Take a look at this, it may be what you need. http://www.yandina.com/24VoltBattery.htm

 

[William_H]

You don't say what kind of appliance you want to run. If it is like a laptop computer ie 1 or 2 amps then a converter is the way to go. Do search on powering laptops. If it is high current then batteries in series is the way to go. This requires that the negative of the battery be removed from the negative (earth) of the ship and switched to connect to the ships positive line. The positive of the battery must be disconnected from the ships positive where it has presumeably been charged from and connects to your appliance. This will reqire a double pole double throw switch or relay.
Doubkle throw means that the switch has one wire in which connects to one or two contacts. The double pole aspect means that this switch mkust be duplicated. ie you need 6 contacts on the switch or relay. The switch or relay must be able to carry the current of the appliance plus charging current for the battery and even start current for the engine if you have a dual battery system and want redundancy in batteries for starting. ie you don't need another battery if you have 2. Do not try to use 2 separate switches for the 2 poles as you could end up with only one switch operated (even momentarily)producing a short circuit across the battery and smoke and fire. good luck olewill

 

[oldharry]

If you only need 2 - 3 amps, Maplin do an 'Auto DC regulated Adapter' specifically intended as a laptop power supply. It has a switched output of 15 - 20 Volts in 1 volt increments, at 3.5 amps, and 22 or 24 volts at 2.9 amps (70 watts) maximum, with a stabilised output.

 

[changeman]

Thank you all.
Have discovered I need max of 100 watts and 10 amps starting juice for this 24v appliance.
Am going to try to find a 12v appliance instead.

 

[Anonymous]

Out of pure curiosity, what is it?