Mixed 24V & 12V systems

[ccscott49]

If the 24 VDC is only used for engine starting Vetus have a system for their 24 VDC bow thruster when the boat normally has 12 VDC that for a short tine (when the bow thruster is running) connects 2 batteries normally in parallel (12 VDC) to series (24 VDC).

Here

http://www.vetus-shop.com/vetus-ser...olt-thruster-with-12-volt-charging-p-941.html

Excellent system, but he also has a 24 volt alternator, charging the battery bank, so his bank is 24v not 12v.

 

[rogerthebodger]

Excellent system, but he also has a 24 volt alternator, charging the battery bank, so his bank is 24v not 12v.

Ok didn't see that.

 

[lw395]

As a matter of interest, how energy efficient are these converters? How much is lost as heat?

I would expect typically 85% efficient at full load. As it only works when the engine is running that is going to a be a small fraction of a BHP lost.

I would be a bit wary of running stuff that was rated for 8 to 30V on a '24V' system, it will be 28.8V when charging and possibly a big old spike now and then, for instance when the engine starts and drives the starter motor.
Stuff intended for marine/auto use should be OK, but maybe not everything.

 

[prv]

I would be a bit wary of running stuff that was rated for 8 to 30V on a '24V' system

In the case of marine electronics with that rating, I'd be happy enough. The clear intention is for the gear to work on both 12v and 24v boats without having to stock two versions. Printing "30v" on the label doesn't mean it doesn't have regulation against occasional spikes that go higher.

Pete

 

[NormanS]

I would expect typically 85% efficient at full load. As it only works when the engine is running that is going to a be a small fraction of a BHP lost.

Do you only use the converter when the engine is running? What about, for example, a VHF, which usually seem to be 12v?

 

[Bodach na mara]

This set-up is common on boats with the Watermota engines as they needed 24 volts for starting. When I bought Wight Dawn, it used the center-tap method for 12 volts but this does knacker batteries.

What I have done was to use 24 volt equipment where possible when installing new stuff. To date this includes the heating system and the fresh water pump. The rest is supplied from an Alphatronic DC-DC converter which gives 12 volts from the domestic bank of two series-connected batteries. I also considered the Sterling convertor but the off-load draw for it was a rather high 250 mA. The spec for the Alphatronic is 80 mA. The maximum current output is 25 amps.