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# Convert 48V battery bank to 12V for boat appliances - Is this inefficient? Answered

I need a 48V bank for an electric motor on my boat. I also need 12V for my appliances. Obviously keeping both a 48V and 12V bank would be most efficient but the space required and cost of maintaining 2 banks is a bit much. So I was thinking of using a 48V DC to DC convertor to convert a 48V bank to 12V for my boat appliances(lights, pumps, etc.)

http://pt.mouser.com/ProductDetail/Murata-Power-Solutions/HPQ-12-25-D48N-C/?qs=sGAEpiMZZMtwaiKVUtQsNaluUzA10QGezHFBNv8sYMI%3d

But how much would I lose in terms of efficiency? Would the losses be too great?

Would the bank of 4 x 12V 100AH batteries connected in series give me roughly 4800W ( 4 x 12 x 100 = 4800) or 16 hours of 300W use when drawing only 12V after the conversion?  Or would the available AH be much less due to the losses from the conversion?

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## 6 Replies

ANDY! (author)2013-11-17

If you go on Ebay and search DC to DC converters that aren't too expensive, claiming 98% efficiency. Although the efficiency is most likely lower than that in most cases, something that I guess would be around 90-95% is pretty decent, unless you need to use a lot of power at once. Then again with just four batteries, I don't think using that much power is a very good idea, so I think this is a pretty simple solution.

mchin2 (author)2013-11-19

When you say "unless you need to use a lot of power at once". You mean like for a microwave?

ANDY! (author)2013-11-20

Yes, a microwave uses a lot of power at once. About 1500 watts I think... Although microwaves usually run off of 120V AC, which means you could get a 48V DC to 120V AC inverter as well..

mpilchfamily (author)2013-11-17

If the bank is made up of 12V batteries wired in series then why not tap onto a single battery for the appliances?

How are you charging the bank? Is this motor the primary propulsion on the vesle?

mchin2 (author)2013-11-19

Hi,
1KW bank of solar panels is the main charging for the bank. As explained by Steveastrouk, batteries need to remain fairly uniform in their charge so tapping one would severely affect the longevity of the bank.

steveastrouk (author)2013-11-17

Generally, it's a bad idea, unless you can evenly discharge the whole chain.