Convert 48V battery bank to 12V for boat appliances - Inefficient?

Question

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 400AH of use when drawing only 12V after the conversion? Or would the available AH be much less due to the losses from the conversion?

Answer 1

Here's the item you linked: -

• It's a 12V output capable of supplying up to 25 A - is this enough for your appliances
• You can power it from 36 V to 75 V - is this OK for your set-up - Any unforeseen voltage spikes that might mean you need to consider over-voltage protection feeding the supply to it?
• Efficiency of 94.5% means probably 90% if you read the small print but still this means that if you take about 300 W out (12 V x 25 A) you can expect to have to provide 333 W in and this means about 7 A taken from your batteries (48 V). As battery voltage drops to possibly 42V you can expect to have to provide almost 8A.

I have used one of these and it did the job. I also powered it from 48V.

Each battery (wired in series) provides the same current and so the Ah rating stays at 100 Ah but obviously the current draw is significantly less when using a switcher. At full load (12 V x 25 A), I would estimate that this will work for about 11 hours before the batteries need a recharge.

Answer 2

I have a similar setup, 400w pannels in series to give me a 48v-60v charge, 30amp mppt to 4 x 100amph in series giving me 48v 100amph. From there I tap off 48v to a 3.6kw 220 inverter, also taping of the 48v side have a 36 V to 75 V input to 12v output. On the 12v I run 5amp freshwater pump, 5amp saltwater pump, small bulge pump and around 100w of LED lighting. On the 220AC side I run various woodwork tools and a few 100w spot lights. I have never tripped and my battery bang stays above 80% charge. Will be adding 200w freezer and a 80w TV soon as well as Navigation equipment to the 12v side. For this I am looking for a 48v alternator + alternator charge regulator to help out with the extra load. The loss experienced from stepping down 48v - 12v is not noticeable, I may end up piggy backing a second dc-dc as I may need more amps running Nav gear.

Answer 3

I'd go with the 48v to 12V DC-DC Converter. This allows one to fully use all 4 batteries' reserve power as against using just the bottom Battery (single reserve power).

Whether this device is rated 100% efficiency, or 90% efficiency or as low as 80% efficiency, 80% of 4 Batteries is still much better than 100% single Battery.

Furthermore, the more current you draw out from a single battery (or battery banks), the less efficient that battery becomes. ie, drawing 40A from a 12V battery will lasts shorter than drawing 10A from the same battery (check your battery's Reserve Power rating chart). Therefore, the fear/concern of "lower efficiency" due to a converter devices (such as this), is practically debunked!