Taking 6v from 12v Battery

[cindersailor]

On my boat I have two 3 cell (6V) batterys wired in series to provide the 12V supply. I want to add a new radio/cd which requires 6V. Rather than pay silly prices for alkaline batteries I was planning to wire it up to just one of the boat's 6V batteries. However, I am not sure whether this will cause any long term problems with this or the other battery. Anyone able to comment?

An alternative possibility would be a transformer to convert 12V to 6V. Are simple/cheap ones available?

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[Evadne]

No problem, IMHO. There are only two things to watch out for when doing this:
1) Don't deplete the battery by too much. A small drain such as a CD player is unlikely to do this, unless the batteries are particularly small (say, less than 10Ah capacity). But don't leave it switched on when you leave the boat.
2) Don't allow any stray earth paths or short circuits. Make sure that the 0V of the CD player is the same as the boats earth, even if you are sure they are isolated and don't allow the +6V line to indirectly contact anything else electrical, especially the +12V line, or you may do the batteries in.

For the record the option for higher current draws are a DC-DC 12V:6V (step-down) converter or switched-mode power supply. Transformers only work with AC voltage.
Dave


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[john_morris_uk]

As Dave says- it will work, but I am not sure that I agree with his assessment of a CD player as a light load. It depends how much you crank up the volume. Some CD players uses several amps when playing loud music.

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[andyball]

Don't think a "6V" cd player'll have that much puff,presumably it's a portable thing, not a car one.

If the batteries are charging; you'll see perhaps over 7V- as long as your cd is happy with that.

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[Rowana]

I have a gadget that I've had for years. It plugs into the lighter socket on the car, the other lead has a plug which fits my tape or cd player. On the box itself is a switch to select 4.5, 6, or 9 volts.

As I said, I've had it for years, and I don't know if they are still made. You could try Halfords or similar places I suppose.

Jim

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[Alex_Blackwood]

Agree with Dave, Yes it is possible but word of caution! If you connect the CD player 0 volt line to boats earth, depending on which battery you have taken the + line from, with batteries in series you could end up with 12 volts across the CD Player. You are better taking the 6volts directly from the + & - of ONE battery and making sure it is all insulated from earth. Or be really safe and as DAve suggests buy a DC-DC convertor or power supply. Try any good audio shop or Maplins/RS or car accessory shop.
Happy listening!

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[Tantalus]

Am I over simplifying something by asking why you don't just take a second set of leads off the battery bank in parallel? Wouldn't you end up with 6v drawing equally on both batteries?

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[Evadne]

Unfortunately you'd turn a 12V boat into a 6V one by doing that. If two batteries are parralleled you can't use them in series as well. The dilithium crystals just won't take it.

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[cindersailor]

Thanks for the helpful advise. I have now found that both RS and Maplins sell cheap step-down voltage converters which plug into cigarette lighter sockets which will solve the problem.

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