12v/6v question

I just finished my thro scupper bait tank. Got the Attwood A 500 pump at wally world for $7.50( 2 of em on sale..took em both) and a plastic container for around $5. It tested well on water, but the pump was over powered by a 12v7ah lead acid "brick". I have a few of these scavenged from puter backup power supply. I saw Hobie's new tank uses the same pump as mine (just the newer model, called the Tsunami 500) , but has a 6v supply (6v12ah, I'm guessing). Had i surfed less and paid attention in Physics class, i might be able to answer this myself....but alas....
I know I can get a 6v12ah batt  + charger from Hook One, but to keep costs down and only need 1 charger, is there a way to cut the voltage in half and increase Ah on a 12v brick (stepdown transformamajiggy/resistamasomething)?? Possibly from Radio$$$$$hack or autoparts store.

You can do a cheap knock down by putting a resistor in series.  This would not increase the Ah, rather it would burn the wasted power as heat.

Or you can get a DC-DC Converter to do it more efficiently.

Either way, make sure your solution can handle the necessary amps.

-Allen

What you are looking for is a 12v to 6v voltage regulator.  I'm not sure it would be worth your time to find one beefy enough to support charging current rather than just buying the 6v charger.  Be careful with using resistance to knock down voltage.  A series resistor will limit current, get hot, and not compensate for any changes on the line or load side.

Kevin

Xsquid,

I think he wants to use his 12V batteries in a 6V application (the live bait pump).  I think the line load and the tolerance are such that he could get away with a resistor.  But yes, you need to size it right for the current, which means you need to know the current.  From that you can figure out if you have a heat problem or not.  I sort of oversimplified it in my response.  Thanks for following up.

-Allen

Allan and Kevin
Thanx for the comeback. Allan i immediately thought of you when I confronted this dilemma and was going to PM you, but thought that was akin to calling the fire dept to put out a cigarette
I found both the batt.(6V 12Ah sealed lead acid) and the charger online for about $16 ea....so instead of getting both, in gonna get 2 6V12Ah batteries and charge them series, after having drained them both on consecutive trips. This way i can use my digi 12v husky smart charger, or even alternator. Should both be somewhat drained to charge them in series, or can i hook up 1 fully charged and one somewhat drained and charge? It seems if one is charged, one is drained , charging them in series may be bad for the one or the other (just a hunch).

  Deplete both batteries then charge together.(in series)  What will happen otherwise is one battery won't get "Cycled" properly (And extend its life) the more depleted battery will take longer to charge, and get a better charge.  The battery with more of a charge to start, will charge less, and not as deep.