6v system powered by 12v coil

I dont see why not, however building your own would produce the same effect for far cheaper (you have to buy one of these for everything). I've been looking into voltage regulators, transformers and just general electronics. Because the power produced is AC voltage, you can actually easily convert it to 6v using a 2:1 wound coil (about $2, confirmation? I'm still learning), then use the rectifier found on the forums here (about $1.25) to get roughly 6vDC (I say roughly because the voltage changes as the motor revs change). a project box would cost about $5 and you could slip all this and a voltage regulator (~$0.62) into it, and get a stable 6v DC (-+0.01v) current for just shy of $9 not including price of wires. Pricing is using bgmicro.com so it may be more or less expensive, but likely in that area..

The output from the generator coil you have will be AC. This does not mean that the manufacturer did not include a rectifier someplace...

First thing to do is measure the output from the coil to determine the current type & voltage. If it is a 12v unit, it may only produce 9v @ idle speeds.

If you have an AC output, then you should run a bridge rectifier to make DC power.

That link you posted is a cheapo 3 terminal regulator, like an LM7806 Not a very good choice for limited power systems. regulators like that are good for about 1 amp,and need a decent heat sink. They "regulate" power by pissing away the un-used portion as heat.

What you really need is a decent Buck Converter. Rectify the 12v, and switch regulate it down to whatever charge voltage the battery pack really needs. That way you can have full voltage at idle too.

A small buck converter like this:

http://www.ebay.com/itm/NEW-Mini-DC-DC-Buck-Converter-Step-Down-Module-input-4V-35V-Output-1-23V-30V-/261077016268?pt=LH_DefaultDomain_0&hash=item3cc9671ecc

Will do the job just fine, and can hit 90% efficiency.

Since it is adjustable you would need to know the proper charge voltage for the battery you will be using, and set it accordingly.

B.