> Why don't you just buy a 6V battery? And trickle charge it off
> your 12V system with a 12V/5W light bulb?

JT> Because it'll only go for as long as the 6v battery has enough
JT> herbs to make it go.

 You mean, like the 12V battery? They make 'em in all sizes, John.

 Years ago, when NSW was suffering blackouts, I built a 12/240v
inverter to run a large screen TV set. The standard 12V car batery
gave 12V at 4A and ran the set all night.

 David's VCR is rated at 6.3V and 3A, but a VCR only takes high
current when the motors are starting (or rewinding). If *that* current
is 3A, then just playing a tape would be closer to 1.5A, and a 6V
lead-acid battery would be good for 8 hours or so. If he only wants to
play a movie (or record one), a little 4AH gel-cell would go close to
what he needs.

 I assume he already has a trickle-charging system in place for his
12V lead-acid battery(s?).

JT> That and, that "light bulb" charging technique will evenutally
JT> float charge the 6v battery to 12. Or, at least try, killing it
JT> in the process. 

 Not lead-acid... they *need* a trickle charge because they have a
natural reverse leakage. They go flat, just sitting there. 150mA is
perfectly safe for a 50AH lead-acid battery, but if it worries you,
use a 5V zener in series with the light bulb. 

> Lazy is best, and it always works. Sometimes, you even finish the
> project.

JT> Geeze, do it properly.

 "Proper" is cheap and easy, with minimum risk for someone who has
never designed a coil, let alone used it in a SMPS. I can't think of
anything with more "traps for young players" than an SMPS.

 How do you test it, BTW? What if is generates 12V? Do you blow the
VCR? What happens if the motor surge kills it? What if it makes so
much interference that you can't watch TV?

 Too many what-ifs, for me.

Regards,
Bob

 

--- BQWK Alpha 0.5