Al salaam a'alaykum Bob

24 Nov 03 09:44, Bob Lawrence wrote to David Drummond:

 DD>> No, the PSU definitely puts out DC. It was the rating sticker
 DD>> on the bottom saying "6.3C 3A" that made me think it might need
 DD>> 6.3V 

 BL>  For God's sake, David. Don't you know that a "6V"
lead-acid battery
 BL> is actually 6.3V, or to be precice, 6.0V flat, 6.3V nominal, 6.7V 
 BL> full charge, 7.0V maximum standby charge, 7.4V maximum cycle charge. It
 BL> varies a bit with temperature too, and an old battery tends to 
 BL> increase in voltage a bit.

Yeah - OK....

 BL>> An extra 6V battery looks better all the time! Or just tap into
 BL>> half of your 12 volts. You can usually see where the connectign
 BL>> bars are... just screw in a self-tapper. 

 DD>> I have 6 x 2V cells. Each cell has a "bolt-on" +ve and -ve
 DD>> terminal.

 BL>  How easy is that? Just run an extra wire from the bottom three cells
 BL> and you're laughing. They *are* lead-acid, I suppose?

Yes - big gel cells to be precise. I chose those over liquid batteries as
they require much less maintenance. I'm not there for weeks on end
sometimes and could therefore not top them up (electrolyte).

 BL>> How do you charge your "country mansion" battery?

 DD>> Solar panels, and a small petrol generator for when I get too
 DD>> many cloudy days in a row. 

 BL>  Terrific! That's a great setup. What's the ampere-hours? About 80?

Errr no, they're rated at 450Ah -  but like audio speakers, there's a few
ways of calculating that too....

 DD>> In the winter, when the sun is at a lower angle, the panels are
 DD>> shaded by trees a bit too. If we're there more than a few days
 DD>> I need to run the generator to bring the state-of-charge up. In
 DD>> the summer the sun passes almost straight overhead and I get a
 DD>> shitload of amp-hours from the panels each day. The 12V fridge
 DD>> draws more power in the summer. 

 BL>  What a great setup.

 BL>  IMO, you'd be mad if you didn't just run a 6V point out of your
 BL> batteries. Lead-acid batteries are quite tolerant of unequal charging
 BL> (over-voltage), so if you ran one half a bit flat and then charged
 BL> the whole thing together it wouldn't matter too much. If it's not
 BL> lead-acid, you'd have to be a bit more careful about running one half
 BL> flat.

OK - Of course, I'll have to run more wiring (and the six volt load won't
be controlled by the "intelligent" regulator.....

[...]
 BL>  No! Just run it straight off three cells! If you're worried about
 BL> it, there'll be a series regulator inside the DVD. Just put your
 BL> finger on it and see how hot it gets. My guess is that the
 BL> DVD actually runs off 5V (maybe the motor has its own regulator).
 BL> Worse case, with the battery charged right up to 7V, you're looking 
 BL> at a total loss of (7-5)*3A = 6W. That's bugger all.

 BL>  Plus, I'd be really surprised if the DVD takes as much as 3A (once
 BL> the motors are up and running). 1A sounds more likely... and 2W is 
 BL> nothing.

I hope to test it this weekend.

Regards,
David

--- Msged/LNX TE 06 (pre)