Al salaam a'alaykum Bob

16 Nov 03 10:07, Bob Lawrence wrote to David Drummond:

 DD>> National Semiconductor claim 70-80% efficiency....

 BL>  ROFL! As the Arab replied whn asked the price of his camels... it
 BL> depends on whether you are buying or selling.

Hmmm - false advertising... in this country. Isn't that illegal?

 BL>  By the time you wire it up, rectify it and filter it, and remove the
 BL> interference... 50% is pretty good. At 6V, you are going to lose 1V 
 BL> in the rectifier, for a start, and there's 85% before you've even
 BL> switched your first pulse.

I thought a silicon junction dropped 0.6V.....

 BL>> He'll lose 10W+, which is why I suggested an ordinary series
 BL>> regulator as a viable possibility. He can just wire the whole
 BL>> thing onto the heatsink and put it in a shoe box with his other
 BL>> inverter.

 DD>> Shoe box, other inverter?

 BL>  I assumed you already had a 6/240V inverter. As for the shoe box...
 BL> you have to be neat, to at least keep the spiders out.

 DD>> The main SMPS would be left here in the big city where we have
 DD>> 240V coming out of the socket on the wall. The wall sockets at
 DD>> my "country estate" only deliver 11.5-14V

 BL>  Ahh. I see. It's the other way around! Your VCR runs off 6V and the
 BL> inverter is 240/6V. NOW, I understand why you think it won't run off
 BL> a 6V battery... you think it may be AC! I'd be surprised if it was.

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

 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. 

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

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

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

In the winter, when the sun is at a lower angle, the panels are shaded by
trees a bit too. If we're there more than a few days I need to run the
generator to bring the state-of-charge up.

In the summer the sun passes almost straight overhead and I get a shitload
of amp-hours from the panels each day. The 12V fridge draws more power in
the summer. 

 BL>  BTW, I'm not knocking SMPS as the solution... only that it's fiddly
 BL> and you'll never actually get it working - assuming you can find a
 BL> shoe box.

Yeah - I've now been looking at their adjustable 3A series regulator chip.
Much simpler circuit with only a few components.

Regards,
David

--- Msged/LNX TE 06 (pre)