From: "Brenton" 
Reply-To: Brenton , Fidonet AVtech Echo
	

Bob,

You're getting old mate.  The first signs are now starting to show.
You're loosing it :)

David has a DVD player, not a VCR.  The DVD player has a plug-pack power-supply
which normally plugs into a 240v GPO and has an output rated at 6.3v 3A  His
country pigeon coop has a battery powered DC supply where the output can vary
from 11.5v to 14v.

He does NOT have a 6.3v to 240v inverter.  The plug-pack which was supplied with
the DVD player is the reverse of that.  It is a 240v AC to 6.3v DC switched-mode
supply which is rated at 3A


David, the one smart thing Bob suggested was to look at how your batteries are
wired.  It is not uncommon for large DC battery banks as used in outback
situations to consist of half a dozen 2v cells hooked up in series.  I have seen
a few setups like this in the north west corner of South Australia and 2v cells
seem to be the go.  If your battery pack does indeed consist of 2v cells, then
you could just take a tap off of the third one which would provide you with an
output voltage close enough to power your little DVD player with 100%
efficiency.  My bet is that the DVD player itself will have some sort of
regulator internally and the plug-pack is just a primary step-down so it doesn't
have to work to hard.  If you plug it in and it blows up, you will have
discovered why God invented the term Warranty Claim. Just take it back and look
surprised that it failed.  They won't be able to prove anything.

If John can't supply you with the part numbers from Jaycar for the components
you need to build the switcher, I will have a look for you in the next few days.
I may even have a PCB here that could be used to build it on, as I do have a
small board in my product which contains a LM2595 switcher and a single MAX202
chip.  The only issue may be that I use a fixed output switcher and for your
supply there will need to be two resistors which the board won't have space for,
but it should still be easier than trying to bread-board it.

Cheers, Brenton


----- Original Message -----
From: "Bob Lawrence" 
Newsgroups: fido.aust_avtech
To: 
Sent: Sunday, November 16, 2003 9:20 AM
Subject: On topic warning!!!!


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

DD> I don't know if it will run off straight 6V - I should test
DD> that....

 Of course it will! Unless Idon;t understand what you've got.

DD> I could also get a small mains inverter and use the original
DD> 100-240V SMPS - with the resultant inefficiency. I'm trying to
DD> minimise battery load.

 Jeeze! How many inverters do you have running this VCR?

 I assumed that you had a standard VCR (that runs off 100-260V
50/60Hz mains, and had bought (or had caught when it fell off the back
of a truck) a 6.3V to 240V inverter. Does the VCR actually run off
6.3V, directly? (probably with a regulator down to 5V)

 *IF* you're using a 6.3V inverter, there is *another* possibility...
maybe your 6.3V inverter will run off 12V! You'd have to get a
circuit, but if it's a straight 6.3V to 240 AC inverter, it's almost
odds-on that it'll run perfectly well off 12V.

Regards,
Bob




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