DD> I guess I should use the centre tap as +6V with the 0V being
DD> common to the DVD and the 12V TV? 

 Aha! Now, we come to technology you understand. You are asking the
right questions.  

 The simple answer is, YES.

 The complicated answer is:

 If you run half the battery flat, then when you charge it, the other
half will get over-voltage until the flat half catches up. Lead-acid
batteries don't mind that. They can tolerate up to 2.5V per cell, so
long as they are current limited.

 It won't be a problem with your solar array, which is current-
limited anyway, but a petrol generator could do damage if you don't
have a current limit on it. Avoid the quick-charge setting (if there
is one).

 A heavy-duty car battery (you can scale according to the physical
size of your cells) can take 20A without exceeding the 2.5V limit per
cell (15V for a 12V battery). A "normal" charge is about 10A. A truck
battery is 40A max, and I guess yours is around that size.

WARNING!

 If you try to be cunning and move the common earth around to
balance the load half at a time, you could end up shorting out the
common-earth connection when you connect the DVD to the TV. Most
electronic stuff isolates the earth, but you'd want to check it first.
Just plug them in, and measure the output sockets with a multimeter to
be sure they're not connected to the common point.

 Personally, I'd just use the common, tap +6V, and hope for the best.

DD> I've been considering Bob's idea of the series regulator - the
DD> LM350 looks like it would do, and the component count is lower
DD> than the switch-mode, with a simpler circuit. What do you think
DD> (assuming the 6V ida doesn't work......)?

 A series regulator loses about a volt before it starts to work.
Forget it. There's sure to be a regulator inside the VCR already (the
same as the TV). If you're worried, take the lid off, find it, and put
your finger on it. If the flesh doesn't sear, it's okay.

Regards,
Bob


    

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