Br> You're getting old mate.

 Watch it. I was 64 last Thursday and I'm a bit sensitive. Bin
Laden isn't the only one who understands suicide bombers.

Br> The first signs are now starting to show. You're loosing it :)
Br> David has a DVD player, not a VCR.

 Finally, I understand (not that it makes any fucking difference,
btw).

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

 I can't get used to things running off low voltage. It seems
unnatural to me. I can remember when the HT supply was acually High
Tension and you got proper electric shocks without having to be
schizophrenic. In fact, I can remember when we had "A" and "B"
batteries. Vbb meant something, in those days.

Br> David, the one smart thing Bob suggested was to look at how
Br> your batteries are wired.

 That was the THIRD smart thing old Bob suggested. The FIRST smart
thing old Bob did was talk David out of building an SMPS. I was
*horrified* when you (and John) suggested it as a beginner's project!
ROFL! I can think of ten things David could fuck up, and that's just
winding the coil! They frighten *me*, and I'm not exactly a beginner. 

Br> It is not uncommon for large DC battery banks as used in
Br> outback situations to consist of half a dozen 2v cells hooked
Br> up in series. I have seen a few setups like this in the north
Br> west corner of South Australia and 2v cells seem to be the go.
Br> If your battery pack does indeed consist of 2v cells, then you
Br> could just take a tap off of the third one which would provide
Br> you with an output voltage close enough to power your little
Br> DVD player with 100% efficiency.

 Oh duh. Didn't I suggest that? I must be getting old. I'll swear I
suggested that as my final solution (having steered David away from
SMPS first and onto a series regulator, second).

Br> My bet is that the DVD player itself will have some sort of
Br> regulator internally and the plug-pack is just a primary
Br> step-down so it doesn't have to work to hard.

 I seem to remember saying that, too.

 What I *can* remember, is what it's like to be a beginner a mile out
of your depth. Of course, that was 50 years ago, so maybe it seems
worse now than it did then, when I hooked up a 90V battery to the 1.5V
valve heater and wondered why it didn't work (except for that one
bright flash). After 50 years, I now understand that simple works
best, and occasionally it works first time.

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

 You keep forgetting the coil. Does he understand little things like
core saturation, braided HF wire, turns ratios, fast diodes, voltage
spikes... and what happens on zero load? A 6v SMPS that provides 300V
on zero load can be almost as effective as 90V on a 1.5V valve heater.

 But what would I know? I'm so old I've already done all this... and
fucked it up.
  
Regards,
Bob
   

--- BQWK Alpha 0.5