Panel Mount Voltage Regulator / Knob

[Lee Roberts]

A variac will give variable AC volts, but that's not what Lee was looking for if I understood his original post correctly - he wanted a bench supply for trying out bits and bobs.. I read that as a DC supply.. Lee?

Yes it DC i am after !

capacitive discharge battery tab resistance welding machine

Ermmm...lmao...O one of them , that unit looks like a nice little thing to have, thats the kind of thing i was thinking about making.

The TT i have are:
Primary x2 120 Volt
Secondary 2 x 15 Volt

I think they maybe a bit big for what i want tho, given how small you can get them and given i only want to test things in the 0 - 30v range maybe.

i also just whanted to make a little gadget as well for somthing to do one night, i cant remember what the ampage is on the TT's but i think it was somthing like 160va, right now i'v got one hooked upto two (big) caps:

http://www.mycncuk.com/forums/showthread.php?t=261

as youll read that little box is nolonger going to be used and the contents going to waste, so i just wanted to make use if it all really, maybe you guys could point me the a direction to go with so as to make the most of what i'm hoping could be a very nice bence supply ? in terms of being able to go from a low out put, to a high out put both in DC and in amps should i need to.

I had a look on ebay and for £15 a ready made one dose look appealing, although i would rather design and make a home made system, i'v got leads BR and so on so all i would need really is an enclosure, display and maybe a few other bits.

I dont know, ill leave it with you guys for ideas and thoughts on the above please.

Cheers,

[irving2008]

Yes it DC i am after !

The TT i have are:
Primary x2 120 Volt
Secondary 2 x 15 Volt

...
Cheers,

Well you have options... wire secondaries in parallel 15v AC 10A will give a 0 - 20v 10A supply, or in series will give 30v 5A will give a 0 - 40v 5A supply.

To make it variable you need to go down the switched mode supply route, else the heatsinking arrangements will be extensive (ask if you want explanation)... this will mean milling a PCB, you can't bird nest a switcher (any more than you can a high current stepper driver, indeed the two are very similar). A suitable fully-integrated chip for this will cost around £10 or a cheaper one with external MOSFET around £3 (again same issues as steppers) with about £10 worth external parts. You might be able to get the chip as a sample tho...

If you want we can do this as a design/learning exercise and I'll take you through it - then you'll have the satisfaction of both building it and designing it. And of course others can chip in with their views...

regards,
Irving...

[Robin Hewitt]

I'd still go with the LM338T, it might run a tadge warm but it's so cheap and easy. Heck, just PM me a mailing address and I'll send you a freebie

[irving2008]

I'd still go with the LM338T, it might run a tadge warm but it's so cheap and easy. Heck, just PM me a mailing address and I'll send you a freebie

Robin, it'll run rather more than warm. On a decent 4degC/W heatsink the dissipation limit is 12.5W (at 25degC ambient) so at 20v input and 5V output the allowable output current before it goes into thermal shutdown is less than 800mA, rising to 2.5A at 15v output. Maximum output would be 18.8v at 5A.

Also there's no current limit, only short circuit protection, again not meeting expectations...

I'm not saying that you couldn't use this, and its cheap and simple, but Lee will have to downgrade his expectations and thats not making best use of his 160VA transformer when a 50VA would do.

regards,
Irving...

[Robin Hewitt]

Robin, it'll run rather more than warm. On a decent 4degC/W heatsink the dissipation limit is 12.5W

OTOH if he's bolting it to an aluminium enclosure he's going to get heaps better than 4degC/W.

I'm not saying there isn't anything "better", but does this particular pudding really require that many eggs?

[irving2008]

OTOH if he's bolting it to an aluminium enclosure he's going to get heaps better than 4degC/W.

I'm not saying there isn't anything "better", but does this particular pudding really require that many eggs?

4degC/W is 300 sq cm of 1.5mm ali sheet held vertically and supported at corners only - I'd be surprised if the enclosure gave anything close to around 10degC/W - aluminium boxes are incredibly poor heatsinks (the type of alloy used makes a huge difference as well).

[Eddy]

A small fan will do wonders for heat dissipation. You can pick up small fans that are 5v and 12v at several surplus shops.

I placed a 50mm fan over a dual 15A motor controller with no heatsink and it kept it sufficiently cool even at the full 15A pull. The most current I could pull with a heatsink and no fan was about 8-9A.

Eddy
www.wrighthobbies.net