Thanks for the info john, I’ve got a few TT's laying about that I had planned to use as a bench supply for testing bits and bob's.
What I would really like, is something that would allow me to turn a knob and change the voltage output to different amounts.
As and when I need to for supplying and testing different things, can you please recommended what it is I should use, what kind of "knob" I need to be looking at.
Panel mount voltage regulator?, I would more than likely use a little digital screen of sorts so I can fine tune the “knob” to just the right volt output each time.
Thanks guys !.Me
I'v just had a quick look on ebay and found this:
This is the kind of thing i was thinking, i would prefer to change the output via a front panel using a knob, over poping inside the unit to change the dip switches everytime i need a new output amount..Me
Its not autoranging tho, so not much use for monitoring a truely variable power supply.
So lets start by listing what you want...
A power unit with an adjustable output voltage from 0 to 25v is a good range for hobby stuff, switched in 2.5 volt steps maybe ?
Output current at 5A maximum, current limited. Maybe a switched limiter, for .1,.5,1 and 5A?
Output voltage and current monitoring, current limit warning (LED, buzzer?)
What transformers etc have you got to start the ball rolling?
Last edited by irving2008; 24-11-2008 at 08:29 PM.
Here's a Variac
and here are some isolating transformers that can handle 110 volt.
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?
What sort of voltage and current range are you looking for?
What I think you need is something like an ordinary lab bench supply. These often come up on ebay for a reasonable price.
Alternatively you can build one easily enough. I have three or four variable voltage bench supplies that I've built, the most recent being one to power my home made capacitive discharge battery tab resistance welding machine (see pic below - it's the silver box on the left with the digital voltage readout).
For my DC suds pump speed control I used an LM338T, just google for LM338 and get the data sheet with circuit diagrams.
Up to 5 Amps, needs a few extra components, but with a bit of jiggery pokery you can solder them on to the pins and enclose with shrink wrap.
Bit of an industry standard, costs a quid.
Although slightly more complex (as in needing 6 more parts) a switch mode supply based on LT series devices needs no heatsink and gives variable current limit as well as voltage.
A similar spec bench supply on ebay is about £60 so by the time you bought the bits and made it up and boxed it for safety its marginal to make them really... except for the fun/satisfaction of knowing you did it yourself.
capacitive discharge battery tab resistance welding machine
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:
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.
Last edited by Lee Roberts; 28-11-2008 at 01:20 AM..Me
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...
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