Modifying power Supply - worth it?

quietguy · 2005-11-07T01:57:06+00:00

Bit the bullet and bought myself one of those 0-30V 2.5 amp powersupplies from DSE. Nice unit, but two problems I didn't anticipate.1. It has a power switch on the front panel - just on/off. Doesn't seemsafe to me, as switching it on with an unknown voltage setting whileconnected to one of my TTL/PIC projects might result in tears if the adjknob was jarred etc while the unit was in the off state - and it seemssilly that I have to either disconnect projects every time I switch thePS off, or fit a 7805 etc on every board.2. The voltage control is rather 'iffy' in that it is difficult to setthe output at (say) exactly 5.0v - a twitch and its 4.5, another twitchand its 5.6 (get the drift) fiddle some more and get 4.9 or 5.2 etcetc. I realise some variations may not be a problem, but I don't likeit. Life should be easy. V should be easy to adjustSo, I am thinking of1. Fitting a load on/off switch - possibly by fitting a mains powerswitch to the rear of the case, and using the current front panel on/offsw as a load switch2. If I can, changing the voltage adj. pot to a multiturn pot, assumingI can find one that will fit in the original pots space - bit doubtfulthere, but there is not really enough room on the front panel to fitanother (fine control) pot.Any comments? Ideas? Anyone else done these (or other) mods?David - who knows the mods will nullify the guarantee, but these PS'sshould be easy to fix, so...

Nov 07, 2005 23 Replies

Rate this thread:

Walter Harley 20 years ago

"quietguy" wrote in message news: snipped-for-privacy@REMOVE-TO-REPLYconfidential-counselling.com...

IME, the first time you power up your circuit, the question is not usually "how well does this handle real world conditions", it's "did I wire this thing up the right way or not". If the answer is "or not," you'd rather find out when the voltage on it is about a volt, not when it's 5v and too late.

David's right that there are circuits that don't handle a gradual ramp up in power; latchup, oscillation. But personally I'd worry less about that than about zapping an untested circuit with full juice.

Current limiting is obviously a very important feature in a power supply. With good current limiting many other sins are forgiven. Sometimes I start the circuit at full voltage but with the current limiting set to zero, and then ramp in the current instead of ramping up the voltage.

Vote

David L. Jones 20 years ago

Yes, adjustable current limiting is an essential feature of any good power supply. Gotta watch it sometimes though, one setting might be OK for the steady state current requiremens of the circuit, but the power on current requirement is often much larger. So the current limiter will kick in for a brief period and can cause latch up problems as I mentioned. Can be really hard to track down if you don't know what's happening.

If you have a current limited supply then the general rule is as you mention - set the volts you want and ramp up the current. If you don't have a current limited supply then you would do the opposite and ramp the volts up and watch the current meter.

Dave :)

Vote

quietguy 20 years ago

OK thanks Walter. Having just got back into electronics after a 30 year break, I am not used to all the luxeries that are around today - Back in those days playing with my Exidy scorcerer and a bunch of TTL interfacing stuff it was a matter of getting right 1st time!

But times have changed, and I need to change too

Thanks for the good advice

David

Walter Harley wrote:

Vote