I'm seeking advice on bench top power supplies

[BillO]

GARTHWILSON wrote:

A page in the 6502 primer:
http://wilsonminesco.com/6502primer/BasicWkbench.html

Good advice Garth. Speaks of experience.

[GARTHWILSON]

Bill, where I worked in applications engineering in the mid-1980's at a VHF/UHF power transistor manufacturer, we used Systron Donner power supplies in the engineering lab. They were about the size of a shoebox, the weight of a car (only a small exaggeration), and were good for about a thousand watts DC output. Switching supplies were just starting to catch on, but these old Systron-Donner ones we had in the lab were linear. They probably had tens of thousands of hours on them, and they never gave us any trouble that I know of. They had some kind of crowbar feature that practically made the whole unit jump when it kicked in to protect something. It was rather impressive. For a project I was assigned to, they got me a supply that could put out something like 110V @ 40A DC. I think that one was linear too. It probably took up four cubic feet, sat on the floor (not the workbench), and they had to install a special circuit to feed it. It was a Kikusui, IIRC. Wow, that's getting close to 30 years ago.

[BigDumbDinosaur]

GARTHWILSON wrote:

For a project I was assigned to, they got me a supply that could put out something like 110V @ 40A DC.

That'll straighten out your hair if you get crossed up with it!

[BigDumbDinosaur]

BillO wrote:

As for a great bench supply, I have a Systron-Donner / Trygon TL8V-3-0V. It's huge and old, but the performance is beyond reproach.

I looked at that one on eBay and it brought back memories. We had several of those way back when I was working on telephone switchgear. We'd use the PS to gently power up the switch, bringing the voltage up nice and slow in hopes that some fatal short wasn't lurking within. Now and then one would be there, but the power supply would simply cut itself off fast enough to avoid filling up the shop with smelly smoke.

[Ken]

Bill,

I also have a Systron-Donner / Trygon TL8V-3 Triple Output power supply, circa 1973, that came out of NASA's Electric Propulsion Lab. I agree that these units are awesome but my +32VDC output has stopped working and I'm finding it almost impossible to find anyone/anyplace that can repair it. I have the user/service manual for it and have done the suggested troubleshooting as much as I can but I am not equipped for more indepth testing or repairs. Unfortunately, the company that made this is long gone.

Do you know of any good repair source for test equipment or can anyone else point me in the right direction? I'd much rather fix this fine old unit than buy a new, cheap Chinese made device but I'm stuck.

BTW, newbie here, sorry if this post is out of place but this is one of the very few discussion forums on the internet that mentions this piece of equipment!

[BillO]

Unfortunately I don't know of any place that services these. However, they are not incredibly complicated and any electronics technician worth his salt should be able to fix it up.

[Dr Jefyll]

BillO wrote:

any electronics technician worth his salt should be able to fix it up.

Agree.

Ken, it might be helpful to let us know where you're located. ( and btw, welcome! )

-- Jeff

[BigDumbDinosaur]

Ken wrote:

Do you know of any good repair source for test equipment or can anyone else point me in the right direction? I'd much rather fix this fine old unit than buy a new, cheap Chinese made device but I'm stuck.

BTW, newbie here, sorry if this post is out of place but this is one of the very few discussion forums on the internet that mentions this piece of equipment!

It would be helpful if you'd indicate your geographic location in your user profile. We have members from around the world who might be able to advise you if they knew where you are.

[cjs]

BillO wrote:

cjb wrote:

Linear semis also have a significant piracy problem, in that it's good practice now to just test any of their devices you have for being on-spec.

Do you have any evidence of this? Not trying to be confrontational, but it seems to me to be counter productive for a company to copy items that sell for so little, even from sources like TI and such.

Well, a couple of days ago I was checking out an LM7805CV that came out of my parts box and was likely (but not surely) bought from AliExpress. It turned out to be way out of spec at low currents, if I was measuring it correctly, but maybe I wasn't. I had left off the .1 and .33 μF caps at the input and output, but for small constant loads would that really make a difference? (I'm going to try an LED again with the caps this time when I get around to it, though I'll have to use a second 7805 since the first is now on a board—one that pulls enough current that it's not an issue.)

[Chromatix]

For regulators, the input and output capacitors are required for stability, even at low nominal load. It's even more true for switching regulators, but linear regulators need them too.

[cbmeeks]

I'm not sure if this has been mentioned or not. A few years ago I bought a <$100 bench top PSU. It got good reviews on Amazon and, for the most part, I've been happy with it. Despite it arriving with a ding in the metal case (and a weird smell..lol).

Anyway, the thing I hate the most is that it doesn't have a shutoff button other than the main power. I didn't think that would be an issue but it is annoying. If I want to kill the power, I have to turn off the entire unit.

Plus, it remembers the last voltage/amp settings. So if I don't remember to disconnect the leads, I could potentially fry a circuit if I was experimenting with high voltages previously.

It would be nice if the unit came on with the output disabled.

I plan on upgrading it one day but if you're in the market for one, I highly recommend getting one with a disconnect feature.

[BigDumbDinosaur]

cbmeeks wrote:

A few years ago I bought a <$100 bench top PSU...Anyway, the thing I hate the most...

This is a textbook example of the old adage "You only get what you pay for."

[GARTHWILSON]

cbmeeks wrote:

the thing I hate the most is that it doesn't have a shutoff button other than the main power. I didn't think that would be an issue but it is annoying. If I want to kill the power, I have to turn off the entire unit.

Plus, it remembers the last voltage/amp settings. So if I don't remember to disconnect the leads, I could potentially fry a circuit if I was experimenting with high voltages previously.

It would be nice if the unit came on with the output disabled.

I plan on upgrading it one day but if you're in the market for one, I highly recommend getting one with a disconnect feature.

Interesting. I've used power supplies up to 4KW, and computer-controllable, and I've never heard of these features, and it's never been a problem.

[cbmeeks]

GARTHWILSON wrote:

Interesting. I've used power supplies up to 4KW, and computer-controllable, and I've never heard of these features, and it's never been a problem.

Maybe I didn't explain it very well.

The PSU I have is always "on" and delivering power unless I physically turn the entire unit off. So, for example, if I am tinkering with a circuit and I am outputting 25V / 1A or so. I turn the unit off, wait a couple weeks and move on to another project. If I don't remember to check what the last settings were when I powered down the device, and plug it into a 3.3V project...well, the magic smoke would suddenly appear.

[GARTHWILSON]

cbmeeks wrote:

The PSU I have is always "on" and delivering power unless I physically turn the entire unit off. So, for example, if I am tinkering with a circuit and I am outputting 25V / 1A or so. I turn the unit off, wait a couple weeks and move on to another project. If I don't remember to check what the last settings were when I powered down the device, and plug it into a 3.3V project...well, the magic smoke would suddenly appear.

That's pretty normal. You always have to set it up correctly before connecting things.