Free stuff in Western suburbs of Chicago

E-Mail me, I'm in NWI and might like this.

emailed to your address without SPAM

i

If you want this to work, and it has the sense terminals, tie the +10v to

+sense and -10 to -sense. Should work fine. If you tie the 10v lines back to the sense terminals at the powered device end, it will maintain the voltage level to the device overcoming line loss. Hope this helps. Respectfully, Ron Moore

OK, will try tonight.

i

Ron, sorry, forgot to say thank you.

i

Ron, you are DA MAN!!! You got it! The power supply is working perfectly fine!!!

i

On Sat, 22 Jul 2006 04:29:03 +0000 (UTC), with neither quill nor qualm, Ignoramus5766 quickly quoth:

As opposed to imperfectly fine?!?

-- Heard of the Frisbee Religion? They believe that when you die, your soul goes up on the roof and you can't get it down. ----

Comprehensive Website Development

Yep! I am very happy.

i

I picked up a nice pair of Power Designs 2005 supplies in a shared rack mount for peanuts at a hamfest, because the seller could not make them work. While I could not test them there, I felt sure that was the only problem, and once I got them home, it was indeed the case.

These power supplies, for those who have never seen them, are particularly nice sources of precise low voltages. The range is form 0 to 20.000 V in steps of 0.001V, plus a fine adjust pot which sweeps it through the 1 mV range marked with 100 uV increments.

Maximum current output is 500 mA, and it has a current limit adjustment as well -- though nowhere as precise as the voltage output adjustment. But it is still a nice thing for testing something without risking burning it out by a wrong connection.

Even when they are turned off (but still plugged in) you will see a pilot light marked "oven" cycling. This keeps the voltage reference zener at a constant temperature, so it makes a reliable source of voltage.

Among other things, I use these when testing a brush type servo motor and amplifier, to see how low an input control voltage still produces perceptible motion on the motor shaft. When set for full speed at 10.000 V input, I can see the difference between 1 mV and 100 uV -- as long as I have a piece of tape stuck to the shaft to serve as a "minute hand". And yes -- I can also see a difference between 100 uV and 0 V. When the input is 0 V, and the balance is properly adjusted, it *will* stay still for as long as I am willing to observe it -- or at least until the room temperature shifts, changing the balance. :-)

Enjoy, DoN.

DoN, that's great and I must comment on just how generally honest such people are. He could have lied that the supplies were working, but he did not do it.

Sounds very nice. It is good to have a nice, versatile accurate and (preferably) powerful power supply. I would really like to find something like that, I have a few supplies, but none quite fit what I want.

My ideal spec, I think, would be 0-50V, 0-20A with some precise adjustment.

i

[ ... ]

This is typical of hamfest people.

Hmm ... that might be hard to get in something which could be lifted easily.

The closest which I have is also a Power Designs (but without the precision voltage selection), which is 0-36V 0-5A with current limit.

It has a doghouse on the back which contains the pass transistors and heat sink for better cooling, and an interesting design to minimize the dissipation in the pass transistor. There is a variac before the main power transformer (separate transformer for the internal circuitry) which adjusts the output voltage of the transformer/rectifier/filter combination, so it is not *too* much above the desired output voltage. The front panel voltage control knob turns both the Variac and the pot which controls output voltage.

Even at that reduced output compared to what you want, it is still a heavy little lab supply. (These are all linear regulator power supplies, not switching regulated ones -- but they are from the time when things were built with individual sold-state components, not ICs.)

Like the 2005, it has a switch to select the meter monitoring either the output voltage or the output current.

Looking through eBay for the "Power Designs" name (be sure to put the quotes around that, or you will get gazillions of unrelated hits), I find one which looks interesting, a model 5015 (which is 50 volts, 1.5 A maximum, but which is otherwise similar to my 36V 5A one). There are back panel terminals for remote sense, if that is how you need to use it, but the front panel has just three binding posts, Ground, '-' and '+' It has the same "doghouse" on the back. The price is a bit high for hamfest/ebay prices, but it is apparently a dealer who refurbishes them as he has lots of Power Designs supplies for sale at the moment.

Look at auction number: 180008703295

None of the 2005 model (or others with the precision voltage dialing) visible, however.

Hmm ... Mastech DC power supply 0-30V 0-20 A -- 250008015015

Nope -- only 2% accuracy and only tenths in the voltage readout. It might do for a lot of your needs.

Not the same as the 2005 where you can select true precision. The voltage is set by two pairs of concentric knobs, making it easy to read the voltage selected in a reasonably tight cluster of digits.

Good Luck, DoN.

Don, thank you for taking time to answer my question (about finding an ideal power supply). I appreciate it. And I looked at those ebay auctions. Maybe I will keep my 0-30v 0-5A Mastech power supply I have on auction now.

I wanted to give a completely different line of thought here, which is that I already have a very powerful and expensive power supply, namely, my modified welder.

It has a sophisticated SCR firing circuit, a microcontroller etc etc etc. It has several modes (all simply programmed in BASIC), several for arc welding/cutting, but also two general low voltage high current and high voltage low current modes. The last two I call the "power supply" modes.

They work.

The SCR fired DC that I get, probably has a 360 Hz ripple of about

1-sqrt(3)/2 percent, which is about 13.5%. A little bit of filtering could give me basically a smooth DC of any voltage and power that I may want to get in my "home lab" or to drive big motors etc.

So, maybe some improvements to the "power supply" modes, adding a vernier potentiometer for fine adjustments as well as a filter for filtering out ripple (LC or whatever), would do the trick?

To condense what I said above in one paragraph, I already have a high power power supply, but it may need to be improved a bit for finer control and for better output DC quality. Right now the controls and filtering are okay for rough stuff like welding, but may need to be improved for general bench lab work purposes.

The obvious minus of this supply is that it is in my garage, I need to walk there to turn on the phase converter, etc. (I could easily set up some controls for the power supply, in the basement, to control it remotely by some very simple means, but I would not do it to the phase converter)

The obvious benefits are that I am not using any space (since I already have this welder), I am not spending much money to get a power supply, etc. Plus I can customize whatever I want.

Any thoughts?

Right now I am in a mode of cleaning out my basement and garage, getting rid of junk etc, but once I am done, I could work on it.

i

According to Ignoramus18660 :

It sounds like a good one to keep for general purpose. (did I wind up finding your auction in my searches?)

O.K.

If you want the kind of precision voltage output which I described from the Power Designs 2005, you would need to do some serious work. I think that it would be something like the following:

1) A precision reference supply, with a temperature-stabilized zener diode as the reference. 2) A Kelvin-Varley voltage divider to produce the desired voltage as a standard for comparison. 3) A comparator to compare this standard against the output of the main supply, and to call for more or less output as needed.

I'm not sure that this would work as well with the switched-mode output from your welder as it does with the linear regulator circuits of the Power Designs units. Especially, the cycle time (2.8 mS from your

360 Hz SCR firing) may preclude keeping the voltage within the limits set by a voltage switch setup calling for 0.001 V resolution.

I think that for that kind of precision, you would want something designed from scratch for the purpose -- and not something as brute force as a welding supply *must* be.

Another is if you fire it up to weld -- what makes sure that your load is disconnected down in the cellar? You could fry something seriously as you start welding a bead. :-)

Agreed.

You have mine above, where I thought of them.

O.K.

Good Luck, DoN.

Glad it worked. Gotta get lucky once in a while. Have a good weekend. Respectfully, Ron Moore

Ron, if you want some exotic tig filler rods from me, let me know, I owe you one big time. See my another post about them.

i

No, it was someone else's.

Yes. I think that I would have to give up quite a bit of precision, but that should be fine with me -- I am more interested in generally OK quality DC, with a wide range of voltage and current.

Agreed.

I think that I could make the work lead plug into the same quick connect as the basement circuit, so that either the basement circuit is connected, or the work lead, but not both.

That could help. Generally, though, there are many safety/fire issues here that may not be easily solvable. Capability like 300V/80A or so is serious stuff, hard to find circuit breakers for that etc. (that is, what if something goes wrong, how can I stop this thing RIGHT NOW (manually or through a safety breaker etc).

Perhaps I could have a circuit that would, based on human command or safety event tripped, stop a contactor supplying power to the phase converter, rather than try to break the DC circuit.

Thank you Don.

i