A homebrew bench test unit-Variac-isolation box

[W7TFO]

A few pix of this new project.

More data to come down the road.

More loving of old-school parts...

73DG

[W6TOM]

  I like the meters, looks like they are from an old control board in a substation.
 
  I made something along the same idea that I can plug into a variac and then use that in series with a new piece of equipment I want to bring up for the first time. Keeps all the "magic" smoke from escaping!!

[N8ETQ]

    Yo'

         You may be interested in some of the concepts
Involved with this.  Your limited Variac could control
higher "I" devices using this scheme..

http://amfone.net/Amforum/index.php?topic=40930.0

     Doesn't need to be "Automatic" like this one
but an easy way to let your 5A Variac "Deal" with
50A or more.....

        Back to Back Fil. Xfmrs will give you a bit
of isolation.  Look at the manual..


GL

/Dan

[MikeKE0ZUinkcmo]

My isolated AC is pretty simple, a 1KVA Iso transformer, followed by a Kill-A-Watt, then if necessary a plug in variac with a volt meter.   BTW the ground lug has no connection, I don't want any surprises.

[W7TFO]

It is done, works fine.

Can handle 1.2kVA in direct, 375VA in isolated mode.  0-600ACV output

Schematic, rear wiring, cased and ready to go to work.

73DG

[KL7OF]

very nice...practical too....I like the screw in fuses..if you could find some  "all glass fuses",  it would be perfect ...Tnx for the show and tell.....

[KB2WIG]

There's nothing you can do that can't be done. Nothing you can make that can't be made. It's easy.
All you need is money, money. Money is all you need.

              $6.27

Try the homely despot.

http://www.homedepot.com/p/Cooper-Bussmann-TL-Style-Plug-Fuse-15-Amp-4-Pack-TL-15PK4/100057456

klc

       

[kg7bz]

I suspect he's talking about a glass fuse like this.

[W7TFO]

Glass top Edisons are tough to find in smaller Amperages.

73DG

[W2JBL]

The whole variac thing is BS. If your radio can't handle modern day line voltage or is unrestored and sitting many years you might as well just re cap the thing and get it over with. Bringing old radios up slow with a variac only delays their eventual failure. Fix it right befor putting power to it and save yourself some aggravation..

[K4RT]

Dennis, very nice work there.

I have benefited from bringing up gear slowly on a variac and seeing smoke or hearing arcing at much lower voltages.  Also, line voltage here is typically 121 VAC and sometimes higher so I prefer to run my transmitter & receiver off a variac set at around 115.  I have yet to try reforming electrolytics, replacing with new caps instead.

[W7TFO]

The whole variac thing is BS. If your radio can't handle modern day line voltage or is unrestored and sitting many years you might as well just re cap the thing and get it over with. Bringing old radios up slow with a variac only delays their eventual failure. Fix it right befor putting power to it and save yourself some aggravation..

I didn't build the thing for servicing receivers, and it sure as Hell ain't BS.

Put something you've built on here and we'll tell you what we think...

[KC4VWU]

Very nice!
I hope that someday I'll have enough time to finish all the homebrew test gear for my bench. Right now, it's just the Variac and series light bulb kinda cobbled together with clip leads whenever I need it. I do like a precursory test on some stuff BEFORE I dig in and start stripping out old parts to replace, just as a benchmark.

The question should be: If a Variac is BS, then why do they make them in the first place?

73, Phil

[N4zed]

Nice wire lacing...

[N2DTS]

A fuse works for me.
My line voltage is high, I do not care.
I have a variac on my 32V hv (outboarded)  and run that at 700 volts, any more then 750 and it starts arcing.

If you really want to be careful with priceless vintage equipment, you should replace all the caps and go over things so nothing melts however you power it up.

[k7mdo]

Maybe I have read incorrectly that the higher filament voltage produced by the higher line voltages seriously shortens tube life.... that is my excuse for a system to reduce line voltage for old tube equipment.

CL

[N2DTS]

I am sure that is true.
However I have had all the same tubes in all my equipment with only a few failures (6146's) that I turned into slag by mistake.
The 32V has all the same tubes I got it with 30 years ago.
All my homebrew stuff has the same tubes, and most small tubes are dirt cheap on line.

[Opcom]

The whole variac thing is BS. If your radio can't handle modern day line voltage or is unrestored and sitting many years you might as well just re cap the thing and get it over with. Bringing old radios up slow with a variac only delays their eventual failure. Fix it right befor putting power to it and save yourself some aggravation..

No that's wrong. It's not BS and the caps, reformed or not, are not the problem when using 125V on 117V stuff. It needs no explanation what the issue is, just thought.

All my stuff is run at 117V. Its in spec for just about everything from 1940 to 2015. A couple of 6KVA Stabilines for bench and commo racks, and eventually to install the pair of 200A GE Inductrols for the whole building. No sliding contacts. There's really no BS about using the proper voltage that I am aware of.

[KJ4OLL]

Very nice symmetric arrangement, looks fun to use too!

Design aesthetics match up well w/ BA's .

73
Frank
KJ4OLL

[Opcom]

It is done, works fine.

Can handle 1.2kVA in direct, 375VA in isolated mode.  0-600ACV output

Schematic, rear wiring, cased and ready to go to work.

73DG

How's this working out? What kind of switch was used for the 600V switching?

[W7TFO]

It has been just right for my projects, very handy.

The VM and the transformer secondary switches are by Grayhill, rated for far more than required.

73DG

[N0WEK]

This box followed me home as a freebie from a garage sale and seems to to work well. Other than what you can see in the picture it's got no manufacturer or ratings on the box. I've run a few amps through it with no problems. All it's got inside is the sense coil/transformer for the amps reading and two small transformers feeding power supplies for the two meters.

The picture is the load for the 10,000 BTU AC unit in the office. It shows a 6 volt line drop with the compressor running (10 amps avg) compared to fan only.

[WBear2GCR]

    Yo'

         You may be interested in some of the concepts
Involved with this.  Your limited Variac could control
higher "I" devices using this scheme..

http://amfone.net/Amforum/index.php?topic=40930.0

     Doesn't need to be "Automatic" like this one
but an easy way to let your 5A Variac "Deal" with
50A or more.....

        Back to Back Fil. Xfmrs will give you a bit
of isolation.  Look at the manual..


GL

/Dan

Very nice trick!!

Aka, "why didn't I think of that"!!


                    _-_-

[Opcom]

The manual is a fun read too.

Another brand designed like that GR unit is the Superior Electric "Stabiline". When those type things show up at fests they are usually <$100 and well worth every cent.

The trade off for a small variac is a limited range of variable voltage. It also needs a center tapped variac to give a symmetrical variance, but if a DPDT switch is tolerable to choose buck or boost, then it's the cheap seats for all!

[Opcom]

This box followed me home as a freebie from a garage sale and seems to to work well. Other than what you can see in the picture it's got no manufacturer or ratings on the box. I've run a few amps through it with no problems. All it's got inside is the sense coil/transformer for the amps reading and two small transformers feeding power supplies for the two meters.

The picture is the load for the 10,000 BTU AC unit in the office. It shows a 6 volt line drop with the compressor running (10 amps avg) compared to fan only.

That reminds me of a demonstrator for one of those 'motor economizer' devices. Sometimes you see them in a hardware store with a motor plugged in and throwing the switch kicks the thing in and out and you can see the amp draw change,