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Old 27th February 2020, 09:46 AM   #21
Vovk Z is offline Vovk Z  Ukraine
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CL60 can help. I'm not sure how long it will withstand but you definitely have to try it if you don't have something much powerful.
Be careful with termistor because it can crack some time into two parts, so you have to mount it properly, both two legs, to something steady (or you'll have flying energized wires).
10 R nominal resistance means 120V/10R = about 12 A peak inrush current. That means about 12^2*10 = 1440 W in one small thermistor body (it can be too much for 20mm thermistor).
So it is better to use several thermistors of less nominal resistanse, or larger size.


That "energize" sound is well heard because of large current inrush causes turns movement (and magneto-striction of cause too). It is so as in any transformer, but "usual" transformers have lesser peak inrush current and larger primary winding DC resistance so inrush current (and sound) is weaker.

Last edited by Vovk Z; 27th February 2020 at 10:03 AM.
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Old 1st March 2020, 09:39 PM   #22
SyncTronX is offline SyncTronX  United States
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Vovk Z, Thanks for correcting my error thermistor, not Varistor.


Before doing anything after unplugging my Variac W10 from General Radio,
I took the back cover off to examine the unit. I see nothing out of the ordinary.


Then I figured I would check continuity, seeing if anything arched or burned out.


With on/off in OFF position everything checks normal.
With on/off in ON position, and with the amp fuse set for either 2A or 10A,
every wire in the variac has continuity with line in wire,

that is everything in the variac is hot. ?


Now, I added and ON-OFF-ON switch to the 2A/10A fuses after I rebuilt
the Variac because it started making shoring noises internally. After replacing
the amp fuse switch the noises went away and the Variac work flawlessly.
I thought the ON-OFF-ON switch would come in handy.


With the Amp switch in the OFF position only some of the wires
have continuity.


This leads me to think the main ON/OFF switch became faulty.


When power is applied and the Variac power switch is ON,
and when the dial is turned up from Zero, there is no indication
on the Voltage meter, when the amp switch is in any position.


Again this leads me to think the problem is the main ON/OFF Switch.


Film at 11.


Cheers,
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Old 3rd March 2020, 04:20 AM   #23
1audio is offline 1audio  United States
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Variacs
At DC the variac is almost a short between the terminals. You cannot tell much from that. If its well used it may need a new brush. They are really pretty simple and you should be able to connect it using the rating plate info.

You should have an input fuse that matches the Variac rating. An output fuse to protect the variac from a short. Adding an inrush limiter probably is not necessary Do not add anything on the neutral side, that could be dangerous.

I'm not clear why you have an on-off-on switch. It should be on the input side.

If you don't need the full range you can use a transformer with it to boost or cut the supply a small amount. A 12V transformer with a suitable secondary (e.g. 15A) can provide +/- 10% for a 1500W load with a 150 VA Variac. This is similar to what is in the GR automatic regulator.

Be sure you really understand what you are doing, how this stuff works and take proper safety precautions. The life you save might be yours.
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Old 11th March 2020, 05:50 AM   #24
SyncTronX is offline SyncTronX  United States
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Default UnClean but usable W10 Manual

Demian,

Yes, it seems it is almost a short between the terminals.
I replaced the brush a few years ago and cleaned up the
inductor/winding. It worked fine until I turned it off and
then nothing...at all.

At first I thought I blew a fuse in the free standing outlet
receptacle but that's not the case. The variac's two fuses
2A, 10A are fine and have continuity.

I was surprised that when the on/off switch is ON, there is
continuity between the LINE in and NEUTRAL on the switch.
Taking what you mentioned into consideration then this would be expected
as there is no continuity when on/off switch is OFF.


When I measured the inductor and it's various connections they appear
to give correct readings on DER DE5000 LCR meter.

Because the inductor winding is offset:
|<--20V-->|<----------100V---------->|<--20V-->|

The measurements are symmetrical when the offset
connection is accounted for. And it includes measurements
that include the brush at start, physically centered, at end.

So that is still puzzling to me.
I've attached 3 pics and a clear pdf of the manual.
Nope, not the manual as it is.2KB too large, bummer.

Note: The onOFFon switch for the ammeter was the only
one that I had with a 20A switch rating.
Attached Images
File Type: jpg 01. Variac W10 Switch-Continuity.jpg (293.0 KB, 34 views)
File Type: jpg 02. Variac W10 Measurement.jpg (272.3 KB, 32 views)
File Type: jpg 03. Manage Attachments.jpg (18.8 KB, 30 views)
Attached Files
File Type: pdf GenRad_W10_Variac_manual.pdf (317.7 KB, 3 views)
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Last edited by SyncTronX; 11th March 2020 at 06:08 AM. Reason: .2KB too large on the manual. :(
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Old 11th March 2020, 02:03 PM   #25
SyncTronX is offline SyncTronX  United States
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Here is a pic of the Variac's front panel:


Click the image to open in full size.






Here is a pic of the Variac's innerworkings:
The left "Range" switch is the onOFFon switch while the right switch is just .................................................. .....................................ON/OFF

Click the image to open in full size.




Here are both the onOFFon switch and the ON/OFF Switchs.
The onOFFon switch was wired with both contacts for longevity
while the ON/OFF switch was wired the same as the broken original.
When you look at the wiki, you can see that I just had to pull the wiring
and the switch just came apart.












The left hand switch was replaced a few years after the ON/OFF switch with the same brand a very high quality
20 amp switch. When in use I could still hear arching inside the variac, which at first I attributed to the inductor.
Then the on/off switch came apart as shown in the wiki link (LINK [linked here again for convenience]).

The Range switch was arching also, so I replaced it with the only high quality switch I had left, of the onOFFon, which is
acceptable in this case as the range switch is set before energizing the Variac, or when dialed back down to zero.
Attached Images
File Type: jpg 04.Switches.jpg (228.1 KB, 12 views)
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Last edited by SyncTronX; 11th March 2020 at 02:32 PM.
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Old 11th March 2020, 02:36 PM   #26
SyncTronX is offline SyncTronX  United States
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Here is the image of the switch I'm surprised the variac still worked in that condition.


Click the image to open in full size.
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Last edited by SyncTronX; 11th March 2020 at 02:37 PM. Reason: Ran out of time editing the prior post.
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Old 11th March 2020, 03:38 PM   #27
SyncTronX is offline SyncTronX  United States
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I'm pleased to say that I got the Variac working again.
After measuring everything I couldn't find anything
wrong or that stood out with the variac.
I cleaned the inductor and brush with
reagent grade isopropyl reassembled it.

I also checked out the dim bulb test (DBT) fixture
and couldn't find anything wrong with it,
then reassembled it.

I plugged the variac into a power strip
and it worked, followed by plugging
variac into DBT and it worked also.

CONCLUSION
I either plugged the variac into the DBT with
out the bulb when I was tired.
OR
There was a build up of gunk under the wiper
preventing the variac from operating.
However, that wouldn't prevent the variac
from energizing and it wouldn't prevent
the variac's voltage meter from displaying
the output voltage.

Therefore, for the time being, it must have
been human error plugging it into DBT
without the bulb.

I could have sworn that I plugged the variac
into several different power sources and none worked.

Obviously, I'll keep and eye on it and me too.

Cheers,
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Old 11th March 2020, 04:28 PM   #28
SyncTronX is offline SyncTronX  United States
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Here is a pic of Variac working through the DBT and
operating the 60Hz LED on powered breadboard.

Obviously there is very little current being drawn,
just a needles width to the right of 0 A.C. Amperes and
to the left of the larger hash mark which would be .2 A,
Below 100mA I would surmise.

Interestingly this little LED circuit is supposed to have
a 50% duty cycle. This should mean that of two pics taken
with my iPhone one should be with the LED on. About 50
pics later I finally got an ON-LED shot. Maybe the iPhone
camera is set up for no or little flashes into its CCD camera
I would suspect otherwise I should have 25 ON-LED pics.


Cheers,
Attached Images
File Type: jpg 05.Variac_DBT_60HzLED_EE5000.jpg (290.6 KB, 7 views)
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