Tangent alert: Sanity check on adding DMM display to a variac?

[SoulFetish]

IMG_5101.jpg

Twinning is winning?

[sluckey]

Ah gotcha, yeah I'm not messing with that. Too many functions for one button.

It's really not too complicated. The trickiest part will be remembering this 6 months later.

Here's a video that shows the switch operational modes...

[turbofeedus]

IMG_5101.jpg

Twinning is winning?

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[ChasW]

I performed this mod today per the schematic and details posted above. The schematic made sense, the video not so much.

First I did the 4 wire hookup to meter and it worked as expected with panel powering up and working at around 45v and was good all the to max 145vac.

After that I did the full Monte version of mod with chassis work and the 5th wire mod. Meter worked right away at 0v and then at around 85v is started flashing and went off. The variac continued to work fine all the way to 145vac. Check everything and found nothing wrong. Reverted the 5th wire mod and no issues again from 45v to max. I think I will just leave it this way as the voltages are not too critical to me until near normal operating voltages 115-125vac. My PZEM-021 is Rev 5.

This thread motivated me to do that mod. Thanks for the conversation on this topic.

[SoulFetish]

Nice. Looks much nicer with the meter installed in the front panel. I would like to install my entire variac into another enclosure with a front panel large enough to fit the digital meter, with another analog ammeter for a faster response time to monitor in real time. Plus an upgraded power switch and current limiting bulb socket with bypass.
Can anyone recommend a good enclosure for this? I'm not finding much in my searches.

[ChasW]

What sure of enclosure? Desktop or rackmount?

[SoulFetish]

Benchtop

[turbofeedus]

I performed this mod today per the schematic and details posted above. The schematic made sense, the video not so much.

First I did the 4 wire hookup to meter and it worked as expected with panel powering up and working at around 45v and was good all the to max 145vac.

After that I did the full Monte version of mod with chassis work and the 5th wire mod. Meter worked right away at 0v and then at around 85v is started flashing and went off. The variac continued to work fine all the way to 145vac. Check everything and found nothing wrong. Reverted the 5th wire mod and no issues again from 45v to max. I think I will just leave it this way as the voltages are not too critical to me until near normal operating voltages 115-125vac. My PZEM-021 is Rev 5.

This thread motivated me to do that mod. Thanks for the conversation on this topic.

Yep, just realized mine does this flickering as well. (I have the 5th wire mod)
Unloaded it didn't flicker, but I tried it with an amp ( and bulb limiter) today and it starts to flicker around 80V, with the flicker slowing as VAC output increases. I got up to 95V and didn't want to push it further.
I also can't tell if it's just the blue backlight flickering, or the entire display.

[sluckey]

I also can't tell if it's just the blue backlight flickering, or the entire display.

Quickly push the button to turn the backlight off/on.

[turbofeedus]

I also can't tell if it's just the blue backlight flickering, or the entire display.

Quickly push the button to turn the backlight off/on.

So for me, the backlight is flashing, but the entire display turns off around 100VAC output.
I'm just going to undo the mod for now. Not sure what's going on, but I agree with ChasW, it's not that important to me to see those low voltages, and I have a bulb limiter to limit current anyway.

EDIT: Reverted the mod and just like ChasW described, my meter works from ~45VAC to the max AC voltage from the variac, verified with a second DMM.
An interesting thing which I bet is a clue to fixing the flickering with the mod, the display has the same flickering behavior now, execpt in reverse. In other words, as the variac approaches 40VAC, the display slowly comes on and the backlight flickers, with the flickering increasing in speed as VAC output increases.
Whatever is determining when the display actually turns on, or whatever circuitry is involved, is for some reason reversing it's operation with the mod installed. There's also so symmetry in that, without the mod, ~40 VAC output the display flickers and comes on, while with the mod, it's starts at ~80VAC. In both cases, we're about 40VAC from the "ends" of the input voltage (0-120VAC) maybe a coincidence but I doubt it.

[ChasW]

I also can't tell if it's just the blue backlight flickering, or the entire display.

Quickly push the button to turn the backlight off/on.

So for me, the backlight is flashing, but the entire display turns off around 100VAC output.
I'm just going to undo the mod for now. Not sure what's going on, but I agree with ChasW, it's not that important to me to see those low voltages, and I have a bulb limiter to limit current anyway.

Is your board revision 5 ? Just asking because every video showing this 5th wire mod seems to be the rev 3 board. I though about adding a switch to flip the mod in an out for when I need lower voltages.

[turbofeedus]

Quickly push the button to turn the backlight off/on.

So for me, the backlight is flashing, but the entire display turns off around 100VAC output.
I'm just going to undo the mod for now. Not sure what's going on, but I agree with ChasW, it's not that important to me to see those low voltages, and I have a bulb limiter to limit current anyway.

Is your board revision 5 ? Just asking because every video showing this 5th wire mod seems to be the rev 3 board. I though about adding a switch to flip the mod in an out for when I need lower voltages.

Not sure, I'll check. If 5 is the newest version than probably yes, I bought the thing a few weeks ago.

[ChasW]

So for me, the backlight is flashing, but the entire display turns off around 100VAC output.
I'm just going to undo the mod for now. Not sure what's going on, but I agree with ChasW, it's not that important to me to see those low voltages, and I have a bulb limiter to limit current anyway.

Is your board revision 5 ? Just asking because every video showing this 5th wire mod seems to be the rev 3 board. I though about adding a switch to flip the mod in an out for when I need lower voltages.

Not sure, I'll check. If 5 is the newest version than probably yes, I bought the thing a few weeks ago.

No point taking it apart again. The rev 5 is hidden along the edge in small font compared to the rev 3 in middle and large. Mine is new too. Now I want a rev 3 to see if the mod works as shown on the internet. I also concur on your finding about the near symmetry of how the display functions within that ~40v window on either end depending on mod state.

[sluckey]

Y'all got me interested in adding a meter to my old vatiac. So I got the PZEM-061 model that uses a current sense loop rather than a built in sense resistor. The wiring is much more straightforward than the wiring for the PZEM-021. I did the zero mod on mine and it works very well. Here's a short pdf of my unit...

http://sluckeyamps.com/misc/variac.pdf

[turbofeedus]

Y'all got me interested in adding a meter to my old vatiac. So I got the PZEM-061 model that uses a current sense loop rather than a built in sense resistor. The wiring is much more straightforward than the wiring for the PZEM-021. I did the zero mod on mine and it works very well. Here's a short pdf of my unit...

http://sluckeyamps.com/misc/variac.pdf

Yeah screw it. If the PZEM-061 senses current better and doesn't flicker with the zero mod, it's work the extra $5.
Nice work as always Sluckey.