I have a Powerstat 3PN116B and bought a PZEM-061 Opened it up to wire in the meter and noticed the fuse is on the primary side of the transformer not the secondary like Sluckey's diagram. All else looks the same. I got this second hand and the switch has been replaced as well as some internal wiring.
Should I move the fuse to the secondary side inline with the output?
Thanks
EDIT: Got it wired up and works perfect. Still wondering if I should move the fuse... And have to figure out where to fit the current sense loop so I can get the cover back on.
I'd leave the fuse as is. Heck, if I was building a variac from scratch I would put the fuse on the input.
It is crowded inside that cover. My 216 is laid out exactly like your 116. I moved the switch to the front just above the outlet so I could mount the meter on the top. I peeled the label off the front, and put it on the side of the can. Then drilled a hole in the front for the switch. I used the vacant switch hole to pass the 5 wires to the meter. Had to drill a mating hole in the back of the meter. This allows my meter to sit on top of the cover and no external wiring. I used two 4-40 screws to attach the back cover to the top of the variac cover. My CT fits snuggly right beside the switch body. I had to use a longer wire to be able to pass through the CT to the outlet.
If you leave the switch on top of the variac cover the CT should fit next to it. I assume you have the 'closed' doughnut shaped CT? That 'open' frame CT looks to be bigger than the doughnut and would likely be a challenge to get inside the variac cover.
I managed to cram it together last night but liked your idea of moving the switch and mounting on the top with no exposed wires. Only thing I did different was to cheat and just use double back tape to mount it.
Sorry to hit a dead thread but thanks very much for this schematic and description of how you solved your problem.
I had a very similar issue: my variac didn't start humming or anything but I was clearly not seeing the full current on the PZEM-021 and I knew when I was following the directions from all those videos that it seemed really jinky to just attach the meter load N to the switch when there was already a N jumper from the switch to the variac plug. But I didn't have confidence to just lift that connection until I read that fixed it for you. Once I clipped that wire everything was pretty close to spot on. My panel meter unfortunately has 7mA of baseload but once I subtract that out I get exactly the same current when I compare loads to what I get on my KillAWatt meter.
I can't believe how ridiculously complicated this project got when it looked like it would be so straightforward but there really are a couple of bad videos out there that I'd have been much better off having never even watched. I do wish I'd read this thread before I bought the PZEM-021; I specifically got it over the 061 because I thought hard wiring would be more accurate than the CT but after all this I'd have rather gone with simple, especially since it's got that little bit of parasitic load anyway.
Also, I'm not sure what you mean by current transformer?
There is another unit that looks just like your unit except it has a current sense transformer (doughnut). Much better than using a sense resistor IMO. This type does not require the entire load current to pass through the meter. The current transformer picks up a sample that represents the actual load current. Here's one...
turbofeedus wrote: ↑Sun Aug 25, 2019 6:23 pmSo this makes sense to me, except that all the current will be going through the meter, and I'm not sure it's designed to work like that?
All of the current is supposed to go through the meter. That's how it measures current!
Also how will this effect the mod that allows the 0V reading?
It should work correctly. It measures only what's going to the output plug. Actual voltage and current (and calculated power.) If the variac will go to zero volts, then that's what will show on the meter... assuming the meter is accurate.
EDIT: I just scanned the video to see what the 5th wire mod is all about. To get the meter to work at low voltages you need to connect that wire to a voltage source that's a steady 115V.
I'd really like to nail this down, not only for my meter, be hopefully I can make a guide/schematic for others doing the same thing.
The meter should be very simple to use in any application. Insert it in-line before any load and it measures both voltage and current. But, you need to have all of the current through both wires pass through the meter. There should be no electrical paths between the source and load that go around the meter, except for earth ground of course.
Alright let's see if I've got this correct for at least the version of the DMM display I have:
My recommendation to EVERYBODY is to go to ebay and buy yourself a good used General Radio or Powerstat variac/variable transformer and just try to forget you have one of those red Chinese gadgets that vaguely resembles a variac.
With many of them selling for under 100 dollars, you really don't have any excuse not to get one! I've seen them for under 70 and the red Chinese ones usually sell for 75 dollars.
Mine is a 2 KVA 15 amp Powerstat. Got it for 100 dollars. The power cable is 10/3 SJ cord. HUGE.
Redwood wrote: ↑Mon Mar 07, 2022 1:55 am
Sorry to hit a dead thread but thanks very much for this schematic and description of how you solved your problem.
I had a very similar issue: my variac didn't start humming or anything but I was clearly not seeing the full current on the PZEM-021 and I knew when I was following the directions from all those videos that it seemed really jinky to just attach the meter load N to the switch when there was already a N jumper from the switch to the variac plug. But I didn't have confidence to just lift that connection until I read that fixed it for you. Once I clipped that wire everything was pretty close to spot on. My panel meter unfortunately has 7mA of baseload but once I subtract that out I get exactly the same current when I compare loads to what I get on my KillAWatt meter.
I can't believe how ridiculously complicated this project got when it looked like it would be so straightforward but there really are a couple of bad videos out there that I'd have been much better off having never even watched. I do wish I'd read this thread before I bought the PZEM-021; I specifically got it over the 061 because I thought hard wiring would be more accurate than the CT but after all this I'd have rather gone with simple, especially since it's got that little bit of parasitic load anyway.
Cheers,
Redwood
We should probably clarify the meter reading people are getting when installing the current sense resistor/transformer in the neutral line; This isn't a phantom reading, or parasitic load. What you're reading is the magnetizing current. It's always present when you apply a voltage across the primary coil of a transformer. In fact, if you were to install a moving vane meter, you would see the needle jump momentarily from the effects of inrush current whenever you switched the variac on. Both are normal.
If you wanted to zero out the current reading on the meter so as to only read current to the load, you would need to install the current sense component inline from the wiper to the "outlet". With no load connected to the variac, there's no current in this conductor, so no reading on the meter. (See photo). ps. Make sure to fuse the load connection on your variac! If you exceed the current rating at low voltages, your primary fuse won’t blow and you’ll cook your variac.
999076CE-6A8D-42EC-B77E-8D27E5A3B26D.jpeg
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Matthews Guitars wrote: ↑Thu Mar 10, 2022 5:35 am
My recommendation to EVERYBODY is to go to ebay and buy yourself a good used General Radio or Powerstat variac/variable transformer and just try to forget you have one of those red Chinese gadgets that vaguely resembles a variac.
With many of them selling for under 100 dollars, you really don't have any excuse not to get one! I've seen them for under 70 and the red Chinese ones usually sell for 75 dollars.
Mine is a 2 KVA 15 amp Powerstat. Got it for 100 dollars. The power cable is 10/3 SJ cord. HUGE.
FWIW, I've been using the red chinese variac from this thread for a couple years now with zero issues.
angelodp wrote: ↑Fri Jul 12, 2024 3:57 pm
Late to the party, just looking for confirmation on my plan so I don't screw up my Variac? This look correct?
We've been using the term Variac, and I hope loosely, as it does vary the output voltage. But for safety I hope these are all isolation transformers, not just a variac. I saw a pic of the General Radio variac, and it says on the front there's a shared common connection to both sides. So the output is not isolated from the line right?
Tube junkie that aspires to become a tri-state bidirectional buss driver.
TUBEDUDE wrote: ↑Fri Jul 12, 2024 5:39 pm
We've been using the term Variac, and I hope loosely, as it does vary the output voltage. But for safety I hope these are all isolation transformers, not just a variac. I saw a pic of the General Radio variac, and it says on the front there's a shared common connection to both sides. So the output is not isolated from the line right?
Very few variacs (autotransformers) have an isolated output. Isolation is usually not needed. I'm not worried.
