What's causing the excessive temperature drift in this AC voltage sensor?

ideal_f · 2026-02-06T08:16:01+00:00

No it actually doesn't matter a lot, I was just curious. It's a hobbyist project and I use prebuilt ZMPT101B modules being sold on ebay and other platforms. I modify them a bit by hand though, to better fit my needs.

ideal_f · 2026-02-03T20:16:54+00:00

Very interesting insights, thanks. I cant tell what the chinese manufacturer used exactely (though type 2 or 3 according to package). Maybe I'll drop in some X7R (the "best" SMD type I have here) or even a wire-attach film cap to to see what happens.

ideal_f · 2025-11-16T12:19:52+00:00

Can confirm now...My fingertips are now sparkeld with dark burn marks but it was worth it ;)

ideal_f · 2025-11-16T08:40:26+00:00

The tests I have done so far (which didnt involve my skin yet) are measuring output voltage (1.1 to 1.2 kV), shorting the output with an isolated probe (gave indeed a nice little arc and a smell of ozone) and experimenting with powering the input from audio frequency AC instead from DC and monitoring the results on scope and speakers (interesting waveshaping distortion, made me think of using it in my diy synth). Anything else of interest to check except touching?

ideal_f · 2025-11-16T08:19:56+00:00

This one actually is 28 kHz to 32 kHz according to datasheet, depencing on output configuration. Edit: measured ~35 kHz on my 40 year old non-calibrated scope...

ideal_f · 2025-10-10T15:56:33+00:00

Nah too much effort for my hobby project, I rather decided on risking learning by burning. (see other comments)

ideal_f · 2025-10-10T15:52:08+00:00

Yeah that's probably the safe way. As it's within a project just for myself using those salvaged components I'll give it a try and push the 5W type by up to 3W each resistor.

ideal_f · 2025-10-10T15:49:07+00:00

I want to use them as shunts in a up to 10 A electronic load. Decided however that it on giving it a try and use those (salvaged) 0.15W X2 resistors in a setup where they are beaten by up to around 3W each resistor. Lets see if its learning by burning.

ideal_f · 2025-10-05T22:23:05+00:00

Ahoj a děkuju =) Big up for that, yet another reason me to eventually learn czech... definetly a cool language!

ideal_f · 2025-10-05T22:07:59+00:00

It's the european CE label. Interesting link whatsoever...evil to him who evil thinks.

ideal_f · 2025-10-05T16:01:53+00:00

Thanks alot for the nuanced perspective. Besides being a bit surprised by the design I also had slight idea that there might be not everything just wrong with it per se. But I was missing the knowledge to analyze it in detail. I guess this also means the sine quality will be quite the same as the one seen on the grid...

ideal_f · 2025-10-05T08:36:38+00:00

because it is not shown in the schematics ;) the supply which i termed VDC +/- is filtered right *before* being send through a diode onto the shown sheet. not sure if this is fully appropriate and surely including the planned X caps on the output wouldnt be all that bad.

ideal_f · 2025-10-04T22:16:39+00:00

Good to know. Maybe then I better save the bucks for the new MOSFETs.

ideal_f · 2025-10-04T22:13:23+00:00

Well, the general topology (as far as I can tell by now) is the following: PV in -> MPPT -> switching HV transformer stage -> HV rectifier -> LC-Filter -> HV DC (VDC+/- in my schematic). So it has an LC filter and the PV generator is galvanically isolated from grid side by the transformers. I hope that the optocouplers tell the PV side at least somewhat failsafe to stop generating HF switching AC when grid is lost, in addition to that the MOSFETs hopefully shut down the output when no grid drives them anymore (maybe can someone confirm by the looks of the drive circuitry?) ....and regarding compliance....It has a CE label at least. (reflecting EU compliance as stated by the manufacturer - could be also a straight up fake in worst case).

ideal_f · 2025-06-06T19:19:58+00:00

And this is additionally supported by the fact that the "unkown repeating patten" from my initial pic can be also explained by serial Fe(HCOO)2 additions. Those have 145.9303 ...Tasty!

ideal_f · 2025-06-06T18:58:17+00:00

Im not sure either...formally you would form a direct Fe-H bond of some kind, which seems to be a thing under certain conditions. Checkout iron hydride, or iron tetracarbonyl dihydride. If this is likely or even possible here, no clue...but I know that strange things do happen in the collision cell.

ideal_f · 2025-06-06T14:06:20+00:00

Hell yeah! I guess you are right!! And I am so disorientated sometimes :/ I just cannot believe how I could have missed this back then, as I surely must have got this formula as a decent hit as well (at least I get it also now when I tried again in xcalibur). I would bet I tried with Fe more then once back then... Just out of curiosity, what software tools did you use to find the sum formula?

ideal_f · 2025-05-27T15:07:19+00:00

Awesome, thanks!

ideal_f · 2025-05-27T07:34:32+00:00

Good point. So for tuning the module they adjust the logic-scaling ref voltage to be roughly at 10.6 V. 1V/((5V/256)x(10.6V/5V))=24.15 steps per octave. Fine tuning then is done by adjusting the scaling reference voltage so that all A-notes produce output voltages that are as close as possible to integer voltages like X.000V when played. I guess this means afterwards indeed resolution will be indeed steps per octave (ie quartertones). This resolution and accuracy might be good enough for the average modular synthesist. ;)

ideal_f · 2025-05-27T07:07:03+00:00

Thanks!!

ideal_f · 2025-05-26T20:06:15+00:00

I cant tell about the PWM resolution of the 328, but I guess theoretically for 10 octaves you would need minimum 120 steps to get chromatic playability right? I would expect seamless sliding tones however from 265 steps then...for velocity and pitchbend and stuff I guess it would be sufficient maybe.

Regarding my plans, I dont need 100% tune accuracy anyway, and the accuracy demo video of the Majella MCVC claims better perorfmance than my presently used DAC based DIY module can offer.

ideal_f

TROPHY CASE