Reading Solar Power "Generation" in the dark with the circuit switched off

In case it helps anyone, here is my setup for “Power2” (solar)
Screenshot_2020-12-29_20-14-40

Using “allow positive” is one less step instead of “check size” and “set to zero”

Steve

A thought. As my Solar is never going to get near to the 100A that the supplied CT is rated for, would the 20A version make a difference to my setup?

Obviously it would need a multiplier to adjust to the differing sensitivity. Is it terminated in the same jack plug as the 100A version?

Don’t believe the 20 A bit, and read the report in ‘Learn’ - in short, it won’t make as much difference as it appears.

Yes.

I have two completely independent monitoring systems, one based on an Arduino the other being emonpi. At night both systems indicate a variable low level of PV between 0 and 20W. I have always assumed this to be due to the extremely poor power factor that 14 micro inverters present to the system.

Although this is odd, I have not seen it as a problem worth worrying about during the last 5 years of operation.

I don’t know where Steve lives, but I suppose being 15 W in error out of 25 W on a day like today is a fairly big deal. In terms of a decent day, probably not so much.

I would expect the inverters ‘asleep’ to show as a load with a very poor power factor. But if the phase calibration is not perfect, it’s very easy for a power factor close to zero to swing into the adjacent quadrant and appear as generation, and that may well be what’s happening in both your cases. Unfortunately, current transformers’ errors increase rapidly at very low currents, and short of throwing money - lots of it - at the problem, there’s little that can be done about it while having something safe for DIY installation.

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Firstly, again let me emphasise how much I appreciate the replies and help I’m getting. Thanks!

Brian: I guess it’s not a problem. It’s just not quite what I was expecting.

https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/measurement-implications-of-adc-resolution-at-low-current-values

Looking at “Learn” on CT sensors, this page is basically saying because of the way that it, and the Sampling works on the Arduino, it’s accurate to about 30W.

https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/extending-ct-cable
This page mentions that an extension for CT cable might pick up noise. I don’t have an extended CT cable, but will see if I can re-route away from other cables.

It also mentions earthing the case of the emonpi. I may try that and see if it makes a difference. I checked with my cheap voltmeter and resistance meter, and couldn’t find any measurable voltage or resistance problems as discussed, however I did feel a small tingle at one stage as I touched something in one hand and an earth in another - the display corrupted and I had to cycle the power. I could not reproduce it, and as I said, I couldn’t see a measurable voltage between anything and earth.

Something else: If the power is to the emonpi, moving my finger across the case feels normal. If the power is on, moving my finger across the case, my finger seems to vibrate. I’ve noticed this effect before on a bedside-light that has metal case with a capacitive-touch-sensitive on/off switch. Is that normal?

https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/yhdc-sct006-ct-sensor-report
I’ve tried to read about the different sensors. I’m afraid the electronics characteristics went over my head a bit, but given the price of the alternative CT sensor, I may try it anyway despite the difference “being the equivalent of having an 11 bit ADC instead of a 10 bit” - well it’s a bit different. My solar will be around 10A max I think. 10A on the SCT006 seems to give 12.5mA approx, wheras on the SCT-013-000 it seems to give 5mA. This ties in to the comment that there’s about a 2.5 times advantage for the SCT006 over the other one, so I guess if I try it I’d have to divide the sensed figure by 2.5.

I think a word is missing somewhere, but you shouldn’t feel anything when touching isolated metal. If you do, then there’s some leakage current that you’re feeling. It shouldn’t be dangerous, the a.c. adapter, the c.t. and the 5 V USB power supply all provide isolation between the mains and the emonPi, but there will be a small capacitance that could carry a very small current.

Your 10 A of PV will give you 10 A * 50 mA ÷ 100 A = 5 mA out The SCT006 will give you 10 A × 25 mA ÷ 20 A = 12.5 mA exactly. So the correction is 5 ÷ 12.5 = 0.4 (N.B. you can only multiply :wink: )

You’re correct about the missing word. That should have read
“Something else: If the power is off to the emonpi,…”

Thanks. Will try earthing the case, and will try the alternate CT when it arrives next week.

Thanks again for your help.

Steve

We have a winner!

Earth wire connected. Tingling feeling when running finger over case, gone. Solar “generation” now (it’s dark, nothing being generated) is -4, i.e. the inverter is consuming power. NB That’s raw unprocessed reading (without the adjustments that I put in as mentioned above)

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I checked my emonPi that’s using just one c.t. on a meter tail (line), a.c. adapter, 5 V USB adapter and optical pulse, and using a DVM with an input impedance of > 10 MΩ, I measured approx. 1 V from case to earth.

If you can feel a tingling, that would suggest a current of up to around a milliamp or two flowing through your body, and that implies a voltage much greater than the 1 V I measured.

My voltmeter, (UNI-T from Maplin) claims impedance on “10MW” (sic - presumably they mean 10MΩ!) Accuracy is claimed to be 0.01V in the range I used. I put a fresh battery into the meter, but I’m not 100% confident on how accurate the meter is.

I disconnected the earth, then measured a voltage between the case & an earth. It was never stable & fluctuating between 0.01 and 0.1V.

Touching the case and the “tingle” was there. The Solar read approx +20W generation (should have been zero to -5W).

I tried my alternate 5.25V power supply. I didn’t measure the voltage between the earth and the case, but the tingle was not present with the alternate supply, and the Solar generation read -4W. This was without the extra earth cable.

I tried the supplied Power brick without the AC sensing power brick, and the “tingle” was still there.

This tells me that the problems I am experiencing are caused by the supplied 5V 2A Power supply. Do you think this qualifies as faulty? If not, can I use the other power supply, a Raspberry Pi Power supply (5.25V 2A), or similar Raspberry Pi Power supply (5.25V 2.5 or 3A) or is 5.25 too much voltage? Obviously I’d have to get a adaptor to get the right end on the cable.

If desired, I can return the supplied power supply to be checked, (providing I can run it on the 5.25V for a while).

Any thoughts?

Steve

from The Shop?

Probably, it’s high frequency from the SMPS, and that’s a good reason why your meter couldn’t see it, because from memory it won’t be good above a few hundred Hertz.

Let’s see what @Gwil, @TrystanLea or @glyn.hudson have to say, but it does sound wrong to me.

The Pi should be OK at 5.25 V, the regulator on the front end “Shield” is a “MC1700” on the circuit diagram (I assume that should be MCP1700) which is good to 6.0 V, so you should be OK at 5.25 V.

Yes, from https://shop.openenergymonitor.com/

Will wait until next week and return to work for comments from above.

@Robert.Wall, sincere thanks for spending so much time talking to me, an unknown noob, about this. :slight_smile:

Can I just point out that we were all unknown noobs once upon a time. :wink:

I’ve done some measuring. Firstly, I can’t measure anything on the case - the anodising on the extrusion is making a good job of insulating it. But it wouldn’t take much to cut through the anodising. I could measure on the screw heads - so I did. Running without the a.c. adapter, I see this:


1.08 V rms and 4.92 V p-p, at 50 Hz.

Measuring on the USB connector shell, I get a bit more:

And with the a.c. adapter, back on the screw heads, I get:

And with the c.t. nowhere near a mains cable, it’s reading 0 or 1 W.

The shop is back on Monday, one of them might visit the forum before then, so we’ll see what’s said. But my money is going to be on a faulty 5 V USB power supply. There shouldn’t be so much leakage current that you can feel it, and that it’s coupling into the input to show as ~ 20 W corroborates that.

Hi Steve,

Very sorry about all this (as well as wishing you a Happy New Year!).

Would it be possible for you to post a photo of the power supply and cable you received from the shop?

As a first step, perhaps we can send you a replacement power supply and cable next week? Please PM with your order details or email the shop at [email protected].

PMed.

Steve

These are the photos I PMed to @Gwil

I was using the 1.2 A Ideal HK-U-050A120-CP

OK, well the replacement PSU and cable arrived earlier this week. I tried them as soon as I could, but haven’t had a chance to report. Also arrived this week are a Micro USB socket to mini USB plug (so I could try more power supplies), and the alternate CT sensor, described above.

As I said before, my voltmeter doesn’t seem accurate enough to measure much voltage between the case and an earth. My earth is a gas pipe that has an earth wire from the circuit breaker connected to it.

With the the original PSU plugged in, as documented, without an earth, there is a “tingle” when I touch the case. Also, I can wiggle the power cable where it enters the emonpi and this causes the display to flicker slightly. However, I don’t think this flicker is significant.

With the replacement PSU and cable that arrived this week, unfortunately, exactly the same happens.

As well as those two PSUs, I tried 3 others.
A genuine Raspberry Pi 5V 2A. The “tingle” when using this was less, but still there.

A 5.25V 2A unofficial Raspberry Pi PSU from ModMyPi with integrated cable.
This has as much “tingle” as both emoncms PSUs.

A 5.25V 2A unofficial Raspberry Pi PSU from ModMyPi with detachable cable. This is the ONLY PSU that does not generate a “Tingle” without an earth.

Both 5.25V PSUs make the display run brighter than with the 5v PSU.

I wondered if it was the CT sensors or the temperature sensor that were causing the tingle. I disconnected the CTs from their mains cables, and from the Emonpi, and disconnected the temperature sensor, leaving only the original 5Vdc official PSU and the AC sensor input plugged in. The tingle was still there.

So, I’m now trying the alternate CT sensor (SCT006). Unfortunately, I’ve done this slightly too late in the day to measure generation, but I’ve put “x 0.4” into my input to see if that gives me roughly the right readings (as described in a previous post)

To get correct PV readings, and no tingle from the case, I either have to use the a specific 5.25V modmypi PSU, or add an earthing cable to the emoncms case.

I’ve attached pictures of my setup. PV Meter and CT sensor, out of picture top right. Mains meter just visible right of picture. “Fuse box” top left. Gas meter bottom left.

I’m a bit reticent about leaving an earth cable connected without some specific advice. As you can see from the pictures, the main earthing cable from the fuse box is connected to the gas inlet pipe. I have connected a cable to a redundant earth cable connection slightly above it. The other end of the cable goes to one of the small screws that connect the black plastic mounts to the emoncms case. Does this cable have to be a specific size or rating? Is it safe to connect it as described/pictured? Where is the best place to connect it to the Emonpi - as current, via the display’s screws, or via the screws on the edges of the case?

I think I’d be happier running the emoncms from the 5.25V PSU that doesn’t produce a “tingle”, but there’s a snag as it won’t quite fit in the mains socket as there is something next to the mains socket stops it fitting & would require a multiplug or extension lead. Is it safe to run the emonpi from the 5.25v 2a PSU?

@Gwil I can return the replacement PSU and cable as it doens’t seem to make a difference?

So 3qns 1) about earthing 2) 5.25v OK 3) return the replacement PSU?

Any comments gratefully received.

Steve

20210106_210853

Your gas pipe should have earth bonding, but you must not use it as an earth for anything else. Your main earth should be provided as part of your electricity supply. If not, and like mine it is an older house that has not been upgraded, you can use a water pipe for your main earth as long as there is not an electrically insulated section in it, which would make it ineffective.
The best place to pick up an earth is either your main earth block (if you have one), or the back of the socket outlet that you’re using.

That’s a good question. I would use a ring crimp (or solder tag) under the head of one of the screws fastening the end plates, because the anodising on the aluminium makes quite a good job of providing an insulating layer. On the emonPi that I checked, I don’t have continuity between the end screws and the display screws - it might be necessary to scrape the anodising off the ‘runner’ edges of the display panel to provide continuity. (I’ll try that.)

It should be, as that’s the voltage of the official Raspberry Pi power supply, as I wrote earlier.