Mysterious null results on a single monitored branch circuit

TrystanLea · 2024-11-25T12:20:50.700Z

Hello @davidski just saw your shop message.

davidski:

If I move the CT to another circuit, keeping the lead plugged into the same socket (CT 8 on the EmonTX), I get valid readings

This is confusing me, so with that same 20A CT plugged into CT8 it doesn’t work on the UPS circuit but it does work on another circuit?

davidski:

I’ve just taken a CT giving me good readings (plugged into another port) on another branch and moved it over to the target branch. When plugged into its original port, readings of the target branch using the known good CT are fine. When plugged into port 8 on the EmonTX, no readings occur.

Does that CT plugged into port 8 work when clipped around another circuit?

davidski · 2024-11-25T12:29:26.332Z

TrystanLea:

davidski:

If I move the CT to another circuit, keeping the lead plugged into the same socket (CT 8 on the EmonTX), I get valid readings

This is confusing me, so with that same 20A CT plugged into CT8 it doesn’t work on the UPS circuit but it does work on another circuit?

Ack. Sorry. I must have gotten confused with all the various configurations I’ve been trying. Checking the feed that this port this is logging to in EmonCMS, I’m pretty sure this port has never seen a valid reading. There’s a couple of 2W spikes that I want to verify. It may be a day before I can take this apart and take another look, but I’ll do that as soon as I can and report back!

Robert.Wall · 2024-11-25T15:11:10.679Z

TrystanLea:

CT8 it doesn’t work on the UPS circuit

This is the first time a UPS has been mentioned. @davidski What do you mean by this - is it the only connection (apart from instrumentation or alarms) between the breaker in your load centre and the UPS (so it’s 120 V or 240 V 60 Hz a.c., or something else?

Bill.Thomson · 2024-11-25T18:21:50.038Z

Robert.Wall:

This is the first time a UPS has been mentioned.

David mentioned a UPS in the 3rd paragraph of the first post in this thread…

davidski:

This circuit is where my network/compute equipment is located, almost all of which is behind a UPS (if that matters).

davidski · 2024-11-25T21:31:41.959Z

TrystanLea:

Does that CT plugged into port 8 work when clipped around another circuit?

Okay. A bit more testing:

Moving a known working CT onto the desired circuit and plugged into a known working EmonTX circuit = valid readings.
Moving the known working CT onto the desired circuit and plugging into the suspect port = no readings.
Moving the questionable CT onto a different circuit, but keeping on the suspect port = no readings.
Moving the questionable CT onto a different circuit, and moving to a known working EmonTX port = valid readings.

It looks like this port is completely dead.

TrystanLea · 2024-11-26T09:47:59.238Z

Thanks @davidski this sounds like a dry solder joint somewhere, thinking about it the most likely place would be on the connector between the expansion board and the base board… could you take it out of the case and take a picture of the expansion board connector? top and bottom…?

davidski · 2024-11-26T21:12:45.054Z

EDIT: Looks like using Chrome allows my images to upload correctly

Attached are photos of the expansion board and the connector mate on the main board. Nothing jump out at me, though my soldering skills are pretty basic.

expansion_ct - 21920×1440 219 KB

expansion_ct - 11280×960 146 KB

expansion_main_connector - 11280×960 203 KB

expansion_main_connector - 21280×960 77 KB

dBC · 2024-11-26T21:57:04.560Z

Might be just the lighting in the photo, but have any of those solder blobs on the expander connector on the back of the main board flowed together?

davidski · 2024-11-27T13:43:11.167Z

Good catch! I carefully used a fingernail and a small flathead to clean out the spaces between the blobs. Unfortunately, no change. CT8 still gives me no readings. Here’s a close up of the connector after my clean up work.

fluxy_flux - 11280×960 146 KB

davidski · 2024-11-27T14:28:10.567Z

To add on to this, I’ve now realized that not only is CT8 affected, but so is CT7. CT9-CT12 look to be working as expected.

Known working loads, when plugged into CT7, give no readings. Taking the CT that is plugged into CT7 and putting it on another port, gives good readings.

davidski · 2024-11-28T15:45:43.514Z

A bit of testing across the various resistors on the expansion board show no obvious differences in connectivity in the good v. bad ports. I’d appreciate any tips on specific bits to look at to diagnose further.

Bill.Thomson · 2024-11-28T18:50:43.877Z

Dave,

The 2nd, 5th, 8th and 9th joints on the bottom of the green PCB (1st picture)
look suspect to me. Especially, the 2nd one. It may just be the way the light is bouncing off of it, and the camera angle, but they sure look like hitting them with an iron and some
solder wouldn’t be a bad idea.

Couldn’t hurt to re-do all of them.

dBC · 2024-11-29T04:20:48.351Z

I don’t claim any expertise in this h/w, but it looks like CT7 and CT8 are the two right-most solder blobs in your zoomed in photo above. Things look a bit beat up around there - it might be worth buzzing them through to their corresponding processor pins to make sure the tracks aren’t damaged - you can just follow the tracks to see which pins.

Robert.Wall · 2024-11-29T13:16:12.425Z

dBC:

it looks like CT7 and CT8 are the two right-most solder blobs in your zoomed in photo above.

I’m fairly certain this is correct. From right to left:
CT7, CT8, CT9, CT10, CT11, CT12, VrefA, 3.3V, GND.

image1161×607 266 KB

@davidski
With the expander board unplugged, can you temporarily connect the socket for CT7 & CT8 (separately) to the equivalent point on any one of CT1 - CT6 inputs, which is the cathode of the protection diode (next to the label, the non-grounded end) – whichever is convenient, and report what CT7 (8) displays. It should read the same, as a percentage of the CT rating, as the ‘host’ channel reads. If it does, the main board is OK and it’s the expansion board. Be careful - this is the processor input pin.
This is in essence equivalent to @dBC 's suggestion, but will, if it reads a sensible value, also prove the software (even though the non-zero readings seem to indicate this is not the problem).

@TrystanLea Is there any chance of a set of Kicad (preferably) or Eagle files for the emonTx5/emonPi2 board? I can’t find them in Docs.

davidski · 2024-11-29T13:36:29.199Z

Hi, Robert.

Reading this back to make sure I understand your suggestion, we want to take the input on a known working socket and feed it into the main board side of one of the non-working expansion inputs, thereby verifying that the main board paths are good.

That would involve a jumper from the pad next to the appropriate CT label on the main board to either CT7 or CT8s expansion input on the flip side of the board, as annotated below.

Do I have that right? I just want to make sure I get this correct. I’m getting a bit fatigued with working on this project and don’t want to rush in and make things worse.

annotation1280×960 209 KB

davidski · 2024-11-29T13:41:54.793Z

Robert.Wall:

Is there any chance of a set of Kicad (preferably) or Eagle files for the emonTx5/emonPi2 board?

I was searching for those a while back myself. I believe these are the sketches for the main and expansion boards.

Robert.Wall · 2024-11-29T14:06:54.956Z

It looks as if you’re right (I can rarely find anything on Github - it’s a more of a badger’s sett than a rabbit-hole).

I’ll get hold of those and load them into KiCad.

davidski:

Reading this back to make sure I understand your suggestion, we want to take the input on a known working socket and feed it into the main board side of one of the non-working expansion inputs, thereby verifying that the main board paths are good.

Correct. It’s what I did with the emonTx4 before I got the expansion board, to prove the library and sketch were doing as they ought.

davidski:

That would involve a jumper from the pad next to the appropriate CT label

No - the end of the protection diode - but your “D2” etc isn’t where the drawing says! You need the non-earthy end of those diodes D1 - D6, in the left-hand block of the schematic: the place labelled “CT1” etc.

image805×603 97.9 KB

And the pin you’ve pointed to on the annotated image is actually Vrefa - CT7 is at the other end.

TrystanLea · 2024-11-29T16:54:28.812Z

CT8 is 2nd from the left, hopefully this image clarifies:

image483×437 88.4 KB

This pin on your CT8 looks a bit dodgy:

image764×781 71.2 KB

and also this one that relates to CT7

image611×515 62.5 KB

Please accept my apologies for this, we would be happy to send a replacement if you do not wish to solder these or if after soldering there is still an issue. This shouldn’t have been dispatched with these issues!

davidski · 2024-12-01T19:25:06.313Z

Thanks, Trystan! I’m pretty naff when it come to soldering. I’ve attempted to resolder both those points with no effect. I’ll take this over to OEM shop email.

davidski · 2024-12-08T14:17:11.115Z

For any future readers on this thread, a replacement main board and expansion board from the shop has corrected this problem. All CTs seem to be working so far. I’m hoping to take the old boards and try to figure out what was off with these when my troubleshooting and soldering skills improve.