Weird power readings

Hi all, I recently bought an emonTx to add to my existing emonPi setup (which has been running nicely for years). It’s transmitting through wifi to my emonpi and all fine, but the power readings dont appear to be correct.

I’ve got the main house +ve (between the main fuse and the meter) on P1. Everything else should be less than that. And i’m quite sure i’m using more than 11w at the moment :smiley: (this is a farm with a number of outbuildings, two dwellings, 2 EVs, electric heating etc!)

What’s going on (i.e. what have I done wrong!)

Did you connect the sensors (c.t and a.c. adapter) before you powered it? (It looks as if you did - just checking.)

Where have you put the c.t - on what sort of cable?
Take a look here Home Energy - Guide | OpenEnergyMonitor

Hi Rob, the unit was turned on without the CTs initially (on my desk), then turned off and CTs plugged in and unit turned on. I’ve physilcally power-cycled it and tried each of the clamps in each of the four 3.5mm jacks. The clamps are on single core - the first being one of the main 25mm tails from the main fuse to the meter, others are on various other single core cables (2 in the CU and one on a henley block going to other buildings)

You were not wrong when you put “weird” in the topic title. I can’t think what could be the problem other than a faulty c.t. I’m assuming its a YHDC SCT-013-000?

Typically, low numbers like 10 W are noise pickup. Are P2, P3 & P4 the sort of values you expect? What do you see if you put all four c.t’s on the same cable? They should all read the same (provided the current is less than 16 A - above which CT4 input won’t be happy).
If you have a multimeter that can read 100 Ω reasonably accurately, unclip CT 1 from its cable and measure the resistance tip to sleeve - you should see about 100 Ω.

Maybe I got ahead of myself. At least now i’m getting one good reading from the solar (P3 in this case). Still very oddly getting nothing much on P1 (main in from fuse to meter).

I shall fiddle…

Please do so constructively :smiley:
Power is the product of current and voltage. You have a sensible voltage so that’s OK.
You have three inputs good to 100 A and the 4th is OK up to 16 A (~ 3½ kW), so putting all 4 c.t’s on the same cable will tell me quite a lot - the numbers won’t be identical, but they should be within a few percent of each other.
Measuring the resistance of the c.t. at the plug - it MUST be off its cable - will tell me if it or the wiring is faulty.
The fact that you are seeing a number, albeit silly, says it’s likely the emonTx is working properly.

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Looks like a dodgy CT clamp @glyn.hudson
I have two clamps on the main line in (P1 and P2) and have swapped the two clamps around and i’m getting the fault following the CT clamp.

Why I couldn’t diagnose that all by my myself I’m not sure. :smiley:

If your current transformer is faulty, email The Shop with your order number etc. and refer to this topic.
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