OpenEnergyMonitor Community

CT Clamps 100A or 20A

Looking to buy either emonPi or emonTx and emonBase.
Based in the UK. so 230v a.c.
I have a PV instalation with 3.25kW Solar and HAD a geo Chorus display which has worked fantastically for 8yrs. But last week the display unit stopped working. You cannot buy them anymore and there are none on Ebay uk, and lets face it. It would be 8+ yr old.

So looking at either a emonPi or emonTx & emonBase.

But with only 3.25kW (max 15A approx) solar do i really need a 100A CT clamp so was thinking if i went emonTX route i would get the 20A CT clamp on sale in the shop. Would this be more accurate than the 100A CT clamp and more accurrate.

Fusebox is in the porch which tracks outside temp and humidity will either unit cope with the outside temps and harshness of winter or should i look to have the unit in the house and feed the CT clamp cables through the wall too where the fusebox lives…

Help would be appreciated while my journey into the emon world begins…

Not quite - the UK centre voltage remains, as far as I know, at 240 V. Only the specification changed to 230 V, with the tolerances opened up to take in 240 V + 6% and (for continental Europe) 220 V - 5% (I think), the old standards.

Read the test report in ‘Learn’ - there actually isn’t much in it, especially as the “20 A” rating doesn’t hold up when measured on a 50 Hz supply and at the output voltage we must use.

Whether you have an emonPi or emonTx + emonBase depends more on how many inputs you might have in the future. For your present requirement, the emonPi would seem to be the more obvious choice.

One question: Are you confused by the SCT006 and the 18 A input (CT4) on the emonTx? As you’ll see from the report, the SCT006 performs very poorly and works only up to about 5 A when used with a 120 Ω burden and the CT4 input of the emonTx. It should only be used with the emonPi or inputs CT1 - CT3 of the emonTx. You don’t need the emonTx to use the SCT006.
The high sensitivity input CT4 of the emonTx is for use with the standard SCT-013-000.

Both - especially the emonPi because it generates rather more heat - should be OK in the porch, provided it’s protected from the weather. But personally, I’d prefer to have it inside if that’s feasible, if only to make it more comfortable if you need to work on it.

I have been reading the ‘Learn’ info regarding CT clamp and i am a little more with it and for my solar i would be thinking to use the standard SCT-013-000 clamp and eventually in the future connect it to CT4 input of the emonTx for higher sensitivity.

Our old geo Chorus had Tx units at the fuse box and a similar unit to the emonBase connected to the wifi hub.

So i think i will be going the same route with an emonTx (future proof capable) and an emonBase at the wifi hub. But presently the emonBase units for sale have sold out of case’s…
What case can i buy from say thepihut or elsewhere… But with the RFM69Pi add-on board not causing an issue…
Do i need a case with a fan, as the add-on board looks to occupy some of the space in the case the fan would require…

I’m not a Raspberry Pi expert, I think @borpin might need to answer this.

For what it’s worth, the RFM69Pi stands about 15 mm above the surface of the Pi’s PCB. It’s exactly the height of the RCA phone socket on my Pi 2B.

BTW, a current transformer isn’t a clamp. In particular, ferrite cored c.t’s like we use must NEVER be clamped or wedged onto the cable, or you risk snapping the very brittle ferrite core, which effectively destroys the c.t. I think “clamp” is a Chinese mis-translation, I’ve known the thing as a “current transformer” for the last 50 years, and that’s the English name for it.

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That I don’t know. Email the shop - they may be able to help.