OpenEnergyMonitor Community

Before the beginning

Looking to purchase EmonPi but I want to monitor 3 CT ccts. Home is a single phase UK supply. I have a 3kW Solar system installed (16 Panels) plus a Solar Boost. I am keen to monitor the power usage of the house and the power generation of the Solar panels, plus when the Solar Boost is active. My assumption is I need an EmonPi and a an EmonTx, is this correct? if so how far can the Tx be separated from the EmonPi? The house is also CAT5e cabled so could connected them directly. I’m just trying to get the correct hardware to get started on my monitoring journey. If this has been covered before then my apologies to all.

Welcome, Jim, to the OEM forum.

There’s no need to apologise for checking before you buy. I’d much prefer that to have you distressed because you have the wrong kit.

Your question “how far can the Tx be separated from the EmonPi?” makes me wonder whether there’s something you haven’t mentioned - the physical placing of your 3 c.t’s. The distance over which the radio link can operate depends quite a lot on what’s in between - foil-backed insulation or thick stone walls will severely attenuate the signal. If there’s a clear line of sight, 30 m isn’t a problem, and it’s said that 100 m is possible, though I can’t confirm it.

If you think a radio link is not viable, then you could look at a serial to Ethernet adapter for the emonTx and use your cabled LAN to the emonPi - assuming you’ve separated them because the places you need to monitor are some way apart.

Is that the case? Because if the answer is a no, and your 3 c.t’s are roughly in the same place, then you don’t want an emonPi, you want an emonBase instead. That’s effectively the same but without any energy monitoring and the LCD display, so significantly cheaper.

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Thanks for your reply I will want to monitor my energy usage so perhaps EmonPi is the way to go. Currently the Solar boost is in the loft and the Consumer unit is under the stairs, so I had not worked out if it is necessary to place the CT for it on the source or load side (or even both!). I do have an option to move the solar boost within reasonable distance of the consumer unit, a small job but a nuisance. My objective like most people is to understand the usage, record it and make informed decisions for energy usage and possible storage. This is a great start to my adventure!

The point is, where do the PV feed and the Solar iBoost connect into your system? Because if you want to know separately what the powers/energies they contribute or use, you have to get at the wiring and be able to separate out a single conductor before they get to a point that’s common to other appliances. So if the iBoost is connected to the upstairs ring main for example, you need to get at it downstream of the plug or fused switch supplying it. The safe answer to “which side” is the supply side of the iBoost - because at least one make of diverter appears to feed the immersion heater d.c., and c.t’s don’t work on d.c. (Nor does any transformer.) You’re wasting money putting one on both sides, because the power absorbed by the control unit itself will be only a few tens of watts at the most.

And the same goes for the PV infeed.

Robert thanks again. I will check this out but I can get to the power of the Solar boost on the supply side and arrange for a single core. All of these cables are within easy range of the consumer unit. The Solar boost is in the loft but takes its power from the immersion supply. I only need to double check the PV connections then I think I’m good to go ahead. Noting other posts I shall get the 20A c.t for the Immersion circuit as it is only 13A, that should give me more accurate readings.

If you do that, you must be prepared to modify the emonTx (or emonPi) because the YHDC SCT-013-020 20 A c.t isn’t a “proper” c.t. - it has its load, or properly the “burden” resistor, inside its own case - which would be OK but for the fact that there’s a burden in the emonTx or emonPi already, and you must not have two.

If you can unsolder the burden on the channel you use, that’s OK. If not, get the 100 A c.t. that has the 50 mA output, rather than the 1 V output (that’s how you tell the difference).

Channel 4 of the emonTx has a higher value burden fitted as standard, giving it a 0 – 16 A working range, so that is immediately suitable for measuring 13 A with a 100 A c.t.

[Edited to clarify: SCT-013-020 is the voltage-output c.t.]