New Comms Hub 🐙 - No gas 1/2 hourly readings

SuzeQStan

Sorry the MSE app is so slow tried about 10 times to post that diagram!  We had several 🐙 engineers out to try and sort the EV charger draining the solar battery and my OH had to find out this solution. 

The next to last engineer said ‘oh just move this clamp it will be fine’ but it wasn’t. Henley block required which means the charger is split off before the inverter/battery so the EV charger doesn’t register with them.

matt_drummer

Thank you @SuzeQStan

Heedtheadvice

A solid solution....

But it is much easier employing a second Current Transformer to measure and subtract the EV current in series with the ordinary inverter CT output  on the mains incomer.

EDIT not something now I recommend.

It depends upon the CT type, and usually is done by CTs in parallel ( rather than in series) and that is more difficult to get right for technical, compatibility and accuracy reasons.... and potentially can lead to a much higher and lethal shock risk in  certain circumstances. 

Two CTs are a feature of some EV chargers to take into account AC connected storage battery charge/discharge, such as in a Zappi. That is a far better professionally designed solution.....and safe!

SuzeQStan

Interesting - have you got a diagram pls? 

Heedtheadvice

I could do but an even easier solution is to feed the negative wire that feeds the EV Charger through the single CT that monitors the mains grid input positive.

The CT measures the size of the current and the direction. From the grid the live wire measures positive on the CT ( when it is fixed on it the correct way round ) usually with the CT between main fuse with the arrow pointing towards the consumer unit.

I.e. + grid current 

If it is on a negative wire such as the EV Charger then it measures -EV

The Grid supply current is the total of EV current and the rest of the property (P)

So G=EV+P measured by the CT

adding the EV negative wire and 

G=EV + P - EV

which results in P ( the property without the EV ) being measured.

I'll post diagrams of both tomorrow ,( unless someone else does first! ) [EDIT. On reflection I am not producing a diagram for the dual CT scheme on safety and feasabity grounds]

There is a technical reason ( current phase difference if there is one) that produces a small error but it will be so small to be ignored.

Qyburn

Heedtheadvice said:

I could do but an even easier solution is to feed the negative wire that feeds the EV Charger through the single CT that monitors the mains grid input positive.

Or pass the L that suppliers the EV charger through the CT, but in the opposite direction.

By the way does the slight error you referred to, also apply if the main CT for the inverter/battery is installed on Neutral of the incoming supply? That's how ours is installed, for physical reasons.

Heedtheadvice

Qyburn said:

Heedtheadvice said:

8I could do but an even easier solution is to feed the negative wire that feeds the EV Charger through the single CT that monitors the mains grid input positive.

Or pass the L that suppliers the EV charger through the CT, but in the opposite direction.

By the way does the slight error you referred to, also apply if the main CT for the inverter/battery is installed on Neutral of the incoming supply? That's how ours is installed, for physical reasons.

Quite correct re which wire to use.

Re the slight error.

It mainly depends upon the phase angles of the current being drawn by the various loads. For domestic power any out of phase ( voltage vs current) is usually insignificant but can be  a little out of phase where electric motors are involved as an example. Even with two different loads ( property in general and the EV charger)  If those are slightly out of phase there will be no material affect on the overall result.

For a single CT having it on neutral rather than live is( for a single load rather than where the neutral is combined with other loads) irrelevent as , as you will be aware, it is only direction that is affected and this is solved by reversing the ct orientation.

Re. Diagrams. I will produce one for this wiring re-routing but not for the earlier suggestion using two ct clamps. It is, on reflection  not something that I think should be done by a DIYer or basic electrician for safety and technical knowledge reasons as most CTs supplied for solar/chargers are not suitable without modifications. Those mods can in reasonable shock risk. EDIT [ that last sentence does not make sense, sorry. Perhaps better is 'attempting to modify one of those CTs may result in a severe shock risk!' .Just don't do it! ....that's a bit better!!]

SuzeQStan

Thanks @heedtheadvice - OH looking forward to those diagrams and fully appreciate the h&s warning. 

SuzeQStan

Bit confused now looking at all the edits @heedtheadvice - so there isn’t an alternate suggestion for the posted solution my OH found out online which has been working for us for a year now?

edit to add - we didn’t DIY that solution - 🐙 came out multiple occasions and couldn’t make it work without draining the solar battery.

So OH found the posted diagram solution online relatively easily and presented it to 🐙 tech on phone who sent someone out who thankfully had a bit of nous as the others quals must have been limited.

QrizB

This isn't very different to @SuzeQStan 's diagram, but uses only one set of Henley blocks and also shows the more conventional arrangement where the grid-tied inverter is wired via the consumer unit:

This is how my system is set up and it works for me.

With my particular installation it's a simple change to move the inverter CT to be before the EV charger, if I want to use the solar battery to support EV charging.