EVSE Minimum Current for 3Phase

Ah… so you have 3ph inverter but only metering a single phase of it’s generation… hence why it’s not cycling. You also have a largish system. Mine is 7kW, with a 3ph inverter and all phases count in my utility monitoring.

I use Octopus which gives me 7.5p per kWh between 00:30 & 04:30 and have a schedule set in EVSE accordingly. However, because I’m such a tight wad, in times of solar I may disable this and get the car charged on free electricity as much as possible over days as opposed to paying for at night. In the winter, the process will invert (as much as possible in the 0030-0430 window).

I’ve been thinking on how to solve this problem, and maybe @glyn.hudson or @jeremypoulter can weigh in.

If you changed the contactors in the system to 2 x 2pole instead of 1x 4 pole, this would first, give you commonality of parts.

In the 3ph system, both are operated by the same signal from EvSE board, but the one that would have L2&L3 on would have a Normally Closed relay on it. This means, unless commanded otherwise it would be engaged and we’d be feeding 3ph to the car.

Now, in times of PV divert, the relay could be commanded open by a spare GPIO on the Wifi board, and the car would PV charge single phase. Of course, this could be configurable.

To my simplistic mind, this is a simple change to make and would allow much more excess solar to be used. What do you think ?

Not really. I am metering all phases of it’s generation and a whole bunch of other stuff. The key difference, and the reason your EVSE is cycling is that the PV Divert setting is built to work with a single phase reading, so I have set my EVSE Solar PV divert feed to use only 1 of the phases import / export registers

So by you using your 3 phase solar excess as the feed to the PV Divert in the EVSE you are telling the EVSE you have say 2kW Export (albeit over 3 phases), so it determines more than 6A is available and starts charging the car. As per Glynn’s explanation, it’s 6A per phase minimum, hence the EVSE supplies around 4kW to the car, causing your Import / Export to go back to an Import state and cause it to cycle. If you change the PV Divert setup in the way I have explained you will have less cycling and a closer tracking of solar charging to solar generation. But you will of course be limited to charging when you have around 4kW excess. If that’s not very likely then you will be better served switching to single phase charging and leaving your solar PV Divert configuration as is. The net metering situation would then cover the imbalance on the phases hopefully.

I didn’t realise Octopus was still as cheap as 7.5p overnight (albeit for only 4 hours). I have a standard economy 7 tariff from Scottish Power currently, so around 18p I think for 7 hours of overnight energy. Bizarelly, 4 hours would be enough for me even in winter as I could put 44kWh into the car in that time, since my Id3 is 58kWh and I tend to stay between 10 and 80* SoC, the 70% charge that I supply is only just over 40kWh. Having said that, as a significant user of electricity, I am looking to put around 30-50kWh of power into batteries overnight for daytime usage so maybe I will need that 7 hour window! :slight_smile:

Im also trying to be as tight as I can. I have my some automations in place to change my cars target SoC in the cheap electricity window to 40% and 80% during the day. In tandem with this, the automation sets the EVSE into normal mode during the E7 window and into Eco mode for the rest of the time, so if I leave the car plugged in, it will only charge from solar, but if we don’t get enough, it will top to 40% using cheap electric regardless without intervention which is handy.

If your advertised solution about the contacts was viable that would still be interesting (although the batteries would negate it if I get them), especially if I could use further automation to manage the switch between single and 3phase based upon energy availability. That said, I’m not sure if the car can tolerate that changeover dynamically, or if it would require a stop and start of the charging process, or worse still, need to be unplugged and replugged…

Yes, I wouldn’t advocate switching while charging… that’s likely to cause issues.

For automation of loads, I have some of these: https://shop.openenergymonitor.com/wifi-mqtt-relay-thermostat/
They can be controlled via MQTT and/or inbuilt schedules.
One of them controlling a contactor would work as a poor mans solution.

If your three-phase inverter is outputting 1.4kW, this is only about 2A per phase so not enough to charge an EV, even if the charge point could be set to only use a single phase.

Correct, battery will be a great solution.

But the point being, if I could enable it as a single phase charge at 6A, I would not pay for this due to net metering and the car could be charged. eg, take the 2A from the 1 phase, draw an addition 4A on that phase from the grid, but not be charged for it because it would be offset by the other 2 phases of 2A spare energy which will net off at the meter.

It’s not a solution that I want to chase down, as I think there is too much complication in either having to change charging cables or getting the car / charger to switch between single and 3 phase charge modes. But theoretically, it’s a window of free solar energy that 3 phase EVSE users are not able to make use of.

If your PV inverter is outputting 1.4kW across 3 phases, and you manage to find a way to pump 1.4kW down a single phase into your EV, then you are charging it for free. That’s how bi-directional 3-phase meters work. They are constantly doing a signed sum of the energy over each of the phases. If the result is positive it gets added into your import register, if it’s negative it gets added into your export register. If it’s 0 as in this example, nothing gets counted.

Yes, it’s messy, but it also seems a shame to invest in more batteries (and presumably inverters) when you have a perfectly good battery in your car willing to soak up the excess rays.

Ah fair enough, I’m not totally sure exactly how net metering works on 3ph, you may want to double-check this theory is correct. But you’re probably right, I’ve heard others mention this, seems rather strange the DNO would allow this. In that case the easiest option is just to use a single-phase T2-T2 EV cable, you could even get a cheap 16A one.

I guess the alternative would be to effectively have 3 single phase meters, each with their own import and export registers. So the meter reader comes away with 6 numbers instead of 2, and then they could decide how to add them up and charge you accordingly. I’m not aware of anywhere that operates like that, but maybe it exists.

A very common scenario here is single phase PV on a 3 phase house. There’s no need at all for the homeowner to try to match their loads to the phase the PV is connected to (unless they’re trying to be kind to the grid).

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Neither am I! :slight_smile: But others seem quite confident.

In fact I am a little surprised, given that if they did have 6 registers they would be pounds in, because of the difference between the buy and sell price for consumers…

Personally I think they should be netting the whole import/export piece, with maybe a small charge per netted kWh for transport costs to cover the infrastructure. That way, instead of people having to spend money on batteries to help with the energy crisis, they could focus on generation technology rather than storage which would be a better environmental result also.

Never heard of it in the UK, but they have started it in Romania (have a pal out there) and I believe they may do it in some other European countries currently too (albeit for a fixed length of time, something like 10 years). If they did it here I wouldn’t need to drop a large sum of money on batteries. Knowing my luck they will announce such a feature shortly after I’ve emptied my wallet!

OK, after a bit more googling and re-reading @alandpearson 's replies above, maybe I’m only confident that’s how it works in Aus - which is not much use to you. Metering in the UK seems a bit more ummm… ad-hoc.

As well as Alan’s warning above, I came across this link.