EVSE Minimum Current for 3Phase


I have a 3 phase OpenEVSE and have been observing its Eco charging behaviours. I note that it will not start charging until there are 6A available as a minimum. Whilst I get that this makes sense for the single phase EVSE as 6A represents around 1.3kW, this isn’t the same for the 3 phase version which effectively has 3 times the supply of 6A, meaning it doesn’t start charging until I have roughly 4kW of spare solar.

I found the following post where @glyn.hudson indicates the minimum charge Amps (ESP8266 OpenEVSE WiFi V2.9.0 beta: Significant update Solar PV Divert 🎉 - #80 by glyn.hudson), but would like to ask the question if this should be the same for a 3 phase charger as there are many times where I have more than 1.3kW but less than 4kW of solar divert available and it it being returned to the grid rather than charging my car?

I appreciate I’m probably a minority with a 3 phase charger. I am running firmware currently and Wifi firmware 4.0.1


Hi Barry,

I’m afraid 6A is the lowest current that’s supported by EV’s, there’s nothing we can do to lower the current further. Your only option would be to use a single-phase EV cable to force your car to charge on a single-phase.

Hi Glynn,

Thanks for the reply, just so I understand then, the minimum charge is 6A per phase, and although if plugged into a single phase charger I could charge at 6A, by virtue of using a 3 phase charger, my minimum is in fact 3x 6A. Makes sense.

I guess my only option then is to buffer the spare solar I have into batteries (which I don’t have) and then discharge them once sufficient energy is stored at a higher rate in order to prevent the energy from going back to the grid.

Maybe a future version of the EVSE could be configured where it can dynamically switch between single and 3 phase, it could then switch to single phase in Eco mode for PV divert. I guess this would depend on the PV only being attached to a single phase… How do you go about setting up PV in 3 phase (home) systems?

That is theoretically possible but would require 4x separate 1P contactors instead of the single 4P contactor we use in 3ph EVSEs, the current openevse controller wouldn’t support this, so considerable hardware changes would be required. I doubt there is much of a use case for this because of 3ph inverters :arrow_down:

Solar PV inverters can either be single or 3ph, if the PV array is largish and 3ph is available the inverter will almost certainly be 3ph in order to comply with DNO export limits per-phase. If the PV inverter is 3ph then charging at 1x6A on L1 would not be of any benefit since the output of a 3ph inverter should be equal on each phase.

On my initial review of this Glyn, I wasn’t following and didn’t agree. But as I was compiling a response, it’s become clear.

My issue is that there are many times that I have circa 1.4kW of solar spare (6A single phase) and less than 4kW, meaning that my EV doesn’t take this charge as it needs 6A on all three phases ( > 4 kW).

However, during these times, the spare solar that I have in the range of 1.4 to < 4 kW is actually spread evenly across 3 phases and therefore cannot be supplied to a single phase of the charger. The only way to do this is to aggregate the 3 phases of energy into 1 for directing into the car somehow. Since that isn’t possible as far as I know in the AC domain (or may be possible but not simple or efficient), the only option is to store it into a DC battery bank and then have a individual single phase inverters from the batteries to the house supply (including EV charger) which can discharge at different rates across the phases as needed, thus allowing the supply to a single phase (assuming you have a charger that can switch to single phase).

But it seems completely over the top to have a charger that can dynamically switch to single phase for lower charging rates when the batteries may as well just absorb the solar at lower rates per hour and then discharge them at higher rater for a shorter period into the car if it were absolutely necessary.

I think once I have the batteries it will allow me to capture the marginal amounts of solar that I am not able to divert today and consume them wherever it suits me to maximise my self usage.

While that’s true from a physics point of view, I don’t think it’s true from a revenue point of view. Your 3-phase revenue meter will be measuring net power across all 3 phases, so even with 2 exporting (say) and 1 importing, it can still work out as no power flowing.

The classic case in these parts is a single phase inverter installed in a 3-phase house. There’s no requirement at all to ensure your daytime loads are on the same phase as your inverter - at least from a revenue point of view. From a be-nice-to-the-grid point of view, it makes sense to align them if you can, but at the low power you’re talking about (< 4kW) it’ll quickly get absorbed in the randomness of all the other consumers in the 'hood.

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I was / am never really sure how the three phase meter works, as to whether it nets the usage across phases. I would assume so as the phases don’t have individual readings, but since it’s black box to the consumer I would never know without throwing some test scenarios and measurements.

From a revenue perspective it’s still an issue albeit slightly lessened. The two phases sending back to the grid will be significantly less revenue to me, compared to the single phase consuming from the grid costs me.

Still got to look to batteries for this I think, until the grid provides true net metering including solar feedback (which I would support as it is fairer to those of us producing energy and also save the environmental costs of all these battery installations…)

Hi there Barry
Can I ask a question… I’m not sure exactly how it works, but on my i-Pace the pilot tells it to take 6A and I believe then it should pull 2A per phase. The Pilot tells the car what capacity the charger has and I’d imagine that can come from either single phase, 3 phase or DC ?

I’m not expert and have just had my 3 phase EVSE installed, but only running a single phase at the moment.

If this is not the case, I can imagine this will run havoc with the PV Divert function as it will need 3X the amount of power it thinks it has available…

Can you confirm if this is true in practice or theoretical (Pilot tells car TOTAL to pull, not per phase?)


On the question of the 3 phase metering… all meters will meter across all 3 phases for import, but not for export. The term to google is ‘polyphase metering’

Example - you generate 3K on 1 phase and pull 1Kw from each of the remaining phases - without a polyphase meter you will be PAYING for that 2Kw. With a polyphase meter you will not be.

All SMET2 meters (latest smart meters) are polyphase and net the generation regardless of phase. My older (5yrs) non-smart was not and was silently hurting my wallet when I found this out.

For my 3 phase incoming / out going metering, I look only at the total KW, I do not look per phase. This is easy for me as I have a Socomec Dirus A40 power meter hooked up on the utility talking to emonCMS via modbus, so I know my data is accurate (and the meter also deals with import/export properly).

Hi Alan.

I have a VW Id3 for reference. Max Ac charging is 11kW rather than the EVSE 22kW capability.

So I was unaware of the 6A minimum that Glynn indicated. Quite how the car or charging standards deal with this depending on single or three phase implementation I don’t know.

All that I do know is that my EVSE won’t engage until I have around 1.6kW of excess solar registering (on a single phase) and that when it does engage it consumes circa 4kW. I could have something wrong in my inputs / feeds I guess, hence my original question.

Meant to add that I have my eco mode set to monitor grid import export and have it pointed to an MQTT feed for my L1 import / export register.

Thanks Barry, that’s really useful to know, and matches what Glyn says. As usual, he’s right… the specs can’t go below 6A (as the PWM signal is considered either invalid or signals digital control needed to the car). The issue seems to be that is 6A per phase, which leaves you and I in a rather unfortunate situation.
18A = 4Kw as you say… I rarely have that available.

My i-Pace is also 11Kw.

I think using a single phase charge cable is the answer. Even with 7Kw of power (during the night) I can get quite a few miles in - 55 or so. In the winter when solar won’t be doing anything, I’ll switch to a 3phase cable so that I can get 11Kw to the car at night (probably an extra 25 miles over the 4 hours).

Its not ideal, and maybe in the next iteration of the hardware as glyn says, individually controlled phase contactors may be better. But then that’s also going to need more digital control outputs from the micro and some non-trivial software changes between the 3ph and 1ph units.

Much as it sucks, I’m going to go buy a single phase cable… (for now I only have 1 phase connected to the EVSE).

If you were clever, you could have 2 individual contactors up-stream of the EVSE and have them controlled by either a timer (come on at night) or by any other logic (power available). I may look into that…

Actually… adding an external 3 phase contactor on the supply lines to EVSE would be quite easy.
You’d have L2 & N going direct to EVSE and L1 & L3 through the external contactor, controlled how you wish…
A quick google shows them available from £40.

Not knowing anything about EV chargers… but a bit about electrical engineering, you could equally have a 3-phase and a single-phase contactor with the contacts wired in parallel - provided of course that the charger does not parallel the 3 incoming lines for single phase use. This should simplify everything - close the 3-phase contactor for 3-phase operation, and the the single-phase one for single phase use.

This thread does throw up an issue with EVSE and 3phase installs with Solar.
The current pv divert code kicks in at 6A or so, but in fact will consume 18A in a 3 phase charging scenario, causing cycling if that amount of PV is not available - as well as drawing significant KW from the grid.
@glyn.hudson You did the code change for 3phase in EVSE where the consumed wattage is X3. Is it worth doing something similar for the pv_divert on 3 phase EVSE ? This is a problem even with 3 phase inverters (which I have) as the mismatch in required watts will cause issues. Ideally this should be configurable as it will break the solution if we cheat and use single phase cables or upstream contactors…

Indeed, several ways to skin this cat… but they all involve AC power manipulation vs software bits & bytes :frowning:

While this is the case, as DBC says above, that should be irrelevant as your electric meter (SMES2) will not care. It sees all 3 phases feeding in and will balance (from a £ point) the loading. In the example above, if I feed in 6kW in my 3ph system with 3ph inverter, that is 2kW per phase. If I then pull out 6kW on only one of the phases then I’m neutral and won’t pay the power company anything. This is super important on 3 phase solar systems as you rarely have equal loads on the phases, therefore if you don’t have a SMES2 meter you will be paying for everything you import on each individual phase despite what you are exporting. In that example I will be paying the power company for 4kW of power unless I have a SMES2 meter.
TLDR; get you meter changed to a SMES2 smart meter - it’s free and will save you money (both those who only have single phase inverters on 3 phase systems and 3 phase inverters).

The correct abbreviation for kilowatts is kW.

I don’t experience a cycling issue. I monitor a single phase of my import/export, when it hits roughly 1.6kW export on 1 phase, assuming a fairly balanced load elsewhere in the house, I will actually have 4kW of energy exporting across all 3 phases. So as far I see, there is no cycling issue with it constantly engaging / dis-engaging the charge under solar conditions.

I am fortunate enough to have a 25kWp array so 4kW export is quite regular, but I am also solar diverting for swimming pool pumps / heating and other functions in the house too, so have experienced this year higher consumption, with marginal solar left which has identified this scenario.

As you say, the main issue is that with a 3 phase charger, the minimum charge rate is higher than a single phase charge, so in marginal conditions isn’t being used.

It’s a shame the cars don’t have the option to determine the level of charge they want to accept and in particular if this then impacted if it could request the power over a single phase rather than 3 phase.

I wasn’t aware there was a difference in cables where one could buy a single phase only cable. I guess as such this offers a partial solution, whereby if you never have 4kW of spare solar in the day that this cable would enable you to at least consume the marginal solar down to 1.6kW. Bit of a pain having to then swap the cable over at night if you need to top up. Although if you forget and you only have a 4 hours cheap rate window then you’re only giving up 16kWh of possible charging.

What energy tarrifs / timings do you get for cheap overnight energy currently?