Low Speed charging rate variable

[JonE]

I have a 7kW wall charger. Sometimes when I plug in my MG4 LR it charges at 6.8kW but other times it chooses 3.3kW. It seems quite random. Once it has decided on the lower rate no amount of plugging in / out / restarting the charger etc. will change its decision. On the dash it is set to "maximum" charge rate. Has anyone else seen this?

 

[Martinonline]

Are you sure it is random? What limit has been set for the battery level? Does the 3.3Kw occur when nearing the charge limit?

Note, Posters have reported the charge level changing, usually upwards, but other events may occur.

 

[Jomarkh]

Do you have an EVSE with load monitoring which is see extra load coming from the house?

 

[JonE]

Are you sure it is random? What limit has been set for the battery level? Does the 3.3Kw occur when nearing the charge limit?

Note, Posters have reported the charge level changing, usually upwards, but other events may occur.

Yesterday when this happened the car was at about 70% when I started so I don't think so.

Do you have an EVSE with load monitoring which is see extra load coming from the house?

Well I was taking advantage of Octopus Energy "power up" which gives free electricity for 2 hours so the consumption on my house would be high as I was also charging my solar battery etc. But I can't see how the EV charger would have known this? As far as I know it doesn not monitor overall consumption of the house.

 

[Surfdog]

If you are on an Octopus tariff then I presume you are using an Ohme charger. Then power fluctuations are quite normal during smart charging. The amount of power supplied through the charger will vary depending on amount of electricity available on the grid. For past 2 months all my charging session have all been at 7.4kwh from the moment I ask for a charge, even during peak times. Prior to this, Octopus would calculate a variable smart charge schedule, mostly during off peak hours with varying rates if charge.

 

[JonE]

I wish I had an Ohme but I have a brain-dead BP Chargemaster unit which was installed a few years ago before I switched to Octopus and before I had the MG4.

I have found that the car charges consistently at 7kW during the night and 3kW during the day. If I look at the grid voltage through my PV system data I see that the grid voltage is 240-245 at night and 230 - 235 during the day. So I assume this is why the rate is being limited. My question is: "Does the charger determine the rate or does the car?" I assume this is agreed during the intial negotiation between the two. If it is the charger I will buy a new charger but I don't want to spend that money and find it makes no difference. Does anyone know?

 

[DrAndyPerry]

I've just caught mine doing this (MG4 XPower). It's really annoying, cheap electric and we're trying to charge up both of our cars. Mine is holding out at 4kW... grrrrr

 

[JonE]

Yes, it is very annoying - we have Octopus "powerups" which provide 2-3 hours of free electricity during the day from time to time. I want to charge the car at max. In the end I replaced my charger with an Ohme one which improved things a bit but I still never get 7kW during the day. Usually around 5kW but last week it was only 4kW. I always get 7kW at night. My assumption is that either the charger or the car is assessing the supply (by voltage or frequency or both) to determine if it thinks the supply is in danger of being overloaded. If so it reduces its demand. Just a theory.

 

[Martinonline]

Does Octopus have access to your EVSE? (eg, via its sim.) And if so could Octopus be controlling the power.

 

[Checo]

I'm not sure if there has been anything closer to a conclusion on this, but I have noticed a related issue several times, including today. On the AC charger at work I connected this morning with about 36% charge and it was happily charging at the normal 6.4 kW, as expected. I checked occasionally using the iSmart app and it stayed there for at least an hour, before dropping to 2.9 kW and then holding out at 3.0 kW for the rest of the charge (lots of hours!). The change occurred when it was probably still only around 50%.
I've seen this before and also seen a full charge at 6.4 kW. I can't help wondering if it is temperature related, as the weather here is warming up during the day.

 

[DBedford]

It could be the charger is programmed to reduce current delivered after a set time!

 

[siteguru]

Was it a dual bay charge point with two ports? If yes then maybe someone else connected to the charge point and so it shared the capacity between both cars.

 

[Checo]

No, just a single charge point. Perhaps it is something to do with the charger, but it's very hard to get any information about it. At other times I have definitely had it do a full charge without a reduction in current, so I think it's more likely to be the car doing the limiting.

 

[Coulomb]

If you're looking at the charging screen in the car, note that the reported power is the net power into the traction battery after losses, 12 V loads via the DC-DC, and HVAC load. Now that the temperature is warming up in Brisbane during the day, you probably have the air conditioning left on. Try just toggling off the air conditioning using the switch at the left; depending on the air conditioning settings, this can affect the net power into the battery by several kilo watts. Just a possibility.

I wish that there was an easy way to see what power the car is drawing from AC, as this should roughly match what the EVSE is rated at, less a few tens of watts lost in the cabling.

 

[siteguru]

HVAC shouldn't be on if you're out of the car and the car is locked (unless you've activated remote HVAC via the app, which I don't think @Checo has).

 

[ReintjeWA]

HVAC shouldn't be on if you're out of the car and the car is locked (unless you've activated remote HVAC via the app, which I don't think @Checo has).

I don't know what Brisbane is like, but a lot of chargers in Perth end up in industrial estates, away from anything interesting. I think North of the river here in Perth there are only two shopping centres that offer EV charging, and as far as I know, none of the supermarkets. I often end up just sitting in the car and going over work stuff or something else, after having a stroll in the local area. And so I run the AC while charging. To be fair, this is also one of the reasons I opt for DC chargers more than I should I guess.

We could really do with some better distribution of chargers around here.

 

[Coulomb]

HVAC shouldn't be on if you're out of the car and the car is locked

Yes, but my thought was that to check the charge current, he trundles out to the car at lunch time, sits on the seat to look at the charging page, and that triggers the air conditioning to come on to the setting it was when he parked. He's not tempted to turn off the A/C as the car is still quite hot.

You've just made me realise that possibly he's checking the charge current via the app.

@ReintjeWA , @Checo has said that he's charging at work. Now that I checked this, I see that he's also checking the charge current via the iSmart app. Sigh. So unless he's using that app to turn on the air conditioning (seems pointless), my theory is shot.

 

[ReintjeWA]

@ReintjeWA , @Checo has said that he's charging at work. Now that I checked this, I see that he's also checking the charge current via the iSmart app. Sigh. So unless he's using that app to turn on the air conditioning (seems pointless), my theory is shot.

Oh yeah... fair point lol

 

[Checo]

I've been checking remotely with the app, with the car locked and everything switched off. There are six independent chargers in the carpark and they are definitely capable of 6.4 kW, since that is how it normally starts. One thought I had was that perhaps when they are all in use the total current is being limited, so they might all slow down. Hard to test though.
On a related note, how is the current limited? The only way I can think that the charger can do it on its own is to drop the voltage a lot, but that can't really be it. Does the charger tell the car to back off?

 

[Tig170]

Around the world we all have ever so slightly different charging regimes. We pass everything through the battery, so want a slower rate such that everything in the house/car/ heat pump is less than 5kW (otherwise the unit rate from the grid is 3 times higher) - so in my view just set it to a lower charge rate (in our case this is done via the electricity company/EV charger) each (of every few) days