Stop and start granny charging via power lead

[Martinonline]

From the manual:

 

[gwatuk]

What I'm doing is this:

1 Ensure the vehicle is power OFF and all doors are closed.
2 Open the charging port door.
3 Connect the 7 pin charging plug to the socket on the vehicle. Lock the vehicle.
4 Connect the charging device plug to the domestic electricity supply.

Slightly different.

So I just tried to do what the manual recommends and this happened:

1 Ensure the vehicle is power OFF and all doors are closed.
2 Open the charging port door.
3 Connect the 7 pin charging plug to the socket on the vehicle.
(And after a few seconds...)
The vehicle locks itself.
4 Connect the charging device plug to the domestic electricity supply.

 

[Martinonline]

The car will lock itself again after 30 seconds if no driver/passenger door is opened. You could experiment again with opening a door to see if it makes any difference. If not then the car is saving the trouble of locking the car.

 

[siteguru]

When using the granny lead my process is this:

1. Park up
2. Open charge port door
3. Plug granny into car
4. Plug granny into extension lead (usually)
5. Plug extension into mains and switch on
6. Switch on at the extension
7. Car will make noises and lock the granny into the car port
8. Press lock on keyfob to lock the car
9. Check all is charging OK then go get trolleyed (as I'm usually down at my cousin's when doing this)

 

[Everest]

When the Shelly relay switches on the granny charger doesn't respond for 6 seconds, it then draws 7.3 watts for exactly 8 seconds and then draws the full 2.16 kW.

That's interesting and good to know.

There was me thinking the granny lead was a simple 3-core length of wire!

To me it looks like the granny charger handles everything quite gracefully.

But what about disconnecting - I think that was the point @Coulomb was telling me earlier. If your Shelly just disconnects the AC supply, what does the MG4's inverter do then (apart from stress its snubber circuit / varistors)?

(But perhaps @Everest likes a challenge )

I'm always up for a challenge all I will want to do until getting a proper OpenEVSE set up is to switch on and off 10A charging during the day, without destroying the (yet-to-be-purchased) MG4.

@Martinonline - interesting thread-within-a-thread... all good info. But am puzzled about having to lock the car to charge - presumably that is just for 'granny' speed charging? If one is out and about, I'd want to sit in the car when it's being charged, not stood out in the cold?

 

[gwatuk]

...But what about disconnecting - I think that was the point @Coulomb was telling me earlier. If your Shelly just disconnects the AC supply, what does the MG4's inverter do then (apart from stress its snubber circuit / varistors)?

I don't know.
But surely the effect on the car is the same as when someone is charging at a commercial charging point and they return to the car while it's still charging and they tell the charger to turn off.
(I'm assuming that's possible, but I don't have much experience of this, I always charge at home on my little old granny charger.)

 

[Everest]

But surely the effect on the car is the same as when someone is charging at a commercial charging point

No experience either, but I wouldn't have thought so. If you tell the rapid charger to turn off, it will surely do its comms thing first and stop charging. I don't think there will be 350A at 400V flowing thought the cable as you pull it out. Nice fireworks if there is.

 

[gwatuk]

When using the granny lead my process is this:

1. Park up
2. Open charge port door
3. Plug granny into car
4. Plug granny into extension lead (usually)
5. Plug extension into mains and switch on
6. Switch on at the extension
7. Car will make noises and lock the granny into the car port
8. Press lock on keyfob to lock the car
9. Check all is charging OK then go get trolleyed (as I'm usually down at my cousin's when doing this)

Aha - breaking the rules, you missed point 1:
1 Ensure the vehicle is power OFF and all doors are closed.

 

[Everest]

Oh... Is there any 'protocol' used when granny charging?

Perhaps protocol is a little strong, but yes even "dumb" EVSEs have to implement the control pilot: the ±12V square wave of suitable duty cycle (representing max allowed current), and it must not enable the contractor until the car signals readiness by changing the amplitude.

Ah! Whirr, Clunk.. brain going a bit slow here today... Right, got it now. There actually is nothing different between granny charging and EVSE AC charging - apart from the current draw

Just looked at your link thanks... where the image shows the duty cycle settings, do you know if these are the only possible fixed currents, or is it completely analogue depending on mark-space ratio?

e.g. would a duty cycle of 15% trigger the car to charge at 9A? Guess not as 40A is not half the duty cycle of 80A.

 

[DixieTGS]

@Martinonline - interesting thread-within-a-thread... all good info. But am puzzled about having to lock the car to charge - presumably that is just for 'granny' speed charging? If one is out and about, I'd want to sit in the car when it's being charged, not stood out in the cold?

I don't lock the car while charging quite often - you can then check how the charge is progressing without the charge stopping and restarting when you unlock the door. But I do have to lock the car when starting a scheduled charge.

 

[Martinonline]

@Martinonline - interesting thread-within-a-thread... all good info. But am puzzled about having to lock the car to charge - presumably that is just for 'granny' speed charging? If one is out and about, I'd want to sit in the car when it's being charged, not stood out in the cold?

The instructions heading was 'Residential Charging' which I assume includes wall box EVSEs as well as granny charging. I have sat in the car when granny charging - when I was trying to catch the elusive 'Balancing' message. When out and about charging AC or DC I often sit in the car; you don't have to be outside. Perhaps MG are hedging their bets in case something nasty happens.

 

[siteguru]

Aha - breaking the rules, you missed point 1:
1 Ensure the vehicle is power OFF and all doors are closed.

I've never done that ... I always follow the process stated. Even when using my 7kW EVSE I never turn the car off first.

 

[DixieTGS]

would a duty cycle of 15% trigger the car to charge at 9A? Guess not as 40A is not half the duty cycle of 80A

Up to 80% 48A it looks linear, so for your example it looks possible. After 80% it looks like they tried to squeeze in a much bigger current range in the last 20% so it's non-linear.

I have a feeling you might be going to find out .

 

[siteguru]

Ah! Whirr, Clunk.. brain going a bit slow here today... Right, got it now. There actually is nothing different between granny charging and EVSE AC charging - apart from the current draw

Just looked at your link thanks... where the image shows the duty cycle settings, do you know if these are the only possible fixed currents, or is it completely analogue depending on mark-space ratio?
View attachment 34151

e.g. would a duty cycle of 15% trigger the car to charge at 9A? Guess not as 40A is not half the duty cycle of 80A.

Looking at the chart, each 10% increase in duty cycle equates to 6A increase in charge current, all the way up to 80%/48A. Thereafter it changes. (i.e. 60% duty cycle is likely to be 36A, with 70% being 42A).

Edit: as per above - @DixieTGS typed quicker than me.

 

[Everest]

Only wondering out of fascination. It could be that 5% to 15% charges at 6A, 15.1% to 25% charges at 12A etc. .

Not that it really matters, the 6A to 30A range in steps of 6A would work for us. That's from approx. 1400W to 7000W in steps of 1400W, so I can match the charge rate against home usage and solar production with the battery helping as a buffer between those values.

 

[gwatuk]

I don't know.
But surely the effect on the car is the same as when someone is charging at a commercial charging point and they return to the car while it's still charging and they tell the charger to turn off.
(I'm assuming that's possible, but I don't have much experience of this, I always charge at home on my little old granny charger.)

No experience either, but I wouldn't have thought so. If you tell the rapid charger to turn off, it will surely do its comms thing first and stop charging. I don't think there will be 350A at 400V flowing thought the cable as you pull it out. Nice fireworks if there is.

So I've convinced myself that what I'm doing is OK when starting the charge, but I also often stop the charging process while it's running (by disconnecting the granny charger from the mains).
Can anyone see a problem with this (although it's not the ideal thing to do)?

 

[Everest]

Can anyone see a problem with this

The issue is what @Coulomb pointed out to me in post #5 above.

 

[gwatuk]

The issue is what @Coulomb pointed out to me in post #5 above.

Thanks for that, and apologies to @Coulomb for not paying attention to it.

However I think I may be able to solve this problem.
The Home Assistant system enables me to open and close the car doors.
When the car is charging opening the doors stops the charge - I can see that the current going into the granny charger goes down to 1.5 watts for 40 seconds and then returns to the full 2kW (I think this is the car re-locking itself).
So if I open the doors, and then make the Shelly relay turn off power to the granny charger then hopefully all should be well.
(Need to do some more research.)

Another solution would be to always charge to 100% (it's an SE SR).

 

[ReintjeWA]

I don't lock the car while charging quite often - you can then check how the charge is progressing without the charge stopping and restarting when you unlock the door. But I do have to lock the car when starting a scheduled charge.

I thought you had to lock the car to lock the charger in place? Then once you’ve started charging you can unlock the car again and wait inside if you want.

To be fair the dealer told me this is how it’s supposed to work and they also said you can’t get in while charging which was clearly inaccurate, so maybe they were wrong about having to lock in the first place

 

[DixieTGS]

There have been a lot of different sequences people use to get charging to work reliably over the time I've been on this forum, so it seems likely that different models or firmware versions have slightly different behaviours. Also different EVSE's could play a part too such as the issues with my 3rd party granny not working for schedules over 12 hours in the future.

I guess the bottom line is if you're having problems, find a way which works for you and stick with it regardless of what others or the manual says to do.