Stop and start granny charging via power lead

[Everest]

Will the MG4 automatically start charging when power is applied via a 'granny' lead or does something have to be set within the car to initiate charging?

If the latter, is it possible to stop and start charging simply by switching the power to the granny lead off and back on, without having to do anything in the car?

Reason for the question is, I am thinking when I get the car and before I install an EVSE, can I just control charging by automatically switching the power socket? I will want to do that to limit power drawn by the car from my inverters depending on other house loads.

 

[Martinonline]

I think it might be better to use the App to control the charging.

 

[DixieTGS]

Assuming you're not inhibited by a schedule or 80% limit etc, simply plugging in and switching on at the wall has been faultless for me irrespective of whether the car is locked or not, possibly also when the car is still on.

For turning off I always stop the charger by unlocking the car or via the app first. This is to save unnecessary wear on the switch contacts which will have 10A running through them.

 

[Everest]

I think it might be better to use the App to control the charging.

Yes, but I don't want to use the app for security / privacy reasons. But unfortunately that wouldn't be practical as the power may switch on or off many times a day depending on solar production and house usage. e.g. turn off car charging when washing machine starts heating up etc.

Assuming you're not inhibited by a schedule or 80% limit etc, simply plugging in and switching on at the wall has been faultless for me irrespective of whether the car is locked or not, possibly also when the car is still on.

That's great - sounds as though just applying power will do what I want then.

For turning off I always stop the charger by unlocking the car or the app first. This is to save unnecessary wear on the switch contacts which will have 10A running through them.

I'd use a contactor for the switching.

 

[Coulomb]

If the latter, is it possible to stop and start charging simply by switching the power to the granny lead off and back on, without having to do anything in the car?

Stopping the charge mechanically (including by relay contacts) is brutal in the switch/relay contacts and also on the on-board charger. The first part of the AC->DC conversion process is a boost converter, which starts with a hefty inductor. When you interrupt the AC power mechanically, the inverter produces an enormous (multi-kilovolt) potential to try and keep the current flowing. There are movistors in the on-board charger to absorb transients, but they lose a little effectiveness every time that they absorb energy.

Terminating the charge electronically allows the inductor to discharge its magnetic energy into capacitors and partly into the HV battery. Residual capacitor energy is bled off slowly and safely.

It's a pity, because switching the input AC feels natural and is convenient.

 

[DixieTGS]

I should add that I had the devils own job working out why scheduled charging only worked occasionally. It turns out my 3rd party granny with a 10m lead only waits for a charge to start for exactly 12 hours, then gives up completely. This meant test charges always worked, but proper timed charges maybe would or maybe wouldn't (especially if i forgot to lock the car).

I assume the MG granny doesn't have this issue, as using the schedule may also be a way to do what you need.

 

[Everest]

Terminating the charge electronically

Can I terminate the charge via a CANBus message?

 

[JohnV6]

I use a clamp on the main power in/ out cable that works a switch . This switch ensures when my PV panels start to export it goes first to heating hot water. I believe you can have multiple switches so you could feed the charger when exporting.

 

[DixieTGS]

Also look to see if the home automation stuff can start/stop charging.

 

[Everest]

I believe you can have multiple switches so you could feed the charger when exporting.

Also look to see if the home automation stuff can start/stop charging.

Yes, these thoughts are exactly what I would like to do, before I install an EVSE.

 

[gwatuk]

I use a Home Assistant automation to control charging our car with a granny charger. It switches the power to the granny charger by controlling a Shelly relay (Pro 1PM) which has various protection systems. I've been using this for about six months without any problems. The Shelly relay can also be controlled with an app.

Shelly Pro 1PM | Shelly Store UK | Smart Home Automation

Purchase Shelly Pro 1PM from the only Shelly authorised reseller in the UK. Shop Wi-Fi smart home automation now!

shellystore.co.uk

 

[Coulomb]

Can I terminate the charge via a CANBus message?

Sure, if you can get the message into the car, and know the CAN bus details. That counts as electronic charge termination.

 

[Everest]

know the CAN bus details

is that info published somewhere?

 

[Coulomb]

It switches the power to the granny charger by controlling a Shelly relay...

Unfortunately, this is a mechanical interruption. You are slowly killing the movistors in the on-board charger, as well as hammering the contacts on the Shelly's relay.

I forgot to add that if the Shelly or any other mechanical interruption is on the control pilot signal, then that's fine, as it causes electronics in the car to initiate an electronic charge termination. That requires you to get inside your EVSE, and of course many people prefer not to do that. I get the feeling that @Everest would be happy to, am I right?

 

[Everest]

Unfortunately, this is a mechanical interruption. You are slowly killing the movistors in the on-board charger, as well as hammering the contacts on the Shelly's relay.

Makes sense.

I forgot to add that if the Shelly or any other mechanical interruption is on the control pilot signal, then that's fine, as it causes electronics in the car to initiate an electronic charge termination.

Brilliant - there's the answer then. I didn't realise the granny cable used the control pilot signal. So, disconnect pilot signal with a low power relay and then few seconds later, disconnect the AC via a heavy-duty contactor - or possibly even a Triac.

That requires you to get inside your EVSE, and of course many people prefer not to do that. I get the feeling that @Everest would be happy to, am I right?

Oh yes... no issues with that.

 

[Coulomb]

[ CAN bus details ] is that info published somewhere?

I'm not aware of a charge termination message, unfortunately. It might be worth checking information from the Slack group working on OVMS. They have a lot of that sort of information. Some of it might be on this forum, but it's tricky to find. I haven't been active on the Slack group for months.

The invitation to join the slack group is in one of the early poster's signature. I think RES is in his username, sorry for the vague information. I may find time to hunt down the details.

 

[Coulomb]

So, disconnect pilot signal with a low power relay and then few seconds later,

Yes. Though it may be better to use a changeover relay, and change over to +12 V. The EVSE will have +12 V available somewhere, as that's part of the protocol. This may only be important if you want to pause the charge (e.g. big load or cloud), otherwise the car may decide that protocol has been violated and throw some sort of error.

I do this in my Franken-EVSE.

 

[Everest]

The EVSE will have +12 V available somewhere, as that's part of the protocol.

Oh... Is there any 'protocol' used when granny charging? Thought it was just AC or no AC . Hence why keen on your pilot signal idea. My idea for this thread is just for a temporary solution - once I have got an OpenEVSE installed, then I should be able to control charge rates via MQTT (I hope).

 

[Coulomb]

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. The EVSE should also perform the "diode check", although some EVSEs seem to regard this as optional.

The page below is a little American centric, but the control pilot is identical in Type 2.

Basics of SAE J1772

Introduction Basics of the J1772 standard. Charging Voltage Max Current Level 1 (L1) 120VAC 16A max per J1772 Level 2 (L2) 208 - 240VAC 80A Pilot Max Current Duty Cycle Max Current < 3% Error 3% - 7% Digitial Co...

openev.freshdesk.com

 

[gwatuk]

Unfortunately, this is a mechanical interruption. You are slowly killing the movistors in the on-board charger, as well as hammering the contacts on the Shelly's relay.

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.
So I don't think the relay contacts are getting hammered.
(And the relay has temperature, overpower, and overvoltage load protection.)

To me it looks like the granny charger handles everything quite gracefully.
But maybe there's some guidance in the manual that says plug the granny charger into the mains before plugging it into the car?

(But perhaps @Everest likes a challenge )