Charging house battery with MG4?

[kirst777]

I currently live off grid with a tiny house and use a 1600W array with a 10kWh lithium battery. I live in North East Victoria (Australia) so during the summer I have more than enough power but in winter I need to top up with a generator.

I’d really like to get an EV and top up from the EV and ditch the generator. I can charge the EV at local public charging stations - my array is too small to charge the EV. I know the MG4 does V2L but I also know the voltage is closer to 220 V than 240 V. I’d really like to know how well this arrangement works before I buy but I live in a country town with no EV rental companies nearby. My nearest MG dealer is 1.5 hours away. I did visit the dealer and plugged a hairdryer in with an energy meter which is how I know the voltage is a bit low. Some others have reported this online also.

Has anyone tried to charge a house battery from the MG4? Were there any issues?

 

[decrep]

I'm planning to do it in the near future, but don't have any expertise yet.
I think there are problems with earthing, but there are workarounds.
Yes, there are a few threads here from people who've done it.

This one from Terry, is a bit different and more than you need, but he's one of the relevant experts.

Thread 'Converting a non working V2L to a 7kW supply from my MG4'

May 27, 2025

First, apologies but I copied and pasted this here from the AEVA forum Converting a non working V2L to a 7kW supply from my MG4 - AEVA Forums cause I doubt I could get it right a second time, I had to redo it some many times to get that one sort of readable

This is not intended as a guide or instructions on how to make a 7kW V2L on the cheap, this is just how I did it. If anyone chooses to follow this path, it's on you to do it safely and on your head if it doesn't work out as intended and becomes an electrical hazard ..... you have been warned...

• T1 Terry
• 7kw mg4 supply v2l working
• Replies: 2
• Forum: MG4 Upgrades & Accessories

• 
• 

If you search here for charging house battery from car, you should find a few threads.

Apparently the low voltage isn't a problem.

 

[T1 Terry]

Welcome to the forum. What voltage are your house batteries and what brand inverter do you have?

The Victron Multiplus and Multiplus 2 series have a low input voltage parameter setting that will handle down to 195 VAC, I know it charges the battery down to the 195 VAC and I believe it passes that voltage through .... judging by the length of time it takes the boil the kettle and cook toast.

The mains voltage in the Mannum area I'm in, must be tapped low to allow all the solar in the area to be absorbed into the grid, but on a cold evening or morning, before the sun starts to achieve much as far as rooftop solar, the grid voltage will drop below the 195 VAC threshold and the inverter will drop the mains supply and just run in inverter mode only.

The V2L adapter I modified and a 2.5mm² conductor 10 mtr cable holds the voltage up at 220 VAC, even with the rooftop rattler air con on heat cycle, the microwave running, the air fryer in full swing and still boil the kettle in a satisfactory time frame ....... while loading the system that high, the inverter dials back the battery charging rate, until the load reduces, then it returns to being a battery charger at a good rate, 95 amps in our case because the house battery is a Sodium Ion 12V 600Ah system and we programmed the max charge rate to 100 amps, up to 1.4kW, to leave plenty available for house power before the upper limit we have set at the moment of 3kW.

I'm happy to guide you through any set up issues you have, if you want me to, I did this stuff when T1 Lithium was up and running, but I've retired now, so avoid the hands-on work like the plague

A good source for an MG4 EV battery set up, is to find a total write-off @ Pickles auctions. Plenty of info on here regarding getting unbricked ( After a frontal or serious side collision that activated the air bags, the main battery is isolated ... bricked just seems to be the term that caught on) and it will supply you with a heap of spares for your MG4 if you chose to buy one later on.

T1 Terry

 

[kirst777]

Thanks for your replies. I believe my house batteries are 48V and I have a Victron Multiplus II 3kVa inverter. Your reply, Terry, has prompted me to reach out to my Victron dealer, Commodore, and ask them the question - I had not thought to do that!

 

[wattmatters]

See this test of using my MG4 V2L to charge our off-grid home battery using one of those cheap AIO inverter charge controllers.



The AC input voltage being on the low side is not an issue for these units, as long as it's in spec.

We've since moved home and I'm not using the off-grid system at the moment. I'm kind of hopeful I'll be able to use the V2L as generator input direct to my new system. It's not full operational as yet so I can't say.

I had used this a number of times as a supplemental charge source during long grid outages. Most I drew was 22 kWh one afternoon and night.

 

[T1 Terry]

I had to plug the MG in this morning. No idea what went wrong during the evening/night/early morning, but the air con wouldn't turn on and the battery was down to 11.45v It is recharging at 90 amps now, give or take half a brick with other loads pulling the charge rate down for a bit, but the MG is putting out 4kw......

Found what the problem was, water heater looks to be on its last legs and corrosion from the aluminium back plate the thermostats are connected to, had reached the point where it touched the positive contacts creating enough of a short circuit to trip the RCDs. A hose-out with WD 40 and all is well again ..... but I'll enjoy my cup of coffee before I plug back into mains power

T1 Terry

 

[T1 Terry]

Thanks for your replies. I believe my house batteries are 48V and I have a Victron Multiplus II 3kVa inverter. Your reply, Terry, has prompted me to reach out to my Victron dealer, Commodore, and ask them the question - I had not thought to that!

You can buy the interface from Victron to plug into your computer or smart phone and adjust the programming once you down load the app.

I can ask Margaret to give me a copy of which screens and what setting to adjust to get it running off the MG4 if you need it.

I'm about to look for a bluetooth dongle thingy to plug into our inverter, because I just finished building a box around it, so plugging the adapter box in is no longer a simple task

T1 Terry

 

[T1 Terry]

OK, found this Video Google Search with the smart adapter bluetooth model and how to install it.
Found these on Evilbay https://www.ebay.com.au/itm/3881839...V85fzDX4qUSCCU0g5VQnOpYQ==|tkp:Bk9SR9DlmublZQ but see if your dealer can supply at a better price.

T1 Terry

 

[ReintjeWA]

Not to dissuade you from buying the MG4, as it is an excellent car in its price bracket, but if you are looking at a V2G (vehicle to grid) setup for your home, perhaps looking at cars that are V2G ready would be more beneficial?

There aren’t many in Australia, but the Cupra Born is one of them I think, and then a ton of Audis and BMWs which of course have a different price tag. A V2G EV with a V2G charger should make life easier with an off grid system I would like to think. More V2G capable chargers are expected to come to market any time now.

 

[MickeySw]

Thanks for your replies. I believe my house batteries are 48V and I have a Victron Multiplus II 3kVa inverter. Your reply, Terry, has prompted me to reach out to my Victron dealer, Commodore, and ask them the question - I had not thought to do that!

The Multiplus II doesn’t have a dedicated generator input for the V2L to connect to.

If found the easiest (but not the most efficient) way to make use of the V2L is to top up the batteries directly using a dedicated AC to 48V DC charger (or a second Multiplus).

It worked a treat during an extended power outage in our area. Lucky the nearest rapid charger wasn’t affected, so I could top up the car (MG5) regularly.

 

[T1 Terry]

The Multiplus II doesn’t have a dedicated generator input for the V2L to connect to.

If found the easiest (but not the most efficient) way to make use of the V2L is to top up the batteries directly using a dedicated AC to 48V DC charger (or a second Multiplus).

It worked a treat during an extended power outage in our area. Lucky the nearest rapid charger wasn’t affected, so I could top up the car (MG5) regularly.

Connect a short lead from the Victron Multiplus mains inlet with heavy cable to a 15 amp wall mount plug.
If you are going on mains, plug the cable into there, if you are going to use the MG4 V2L, then plug that into the wall mount plug in point. If you want to run a generator, then plug that into the wall mounted plug.
This way, no two supplies can be joined to the Victron Multiplus mains supply at the same time, so no need for a change over switch.

T1 Terry

 

[wattmatters]

A V2G EV with a V2G charger should make life easier with an off grid system I would like to think. More V2G capable chargers are expected to come to market any time now.

How does V2G help an off-grid system?

 

[MickeySw]

How does V2G help an off-grid system?

V2L can provide about 2-3kW of power, just about enough power to boil a kettle.

V2G is essentially rapid charging in reverse and requires an external, bidirectional EVSE.

 

[T1 Terry]

V2L can provide about 2-3kW of power, just about enough power to boil a kettle.

V2G is essentially rapid charging in reverse and requires an external, bidirectional EVSE.

Depends on the resistor used in the V2L, the 2k resistor limits the output to 2.2kw, give or take half a brick, 10 amps @ 220vac.
The 470ohm resistor allows the full 7kw to be drawn, but make sure you use a 5mmsq conductor cable, 32 amps is approaching the limit for 5mmsq over 15 mtrs of cable in open air, it would turn a 2.5mm sq "15 amp caravan cable" into a smoking mess and the pathetic 1.5mm sq conductor cable some try to sell as heavy duty, would probably catch fire I have no wish to test that one .

The V2G requires a device to convert the DC direct from the battery into AC at the correct hz and matched frequency .... and the approval of the local electricity authority .... over here, you would need to be right up on the electrical trading market to make it worth the effort .....
but
V2L as a support for the house battery when off grid, brilliant and well worth the effort.

T1 Terry

 

[T1 Terry]

How does V2G help an off-grid system?

Not in the slightest

T1 Terry

 

[wattmatters]

V2G is essentially rapid charging in reverse and requires an external, bidirectional EVSE.

What does the G in V2G stand for?

Hence my question:

How does V2G help an off-grid system?

 

[decrep]

G = Grid

Means the grid operators have full access to your battery at DC levels.

 

[ReintjeWA]

How does V2G help an off-grid system?

Isn’t an off-grid system basically its own little “grid”? I guess V2H would be more accurate for an off-grid system then, regardless, the MG4 still doesn’t provide this.

 

[Everest]

Isn’t an off-grid system basically its own little “grid”?

No. A grid-tied inverter or V2G system requires a grid connection to be operational and they will intentionally disconnect if the grid is disconnected.

 

[ReintjeWA]

No. A grid-tied inverter or V2G system requires a grid connection to be operational and they will intentionally disconnect if the grid is disconnected.

would you need a grid connection for bidirectional charging though? I just don’t think the MG4 V2L is a robust enough system for an off-grid system, not robust enough to recommend someone buying it for that purpose anyway.