Converting a non working V2L to a 7kw supply

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T1 Terry
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Converting a non working V2L to a 7kw supply

Post by T1 Terry »

I'm guessing anyone who clicked on the heading has done so to find out what the hell I'm talking about :lol:

Our recently purchased MG4 EV has a 51kwh battery, roughly equivalent to a 4250Ah 12v lithium battery ....... I wanted to use this stored electricity to run things in the motorhome when free camping if required.

The MG4 has a function called V2L (vehicle to load) where the electronics used to charge the car battery from an AC supply, can be reversed to supply AC @ 220vac at up to 7Kw, about the same amount as my 5kva Victron inverter supplementing a 15 amp caravan park supply can achieve.

I had the choice of:
Buying genuine for around $250 but that is restricted to around 2200w, they claim more, but in reality, that is all you can get.

Buy a unit from EV Chargers Australia for around $500 with a built in RCD and 2 x 10 amp power points ..... but still only 2200w

Buying UK genuine at around $750 and up to $975, output a full 7kw but came with all sorts of additional bits related to functioning to suit powering multiple UK devices with those strange UK plugs sockets

Buying an adaptor that would suit a 10 amp extension cord from evilbay for anywhere between $45 and a rather expensive $120 https://www.ebay.com.au/itm/37626173781 ... R_rIp5HiZQ that looks exactly like the one I bought for $25 from Aliexpress

When it arrived, naturally, it didn't work :roll:

A few hrs on Google looking at everyone's idea of what was safe, what worked and didn't work and what would happen if you didn't buy a genuine MG part, like you future birthdays would be cancelled or something .....

So, lashed out and spent $4 on a mix of resistors, pulled the non working item to bits to find out why it didn't work, and discovered this
Cheap V2L reconstruction showing original resistor and diode connected to CP pin and earth pin.jpg
This is the resistor and diode required to make the socket a 6 amp battery charger :roll: If you are going to copy stuff, at least start with the right thing ....

So, armed with the knowledge Dr Google supplied, after running through the critical thinking filter, I came up with this to replace the incorrect bits
Cheap V2L reconstruction resistor connected to CP pin and earth pin with heatshrink and liquid electrical tape.jpg
Heatshrink and liquid electrical tape to protect from any cross contact shorting inside the rather compact enclosure
Cheap V2L reconstruction 3 screws showing with pins in place.jpg
The photo looking in from the top doesn't actually make sense unless you saw it up close :lol:

The end result

Extension lead powering the Winnie
Cheap V2L reconstruction powering motorhome rooftop rattler on heat cycle drawing for MG4.jpg
Rooftop rattler set to heat, outside temp 16.5*C
Cheap V2L reconstruction powering rooftop rattler on heat cycle 16.5C.jpg
The amount of power being drawn from the MG4 shown on it's information screen. It also shows the limit it will allow the MG4 battery to be discharged before it shuts the V2L function off, and the guestimated range that will give me to find somewhere to recharge it. That can be adjusted from the 20% min up to 90% SOC if you wanted
Cheap V2L reconstruction powering rooftop rattler on heat cycle draw for MG4.jpg
This is powering the whole motorhome, including the Victron inverter's battery charging ability, the microwave, electric hot water element and the 3 way fridge running on mains power, along with the 12v lights and water pump and electric blankets for later tonight.

This makes a very handy electrical jerry can that doubles as a run around vehicle with a range of 320kms driven the way I drive, or 420kms driven the way whoever sets the mixed use cycle range they advertise on the stickers ;) :lol:

I'm happy with the way it has turned out. I will be buying an RVD from RVD safe to add into the supply side, to both add an additional protection path in case the 2 RCD's in the circuit don't trip .... although the Victron Multiplus is set up to create an earth/neutral link if it doesn't sense one in the supply side, and to protect against reverse polarity wiring at a caravan park ..... found a lot of those over the yrs, the handyman trying to be an electrician and stuffing it up :twisted:

T1 Terry
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Re: Converting a non working V2L to a 7kw supply

Post by Greynomad »

T1,
1. If you plug your vehicle into a CVP point with reversed polarity, does it suck all the power out of your battery/s?🤪

2. Serious question: Is there a way I can resuscitate a lithium battery pack for a Coleman lantern which has been left discharged for about 2+ years?
Plugged into its charger for 36hrs the charge indicator light turns green, but when I switch the light on — nada.
Can it be saved? Or do I face the music and order a new one?

ps. I have not put a multi meter on either the battery or the lantern yet.
Regards & God bless,
Ray
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Re: Converting a non working V2L to a 7kw supply

Post by T1 Terry »

Greynomad wrote: Thu May 29, 2025 3:16 pm T1,
1. If you plug your vehicle into a CVP point with reversed polarity, does it suck all the power out of your battery/s?🤪

2. Serious question: Is there a way I can resuscitate a lithium battery pack for a Coleman lantern which has been left discharged for about 2+ years?
Plugged into its charger for 36hrs the charge indicator light turns green, but when I switch the light on — nada.
Can it be saved? Or do I face the music and order a new one?

ps. I have not put a multi meter on either the battery or the lantern yet.
Serious answer for the non serious first question:

Reverse polarity in an RV isn't serious electrical hazard because the power points are double pole, they open both the active and neutral or line one and line two in a floating system powered from an inverter.

The appliances, however, as not double pole, where they would normally be cutting the active, if the polarity is reversed, they are cutting the neutral ..... so the active is still applied to anything after the switch .....

The other problem is a reverse polarity connection destroys a voltage sedative RCD if it is test tripped or fault trips and here is a bit from RVD Safe https://www.rvdsafe.com.au/about-us/

Question 2, the more serious one.

If you can disassemble the battery pack, measure each cell in the pack and mark the voltages on the cell and on a piece of paper for future reference. If any cell is a lot lower voltage than the other cells, find a low voltage DC charger that is often used to power a small electrical device to recharge its battery, the output voltage is marked on the label and DC is signified with a long flat line and a line of dashes under it, AC is a wave pattern sign.

If you don't want to cut the plug off, the centre of the round plug is positive and the outside sleeve is negative.
Identify positive and negative on the low voltage cell, connect up the charging wires and charge the cell until the voltage is slightly higher than the highest cell in the rest of the pack.

Disconnect the mini charger and measure the cell voltage, it will have dropped a bit, but write down what it was when it was charging and what it was when disconnected ..... leave it for an hr or so, then check it again, if the voltage has dropped a lot, reconnect the charger and feel if that cell is getting warm or hot to the touch, disconnect the charging if that happens, the cell has an internal fault. Identify if it is an NMC or LifeP04 cell, an NMC will have a voltage of higher than 3.5v, an LiFeP04 cell will be less than 3.5v, so the highest voltage cell in the pack should tell you which chemistry it is .....

These are available on line or at a Jay Car store, get a cell with the tabs already spot welded on it, much easier to solder the tabs together without damaging the cell with excessive heat.

If the voltage is similar to what was measured after the charging stopped, then reassemble the battery pack and try charging it again, it should work this time.

The reason for the charger saying it is fully charged, but nothing happens, is the charger is controlled by a heat sensor inside the battery .... if a cell gets hot because it fully charged, the charging stops. Most of these batteries do not have a balancing circuit as part of the battery build, yet Aldi tool batteries do, and they can be a great source of replacement cells at a bargain price.

T1 Terry
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Re: Converting a non working V2L to a 7kw supply

Post by BruceS »

Terry do you know what year double pole switches were commonly installed in caravans & MH's?
...... and earth wires to lights?
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Re: Converting a non working V2L to a 7kw supply

Post by T1 Terry »

BruceS wrote: Thu May 29, 2025 8:19 pm Terry do you know what year double pole switches were commonly installed in caravans & MH's?
...... and earth wires to lights?
Sparky Dave will know the earth wire to 240vac lights one, that is very recent, the double pole power points go back to the first set of standards for transportable premises that go in conjunction with the normal house wiring standards.
Can't remember what they called the standards supplement originally, but it changed to that name when they included converted containers into site offices, accommodation, shower facilities and lunch rooms etc ..... seems a few accidents happened when dodgy extension cables were used to plug them in ..... so, all the extension cables had to be tag tested and recorded as well ..... although that really dates back to the '80s or 90s I think, it just wasn't heavily policed back then. Still only really policed these days on construction sites ..... can you imagine taking a cheater lead or one with the 15 amp negative pin filed down to fit in a 10 amp socket to be tested and tagged :lol:
None of the so called "caravan" leads sold by a lot of places would pass either, the conductor sq mm size is way too small for 10 or 15 mtrs at 15 amps .....

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Re: Converting a non working V2L to a 7kw supply

Post by Greynomad »

T1,
Thanks for the comprehensive instructions, but I think I fall at the first hurdle — disassembling the battery pack.
Not confident doing that. 🥺
I think I’ll just bite the bullet and order a replacement pack.
🙁
Regards & God bless,
Ray
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Re: Converting a non working V2L to a 7kw supply

Post by T1 Terry »

Take it to the local Mens Shed, someone there will pull it apart for you, then you can test it and share the knowledge on how to repair them. I'm sure you're not the only one with dead battery problems that can be easily fixed ....

T1 Terry
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Re: Converting a non working V2L to a 7kw supply

Post by supersparky »

BruceS wrote: Thu May 29, 2025 8:19 pm Terry do you know what year double pole switches were commonly installed in caravans & MH's?
...... and earth wires to lights?
Double pole switches have been a regulation since the 80's or so.
Earth wire to lights, sometime this century.
Historically, this all came about because of reversed polarity on extension leads or dodgy maintenance on CP pillar boxes. One little fault and the van became alive. It's a lot harder to do now, but still possible. RCD's have saved a lot of incidents.
Is this a question for you h/boat Bruce?
Cheers
David

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Re: Converting a non working V2L to a 7kw supply

Post by T1 Terry »

Dave, have you found RCD's that had been compromised due to reverse polarity? Had a few caravans come into the workshop back when, that the RCD didn't trip with the test device plugged in, but it would if the test button was pushed, that was yet another reason for switching to RVD's in RV's, it trips if it senses a reverse polarity.

Had it mentioned a few times on the lithium forums and some saying after futile arguments with park owners and showground supervisors, they made up a short reverse polarity lead to get the supply back around the right way so the RVD would work ....

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Re: Converting a non working V2L to a 7kw supply

Post by supersparky »

I haven't personally seen that with a reversed input. But I have seen plenty that don't trip when the prescribed time test instrument is used , but do when the trip button is used.
A good investment I would suggest, is one of the inexpensive Cabac or similar RCD testers. They also include a couple of light that indicate reversed polarity and/or neutral/ earth issues.
I'll try to find a link and put it up.

Edit, I can't find a link to what I want while we are not home. I keep getting links to very expensive gear.
The one I was suggesting was around $40, depending if you got one at the green shed or a wholesaler.
Cheers
David

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