Solar battery and V2L

[Cowton jb]

What are the specs of the battery you wish to charge?

Note that the small All In One inverter/charge controller I use enables me to set charge voltages in 0.1V increments anywhere from 48.0 to 64.0 V.

Also enables charge current to be set in 10 A increments (which is roughly 500 W increments).

Wondered if this charger via Amazon would work

 

[wattmatters]

Wondered if this charger via Amazon would work

It charges to 58.4 V, which is right at the upper limit for a 16S LFP battery. If it were programmable to drop that charge voltage down then it would perhaps be OK.

58.4 V is an average of 3.65 V per cell.

In reality the battery won't get to 58.4 V because your battery BMS will shut off charging before then with a cell over voltage alarm as one cell will always peak in voltage before the others. Using a BMS for charging control is not a good idea - its job is to be a safety backstop, used only when necessary and not for regular charge management duty.

Note the voltage range your battery spec shows is up to 57.6 V, so I would suggest not exceeding the manufacturer's recommended charge voltage specification.

You also need to know how the charger behaves once charging has been completed - is it going to keep the voltage pressure on or will it eventually relax back to a float level voltage?

 

[johnb80]

He said that there was nothing in the GivEnergy specs about any other way to charge the battery, other than the mains.

So your solar panels dont charge it?

In reality the battery won't get to 58.4 V because your battery BMS will shut off charging before then with a cell over voltage alarm as one cell will always peak in voltage before the others. Using a BMS for charging control is not a good idea - its job is to be a safety backstop, used only when necessary and not for regular charge management duty.

Some BMS's have active balancers eg Seplos Ver 3, JK etc, theyre absolutely fine to control the battery charging i.e. switch off when it's full. The easy way to do this is by a Switch Mode Power Supply Unit (SMPSU) rated at 2400W so as not overwhelm the MG4 V2L and set the output voltage to 53.2V (90% charge on 16S). As the house battery discharges from 100%, the SMPSU will take over from the battery discharging from the car. As the house load decreases, it will start to charge the house battery with the current falling away to zero at 90%. Essentially charging with constant current until the voltage is reached and then constant voltage. It works absolutely fine this way, it's useful to have a voltage trim to tweak the output voltage of the SMPSU to get the desired charge rate etc.

 

[wattmatters]

Some BMS's have active balancers eg Seplos Ver 3, JK etc, theyre absolutely fine to control the battery charging i.e. switch off when it's full.

I have no idea what BMS that battery has but IMO the BMS is there for failsafe reasons, not for regular switching on/off of charge (and discharge).

Charging should be managed by a charge controller (which may well have communications with the BMS) while discharge control should be managed by the inverter.

Relying on a BMS to switch off charging is asking for trouble. Its primary purpose is for backstop protection when something else has failed.

The easy way to do this is by a Switch Mode Power Supply Unit (SMPSU) rated at 2400W so as not overwhelm the MG4 V2L and set the output voltage to 53.2V (90% charge on 16S).

Charging to 53.2 V will chronically undercharge a 16S LFP battery. It will also result in poorly calibrated SOC readings.

During charging, at 53.2 V my LFP is around the 40-50% SOC range.

 

[Coulomb]

Does the inverter have a separate AC input? If that's the case, you can use that to supply power to it via the V2L system of the car.

The problem with that is that the inverter will likely rely on the AC-in port to connect the neutrals to earth. You need that connection for safety; Residual Current Devices (RCDs) won't work without this.

Assuming that any house will have a proper earth system, you could probably make use of that earth and bond the V2L neutral to that earth. I have no idea how compliant this would be in various countries; this sort of thing has to be squeaky clean legally for your home insurance to be valid. And of course you want to be electrically safe.

A few inverters have a separate generator input, distinct from the grid connection. Generators generally don't have a proper earth, especially portable ones, so the inverter probably won't rely on its neutral to earth bond. I have not looked into generator inputs, but at first glance, they would seem to be ideal. V2L is much like a portable generator.

 

[Tig170]

Wondered if this charger via Amazon would work

No- I've attempted this via MPPT DC coupled system, forget it !

 

[wattmatters]

e.g. the voltage and state of charge for each of my three LFP batteries over the last 2.5 days:

 

[Tig170]

mine over the past 2 days... ? - &?

 

[Rolfe]

So your solar panels dont charge it?

Well, yes they do, obviously. I phrased that badly. He said that there was nothing in the specs about an external socket to plug in a battery charger. If you know different I'd be pleased to hear about it.

 

[Coulomb]

Assuming that any house will have a proper earth system, you could probably make use of that earth and bond the V2L neutral to that earth. I have no idea how compliant this would be in various countries; this sort of thing has to be squeaky clean legally for your home insurance to be valid.

I've just done a little research and it seems that a changeover switch with generator input installed to Australian standards uses the house earth, and portable generators usually don't connect their neutral output to the "earth" terminal. So presumably, a properly wired standards compliant connection would be safe. I don't know the details of the earthing system, but it doesn't matter as an electrician will sort all that out with the installation.

Now I'm wondering if there is an automatic version of the changeover switch that maintains power during a blackout. This could be useful in areas with frequent grid interruptions. I'd say it should be possible.

 

[Tig170]

I've just done a little research and it seems that a changeover switch with generator input installed to Australian standards uses the house earth, and portable generators usually don't connect their neutral output to the "earth" terminal. So presumably, a properly wired standards compliant connection would be safe. I don't know the details of the earthing system, but it doesn't matter as an electrician will sort all that out with the installation.

Now I'm wondering if there is an automatic version of the changeover switch that maintains power during a blackout. This could be useful in areas with frequent grid interruptions. I'd say it should be possible.

From a consumer in the UK, it might be similar, the standard is TN-C-S, or at least thats what Ive just been given from my DNO, when updating my supply to the electric meter, after asking for a quote for an earth. (they also included a new pole, and upgraded 4 neighbours supply at the same time - 5 days work (8-10 persons/ 2 vans / 2-3 4x4's, a digger machine & hoist van (+welfare unit), all for free ) - the earth rod that they installed at the bottom of the pole was ironically next to my exisitng earth rod, which begs the question should I add the old one into the mix, given that the MG4 doesn't have one

 

[johnb80]

Charging to 53.2 V will chronically undercharge a 16S LFP battery. It will also result in poorly calibrated SOC readings.

During charging, at 53.2 V my LFP is around the 40-50% SOC range.

The aim of this was not to charge the house battery but to feed into the house system energy from the vehicle battery. By setting the voltage to 53.2V it avoids heading up to higher states of charge whilst still providing a useful addition the the house battery capacity.
The SOC wont be affected to any great extent, recalibration would happen at the next full charge from the grid supply. I don't find any great effect at all on my system.

I have no idea what BMS that battery has but IMO the BMS is there for failsafe reasons, not for regular switching on/off of charge (and discharge).

Whilst regular switch on / off charging from my suggestion above would not occur, why do you see it as a problem?

Charging should be managed by a charge controller (which may well have communications with the BMS) while discharge control should be managed by the inverter.

Charge controller would have no knowledge of individual cell voltages nor could it do anything about it if it did. Ditto the inverter during discharging, it cant do anything if one individual cell is lower voltage than the rest, when the BMS detects minimum voltage it will stop the discharge.

Relying on a BMS to switch off charging is asking for trouble. Its primary purpose is for backstop protection when something else has failed.

Please share with us how it's asking for trouble?

Well, yes they do, obviously. I phrased that badly. He said that there was nothing in the specs about an external socket to plug in a battery charger. If you know different I'd be pleased to hear about it.

Your inverter will run as a battery charger at times e.g. off peak overnight. Your inverter will plugged into the battery and therefore that proves the battery can be charged via the plugs on it. If your inverter provides say 56V to charge the battery if a mains driven power supply also provided 56V how would the battery know any difference? The inverter would also see this charge voltage and also use a few amps from it to do it's job. A volt is a volt at the end of the day, neither battery nor inverter will know where it's coming from and they really won't care.

 

[JohnV6]

So I have a Ginlong AC to DC inverter to feed my home batteries. They were put in after the solar PV array which has its own inverter.

Can I then take V2L power from car and just plug that into a mains socket to charge the house batteries?

 

[johnb80]

So i have a ginlong ac to DC inverter to feed my home batteries. They were put in after the solar pv array which has its own inverter.

Can I then take v2l power from car and just plus that into a mains socket to charge the house batteries?

Yes you can as long as the output of the inverter is the correct spec for the batteries and that your V2L is suitable for your inverter. If the batteries require xxV to charge, it doesnt matter what the source of that supply is.

 

[JohnV6]

Great news. I am getting a zappi charger. Can they also be set to take v2l power back. I'm thinking in winter although I charge the house batteries overnight the 4. 2 kWh they provide will be gone and before importing using the car would be good

 

[Coulomb]

Can I then take V2L power from car and just plug that into a mains socket to charge the house batteries?

If you mean can you push power into a general purpose electrical outlet in the house via a "suicide lead" (one with a plug at both ends), don't do it! If the grid is on, the voltages won't be synchronised, and there will be an expensive bang. Even if the grid is off and you can guarantee that it won't come back, you can't limit the power draw (e.g. a water heater might come on), and it's just too dangerous.

If you mean can you use the Ginlong inverter (I'm not familiar with them) connecting its AC-in port to the V2L output, and the house battery to the battery port, and the voltages are compatible (e.g. 48 V inverter and 48 V battery), and everything is configured correctly, then yes.

 

[wattmatters]

Charge controller would have no knowledge of individual cell voltages nor could it do anything about it if it did. Ditto the inverter during discharging, it cant do anything if one individual cell is lower voltage than the rest, when the BMS detects minimum voltage it will stop the discharge.

For a system without closed loop communications that's correct, however charge controllers and inverters should have charge and discharge voltage limits set that are within the safety limits used by a BMS for shut off and those charge controller and inverter limits should not see individual cells exceed their upper and lower voltage limits, unless something goes wrong or it is a very badly out of balance pack.

Please share with us how it's asking for trouble?

Using a BMS to regularly cut power is not a job they are designed for. They are designed to do it as a safety backstop when charge controllers / inverters have not done their job, or some other fault occurs. The BMS should be a last line of defence, not the first.

The aim of this was not to charge the house battery but to feed into the house system energy from the vehicle battery. By setting the voltage to 53.2V it avoids heading up to higher states of charge whilst still providing a useful addition the the house battery capacity.

Ah, OK, I see what you are saying.

I was not considering that given the OP was referring to using a plug-in battery charger without the ability to set a charge voltage. IOW it was all or nothing.

I guess if that is the application then using a basic 15S charger on a 16S battery will work to provide supplemental energy supply when the home battery drops to a lower SOC.

It's not an approach I would take however as I would want to recharge the home battery more than that as the car may not always be available, so charge the home battery up when you can.

 

[Rolfe]

Your inverter will run as a battery charger at times e.g. off peak overnight. Your inverter will plugged into the battery and therefore that proves the battery can be charged via the plugs on it. If your inverter provides say 56V to charge the battery if a mains driven power supply also provided 56V how would the battery know any difference? The inverter would also see this charge voltage and also use a few amps from it to do it's job. A volt is a volt at the end of the day, neither battery nor inverter will know where it's coming from and they really won't care.

I'm struggling here. Where would I plug it in?

 

[johnb80]

I'm struggling here. Where would I plug it in?

Usually the batteries and the inverter have plugs and sockets between them, batteries usually have double sockets in case you are installing more than one. The charger can be plugged into this vacant socket.

 

[wattmatters]

Usually the batteries and the inverter have plugs and sockets between them, batteries usually have double sockets in case you are installing more than one. The charger can be plugged into this vacant socket.

Mine all connect to a common busbar (a Victron Lynx Power In), enabling fused connections to each battery. For the spare charge controller I have a fused connection to the busbar with an Anderson plug on the other end to make connection/disconnection easy.