Is it safe to connect a large inverter to the 12V battery?

[REDFIVE48]

Boiling this all down, it appears that it is possible to run a large inverter directly off the 12V battery and it will be replenished by the high voltage battery. With that, how is this for a situation:
Home with solar panels that are grid tied
Grid goes down
Hook pure sine inverter to 12V battery and plug that into the house power after disconnecting from the grid
would this 'trick' the solar micro-inverters into thinking the grid is up?
If you plugged the EVSE into the wall and the car, would you basically be replicating a solar power installation with batteries?
Would think that this would basically allow the solar panels to power the house (limited by how much power they are producing of course) and any unused power that is generated would serve to charge the Tesla? Or would stuff just start to melt?

 

[David99]

Boiling this all down, it appears that it is possible to run a large inverter directly off the 12V battery and it will be replenished by the high voltage battery. With that, how is this for a situation:
Home with solar panels that are grid tied
Grid goes down
Hook pure sine inverter to 12V battery and plug that into the house power after disconnecting from the grid
would this 'trick' the solar micro-inverters into thinking the grid is up?

I doubt it would work. The power from the solar panels need to go somewhere. There is always enough demand on the grid. But if you are only connected to your home and your panels produce more than the house uses, where would the power go? Not sure what would happen.

 

[REDFIVE48]

I doubt it would work. The power from the solar panels need to go somewhere. There is always enough demand on the grid. But if you are only connected to your home and your panels produce more than the house uses, where would the power go? Not sure what would happen.

I was thinking the power would go into the high voltage battery thru the EVSE.

 

[mspohr]

Hook pure sine inverter to 12V battery and plug that into the house power after disconnecting from the grid
would this 'trick' the solar micro-inverters into thinking the grid is up?

Most grid tied microinverters try to prevent you from tricking them. They won't turn on unless the grid frequency is very stable and within a very narrow range and they usually take about 5 minutes to verify that it is OK to turn on.
- If you did get them to turn on, they would produce more/less power than existing load leading to over/under voltage shutdown. (or they could just burn things up)
I have a new SMA string inverter (SunnyBoy 5kW) which does have the ability to provide up to 2000w/120v from the solar panels when the grid is down and this could be used for charging. This is a separate regulated circuit with a switch and won't feed into the grid and won't operate with the grid is live. SMA does caution that the power from this may not be stable due to varying load and sun on the panels.

 

[miimura]

Boiling this all down, it appears that it is possible to run a large inverter directly off the 12V battery and it will be replenished by the high voltage battery. With that, how is this for a situation:
Home with solar panels that are grid tied
Grid goes down
Hook pure sine inverter to 12V battery and plug that into the house power after disconnecting from the grid
would this 'trick' the solar micro-inverters into thinking the grid is up?
If you plugged the EVSE into the wall and the car, would you basically be replicating a solar power installation with batteries?
Would think that this would basically allow the solar panels to power the house (limited by how much power they are producing of course) and any unused power that is generated would serve to charge the Tesla? Or would stuff just start to melt?

You are talking about AC coupling solar to an inverter. Generally this requires a battery inverter-charger that has a higher watt rating than the solar grid-tied inverters. You would also need a battery large enough to buffer the energy flows. This basically doesn't work with an inverter connected to the 12V system of an EV.

If you have a Powerwall, it will automatically island your house from the grid when it fails and it will keep your solar producing energy. If the solar over-produces and the Powerwall gets full, the Powerwall will shift the line frequency higher and the solar inverters will either curtail their output or completely shut down when the frequency goes out of range. If you don't have enough solar production and the Powerwall is in danger of shutting down due to low battery, you can connect a grid-tie type inverter to the 12V on your EV and push some energy from your car into the Powerwall. I have proven that this works.

 

[widodh]

You are talking about AC coupling solar to an inverter. Generally this requires a battery inverter-charger that has a higher watt rating than the solar grid-tied inverters. You would also need a battery large enough to buffer the energy flows. This basically doesn't work with an inverter connected to the 12V system of an EV.

If you have a Powerwall, it will automatically island your house from the grid when it fails and it will keep your solar producing energy. If the solar over-produces and the Powerwall gets full, the Powerwall will shift the line frequency higher and the solar inverters will either curtail their output or completely shut down when the frequency goes out of range. If you don't have enough solar production and the Powerwall is in danger of shutting down due to low battery, you can connect a grid-tie type inverter to the 12V on your EV and push some energy from your car into the Powerwall. I have proven that this works.

To add to this, the StorEdge product of SolarEdge does this. It requires a relais between the mains and your house so that it can indeed isolate you from the grid when required.

 

[mspohr]

If you don't have enough solar production and the Powerwall is in danger of shutting down due to low battery, you can connect a grid-tie type inverter to the 12V on your EV and push some energy from your car into the Powerwall. I have proven that this works.

I don´t understand this part. A grid-tie inverter would require grid-tie to work but the grid is down. If you want to push energy into the Powerwall, wouldn't you just use a simple inverter (not grid-tied) from the 12v to charge the Powerwall?

 

[miimura]

I don´t understand this part. A grid-tie inverter would require grid-tie to work but the grid is down. If you want to push energy into the Powerwall, wouldn't you just use a simple inverter (not grid-tied) from the 12v to charge the Powerwall?

You need the 12V inverter to sync to the Powerwall. The Powerwall is the master inverter when the grid is down. Solar and your runtime extender both need to sync to the Powerwall like it's the grid. A simple inverter is free running just like an ICE generator. If you connect two asynchronous power sources together you will get a big spark and you'd better hope you have a breaker or other OCPD in between them.

 

[REDFIVE48]

You are talking about AC coupling solar to an inverter. Generally this requires a battery inverter-charger that has a higher watt rating than the solar grid-tied inverters. You would also need a battery large enough to buffer the energy flows. This basically doesn't work with an inverter connected to the 12V system of an EV.

Thanks for this, I was thinking there would be an issue but was trouble reconciling it. Always comes back to needing batteries and an inverter/charge controller which I was hoping could all be done with the Tesla from the two different batteries.

Cheers!

 

[miimura]

Thanks for this, I was thinking there would be an issue but was trouble reconciling it. Always comes back to needing batteries and an inverter/charge controller which I was hoping could all be done with the Tesla from the two different batteries.

Cheers!

Your idea is good. In theory, someone could make what you want, but it would be expensive. I can imagine a large inverter system (~10-20kW) that plugs directly into the Tesla charge port and gets DC access to the battery just like a Supercharger. The inverter could be designed to be the master inverter for the home and absorb whatever solar is produced by AC coupled grid tied inverters. With a built-in transfer switch, it could also isolate the system from the grid, whether the grid is up or down.
However, I have never heard of anyone making a system like this.

 

[mspohr]

Thanks for this, I was thinking there would be an issue but was trouble reconciling it. Always comes back to needing batteries and an inverter/charge controller which I was hoping could all be done with the Tesla from the two different batteries.

Cheers!

It looks like the new IQ8 inverter series from Enphase will be able to operate without the grid and adjust output to local load and not require a battery buffer.
Solar inverter from Enphase to run when the grid crashes or doesn’t exist – without batteries
Should be interesting.

 

[REDFIVE48]

It looks like the new IQ8 inverter series from Enphase will be able to operate without the grid and adjust output to local load and not require a battery buffer.
Solar inverter from Enphase to run when the grid crashes or doesn’t exist – without batteries
Should be interesting.

Nice find - and from the article:
"In a complex moment, if you really wanted electricity, you could do some creative wiring to trick your inverter into thinking the grid was up, or you can buy simpler/small solar systems and literally plug them into an outlet. If this feature is added to the Enphase line of hardware, expect more groups to do the same."

This trick is exactly what I was trying to come up with plugging the 12V tesla battery thru a pure sine wave inverter into the house power.

Cheers!

 

[David99]

I tried this recently. I connected a small grid tie inverter directly to the 12 VOlt system in my Model S. The DCDC converter kept running even when my car was off and parked. The grid tie inverter was somewhat limited. At 13 Volt it could only generate aprox 450 Watt. Theoretically it would be able to generate a little over 10 kWh a day. In reality it's far less as your car is not at home 24 h a day. At night you are usually not using much power in the house so it's not getting used. You would just send it back into the grid. A good idea in theory but in reality it didn't really make much sense.

What EVs would be awesome for is acting as grid buffers when they are connected to a charger during the day. They could help the grid by providing power when demand is high and charge at night when demand is low. It doesn't have to be much. If every EV would just provide 5-10 kWh that would already make a big difference as there are so many EV that are parked all day at a work place. BMW has experimented with it. I doubt Tesla will as they want to sell battery storage as a separate product.

 

[mspohr]

I tried this recently. I connected a small grid tie inverter directly to the 12 VOlt system in my Model S. The DCDC converter kept running even when my car was off and parked. The grid tie inverter was somewhat limited. At 13 Volt it could only generate aprox 450 Watt. Theoretically it would be able to generate a little over 10 kWh a day. In reality it's far less as your car is not at home 24 h a day. At night you are usually not using much power in the house so it's not getting used. You would just send it back into the grid. A good idea in theory but in reality it didn't really make much sense.

What EVs would be awesome for is acting as grid buffers when they are connected to a charger during the day. They could help the grid by providing power when demand is high and charge at night when demand is low. It doesn't have to be much. If every EV would just provide 5-10 kWh that would already make a big difference as there are so many EV that are parked all day at a work place. BMW has experimented with it. I doubt Tesla will as they want to sell battery storage as a separate product.

Here's a pilot study done with Nissan cars.
European Vehicle-To-Grid Plan Pays Off For Electric Car Owners & Extends Battery Life | CleanTechnica
How Electric Cars Could Help The Power Grid Become More Efficient, Less Expensive

 

[n2mb_racing]

Quick question. In the fuse box below from a 2016 Model S P90D, is the highlighted terminal direct to the battery without any fuse? It is labeled as the B+ jump post. The 250A fuse on the right seems to go to the DC / DC converter. I'm looking for good locations for a temporary connection for an emergency inverter.

View media item 118880

 

[FlatSix911]

Quick question. In the fuse box below from a 2016 Model S P90D, is the highlighted terminal direct to the battery without any fuse? It is labeled as the B+ jump post. The 250A fuse on the right seems to go to the DC / DC converter. I'm looking for good locations for a temporary connection for an emergency inverter.

View media item 118880

If you are looking to bypass the 50A fuse on the jump terminals, I would recommend going directly to the 12V battery.
Use caution if you are going directly to the HV inverter...

 

[n2mb_racing]

If you are looking to bypass the 50A fuse on the jump terminals, I would recommend going directly to the 12V battery.
Use caution if you are going directly to the HV inverter...

Well, I don't think there is a 50A fuse on that terminal. I didn't try the terminals behind the nose cone. I only tried the one at the fuse box. I pulled 1000W from there for a few minutes of testing running a shop vac. Seemed to work. I need heavier gauge wires, though.... they got warm.

 

[polymathic]

I tested it with a 600 Watt load (50 Amp). It keeps the DC-DC converter running.

Thanks for the information. Was 600 Watt the minimum load to keep DC-DC running at all time?

 

[David99]

Thanks for the information. Was 600 Watt the minimum load to keep DC-DC running at all time?

Not sure there is a minimum load to keep the DCDC active. The car is very much aware of the load on the 12 Volt system. Based on that it will keep the DCDC running taking into account what the rather small 12 Volt battery can handle on it own. I have noticed the DCDC stayed on all the time. Once was it shutting off, immediately kicked back in when the car noticed the 12 Volt battery couldn't handle the load. That was after several hours. But honestly Tesla is always optimizing things. In the beginning the way the 12 Volt battery was charged wasn't the best way. They fixed that via software over time.

 

[polymathic]

Not sure there is a minimum load to keep the DCDC active. The car is very much aware of the load on the 12 Volt system. Based on that it will keep the DCDC running taking into account what the rather small 12 Volt battery can handle on it own. I have noticed the DCDC stayed on all the time. Once was it shutting off, immediately kicked back in when the car noticed the 12 Volt battery couldn't handle the load. That was after several hours. But honestly Tesla is always optimizing things. In the beginning the way the 12 Volt battery was charged wasn't the best way. They fixed that via software over time.

So at this point, based on your observations, running an inverter from my MX will keep the 12v battery from cycling up and down, and preserve its life? I had a five-day outage due to the fires, and ran a 1200 watt inverter hooked to my MX battery to power refrigerator, freezer, and furnace. I was thinking all along I was cycling my 12v battery, and worried a few month from now it would be dead. In sum, running an inverter from an ICE car or the Tesla is roughly equivalent? Thanks.