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

[George S. Bower]

Yes, the remote charging terminals are protected with a 50A fuse ... you need to go directly to the battery if you want more
I chose the convenience of accessing the nose cone charging posts vs. some disassembly of the frunk to access the 12V directly.

thx flatsix,
where is that fuse ???

 

[widodh]

thx flatsix,
where is that fuse ???

Indeed, as far as I know there is no fuse on the 12V poles.

I want to charge a big 12V battery from my Model S (long story!) on a very remote location.

I want to connector jumper cables and see how that works out.

 

[BrettS]

Indeed, as far as I know there is no fuse on the 12V poles.

I want to charge a big 12V battery from my Model S (long story!) on a very remote location.

I want to connector jumper cables and see how that works out.

There absolutely is a 50 amp fusable link on the 12V poles. A number of people have accidentally blown it. There is some additional detail and a picture in this post from this thread:

Is the battery post under the nose cone fused?

Yes, I believe there is a fuse, but I'm pretty sure the fuse is actually sitting on top of the battery. Let me see if I can find the photo I saw a while back that showed this...

- - - Updated - - -

Found it here:

12 V battery pictures

View attachment 50877

Would be interested in hearing what kinds of fuses those are and how hard it is to get to them to replace them.

 

[George S. Bower]

Thx BrettS. Looks to be a bit of a PITA to replace that inline fuse.

 

[George S. Bower]

Just hooked up my 400 W inverter to the charging lugs with 220W load. I noticed the voltage at the lugs jumped to 14 V....presumably because the DC-DC converter kicked in.

Do you guys think I might overcharge the 12V battery in the car? or will it just top off the battery to 14.5 and then shut off.

 

[FlatSix911]

thx flatsix, where is that fuse ???

There absolutely is a 50 amp fusable link on the 12V poles. A number of people have accidentally blown it. There is some additional detail and a picture in this post from this thread:
Is the battery post under the nose cone fused?

Here is the Battery-Mounted Fusebox Layout ... the 12V posts are confirmed to use a 50A fuse
View attachment 274834

​

 

[George S. Bower]

Here is the Battery-Mounted Fusebox Layout ... the 12V posts are confirmed to use a 50A fuse ​

Great info thx. This is where the high amp fuses are....makes sense.

 

[David99]

Just hooked up my 400 W inverter to the charging lugs with 220W load. I noticed the voltage at the lugs jumped to 14 V....presumably because the DC-DC converter kicked in.

Do you guys think I might overcharge the 12V battery in the car? or will it just top off the battery to 14.5 and then shut off.

I ran an inverter for a while. As long as there is a high load on the 12 Volt system the DCDC converter will keep the voltage at around 14.1-14.2 Volt. I'm not sure if that is bad for the lead acid battery in the long run. I don't know what these batteries are able to take for a longer period. I was under the impression that 13.8 Volt is the max for a sealed lead acid battery as a continuous voltage. But I might be wrong.

 

[FlatSix911]

I ran an inverter for a while. As long as there is a high load on the 12 Volt system the DCDC converter will keep the voltage at around 14.1-14.2 Volt. I'm not sure if that is bad for the lead acid battery in the long run. I don't know what these batteries are able to take for a longer period. I was under the impression that 13.8 Volt is the max for a sealed lead acid battery as a continuous voltage. But I might be wrong.

I did a few tests with my 750W inverter and found no issues with the 12V battery.
The main high voltage 350-400V traction battery recharges the 12V when required.

​

 

[David99]

I did a few tests with my 750W inverter and found no issues with the 12V battery.
The main high voltage 350-400V traction battery recharges the 12V when required.

Yeah, that's exactly my experience, too. Even if the car it parked/locked and 'off', the DCDC converter will always kick in to keep the 12 Volt system/battery at a good level. The only concern was that I measured the voltage and it was at 14.2 which might be a little high for the lead acid battery in the long run.

 

[FlatSix911]

Yeah, that's exactly my experience, too. Even if the car it parked/locked and 'off', the DCDC converter will always kick in to keep the 12 Volt system/battery at a good level. The only concern was that I measured the voltage and it was at 14.2 which might be a little high for the lead acid battery in the long run.

I am seeing 13.4 - 13.6V input from my 12V battery when testing.

 

[David99]

I am seeing 13.4 - 13.6V input from my 12V battery when testing.

Interesting. Mine went up to 14.2 with a load of aprox 600 Watt.

 

[widodh]

I did a few tests with my 750W inverter and found no issues with the 12V battery.
The main high voltage 350-400V traction battery recharges the 12V when required.

750W? That's 62,5A at 12V. Posts above suggest that there is a 50A fuse.

For how long did you run a 750W load on it? Because with 50A the posts behind de nosecone should only be able to provide 600W.

 

[FlatSix911]

Indeed, as far as I know there is no fuse on the 12V poles.
I want to charge a big 12V battery from my Model S (long story!) on a very remote location.
I want to connector jumper cables and see how that works out.

See my post above... 50A protection is shown on the fuse diagram. ​

750W? That's 62,5A at 12V. Posts above suggest that there is a 50A fuse.
For how long did you run a 750W load on it? Because with 50A the posts behind de nosecone should only be able to provide 600W.

Remember to use 80% of the rating for sustained loads...the design voltage is 12-15V.

 

[widodh]

See my post above... 50A protection is shown on the fuse diagram. ​

Remember to use 80% of the rating for sustained loads...the design voltage is 12-15V.

Yes, but still. You can't draw 750W from the nosecone that way I assume, right?

50A fuse at let's say 14V would be 700W, not 750W.

So is the fuse really 50A? Or is it 60A and designed for 50A in all environment?

 

[zap fizzle]

See my post above... 50A protection is shown on the fuse diagram. ​

Remember to use 80% of the rating for sustained loads...the design voltage is 12-15V.

OK, so we can't get enough current from the nosecone terminals. Can we attach directly to the 12V battery terminals - are they accessible enough?

 

[David99]

OK, so we can't get enough current from the nosecone terminals. Can we attach directly to the 12V battery terminals - are they accessible enough?

Yes that's what I did. You need to remove the cover above the frunk. Depending on the year built, the battery is either to the left under the air filter or in the center. There is a main 240 Amp fuse so you are still protected from disaster. The DCDC converter is rated for 2.4 kW. I would limit to 1 kW to make sure the car has the rest available when it needs it.

 

[zap fizzle]

Yes that's what I did. You need to remove the cover above the frunk. Depending on the year built, the battery is either to the left under the air filter or in the center. There is a main 240 Amp fuse so you are still protected from disaster. The DCDC converter is rated for 2.4 kW. I would limit to 1 kW to make sure the car has the rest available when it needs it.

Thanks. There are a lot of wobbly 1950s utility poles between our house and "civilization". It would be very nice to be able to run the fridge and [gas-fired] central heating off the car for a while next time the power is out for a day. Glad to hear it's possible; it was easy enough with the LEAF.

 

[Dr. Smoke]

Really, connecting to the 12v system is not a good solution. Best would be having a qualified shop install a HV inverter near the rear HVJB and run 120vAC outlets where convenient. Camping mode.

 

[David99]

Really, connecting to the 12v system is not a good solution. Best would be having a qualified shop install a HV inverter near the rear HVJB and run 120vAC outlets where convenient. Camping mode.

Ideal would be a two way connection to the grid so every EV would act as an energy buffer for the grid. Tesla knows this but wants to sell this concept as a separate product (Powerwall), so there is no hope Tesla will implement it in their cars. They also don't want you to get free energy from Superchargers and then power your home with it.

For DIY home use I think going into the 12 Volt system is the cleanest and safest. It also requires no artificial camper mode. If there was a simple way to connect to the high voltage system, I would prefer that. It's just too much trouble and much more expensive.