Advice on using a DC -> AC inverter to charge my tesla from an ICE 12V battery

[Thot]

I live in an apartment complex with no place to plug my car and rely to periodic supercharger trips (less than ideal, I know).
After coming back from vacation oversea I found that my car showed 1% charge, or 2 miles, enough to reach the supercharger 1.6 miles away (sigh of relief...).

I was thinking that in an emergency I could use an inverter like this: 1,500W, 12V DC -> 120V AC Inverter from my other (ICE) car to give enough juice to the car to reach the closest (super)charger.
Any advice?
In particular, what charging Amps should I set? Should I leave 48A and let the car figure it out? I am afraid that if I try to draw too much current I will melt the inverter (or the battery).
Do I need this Neutral-Ground Bonding Plug ?

Thank you for any advice

Luca
P.s. I am attaching the manual of the inverter in which, surprisingly, I could not find an Amp limit.

 

[cali8484]

That inverter won't work. You'll need a purse sine wave inverter. And you will need a neutral-ground bond.

 

[RayK]

That inverter won't work. You'll need a purse sine wave inverter. And you will need a neutral-ground bond.

In case @cali8484 doesn't come back and edit their post.... it's a "pure sine wave" inverter.

 

[Sophias_dad]

The car will limit current to 12A by default when you are using the 5-15 plug.

Even a pure sine wave inverter isn't good enough. I have a good quality(well known) 2000w pure sine inverter and the built-in GFCI trips immediately when charging starts. A neutral/ground bonding plug MIGHT fix it, but I haven't tried.

Realize that the absolute maximum you'll get is four miles per hour, and to not drain the donor ICEs battery you'll have to be holding it well above idle speed. A typical automotive alternator is good for ~120 amps, so you are looking at 120x12V=1440W best case, and that alternator won't be putting out its maximum anywhere near idle speed. Add to that the ~90% best case inverter efficiency and the power actually used to keep the ICE car running, and you'll probably need to turn down the amperage.

 

[BitJam]

Welcome!

I would consider getting a portable power station such as those sold by Jackery. It doesn't require a 2nd car, It can be useful during power outages and it can be used in your car, for example to run a fridge or something similar. You might have to run the ICE vehicle to keep from fully discharging its battery which is probably not a good idea inside of a garage. IIUC you will get about 4 miles from fully discharging a typical 12V car battery.

Also, I would try to figure out why your car lost almost all of its charge while you were away. Even if you had sentry mode enabled, it should automatically turn off when the charge drops below 20%.

 

[Thot]

Welcome!

I would consider getting a portable power station such as those sold by Jackery.

Also, I would try to figure out why your car lost almost all of its charge while you were away. Even if you had sentry mode enabled, it should automatically turn off when the charge drops below 20%.

Thank you for all your replies, I learned a lot!
Buying a Jackery power station was my next idea, it’s relatively light and I can charge it at home, looks like that’s the way to go.

@BitJam you are raising a good point. Sentry mode and summon were off and after a few days it occurred to me to turn off cabin overheat protection as well, but not the dashcams (but then again, sentry mode was off) but the discharge continued. The only thing I can think is that the 12v battery needed replacement (I could not get to it before leaving), I have replaced it now so we’ll see.

One thing is not clear though, is there a chance that with the neutral-ground bonding plug my impure sine wave little inverter will work or the lack of purity precludes it? I guess I could just try but I don’t want to fry something.

Thanks
Luca

 

[cali8484]

One thing is not clear though, is there a chance that with the neutral-ground bonding plug my impure sine wave little inverter will work or the lack of purity precludes it?

Modified sine wave inverters won't work. Tesla is very sensitive about power quality. A good pure sine wave inverter is necessary. One that does not have too much voltage sag under load. The target load is 12A@120V = ~1400W. So, the inverter power capacity (continuous) should be at least 25% higher.

 

[ATPMSD]

After coming back from vacation oversea I found that my car showed 1% charge,

Honestly, you need to avoid this ever happening. With Sentry and Overheat protection off, the car draws less than 1 kWh per day. Assuming you have the smaller 57 kWh battery that gives you 57-days to go from 100% to 0%

 

[davewill]

This should never happen. How long were you gone and what was the battery level when you left? Even if you left Sentry and cabin overheat protection on, they should have automatically turned off long before the battery got that low to let the car sleep and preserve some charge. Do you use any third party services or apps that access the car? Do you have any further information about WHY the car ran down this far?

If it does happen, it's time for roadside assistance to TOW the car someplace it can charge.

 

[BitJam]

Sentry mode and summon were off and after a few days it occurred to me to turn off cabin overheat protection as well, but not the dashcams (but then again, sentry mode was off) but the discharge continued. The only thing I can think is that the 12v battery needed replacement (I could not get to it before leaving), I have replaced it now so we’ll see.

Cabin overheat protection only operates for 24 hours. I have mine set to "no A/C" to save energy. It's a safety feature in case you accidentally leave kids or pets in the car.

I hope the battery replacement fixes the problem. Please keep us posted!

 

[fhteagle]

was thinking that in an emergency I could use an inverter like this: 1,500W, 12V DC -> 120V AC Inverter from my other (ICE) car to give enough juice to the car to reach the closest (super)charger.

If you do rig this up, watch the temps on your alternator. Most are not adequately cooled to be pulling their max output for more than 1 or maybe 2 minutes at most. Hood open, extra fan pointing at it, etc.

As others said, 120VAC pure or true sine wave, N-G bonded, pull the amps way way down (< 6?) to not overheat your alternator and ICE 12v. If you can find a 12v to 240VAC inverter that would negate the need for N-G bond. But depending on your EVSE it may still demand a proper ground.

If all of that looks like Greek, EcoFlow or similar battery + inverter all in one might be the way to go for you.

TeslaBjorn had some some demonstrations of what it's like using one of those to put some emergency power into the car. Very slow, and you'll get very very very few miles after all the losses from any unit that you can pick up without killing your back.

 

[Sophias_dad]

I gotta agree with others.... this whole thread seems like its unnecessary and the solutions are quite expensive for what they achieve. If the HV battery is getting down to 0% before OP gets home its probably not TOO long before true battery damage will be occurring.

 

[Thot]

@ATPMSD , @davewill and @BitJam, I have the long range model, so about 70 KWh battery. I stayed away for one month in August and the car was not fully charged when I left. I don't remember exactly but was definitely less than 50%, more likely 30% or so. I didn't realize it could lose 1 KWh per day when idle and without sentry, summon etc. running, but just that might explain it.
I use the official Tesla App and Tesla Remote which I had used sparingly because they both need to awaken the car to give me readings, so I am pretty sure that neither is always keeping the car awake.
It seems to me that since I replaced the 12V battery she holds the charge better but I use it almost every day so I won't have a long idle time sample until next vacation. Incidentally, I wonder if there is an app that can automatically log charge % over time, that would be useful.

Thanks again all
Luca

 

[Thot]

....
If all of that looks like Greek, EcoFlow or similar battery + inverter all in one might be the way to go for you.
.... Very slow, and you'll get very very very few miles after all the losses from any unit that you can pick up without killing your back.

LOL, believe it or not your explanation was quite clear (except for "EVSE", which I had to look up). It seems to me that the consensus is not to (try to) use the little inverter.
I am NOT planning to let her discharge to 0% ever again, but as you and @BitJam suggested, a portable power station is the way to go in an emergency. I am looking at the Jackery Explorer 1000 which outputs 1000W steadily, weights 10 Kg and has a capacity of 1002Wh which, if I learned correctly what was said in this thread, should add about 4 miles of autonomy, enough to get to the closest supercharger.

Thanks

Luca

 

[Tiger]

Wouldn't a simpler option be to get a sufficiently rated (and long) extension cable and pull power from your home or something. If necessary, drive the car a bit closer for the charging.

 

[Thot]

Wouldn't a simpler option be to get a sufficiently rated (and long) extension cable and pull power from your home or something.

That was another idea, a 200 ft ( 2 x 100 more likely) 14 AWG cable should probably do. I would have to do it in the middle of the night so that he property manager doesn't shoot me (they specifically forbid to do that, but I take it they mean on a routine basis).

Thanks

Luca

 

[BitJam]

Thanks for the extra info!

. I am looking at the Jackery Explorer 1000 which outputs 1000W steadily, weights 10 Kg and has a capacity of 1002Wh which, if I learned correctly what was said in this thread, should add about 4 miles of autonomy, enough to get to the closest supercharger.

It might be less range than that depending on your wH/mile. Jackery derates their storage by 15%. And charging from 120 v. is less efficient. Bjørn says his car uses about 150 watts while charging. If the battery is really cold then you might not be able to charge at all using 120 v. since almost all the power will be used to heat the battery.

I went for a refurbished 1500 that costs less than the 1000. There is a 90 day window for returns.

Oh yes, the newer (mid 2021+, I think) M3 LR and P start with an 82 kWh battery. You may be able to detect the roughly 1 kWh/day drop in less than a day by looking at the range. One reading wouldn't mean much but if you average over 10 then you should get a good idea. Unfortunately there could be a systematic error due to the range changing with battery temperature.

If you were getting warnings that the 12 volt battery needed to be replaced then my bet is you probably fixed the problem by replacing it. I doubt the 12 volt battery was sucking up 1 kWh/day but there is a lot of overhead in the Tesla when it wakes up to charge the low voltage battery.