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Stupid Question: Emergency Charging on a Gas Generator

Vince Cobelo

Member
Nov 1, 2015
271
37
Palmetto, FL
This is a curiosity question as much as anything. I did a search on this and not much came up beyond very early threads about Roadsters.

I understand that the problem with using any electrical source it has to be clean for the MS to accept charging. With today's inverter generators that generate very clean energy why couldn't one be used in a pinch. Say my wife runs out of power and is stuck a few miles from the house. Put the inverter generator in my pickup and plug the car into it for a hour or two to get the car home. Probably very slow charging...I get that. But like I said....in a pinch.
 

jeffro01

Active Member
Jan 30, 2013
2,688
1,944
Teller County CO
If you can clean up the power sufficiently enough before it hits the UMC then depending on voltage and amperage it could work. The problem though, is getting the electricity signal cleaned up enough before you get to the UMC...

Jeff
 

cinergi

Active Member
Sep 17, 2010
2,176
40
MA
I've done it.

That said, I was never able to get the UMC to work by directly hooking it up -- it didn't like the grounding situation.
 
Last edited by a moderator:

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
I've done it.

That said, I was never able to get the UMC to work by directly hooking it up -- it didn't like the grounding situation.

Generators have always been an interesting item to deal with when it comes to bonding and grounding.

If run completely standalone with plug-connected loads only, in theory the generator's neutral and ground should be bonded together to the generator's frame, and a ground rod should be driven into the earth. In many generator sets, however, the ground is left floating from the neutral and has no defined relationship to the ungrounded conductors. The reason it works for most appliances is that they frankly don't care whether ground is present and/or stable. The Tesla does care - and as a result it doesn't like when it can't detect a stable relationship / steady voltage between a line conductor and ground.

The reason many generators don't have this bonding done by default is that occasionally they are used to feed a home electrical system where the bonding is already done, and having multiple points where EGC and neutral are bonded can create undesired current return paths.

If you do use a generator to charge Model S, look in its instructions for a way to bond neutral and ground together. In some cases, generator manufacturers will sell a dummy plug and/or an adapter that will provide the necessary bonding (and therefore voltage stability).

EDIT: I should also note that there are certain types of inverter generators that use floating-neutral configurations where you cannot bond ground to neutral. It is reported the Honda 2000 & 3000 models are this way -- for 120V, their inverters generate +/- 60V from ground for the "hot" and "neutral" of the 120V outlets, so it's not really a "neutral". Bonding neutral to ground here will cause problems for the generator (it's like shorting hot to neutral). Be sure your generator manual or its manufacturer contemplate bonding ground and neutral together.
 
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samcarney

Sam C
May 22, 2009
261
16
Great Lakes, Sonoran Desert
I've done it.

That said, I was never able to get the UMC to work by directly hooking it up -- it didn't like the grounding situation.

I have charged my Roadster and MS 85 with a portable generator. It works best when the generator is plugged into the house and I plug the car into a NEMA 14-50 outlet.
This confirms the grounding issues previously discussed.
 

supratachophobia

Active Member
Sep 24, 2014
3,851
2,681
Columbus, Ohio
Basically, if the UMC doesn't complain, it should be fine. The UMC knows what the car should and should not have plugged into it, and will refuse to charge or sacrifice itself to save the on-board charger.
 

modelx007

Member
Sep 1, 2015
259
41
boca raton, fl
I have a generac 22kw generator. For emergency purposes what is best way to charge model s 90d? Someone told me to just use my dryer outlet? I'd say the run would be about 20 ft.
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
I have a generac 22kw generator. For emergency purposes what is best way to charge model s 90d? Someone told me to just use my dryer outlet? I'd say the run would be about 20 ft.

Assuming your Generac is a whole-house genset connected via a transfer switch and your dryer receptacle is on the panel getting backup power, then that's probably the best option you have in an emergency. Also assuming - just because you asked the question - that your 14-50 is not on the backup panel.
 

modelx007

Member
Sep 1, 2015
259
41
boca raton, fl
Assuming your Generac is a whole-house genset connected via a transfer switch and your dryer receptacle is on the panel getting backup power, then that's probably the best option you have in an emergency. Also assuming - just because you asked the question - that your 14-50 is not on the backup panel.
Correct on your assumptions. What can I run with charging the model s in emegency? Ac?
Also what cord do I use that I would run from the dryer outlet? I've seen a few and not sure which is the best?
 

Vince Cobelo

Member
Nov 1, 2015
271
37
Palmetto, FL
I was talking portable generators. A whole home backup generator naturally would do the trick no problem.

I'm going to pickup a 1600 watt inverter generator and give it a try. I know it will be a very slow charge but if it is clean it should do just fine with a 110 adapter. If not, I'll have to have plan B.
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
Correct on your assumptions. What can I run with charging the model s in emegency? Ac?
Also what cord do I use that I would run from the dryer outlet? I've seen a few and not sure which is the best?

There are two types of dryer receptacles, 10-30 and 14-30, depending upon when your home was built. There are some Tesla adapters available for the UMC plugging into these receptacles, but you noted 20 feet which is beyond the 18 ft of the UMC. Your best bet, for emergency use only, is to create an emergency cable, about 6 feet long, appropriately wired and labeled "for emergency Tesla charging only" (or purchase from a place like EVSE adapters). See my FAQ for more details.

As for what you could run with the Model S charging, a 22 kW genset can run about 90A of load. With Model S charging at the full 24A off a 30A dryer receptacle (the continuous limit of that receptacle), you'd still have quite a bit of room for other loads - certainly your A/C and many other appliances.

- - - Updated - - -

I was talking portable generators. A whole home backup generator naturally would do the trick no problem.

I'm going to pickup a 1600 watt inverter generator and give it a try. I know it will be a very slow charge but if it is clean it should do just fine with a 110 adapter. If not, I'll have to have plan B.

Some inverter generators won't work, depending upon how their grounding is set up. If it's a "floating neutral" generator, the Tesla UMC will flash red four times because ground won't be stable relative to the line voltage. Some generators can use a special plug to bond ground to neutral to make it work, but in others it will not work (and will destroy the generator).
 

miimura

Well-Known Member
Aug 21, 2013
6,186
5,781
Los Altos, CA
I was talking portable generators. A whole home backup generator naturally would do the trick no problem.

I'm going to pickup a 1600 watt inverter generator and give it a try. I know it will be a very slow charge but if it is clean it should do just fine with a 110 adapter. If not, I'll have to have plan B.
In addition to what FlasherZ said, you should check the continuous rating of that generator. 1600W is not very much. At the most, you should pull 80% of 1,600W, which would be dialing down the amps on the main screen to 10 amps from 12 amps.
 

modelx007

Member
Sep 1, 2015
259
41
boca raton, fl
There are two types of dryer receptacles, 10-30 and 14-30, depending upon when your home was built. There are some Tesla adapters available for the UMC plugging into these receptacles, but you noted 20 feet which is beyond the 18 ft of the UMC. Your best bet, for emergency use only, is to create an emergency cable, about 6 feet long, appropriately wired and labeled "for emergency Tesla charging only" (or purchase from a place like EVSE adapters). See my FAQ for more details.

As for what you could run with the Model S charging, a 22 kW genset can run about 90A of load. With Model S charging at the full 24A off a 30A dryer receptacle (the continuous limit of that receptacle), you'd still have quite a bit of room for other loads - certainly your A/C and many other appliances.

- - - Updated - - -



Some inverter generators won't work, depending upon how their grounding is set up. If it's a "floating neutral" generator, the Tesla UMC will flash red four times because ground won't be stable relative to the line voltage. Some generators can use a special plug to bond ground to neutral to make it work, but in others it will not work (and will destroy the generator).
Ok I'll take a photo and paste it here tomorrow to confirm which I have. :)

I found this on amazon and someone in a review said they used it with the umc cable. Camco 55195 50 AMP 30' Extension Cord with PowerGrip Handle
Where would I exactly plug this into?

On a new question what would I use if I park at a hotel or friends house that has only 110? Can you send me to a link? I assume this would plug into the umc cable like the above Camco but need it to be 110.

Thanks for your insight! This is hard stuff to get all straight. Lol
 

green1

Active Member
Mar 25, 2014
4,548
1,121
Calgary, Alberta, Canada
On a new question what would I use if I park at a hotel or friends house that has only 110? Can you send me to a link? I assume this would plug into the umc cable like the above Camco but need it to be 110.
Use the 110 adapter that comes with the UMC, and a heavy gauge extension cable (not the normal cheap indoor ones) I have one, but I can't for the life of me remember where I got it (was a long time ago) and the car charges just fine on it.
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
Ok I'll take a photo and paste it here tomorrow to confirm which I have. :)

I found this on amazon and someone in a review said they used it with the umc cable. Camco 55195 50 AMP 30' Extension Cord with PowerGrip Handle
Where would I exactly plug this into?

You still need an adapter that will take your 14-50 extension cord and allow you to plug it into the 30-amp dryer outlet. EVSEadapters.com has some cables that should work.
 

green1

Active Member
Mar 25, 2014
4,548
1,121
Calgary, Alberta, Canada
You still need an adapter that will take your 14-50 extension cord and allow you to plug it into the 30-amp dryer outlet. EVSEadapters.com has some cables that should work.
I remember hearing somewhere that the UMC didn't actually use the neutral plug, and as a result you could effectively saw the neutral pin off a 14-50 and then it could be used in either 14-50 or 14-30 outlets. EVSEadapters has an extension cord pre-built that way too:
Heavy-duty NEMA 14-50 extension cord for Tesla, 20 ft.
Seems like a simple enough solution to get extra versatility (just remember to dial down those amps on a 14-30!!!)
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,013
I remember hearing somewhere that the UMC didn't actually use the neutral plug, and as a result you could effectively saw the neutral pin off a 14-50 and then it could be used in either 14-50 or 14-30 outlets. EVSEadapters has an extension cord pre-built that way too:
Heavy-duty NEMA 14-50 extension cord for Tesla, 20 ft.
Seems like a simple enough solution to get extra versatility (just remember to dial down those amps on a 14-30!!!)
Correct. Someone had even surgically removed only half of the neutral blade so it could fit in either as well. Not really needed, but helped stabilize the plug a bit.
 

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