Is it safe to charge MS from a portable generator in power-out emergency

Is it safe to charge MS from a portable generator in power-out emergency

One of those, "how many angels can you fit on the head of a pin" questions just came up in my house. We are in the process of ordering a P85 now (won't bore you with the logistical details) and am running the line for the charger. My wife asked, "What if we lose power (which we do about once a month)"? I said, "we can always use our emergency generator to charge the Tesla" (generator is a propane driven, 8000 watt peak portable -- not a standby -- with the same nema 14-50 output connector that the Tesla uses). This is one of those $1,000 Home Depot jobs that I connect up to a transfer switch on my house when the power goes down.
Question: if I need to do so during an outage, is it safe to connect the car charger directly to the generator output to charge the car? I don't know what type of surge suppression or voltage stability the generator provides.
Separately (as long as I am asking), does anyone know if there has been any talk about being able to use the Tesla as a power source in an emergency (i.e., plugging it into my transfer panel and using it as the power source, instead of a generator)? Not something I am thinking of, but just curious.

jai9001 | February 2, 2014

How many miles do you drive a day?

How long do your outages last?

I typically just wait for the outage to end and then charge as I have more than enough charge.

PaceyWhitter | February 2, 2014

There is no danger to the model s. If the power produced is not stable enough, the S just won't charge from it.

Captain_Zap | February 2, 2014

I know that Roadsters wouldn't charge on generators. I haven't heard about any Tesla tests. I would think that the car wouldn't like the unsteady power due to changing loads on a household generator.

When the power goes out and I know it is only a few hours I'll go sit in the Tesla, and keep warm. It was the only way I could send out mail on one occasion. We only use the generator if we are out more than 12 hours.

We'll run out of generator gas long before we run out of battery power in the Tesla. We keep a lot of generator gas on hand too. By the time we run out, the gas stations run out too.

Al1 | February 2, 2014

"We'll run out of generator gas long before we run out of battery power in the Tesla."

And then when you run out of generator gas you'd better have enough miles in your car to get to the point where there is gas and bring it back.

PorfirioR | February 2, 2014

Barring a zombie apocalypse, or unless you are driving laps around the yard, I am not sure how you would run out of miles before driving past some semblance of civilization where you can get a charge.

Just charge your car every day and you will be fine. Use your generator for other more important stuff, like your refrigerator. When you go to get gas for the generator, take advantage of the opportunity to get a few miles of charge.

I saw in one of Björn's video how he left his Model S unplugged at the airport for 4 weeks and still had plenty of charge left when he got back ( If you go 4 weeks without power, you have bigger things to worry about.

Captain_Zap | February 2, 2014

@A1 - We live in an area where we can be without power for 5 days at a time, and that is an big improvement! Now it happens only once every couple years, but it used to be several times a year, so we are prepared. When we moved here we routinely lost power a couple times a month from fall through spring. We still lose power any time it snows or the wind picks up.

The entire region gets isolated by flood water every few years. The gas stations run out of gas and can't run their own generators because gas can't get to the stations. It's the wild, wild west.

I don't worry about the Tesla battery running out because we can't go far anyway with I-5 flooded, bridges shut down or washed out and all the alternative routes closed. Nothing is open either.

Floods here are apocalyptic. They happen with more frequency and severity too. Flood plains are filled because it is cheap land and replaced with big box stores, warehouses and other large facilities. The mountains are not holding water like they used to either.

I never could figure out how those big box stores and warehouses got around all the rules about filling and building on flood plain. It used to be sacred and protected land because it was so critically important. At one point they couldn't get authorization to add to I-5 and raise the elevation of it because of the laws.

logicalthinker | February 2, 2014

I know for the Volt you can charge with a generator as long as it's a pure sine wave generator, or maybe also square waves... anyway, you can also get some gizmo that makes the power output into pure sine waves.

SamO | February 2, 2014

I would assume that if you can plug the generator into the house, you can plug your MS into a 110 or 220 plug INSIDE the house, right?

Dcwittenborn | February 2, 2014

I can report that our 20KW propane powered genset charges my Model S with no problem whatsoever. Actually better than grid power. My 14-50 outlet on grid power frequently causes the S to drop amperage by 25% with the latest software update. The other night, we had an outage and the S was fully charged in the morning and charging amperage had not been rolled back.

logicalthinker | February 2, 2014

SamoSam, see my comment.

The power delivered by a lot of generators is crude compared to the power delivered by the power company.

At least for the Volt, a pure sine wave generator is advised.

PBEndo | February 2, 2014

Bob W posted a video to YouTube about charging the MS with a generator

Brian H | February 2, 2014

Drawing power from the car was discussed by TM in design phase, but is off the table for the present.

brooklynrab | February 2, 2014

Thanks to all of you. As I said, this was a "how many angels on the head of a pin" type question. Too bad they won't permit us to reverse the power flow out, per Brian H. That would be pretty cool.

shop | February 2, 2014

The consensus from other threads is that charging from a generators can work, if the generator produces clean enough power (sine waves versus square waves, voltage drops under load, etc.). So YMMV.

Also, for your generator, make sure to reduce the amperage draw from your vehicle before plugging it onto the generator. The Tesla will by default try to draw 40A/240V, or 10,000 watts from a NEMA 14-50 outlet.You said your generator only outputted 8,000 watts. So you'd have to reduce the amerage draw to something like 20A to be safe.

Pungoteague_Dave | February 2, 2014

We have a stationary 55kw Generac propane generator at the farm for whole property backup in the oyster operation (spat would die without continual saltwater pumping, and the walkin inventory chillers are mission critical). We have regular outages and the car is often charged by our unconditioned generator power with no issues. Interestingly, we must have the generator despite having 27kw solar panels that produce more than twice our average electricity requirements, as the PV panels must be automatically shut off whenever the grid power is interrupted. Something about not backfeeding the grid while repairs are underway in order to protect the power company workers. The generator supplies power to the property after the switch gaps out the grid. Inefficient, redundant, and expensive, but until battery storage systems can handle these kinds of loads for several days, the best we can do.

I would attach pretty much any 120 or 240 generator to a Model S, and let the car's charging system determine how and whether to use the power. You cannot damage the car with "bad" power, as it is self-diagnostic and protects against bad sources.

DallasTxModelS | February 6, 2014

The charging instructions from Tesla say not to use a portable generator. I would think because the system that monitors charging shuts down if the electricity supply isn't a constant stable flow. Portable generators spike and drop and are not consistent. I was out in a machine shop that was using Honda generators to supply electricity and the incandescent flood lights flickered so I assumed it was the unsteady supply of electricity produced by the ever changing speed of the gas motor driving the generator.

jeffsstuff | February 6, 2014

One word of caution. Many portable generators have a floating neutral. A workaround for this (I'm not an electrician so do this at your own risk) is to bond the neutral to the ground (I think you can do this in a different plug) and then ground the unit to some reasonable ground (cold water pipe, ground rod, etc.

triss1 | February 7, 2014

@jeffsstuff- What's the point of bonding the neutral? The MS uses 240 volt, so it has no use for neutral. In fact, it will work just fine on a 240 circuit that has no neutral.

David70 | February 7, 2014

I'm dubious about the 240V working with a floating neutral. I know it won't work for 120V if the neutral is floating.

jeffsstuff | February 7, 2014

I've heard that this can be an issue. Im not sure why. Now if someone would like to publish some schematics for us, I'd be delighted to look at those.

GeekEV | February 7, 2014

It's not the neutral at 240V, it's the ground. EVSEs (including the Tesla UMC) require a true ground so you'll have to sink the ground to Earth for it to work properly. Bonding the neutral to ground is also necessary if it's only a 120V generator - as you say, 240V has no use for neutral.

You will also want a generator that produces a true sine wave, not a square wave. Once you've done all of those things, it should work, but I've not done it myself.

See this thread (and other threads) on the LEAF forums for more details:

Sudre_ | February 7, 2014

PD - about the solar and not back feeding the grid. I was given the same speech when my solar was installed.

What you have is what is allowed. Realistically (outside code just thinking) if the solar is on the other side of the transfer switch with the generator then the solar can remain on but without batteries to keep it balanced I don't know if it would play nice with the generator. Whenever there are two 60hz sources one has to keep the cycle locked in and the other matches. I don't know how that would work. I just know it's a lot more complicated than not back feeding the grid.

OK back to the charging on generator topic :-)

Pungoteague_Dave | February 7, 2014

@sudre, My generator is a 55kw unit, so way oversized for the property anyway. One of the problems with it is that it does not get enough exercise in terms of load demand. Apparently a generator should be sized to the maximum load but not exceed it by much, as it runs with too little generation. I don't know all the details, but was told after the fact that my 8-cyclinder GM engine that runs on LP gas is way too much for our farm's needs.

I originally told the electrician that we wanted to be able to run everything on the property simultaneously, including five A/C units, upweller pumps, etc. Now every Wednesday we hear it fire up from 1/4 mile away and it runs for a half hour to prove it is still all good. We have no neighbors to object, but in the future I would install something less than half that size for better efficiency. Ultimately the answer may be a battery bank to absorb the excess solar production, but it will be many years before that solution becomes price-competitive with a generator, and it is questionable whether it could bridge a long outage during a storm when no solar production happens.

JeffreyR | September 22, 2014

I am glad this topic is already so well covered. My wife just had her first test drive and she was curious about our options for charging during power outages as we live on the Gulf Coast in "Hurricane Alley." We are planning the triple threat: solar panels, battery, and generator. The generator would be for Ike-like outages (3+ weeks) and the solar + battery would be used for day-to-day operations.

Other resources:

charging options when lose power

PV_Dave @US-PA | September 22, 2014

I agree that for short outages, you might not need to charge. If severe weather has caused an extended outage, conditions might not be safe to venture far anyway. I do sometimes bump my car's charge level up to 90% when questionable weather approaches, vs. typical 75% for daily driving, just in case.

If you have battery backed solar, that should be fine for charging.

If you have a sine wave "inverter" style generator that's properly grounded and not overloaded, that should be fine for charging.

Other emergency power configurations may work, but I'm more comfortable with one of the above. I don't want to feed crappy power to my computers or my car, personally, and most generators produce pretty crappy power.

We love our Honda EU6500is, and intend to keep it until we've got a whole lotta battery backup for our solar. Quiet, efficient, and good quality power output relative to typical generators, and runs all of our "critical loads" easily. I haven't needed to use it to charge our Tesla yet, but I certainly can if needed.

Brian H | September 23, 2014

Have a look at this, too: .

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