The only reason I doubt the purchase

[Doug_G]

A 30 A 240 recpticle from your generator should charge at 6.6 kw/hour. Depends on the capacity of your generator, and the type of power and recpticle it provides.

I know the Roadster is very fussy about the power quality. It will refuse to charge from most generators. Probably the Model S is the same.

 

[Lloyd]

I know the Roadster is very fussy about the power quality. It will refuse to charge from most generators. Probably the Model S is the same.

That makes sense. We have a cogeneration plant about a mile from my house. At a Tesla roadster test drive day we hosted at my house last year we had trouble charging here. The charge cycles kept tripping off line with a high voltage warning. When I called PG&E to complain they indicated that the cogeneration plant had been throwing "spikes" that were causing the issue. The cogeneration had to shut down until they could clean up the power.

 

[Doug_G]

Modern generators use power inverters, and they definitely will not work. But you can't expect even an older model to work. Transport Canada tried charging their Roadster from five different generators of different types and vintages, and not one of them worked.

 

[evinfairfax]

Modern generators use power inverters, and they definitely will not work. But you can't expect even an older model to work. Transport Canada tried charging their Roadster from five different generators of different types and vintages, and not one of them worked.

When you say it won't work because it's a power inverter, can you help the software guys in the room understand that?

 

[rlawson4]

So your average speed is likely to be well above 55mph, and so your actual range is likely to be 20% or more below the ideal miles. Something to bear in mind.

Good point.

 

[Doug_G]

When you say it won't work because it's a power inverter, can you help the software guys in the room understand that?

A basic generator is a small ICE turning an alternator. The frequency output of the alternator depends on the motor RPM and gearing. Applying more load to the generator causes the motor to slow down, so it would have some kind of automatic throttle to compensate for that and keep the RPM and therefore AC frequency roughly constant. The frequency would probably end up varying quite a bit anyway. That plus any spikiness would probably cause the Roadster to refuse to eat the juice.

I've been told (but I've not researched this myself) that many modern generators have a built-in power inverter. An inverter is an electronic device that converts power from one voltage/frequency to another. The PEM in the Roadster does that same job, in fact, converting DC from the batteries to 3-phase AC for the motor.

I expect putting an inverter in a generator would have advantages in that you could build the mechanical and magnetic parts in a fashion that was optimal for their operation, but that wouldn't produce 120V 60 Hz. You then use an inverter to convert the output voltage to the needed 120V 60Hz (or 240V or 50Hz... maybe even switchable by the user).

The problem with inverters is they tend to generate a lot of harmonics, and that's probably also something a Roadster wouldn't like to eat.

 

[Dave EV]

The problem with inverters is they tend to generate a lot of harmonics, and that's probably also something a Roadster wouldn't like to eat.

It's not so much the harmonics that generators tend to have issues with - it's that cheap ones tend to put our either modified sine waves or even worse - square waves instead of clean sine waves. Another issue that the car may have is with grounding.

Here's a page which discusses the quality of power a good vs bad generator can put out: ScreenLight & Grip's E-Newsletter - Portable Generators in Motion Picture Production - All Generators are not created Equal

 

[Doug_G]

It's not so much the harmonics that generators tend to have issues with - it's that cheap ones tend to put our either modified sine waves or even worse - square waves instead of clean sine waves. Another issue that the car may have is with grounding.

Actually, there's no difference whatsoever between distortion and harmonics. They are two different ways of looking at the exact same phenomenon.

You can make any arbitrary waveform by combining a fundamental (sine wave) with a series of harmonics. For example, a square wave is equivalent to a sine wave plus a series of odd harmonics falling off as 1/k. Here's a diagram that shows how this works:

If you continue adding harmonics out to infinity you get a perfect square wave. Similarly you can build any other waveform from a series of harmonics. If you're mathematically inclined look up Fourier Analysis.

Another issue that the car may have is with grounding.

Good point.

 

[evinfairfax]

Doug_G and drees, thanks for the explanations.

 

[Andrew Wolfe]

The problem is not using an inverter - it's using a low quality inverter. My PV Solar uses an inverter that is allowed to feed right into the grid. I'm sure it is quite clean.

 

[cinergi]

Having researched generators recently for another purpose, I see 3 basic categories -- general purpose (the most common), tech-friendly (not common), and inverter (typically lower power and very expensive). The tech friendly model does NOT use an inverter, but is somehow designed such that THD is low and frequency is well-maintained. I don't know if an inverter-based one would work particularly well -- depends on the quality. And as far as output quality goes, I'd guess the Honda ones would take the prize ... would be interesting to know if the Roadster would charge from one of those. But they're horribly expensive. If I end up getting the tech-friendly generator (probably 6.5-8KW) I may see if the Roadster will charge from it.

I wonder if the inverter models are generating DC and converting to AC or if they're AC-DC-AC ... going to have to read Drees' link -- looks like the stuff I want to know as I select a generator (thanks!)

To rlawson4 -- I've done a couple long-range trips in the Roadster and I think you'll be OK if you charge on a NEMA14-50 @40A for 2+ hours. You'll still need to take it slow and not detour significantly. Weather and other factors can come into play so if you can, the HPC would be helpful in giving you a lot of breathing room plus the ability to drive faster. Personally I'd go for the HPC in your case (depends on your financial situation).

 

[rlawson4]

Having researched generators recently for another purpose, I see 3 basic categories -- general purpose (the most common), tech-friendly (not common), and inverter (typically lower power and very expensive). The tech friendly model does NOT use an inverter, but is somehow designed such that THD is low and frequency is well-maintained. I don't know if an inverter-based one would work particularly well -- depends on the quality. And as far as output quality goes, I'd guess the Honda ones would take the prize ... would be interesting to know if the Roadster would charge from one of those. But they're horribly expensive. If I end up getting the tech-friendly generator (probably 6.5-8KW) I may see if the Roadster will charge from it.

I wonder if the inverter models are generating DC and converting to AC or if they're AC-DC-AC ... going to have to read Drees' link -- looks like the stuff I want to know as I select a generator (thanks!)

To rlawson4 -- I've done a couple long-range trips in the Roadster and I think you'll be OK if you charge on a NEMA14-50 @40A for 2+ hours. You'll still need to take it slow and not detour significantly. Weather and other factors can come into play so if you can, the HPC would be helpful in giving you a lot of breathing room plus the ability to drive faster. Personally I'd go for the HPC in your case (depends on your financial situation).

Thanks. I think I understand charging better and my concerns are well-addressed. I am very much looking forward to this vehicle.

 

[W.Petefish]

If anyone gets a generator, make sure it has a Pure Sine Wave output. Otherwise you are just wasting your money. I've done some research into the topic as well and if you have the frequency too high it (the car) will throw a fault, same goes for too low as well as too high voltage (255v) or too low (200v).

 

[vfx]

Is the point of this conversation that a Roadster will not charge on a genny? Because Tesla does it all the time from their trailer.

Large trailered event-film quiet generators work fine as I have plugged in a few of them with success. Never tried a construction trailer genny though.