Generator Charging

[ajdelange]

You can find videos of people charging their Teslas (or trying to) from various portable generators. Some figure out the ground thing and some don't.

I've charged my X from a 1 kW Jackery potable power pack. It's my 3.5 mile jerry can.

Sponsored

 

[Newton]

these guys a connect a small generator they had to use a bonding plug to fool the ground

 

[Newmanr12]

these guys a connect a small generator they had to use a bonding plug to fool the ground

Yea I saw that video, it's what really got me thinking.

One of the generators they used did cause the car to stop charging at some point, even though the generator was still going. Didn't really get a lot out of the small one.
They did go to a larger, grounded, 7KW honda generator, which I believe was putting out a pure wave, and got better results.

I didn't see anything really talking about whether their original issue was size, grounding, or sine wave cleanliness... I didn't watch the 3rd video though.
I'd like to nail down wether or not it needs a really clean wave because that triples the cost, and really limits the size. I was also curious about warranty type issues.

I guess in a couple years, I'll test it out with my buddy's conventional 10kw as long as the manual doesn't forbid it... Maybe with the site posted about there will be some prefabricated riggs made to slide in and out of the truck

 

[ajdelange]

In the video linked above one can clearly see on the panel of the genertor "Floating Neutral" in three languages. And he wonders why he needed a grounding adapter?

In the Tesla charger the "AC" enters the through the charging port and goes straight to bridge rectifier where the positive voltage portions of it go straight through and the negative voltage portions are flipped so they are positive too. The output looks like a bunch of nice smooth half sinewave pulses if the input is a pure sinewave or a train of stepped pulses, at 120 per second in either case, if the input is a modified sine wave. Both types of pulse train have a large DC component and large AC harmonic content too. The AC is easily suppressed by putting a capaitor across the output of the bridge. The hardest harmonics to suppress are the 120 Hz ones so I don't see why it makes much difference if the input is sloppy modified or neat sine. But I haven't worked in a power supply factory for 50 years.

The smoothed DC gets chopped up into higher frequency (kHz) square waves whose widths are modulated (for voltage regulation). These are stepped up to battery level voltage in a transformer, rectified again and the resulting DC sent to the battery.

Beyond that I'm not sure that the generators produce modified sine wave (but I've never worked in a generator factory). All the machines I've ever owned had an engine with a governor that regulated the speed to 3600 rpm (and in the newer ones to 1800 which makes them quieter). Some AC was tapped and rectified to get field current and the field current adjusted to regulate voltage as load varied. In the generators that are equipped with inverters the motor is spun at whatever speed makes it most efficient and a three phase alternator is rotated at that speed. The output is rectified and the DC passes to an sine wave inverter. The inverter's PWM reference signal is referenced to a crystal which makes it very stable and that reference can be passed to another machine so that two or more of these can be bonded together for more power output.

Now I guess you could save a few bucks by using this basic design with a modified inverter instead of a sine wave inverter an that is, perhaps, where the notion of a non pure sine wave in a generator comes from. The old style generators produced something pretty close to a sine wave but there definitely was harmonic distortion depending on, for example, how it was wound.

 

[Bill906]

In the Tesla charger the "AC" enters the through the charging port and goes straight to bridge rectifier

I do not believe the input of the Tesla charging circuit is a simple passive (diode) rectifier but some kind of active (transistor) converter. I do not know for sure how Tesla does it, but I’m guessing they would need to synchronize the gating of the transistors with the AC line. The charger may not be able to synchronize with a non-sinusoidal waveform, hence requiring a “pure” sine wave generator.

 

[jonny]

I live out west and Im getting the 500 because I need it. but if you should go off road what about these new batteries could it be possible to give someone a little of my charge to get them back to the road? like getting a friend out of trouble.

 

[Bill906]

I live out west and Im getting the 500 because I need it. but if you should go off road what about these new batteries could it be possible to give someone a little of my charge to get them back to the road? like getting a friend out of trouble.

We of course do not know for sure, but I suspect you could charge a friend in need’s BEV from the power outlets in the vault. Just like they said you could charge the cyberquad.

 

[ajdelange]

I do not believe the input of the Tesla charging circuit is a simple passive (diode) rectifier but some kind of active (transistor) converter. I do not know for sure how Tesla does it, but I’m guessing they would need to synchronize the gating of the transistors with the AC line. The charger may not be able to synchronize with a non-sinusoidal waveform, hence requiring a “pure” sine wave generator.

There's the quote but where's my response? Anyway: The input bridge may well be made up of active devices for a variety of reasons such as that if they are gating over only part of a cycle can be used to regulate current draw (from the minimum 5 A up to the maximum 48 A) and, of course, the bridge is, with active devices, bidirectional (ready to be used as an inverter if Tesla eventually decide to add V2H or V2G and, prior to that, it could be used for the in-bed AC source. With a sine input output energy per cycle would be a smooth function of firing angle. With a stepped one it would not and that might make regulation more difficult indeed that stage is used for regulation as it can be done at the inverter stage as well and that bridge must be gated and so must contain switches rather than diodes.

Synchronization would not be a problem as both stepped and true sinewaves obviously have huge 60 Hz components and the PLL would be designed to lock to that. In fact the first thing it probably does (the PLL) is hard limit the input waveform (converting it to a square wave) so that it can lock equally well to any input voltage in which case the shape of the incoming wave is immaterial.

The cars do do some checking on the quality of the input signal. In particular they look for amplitude modulation at a high rate which then interpret as fluctuating source impedance signifying a poor mechanical connection. If they see this they reduce charging current drawn. This is mentioned in the manual. But there is no mention (that I can find) about avoiding generators or modified sine wave inverters as charging sources.

 

[ajdelange]

My previous post sat there with a quote of the material I wanted to comment on but no comments. ??

Anyway, I just edited it to put the comments back in so have another look if interested in what was being discussed.

 

[Bill906]

I have been researching this very subject recently. I have found may posts, videos and articles saying Tesla does not recommend using private generator. With that said most say you can do it as long as you make sure you have two things, you need a pure sign wave generator, and you need to have neutral bonded with ground. I also read the article by Electrek stating the model 3 has the hardware available for Bidirectional charging, and it was assumed the feature was waiting to be activated by an over the air update. I also watched the video of a very smart person who took the time to show that bidirectional charging is not possible in that charger. He pointed out that there were some components that were assumed to be transistors but he later showed they were in fact diodes. He even made a follow up video showing that they definitely are diodes as apparently he got feedback from people claiming they were not. Diodes are passive devices that only allow current flow in one direction. Therefore they prevent bidirectional charging.

In that video it showed the input to the charger to be an active converter using transistors. With that information I posted to this thread that the input to the charger is not a simple rectifier as previously stated in this thread, but an active converter. I then explained a true sinewave may be needed to synchronize the active converter to the AC line.

Now it is suggested In a new post to this thread that the active converter is either for current regulation, or bidirectional charging. I admit it could be for current regulation, but I doubt it. If that was the only reason they used transistors, they could have simply used diodes (passive converter) and did the current regulation in the next stage of the charger (The DC to AC inverter). As far as bidirectional charging goes, the video that debunks Electrek’s findings shows the circuit is not capable of bidirectional charging.

The video does say the active converter, along with an inductor are used for power factor reasons and also says the active converter with the inductor boost up the voltage. I agree with the video that the active converter along with an inductor can be used to bump up the voltage. (Think points and condensers in an old ICE used to create the high voltage needed to make spark plugs spark). I believe the timing of this transistor gating would need to be critical to the voltage level at the time of firing of the gates. I believe the phase lock loop (PLL) algorithm would need to latch on to a true sinewave voltage waveform to time that gating correctly.

I do question the video saying the active converter is used for power factor reasons as I don’t see any reason power factor would be an issue. What I think he meant was not so much for power factor correction, but for harmonic mitigation. Non-unity power factor and harmonic distortion are two completely different problems in the electrical engineering world. They both however can be solved with a propertly sized and purposed active converter. Harmonics are caused by, among other things, non-linear loads. Non-linear loads are loads that are not constant throughout the sine wave cycle. Passive converters only conduct when the voltage of the signwave is greater than the DC voltage on the other side of the rectifier, making them non-linear loads and sources of harmonic distortion.

Maybe you can charge a Tesla with a generator that produces other than a pure sine wave voltage waveform, but with the evidence I’ve seen so far I’m leaning toward true sine wave is required. I guess the only way we’ll know for sure is if Tesla tells us, or if someone has access to a modified sine wave or square wave generator and wants to try charging their Tesla from it. I’m thinking square wave power generators are going to be very hard to find and with inverter technology were it is, modified signwave generators also hard to find.

Here is a link to the Electrek arcticle. Being good jounalists they‘ve included the video debunking the article.

https://electrek.co/2020/05/19/tesla-bidirectional-charging-ready-game-changing-features/

 

[Newmanr12]

I have been researching this very subject recently. I have found may posts, videos and articles saying Tesla does not recommend using private generator. With that said most say you can do it as long as you make sure you have two things, you need a pure sign wave generator, and you need to have neutral bonded with ground. I also read the article by Electrek stating the model 3 has the hardware available for Bidirectional charging, and it was assumed the feature was waiting to be activated by an over the air update. I also watched the video of a very smart person who took the time to show that bidirectional charging is not possible in that charger. He pointed out that there were some components that were assumed to be transistors but he later showed they were in fact diodes. He even made a follow up video showing that they definitely are diodes as apparently he got feedback from people claiming they were not. Diodes are passive devices that only allow current flow in one direction. Therefore they prevent bidirectional charging.

In that video it showed the input to the charger to be an active converter using transistors. With that information I posted to this thread that the input to the charger is not a simple rectifier as previously stated in this thread, but an active converter. I then explained a true sinewave may be needed to synchronize the active converter to the AC line.

Now it is suggested In a new post to this thread that the active converter is either for current regulation, or bidirectional charging. I admit it could be for current regulation, but I doubt it. If that was the only reason they used transistors, they could have simply used diodes (passive converter) and did the current regulation in the next stage of the charger (The DC to AC inverter). As far as bidirectional charging goes, the video that debunks Electrek’s findings shows the circuit is not capable of bidirectional charging.

The video does say the active converter, along with an inductor are used for power factor reasons and also says the active converter with the inductor boost up the voltage. I agree with the video that the active converter along with an inductor can be used to bump up the voltage. (Think points and condensers in an old ICE used to create the high voltage needed to make spark plugs spark). I believe the timing of this transistor gating would need to be critical to the voltage level at the time of firing of the gates. I believe the phase lock loop (PLL) algorithm would need to latch on to a true sinewave voltage waveform to time that gating correctly.

I do question the video saying the active converter is used for power factor reasons as I don’t see any reason power factor would be an issue. What I think he meant was not so much for power factor correction, but for harmonic mitigation. Non-unity power factor and harmonic distortion are two completely different problems in the electrical engineering world. They both however can be solved with a propertly sized and purposed active converter. Harmonics are caused by, among other things, non-linear loads. Non-linear loads are loads that are not constant throughout the sine wave cycle. Passive converters only conduct when the voltage of the signwave is greater than the DC voltage on the other side of the rectifier, making them non-linear loads and sources of harmonic distortion.

Maybe you can charge a Tesla with a generator that produces other than a pure sine wave voltage waveform, but with the evidence I’ve seen so far I’m leaning toward true sine wave is required. I guess the only way we’ll know for sure is if Tesla tells us, or if someone has access to a modified sine wave or square wave generator and wants to try charging their Tesla from it. I’m thinking square wave power generators are going to be very hard to find and with inverter technology were it is, modified signwave generators also hard to find.

Here is a link to the Electrek arcticle. Being good jounalists they‘ve included the video debunking the article.

https://electrek.co/2020/05/19/tesla-bidirectional-charging-ready-game-changing-features/

Thanks for all the information.

 

[ajdelange]

I have been researching this very subject recently. I have found may posts, videos and articles saying Tesla does not recommend using private generator. With that said most say you can do it as long as you make sure you have two things, you need a pure sign wave generator, and you need to have neutral bonded with ground.

There are lots and lots of posts and videos by people who do not know what they are talking about. You can charge from a generator as long as the EVSE measures more than 100 V between L1 and L2. There is no requirement for pure sine wave. There is no THD spec.

This rather direct statement is based on 3 things:
1)Demonstration that one can charge from a generator no matter who owns it
2)Common sense.

I did find that the caveat against "private generators" still exists -not in the manual for the car where I had been looking but in the manual for the Universal Mobile Connector (as it is called) and the Gen 2 and 3 HPWC. "CAUTION: Do not use private power generators as a power source for charging". I did not find any caveat against poor power quality nor would I expect to as waveforms can be quite distorted even from a utility depending on what your neighbors have connected.

I also read the article by Electrek stating the model 3 has the hardware available for Bidirectional charging, ... very smart person who took the time to show that bidirectional charging is not possible in that charger ... assumed to be transistors but he later showed they were in fact diodes.....they prevent bidirectional charging.

Enough material has been posted, including photos of PCB and filched schematics to make it clear that the architecture of the Tesla charger is

==> Bridge --> Bridge ==>Transformer ==> Bridge --> Battery

==> AC; --> DC.

That architecture can be used in either direction requiring all three bridges to have transistors or as a power supply for charging the battery in which case the first and third can use diodes but they can also use transistors in order to allow regulation.

...Now it is suggested In a new post to this thread that the active converter is either for current regulation, or bidirectional charging. ...they could have simply used diodes (passive converter) and did the current regulation in the next stage...
...The video does say the active converter, along with an inductor are used for power factor reasons ... inductor can be used to bump up the voltage. ..I believe the timing of this transistor gating would need to be critical to the voltage level at the time of firing of the gates. I believe the phase lock loop (PLL) algorithm would need to latch on to a true sinewave voltage waveform

A lot of I believes, coulds and maybes. It is not at all clear from what we actually know what algorithms are used to do which functions is which part of the circuit. It is clear that the following functions need to be performed:

1)Rectification of the input AC, however sloppy the waveform (within limits)
2)Power factor correction (now required by regulation if you want your doo-dad listed)
3)Inversion to AC
4)Transformation of AC to high voltage
5)Rectification back to DC at high voltage
6)Regulation of DC voltage/current

There are other ways to do 3, 4 and 5 using flyback techniques (llike the old Kettering ignition system) but they are deprecated because silicon is cheaper than copper and steel.

I then explained a true sinewave may be needed to synchronize the active converter to the AC line.

One thing you need to be aware of is that synchronization to sloppy waveforms is a piece of cake.. Here's a picture of a VCO starting at 63.5 Hz locking to a rather assymetrical, noisy 60 Hz waveform. Note that it is locked (the in phase VFO voltage crosses 0 at the point where the inverter waveform starts) by the 6th cycle.

I do question the video saying the active converter is used for power factor reasons as I don’t see any reason power factor would be an issue. What I think he meant was not so much for power factor correction, but for harmonic mitigation. Non-unity power factor and harmonic distortion are two completely different problems in the electrical engineering world.

Not any more! As I said above if you want your device listed it better meet the prescribed harmonic content spec (out to the 39th harmonic!) and lag power factor too. Harmonics do nasty things to building, distribution and generation systems. The negative sequence current is rich in harmonics, can result in excessive heating of transformers and generators etc.

Harmonics are caused by, among other things, non-linear loads. Non-linear loads are loads that are not constant throughout the sine wave cycle.

As I said flyback converters are (except I suppose in very small supplies) a thing of the past AFAIK. That aside the power supplies are switched that is they draw current when they need to draw current. That means current pulses with steep risetimes (as energy is wasted during the switching transition) and that means lots of harmonics. Curious as to how good a job an HPWC does on "power factor" correction I took a picture of an Gen 2 HPWC running at 40 A (rms). Here it is

Clearly the charger in the car does a bang-up job of cancelling harmonics.

Maybe you can charge a Tesla with a generator that produces other than a pure sine wave voltage waveform, but with the evidence I’ve seen so far I’m leaning toward true sine wave is required.

It seems pretty clear at this point that one ought to be able to use modified sine. It is certainly clear at this point that one does not require an inverter generator to charge a Tesla because the car does not require 3% THD. The 9 - 10% that most generators produce is fine. The cars power supply will cancel it.

 

[Bill906]

You cannot have bidirectional power through diodes!
The model 3 charger in the video uses diodes in it’s last AC to DC conversion.
The packaging of those diodes looks like transitors. Which confuses people who do not take a closer look.
There is no circuitry found on the board to support gating of those devices that people mistake for transistors which is further evidence the devices are diodes. (Transistors would need circuitry to control their gating).

The first active converter is what I believe is used for harmonic mitigation. If the AC input was a modified square wave, how would the active converter latch onto that square wave and reduce harmonics? The square wave would be causing harmonic distortion.

There are three ways Tesla could go in how they design the charger. Tesla could design the charger to work on utility power which would be a very pure sine wave but would require them to take measures to keep from creating harmonic distortion on that power system. Or... they could design the charger to work on any power waveform coming in regardless of if it was sine, square, triangle, sawtooth or even DC and not worry about creating harmonic distortion (it would be virtually impossible to mitigate harmonic distortion on a waveform that wasn’t pure sinewave). Or... they could design the charger to determine if the input was pure sine wave or not and turn on/off harmonic mitigation depending on that determination. I believe they only designed it to work on pure sine wave voltage waveforms because they come out and tell you not to use anything other than utility power. The option to do both would be complicated and, in my opinion possibly unreliable. Should a power event occur (brown out, spike etc.) when it was sampling the signal, it may put itself into non-sinewave mode accidentally. I believe Tesla just decided it is way easier to built the charger for pure sine wave and tell you only to use utility power.

There are only 3 reasons I can think of to have the first converter be an active (transistor) converter.
1. Bidirectional charging. (Which this one DOES NOT do because of diodes later in the circuit).
2. Power factor correction. This might be used for that purpose, but not sure why as I do not see any thing in the circuit to cause PF be far off from unity. (explanation later)
3. Harmonic Mitigation. I believe this is the reason the first converter is an active converter. By locking onto the sine wave voltage waveform to draw current throughout the cycle to mimic a linear load.

Power Factor issues and harmonic distortion are not the same thing. But both can be corrected with an active converter.

Power Factor:
Inductive loads cause a shift between the voltage and the current of an AC system. This causes problems with power generation. When the voltage and current have no shift it is known as a power factor of 1.0, or unity power factor. As you add inductive loads to the system the power factor drops below 1.0. Capacitive loads can also cause power factor issues But are rare. Actually capacitive loads cause the voltage current shift in the other direction. One way to combat power factor issues is to add power factor correction capacitors to cancel out the shift caused by the inductive loads. Power factor has to do with the shift between voltage and current. It has nothing to do with the shape of the waveform. If your power factor is to far from 1.0 your power company may have a talk with you. I do not believe this is an issue for most (if any) residential customers.

Harmonic distortion:
Harmonic distortion is a very complex subject. To fully understand it we need to talk in the frequency domain instead the time domain. This is not the place for that discussion. For the purposes of this conversation harmonic distortion is caused by irregular waveforms. A perfect sine wave will have no harmonic distortion. If we used a passive (diode) converter as the first converter it would only conduct when the input waveform voltage was greater than the DC voltage on the other side of the diode. By only turning on during a part of the waveform it creates harmonics by distorting the sine wave. Harmonic distortion, if great enough, will cause problems with other electronic devices in the area. Most noticeable would be noise / interference with radio and TV signals but other serious problems can also be caused by harmonic distortion.

This rather direct statement is based on 3 things:
1)Demonstration that one can charge from a generator no matter who owns it
2)Common sense.

1) I have not seen a demonstration of anyone using a square wave or modified sine wave generator to charge a Tesla vehicle. Most of the ones I’ve seen they specifically state they are using a pure sine wave generator and even then they have issues, even after bonding the ground to the neutral.
Little confused on the “no matter who owns it” part. I’m guessing you are refering to how Tesla states not to use PRIVATE generators. The point of this discussion is if you can use a generator that does not produce a pure sine wave. I believe Tesla is requiring us to use non-private generators, meaning utility power, because they know that will be true sine wave.

2) Common sense - another phrase I find people use a lot when they think something is true but do not know why or are not able to provide evidence to support it. I can do that too. The earth is flat! it’s just common sense. <sarcasm>.

3). You forgot 3.

As I said flyback converters are (except I suppose in very small supplies) a thing of the past AFAIK.

Passive (flyback) converters are still used in the industrial world quite a bit. But there has been significant movement toward active converters replacing passive ones.. I suspect the move toward active converters is even faster in the residential world because the systems are significantly smaller and the cost difference between active and passive devices is approaching insignificant. I have wondered about the circuits of LED light bulbs and if they use passive converters. Have not had the time to investigate. Again, I only can think of three reasons to use active converter instead of passive. Powerfactor correction, harmonic mitigation, and bidirectional powerflow. I believe Tesla uses an active converter for harmonic mitigation and MAYBE power factor correction. If all the converters in the charging circuit were active (transistor) converters then I would say they also would be able to have bidirectional charging. But as it has been proven and brought up many times, the final converter in the Model 3 charging circuit is made of diodes which prevents the circuit from sending power from the high voltage battery back to the grid/home/whatever.

It seems pretty clear at this point that one ought to be able to use modified sine. It is certainly clear at this point that one does not require an inverter generator to charge a Tesla because the car does not require 3% THD. The 9 - 10% that most generators produce is fine. The cars power supply will cancel it.

I have provided evidence and explanation that clearly points out that you probably cannot charge a Tesla from a square wave or modified sine wave generator.

Contrary to what many have said on the internet, a non-inverter generator has the ability to produce a pure sine wave. The very large generators at the power company are not inverter generators yet produce very nice sine waves. If a non-inverter generator was sized significantly larger than the load, it’s sine wave would not be distorted by the load and should work fine. There are calculations that can be done, and it varies greatly on how the generator is designed, but a very rough rule of thumb for passive converters is have the generator twice the size of the load or larger.

The cars THD (Total Harmonic Distortion) requirement is moot. We don‘t care what the car can accept, we care about what distortion the charger is creating on the power system that can affect other devices. If the old lady next door can’t watch her stories on TV because of interference caused when you’re charging your car, that would be bad. The charger is designed to work on utility power and not cause harmonics on the power system.

Clearly the charger in the car does a bang-up job of cancelling harmonics.

What would the current look like if the voltage was a square wave? Would their be harmonics? If yes, would the active converter be able to address the harmonics? With a perfect sinewave voltage waveform the charger is able to mitigate harmonics and (if needed) correct power factor. The waveform shows exactly what I’m saying. Do the same test using a modified sine wave or square wave power generator and see what happens.

As. I type this I realize there is a forth possible reason for the active converter which I did allude to in my previous post. The active converter can also be used to boost the DC voltage higher than the peek voltage of the incoming sinewave. To what extent Tesla uses that function , I do not know.

A lot of I believes, coulds and maybes.

Of course I state “I believe” because I do not know. I do not trust people who state their beliefs as fact. When discussing how something works without actually knowing, a fairly standard format is to state your belief, followed by evidence and explanation of why you believe that. Another approach could be to state your belief as a fact. Then defend your belief from anyone who disagrees with your belief using confusing rhetoric hoping they will give up.

It’s just common sense. It is now perfectly clear that what I said is the way it is. <satire>

 

[ajdelange]

You cannot have bidirectional power through diodes!

You apparently have some familiarity with electronics but clearly not enough to understand the things I am trying to explain to you as you have missed most of what I have been saying. So I'm not going to waste any more of your time or mine. There are just so many errors/misconceptions/misunderstandings in your last post that I'd be here all night and I don't see the results of setting the record straight being of much interest to the general readership.

Exception (because I got curious). I threw the mains breaker so the generator started. It's a Kohler and pretty good on the harmonic distortion - probably 6 - 8% - but it is clearly visible on the scope. The voltage waveform is not as as smooth as that from Hydro. Next step was to start the Tesla charging at 40 A. As the car ramped up its current draw a really nice sinusoidal current waveform grew on the screen as expected. What I did not expect (though I should have) is that as the current waveform expanded the voltage waveform cleaned up. As I mentioned in a previous post modern power supplies (of which, clearly, the Tesla charger is one) are required to draw sinusoidal current from a distorted supply voltage waveform AND to clean up the supply voltage waveform to the extent they can. All this is set out in the standards which probably have a limit

Thus it is pretty clear, accept it or not, that the Tesla is designed to handle lumpy source voltage waveforms, draw sinusoidal current and inject harmonics into the line of appropriate magnitude and phase to cancel the line harmonics to some extent. I don't know the details of how this is done or which bridge in the Tesla architecture does it. It may be done by another circuit between two bridges - that's evidently a common architecture. A power supply is no longer a simple thing.

I also don't know what the THD limits are if there are any - if harmonics were a problem don't we think the manual would have a cautionary note about that?. Clearly it can handle the 6 -8 % of my generator but could it handle the 107% THD of the waveform I used to illustrate phase locking in my last post? That is, of course, very extreme. A modified sine wave consisting of 20% of a cycle off, 30% +, 20% off, 30% -, 20% off etc has only 34% THD (out to the 39th harmonic).

 

[Newmanr12]

There are lots and lots of posts and videos by people who do not know what they are talking about. You can charge from a generator as long as the EVSE measures more than 100 V between L1 and L2. There is no requirement for pure sine wave. There is no THD spec.

This rather direct statement is based on 3 things:
1)Demonstration that one can charge from a generator no matter who owns it
2)Common sense.

I did find that the caveat against "private generators" still exists -not in the manual for the car where I had been looking but in the manual for the Universal Mobile Connector (as it is called) and the Gen 2 and 3 HPWC. "CAUTION: Do not use private power generators as a power source for charging". I did not find any caveat against poor power quality nor would I expect to as waveforms can be quite distorted even from a utility depending on what your neighbors have connected.

Enough material has been posted, including photos of PCB and filched schematics to make it clear that the architecture of the Tesla charger is

==> Bridge --> Bridge ==>Transformer ==> Bridge --> Battery

==> AC; --> DC.

That architecture can be used in either direction requiring all three bridges to have transistors or as a power supply for charging the battery in which case the first and third can use diodes but they can also use transistors in order to allow regulation.


A lot of I believes, coulds and maybes. It is not at all clear from what we actually know what algorithms are used to do which functions is which part of the circuit. It is clear that the following functions need to be performed:

1)Rectification of the input AC, however sloppy the waveform (within limits)
2)Power factor correction (now required by regulation if you want your doo-dad listed)
3)Inversion to AC
4)Transformation of AC to high voltage
5)Rectification back to DC at high voltage
6)Regulation of DC voltage/current

There are other ways to do 3, 4 and 5 using flyback techniques (llike the old Kettering ignition system) but they are deprecated because silicon is cheaper than copper and steel.



One thing you need to be aware of is that synchronization to sloppy waveforms is a piece of cake.. Here's a picture of a VCO starting at 63.5 Hz locking to a rather assymetrical, noisy 60 Hz waveform. Note that it is locked (the in phase VFO voltage crosses 0 at the point where the inverter waveform starts) by the 6th cycle.

Not any more! As I said above if you want your device listed it better meet the prescribed harmonic content spec (out to the 39th harmonic!) and lag power factor too. Harmonics do nasty things to building, distribution and generation systems. The negative sequence current is rich in harmonics, can result in excessive heating of transformers and generators etc.


As I said flyback converters are (except I suppose in very small supplies) a thing of the past AFAIK. That aside the power supplies are switched that is they draw current when they need to draw current. That means current pulses with steep risetimes (as energy is wasted during the switching transition) and that means lots of harmonics. Curious as to how good a job an HPWC does on "power factor" correction I took a picture of an Gen 2 HPWC running at 40 A (rms). Here it is

Clearly the charger in the car does a bang-up job of cancelling harmonics.



It seems pretty clear at this point that one ought to be able to use modified sine. It is certainly clear at this point that one does not require an inverter generator to charge a Tesla because the car does not require 3% THD. The 9 - 10% that most generators produce is fine. The cars power supply will cancel it.

Thanks for all this information..

You apparently have some familiarity with electronics but clearly not enough to understand the things I am trying to explain to you as you have missed most of what I have been saying. So I'm not going to waste any more of your time or mine. There are just so many errors/misconceptions/misunderstandings in your last post that I'd be here all night and I don't see the results of setting the record straight being of much interest to the general readership.

Exception (because I got curious). I threw the mains breaker so the generator started. It's a Kohler and pretty good on the harmonic distortion - probably 6 - 8% - but it is clearly visible on the scope. The voltage waveform is not as as smooth as that from Hydro. Next step was to start the Tesla charging at 40 A. As the car ramped up its current draw a really nice sinusoidal current waveform grew on the screen as expected. What I did not expect (though I should have) is that as the current waveform expanded the voltage waveform cleaned up. As I mentioned in a previous post modern power supplies (of which, clearly, the Tesla charger is one) are required to draw sinusoidal current from a distorted supply voltage waveform AND to clean up the supply voltage waveform to the extent they can. All this is set out in the standards which probably have a limit

Thus it is pretty clear, accept it or not, that the Tesla is designed to handle lumpy source voltage waveforms, draw sinusoidal current and inject harmonics into the line of appropriate magnitude and phase to cancel the line harmonics to some extent. I don't know the details of how this is done or which bridge in the Tesla architecture does it. It may be done by another circuit between two bridges - that's evidently a common architecture. A power supply is no longer a simple thing.

I also don't know what the THD limits are if there are any - if harmonics were a problem don't we think the manual would have a cautionary note about that?. Clearly it can handle the 6 -8 % of my generator but could it handle the 107% THD of the waveform I used to illustrate phase locking in my last post? That is, of course, very extreme. A modified sine wave consisting of 20% of a cycle off, 30% +, 20% off, 30% -, 20% off etc has only 34% THD (out to the 39th harmonic).

I appreciate the time you've taken to pass along your knowledge. This is kind of information I was looking for. Sounds like Tesla is forgiving enough to use a decent portable generator, as long as it's grounded properly.

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