Charging with a generator

[Riviot]

Why ever would you think that? You might be interested to know that is a few places around the US there are services with generators mounted on trucks that will come out to you if you run out of electricity and give you enough of a charge to get to a DCFC.

If I have a 10 day power outage here (not common but it happens) I'll be charging my BEV from a generator for sure.

How is either of these dumb?

First case, even with ICE, boils down to either poor planning or pushing your luck on how far your energy (gas/diesel/kWh/whatever) will get you. I'm still gonna call you dumb as I hand you my spare gas can. ESPECIALLY if your 90k smart truck TELLS YOU HOW FAR YOU CAN GO WITH YOUR CHARGE. You definitely get the "way to go, bub!" honk.

In a power outage I have the ability to do the same, but from my propane genset on the house, not a portable generator. I'm not going to blow through all my propane to charge my truck, that's poor resource allocation. I'll run down to the EA station at Fred Meyer (Kroger) to fill up.

Let me be clear, I just think we need to think on things a little before we do them. And also lean on our friends/neighbors for help. I may call you dumb but I'm still buying you a beer ?

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[ajdelange]

First case, even with ICE, boils down to either poor planning or pushing your luck

The wise man has backups for when his plans, as the poet said "gang aft aglay".

 

[NorthernOak]

I find it hard to believe Rivian's engineers, designers, and testers wouldn't have thought of generator charging use cases. They are marketing these as adventure vehicles capable of going to very remote regions. Then there are power outages, storms, and emergency situations. I'd honestly find it more concerning if the vehicle wasn't capable of plugging into a "dirty" power source. If I needed the charge, I wouldn't have a concern plugging into a generator. If they want people to use a specific type of generator or not one at all they'll need to come out and say it.

 

[Riviot]

The wise man has backups for when his plans, as the poet said "gang aft aglay".

 

[ajdelange]

I find it hard to believe Rivian's engineers, designers, and testers wouldn't have thought of generator charging use cases. They are marketing these as adventure vehicles capable of going to very remote regions. Then there are power outages, storms, and emergency situations. I'd honestly find it more concerning if the vehicle wasn't capable of plugging into a "dirty" power source. If I needed the charge, I wouldn't have a concern plugging into a generator. If they want people to use a specific type of generator or not one at all they'll need to come out and say it.

The voice of common sense - so rare!

 

[zipzag]

I find it hard to believe Rivian's engineers, designers, and testers wouldn't have thought of generator charging use cases. They are marketing these as adventure vehicles capable of going to very remote regions. Then there are power outages, storms, and emergency situations. I'd honestly find it more concerning if the vehicle wasn't capable of plugging into a "dirty" power source. If I needed the charge, I wouldn't have a concern plugging into a generator. If they want people to use a specific type of generator or not one at all they'll need to come out and say it.

I would also expect that Rivian would provide an inverter to run power tools well. They didn't. In addition I would also expect Rivian to label their 120V nominal plug "120". They didn't, it says "110", at least on pre-production vehicle.

In the vastly complex effort of a new company building a new vehicle there are likely plenty of things missed and designs that should have been done differently.

I clearly have a beef with 120V inverter engineer guy.

 

[ajdelange]

I would also expect that Rivian would provide an inverter to run power tools well. They didn't. In addition I would also expect Rivian to label their 120V nominal plug "120". They didn't, it says "110", at least on pre-production vehicle.

I would expect the Cybertruck to do that as it is sold into that market but I wouldn't expect the Rivian to as it is not. Doesn't mean I don't wish it would. I too am puzzled by the 110 spec/label. Which is it? Anyone measure it?

I'll note that the Jackery inverters are 110V machines (but Yetis are 120). Is that just simpler to get from Li ion packs (eliminate a DC/DC conversion)?

 

[zipzag]

I would expect he Cybertruck to do that as it is sold into that market but I wouldn't expect the Rivian to as it is not. Doesn't mean I don't wish it would. I too am puzzled by the 110 spec/label. Which is it? Anyone measure it?

I'll note that the Jackery inverters are 110V machines (but Yetis are 120). Is that just simpler to get from Li ion packs (eliminate a DC/DC conversion)?

The testers were apparently interested in powering their decorative patio lights and electric hookah. Some non-hipster testing would have been beneficial. Perhaps testers who wear plaid for non-ironic reasons.

The only reason I can think the plugs could actually be 110V nominal is if the inverter is attached to 12V.

 

[ajdelange]

The only reason I can think the plugs could actually be 110V nominal is if the inverter is attached to 12V.

It well may be and I suspect that may be the reason (even though I said something about Lithium in the earlier post).

 

[Zoidz]

I'm calling BS here because it violates common sense. Today's semiconductors are very robust. Semiconductors aren't designed for a particular waveform or a particular duty cycle. They are designed to switch at a certain rate, dissipate a certain power and withstand a certain PIV.
.....
No, I'm afraid it is still BS. If you were working for me in the rectifier design section of Rivian or Tesla and came back with a design that wouldn't robustly withstand 20% THD I'd send you back to the drawing board.

Lol, It is not BS that a transistor in a power switching circuit has a duty cycle, and that harmonics can and will affect that duty cycle, possibly causing failure, which was my original statement and intent.

You''re morphing the conversation beyond that to suit your narrative. I can continue morphing by saying that the engineering director overrides your 20% THD margin requirement because the cost analysis team said the additional cost impacts budget, and the body systems designers complained that the physical size exceeds what they allocated space for.

I'm sure you know that's how it works, lol. In mass production product design & engineering, everything is a compromise.

Cheers!

 

[Zoidz]

I have a friend that is a genius in power electronics with many years building power supplies for mainframes. I will ask him and report back.
Those generator waveforms do look terrible. This surprises me because our whole 60hz AC system is historically based on spinning wires through magnetic fields at some multiple of 3600RPM. I know that Portable generators do struggle to keep the RPM/Hz steady but I don't see a reason why the waveform would have significant harmonics to it. I though that a sine wave was the natural shape of a generator waveform. I am not saying you're wrong, but now I am curious as to why. Perhaps magnet arrangement, inconsistent magnet materials or some such.
I did once try to power a computer off of a cheap generator and it did not even power on. Switched to an inverter one and then no problem. The inverter one was half the watts of the non-inverter one.

A perfect 60 hz sinusoidal waveform is the result of passing a perfect coil with a perfect core through a perfect magnetic field (all perfectly aligned) with perfect electrical contacts and perfect wiring and a perfect resistive, or no load on the generator. I think you note the keyword perfect? Variations in any these can and will affect the waveform, some of which contribute to THD.

 

[Zoidz]

I find it hard to believe Rivian's engineers, designers, and testers wouldn't have thought of generator charging use cases. They are marketing these as adventure vehicles capable of going to very remote regions. Then there are power outages, storms, and emergency situations. I'd honestly find it more concerning if the vehicle wasn't capable of plugging into a "dirty" power source. If I needed the charge, I wouldn't have a concern plugging into a generator. If they want people to use a specific type of generator or not one at all they'll need to come out and say it.

Perhaps they did. And perhaps their design was compromised by the budget/fiancial/bean counters who said it added too much cost to accomodate any generator source. This scenario happens all the time in product design.

My point was and is that we don't know. I'm perfectly happy letting others be the guinea pig and charge their Rivians on Harbor Freight Predator generators.

 

[blturner]

I talked with my friend and he thought that charging from any appropriately sized generator would work but that it would not be a guaranteed sort of thing. It also could be that a fine enough waveform comes out of the generator normally but hook some weird load with a bunch of power switching to it and then it goes south.
So yes, Zoidz you are right. There is some risk. And that risk is easily greater than the savings.
The interesting thing is that he pointed out that an inverter generator does not nessasarly put out a clean waveform either. It can make one of those sine approximations that cheap UPSes make.
So YMMV. I am going to wait to try this till both someone else goes first and the Rivian service centers are stocked with parts and experienced enough to fix it in a day or so.

 

[ajdelange]

Lol, It is not BS that a transistor in a power switching circuit has a duty cycle, and that harmonics can and will affect that duty cycle, possibly causing failure, which was my original statement and intent.

Think you may be confusing active rectification with inversion. In active rectification you turn the switch on when you want it on and off when you want it off. In the simplest case you would not use active rectification but rather just diodes (as evidently Tesla does in this application). Whenever the voltage on L1 > L2 by more the stored voltage on the output cap diode A and D conduct. When the line reverses so L2 < L1 by more than the voltage on the output cap then B and C conduct. The duty cycle is determined by how fast C is being discharged i.e. by the load imposed on the circuit by the rest of the rectifier. It is this which primarily determines the bridge duty cycle. Looking back at all those crappy waveforms posted a few numbers back, take note of the ones with the incredible 2nd harmonic. In those if the rectifier is lightly loaded the cap voltage will be high and the diodes may turn off when the voltage takes that dip in the middle of each cresting part of the waveform, In that case instead of two nice smooth half sinewave shaped current pulses you would have 4. How does that increase dissipation in the diodes?

Now you keep talking transistors (or other active devices) here. One certainly can control the output of a rectifier by gating the input devices and input devices are often switched in 3ø systems (Vienna rectifier) for power factor (including harmonic content) control in the current drawn. But Tesla (can't speak for Rivian) evidently does not do it that way rather gating the high frequency inverter transistors. This pretty much renders the input semi conductors immune to input wave shape so I am afraid your argument remains jejune.

 

[ajdelange]

A perfect 60 hz sinusoidal waveform is the result of passing a perfect coil with a perfect core through a perfect magnetic field (all perfectly aligned) with perfect electrical contacts and perfect wiring and a perfect resistive, or no load on the generator.

As I posted earlier, a clean waveform comes from a properly wound stator (the part that stays stationary) in which the effective mmf is sinusoidal both spatially and temporally. This is a bit of an art. The magnetic field is generated by coils on the rotor i.e. it is the field that spins past the stator, not the other way round.

As the stator is stationary it is easy to connect to (the connections are virtually perfect) and in a modern generator the rotor is excited by auxiliary coils in the stator (excited by DC) and in the rotor connected to a bridge thus producing the required field DC.

Now for perspective I'll note that I just installed an off grid Powerwall system which is backed up by a Kohler RES20CL (20 kW) generator which does NOT have an inverter but which DOES have brushes (yes, in 2022). I did not choose this generator. Tesla told me that this is one of two generators they accept for Powerwall backup. So if it is good enough, according to Tesla, to drive their dainty semiconductors in the Powerwalls it is, IMO, good enough to drive the dainty semi conductors in my Model X.

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