Front vs rear frequency

[LiteNing]

For all the other F-150 Lightning nerds out there:

As we all probably know, the frunk and cabin 120V outlets run off a 2.4kW inverter, while the bed outlets run off a pair of 3.6kW inverters. The bed inverters are obviously phase locked to produce 240V split phase. Well, curiosity got the better of me today, and I finally got around to something I had meaning to measure for a while: "What's the phase between the front and rear inverters?"

What I was hoping to find was that Ford did something nice, like phase lock the front inverter to either 0 or 90 degrees. At 90 degrees off, it would be somewhat doable to produce 208V 3-phase with some isolation transformers and a trio of variacs in a phase-shifting arrangement (don't try that at home, kids!) for all sorts of fun projects.

It looks like Ford wasn't so nice to us as I hoped because the front inverter runs at a very slightly different frequency (about 0.03% different if I'm doing the math right) from the rears. This is with no load on either one. I might try hooking up a space heater later this week to measure how much the frequency changes under load.

My experiment setup was as follows (Don't try this at home and be sure to follow all safety precautions while you are not doing what I did):

• Run an extension cord from the rear seat 120V outlet to the bed.
• Set the multimeter to AC Volts and appropriate range
• Connect the multimeter between the extension cord hot and bed outlet hot (using proper leads and wearing all appropriate PPE, of course).
• Turn on both front and rear inverters
• Record a video of the indicated voltage

The indicated voltage slowly swings between approximately 0 and 240V as the two power supplies drift in and out of phase. I measured the period between successive rises through 120V as approximately 50 seconds. As a reality check, I also measured the period between successive maximums and minimums (less accurate) and got the same result.

Over 50 seconds, we should have 3000 cycles, plus or minus one extra cycle that we observed on the readout. So that's 1/(3000) or about 0.03%. I'll probably dig out my boat anchor of an oscilloscope later if I get around to load testing with the space heater. Then I can see which one is faster.

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[K6CCC]

Would be nice, but I would not expect them to be in sync. You would also likely have to play some games to keep the GFCIs from tripping.

Thanks for testing that and looking forward to your additional testing.

 

[chl]

Yes, thanks for doing the testing I had thought about combining the two outputs to get the full 9.6kW, but wondered about the phase being out of synch. Now we know.

So I wonder if there is a synchronization kit that would work with these inverter generators.

Since the rear 7.2kW output is the combination of two 3.6kW inverter generators in a parallel or series combination, then some synchronization control is going on with those two by necessity.

So there may be a control signal enabling the synchronization that could be used.
Possibly, but maybe not likely, that way the third inverter could be similarly synchronized with the other two. But that's probably not a straightforward task.

EDIT: just looked it up and it seems the 2 inverters are a combination of two 180 degree phase shifted solid state inverters tied together in series so deleted the paragraph that was here.

Absent the ability to synchronize the three inverters, the best alternative solution to getting the full 9.6kW it seems to me is probably tapping into the HV battery with an external inverter (the way the Delta BID of the SunRun system does) but to get the Lightning to do that with any external inverter would require "hacking" the control in the Lightning (and maybe the FCSP also) to allow access to the two DC pins for V2H or V2G use.

It would be nice if Ford would allow owners to do that and facilitate it with an App. Obviously Ford would need to certify what ever external inverter we'd use, if not the SunRun system.

Other companies are making such systems (like Franklin) but will Ford allow them to work with our Lightnings?

 

[chl]

So if the synchronized inverters use a phase lock loop for synch, maybe that technique could be used to synchronize the third inverter, in theory anyway. It would have to have been designed in such a way that it can be phase locked.

Would have to see the detailed circuitry of the three solid state inverters to figure out how.

It would be like when utilities have multiple generators that have to be synchronized to provide a combined output. It can be done, but at what cost?

The idea of a three phase output is interesting. But combining three inverters to achieve that would mean carefully/closely controlling the inverters to be 120 degree phase different from each other.

A single phase output can be made into a 3 phase output with a phase converter using capacitors for example, but taking three separate inverters and combining them to get 3-phase out is more complex and probably not an easy task...unless the inverters were designed to be combined that way which is doubtful.

 

[LiteNing]

Mini update. The scope is under too much stuff to dig it out tonight, but I have an HP universal counter with a questionable calibration history which is a) light and b) not buried under a pile of stuff.

Nothing terribly exciting, I'm afraid. Front inverter on my truck reads as 59.938 Hz, rear reads 59.919 Hz... which is pretty darn close to what I measured before (0.03% difference).

The frequency of the rear outlet was jumping around a bit... +.001/-0.009 Hz, and the front was much more stable. I don't want to read too much into that. I'm not 100% certain that the sensitivity (hysteresis) control on the B channel is working correctly, and I had to turn both down to near the minimum to see anything that made sense. Also, the probes's compensation range does not extend to the counter's input capacitance... but we're measuring nice low frequency sine waves, so that shouldn't matter too much... right? Sounds good to me. Send it!

Setup:
* Front 120V Outlet -> multi-outlet extension cord -> 10x probe -> counter channel A
* Rear 120V Outlet -> 10x probe -> counter channel B
* Both channels set to 10x attenuation, AC coupling, 1M input impedance
* Both channels set to minimum sensitivity (adjusting sensitivity forces the trigger point to 0V)
* Counter set to 1 second gate interval.
* Attach 1500 W space heater to either front or rear plugs.

Turning on and off the space heater had negligible effect on the frequency... any change is in the sub-millihertz range. Well under the measurement noise. This is true for both channels. So... yea, no hope of dragging them to the same frequency by loading one down.

 

[LiteNing]

So if the synchronized inverters use a phase lock loop for synch, maybe that technique could be used to synchronize the third inverter, in theory anyway. It would have to have been designed in such a way that it can be phase locked.

The idea of a three phase output is interesting. But combining three inverters to achieve that would mean carefully/closely controlling the inverters to be 120 degree phase different from each other.

A single phase output can be made into a 3 phase output with a phase converter using capacitors for example, but taking three separate inverters and combining them to get 3-phase out is more complex and probably not an easy task...unless the inverters were designed to be combined that way which is doubtful.

Yup. My understanding is that all F-150's with 2.4kW pro power are 120V-only, and all F-150's with 240V use a pair of inverters capable of 7.2kW. Our Lightnings are special in that they have both. Since none of the other applications of the 2.4kW inverter do 240V, my bet is that the front inverter hardware just doesn't support it. At least not without going in and doing some warranty-voiding surgery.

Absent the ability to synchronize the three inverters, the best alternative solution to getting the full 9.6kW it seems to me is probably tapping into the HV battery with an external inverter (the way the Delta BID of the SunRun system does) but to get the Lightning to do that with any external inverter would require "hacking" the control in the Lightning (and maybe the FCSP also) to allow access to the two DC pins for V2H or V2G use.

Agree with you on that. There are some people over on OpenInverter, who are trying to do just that. Last I read, they were sending fake CCS signals to trick cars into closing the main contactor. But 400V with near-zero source impedance is... just not something I want to play with right now.

 

[K6CCC]

But 400V with near-zero source impedance is... just not something I want to play with right now.

Smart man! Knowing your limitations.

 

[chl]

Smart man! Knowing your limitations.

Agreed.

When I watch videos of people removing EV HV batteries, I think to myself I would never.

But any V2H system is going to have to access the 400VDC battery and pipe it through a big inverter.

The best thing would be Ford licensing other V2H/V2G systems to use their control software.
Any 'emulation' could run afoul of copyrights or other intellectual property protections, not to mention voiding the battery warranty.

 

[v2h8484]

Even with the same frequency and synchronized I doubt the 2 inverters can work with combined outputs in parallel as they have only GFCI outputs.

 

[chl]

I don't think the GFCI would be a problem in parallel synchronized inverters in general technically, but still pondering whether it could work in the three in the lightning...

I suppose it would be like having any circuit with GFCIs in parallel like in any house with a branch circuit that has multiple GFCI outlets?

Have to think about it though...

 

[chl]

Anyway, I think the rewiring required to synchronize all three of the Lightning inverters would be a challenge if even possible at all.

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