Portable Generator with solar

fastline said:
In brief, no.
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Would you mind expanding a bit?

My guess is that the combination of inverter and generator (if PV production exceeds local consumption, and if the inverter actually synched in the first place) would _try_ to do something ugly such as a generator overspeed or voltage excursion, but that the operating limits of the inverter or generator would cause something to shut down before the magic smoke escaped. I'd love to have more details.
 
winnie said:
Would you mind expanding a bit?

My guess is that the combination of inverter and generator (if PV production exceeds local consumption, and if the inverter actually synched in the first place) would _try_ to do something ugly such as a generator overspeed or voltage excursion, but that the operating limits of the inverter or generator would cause something to shut down before the magic smoke escaped. I'd love to have more details.
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I recall 10+ years ago someone on a different forum posting a photo of a generator throwing a ground fault error when someone had an SMA inverter hooked up to it. Don't ask me to find it now.

I think the main thing here is that if you don’t have a competent person who can figure it out, you may defeat the purpose of having the generator.
 
Just as a thought experiment, I'm trying to picture the chain of events if you hooked a grid tie into a synchronous condenser and then cut grid supply to the circuit. Would the system stay stable?

Just for this thought, this is a pure synchronous condenser without any logic. Just a synchronous motor/generator with a rotating mass

On edit. Thinking maybe it should have logic, but limited to controlling field current
 
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Joethemechanic said:
So what is the tolerance +/ - of the frequency a typical grid tie inverter will sync to? 59-61hz? There has to be some kind of tolerance. 59.5 - 60.5?
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Exactly. Inverters will have a very tight range on frequency. Then you look at generators. Typically people go get the cheapies, which I call screamers. 3600rpm Direct AC induction. In short the engine rpm is directly tied to the frequency, which makes them SUPER suck at frequency regulation, meaning an inverter is not likely to stay linked to them very long before locking out. Far before a generator failure.

It gets more complicated with inverter generators as both are designed to "sync".

There's just a lot of reason I try not to go down this rabbit hole with customers because I waste far too much time working up a solution.
 
fastline said:
Typically people go get the cheapies, which I call screamers. 3600rpm Direct AC induction. In short the engine rpm is directly tied to the frequency, which makes them SUPER suck at frequency regulation,
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Yeah well the governors on them are crude and manufacturing tolerances are wide, so there can be either tightness or lost motion in them. But they are simple, cheap, and reliable. I'd say they also compromise rotating mass for overall weight of the product.
 
Joethemechanic said:
Yeah well the governors on them are crude and manufacturing tolerances are wide, so there can be either tightness or lost motion in them. But they are simple, cheap, and reliable. I'd say they also compromise rotating mass for overall weight of the product.
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🤓 So.... 3600rpm generators are craptastic all the way around other than reducing price. They generally are doing good to maintain even +/- 5hz and that is because an engine MUST be operated in the sweet spot of torque, not HP. At 3600rpm, an engine is around peak HP, but well after peak TQ. This allow OEMs to claim high power ratings and use smaller engines. Due to being operated at this engine speed, any real load against it will decrease rpm dramatically.

Proper designed generators will either run direct at 1800RPM, with a 4 pole generator. The engine can hold speed very well, is in the meat of the TQ band, but due to running at the lower speed, engine size is nearly double. there are also speed ratio generators such as the Onan RV units. Yes, a good 1800rpm generator will also have a hefty flywheel to handle inertial hits and be rated for such.

Inverters I think most are using a BLDC with high pole counts, 6 or more. This is primarily to maintain good performance at the reduced, near idle, RPM. Because the output stage is digital, they have outstanding frequency stability, even better than the grid. Voltage is the only thing that takes a hit with high loads.

The main thing to figure out with customers IMO, is what they both expect and expect to pay. Most of the time their expectations don't match their wallet. Good luck trying to do an AGS on a screamer, and to a fail safe ATS design. This is where true standbys come in. Otherwise I generally try to find out outage frequency/duration/general urgency. IE, outage of about 1hr, 1x per yr. IF you happen to be home, that generator might run 15min before power is restored....lol Gotta drag it out, flip some switches, etc, etc. Then if you didn't maintain the generator, it won't start anyway.
 
winnie said:
The _risk_ is that the inverter will try to sync to the generator. @electrofelon suggests that the inverter will likely not sync to the generator and try to backfeed, but good practice is to make sure the inverter is disconnected if the generator is supplied.

I was answering post #11 where @pipe_bender said he'd want the solar working when on generator; @ggunn described that such generally isn't worth the ha
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Actually, the risk is that the demand from the loads will fall below the output of the PV system, which will cause the PV system to backfeed the generator. If the PV cannot sync to the generator, the PV will simply error out and shut down.
 
fastline said:
Then if you didn't maintain the generator, it won't start anyway.
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I think they do better with propane. The majority of small engines I encounter that ran good then were stored, and now won't run for crap are fuel related problems. Slop in the float bowl, crap sucked up in the main jet, fuel filter, water contamination, etc.

Propane eliminates all that. And you can store it forever.

Screenshot 2025-10-29 180458.png
 
Joethemechanic said:
I think they do better with propane. The majority of small engines I encounter that ran good then were stored, and now won't run for crap are fuel related problems. Slop in the float bowl, crap sucked up in the main jet, fuel filter, water contamination, etc.

Propane eliminates all that. And you can store it forever.
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I'm an engine guy. Design/mfg/sell race parts. Yes, near certainty that generator issues will be fuel related. I could go down that rabbit hole.

Yes on LP! Love it BUT you will take power hit when using it. No biggy if you account for that. The issue with LP generally is ease of use and cost. In general, 20# bottles fill for a fixed rate of about $20. They hold about 4.3gal depending on density factors. $4.6/gal and LP has less energy density than gasoline. But overall, fully agree, if you want reliable, you either want LP or better yet, get it sniffing on CNG. Main issues with LP/CNG is valve seat wear from a lack of cushion, but you need a LOT of hours to cause drama there.
 
fastline said:
Main issues with LP/CNG is valve seat wear from a lack of cushion, but you need a LOT of hours to cause drama there.
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Like 45 years ago I had a pair of small block chevy heads on the bench to do a valve job on. (Using a B & D Virbrocentric machine that I thought was all that because it had a coolant pump lol) and when I disassembled them the exhaust stems were way big. I showed them to my uncle and he looked and said "Sodium Valves" and of course that was followed by a ton of questions from me. The heads had stellite seats in them too.

I had bought the small block as a core because it was 4 bolt main and forged crank. When I saw the guy I bought it from I asked and he said he thought they pulled it out of a forklift
 
Joethemechanic said:
Like 45 years ago I had a pair of small block chevy heads on the bench to do a valve job on. (Using a B & D Virbrocentric machine that I thought was all that because it had a coolant pump lol) and when I disassembled them the exhaust stems were way big. I showed them to my uncle and he looked and said "Sodium Valves" and of course that was followed by a ton of questions from me. The heads had stellite seats in them too.

I had bought the small block as a core because it was 4 bolt main and forged crank. When I saw the guy I bought it from I asked and he said he thought they pulled it out of a forklift
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On point. I realize I can't really dive off too deep on that tangent as this forum wants to stay on topic, but yes, valve systems are certainly a factor in LP/CNG.
 
fastline said:
On point. I realize I can't really dive off too deep on that tangent as this forum wants to stay on topic, but yes, valve systems are certainly a factor in LP/CNG.
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Yeah I worked on thousands since, but that was my first time seeing that stuff as a teen, worked on 3500 series Cats, Waukesha, 149 Detroit Diesels, and the like over the years. Old now, all that stuff is kinda antique now
 
Joethemechanic said:
If the inverter synced to the generator, and the gen sped up slightly increasing frequency, would the inverter then match the increased frequency, making the generator increase rpm and frequency more? Could this push the gen into overspeed?
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Overspeed protection save the generator?
 
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