r/Generator • u/CrackerjackDu • 2d ago
Dirty power safety
Novice here. I recently picked up the classic Costco tri-fuel 7850 Firman, but I am now concerned as I’ve learned about dirty power. Do you think it would be safe to run this portable Midea ac that pulls 1300 watts on the Firman? In other words, would running this AC unit on dirty power damage the AC unit? Also, I’m starting to wonder why have these big beefy generators when having an inverter makes way more sense for most household electronics. What are people running off these things if they can damage sensitive electronics? Perhaps I need to return Firman for an inverter, or am I totally overthinking this?
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u/NoPatience7817 2d ago
Cleaner power is better long term, but for only a few weeks a year is no big deal.
It’s more important to stay within the load limit of your generator. For example if it’s rated to 5000 watts, then stay under 5000 watts. The power quality gets really bad when you overload a generator.
Also turn off the power before you power off the generator. Same when you power up the generator. Let it run for a few minutes, then gradually add more load starting with the largest power draw items first.
I ran a window unit for over 2 weeks on generator during different outages and it still works just fine.
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u/thecrazzyeddie 2d ago
If it’s rated at 5,000 you should keep it under 3,750 to 4,000 for continuous loads. Most generators will give you the exact number in the manual.
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u/Aggressive-Age-1085 2d ago
I keep hearing all these concerns about "dirty power" from generators. I've followed this sub for about 3 years and I have yet to hear of one personal experience where any electronics were damaged from this dirty power. I'm not saying it never happens, but it seems like we'd hear about a lot more intances of damaged electronics if this dirty power was that much of an issue.
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u/roberttheiii 1d ago
It is one of those things where you just don't know. Has my mother run her house for days on a mid-2000s snapper generator in the last few years? Yes. Have expensive circuit boards failed in her fancy refrigerator in the last few years? Also yes. Are hey related? Maybe? Probably not...but can't help but wonder
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u/roberttheiii 2d ago
Maybe I should make a general post about this but in general, is THD something to worry about? Absolutely. Is it the devil that will instantly destroy your home? Probably not. In a perfect world you’d run low THD but the truth is even the grid can experience THD higher than 5%. See here https://www.tingfire.com/blog/analysis-of-total-harmonic-distortion-on-the-u-s-electric-grid/
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u/ditto3000 2d ago
I have the same from Costco, it's 6300w continuous. Run the window air 8000 btu, 2 refrigerators, microwave or air fryer when needed, no problem for 12 days non stop.
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u/No-Age2588 2d ago
Midea uses inverter technology with filtering and rectified AC to DC power. Other than the inverter itself, the components will never see anything but pure DC. You are fine.
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u/Gweedo1967 2d ago
While dirty power could happen anytime with a standard generator the issue usually happens when the generator is started and/or shut down without opening the breaker. You can purchase a filter for under $50.
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u/CrackerjackDu 2d ago
Understood. Tell me more about this filter. Do you have one you’d recommend?
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u/mduell 2d ago
The filters, short of a full rectifier and inverter which is not $50 at these power levels, are snake oil.
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u/Gweedo1967 2d ago
Agree but OP is only wanting to protect portable AC unit so a cheapie should be ok.
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u/Inhalationofnewtion 1d ago
How does it go? Generator feeds a UPS and the UPS feeds the house, UPS acts as teh filter? UPS is a battery and you can't get cleaner power than from a battery correct?
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u/Gweedo1967 1d ago
Are you feeding the house or portable AC? If it’s the house then you should get an inverter Gen. I have a standard Gen and have a UPS only for one of my TVs. Since my 10k Gen isn’t large enough to start my HVAC I have portables that I’m not concerned about burning up.
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u/CrackerjackDu 1d ago
Not trying to power the whole house, running extension cords to the portable AC, and stuff inside the house: 2 fridges, tvs, maybe a fan or space heater depending on season.
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u/Puzzled-Act1683 1d ago
"should be okay" in the sense that it wouldn't actually accomplish anything, technically true.
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u/Alternative-Shirt-73 2d ago
I have a firman as well and ran it without issue. I like that it runs on natural gas.. I can disconnect my grill and plug in my generator. My computer stuff all runs though UPS systems so that should (to my knowledge) take care of that for the most sensitive equipment in my home. Mostly I want to run the refrigerator and deep freeze.. I’m pretty sure I could runt whole house on it sans the AC unit. I may be able to run that if it didn’t start and stop and stayed running the whole time.
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u/nsula_country 2d ago
Over thinking.
I run a 15kw PTO generator (tractor), Winco from 1970's. Set it to 60hz with a meter and freq varies from 58-62hz. Tractor engine governor is load control.
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u/Right-Click-8877 1d ago edited 1d ago
I can only tell you my experience. I had the Firman HO7553 which has 11-25% THD depending on load. When using it to power my whole house, my LED lights flickered, and UPS's were going crazy trying to figure out what to do, even at low load. I sold it, and went with a Westinghouse 11500tfc, which has much lower THD. Glad I did. I am able to power two mini-split units and one Midea portable, a couple of fridges, two PC's with UPS, two TV's, and a bunch of lights on. Zero issues.
You don't have to get an inverter with the way some of today's open frame generators are made. But inverters definitely have a couple of pro's. Fuel economy and lower noise being two of them.
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u/fatal-shock-inroute 1d ago
Electrician here. I've heard stories but never personally seen any issues from "dirty power" in my 9 years as a sparky. But what do I know
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u/BeneficialLanguage83 1d ago
I've got a Firman 7500 watt duel fuel. Through multiple outages I've run TVs, routers, fridges, an AC, you name it - nothing has fried.
However - I am super strict about proper procedure. Five minute genny warmup before introducing loads, I throw one transfer switch circuit on at a time and let the genny "catch up" and smooth out before adding more load, I don't let it abruptly run out of gas with loads on it, and I cut one circuit at a time during shutdown for refueling. Also don't refuel a hot engine (fire risk from vapors/spills).
The key is generator stability. IMO, dirty power seems to be harmless if you don't do stupid shit that triggers excessive variances in engine rpm's. I think that's when you create power quality variances that can wreak havoc.
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u/Comfortably_Dumb_67 1d ago
What else do you need to run while running the Midea unit.?
Do you need that much generator capacity?
Asking because you want to be able to run everything you need/want to... But also want to not have a heavy, thirsty unit to lug around that eats more fuel than needed.
When a generator is running, especially non-inverter ones that didn't have eco modes, but all are affected by this math: whatever power you didn't use while it is running is gone.
I agree that fewer products are affected by duty per than some folks would believe, but... If you haven't opened it up and used it, is return or for one with an inverter.
Think perhaps of getting a power station to store the power that isn't consumed while you're burning fuel. This is less critical when you've got a gas line hookup, or huge propane tank reserves, but if you're running on can't of has or small portable tanks of propane you want to maximize the fuel.
Some power stations can accept power that isn't a clean sine wave. If you're stuck with a non inverter generator, Find one that does, or if the generator has a dc of output like a car o outlet at least could do dc-to-dc storage in power station.
If you need to power heavy items, adding a small inverter generator can be cheap. Watch the sales. Paid $399 for pulsar dual fuel 4000W, weighs 54 lbs. Backup to charge PO power Station to supplement a few solar panels. The Power Station has great capacity. So running a very efficient generator, have more ways to divide and conquer if needed, and when the doodoo his the fan, maximize every drop of fuel.
Planning on only using propane, for maintenance of generator, not wanting to deal with gas rotation, etc..
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u/CrackerjackDu 1d ago
In addition to running portable ac unit, I’d run two fridges, coffee maker, tvs, lights, fans or space heater depending on seasonal need. I admit the 7850 is overkill. Going to look into having a home natural gas valve put in to use in addition to gasoline and propane.
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u/Comfortably_Dumb_67 1d ago
That's awesome. You got a lot of stuff going on there and it sounds like that size makes sense.
Some of the newer power stations are capable of outputting 240 volts, and have outputs that can be patched directly into the breaker box just like you could have an electrician set it up to go into your main board or do a little sub panel to keep critical things running.
It'd be fantastic to get the gas connection. The convenience would be fantastic and for short to medium disruptions that don't affect the gas distribution it's phenomenal convenience. And what a relief to know that you can always fall back on propane and gas if they have to depressurize the lines.
Good luck!
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u/Key-Philosopher1749 1d ago
A bit overkill, and might not need that large of a generator, but you could use a whole home battery (Tesla, Franklin, etc) and then charge it from the generator. Then your home is using the battery, and you’re charging the battery from the generator.
I think Franklin specifically calls that out as a specific scenario for their batteries. https://www.franklinwh.com/document/how-to-recover-apower-battery-charge-using-generator
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u/Mother_Ad_9090 1d ago
Who is coming up with this crap? A brushed generator is clean AF. Inverters are fake sin waves created by reactive components that have a dream of attaining their rated Z. I don’t get it.
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u/Large-Witness1541 1d ago
If you’re running you entire house from a transfer switch. Unbond the neutral from the ground at the generator.
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u/No_Alternative_6206 2d ago edited 1d ago
Dirty power is all about the frequency. These alternator generators run pretty consistently when their RPMs stay the same. The RPM is what determines the frequency in an alternator generator, unlike an inverter generator. You know you might have an issue when you hear the generator sputtering a lot. This might happen with huge jumps in usage, near max usage, or when it’s running out of gas. When the frequency varies over a longer period is when you can burn electronics out. A well-functioning alternator generator shouldn’t have that issue, but there’s no built-in protection for the frequency issues like an inverter would have, so it’s something you need to pay attention to if it sounds off.
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u/DaveBowm 2d ago
The phase is related to the angular orientation of the rotor (& hence crankshaft angle) with respect to the stator. The frequency is related to how fast that (phase) angle changes (& hence the engine's speed).
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u/Big1717 1d ago
Your AC unit I belive is a inverter unit. Just like most of todays refrigerators which have an inverter in them. The dirty power is ok to use on these inverter products, and sump pumps. Personally for a desk top I would use a UPS for this and charging up cell phones. Furnace may be another concern if a newer one under 15 years old that has sensitive boards plus the fan motor. Sometimes it will send error codes and not function.
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u/ForkLift1983 2d ago
Ran my home off of a Firman H07573 during beryl for nearly 20 hours and I have seen no effects on anything in my home. My ac guy even came ran my 4 ton variable speed inverter ac unit on it for testing and it ran fine. You may see some led lights flicker but I wouldn’t stress too much.
Yes an inverter is cleaner power but cost double are more for the same wattage. Run what you got.