Generator selection - THD and flickering lights

[coleman10]

Hey, guys. I recently purchased a generator for emergency back-up and put in a manual transfer switch to be able to power the water heater, portable AC, fridge, lights, etc. in case of an outage from a hurricane. Not knowing a damned thing about generators other than they cost a lot of money, I picked up the Costco special, a Firman 7500 dual fuel, model HO7552. Got the switch in and wanted to test the generator. I fired it up on propane and powered one circuit that contained some LED lights (that’s all we have here) and they were flickering so badly I thought I was at a disco. Started reading up on generators and THD (should have done this before), and saw that the generator was rated at 25% THD at =full load=. Of course, with everything these days being controlled by sensitive circuitry and reading how that can take a pounding from the dirty electricity, I immediately think I should dump this turd, eat the loss, and get something better. So, I find a Champion dual fuel on Amazon, has great reviews, and according to Champion’s website:

“These generators will put out the standard THD rating of 15% or less unless otherwise noted. They will produce a sine wave, not a modified or square wave. This is perfectly acceptable for running common commodities found in your home such as TVs, computers, your appliances, etc.”

Is THD normally rated at half load? If this generator is 15% at half load, what could it be at full load? (I’m sure Champion will say that they don’t have a stat for that.) Even if it were higher, does what Champion state above balance out the THD? Sine waves are better for sensitive circuitry. I wouldn’t run my TV off this thing, but even my water heater is computer controlled. I’d like to minimize my chances of frying something, but I also don’t want to spend money needlessly. If I’m better off replacing the generator, I’m okay with that. I wonder what kind of inverter the Firman has.

Any schooling and info you guys can offer would be appreciated. Thanks!


Here’s the link the the Firman:

https://www.firmanpowerequipment.com/shop/h07552-7500-watt-dual-fuel-electric/

And here’s the link to the Champion:

https://www.championpowerequipment.com/product/100296-7500-watt-dual-fuel-generator/

 

[MBfreak]

Hi,
15 to 25 % THD is quite a long way from the grid code requirements for residential AC supply in Sweden and Europe.
Flicker, ie THD and voltage swings for a few seconds very occasionally ( like during a grid MV or HV fault being disconnected ) is acceptable. When the HV and/or MV grids are automatically restored/reconfigured during and after a fault this is almost unavoidable,
But steady state THD of residential AC supply ( here 3 phase 400 V, 50 Hz) above 0,8% is not allowed.
The THD reduces efficiency in electric motors and also impact some electronics.

Ola

 

[wyliesdiesels]

Thats awfully high for THD.

Also, you bought it at costco. RETURN IT!

 

[coleman10]

Thats awfully high for THD.

Also, you bought it at costco. RETURN IT!

Wish I could. Been a few months now and no box. Receipt’s been tossed. I didn’t think I’d be in this position. Lesson learned.

 

[wyliesdiesels]

Dont need a receipt as they can look it up. Ive returned plenty of things without a receipt, to costco. and i doubt they would care about the box when the generator may be broken.

 

[coleman10]

Hmm. I’ll give them a call and ask. I’ll have to get a pair of ramps to get this thing onto the truck. Ugh.

I asked Firman what type of power this thing is putting out and it’s producing a modified sine wave. From what I’ve read, AC motors should not be run on modified sine wave power and the motor can actually be damaged by it.

 

[wyliesdiesels]

Yeah I would never buy a generator that does modified sine wave.

 

[coleman10]

Yeah I would never buy a generator that does modified sine wave.

Amazing what you learn once you start digging.

 

[slow]

That firman in the link doesn't look to be an inverter unit, nor is any other inverter unit available close to that price point for that size. How or why would it have modified sine wave?

I do suspect you have a very low load on the unit with only led lights, and the voltage regulator may be swinging the ouptut voltage. Can you add load to see how the voltage stabilizes?

I don't disagree with returning it if it is bad, just seems odd to get a modified sine wave in what looks to be a 3600 machine.

 

[mm08822]

That firman in the link doesn't look to be an inverter unit, nor is any other inverter unit available close to that price point for that size. How or why would it have modified sine wave?

I do suspect you have a very low load on the unit with only led lights, and the voltage regulator may be swinging the ouptut voltage. Can you add load to see how the voltage stabilizes?

I don't disagree with returning it if it is bad, just seems odd to get a modified sine wave in what looks to be a 3600 machine.

A rotating field (or stator) type gen typically produces a very clean sinusoid with little conditioning. I hoped the OP had misread the stated THD, but wow 25% in the specs!!! I never would imagine any unit being sold with that low level of quality.

OP, you want a gen with 2.5 - 5.0% THD. Return/sell this one. Equipment connected to it will be subjected to lots of voltage spikes that won't help lifespan.

This would be a good unit to connect a power analyzer to and see if there were any change under load.

 

[coleman10]

I called Costco and they said that even with the time that has passed, they will take it back. I’ve had it for 3-4 months now. I’m impressed.

According to one review site I pulled up, the champion I listed has a THD of 5%. If that’s true, it’s a great value.

 

[mm08822]

I called Costco and they said that even with the time that has passed, they will take it back. I’ve had it for 3-4 months now. I’m impressed.

According to one review site I pulled up, the champion I listed has a THD of 5%. If that’s true, it’s a great value.

Verify that. I went on the champion website you provided and for that model it doesn't even mention THD.

 

[coleman10]

Verify that. I went on the champion website you provided and for that model it doesn't even mention THD.

It’s not listed in the online specs, but Champion Support has responded to questions about the THD. Their blanket response for all generators is in my original post, that it has a THD of 15% or less. Either way, it’s certainly less than 25%.

 

[kd3pc]

you could also mitigate some of this by using APC UPS, it would be additional cost - but would save your downstream electronics from spikes and brownouts and such.

 

[coleman10]

you could also mitigate some of this by using APC UPS, it would be additional cost - but would save your downstream electronics from spikes and brownouts and such.

That’s true, but I feel purpose of the transfer switch is so I can turn on circuits A or B or what have you and use what I need and not have to worry about this too much. The water heater is hard wired - can’t put anything on that. I don’t want to be bothered with pulling the fridge out and jumping behind there. It’s a tight fit. My blood pressure will be up enough just because of the power failure without having to worry about dirty power possibly hitting our stuff. I’d rather return the Firman and get a better machine. More peace of mind.

 

[theoldwizard1]

A rotating field (or stator) type gen typically produces a very clean sinusoid with little conditioning. I hoped the OP had misread the stated THD, but wow 25% in the specs!!! I never would imagine any unit being sold with that low level of quality.

Concur !

The problem with non-inverting generators is usually load transitions or high inductive load (motors) causes significant fluctuation in voltage and frequency.

 

[theoldwizard1]

you could also mitigate some of this by using APC UPS, it would be additional cost - but would save your downstream electronics from spikes and brownouts and such.

Be careful what you are saying there ! The cheap APC UPS actually output a modified sine wave.

What you want is a "line conditioner/filter" or an "online" sine wave UPS (all incoming power is converted to DC, batteries are charge and the the DC power is converted back to AC). Both are expensive.

 

[Fasthotrod]

One thing that I haven't seen mentioned yet: What actually causes Total Harmonic Distortion?

Here's a good starting point: https://www.packetpower.com/blog/total-harmonics-distortion-defined

I'd be asking the LED light manufacturer what their specifications are... and I'd be looking at what other loads are on line that may also be impacting your system. It's not always the generator that is the root cause.

 

[coleman10]

Will definitely check out the link. Thanks for that. As for the lights, there was nothing else on that circuit. That breaker was for my bedroom and it was the only energized circuit and nothing else was on other than the two closet lights. Yes, it could be the lights, but the modified sine wave has me spooked, especially since we would be running the fridge and a portable AC, both of which have motors. I’m more than happy to spend a few extra hundred dollars for a better piece of equipment. Hopefully, it will never be used.

 

[ant.foste]

There are a few things in life in which a man should not explore the cheapest option. Hookers are always at the top of the list. And generators are in the top ten on that list. With both, the quality and cleanliness are determined in the cost.

 

[htmdude57]

Like the Old Wizard says, be careful about expecting a UPS to put out good clean power. Cheap units just send the same line voltage through them to the "load" and use a relay to switch off the "dead" incoming line, and then put the "produced" 120VAC to your load. The point being that the bad incoming power goes straight through.

What he describes, which produces clean power to the load, used to be called a "Dual conversion" UPS. I don't know if they still use that terminology?

Typically, the dual conversion UPS's are going to cost much, much more than the cheap ones.

 

[wyliesdiesels]

you could also mitigate some of this by using APC UPS, it would be additional cost - but would save your downstream electronics from spikes and brownouts and such.

not so fast.

Not all UPSs are created equal.

Some UPSs have whats called AVR- automatic voltage regulation, which fixes sags and surges without switching to battery power.

But if the THD is too high then they switch to battery power.

I doubt the batteries would last long constantly switching.

Also, a UPS would not be good for running a motor due to the in-rush current...

 

[79firebird]

Firman generators are junk. my boss is on his 3ed he uses it just to charge batters well camping they have sent him 2 replacements. the power from them goes up and down

 

[coleman10]

There are a few things in life in which a man should not explore the cheapest option. Hookers are always at the top of the list. And generators are in the top ten on that list. With both, the quality and cleanliness are determined in the cost.

Best post I’ve read this year.

 

[Git]

Wish I could. Been a few months now and no box. Receipt’s been tossed. I didn’t think I’d be in this position. Lesson learned.

No No No

You don't need a box to take it back to the store or the receipt - they can look up your purchase history. If you ordered it online, it would be easier to just find a box to put it in and they will come pick it up, otherwise take it back to a store for a FULL REFUND

This is why you bought it from Costco to begin with! Your satisfaction is guaranteed

If it is not specifically listed on this page, you can return just about anytime. If you have any doubts or questions, just call them

https://customerservice.costco.com/app/answers/detail/a_id/1191/~/what-is-costcos-return-policy?

 

[checkthisout]

Get a Yamaha or Honda inverter and don't look back.

Neither will ever let you down and hold their value if you ever want to sell.

 

[slow]

A honda or yamaha inverter that does 240 volts is significantly more expensive than the ones he is looking at. I do agree we have an eu7000i at work, phenomenal machine other than the $4500 price tag

 

[checkthisout]

A honda or yamaha inverter that does 240 volts is significantly more expensive than the ones he is looking at. I do agree we have an eu7000i at work, phenomenal machine other than the $4500 price tag

Yeah. Backup power is a lot more expensive when you're trying to power up resistive heating appliances.

Otherwise 3 kw gets you by with flying colors.

There are also non-inverter honda yammy units that would work good.

Yes they cost more but they are also not pieces of ****.

 

[mike93lx]

Yeah. Backup power is a lot more expensive when you're trying to power up resistive heating appliances.

Otherwise 3 kw gets you by with flying colors.

There are also non-inverter honda yammy units that would work good.

Yes they cost more but they are also not pieces of ****.

It isn't just heating. My well pump is 240v,so the small, cheap inverters won't do it.

 

[coleman10]

No No No

You don't need a box to take it back to the store or the receipt - they can look up your purchase history. If you ordered it online, it would be easier to just find a box to put it in and they will come pick it up, otherwise take it back to a store for a FULL REFUND

This is why you bought it from Costco to begin with! Your satisfaction is guaranteed

If it is not specifically listed on this page, you can return just about anytime. If you have any doubts or questions, just call them

https://customerservice.costco.com/app/answers/detail/a_id/1191/~/what-is-costcos-return-policy?

Yep. Called then yesterday. They said to bring it back, no problem. Now I just have to find a way to get it there. Easier to get it down from the truck than to lift it up. May have a rent a truck with ramps from Home Depot.

 

[wyliesdiesels]

Do you know someone with an engine hoist?

 

[checkthisout]

It isn't just heating. My well pump is 240v,so the small, cheap inverters won't do it.

Ah true. Forgot about well pumps.

Even then, I would get a cheap non-inverter vest to run just while I showered and did dishes or whatever and then just run a nice little inverter unit the remainder of the time.

 

[coleman10]

Do you know someone with an engine hoist?

I wish. A buddy of mine will be over tomorrow to give me a hand. I think between the two of us we can lift it up and get it in there.

 

[coleman10]

Success! Got it back to Costco and they gave me a full refund. Have the other one on order and should have it on the 19th. I did find a Yamaha 240v inverter with enough wattage to run what I need, but the 4K price tag is just too much. Hopefully the Champion will never get used, but if it does, at least I know it won't damage my stuff.

Thanks, everyone, for all the info and insight - and especially for telling me that Costco would take back the generator.

 

[Git]

Glad it worked out for you

Consider buying a cheap hour meter like this one - basically wrap the wire around the sparkplug cable and mount the display

 

[coleman10]

Glad it worked out for you



Consider buying a cheap hour meter like this one - basically wrap the wire around the sparkplug cable and mount the display

That's pretty cool. I didn't know something like that existed. The Champion actually keeps track of and displays run time so I can keep on top of maintenance.

 

[ihateminimumwage]

Is your LED lighting dimmable? You'll get bad flickering a lot on generator power since LED lighting is an inductive load, not a resistive.

 

[cybrdyke]

Higher THD is the result of a weird sine wave.
Flickering lights are the result of a weird sine wave.
That doesn't mean that THD is the cause of flickering.
CD

 

[coleman10]

Wanted to give everyone a quick update. I got the Champion generator in over the weekend and powered the same circuit with the same load as last time. The light flickering is barely evident and intermittent at that. You have to be looking for it in order to see it. Night and day compared to the Firman. Glad I was able to return it. Thanks to everyone for all the great info and assistance. Once again, invaluable.