They are different. See...

Firman T08072 10000W Tri Fuel Generator

Comprehensive spec breakdown of the Firman T08072 ✓Electric start ✓8000 running watts ✓10000 peak watts ✓50-amp outlet ✓CO sensor ✓Natural gas ready ✓Long runtime ✓More quiet and better priced than others? Come find out...

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Firman P08008 VS - Spec & Feature Comparison

Let's review the key differences between the and the Firman P08008. Which generator will be the most suitable for your needs? Come find out...

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Oops, I searched for P08003 instead of P08008. The specs on the Firman website are here...

Gas Portable Generator 10000W Remote Start 120/240V with CO Alert

Whether you prepare your home for an approaching storm or power up for your next event, this generator provides power on demand with 8000 running Watts and 10000 starting Watts. The FIRMAN P08008 is an ideal choice of portable generators from our class of performance generators and can do almost...

firmanpowerequipment.com

 

Yes I saw the spec on their website. Looks like the generator part of T08072 is almost 2x better than P08008 for THD. It's why I asked I have doubt on this.
Thanks for your input

 

Yes I saw the spec on their website. Looks like the generator part of T08072 is almost 2x better than P08008 for THD.

Okay. I don't see any reason to doubt the THD differences in their specs. Conventional (non-inverter) generators can be all over the place as far as THD goes. It really depends on the market they are shooting for. Construction class generators can have 20%+ THD and be just fine. A table saw just doesn't care about THD.

Conventional generators can be made with less than 5% THD with careful design and windings.

 

Problem is I'll buy it for my house, including electronic device such as computers. In fact I already bought the p08008 but the box is still not open. I'm thinking of return it to take the 11-14% thd instead. Those computers are all connected throw a UPS but I dont know how those UPS will react with 25% THD

 

Those computers are all connected throw a UPS but I dont know how those UPS will react with 25% THD

It depends on the UPS. Some won't take too much THD at all.

I would suggest that you look into inverter gens, but I guess you have already done that.

 

Less than 5% is the NEC spec and almost a perfect sine wave. 25% THD is the lowest a modified sine wave inverter can achieve. 48.3% THD is a square wave! Its not advisable for sensitive electronics above 5%. Any conventional generator that can be that high is trash for powering a house. Construction site tools...eh I'm sure the tools aren't that picky.

UPS with Line Interactive topology will switch to battery with any THD over 5%. A UPS with Double Conversion "Online" where the incoming power is only meant to charge the internal batteries while the loads are being supplied by the batteries all the time (Incoming AC to DC, then back to AC for the load) is solely dependent on the input charger. Chances are with the Active Power Factor Correction circuit (run by an IC) will not tolerate much beyond 5% THD. It is not often you have a double conversion UPS with a Passive PFC circuit (basically a large capacitor at the input) anymore because such caps are expensive and often have a limited lifespan in such an application.

I'd go with an inverter generator if you want clean under 5% THD.

 

I have a APC Smart UPS 1400 and a Smart ups 750. Like you said, if THD is too high and switch on battery anyway, this doesn't help me at all. Best way should do to try it to see what is really going. on.

 

I have a APC Smart UPS 1400 add a Smart ups 750. Like you said, if THD is too high and switch on battery anyway, this doesn't help me at all. Best way should do to try it to see what is really going. on.

First, see if your generator is putting out power that is within limits of what the UPS can deem "good". So that means 120V @ 60Hz nominal. Oftentimes, the UPS may not accept power because the frequency (Hz) is way off... a common occurrence with non-inverter generators with an improper speed governor setting.

If the generator output is within norms and the UPS still occasionally switch between line and battery backup, the input sensitivity can be changed on APC Smart-UPS series. All my APCs are set to medium. I've had no hesitation from it when running off generator power. APC says that if your load can tolerate generator power, you can lower the sensitivity to medium.

The Smart-UPS detects line voltage distortions such as spikes, notches, dips, and swells, as well as distortions caused by operation with inexpensive fuel-powered generators. By default, the UPS reacts to distortions by transferring to on-battery operation to protect the equipment that you are plugging into the UPS. Where power quality is poor, the UPS may frequently transfer to on-battery operation. Battery longevity and service life of the UPS may be conserved by reducing the sensitivity of the UPS, as long as your equipment can operate normally under the conditions detailed below. The sensitivity circuit monitors Total Harmonic Distortion(THD), Change in Voltage over Time(dv/dt), and Frequency (Hz) out of tolerance.

NOTE:
The sensitivity circuit looks at these three parameters (THD, dv/dt, Hz) and makes a quantitative analysis based on all three things using a proprietary algorithm.

There are not pre-defined limits for each parameter. (IE: There is no way to say "At medium sensitivity, the UPS will transfer at X percent THD.")

Source: Video: What are the different sensitivity settings of a Smart-UPS? - APC USA.

 

My UPS APC and Cyperpower care about voltage and frequency (60Hz =+- 2Hz) Get those right and what ever THD is there, they have not cared. The THD story is more than distortion from the power source but includes the trash reflected back onto the line from reactive loads.

 

Ok more clear now. Wrong voltage and frequency is what ups doesn't like. THD is less important that I thought.

To adjust the frequency---> motor speed. Something like that:

And for voltage---->something like that:

In addition, for the THD, all pc's are switching power supply. Meaning they are first filtered and rectified to DC and raise to about 400v dc, and switching it in a transformer as square wave (already noisy). And re-lower down at acceptable voltage with higher current, again, filtered. Knowing this. I agree that THD isn't the worst problem for electronic.

So, turn off the main breaker, start the generator, be sure voltage and frequency is on spec. When all is looking good, turn on the generator breaker.
Thank you for your advice et your time very appreciated.

Yannick

 

Your research is accurate, but don't discount high THD. Over time high THD will cause failure in your PSUs. Harmonic voltage/current is not real power going to your load, just circulating in the system not actually doing anything other than contributing heat. Many SMPS with Active PFC circuitry can tolerate high THD to an extent, but over time it can wear out the control circuit operating the boost converter after the input filter/rectification stage from the incoming AC line.

Make sure you have the right voltage and frequency for the electrical end, and verify the prime mover is properly tuned so that the speed regulation is as tight as it can be. THD cannot be mitigated on conventional generators unless they are already rated less than 5%.

 

Your research is accurate, but don't discount high THD. Over time high THD will cause failure in your PSUs. Harmonic voltage/current is not real power going to your load, just circulating in the system not actually doing anything other than contributing heat. Many SMPS with Active PFC circuitry can tolerate high THD to an extent, but over time it can wear out the control circuit operating the boost converter after the input filter/rectification stage from the incoming AC line.

That is one of the most misunderstood things about generator THD...damage from THD is often cumulative with electronics. People tend to say "well, it is working just fine with my high THD gen, perhaps making some slight noises, but working fine".

 

Again, there are two problems that I believe we can pull out of an entire dirty power discussion and do something about ... THD and Surges.

Unfortunately, talking about THD only from the gen side is making it sound like all problems are cured by getting a low-THD gen. They aren't ... everything in your house is dumping THD back out on the line (smps devices are among the worst by their very design, UPS, etc). If you were to argue that THD is bad, then your electronics are getting eaten up by the THD that is already in your house wiring, and not from the gen (how often do you run your gen, after all?). My belief (IMHO) is that THD is the lesser evil.

Think of the house wiring as a pond, and everything in the house has dirtied up the water already, because almost every device is dumping THD into that pond. Your "clean power" gen is dumping clean water into the pond, which immediately turns dirty (clean + dirty = dirty). Your "dirty power" gen is dumping dirty water into the pond (dirty + dirty = dirty). In commercial/industrial sites, they can clean their entire lake of dirty water with specialized equipment, and end up w/ less dirty water. The grid requires this of them.

When you transfer back to the grid, clean water is getting dumped into your dirty pond by the grid, along with the occasional (and free) instant-death-dealing surge. Kiss that HVAC goodby, not slowly from THD, but instantly, from a single surge event.

What can you do about a THD problem? I'm no EE, but as best I can tell, little to nothing ... what commercial/industrial sites can do, with an army of EE's at their disposal, isn't what we can do at the home level. Can you stick a $200 UPS in front of something that is supposedly susceptible to high-THD? Sure, but now that same UPS is dumping more THD back out on the wiring.

The only clean pool of water I can find is the small puddle that is internal to your device that has an SMPS in front of it; this is a DC puddle. Behind it, that SMPS is dumping THD back out into the AC house pond. Our prevailing codes in the US say that this is a one-way street only ... clean up incoming power, but do nothing about outgoing power.

What can you do about the Surge problem? I'm no EE, but as best I can tell, you simply install an SPD device in your load center, and smaller SPD devices in front of susceptible devices. Have an HVAC that costs 10k? Stick an SPD in front of it. Same w/ little $$$ electronics. No THD being dumped back out on the line, from your SPD effort.

So, do you get a low-THD gen? Absolutely no problem, if you are willing to trade fuel choice, authorized dealer network only, complexity, low-watts, and other issues for the chance to dump clean water into your dirty pond water. Economics-wise, it's better for the economy when you buy a $5000 honda, than a $1000 westinghouse. Ignore those trade-offs (and issues, costs & headaches) behind the curtain ...

As I run my gen's for 1000 hrs / yr, out in rural nowhere, I too, am excited by "inverter technology" ... but I don't know where the marketplace will go with their designs. A "jet-engine complexity" Honda, and other similar designs, are the first iteration, and they don't fit rural applications easily. They are more like a JD tractor that only the dealer can repair, if you can get it there. I've seen only one open-frame gen w/ an inverter panel, but it had none of the features of a westinghouse non-inverter open-frame.

I took the $4000 in savings, bought $300 worth of SPD's, and called it good, as surges were infinitely more fixable than THD. 5 years later, it's still good. If my $300 TV does die a horrible death (and I can somehow trace it to THD, in some form of electronic autopsy), I still have $3700 left over to buy another $300 TV ...

YMMV, and watch out for those marketing folks ...

 

While it's true that THD will increase with distance from the utility or generator interface (Point of Common Coupling, or PCC), because of voltage sag; and while it's also true that the practical effect of poor THD will vary depending upon the current demand of a load (smaller loads generally being affected less), I'm not sure the dirty pond metaphor is very apt. Plug in a load and the source of the electrons traversing the circuit powering that load come from the utility interface (or generator)... not a mishmash of electrons from throughout the house wiring.

If the dirty pond analogy were accurate, the entire grid would have very poor THD as all those homes and businesses polluted the bigger pond. Fortunately, it doesn't quite work that way. Utilities typically provide grid power with a THD of 5% or less.

People can do whatever they want, of course. But make no mistake... THD is a thing. Part of the problem is that generators have been around for many decades and most of our individual experiences with them is that they "just work." And they usually work just fine for a very long time. But most of the loads that we collectively powered with those generators for all those years were linear loads. And linear loads aren't generally affected by high THD.

Nowadays we have a proliferation of non-linear loads. And non-linear loads are very much affected by high THD.

 

Here is a good presentation that goes into surge protection and harmonic distortion. Two different things, but both should be addressed in our modern world of electronics.

https://www.libertyelectricproducts.com/downloads/Webinar-Surge-Protection-101-and-Harmonics.pdf

As explained, a harmonic is a component of a periodic wave with a frequency that is an integer multiple of the fundamental frequency. Whereas a surge (or transient) is a high rising voltage condition on one or more phases lasting 2 milliseconds or less.

A surge suppressor cannot correct THD because it doesn't even know it exists. A SPD works in a completely different (higher) voltage range than line voltage.

Article 230.67 of the 2020 NEC requires all services supplying dwelling units to be provided with a surge protective device (SPD), as an integral part of the equipment or located immediately adjacent. The SPD must be a Type 1 or Type 2 SPD. This requirement also applies to residential service equipment being replaced.

 

The grid does indeed have low THD ... it puts out "clean water" (under high pressure), as the grid supplier works to keep it that way through constant monitoring at many points.

One problem the grid has is that commercial/industrial sites do throw THD back out on the grid, and cause trouble in the grid "ocean" for other customers downstream or nearby those sites. This is why the grid will punish these offending sites with chargeback fees, and is also why those sites have EE's & specialized equipment to counter the THD levels. If it is a thing on a grid, and in a commercial building's "lake", then it's a thing in our smaller "pond" (the scale changed, but not the problem).

The power comes into our pond, circulates (and some is consumed), and then returns to the source (the grid). The grid (or your gen) keeps the pressure high, so that anything consumed is replaced, but it still circulates.

Is the grid affected by our homes? A very good question, and I don't know how the grid is protected from each of us in terms of THD ... one googled explanation is:

"The proliferation of nonlinear loads and the increasing penetration of distributed energy resources in medium-voltage (MV) and low-voltage (LV) distribution grids make it more difficult to maintain the power quality levels in residential electrical grids, especially in the case of weak grids. Most household appliances contain a conventional power factor corrector (PFC) rectifier, which maximizes the load power factor (PF) but does not contribute to the regulation of the voltage total harmonic distortion (THD V ) in residential electrical grids."

I'd take this to mean the grid is good/bad in your area ... warrants more research & reading.

The other problem the grid has is "surges", and there isn't anything the grid folks can do about those ... your clean water from the grid comes with the occasional free and big surge. Inside your house, more free micro-surges are happening, to the tune of dozens, hundreds, or more. While we can block surges, I don't see how we can block THD, when almost every device in your house is contributing to it.

Linear or non-linear loads? I'll let google answer that:

"with linear loads, the voltage and the current sine waves are going to look the same. Current that is drawn from a regular motor or a light can look like the clean voltage, even if it is not in phase or a little bit leading or lagging—it depends on the power factor of the load."
"with nonlinear loads, the current is not going to look like the voltage. The more drives or the more distorted current we add—the more voltage distortion we have on the system."

And finally ...

"Times have changed. Harmonic problems are now common in not only industrial applications but in commercial buildings as well. This is due primarily to new power conversion technologies, such as the Switch-mode Power Supply (SMPS), which can be found in virtually every power electronic device (computers, servers, monitors, printers, photocopiers, telecom systems, broadcasting equipment, banking machines, etc.). The SMPS is an excellent power supply, but it is also a highly non-linear load. Their proliferation has made them a substantial portion of the total load in most commercial buildings."

So there's the kicker ... the (non-linear load) SMPS is both good and bad! It's good for the device behind it ... it's bad for any other device in the pond, unless they also have an SMPS in front of them. I have dozens, if not hundreds of SMPS "wall-warts" in operation, just walking around my house and doing a quick count. Each one is throwing THD back out on the wiring, by definition of how it works. If I had just one, I'd agree ... nothing to see, move along. But, a dozen ... a hundred? I can't do anything about these devices nor the THD, so I just let them duke it out. After 5 years, I'm still waiting for things to blow up, because THD should've been handled differently.

So, my dirty gen adds dirty water to my already dirty pond, and each SMPS is eating that dirty water, cleaning it up, and presenting clean water to the device behind it, and throwing dirty water back out. Maybe it's possible that I've lost a wall-wart or three, over the 5 years I've operated dirty gens, but I haven't lost a TV or other "sensitive" device behind those wall-warts, or that has built-in power protection. Each wall-wart is ... $10 or so. I might be one of the few that puts 1000/hrs/yr of (in my case, dirty) water into the pond from a gen.

Whereas, almost anyone can point to a single surge event (lightning, grid) and show several devices that fried right after that surge. Nobody can point to a 1000 micro-surges, which happen daily. Yet, a few SPD's later, I've protected against surges from without, and micro-surges from within. I just can't do that with THD, given all the devices in my pond, and given that there are no equivalent THD SPD's (TPD's?). And a $5k low-THD gen? If our use-case is home backup power, that's clean water for 10 hours per year (insert your own number). If the use-case is rock-band sound/audio mobile power generation, at 50 events per year, 8 hours each ... yeah, I'd throw a Honda at it, and hopefully the business income would pay for it. Food truck? Another great Honda use-case ...

I'm not sure ANYONE can point at a fried/dead device and definitively say THD did that. Maybe device manufacturers will one day add autopsy circuits to these things. Tilt this way for surge, and that way for THD.

I couldn't come up with a better metaphor than ponds/lakes/oceans, and perhaps someone will ...

You could argue the total number of electrons with me ... I can't grasp the numbers, where trillions of the little devils are running around in the system. I just see plenty of research that says that our house is a system (in a chain of small to big systems), and things in our house (like an SMPS) actually causes THD themselves (not just a gen causing/not-causing THD), and I extrapolate from there. Then I look for something practical that I can do, right now; SPD's were very practical.

 

I couldn't come up with a better metaphor than ponds/lakes/oceans

I found the analogy examples excellent 50, well said. 👍

 

I know this is a generator fourm, and we like to debate stuff like this, but outside of these types of fourms nobody knows what THD is and nobody cares. I will never argue having a low THD unit is bad, but unless your running a boatload of servers off generator power 24/7, rest easy. The 3hrs every other year you actually need your generator isn't going to wreck your $300 TV.

Sent from my SM-G973W using Tapatalk

 

I have no idea how the UPS increases the volts to 240 from the generators round abouts 230v without using battery power, because it doesnt click over to battery mode and the UPS inverter can't increase the voltage surely?

 

For small corrections like that a "Line Interactive" UPS uses a multi tap transformer called an autoformer. With the use of various relays inside it senses the voltage it will switch to a different tap on the autoformer to either step up or step down the incoming voltage to keep within a given normal range. However if the voltage moves beyond what the autoformer is capable of adjusting to then it will switch to battery power.


In a double conversion UPS the onboard battery charger charges the batteries all the time, and the loads are run by the internal inverter. Such a UPS for simplicity/reliability will have a large inductor and capacitor at its input to the charger called an LC Filter to handle any high THD and then rectify it to DC. Simple circuit and it works, but it sacrifices voltage/frequency range

Take the Triplite SU2200XLCD for example. The specs say a "nominal 100V AC; 110V AC; 120V AC; 127V AC" and either 50/60hz. Nominal 120V means 108-132VAC and either 50/60hz.

On a Cyberpower 1500PFCLCD Line Interactive, constant voltage fluctuations and speed droops on a generator cause it to switch to battery power because the sensing IC circuit for choosing the different autoformer taps/switching to battery power is getting too much noise from the high THD it cannot perform its function so it defaults to battery power. Eventually this unit will fail on generator power either because the IC sensing circuit fails, relay fails from too many cycles, and/or overheating of components not designed to handle it.



I suppose we should discuss PFC circuitry a bit as depending on the design topology, it can either tolerate high THD very well or be completely crippled by it.

Passive PFC: In SMPS is simply a large capacitor/inductor. Its referred to as the Pi filter. Cap is wired across the line/neutral, and the inductor is in series with the hot. Called an LC filter. It is then rectified to DC to be used by the switchmode portion of the PSU. The main advantages are simplicity, reliability and ruggedness, insensitivity to noise and surges, no generation of high-frequency electromagnetic interface (EMI), and no high-frequency switching losses. The main disadvantage is a narrow frequency/voltage operating range, and in greater than 100 watt power applications, those LC components get large and heavy.

***IOTA Engineering makes their DLS chargers/PSUs with this type of topology. I use their 120VAC to 12VDC 90A chargers to replenish my inverter battery bank. They handle high THD of a generator no problem, and the main limitation is the input voltage range can only be between 108-132VAC and frequency between 47-63hz. They have 240VAC variants with the same range too. ***If it were an Active PFC, then you would see specs like 50/60hz 100-240VAC input.

Active PFC: This circuitry use active electronics circuits, which contain devices like MOSFETs, BJTs, and IGBTs. There are so many topologies I could make a novel on it. The two main types are boost (increasing the line voltage on the output) and Buck (decreasing the voltage) on the output. Basically they use an integrated circuit microcontroller to run the MOSFETS turning them on/off really fast in a circuit with an inductor. This precisely controls the current/voltage output.

There is still basic passive filtering before the DC to DC Buck/Boost Stage I discussed above, but it is not made to be as robust to correct power factor since that work is being on by the IC circuit. If enough harmonic distortion enters that PSU, it will heat up those passive filtering components adversely, and potentially cause that IC circuit to malfunction/fail. When that happens any loads connected to it when that IC circuit lets go, then you got cascading damage that costs BIG $$$$.


This should explain why some devices handle THD well and others over time fail. It is a factor in failures on portable generator power, but it is Surge that kills more devices than THD. Its important to look at the specs of devices, and again low THD generators are far less likley to cause all this crap we are discussing. Very informative technical knowledge, but crap to the commoner not familiar with the science.

Cheers!

 

I would say that was impossible thing todo, adding more voltage.
Mine is a Online UPS, but its setup as a Line interactive UPS just because it uses less power and only acts as a Online UPS when the voltage goes over/under 5%

 

The AVR in an interactive UPS uses a multi-tap autotransformer. The UPS logic decides when to boost or trim the voltage so the load only gets to see nominal or near-nominal voltage coming out of the UPS. An autotransformer pretty much is a combination of both a step-up and step-down transformer in a single package. There are other distinct differences which are not relevant here.

Here's a schematic of a typical autotransformer. This design has one level for boost and one level for trim. Some UPSs or dedicated AVRs (non-UPS) have two levels for both boost and trim for a more granular voltage correction.

If the line voltage coming into the UPS is higher or lower than what the AVR can correct, it goes into battery backup mode.

 

Here's my Onan 4.0 BF 4000 watt generator made in 1977. It's my backup and the first generator I used my new meter on. If I'm reading the meter correctly, the THD shows 6.0 at about 2800 watts. HZ was 60.33. Not as good as an Inverter gen, but not too bad for $100.

 

Looks like a generator typically installed into an RV.

 

Onan generators especially from that era are some of the best built generators you can find. Sadly the stuff they push out these days is more crap than ever. 6% at almost 3/4 load is not bad at all. I can't imagine it rising up much further closer to full load.

Keep that dinosaur rolling, very few generators made these days comes close to that build quality.

 

I helped the seller pull it out of a 5th wheel RV. It's surprising how little they cost. Most folks want the newer ones. This one was designed to put out 4000 watts continuously at 1800 rpm. Nest step is to convert it to natural gas.