load, ammeter and black smoke questions

[Jimc]

Thats a super explaination steely. That makes it easier to understand what is happening there.

Not to drag this out but i find this interesting. Concerning the meter, say the pf is not 1 and the load is wasting power. The gen has to put out more to make the load operate which in turn uses up more percentage of rated gen output. The gauge cant read that? I am just trying to figure out why when the pf is not 1 that there is some percentage of power being output that the gauge cant read...am i making sense? I guess i am saying how would the gauge know what the pf of the load is? Any way you look at it a load uses "x" amount of amps doesnt it?

 

[steelypip]

Concerning the meter, say the pf is not 1 and the load is wasting power. The gen has to put out more to make the load operate which in turn uses up more percentage of rated gen output. The gauge cant read that? I am just trying to figure out why when the pf is not 1 that there is some percentage of power being output that the gauge cant read...am i making sense? I guess i am saying how would the gauge know what the pf of the load is? Any way you look at it a load uses "x" amount of amps doesnt it?

The gauge doesn't know what the PF of the load is. All the %load gauge knows is amount of current flowing through the generator output windings. That's real power (actual work being done by the load), not imaginary power. The gauge face is calibrated so that it reads 20% low relative to the nameplate KW rating of the generator. If the load is 20% imaginary (PF=0.8 ), then it reads correctly. If the load is 0% imaginary (PF=1) then it reads high - more of the generator's effort is being converted into useful work than the assumed value. If the load is more than 20% imaginary (like the big air compressor probably is), then it reads low.

One last thing. In AC power, there's a fair amount of discussion of having the current lead or lag voltage (or voltage leading or lagging current if you're a masochist). If a load is mostly inductors (like big electric motors) then the current tends to lag the voltage. If a load is mostly capacitors (like a fluorescent tube without its ballast) then the current tends to lead the voltage (that's why a 277 volt fluoro circuit still needs a ballast (inductor) in line with the tube - to force the PF back close to 1). Clever power factor management for permanent installations can involve the power company putting capacitors on the pole or in the substation to help push the power factor back toward 1 when there's a big inductive customer load being supplied. Here's a fine example.

In this case, you're the power company. Fixing the power factor problem on the air compressor would probably benefit you a couple different ways...

 

[Jimc]

Hey thanks steely for taking the time to explain all that!!

 

[Triple Jim]

The waste comes from things like resistive loss in the wiring, which is proportional to the current, whether the PF is 1 or not. If the PF were zero, you could have the full rated current flowing, and measure the rated voltage, without any power transferred to the load. A low power factor prevents power from being transferred, but doesn't actually absorb power. If it did, something would get very hot, very fast. Theoretically, with a PF of zero, the engine would not need to do any work, even with full rated current showing on the meter, because there is nothing more than a resonance, like the swing mentioned above, that without air resistance or other friction, would keep swinging forever without being pushed at all.

Here's a link to some information about generator power factors that you might like: http://www.yanceybros.com/yancey-po...consultants-corner/understanding-power-factor The table at the bottom shows that as the PF decreases, the current can remain the same, but the load on the engine decreases because less power is actually being transferred to the load.

 

[Jimc]

Wow this is some heavy stuff lol. Funny, i worked at a large yacht co for about 7 years as an assistant to the elec engineer and i dont ever remember any of this ever coming up even when dealing with the generators on the boats. Thanks for yhe link jim. Later tonight when im done work ill give it a read. At this point i am wondering why they even bother putting the gauge on the generator. Unless you know the power factor of your whole elec system at any given moment depending on what loads are running, the reading really means nothing.

 

[Triple Jim]

I'm sure you can find better links that the one I sent if you look around. The reason it doesn't come up all the time, and the reason you didn't hear about it at the yacht company is that in general, when you put a bunch of loads on a generator, together they'll probably average something in the .8 to 1 range, depending on how much of the load is resistive and how much is motors, fluorescent lights, etc.. If you have or get a Kill-A-Watt meter, you can get a feel for the power factor of different household loads. In the end, you normally don't have to be concerned about PF.

 

[Jimc]

this has been a very educational thread. thanks again to 3jim and steely

 

[LuckyDog]

There was thread awhile back that also talked a little about why the units are rated at 0.8PF. Didn't search for it though.

That thread mentioned the different kind of generators. There are Prime, Backup, and Emergency. IIRC, Emergency are rated at something like surge capability, That is why a Generac sold in HomeDump might say it's 10kWatt but it is so tiny. It can surge (put out for a short time) 10kW to start an electric motor or such. Run that generator at 10kW for long and the magic smoke comes out of something. Backup Generators are built a little tougher. There "Ratings" can be based on a PF of 1. So, if your load is 100% resistive, you can run for awhile (don't know how long really) at the full 10kW. Not 24/7, but a couple hours at a time for sure.

Now, a "Prime Power Source" is (I think by law) rated at PF = 0.8. If not law, it is one of the high powered agencies. These will run at 100% 24/7. As mentioned above, Motors (inductive loads) and Flourescent Lights (capacitive loads) cause the load to not be 100% resistive but they are engineered to get closer than not. Hence a safety factor.

So, you can see how Marketing plays in these labels. A 10kW "Emeregency" generator from the box store ain't nuthin like a 10kW "Prime" generator. (Just look at a 10kW Generac or Honda verses your MEP-003A)

For this discussion, the Load meter is just an Amp meter. It over complicates things a bit for the casual user. 100% on the meter is 52.08 Amps.

V×I×PF = Real Load

Voltage (V) is potential to do work. It don't do it though. (Like Pressure in hydralics)
Current (I) is needed to do work. (Fluid flows into the cylinder causing it move. You can put all the pressure you want on the piston in the cylinder, but if the fluid does not flow in, the cylinder rod does move)

Current flowing in wires causes heat. (notice your hydraulic lines get warm?). To much heat will cause things to melt or burn.

So 100% current is 52 Amps and really you can forget about PF (for the most part when running your house).

Ok, that was a little simplistic but I hope it is helpful.

 

[Jimc]

hey lucky, almost everything that can be purchased by the average consumer is overrated or overstated somehow. all marketing bs that i find irritating. i got a feel for pf now and how that all works. my main confusion originally was the ammeter gauge. i could still be wrong but after the postings of the other guys, my understanding is that the 52.08 amp that you say is 100% load may be actually 100% and it may not be. that will change depending on pf which is why the gauge will only read true at .8 pf. is that right?

 

[storeman]

IMO, the gauge at 100% gives you 10KW, which corresponds to pf 0.8 and roughly 52 amps. When you load to 120% on the ammeter you are producing about 62 amps or approximately the output if the unit was pf1.0 rated.

Am I screwed up?

Jerry

 

[LuckyDog]

IMO, the gauge at 100% gives you 10KW, which corresponds to pf 0.8 and roughly 52 amps. When you load to 120% on the ammeter you are producing about 62 amps ... (KISSed)

Jerry

There, Fixed it for ya.

No, you are not screwed up. (Maybe down, but that's another topic....)

If PF = 1.0, V=240, & I=52 (meter showing 100%)
Then Real Power = ~12.5kW (That is why some people say the 003 is like a 12.5kW civy Backup generator)

Or, if you really want to sell it as an "Emergency" generator to a "friend", tell them it is a 35kW generator.

 

[dangier]

Also find this thread very informative. I will use the ampmeter just as a general indication, but not put a lot of stock in it.
Thanks for the in-depth explanation. You guys make it sound easy. I never was really good in math. Just good enough to get by.....