Generac 15KW generator engine tear down
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FairfaxStu
Gold Member
I am still extremely skeptical. As an EE, I can tell you that power factor is important especially for power companies so they typically put in massive capacitor banks in attempt to get the power factor as close to 1.0 as possible. This means that the power they generate which is measured in KVA equals what they sell which is measured in KW. Since they bill you at the KW level, not KVA, I don't entirely understand how this product would save you money.
That being said, for the price, it is probably worth trying. However, with the amount of power you pull, you may want to consider upgrading to one of the larger commercial units. One benefit you would see is that when the generator is running, you would get more power out of it for what you pay in propane.
I to am an EE with 35 years experience in industrial and power. It is true that correcting power factor in a residential setting WILL save money. Most likely up to one dollar per year. This is due to the fact that high reactance (KVA) will result in higher current for the power used (KW). This means that the current is higher and some additional heating losses (I^2R) will occur in wiring. That said, it will only take a hundred or more years to recoup your investment.
On a genset, improving power factor may help, since poor power factor (inductive loads) may push up the current beyond what is needed, and the generator does not have a large reserve for excess current in the form of heavier wiring and excess iron in the stator. You may effectively get less than rated capacity out of the genny if your power factor is poor and you are running it near the full rating. So power factor caps on the generator may be of some small help.
paul
FairfaxStu
Gold Member
Thanks, Paul. That is exactly what I was thinking. Perhaps in some areas of the country they sell power by KVA but not here in Virginia. I can see getting a minor benefit out of it, but mostly when having the genset running.
-Stu
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pclausen
Veteran Member
Makes sense. If such a device was truly able to get you a 15-20% savings, everybody would have one already.
Would the caps aid with the start up current draw of large loads? I think this 15kw gen-set will be border line as far as being able to start the compressor in my 5 ton A/C unit.
Would the caps aid with the start up current draw of large loads? I think this 15kw gen-set will be border line as far as being able to start the compressor in my 5 ton A/C unit.
FairfaxStu
Gold Member
You are probably right. I was thinking maybe you could setup the transfer switch to turn on the AC load before everything else. Then I thought more about it and realized that the AC will be cycling on and off anyway. Do you have a clamp meter that you could measure the current draw of the AC with? I am guessing it is about 40-50 amps. With that information we can probably help you to determine if you will have an issue or not. You may also want to take readings of the other circuits you need to support with the genset.
Most modern ACs and even most digital thermostats will delay the AC startup after a power outage. I know my systems wait about 10-15 minutes and the time is psuedorandom, so my three units will never start at the same exact time. Now my zones are only one 2 ton and two 1.5 ton units. They are easier to start than a larger unit. When I start my 10KW genset (diesel) I just let the ACs come on on their own. No problem starting the 3rd system with the other two running. The only thing I switch off is the hot water heater, and the stove/oven if it was on at the time of the outage.
paul
paul
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aczlan
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- Kubota L3830GST, B7500HST, BX2660. Formerly: Case 480F LL, David Brown 880UE
Might get the "hard start kit" for your compressor. That has a cap which makes it pull less power on startup.
Aaron Z
Actually a hard start kit will increase the initial inrush. It allows for a greater starting torque. Without a hard start kit, the compressor will start more slowly, allowing a longer time at high inrush current. The quicker current spike may assist with getting it started faster and possibly help with the genset.
paul
aczlan
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Is that more inrush to the motor or more inrush from the breaker panel?
I was under the impression that the capacitors in a hard start kit were to store energy so you get increased inrush to the motor with the same (or less) inrush from the breaker panel.
Aaron Z
The hard start capacitor is not used to "store" energy. The capacitor is used to generate a phase shift in current to the start windings. In other words, it generates a starting torque using the start winding. A larger cap, like a hard start cap, will cause higher current in the starting winding, and hence a higher starting torque. In a hard start kit, this extra current and torque, if left on, would cause a high current over heating of the motor, and eventual failure. So the cap in the hard start kit is only applied momentarily during startup.
As I had said earlier, this higher starting current will result in a higher draw from the AC supply. It is possible that the higher current will be offset by the shorter time for startup. Generators have two limitations: copper and iron. Copper is the size (gauge) of wire. Heavier wire can handle more current with less losses. So heavier wire can provide more current with less losses in the windings (due to resistance). You will therefore have lower voltage drop. With smaller wire, during heavy current draws the voltage will sag more below the design voltage.
Iron refers to the amount on iron in the laminated magnetic structure of the generator's stator. As current goes up, so does the magnetic fields in the iron of the stator. At high currents, the iron can reach "saturation" which is the point where the iron can not increase it's magnetic strength any more - it is saturated. This is kind of a hard limit on the output of the generator. So on a big inrush like the AC, you have the inertia of the generator to provide energy (rotational). The copper may cause the voltage to droop at high currents, but if you hit field saturation, you are at a hard limit on current.
The desire to build cheaply, common in many import units, means saving on copper and iron. This is why many low cost gen sets have such a low ratio between the full load and surge ratings. A heavier, more conservative build will have more margins and therefore a higher surge rating.
paul
As I had said earlier, this higher starting current will result in a higher draw from the AC supply. It is possible that the higher current will be offset by the shorter time for startup. Generators have two limitations: copper and iron. Copper is the size (gauge) of wire. Heavier wire can handle more current with less losses. So heavier wire can provide more current with less losses in the windings (due to resistance). You will therefore have lower voltage drop. With smaller wire, during heavy current draws the voltage will sag more below the design voltage.
Iron refers to the amount on iron in the laminated magnetic structure of the generator's stator. As current goes up, so does the magnetic fields in the iron of the stator. At high currents, the iron can reach "saturation" which is the point where the iron can not increase it's magnetic strength any more - it is saturated. This is kind of a hard limit on the output of the generator. So on a big inrush like the AC, you have the inertia of the generator to provide energy (rotational). The copper may cause the voltage to droop at high currents, but if you hit field saturation, you are at a hard limit on current.
The desire to build cheaply, common in many import units, means saving on copper and iron. This is why many low cost gen sets have such a low ratio between the full load and surge ratings. A heavier, more conservative build will have more margins and therefore a higher surge rating.
paul
OP
pclausen
Veteran Member
Appreciate the feedback guys. My unit is actually a 4-ton unit. Trane XE1000 from 1997. Here's it's "plate":
Putting a current clamp on gives me a 18A reading per leg, so that's 36A @ 240V I believe, or 8640W. This would be with the unit already running. Not sure how I would capture start up current. Perhaps the label above would offer a clue?
I used to have a 25kw Generac PTO generator that had a 50kw surge capacity. I guess they didn't skimp on the copper and iron in that guy! I don't seem to be able to locate a surge spec for my 15kw Generac 4390.
Putting a current clamp on gives me a 18A reading per leg, so that's 36A @ 240V I believe, or 8640W. This would be with the unit already running. Not sure how I would capture start up current. Perhaps the label above would offer a clue?
I used to have a 25kw Generac PTO generator that had a 50kw surge capacity. I guess they didn't skimp on the copper and iron in that guy! I don't seem to be able to locate a surge spec for my 15kw Generac 4390.
The only real way to see is to try it. Shed all other loads and flick it on. One bad problem with gen sets is if the start in-rush lugs the generator and pulls down the voltage, the motor will never come up to speed, and stay in the start winding and draw high current. You sit there with the gen pulled down and the motor never starting and hopefully the breaker blows to break the cycle. Leave a small light on and judge the overall situation with how long the bulb stays dim.
Once you are running, you should be fine. Full load amps is only about 25, and that would be with a high load on the AC (hot house, blazing outside temp)
paul
Once you are running, you should be fine. Full load amps is only about 25, and that would be with a high load on the AC (hot house, blazing outside temp)
paul
Gator6x4
Super Star Member
Putting a current clamp on gives me a 18A reading per leg, so that's 36A @ 240V I believe, or 8640W. This would be with the unit already running. Not sure how I would capture start up current. Perhaps the label above would offer a clue?
The old electrician who taught me how to use a volt/amp meter advised to use the reading obtained from one leg of the electrical supply line to determine running amps. If he was right, your running amps is 18 not 36. A 36 amp running device would really make a power bill jump each month.
OP
pclausen
Veteran Member
I noticed that as well when trying to find that spec. Their 15kw portable is advertised as having 22.5kw surge, so I would imagine a whole house of same continuous rating by the same manufacturer would be similar.
OP
pclausen
Veteran Member
Come to think about, that makes sense since one leg is the supply and the other return on a 240V circuit. Much like I would get the same reading on both the hot and neutral on a 120V circuit.
FairfaxStu
Gold Member
Any update for the forum on the generator? Did the Fat ******* and Frank stop by for the engine swap? How close are you to actually powering that bad boy up?
OP
pclausen
Veteran Member
Yep, they sure did. Here's my old engine. We stole the flywheel, shields, governor, oil pump, pickup and misc other parts from it.
Once it was mounted back on the frame we put oil in, spun it with the starter to make sure made spark, oil pressure and compression. It did. Next up was to install all these pieces:
And a shot of the engine and generator sections fully re-assembled:
Only thing left is to install the battery and control board, but I might pull the firewall back off to drill out one of the intake manifold bolt holes and re-tap one size up, as it was somewhat stripped. Seems to be holding but it spun when I tried to toque it down to the proper value. After all the effort in getting this generator in prime condition again, I'd hate for it to develop a leak on the intake side over time...
Once it was mounted back on the frame we put oil in, spun it with the starter to make sure made spark, oil pressure and compression. It did. Next up was to install all these pieces:
And a shot of the engine and generator sections fully re-assembled:
Only thing left is to install the battery and control board, but I might pull the firewall back off to drill out one of the intake manifold bolt holes and re-tap one size up, as it was somewhat stripped. Seems to be holding but it spun when I tried to toque it down to the proper value. After all the effort in getting this generator in prime condition again, I'd hate for it to develop a leak on the intake side over time...
