PTO generator

[Dana Warner]

Just got back from my parents farm in NJ. Power has been out for 7 days with no end in sight. They had 15 gallons of gas on hand when the power went out. We managed to get more before the stations with power ran out of gas. Gas can definitely be hard to get in a wide spread disaster. They had hundreds of gallons of fuel oil. My generator is PTO driven but if I ever got a stand alone generator it would be diesel powered.

 

[dex3361]

Wrong on virtually everything:
1] Find a single phase motor with 90%. Perhaps impossible but at best extremely unlikely,
2] 11.4 X 120 = ~1400 W ~ 2 HP ... 0.75/2 = 38% efficiency. But maybe thats a hi service factor motor and the quoted amps are at its top capability. If SF 1.5 [dont think youll find higher], then motor will output 1.5 x 0.75 = 1.125HP MAX. It probably would do this at SF x FLA = 17.1A ... but to give your scenario the best credence possible lets say it puts out 1.125HP on the ~2HP wattage input represented by 11.4A. Then the motor efficiency is 1.125/2 ~ 56%,
3] Hot steel is irrelevant. Even a small piece of pre hot steel, big enuf to lean on will stop a 3/4HP grinder ... but since grinder motors start slow they dont draw hi in rush - maybe only 15A. Youre saved here, accidently,
4] Are you kidding? is a diversion. Its nice that you can measure nano A, but we can assess this close enuf with one billionth of that resolution. Lets stay on subject. Locked rotor current is the current drawn when the rotor is stationary. It occurs almost instantaneously when power is applied and subsides as the motor starts. With a hard supply Voltage such as available on AC mains, yes, the locked rotor current will blow a breaker ... eventually. Breakers will normally sustain several times their rating for at least a second. By that time the motor should be started,
4] Hard start motors such as used on compressors, washing machines, pumps, general utility, etc, pull 4x+ their FLA in the 1st instant of starting. If this resulting current is above the capability of the gen its voltage drops instantly reducing start torque, perhaps below what is needed. And at the same time reducing run torque available on any motor already running. Such motor slows a little and draws more current. In such a case its likely everything will stall.
5] 3x is not all one needs to know because some motors are employed at their HP rating and start under load. Those motors require full voltage during start. This is trivial on AC mains. A much different situation with a genny sized at 3x. NOT enuf. 4X or more is needed there or the motor does not start.
larry

Well put and I agree fully.

 

[sdkubota]

If anyone wants to discuss the airspeed velocity of a fully laden European shallow I'm here...:drool:

Don't be bringing African swallows into the discussion.

 

[Rob-D]

Wrong on virtually everything:
1] Find a single phase motor with 90%. Perhaps impossible but at best extremely unlikely,
2] 11.4 X 120 = ~1400 W ~ 2 HP ... 0.75/2 = 38% efficiency. But maybe thats a hi service factor motor and the quoted amps are at its top capability. If SF 1.5 [dont think youll find higher], then motor will output 1.5 x 0.75 = 1.125HP MAX. It probably would do this at SF x FLA = 17.1A ... but to give your scenario the best credence possible lets say it puts out 1.125HP on the ~2HP wattage input represented by 11.4A. Then the motor efficiency is 1.125/2 ~ 56%,
3] Hot steel is irrelevant. Even a small piece of pre hot steel, big enuf to lean on will stop a 3/4HP grinder ... but since grinder motors start slow they dont draw hi in rush - maybe only 15A. Youre saved here, accidently,
4] Are you kidding? is a diversion. Its nice that you can measure nano A, but we can assess this close enuf with one billionth of that resolution. Lets stay on subject. Locked rotor current is the current drawn when the rotor is stationary. It occurs almost instantaneously when power is applied and subsides as the motor starts. With a hard supply Voltage such as available on AC mains, yes, the locked rotor current will blow a breaker ... eventually. Breakers will normally sustain several times their rating for at least a second. By that time the motor should be started,
4] Hard start motors such as used on compressors, washing machines, pumps, general utility, etc, pull 4x+ their FLA in the 1st instant of starting. If this resulting current is above the capability of the gen its voltage drops instantly reducing start torque, perhaps below what is needed. And at the same time reducing run torque available on any motor already running. Such motor slows a little and draws more current. In such a case its likely everything will stall.
5] 3x is not all one needs to know because some motors are employed at their HP rating and start under load. Those motors require full voltage during start. This is trivial on AC mains. A much different situation with a genny sized at 3x. NOT enuf. 4X or more is needed there or the motor does not start.
larry

The motor is a 3/4 hp motor. 3/4 of 746 = 559 watts. It was drawing 362 watts running with just a grinding wheel. The hot steel was due to the fact that I was pressing on the grinding stone hard in an attempt to load it down (it did slow) to show the current under load. The 3/4 hp motor I tested came in at 362 watts running and under load it came in at 850.

You have completely missed the point of the test.

We don't care what the motor efficiency is, we are talking about generators starting motors and generators dip when motors start. What are we talking about here, an industrial application with high hp motors running at 440 volts? No people are using PTO gens to run their homes.

Sizing Gen-Sets For Large Motor Starting | Basics content from Electrical Construction and Maintenance (EC and M) Magazine

"Let's look more closely at a motor start. Induction motors have typical starting characteristics. The curve of motor current versus speed shows that during starting, the motor draws approximately six times its full load current; this current remains high until the motor reaches about 80% of speed. This high inrush current causes a dip in generator voltage. The electric power initially required by the motor (with the motor at standstill) is about 150% of rated power. The power required by the motor peaks at about 300% of rated power and 80% of speed with full voltage applied. But, the generator set supplies less than 300% power because starting voltage is lower than full voltage during acceleration, and because the generator set's rotating inertia transfers energy to the motor."

So you're wrong, 3x is all we need. It's an accepted standard. I employ it here and I'm off the grid running inverters and calculating using 3x for years. I haven't blown a fuse or stalled a motor. So if you think that you need 100x overhead than build it into your system, I don't give a fiddle. But tell me how long you've been running off the grid?

Geeze, how many links do I have to post showing this?

You want to be argumentative, find someone else, this is getting silly, the question is how much overhead do we need to start motors.

3 times! How many more links do you need to see?

 

[vwnotrunning]

I'm thinking the swallows may be just as productive.

 

[PineRidge]

Now that I have a 15KW gen set I'm curious as to how many KW I'm using at any given time. If I know that answer I can elect witch circuits to power during an outage and which circuits to keep off. I don't want to do the math or run outside in the cold to clock the elec. meter and besides it's much easier to use a meter connected to the main panel and watch the fluctuations as different electrical items are energized in real time. I found and purchased one of these low cost KWH meters at ebay that uses two clamp on probes similar to a test meter that I use daily for HVAC work (clamp on ampmeter). The readings are then sent wireless to the receiver that I'll have by my desk. I'll let you know how this gadget works once it's connected and working.

 

[SPYDERLK]

The motor is a 3/4 hp motor. 3/4 of 746 = 559 watts. It was drawing 362 watts running with just a grinding wheel. The hot steel was due to the fact that I was pressing on the grinding stone hard in an attempt to load it down (it did slow) to show the current under load. The 3/4 hp motor I tested came in at 362 watts running and under load it came in at 850.

You have completely missed the point of the test.

We don't care what the motor efficiency is, we are talking about generators starting motors and generators dip when motors start. What are we talking about here, an industrial application with high hp motors running at 440 volts? No people are using PTO gens to run their homes.

Sizing Gen-Sets For Large Motor Starting | Basics content from Electrical Construction and Maintenance (EC and M) Magazine

"Let's look more closely at a motor start. Induction motors have typical starting characteristics. The curve of motor current versus speed shows that during starting, the motor draws approximately six times its full load current; this current remains high until the motor reaches about 80% of speed. This high inrush current causes a dip in generator voltage. The electric power initially required by the motor (with the motor at standstill) is about 150% of rated power. The power required by the motor peaks at about 300% of rated power and 80% of speed with full voltage applied. But, the generator set supplies less than 300% power because starting voltage is lower than full voltage during acceleration, and because the generator set's rotating inertia transfers energy to the motor."

So you're wrong, 3x is all we need. It's an accepted standard. I employ it here and I'm off the grid running inverters and calculating using 3x for years. I haven't blown a fuse or stalled a motor. So if you think that you need 100x overhead than build it into your system, I don't give a fiddle. But tell me how long you've been running off the grid?

Geeze, how many links do I have to post showing this?

You want to be argumentative, find someone else, this is getting silly, the question is how much overhead do we need to start motors.

3 times! How many more links do you need to see?

Well, Im less confused about where youre wrong than you are. You seem to lack appropriate attention span on pertinent parameters. This is going nowhere.
larry

 

[tommu56]

Mine is a off grid cabin.
Outback invertor and charge controller and mate here and a grundfos sqflex pump all running on 600watts of panels keyocera and 8 trojan L16h's in a series / parallel at 12 volts and Bogart meter.

I hooked the generator to the invertor last month first time in 8 years because were up there for 2 weeks and not much sun.

 

[tommu56]

go to back woods solar
Backwoods Solar Electric Systems

i dont have the paper work handy but by memory it was a P-SQFlex 6 SQF-3 Pump

with a P-CU200 Interface about $2500 for pump and control

One word of warning the safety rope rings aren't strong enough to lift pump and pipe full of water.
I ended up putting a SS nipple and tee and plug on top of pump and putting a 1/2 poly rope tied to the tee.

 

[Rob-D]

Well, Im less confused about where youre wrong than you are. You seem to lack appropriate attention span on pertinent parameters. This is going nowhere.
larry

Great, denigrating the conversation to insults. Why don't people realize that ad hominem attacks just reflect on their own character?

As for my attention span, I'm bored, to busy to look back and the issue is a moot subject to me after link after link showing that 3 times overhead is the accepted standard.