PTO generator

[JoelT]

Around here this is no longer possible since they addition of 5% biodiesel, so if you need long term storage diesel I have heard that you can possibly get straight diesel for standby generators. They are now recomending a 30-60 day turnover of the diesel fuel stock.

David Kb7uns

Whos got that 5% biodiesel added here in Oregon? I have Wilcox&Flegal's diesel delivered and it supposedly doesn't have that 5% mix, so should be good for at least a year or more.

 

[DarkBlack]

Can this start a motor under load with less source amperage??

Yup. Both methods can slow the progression to full speed, and as a result reduce the power demand at any time interval during that startup time period...even under load.

 

[SPYDERLK]

Yup. Both methods can slow the progression to full speed, and as a result reduce the power demand at any time interval during that startup time period...even under load.

That just doesnt compute. Where does the torque to run the load come from with reduced power being supplied to the motor ... :lightbulb: I guess, for the VFD, more efficiency by feeding it at an only slightly higher than synchronous frequency as it accelerates?
larry

 

[DarkBlack]

Think of it this way: You can allow the motor twice the time to accelerate to full speed.
Beacuse you have a slower acceleration, you need less torque.

Here's a non electrical genealized example:
Truck 0-60mph in 10 sec. 200HP required
Truck 0-60mph in 20 sec. 100HP required

 

[SPYDERLK]

That is accelerating against only inertia. Not a good analogy since required torque is reduced for slower accel. Actual loads often require almost the same torque regardless of speed. For instance - lifting a weight.
larry

 

[dex3361]

VFD use on motors works very well. When starting the amps ramp up instead of surging when driving centrifugal pumps. If you were starting a load that needed more torque then the VFD would need to be configured differently to allow for the torque needed o start the load. We have some single phase services that power 60 HP 3 phase motors. If you are going to use a VFD to drive a 3 phase motor on a single phase service then the VFD has to be oversized. Its best to check with the manufacturer on what the recomended size to use.

 

[DarkBlack]

That is accelerating against only inertia. Not a good analogy since required torque is reduced for slower accel. Actual loads often require almost the same torque regardless of speed. For instance - lifting a weight.
larry

Sorry you didn't like my simplified analogy. I could explain it from an electrical-physics point of view, but if you don't get it from my simplified mechanical example, you will only get more confused. I think all can say useful at this point is, trust me. Both methods are used in industry everywhere-everyday. It's a proven method.

 

[SPYDERLK]

Sorry you didn't like my simplified analogy. I could explain it from an electrical-physics point of view, but if you don't get it from my simplified mechanical example, you will only get more confused. I think all can say useful at this point is, trust me. Both methods are used in industry everywhere-everyday. It's a proven method.

Please explain it from an electrical-physics point of view. The reason the simplified analogy didnt work is it doesnt pass muster on the Physics side by differentiating between driving a load, and encountering a load due to acceleration.
larry

 

[fred239]

Fred, My point was that a $400 VFD, or $100-$200 on Y start, Delta run (if you have the right motor), will be way cheaper than the oversized generator needed to start it the way it is. Not only in initial cost but in fuel savings.

Thanks for all the great advice. All of you guys have been very helpfull in getting me educated. Now I just have to do some shopping.

 

[David_Kb7uns]

Whos got that 5% biodiesel added here in Oregon? I have Wilcox&Flegal's diesel delivered and it supposedly doesn't have that 5% mix, so should be good for at least a year or more.

From state website

In compliance with Oregon's Renewable Fuel Standard [Ref. Oregon Revised Stature (ORS) 646.921 and ORS 646.922] All diesel fuel sold or offered for sale in Oregon must contain a minimum of 5 percent by volume biodiesel, creating a B5 biodiesel blend, except for 1) railroad locomotives, 2) marine engines and 3) home heating applications.


David Kb7uns