Revisiting the PTO-generator question

[WVBill]

Bob:
Sorry, I think it was I who wasn't clear. You have the concept of the transfer switch exactly right. It's very simple.

My drawn out explanation of the consequences of not doing it right was more to explain why your electrician, your electrical inspector, the power company and your liability insurer will not want you build your own transfer switch.

 

[Trev]

Okay, thanks for all the replies..

Our electrician is coming out (he said he'd make it sometime this week) and look at the generator and figure out a plan for us.

Thanks for the electrical education I just got here! At least now I think I know the basic issues .. and our electrician will have less trouble getting the ideas through my moderately dense head (see head at left /w3tcompact/icons/laugh.gif).

With a 200 amp service, which includes an underground run out to a 100 amp box in the garage, I know I need an expert to do this.

Thanks again, all of you, and I'll let you know what we end up doing.

Happy Holidays,
Bob

 

[n6ckv]

Having just run my generator for 10 hours, I had a question about using a PTO generator. In most generators the RPM of the generator determines the frequence of the AC output (60 Hz). On generators there is a throttle control to keep the RPM at the proper speed and it adjusts based on the load. How does the work for a PTO generator? As more load is added the RPM will go down, lowering the frequency, and maybe the voltage, for some motors this could be a problem.


carl

 

[hazmat]

Carl,

A Diesel engine has a governor, (edit here in addition to a throttle), so it is self regulating. Once you set the rpm it will add fuel as necessary to try to maintain that rpm (untill it runs out of power)

<A target="_blank" HREF=http://www.age.uiuc.edu/oree/pdf/R94-01.PDF>U Illinios Diesel simulator abstract (pdf)</A>

Edit here:

A better link

<A target="_blank" HREF=http://www.tpub.com/engine3/en32-83.htm>tpub diesel governor</A>

 

[em14]

Hazmat,
Most diesels that I have ever worked with have both a throttle and a governor where the throttle is used to select the engine rpm (speed) and the governor maintains the engine rpm (speed). Of course there could be many ways to reach the desired RPM Setting then turn the maintaining of that setting as the load on the engine changes due to load etc. Not trying to be pickie ...
Leo
Leo

 

[Anonymous Poster]

The primary frequency/speed regulation that compensates for load changes on a PTO genberator is the momentum and flywheel effect built up by the rotating mass of the generator itself.
While a gas or propane genset responds rapidly to load changes, a larger generator, such as a PTO unit generally handles these changes thru momentum, as does a larger generator, so rapid engine speed response isn't needed.

 

[n6ckv]

I understand the governor answer - worked with a lot of diesel gensets when I did mobile comm for the Air Force, but my Kubota does not have one. The flywheel effect seems to be the way to go. I was staying away from PTO generators because I was worried about the frequency stability. Maybe I should look again. Thanks for the answers


carl

 

[hazmat]

Leo,

Thanks for the clarification/w3tcompact/icons/blush.gif, I always considered a throttle to refer to air/fuel mixture, (as in a gas engine) a diesel throttle only controls the fuel.

From Dictionary.com

Throttle
1. A valve that regulates the flow of a fluid, such as the valve in an internal-combustion engine that controls the amount of vaporized fuel entering the cylinders.

2. A lever or pedal controlling such a valve.

 

[Trev]

Hi Franz,

<font color=blue>2) Manual Transferr Switch- This is basicly a 100 amp 3 pole double throw switch, much like a disconnect switch. It is installed between the meter and the breaker pannel. When the power fails, you start your genset, and then throw the switch from power Co (up) to Genset (down), and the breakers have power.
Wholesale for a 100 amp transferr switch is about $500.oo.</font color=blue>

On re-reading your reply today, now that I have more time, I just realized that you seem here to be describing exactly what it is I want.. what I was struggling to explain! All I missed was that it has to go after the meter and before the main box.

With a 200 amp service, I presume it will be a bit more expensive.. but this sounds like the way I'd like to go.

Again, I'll run it by our electrician and see what he can do.. and again, thanks very much for sharing your knowledge!

Best regards,
Bob

 

[Spencer]

Trev, I have attached an image of the manual transfer switch that you have been trying to describe. This switch is a double pole, double throw (I think). The only problem that I have with this kind of switch is that it does not switch the neutral. I am sure that this kind of switch would meet code and pass inspection but I worry about the neutal (white wire in the image) not being switched. Luckily I have a buddy who worked for Square D so I got a 400 amp triple pole, double throw switch from him. The triple pole will allow me to switch the neutral as well. I only asked for a 200 amp switch but a 400 amp is what I ended up with. I only have a 7500 watt rated, 10000 watt surge portable generator so a 100 watt or even 60 watt switch would have been enough. I wanted at least a 200 watt in case I upgraded generators in the future. I knew we were moving from our last house so I did not bother to hook it up there. I've been in our new house for a little over a year but still have not hooked it up here yet.

You can get a , <A target="_blank" HREF=http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=42162>100 amp, or <A target="_blank" HREF=http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=42163>200 amp</A> Cutler Hammer double pole, double throw transfer switch from Harbor Freight for 179.99, 199.99, or 299.99 respectively. You would want to get the largest one you could but I put the other links in there for everybody else. The link to the 60 amp switch is the only one that shows a picture of the switch.