Generating Power With a Cub

[George Willer]

Rudi,

The engine is producing its rated horsepower only if it's turning at the rated RPM (stamped on the serial plate). Running at 1/2 RPM will only produce 1/2 rated power. That's basic physics.

Kinda reminds me of the chicken farmer who was economizing by gradually substituting sawdust for the grain. He was nearly successful except the chickens all died.

[dirt devil]

Rudi

That is my thinking, it is all in the puleys.

Example (experts correct me if I am wrong)

Take a 9" pulley on the right angle drive with a 3" pulley on the head.

9/3 = 3 so you would take the input rpm of 1200 at the RA PTO to an output of 3600 (3x1200) at the Gen head pulley.

Since the driven pulley (gen head) is 3 times smaller then the driver pulley (RA PTO) the output of the driven pulley's (gen head) rpms will increase 3 times.

If one has access to bigger driver pulleys then you can turn the rpm's down a bit on the tractor and keep the driven rpm's the same.

If I have misrepresented something here please (experts) correct me.

Dave

[kinelbor]

Thats true Dave, but as George said if you decrease the speed of the engine, even if the pulleys are changed, then it wont put out the same amount of power. I think where this would work is if you only needed to run your water pump, freezer, and maybe a few light bulbs, say 2500 watts Max. You could idle the tractor down and change the pulleys to still get that 3600RPM and you could save some fuel by running the tractor slower.

[dirt devil]

Nik

That is very true, I was not taking that into consideration when I was thinking about this, just that I could get the rpms and keep the engine rpms down.

I have been needing a welder/generator so that is probabley the best route for me. Man I hate needing more pennies then I have.

Dave

[George Willer]

Rudi

That is my thinking, it is all in the puleys.

Example (experts correct me if I am wrong)

Take a 9" pulley on the right angle drive with a 3" pulley on the head.

9/3 = 3 so you would take the input rpm of 1200 at the RA PTO to an output of 3600 (3x1200) at the Gen head pulley.

Since the driven pulley (gen head) is 3 times smaller then the driver pulley (RA PTO) the output of the driven pulley's (gen head) rpms will increase 3 times.

If one has access to bigger driver pulleys then you can turn the rpm's down a bit on the tractor and keep the driven rpm's the same.

If I have misrepresented something here please (experts) correct me.

Dave

Your idea would work if you had unlimited power, but we're talking Cub here. You can indeed reduce the engine RPM by increasing pulley size, but you have to also increase torque at the same time. Reducing engine speed will definitely reduce horsepower... reducing the total peak output of the generator.

You'll know when you reach that point because the engine won't be able to maintain speed.

An earlier post asked if a Cub could power a 7200 W generator. Without any allowance for losses (not possible) in efficiency the Cub running full bore at rated RPM could theoretically produce 7.3 KW.

http://www.onlineconversion.com/power.htm

[Dan Robertson]

George is correct in that you need to have the C60 engine rpms running up near it's HP / torgue power band for efficency, power, and good governor response. I choose a 4" pulley on the alternator, and when running the V-belt around the 9" flat pulley in reality makes this something like a 9 1/2" pulley as the bottom of the V-belt travels around this 9" dim. The thickness of the v-belt will efect this dim. This allows the engine to run in the 1600 rpm range while turning the alternator head at the desired speed.

[Rudi]

George:

That is what I love about your answers.. you make me think and dig deeper. Seeing as this is a worthwhile project anyone who lives in areas where power outages are a probability vice possibility.. it is a great topic to understand enough to build and operate one. I just want to be able to understand it.....

Or we could go and buy something like this:
Pad Mounted Generator. Unfortunately these are not as much fun to work with and cost way too much for my budget....


Also, we have to be talking chickens+chickens here and not chickens+turkeys, and I guess I wasn't explaining myself clearly.... cause I am still a little foggy here... I am assuming that 1/3 throttle would produce about 900 RPM to 1,000 RPM -- or am I wrong on that assumption I also assume and yes I know what assume means.. , that 1/3 throttle would be about right for a nice leisurely idle... Eliie at the 1st detent on the throttle quadrant idles at about 475 RPM.. so 1/3 throttle would be about 900 RPM therabouts yes

If that is correct.. what pulley size would you need to generate sufficient RPMs on the Generator Head to provide 5 KW of power would be the question Remember, we were talking about a NorthStar 5500 or 5.5 KW Generator Head



So assuming that this particular Generator Head which is the one in the original How To... requires 3450 or 3750 RPM's on an 11 HP (now this is a Peak Developed No Load Type 2 stroke engine).

Am I correct in assuming as Dave posted, that if Ellie's PTO is turning at 1,000 rpm, then I would need a 9 inch pulley on Ellie and a 3" pulley on the Generator Head - a 3 to 1 ratio ? And if I actually were to increase her throttle so that the engine/pto turned at 1200 rpm then that would generate what.. 3,600 RPM thereabouts which what is stated as required. Is this math right?

A second question then pops to mind. If we are saying that a C-60 only develops 9.3 HP at the drawbar and we need 11 HP from a PDNL style engine.. how does that relate? How can it be compared?

If I were to hook up a C-60 as a backup generator.. sitting on pads.. I would assume that the C-60 has a heck of a lot more torque to overcome the inertia/draw/drag.. whatever you want to call it, than any of the modern conventional 2 stroke engines whose HP rating is questionable at best.

[George Willer]

Rudi,

Your math looks right to me. It's your assumption about the power of the engine that I differ with.

Using the figure you quoted, 9.3 for the rated horsepower of the engine then the RPM of 1200/1800 x 9.3 = 6.2 HP output. Then converting that 6.2 HP to KW = 4.62, assuming no losses. Now, depending on your needs, I'd say that engine/generator combination could be expected to be reliable at maybe 3.5 KW or less. It could lead to trouble at near that load if it were required to start an inductive load.

The bottom line... the setup can be very useful for a standby unit if used sparingly. Probably in the same general league as my 4 KW Onan.

[Rudi]

George:

Em is calling so you KNOW I gotta run... but..

1. I do not understand the relationship between 9.3 hp at the drawbar (Nebraska test data ) and the 11hp of Peak Developed No Load HP (manufacturer's disclaimer) on 2 cycles.... to me that is apples and pumpkins.. not even on the same tree. That has me confused.

2. A 60 cubic inch engine must, in my mind, be able to develop much more power, using less fuel, less wear on the engine and more rpm+torque=useable power than a what 11 hp.. whatever cc that works out to be.

My JD111 has a 20hp engine and compared to Ellie, it is a hunk of junk when comparing amount of work it can accomplish.

What I do not get.. and maybe I am thick.. which is why I am asking I guess, is how come a C-60 will have to run at near peak rpm/full throttle to develop the rpms needed to power the generator. It is the 2 cycle PNLDHP versus C-60 cubic inch question that has me befuddled...

[moe1942]

The rule of thumb is 2 HP for each KW generated. I agree with George. The engine should be run in the max torque band and pulley size adjusted accordingly. Adjustable sheave pulleys are used for fine tuning.

I have a 5KW gen head that I plan on using. Have to reseal my Hyd pump before doing anything..

[cowboy]

Boy started writing this then had to re think it

I was going to say the cub engine is better than a single cylinder. As you get a power stroke every 1/2 turn of the crankshaft. Where you only get one power stroke every two turns on a 1 cylinder four stroke. And the cub engine can react faster to load chages becuse of it.

But since actually since the cub running at 1800 rpm compared to the 3600 rpm of the one cylinder would equal out to one PS per two of the cub rather than one per four as I was first thinking.

Also since their is more rotating mass in the cub engine it will smooth out load spikes better than a 1 cylinder engine. Such as when a well pump starts.

Billy

[beaconlight]

What you say about mass is true. You are only considering the slowing down. The added mass makes for a slower recovery to speed.
Those big ole White Superiors we used in the Aleutians for the Dew Line Extension used a saturable reactor, where the load caused you to add throttle as the load increased and before the engine started to slow. Conversely if the load dropped it cut back on throttle before you over speeded. We fine tuned to keep with in less than 1 second a day by WWRL and the crystal controlled clock in the Radar. If the AC clocks got off the Radar guys had 1 on us. We didn't take well to that. No one wants to be the goat.

Bill

[Matt Kirsch]

What I do not get.. and maybe I am thick.. which is why I am asking I guess, is how come a C-60 will have to run at near peak rpm/full throttle to develop the rpms needed to power the generator. It is the 2 cycle PNLDHP versus C-60 cubic inch question that has me befuddled...

Rudi,

Even though a Cub can out-lug a B&S engine, it's still producing less horsepower at the lower RPMs. Horsepower is torque multiplied by RPM, and Cubs have lots of torque at low RPMs, while B&S engines have lots of RPMs and low torque.

Watts and Horsepower are different ways of measuring the same thing. They rate tractors by KiloWatts in Europe. 1HP = 746 Watts.

Electrical Watts are the same as "tractor" Watts, so to get 5000 Watts of electricity to power your house, you need to have a tractor with at least 5000 Watts available at the PTO (actually more because of efficiency).

Let's assume a good strong Cub maxxes out at 10HP on the PTO. 10HP is 7460 Watts. That means the most electricity you can possibly generate with the Cub is 7460 Watts.

In reality, the system is not 100% efficient. It's probably closer to 67% efficient, so practically speaking, a Cub running wide open can generate about 5000 Watts of electricity.

[cowboy]

Hi Bill

You are right I did not think of that. My thought was most home loads have a high startup load from 1/4 to 1/2 second then the load drops to a running load which is lower than the startup load.

This is the type of generator head I like to use



It is a 1800 input rpm which is close to the rpm of a cub. Which would mean you use close to the same size pulleys for both engine and generator. Rudi with a power unit you could use a direct drive cuppling and set the engine to run at 1800 rpm.

It turns half the rpm of the 3600 gen head which means the brushes and bearings last longer. Plus the bearings are larger making it last longer too. The only problem with them is you have to pull the end covers clean the bearings and re pack them with good grease. Other than that they are great.

ebay listing for a 7.5 head

http://cgi.ebay.com/7-5-KW-ST-Generator ... dZViewItem

ebay listings for gen heads with more of this type listed

http://search.ebay.com/generator-head_W ... 3QQfromZR2


Utterpower and others also sell this type of gen. I can also find out who my brother got ours from.

Billy

[Matt Kirsch]

With all this generator talk, I'd love to be able to do a generator on a trailer like they do with the larger tractors. Trailer generators can be hooked up quickly, which

The hard part is finding a universal joint PTO shaft that both fits the Cub, and is capable of handling 1800 RPMs. Kubota has the same shaft, so there's an adapter from Cub-to-540, but I worry about spinning a 540 PTO shaft at three times its rated RPM.