Coupler Design  

Why a coupler versus belts ?

Before you go off and buy the coupler to mate your engine and generator together read this!

This page will be maintained in the usual 'random' manner you've grown to expect from me, I'll keep adding to the bottom of the page as we learn from personal experience.

Do you ever grow tired of paying taxes? In the State of Washington, we're at 9% and people don't seem to mind at all.

If you look at Vee Belts as a means of moving energy from one place to another, you'll be taxed. Some of us don't care. People who run gen sets more often, should care.

My friend Phil P.  Built a Diesel generator driving an ST head He took the time to set up a proper pulley and Vee belt drive system with engine at full rated output of 2000 RPM, and then load tested the generator. Next he took our Direct Drive coupler and drove the gen head directly at a reduced speed of 1800 RPMs to provide the 60hz frequency (200 RPMs lower).  Phil was able to carry the same load with reduced speed. Some of the added benefits will be engine longevity, Potentially less fuel used, no slipping belts, no belt replacement, no tensioners, no need to build or provide adjusters for belt tension etc.  Small diesels like the 175 thru the 1115, do well with the direct drive. Bigger engines may require bigger drive couplers. MJ McCarroll has a 195 driving a 7.5kW head he uses for driving a digitally controlled welder. This unit runs up to 14 hours a day on the job site, and MJ has yet to replace the rubber spider. This is because he took the time to properly align the drive, it's easy to do but some people don't take the time.

When you buy a gallon of generator fuel, consider that you are being taxed around 6% if you are using a VEE BELT DRIVE, that's approximately how much energy it'll rob as it transfers the energy to the gen head.

What you need to understand is lower rpm does mean less power. I have seen Chinese singles that are rated at higher RPM to get the higher HP figures. If you have a 2200 RPM engine, and you decide to direct drive at 1800 RPM, you will have less power, and you will NOT produce the same power period! A typical 1115 rated at 2200rpms running at 1800 RPMs might carry 8KW continuous, I have not load tested a broken in gen set of this class, so don't quote me. The point is, you won't get 12KW continuous period. If you try, you will push the engine till combustion is incomplete, you'll carbon up things and eventually have troubles, when you see black smoke, you must cut the load back a little till it clears up, this is what you should consider your max load. remember that elevation works against you, your air charge will be less dense, and you will make less power. Air temp and other factors like fuel quality, water content also affect power. In the case of this the 1115, if I wasn't able to produce expected power without producing smoke, I would suspect a dirty injector, and a poor spray pattern. High water content, junk fuel filter, dirty fuel, running the gen set smoking black for long periods of time are all things that will catch up with you, and if you're naturally prone to be a 'victim' you can blame the machine.

 Thanks to Mechanical Engineer Paul A. Bock of Buffalo, NY, and input from fellow DIYers, I am beginning to understand the dynamics of Coupler design.

What's amazing is I was first attracted to engines that seem to require less of a coupler due to their massive flywheels, and the actual learning came to play when DIYers wrote about their personal experience with couplers.

Engines are different, so are generator heads. If you look at the engines I've found interesting, you'll note they all have massive flywheels. This is most helpful in one or two cylinder engines where the power strokes are far spaced and you're trying to run a more constant speed through each revolution.  the other thing I like is massive generator heads, this does factor into the selection of the coupler and does cause one to pay more attention to the design than lighter more compact generator heads.   In a perfect world, you'd want lots of mass in the flywheel, and little or no mass in the head, this would leave the coupler with little or no challenge, but no one has invented the low mass no mass, 4 pole rotor yet.

Some of us DIYers are running into trouble when we try to mate up small 3 or 4 cylinder diesels with a gen head that has high mass. Some of these engines are light in the flywheel, (maybe the worst are French Diesels)...of course this is entirely another subject.... 

When the power stroke comes in, it can hammer an undersized coupler. Take the Love Joy 150, it's good for up to forty horsepower, but one of us found that the stock rubber spider will get hammered to pieces in minutes if there is insufficient flywheel mass, or a severe alignment problem. It stands to reason that the salient pole rotor is not going to appreciate this hammering either, so if one moves to a higher density spider in the coupler, you transfer even more beating along to the generator rotor. There are people who call me and tell me the harder spiders hold up better, that may be true, but the whole idea is to mitigate the the potential for hammering at idle, and slow speeds, and protect the rotor in the generator. Properly aligned couplers won't need a harder spider according to the reports I get from the field.

With the basics understood, you can see that the more mass you put on the gen side of the coupler, the more work the coupler has to do. If we mate up an all to big gen head with a smaller engine, there is little return on the invested dollars for the larger head if we go overboard, and we work the coupler harder than it needs to work.

If you think this is just a coupler problem, think about the pour VEE belt, as the power stroke comes in, it forces the belt deeper into the vee, as the compression stroke comes along, it goes slack, and this action creates a pile of VEE belt dust! The slower the RPM of the engine, the worse the problem can be.

(IMHO) Use a VEE Belt only when there is nothing else available. 

For larger engines Like 4 cylinder Perkins, There are turn key solutions, (more expensive couplers) that are designed to take the beating and soak up the punishment,  but they start at around $400 dollars for an off the shelf solution. Look at the LOVEJOY site, they have engineers that can help select a coupling for you.

Until we get more info on this page, know that the stress on the coupler will be greatest at low speeds, like starting and stopping the engine. Also note there are couplers that have some 'give' that helps with this problem, but as you'd expect they are more money. What you need to visualize is the low speed hammering that can occur at near idle speeds. Picture the power stroke of a diesel and the more violent power stroke versus the gas engine. You can hook an O scope to the generator output and see how uneven the rotational speeds are per revolution at low speeds.

At this point, it should become apparent that slow speed engines have high mass flywheels to even out the speed and make them useful. Higher speed engines, and engines with more cylinders are going to be easier to work with if they have adequate flywheel mass.

Let's take an example where a person is bound to get into trouble. You have a Peugeot diesel out of an automobile  that was fitted with an automatic transmission.  You take this engine and try and couple a generator head up to the flex plate and drive a high mass generator head. At idle, you'll be giving the coupler a severe pounding. 

Added note 7/2003

Another item that is important to mention, some folks are racking up a good number of hours on the standard (inexpensive) Love Joy "L" style couplers with zero problems. Others complain that the rubber spiders eventually wear out and periodically need to be replaced. I've talked to the folks who have no problems and found that they took care in the alignment. If one thinks about rolling clay into a ball in your hands, you'll note that this action is very similar to miss aligned shafts. Alignment problems are bound to eat spiders, and work couplers. It becomes obvious that one needs to spend a moment to align it properly. 

Stay tuned for the DIY solutions. . for the time.. let's all appreciate massive flywheels and know why they made them.

We have three DIYers who visit here that are building VW Diesels, and other small power plants, they all have slightly different design approaches, and will be sharing what worked, and what didn't in the way of direct drive couplings.

A this time, I've found the L150 (rated at 40 HP) to handle the 1115 and 195 just fine. there is a larger L170 that some DIYers are looking at to make an inexpensive coupler for the little 4 cylinder diesels.

Remember... if you have a higher speed diesel and you want all the power out of it, consider a good belt drive system. If you want longevity, reduce the rpm, expect less power, and enjoy the extended life and higher efficiency of a direct drive.  

More to follow.

George B.