Making stationary engines more efficient when loads are reduced

[sl33k3r]

I plan a workshop where I have larger 3 phase motors that need high current to start but very little, in comparison, while operating. I do not wish to operate a generator at 1 gph when the generator is at 10% load or less.

Generators can run for hours with less than proper load. The engines do not idle down or even change rpm to meet load. This not only wastes fuel but it causes wear by putting engine components under stress when the energy producing that stress is not needed in the production of enectricity. Has anyone had experience with dropping cylinders. Like hit and miss engines, exhaust valves could be opened to reduce compression and fuel lines to injectors could have electro-mechanical bypass to fuel return line.

I don't believe this type of system should allow the cylinders to be shut off during times that the engine is not at or near operating temperature. The block and head(s) should be warmed as fast as they normally would. Cylinders shut-off should be rotated to attempt even wear of the engine and to keep even heat throughout the block. I am not sure that the coolant will be enough to transfer enough heat.

I believe the fuel pumps are designed to be able to adjust injection timing, but no method for fuel quantity adjustment. Am I correct in my assumption?

I am no diesel genius, so I thought I would ask for clarity on this idea to see where I might be going if I try this type of system on my own equipment.

 

[DieselAddict]

Power output is a function of fuel quantity. The engines commonly found on these generators are not of a type that can alter timing on the fly.

To be honest these constant speed engines will last longer than variable speed. Its not unheard of for the LP engines on the MEP802 and MEP803 to last 20k hours in continuous operating conditions.

The thing we do for industrial motors to reduce starting loads is put VFDs on them. Assuming this isn't a high starting torque situation a VFD can get the motor going nicely and reduce the starting load by 80%.

If its a woodshop where the starting loads are all just spindle masses, those would be ideal candidates for VFDs.

 

[Scoobyshep]

If you are not changing the electric motor speed you are better off using a soft start vs vfd.

Sent from my SM-G973U using Tapatalk

 

[Chainbreaker]

Generators can run for hours with less than proper load. The engines do not idle down or even change rpm to meet load. This not only wastes fuel but it causes wear by putting engine components under stress when the energy producing that stress is not needed in the production of enectricity.

However, a typical generator must maintain a constant RPM to maintain a constant hertz rating. So changing RPM to meet load would affect hertz. Fuel is metered in relation to load to produce a consistent RPM to produce consistent hertz output. High electrical load = more fuel required to sustain load/RPM, while minimum electrical load naturally uses less fuel at same RPM.

Not sure how much benefit there is to be had on a constant speed engine if shutting down cylinders due to still having to maintaining moving mass & drag at a CONSTANT RPM. On the other hand, if you were to use a generator to only start when required to recharge a battery bank and shut down after recharging that is another thing.

BTW, you didn't mention what generator model are you referring to or considering. What GPH would be acceptable on avg? Members here might be able to make a recommendation if they know your desired parameters.

 

[DieselAddict]

If you are not changing the electric motor speed you are better off using a soft start vs vfd.

Sent from my SM-G973U using Tapatalk

A soft start is a viable option. I suggest looking around because you may be surprised that a VFD can be less costly than a soft start due to how ubiquitous VFDs have become.

 

[Scoobyshep]

A soft start is a viable option. I suggest looking around because you may be surprised that a VFD can be less costly than a soft start due to how ubiquitous VFDs have become.

The last time I had to look into it (approx 2 years ago) it was cheaper to soft start. But you never know you might get the deal of a lifetime. You also have to make sure the motor is rated to operate with a vfd, some of them dont work well with the carrier frequency (burnt windings is a smell hard forgotten)

Sent from my SM-G973U using Tapatalk

 

[sl33k3r]

Currently, I have a MEP-802A, Onan 6.5 Gas, Onan 4.0 gas, Honda 2k and Ryobi 2300 but know I need a larger generator to power some larger machinery.

I will have machines for working with both metal and wood. So far the motor with the highest inrush current is a 208V, 3 HP, 1735 RPM, 8.2A, code K (25.5A) thickness planer. I have a Unisaw I am to pick up this coming week that I do not know the motor specs. I havealso recently acquired a very large Cincinnati Hydro-tel mill with a 20 HP motor (specs unknown as of now). I cannot say how much action it will receive. I may just find a generator to power just this machine should I be able to renovate it.

Soft start or VFD could be the answer to keep operating a smaller, more efficient generator. I'm not familiar with soft start. It is a voltage limiter? VFD varies the frequency, right? Voltage remains the same and current is limited like DCs PWM?

I have a slight understanding of thermister current limiters. To me, limiting current to set point makes sense. Motors are supplied with proper voltage (pressure) but are limited on amps (flow) will spin up without building up heat.

I have, though, considered alternative configurations.

1. Operate two engines connected to one generator head via one-way clutches and jack shaft. Both engines operate on startup then one drops out once the motor has started.
2. Operate one engine turning a large flywheel which in turn turns the generator head. The flywheel absorbs the inrush.

engine = Farymann Diesel air cooled model 43F435 Typ 0110 Trim M5.
generator head = 3 phase, 208-460V, kw to be detemined

 

[Scoobyshep]

Currently, I have a MEP-802A, Onan 6.5 Gas, Onan 4.0 gas, Honda 2k and Ryobi 2300 but know I need a larger generator to power some larger machinery.

I will have machines for working with both metal and wood. So far the motor with the highest inrush current is a 208V, 3 HP, 1735 RPM, 8.2A, code K (25.5A) thickness planer. I have a Unisaw I am to pick up this coming week that I do not know the motor specs. I havealso recently acquired a very large Cincinnati Hydro-tel mill with a 20 HP motor (specs unknown as of now). I cannot say how much action it will receive. I may just find a generator to power just this machine should I be able to renovate it.

Soft start or VFD could be the answer to keep operating a smaller, more efficient generator. I'm not familiar with soft start. It is a voltage limiter? VFD varies the frequency, right? Voltage remains the same and current is limited like DCs PWM?

I have a slight understanding of thermister current limiters. To me, limiting current to set point makes sense. Motors are supplied with proper voltage (pressure) but are limited on amps (flow) will spin up without building up heat.

I have, though, considered alternative configurations.

1. Operate two engines connected to one generator head via one-way clutches and jack shaft. Both engines operate on startup then one drops out once the motor has started.
2. Operate one engine turning a large flywheel which in turn turns the generator head. The flywheel absorbs the inrush.

engine = Farymann Diesel air cooled model 43F435 Typ 0110 Trim M5.
generator head = 3 phase, 208-460V, kw to be detemined

A vfd (variable frequency drive) takes ac inverts it to dc than through a set of transistors created a pulse width modulated synthetic ac output at a user specified frequency. This allows motors to be started slowly and run at different speeds.

A soft start is basically a smaller dumber version of a vfd. They are made to slowly start (and stop) a motor. Difference being they are not made to run motors at a slower speed, just ramp up and ramp down. They can be smaller and cheaper because they dont have to keep running the motor when at speed (smaller transistors) because they can use a set of contacts to bypass the transistors. Some even crowbar 1 phase (one is tied to line in and the other 2 are controlled) .

Theres the quick and simple of vfd vs soft start.

Sent from my SM-G973U using Tapatalk

 

[sl33k3r]

A vfd (variable frequency drive) takes ac inverts it to dc than through a set of transistors created a pulse width modulated synthetic ac output at a user specified frequency. This allows motors to be started slowly and run at different speeds.

A soft start is basically a smaller dumber version of a vfd. They are made to slowly start (and stop) a motor. Difference being they are not made to run motors at a slower speed, just ramp up and ramp down. They can be smaller and cheaper because they dont have to keep running the motor when at speed (smaller transistors) because they can use a set of contacts to bypass the transistors. Some even crowbar 1 phase (one is tied to line in and the other 2 are controlled) .

Theres the quick and simple of vfd vs soft start.

Sent from my SM-G973U using Tapatalk

Thank you, that makes things clearer. I am a one man shop, so could I use a single VFD or soft start large enough for the largest motor in the shop until I can build/buy one for each machine. for the soft start this would not appear inconvenient because it sounds like there is no interaction between the operator and soft start. The VFD, from what I have seen, requires interaction with the operator to adjust power and speed.

 

[Scoobyshep]

Thank you, that makes things clearer. I am a one man shop, so could I use a single VFD or soft start large enough for the largest motor in the shop until I can build/buy one for each machine. for the soft start this would not appear inconvenient because it sounds like there is no interaction between the operator and soft start. The VFD, from what I have seen, requires interaction with the operator to adjust power and speed.

You're welcome,

Once they are setup its pretty much pushbutton start. To be fair the same thing can be done with a vfd, it just takes some more setup.

Sent from my SM-G973U using Tapatalk

 

[robertsears1]

Have you heard of a rotary phase converter? I made my own from a 7.5 hp three phase motor and a small pony motor to get it spinning before feeding it 240v single phase power, then it makes the third leg. I could start a Powermatic 36” bandsaw with a 7.5 hp motor. Any thing like a jointer, planer, bandsaw, shaper start fine like this. If you are looking to start a big three phase air compressor, not so much since it will be starting under load. I never got into using capacitors to balance the legs but you can. Eventually, I bought out someone with a commercially made phase converter.

Robert