Parallel two Generators?

Anyone here ever parallel two older style portable 5000 watt generators?

I'm not even sure if it can be done as I've never tried it.

I should be able to wire a light bulb between the two to indicate phasing and flip a switch when the bulb goes off, but then I got to thinking that the older style generators, like the Coleman 6500 watt unit I have that runs with a Tecumseh engine, only has a single screw to adjust engine speed. Adjusting the governor screw affects both voltage and frequency.

I wonder if using two identical generator models, or close to it, could be made to work. Anyone ever try it?

Hey, its winter here in Michigan, I'm bored and need something to do.

I have done this in the past with two hondas, 3500 and 3000 watt units. pretty much for the same reason as you

Sounds like this post should be in the "Up in Smoke" section of the forum. Many inverter type generators support parallel operation but it requires a sync cable.
The only way I can think of to successfully parallel 2 older, conventional generators together would be to tie the crank shafts together at precisely the correct orientation so at least the frequency would be the same. Probably still wouldn't work unless each of the generators had identical voltage regulation circuits.

brucenolan said:

I have done this in the past with two hondas, 3500 and 3000 watt units. pretty much for the same reason as you

Click to expand...

Anything special? How'd you do it? Patch cables don't count, that's cheating.

I'm with @BentleyJ

I don't see how this will work. There is no way for their sine waves to synchronize since they're based on the rotation of the engine. They need to be at the exact same speed and commutator position.

Many of the new inverter generator models have data cables that allow you to parallel them. This works because you're paralleling two inverters instead of mechanical generators.

I suppose if you had two generators providing input into a black box, you then apply your genius to make your own inverter generator output from that black box, I'm sure it's possible.

Here you go guys:

MurphyGuy said:

Anyone here ever parallel two older style portable 5000 watt generators?

I'm not even sure if it can be done as I've never tried it.

I should be able to wire a light bulb between the two to indicate phasing and flip a switch when the bulb goes off, but then I got to thinking that the older style generators, like the Coleman 6500 watt unit I have that runs with a Tecumseh engine, only has a single screw to adjust engine speed. Adjusting the governor screw affects both voltage and frequency.

I wonder if using two identical generator models, or close to it, could be made to work. Anyone ever try it?

Hey, its winter here in Michigan, I'm bored and need something to do.

Click to expand...

This is an area in which I have some experience. To successfully and safely synchronise two generator sets require CONTINUOUS control over the generator phase angle. I doubt that can be achieved with low cost gasoline engine driven engines as you would probably require electronic engine speed control rather than simple flywheel driven engine governors as well as good quality regulators in the alternator.
Most importantly the generators must remain synchronised in all load conditions. Unless you can guarantee that you may damage the alternators and possibly even the engines.
A "makeshift" control system is unlikely to work for a long time.

BentleyJ said:

Many inverter type generators support parallel operation but it requires a sync cable.

Click to expand...

Hardly any of them use a sync cable. Honda, Yamaha, and Harbor Freight are among those that don't. The second generator to start up senses the phase of the first on it's AC output and syncs with it. Sometime in the past I know Champion and Kipor used sync cables but it looks like the current models don't. Perhaps the Honda/Yamaha patents for syncing have expired or been licensed.

I have one parallelable generator and 2 other generators and several inverters. I have yet to do any experimentation with the parallel stuff, but im definitey tempted to parallel it to not only a non-inverter generator, but a non-generator inverter at some point. I’ll do more research first. ?

According to a Honda patent that I read, their inverter generators have a very narrow range for the AC frequency and its stability. I doubt that their inverter generators would be able to parallel with any small non-inverter generator.

Yes.

Once phased using the light bulb trick and adjustable resistor, if one generator slows down, it gets motored by the other and they stay in phase.

FYI, think about several large dam turbines, gas turbines, nuke turbines etc all on the same grid. There is nothing sophisticated keeping them phased.

mantonis said:

This is an area in which I have some experience. To successfully and safely synchronise two generator sets require CONTINUOUS control over the generator phase angle. I doubt that can be achieved with low cost gasoline engine driven engines as you would probably require electronic engine speed control rather than simple flywheel driven engine governors as well as good quality regulators in the alternator.
Most importantly the generators must remain synchronised in all load conditions. Unless you can guarantee that you may damage the alternators and possibly even the engines.
A "makeshift" control system is unlikely to work for a long time.

Click to expand...

No, a generator is also a motor.

When was the last time you saw an a/c motor get out of phase with its incoming power?

Checkthisout said:

No, a generator is also a motor.

When was the last time you saw an a/c motor get out of phase with its incoming power?

Click to expand...

If you motor an alternator without an engine being coupled to it that would probably cause no problems. However in a genset you would then also "motor" the engine and that could potentially spell a lot of trouble as the alternator is directly connected to the engine flywheel. The alternator shaft/bearing would then be subjected to massively loads which could be out of balance.
In my experience it is never advisable to allow a genset to be motored by another genset or worse still by the utility.

Checkthisout said:

When was the last time you saw an a/c motor get out of phase with its incoming power?

Click to expand...

When was the last time you saw an AC motor get in phase with its incoming power?

"The value of slip in induction motor is can never be zero."



(answer: When the power was off)

MurphyGuy said:

Anything special? How'd you do it? Patch cables don't count, that's cheating.

Click to expand...

I did it just as you described. I built a switch between the two generators and put 240 volt incandescent light across the switch, adjusted speed till phase matched and closed the switch. then feed the load. the two generators ran fine

mantonis said:

If you motor an alternator without an engine being coupled to it that would probably cause no problems. However in a genset you would then also "motor" the engine and that could potentially spell a lot of trouble as the alternator is directly connected to the engine flywheel. The alternator shaft/bearing would then be subjected to massively loads which could be out of balance.
In my experience it is never advisable to allow a genset to be motored by another genset or worse still by the utility.

Click to expand...

Only if the engine quits does it become an issue. At that point you have what amounts to a locked rotor.

The breaker on the other generator will simply trip.

Think about it.

The motoring occurs on a phase level or 60 times a second. If one gen starts to get out of phase, it's load decreases and it speeds up whereas the other generators load increases and it slows down. This correction occurs 60 times a second.

Hedges said:

When was the last time you saw an AC motor get in phase with its incoming power?

"The value of slip in induction motor is can never be zero."

What is Slip in Induction Motor? - Electrical Concepts

Slip in Induction Motor is the relative speed between the rotating magnetic flux and rotor expressed in terms of per unit synchronous speed. It is a dimensionless quantity. The value of slip in induction motor is can never be zero.

electricalbaba.com

Induction motor - Wikipedia

en.wikipedia.org

(answer: When the power was off)

Click to expand...

Certainly you see my point.

Checkthisout said:

Only if the engine quits does it become an issue. At that point you have what amounts to a locked rotor.

The breaker on the other generator will simply trip.

Think about it.

The motoring occurs on a phase level or 60 times a second. If one gen starts to get out of phase, it's load decreases and it speeds up whereas the other generators load increases and it slows down. This correction occurs 60 times a second.

Click to expand...

Having been in this business I am aware of serious damage to out of synch synchronised gensets.
By the way when an engine is seriously overloaded it will "conk out". That will then overload the second engine. End result NO power.
Synching gensets in varying load conditions requires the following:
1. Close engine speed control
2. A good quality alternator AVR
3. Close synch control
Maybe things are a lot easier with a static load eg one single compressor.
Just my thoughts, maybe I am just too conservative as I did this for a living.

mantonis said:

Having been in this business I am aware of serious damage to out of synch synchronised gensets.
By the way when an engine is seriously overloaded it will "conk out". That will then overload the second engine. End result NO power.
Synching gensets in varying load conditions requires the following:
1. Close engine speed control
2. A good quality alternator AVR
3. Close synch control
Maybe things are a lot easier with a static load eg one single compressor.
Just my thoughts, maybe I am just too conservative as I did this for a living.

Click to expand...

Did you ever try it? I mean this is the "danger zone".

mantonis said:

Having been in this business I am aware of serious damage to out of synch synchronised gensets.
By the way when an engine is seriously overloaded it will "conk out". That will then overload the second engine. End result NO power.
Synching gensets in varying load conditions requires the following:
1. Close engine speed control
2. A good quality alternator AVR
3. Close synch control
Maybe things are a lot easier with a static load eg one single compressor.
Just my thoughts, maybe I am just too conservative as I did this for a living.

Click to expand...

As someone who has worked with industrial processing equipment all my adult life, I think I understand your point of view.

That said, there is frequently a difference between large commercial (professional level) systems and small residential stuff. Sometimes you can fudge with the smaller stuff and it works fine, whereas trying the same trick with the more professional equipment can result in tens of thousands of dollars in damaged equipment.

In commercial installations your technology needs to be "fool" proof as operators may have varying skill levels.
In my early days manual synchronising with lamps was not uncommon but once automatic synchronising panels became available as well as affordable things changed.
In addition at that time (>25 years ago) engine speed control was usually mechanical, not precise and slow to react and alternator AVR's were not particularly sophisticated.

By the way it is often NOT the engine that is not able to cope with starting a compressor motor as there is usually quite a lot inertia in a diesel engine with heavy flywheel. It is often the alternator!. We therefore usually overspec'd the alternator to cope with starting large (DOL) motors. That is obviously only an option with new build gensets!

As always, if it works reliably and safely you have a good solution!

mantonis said:

If you motor an alternator without an engine being coupled to it that would probably cause no problems.

Click to expand...

Absolutely correct, in the utility industry it’s called a synchronous condenser, a clutch between the engine and generator.

Comparing synchronizing large multi cylinder industrial diesels fitted with three phase alternators, to a a pair of crappy wobbly single cylinder, single phase gasoline generators is a whole different world.

Are you feeling lucky ?

Warpspeed said:

Comparing synchronizing large multi cylinder industrial diesels fitted with three phase alternators, to a a pair of crappy wobbly single cylinder, single phase gasoline generators is a whole different world.

Are you feeling lucky ?

Click to expand...

What's the difference?

How did they do it in 1935?

Quite a few actually.
Three phases sync together much better than a single phase (more torque per degree of phase difference).
Also the slightest change in load or throttle makes a small gas generator fluctuate mightily in both rpm and voltage.
The big diesels have big flywheels and can be much more accurately speed controlled when trying to reach precise synchronization.

Until you have actually had experience doing this yourself, its probably difficult to know what its like.

Physics has not changed since 1935, only the technology.

Three phases were (and still sometimes are) synchronized with three simple light bulbs . These vary in brightness and appear to rotate in either direction if the rpm is either high or low, and become stationary when the frequencies are matched. Phase is correct when the top bulb is off, and the two lower bulbs are at half brightness.
Later technology uses a synchroscope, which is like a rotating compass needle that spins either way if the frequencies are not matched. Correct frequency and phase is with a stationary needle pointing due north. Later technology still, uses computer control which essentially does the exact same thing automatically.

Doing it single phase is a lot more tricky because it cannot be done so easily with simple equipment. Difficult to tell if you are fast or slow if one generator is at 59.5Hz and the other at 60.1Hz You can hear the beat, but which one is faster ??
Getting them at both the same frequency and perfectly phase matched is really hard if you don't know which way the error is or which way to adjust to reduce it.

With three phases, you know EXACTLY how far and by how much you need to tweak, and with a bit of familiarity with the equipment its dead easy and reasonably quick.