OT generator question for John T

John I promised a question with a little more of a stretch than normal.

You know what happens when I get to much time on my hands sooo.

I have five different standby generators two are 5,500 watt the largest of the four. Of course I didn't plan on buying more but you know what auctions and flea markets can do to a unstable mind.

So lets say the power goes out for a month and I decide to weld, use the electric range, 5 hp (not the big box store 5 hp) air compressor.

And I'm not ever going to try this but would it be possible to hook up two or even four on the same line?

This question came to me the same day my therapist said she seen improvment.

Thanks for baby sitting me, and again thanks for your help in the past as well.

Do not hook up more than one at a time ever. With that said, the watts are amps times volts, stay within the output and all is well. Using two is only possible if a absolute disconnect is made between systems. And as always between the supply from the Power company and the service entry panel. See the info on grounding Home electrical systems (just in the last several days from John T) Putting two gensets on the same circuit will be totally out of phase and cause at very least twice voltage, and sevier damage to equipment, controlls, and the generators controlls. Do Not Do it. JimN

John T. is right, don't do it. The only way to hook two generators up is to phase them in. Basically saying it is to make sure they are in the same phase at the time the two are joined together on the same circuit or line. Even then there is only a small window (of time limit) that this can be done and has to be watched very closely when it takes place.
The generators & engines will be destroyed if not phased in properly along with any other related equipment.
Magnetism has an enormous amount of force that a person can't believe!
I've seen PTO driven generators pulled from their mounts when night properly sized for the load they had to carry.

While waiting for the smart guys to answer....

I see some of the spendier units allow you to hook 2 together, but it takes some special controls to keep them timed properly to each other. So it is possible to do it.

I suspect that would not be possible (dollar wise - anything is possible of you throw enough money down the hole...) to hook together 2 different machines together?

--->Paul

Less time to get answers than it took me to type the question. Thanks to everyone for your help.

I wish you guys could answer questions on the phone because every time I call and ask questions I never get a real answer that soon.

I will take my meds and go to bed now.

A very special thanks again everyone.

So how would you plan on getting them in phase so one doesent fight the other. Running them seperate on their own would work but not together on the same line.

I recall that while in the military we would run 2 that I believe to be 30 KW hooked together. Sometime in the middle of the night they would just for a moment they would be out of phase and the diesel engine would surge and wake me up and perhaps everything else in the jungle. Then all would go back to normal. I wes the assistant operator meaning that I only had to walk by every 12 hours and check the oil. I was not responsible for setting up the units.

Smaller inverter generators are advertised to be run in pairs. See ads on sites that cater to RV people. Small Honda for sure is used this way.

Sell the 5k units and buy a gas powered welder/ac generator.A 5hp motor needs at least a 10k generator to start.A welder can draw 12,000 watts on 240 volt lines.

As everyone else said, the generators need to run in phase, and most small generators are not set up this way.

An interesting characteristic of synchronous generators is that they are really incapable of running out of phase. If you try to couple two out-of-phase alternators, something is going to have to give. My uncle was in the Army Signal Corps in Korea; his job was running and maintaining generators. He said that one day a new guy tried to bring a second generator on-line without phasing it to the first. They immediately lost all power because BOTH generators were ripped off their mounts!

NE, Im glad a bunch of good gents alreaady weighed in (Sunday AM here) AND I TOTALLY AGREE. Maybe I can explain it a bit so you understand why they are right as rain. Hey AC IS NOT the same nor as simple as adding up two or more DC batterys in series or paralell etc, you got all that darn phase n frequesncy stuff to consider....

To begin with, all the 120 and 240 volt and 60 HZ has to do with the frequency (RPM) and timing (1 is fine but if 2 involved) of the sine wave that generator is cranking out. When you center tap a 240 volt transformer theres only 1/2 or 120 votls from either phase to the center and they are 180 out of phase with each other SOOOOOOOOOOO as all the other (probably all smarter then me, I'm long retired n rusty on this stuff remember, most of the other guys are current on this) gents point out IF YOU COUPLE UP TWO GENNYS HOW YOU GONNA GET THEM IN PHASE AND INSURE THE SAME FREQUENCY/RPM ??????? If not they are gonna fight one another as one out of phase is seen as a load versus a helping hand, to put it in layman terms.

That being said and intended as an el cheapo Home Depot or Lowes sold product I cant say if a so equipped better quality genset cant have some sort of phase control system that indeed enables two of them to be synced up????

Like I used to tell my kids years ago when I got asked all sorts of questions (dont ya love them years) DAD DONT KNOW EVERYTHING and while I'm decent on AC Secondary Power Distribution (did that for a living some years) and DC tractor electrical components, AC Generators are NOT really my cup o tea

Merry Christmas to alllllllllll

Ol John T and all

Here are two Generac 8000 watt generators - tied together on my factory-made PTO generator - with one output. Twin units, side-by-side hooked to a common gearbox. I've never peaked inside the control box to see how it's wire since it's always worked fine. It is an older rig.

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AC generators can be paralleled, having said so it is not easy or cheap, the synchronization is critical. The utilitiy companies constantly have numerous generators in sync. The unloaded unit is brought to speed and the voltage is brought to match and then to a slightly higher freq then the loaded unit, as the unloaded unit syncs to the loaded unit the switch gear is closed to bring it on line, at that time it will start to take on some of the load. In power plants units are brought on line and dropped off to match the load requirements constantly. The governors and synchronizers are expensive, plus all the needed safety gear, back feed relays etc.
Lou

I brought a small honda 2000watt invertor which I realy like. Honda sells a $180.00 contector to hook two together. Been thinking of getting another invertor and hooking them together and selling my 4000 watt generator I have. Will have about 1800 invested but I can see several advantages to the setup. The main one being the total weight. They weigh 40# apiece and you could carry them with one in each hand like a pair of suitcases. My 4000 watt weighs in at 135# which I can't lift or move around too easy without help. DoubleR

IF......................the generators to be paralleled were identical then it's easier. IF........the governors are set up for load following or lead/lag. IF......you have the parallel switch set up into indicate the phase relationship before closing the "tie" breaker.
If........you feel like spending more to have a less workable system then just purchasing the proper single large generator in the first place.
A few days ago we got into this over on the "tools" board. Some cheapskates and/or heroes couldn't wait to extol the virtues of purchasing a generator barely large enough for "all they really need".
The price difference to go up one or two sizes from a "just enough" generator is negligible.
It costs within pennies to design, build, shipping, insurance, wages, buildings, profit margin. To build a 3500 vs 5500W machine or a 10KW vs. 15KW.
Best solution would be a couple of months after the last power interruption. Is to find somebody with a short memory who wants $$$ for something else. And purchase a large enough motor or pto driven generator.

Paralleling generators is a sore point dear to myself. Me, just a fool on the tools told the engineers that paralleling our 7 MW gasturbine backup generators doesn't work. They went ahead and spent 10's of millions on a tie and control system that doesn't work.
They were told it would be cheaper to purchase and install a larger dedicated 25MW FairBanks Morris medium speed diesel instead that would work.
They were also asked what if the power grid ever drops like it did in the early 1960's. They laughed in my face.
This was before the August 2003 blackout over the northeast.
I asked them if they though they run a 5MW motor from a 7MW generator. They said it would run fine. I asked how they were going to start the 5MW from a 7MW generator? They said "easy, the 7MW generator has 2MW to spare". I asked if they knew about starting inrush current". One engineer gave me a blank look and the other thought a second then got a panicky look on his face".
Last I seen they quit trying to parallel the gasturbines as they "fight like two cats in a sack". They couldn't "black start" the 5MW backup pump either from one 7MW gasturbine. It took about two seconds to find that out for themselves. The breakers closed, the ammeters pegged off scale high, the governor went max output, the exhaust stack blew black smoke, the exhaust temps started to rise, voltage dropped and frequency dropped. Then breakers and emergency shutdown relays started tripping. It got pretty quiet for a few moments as everybody looked at each other. Then the excuses and "butt covering " started.
The 2003 blackout hit and the nuclear regulatory commission had a screaming fit and asked why didn't they have working backup power in case of a total power grid collapse.
Two reactors had to depend on the backup to the backup of the backup system for cooling. Yes they will cool via thermosyphon just like a model T car engine. There was two more backup systems left in case b.t.w.
So they went out and spent another 10's of millions to a temporary 25MW gasturbine backup genset. Then spent another 10's of millions on another permanent dedicated 25MW gasturbine system.

When i worked at Sharpe Army Depot on Stockton, CA we have three 500 KW Generators powered by big Cat engines. they all three tied together with a power grid then tied into the Main grid from the power company. If you can't use more than one Generator then we must have ruins a lot of them.

The power companies get power from lots of sources including some home wind and solar systems they are not times to the grid.
Walt

It is possible, Reminds me of a tale by an Old Timer of his experience on an English air field. He wanted to hook up several generators in parallel so knowing a little bit about electricity he set up switches to do the job. When he threw the switches with the generators all running, they all stopped instantly and several laid over on their sides. Then he learned about synchronization.

There are fancy synchronizing meters, always backed up by a couple light bulbs. Two 120 volt lamps in series across the open switch indicates by the lamp brightness how much the two circuits are out of phase. At the worst point there is 240 volts across the open switch so it takes the two lamps (240 volt lamps being uncommon, but possible). The operational trick is to adjust the speed of one of the generators to slow the brightness changes to ten or more seconds per light brightness cycle, then pick the middle of the dark period for closing the switch. If you miss zero voltage difference, there will be a grunt from both machines and you might have to stand one or both back up if you miss by too much.

Then you adjust the throttle on the dependent generator to get the two generators to share the load. As the load varies, the load sharing will depend on the quality of the individual voltage regulators and engine governors.

The inverter based generators require a control cable between them to do the phasing, they won't just parallel at the AC output.

Gerald J.

Just an idea. If they both/all have DC out, Run into a proper sized battery bank, then get one inverter to do all the AC. Not the most efficent setup, but no phase issues.

Cheapskates? No, just not made of money like you are. Can't see buying a $6000 genset when a $600 one will do everything I need. And in an emergency, all I need is heat, light, refrigerator, water and sewer. Of course, I can get by driving a small family sedan to the grocery store, and have no need for an Escalade. Your needs may be different.

In the mid sixties I was employed as operator for a village diesel electric plant. The kilowatt capacity of the three phase generators was: 600, 260, 120 and 80. As the plant load varied during my shifts, it was necessary to start up and shut down generators accordingly. Each generator’s speed, once paralleled, was controlled by the load on it, which varied with system load and system generation, as well as its’ own mechanical governor. The synchronization was accomplished with nothing more than the light bulb system Gerald described below.

I would not be reluctant to connect smaller power generators in the same manner as in the above (using light bulbs) but to play safe I would use fusing or circuit breakers equal to each of the generators overload capacity. Because I am in general agreement with what Lou and Gerald posted, I will recycle part of what they said:

“AC generators can be paralleled, having said so it is not easy or cheap, the synchronization is critical. The utility companies constantly have numerous generators in sync. The unloaded unit is brought to speed and the voltage is brought to match and then to a slightly higher freq then the loaded unit, as the unloaded unit syncs to the loaded unit the switch gear is closed to bring it on line, at that time it will start to take on some of the load. In power plants units are brought on line and dropped off to match the load requirements constantly. The governors and synchronizers are expensive, plus all the needed safety gear, back feed relays etc.
Lou”
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“There are fancy synchronizing meters, always backed up by a couple light bulbs. Two 120 volt lamps in series across the open switch indicate by the lamp brightness how much the two circuits are out of phase. At the worst point there is 240 volts across the open switch so it takes the two lamps (240 volt lamps being uncommon, but possible). The operational trick is to adjust the speed of one of the generators to slow the brightness changes to ten or more seconds per light brightness cycle, then pick the middle of the dark period for closing the switch. If you miss zero voltage difference, there will be a grunt from both machines and you might have to stand one or both back up if you miss by too much.

Then you adjust the throttle on the dependent generator to get the two generators to share the load. As the load varies, the load sharing will depend on the quality of the individual voltage regulators and engine governors.
Gerald J.” <>

In the late sixties I did sales engineering work for tie line control instrumentation of systems with considerably more capacity than the one sited above. Nothing that I experienced there contradicted any of the above.
John

Thanks everyone for your efforts. In my original post I should have made it clear that I have no intentions of ever doing this, just was a wondering out loud.

A 3,500 watt gen will do just fine for my house as my only concern is a sump pump, and that pump itself was only needed two days in thirty years. A refrigerator maybe needed after a day or two of outage. But total cost of the contents in the refrigerator will not buy the fuel for the generator probably. The wood furnace needs no power, but does have a fan for better heating. And I doubt if I would ever need the big air compressor as I have six smaller ones that would get me by.

Perhaps the only reason I need a generator at all other than at the job site once in a great while, would be to show the neighbors that it's not stupid to own one.

Another reason is to borrow the generators out to my sons who think they will never ever need one. No they can't keep them/ store them for me as they would never get serviced or started till they were needed. I also know the second the lights flicker they will be enroute to come get one, cause dad doesn't need five of them.

Just for the record $30.00 for a 3,500 watt at auction--1-2 pulls to start. Then another at a flea market same size for $75.00 for job site, 1-2 pulls. Then a old guy had a 5,500 watt one for his house, 2 years old and decided he wanted push button start. He wanted $200.00, usualy 1 pull. (now at my house). A week later a 5,500 watt that had been sitting for a while, not guarenteed to run at auction, (his son workes for me said it was bought new and just played with, never used). $150.00 --oil change and gas 2 pulls, now for work. So the 5th one was on a AC WC tractor and runs off the flat belt 3,500 watt, came with the tractor no charge. The guy burned wood, and insisted on a electric chain saw....no I'm not kidding.

So for $455.00, and some lost time at a auction and a flea market I have five generators, and little room to put anything else.

Maybe my kids, nor neighbors think I'm great, but if we have a power outage, I might be more likeable after all. Just kiddin, I have great neighbors, and kids---but it's up to me to look after them till they understand it could happen some day.

My 400 amp pull top cost me only to bend over and pick it up as it was going to scrap because they went considerably bigger at a farmers place. The wires should have been 2" longer on the loops. I did it all my self, and realy think all my junks total is less money than the damages that could be from one outage.

I loan them out from time to time to friends, so I hope most of you all don't think I real crazy.

Thanks again folks. North East Iowa