2 gensets on same bus

[unimogr]

Hello Everyone,

I've been looking into buying one of these engines for a while now but I've had a question and I'm hoping someone here knows the answer.

My ultimate goal is to use the genset as standby power for an off grid site.  I am thinking a 10/1 with a 5 or 6 KW head will be enough for most applications, but I would like to have a second identical unit on hand in the event the primary fails or I require more power.

Does anyone know what would happen if you were to bring a second genset online while the first is running?  Will the phase of the second unit fall into sync with the first automatically or will I have to run it through some sort of transfer switch that will automatically do a phase shift to bring the two into alignment?

By doing this my hope is that:

- I can run 1 engine under load at all times instead of having an oversized engine run under partial load most of the time
- I can bring one engine down for maintenance and not interrupt service
- In the event one engine fails, I have a second to carry the load until I can repair the problem.

If there is anyone who has done this in the past please let me know if there are any pit falls.

Thanks,

Jason

[GuyFawkes]

personally I'd say go for 2 x 6/1s, it is enough, especially as you can sync em up when required.

we used to have dual or more gens on the boats, and a big box that was used to sync (phase match) before you brought the next one on-line, failure to do this would result it catastrophic failures, an expensive bit of kit, but to my mind the best way of doing it.

also called "line sync" modules, been years since we played with them so best ask the regs in here with AC experience where to buy or source them now

other way is letting the second unit "cog" into the first, which means when the first unit goes down so does the second one innit.

two identical standalone separate units and a line sync is the elegant way to do it, not the cheapest, but probably the best

[listeroidsusa]

An easy way to sync 2 generators is to wire a light socket between the two generators power legs with switches, L1 to L1, and L2 with L2. If the generators are out of phase the bulbs will light. As the engines are running watch the bulbs and soon they will go dark the instant they are in phase. The time it takes will depend on the harmonics of the voltage and frequency but they will eventually go dark, especially if the engines are approximately the same rpm. Throw the main switch between the generators when the bulbs are dark. They will then "lock" into phase with each other. Many old time power panels used this method.

Mike

[mobile_bob]

i think you are going to have alot of difficulty not only sync'ing the generators, but keeping them in sync.

any fluctuation in the govenors is going to cause them to drift apart and cause loading and possible failure.

why would you need to have them sync'd to start with?

bob g

[mobile_bob]

the reason i question the need for sync'ing is based on the reality of what you are trying to accomplish

it would appear that unless you are running life support or some sort of mission critical setup that would require seamless transfer you really don't need to sync at all.

if you are running some critical system requireing seemless transfer, then why are you basing it on listeroid gensets?

a clutching arrangement would do the job much easier, and might require a few seconds of brownout while you clutch one engine out and the other in. this would require much less cost and be far safer in my books. this is for two engines driving one head of course.

if you can sync, and are sure of it, then go ahead, but if for some reason things aren't in sync blown breakers, broken drives, burnt belts and damaged generators can result.

if you have two independant sets, then a reversing contactor set with electrical and mechanical interlocks could be adapted, would suffice and the glitch period would be under a second i would think

do you have a compelling reason to have to sync the two set's

a bit more details as to what you are trying to power off grid might help.

bob g

[mobile_bob]

another thought is the use of a large UPS, you are probably going to have batteries anyway in an offgrid setup.

two gensets with mechanical one arm bandit disconnects feeding into a UPS would allow for seemless transfer and not
be expensive at all. large institutions get rid of these units all the time and can be got for scrap price.

i picked up a 15 kwatt UPS for 25 bucks not long ago, i could certainly accomplish seamless transfer of many gensets easily using it as the intermediary component. with fresh batteries transfer between gensets could take up to 1 hr and have no interuption of power. Also some of these larger units have much cleaner power coming out than the genset produces, as the gen comes online the UPS switches off it inverter section and conditions the power from the genset to pure sinewave at near dead on 60 hz. (+/- .1 hz)

add the aforementioned reversing contactor setup, and with a simple flick of a switch your online with the second genset.

might be an elegant solution to your project

bob g

[Doug]

An easy way to sync 2 generators is to wire a light socket between the two generators power legs with switches, L1 to L1, and L2 with L2. If the generators are out of phase the bulbs will light. As the engines are running watch the bulbs and soon they will go dark the instant they are in phase. The time it takes will depend on the harmonics of the voltage and frequency but they will eventually go dark, especially if the engines are approximately the same rpm. Throw the main switch between the generators when the bulbs are dark. They will then "lock" into phase with each other. Many old time power panels used this method.

Mike

They still build some this way. I built a manual/auto syncronizing panle for Great Lakes power a few years ago that had the three lights along with all the automatics.

Personaly I don't think its realy practical to try and do this in an off grid home to much fussing and baby sitting the system.

Doug

[Andre Blanchard]

the reason i question the need for sync'ing is based on the reality of what you are trying to accomplish

<< snip >>

do you have a compelling reason to have to sync the two set's

a bit more details as to what you are trying to power off grid might help.

bob g

The "or I require more power" is I think the main reason for wanting to sync two generators, say you have an 8Kw main gen set and a 5Kw backup gen set and you want to run an occasional 10Kw load.
Getting the generators synced up is easy with the light bulb setup (you can use a voltage meter in place of the bulb) the hard part is load sharing between them after they are locked together, all the way down to making sure one is not being motored by the other.

I my case I am going with the one large generator and two engines a 12/2 and a 6/1, actually the 6/1 will normally be setup as an air compressor but converting back to and engine will be a simple matter of swapping heads and dropping the valve and injector pump tappets back down onto the camshaft.
Still have the load sharing problem but since the two engines will be bolted to the same concrete block it is a little easier.  Should be able to just mechanically connect the two governors and treat it like one three cylinder engine.

[bitsnpieces1]

  Along Andres line, since Listeroid governors are a little shaky anyway, go with an external governor controlling both engines through a common linkage.  Have a large gen head powered by one engine and the other engine ready to clutch in as needed for extra hp.  Run all three cylinders at first and get them adjusted for even loading to each cylinder.  That way you could run the 2 cy. most of the time, clutch in the 1 cy. when needed and have it pick up its' part of the load.  Or, could run the 1 cy. with the twin clutched out. 
  Isn't automatic, but, only takes a half-minute to switchover, just engage or disengage clutchs.  Don't even need to crank second engine, let the one running do it.  Also could use two identical engines and accomplish same thing, just make sure that governor is driven from a spot that won't allow for runaways, perhaps a connection directly to the crankshaft itself. 

[unimogr]

Thanks for all of you inputs guys, the light idea makes a lot of sense, if I were to go that route it shouldn't be too hard to fit a volt meter in there so that you know when things zero out.

The bottom reason I would want to do this is so that I can double my KW capacity on demand and have a standby unit the rest of the time.  The other option would be to have a 10/1 6KW for day to day use and a 20/2 12KW unit for heavy load days but it would be nice to have two smaller units since they will be cheaper then one big and one small.

Jason

[GuyFawkes]

2 x identical 6/1 has a HUGE advantage, only one lot of spares, everything else is interchangeable, never under estimate the benefit of this "redundancy"

2 x different motors or gen heads and you have zero redundancy, people will say you do, but you don't in the real sense of the word, you jut have a backup, not the same thing.
 

[rleonard]

How about 2 engines pulling the same generator?  For example build a frame with a ST-12 in the center, and the 6-1's on either side.  Clutching could be done by belt cluches, stopping to take one belt off (or on), or electric automotive air conditioner type cluches.

Bob

[fattywagonman]

Hi Unimog,
I would suggest a battery and inverter system... smaller engine does more work and doesn't need to run all the time... you could add solar and wind power if you like.. and could go down for a day or two if the batties are big enough...

[cujet]

I have never done the following:

There has been a bit of talk here about using induction motors as generators. They sync up with the grid and I cannot see why they would not sync up with a 6/1 running a ST head.

From what I understand, turning an induction motor over the syncronous speed, (more than 1800RPM in my example) will proved power. How much faster you turn it determines the power produced. From what I understand, 1830 RPM will be about right. Some here are using this method to run the power meter backwards on the home. Whlie I understand it is not the most efficient method of making power, it is likely such a setup would not be under full time use. So the slight loss in efficiency may be acceptable.

Once again, I have no idea how this really works.

[GuyFawkes]

I have never done the following:

There has been a bit of talk here about using induction motors as generators. They sync up with the grid and I cannot see why they would not sync up with a 6/1 running a ST head.

From what I understand, turning an induction motor over the syncronous speed, (more than 1800RPM in my example) will proved power. How much faster you turn it determines the power produced. From what I understand, 1830 RPM will be about right. Some here are using this method to run the power meter backwards on the home. Whlie I understand it is not the most efficient method of making power, it is likely such a setup would not be under full time use. So the slight loss in efficiency may be acceptable.

Once again, I have no idea how this really works.

Disclaimer, I'm not a sparky either.

From my understanding, once a induction motor is in sync, you can't actucally speed it up unless the driver is much more powerful than the motor, what happens is you *try* to drive it faster and this *pushing* is what generates the power.

If you have sufficient power to drive it faster it goes out of sync, vast currents flow and things melt and spurt flames....

1800 rpm / 60 = 30 revs per second, so 0.5 revs per hz, or full sine wave

1830 / 30 = 30.5 rps, so 0.5083 revs per hz, or full since wave

0.5 hz or sine wave is 180 degrees out of sync, max current flow, things go bang, 60 hz =  0.0167 sec, half that is 0.0083 sec so.....

0.0083 sec times 30 revs per sec = 0.249, or quarter of a armature revolution, which is right for a 2 pole head to be 180 out of sync

0.5083 - 0.5 = 0.0083 so your 1800 and 1830 rpm should put things 180 degrees out of sync every 0.249 / 0.0083 = every 30 seconds

I think that's right, wait for doug or someone to stop by and check my sums, and then tell me there was a 300 times simpler way of working it out... lol