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Author Topic: 2 alternators on one engine ?  (Read 6544 times)

cylinderheadnut

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2 alternators on one engine ?
« on: September 21, 2012, 11:25:03 PM »
Is it possible to belt drive 2 seperate AC alternators from one engine ? could they be made to run in a single phase ?

i'm looking to build a  10 kva generator set, finding a single 10 kva alternator is difficult, two 5's is easy.


dieselgman

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Re: 2 alternators on one engine ?
« Reply #1 on: September 21, 2012, 11:48:46 PM »
Location is everything... we have lots of 10's but can't get enough 5's. Midwest US.

Your question is interesting... we are familiar with paralleling multiple gensets and using switchgear that has control on each governor to bring them into synch... but your case would suppose that both heads were in physical lock-step (via the single belt) and could not be disengaged from one another except via belt slippage or maybe a clutch mechanism of some sort. You would need the output waveforms to be completely synchronized and matched at all times... maybe a number of other issues as well. Does not sound too practical to have them locked together! They could surely be configured to run seperate loads though.

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mobile_bob

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Re: 2 alternators on one engine ?
« Reply #2 on: September 22, 2012, 01:24:18 AM »
technically it is possible with a cogged belt drive (gilmer belt)
the two heads would have to be timed very carefully , but it could be done.

one of the generators would have to be mounted rigid, the other on a slide
the first would have to have a single idler to tension the belt, the 2nd would have to have
two such idlers to not only tension but fine tune the timing between the heads

a 2 channel scope could then be used to make sure the two waveforms are in sync, the second generators idlers adjusted to dial them into exact phase sync.

so yes it can be done, cheap?  no
but it can be done.

now if you want to belt up multiple alternators, such as automotive DC output types, you can
just belt them up and not worry about sync'ing them.

bob g
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ronmar

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Re: 2 alternators on one engine ?
« Reply #3 on: September 22, 2012, 04:06:52 AM »
I don't think you would need cogged belt drive, at least not to feed a single phase...  Separate generators running in parallel don't have any problem staying in parallel/sync once the rotors are excited.  One of the tricks of managing separate generators is usually the governors being synced so the separate engines will load share equally.  You wouldn't have this problem with only one prime mover...

If you lined them up carefully before tensioning the V or serpentine belt, the two should fine tune their angular alignment thru belt slippage due to the mechanical forces created with the electrical outputs connected together.

The issue would then be load sharing between the two generators.  You could tie the two excitations together and feed them from the same AVR sensing the output, but there is no guarantee that two identical generators would excite the same with a common input, but they should be close.  You might need to add some form of bias circuit to allow you to truely balance the two generator outputss.  It might be something as simple as a small ammount of resistance added to the hotter generator based on current readings taken from each separate generator. You want both the generators to have identical current outputs...   

I have spent a lot of time powering ships and LORAN stations on 2 and 3 generators paralleled, and it is not really rocket science.  I could see this working, but I have never tried it...   
PS 6/1 - ST-5.

Thob

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Re: 2 alternators on one engine ?
« Reply #4 on: September 22, 2012, 01:23:12 PM »
I think if I was doing this, by the time I got it done I would have spent more than the 10KW generator would have cost!

But here's an idea: mount the two generators "face to face", and couple the shafts together with something like a lovejoy coupler.  The only thing is you have to get them at the exact rotational spot so that they are in phase.  You might need something more like an adjustable flange to flange coupler.  I wouldn't trust the key ways on both shafts to be in the same spot.

You could then put a sheave on one generator's shaft and drive it with the engine.  But you need to either move the engine to adjust belt tension or put the two generators on a sub-frame so they can be moved together.  Plus, the belt is now captive, you'd have to remove one generator to replace the belt.

This is in addition to the load matching mentioned above.
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mobile_bob

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Re: 2 alternators on one engine ?
« Reply #5 on: September 22, 2012, 03:30:10 PM »
most generators that are made to run in tandem/parallel have a second squirrel cage winding
on the rotor to lock the two in phase in operation. while a pair can run in parallel without the second winding, they are a bit more tricky to get and keep in step with each other.

most especially if driven by two different engine's, which is only made worse with poor quality mechanical governors, on single cylinder engine's.

if it were me, and i had to put two together, i would not want to fuss with having to sync them everytime i started them up.  it just seems to me that at some point something is going to go wrong and something might get burnt or broken, therefore i would want to use some mechanical method of locking them together that i could dial in phase with a scope. once done, i wouldn't have to worry about it again.

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Sfene

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Re: 2 alternators on one engine ?
« Reply #6 on: September 22, 2012, 03:31:47 PM »
You will have to find a way to have each Alt independent as you synch them together, once they are in synch and loaded they will remain so. If one belt (or whatever) breaks, the slower Alt will become motorized with less than optimal results.....

Ronmar, what LORSTA were you at? I spent a year in Okinawa, and a bit of time in Yokota, just missed getting a billet on Iwo but ended up working on Lighthouses in Northern Me.

T.

Thob

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Re: 2 alternators on one engine ?
« Reply #7 on: September 22, 2012, 06:20:25 PM »
Here's another thought:  Wire each generator for 120V, then put the two generators in series instead of in parallel.  That way, if they go out of sync what you get is a voltage drop across the 240V.  Any 120V loads will never notice, but any 240V loads will see a voltage drop.  It seems like it would be much less apt to let the magic smoke out of the generators that way.  Of course, I'm assuming a split 120/240V system where the generators can be safely wired this way.  Plus, each generator can regulate itself at 120V.
Witte 98RC Gas burner - Kubota D600 w/ST7.5KW head.
I'm not afraid to take anything apart.
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ronmar

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Re: 2 alternators on one engine ?
« Reply #8 on: September 22, 2012, 06:25:42 PM »
I stayed inconus mostly. Narrow cape AK, Seneca NY and George WA...    Then there was the Acushnet and Polar sea:)
PS 6/1 - ST-5.

Sfene

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Re: 2 alternators on one engine ?
« Reply #9 on: September 23, 2012, 12:15:13 PM »
Worked on some neat stuff, Waukesha, Lister, Nordberg .... then the usual Detroit, Cat, Cummins, Perkins..

Would love to find a 12hp Nordberg Powercheif..