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Author Topic: ST3 vs 5 for a 6/1?  (Read 5558 times)

38ac

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ST3 vs 5 for a 6/1?
« on: January 06, 2013, 03:01:21 AM »
I am putting together another generator that will run by a 6/1 and only used for occassional stand by 110 V service. Will be wired 110 only so no balance problems to worry about.  ST3 is $100 cheaper and lots lighter than a ST-5. so shipping should be cheaper too. Money is not all important but over kill is waste.  We have a ST-5 on our other6/1 but it is wired 220 and I wanted some extra to better accomdate unbalnced loads.  Will a 3 do? or should I just quit trying to be a cheap skate and get a 5?
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mike90045

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Re: ST3 vs 5 for a 6/1?
« Reply #1 on: January 06, 2013, 04:16:31 AM »
It sounds like you already have a good idea of your loads, and know the limits of the engine & head.  The ST3 will only have it's inherent overload, not the extra margin the ST5 gives you.  You will have to disconnect loads, and let the fan in the head, cool the coils for a couple minutes, not a lot of overhead like the ST5 gives.

ronmar

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Re: ST3 vs 5 for a 6/1?
« Reply #2 on: January 06, 2013, 06:31:39 AM »
IF you knew you would not exceed 3KW of load, the ST3 would be fine.  The problem lies in that the 6/1 has HP enough to meet and exceed that 3KW limit. So if the load creeps up there, you could have an overheat/burnout situation in the generator head without knowing it.  Conversely the 5 KW head can overload the engine, which results in undervoltage/underfrequency.  This tends to set off my UPS's in the house, so is readilly apparent when I let it happen.  I have the generator output  limited to 15A with circuit breakers so I cannot get to out of control without opening a circuit breaker... 

I personally like the 6/1-ST-5 combo...
PS 6/1 - ST-5.

dieselgman

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Re: ST3 vs 5 for a 6/1?
« Reply #3 on: January 06, 2013, 09:25:35 AM »
I have had hands-on a few of the 3kW STs. They are indeed much lighter, but I would also be concerned about overloading unless I had a very specific dedicated load to pull. That idea seems to go against Murphy's Law.  :P
My usual engineer's logic runs to assuming the worst scenario and building things robust enough to have a large margin for error. I think it comes from working in the bush schools where any small problem can quickly cascade into hugely expensive failures. One of the major strengths of the Lister equipment is based on heavy overkill I believe.

One other comment... parts interchange! Consider a possible scenario where you might want (or need) to swap things around to keep a plant running.

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« Last Edit: January 06, 2013, 09:28:50 AM by dieselgman »
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t19

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Re: ST3 vs 5 for a 6/1?
« Reply #4 on: January 06, 2013, 12:36:37 PM »
When Your main unit goes down... that $100 dollar difference will seen like a wise investment.  So it weighs more... its not like your making a mobile application.  Just take the extra time to work out the load balance

Course if your original 6/1 and 5 ST dies and your left with a 3ST ... you will wish you had spend the extra, and it will cost you a whole lot more.

My dad bought a new Firebird with a V6... the whole time he had it he kept sounding like a commercial for a juice company.... I shoulda bought a V8!  LOL
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xyzer

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Re: ST3 vs 5 for a 6/1?
« Reply #5 on: January 06, 2013, 04:39:35 PM »
If you get the 5KW one bag of spare parts will keep both heads alive. The extra 2KW over the 3KW will also help reduce the need for the repair parts in theory. Any time I can duplicate equipment I will, even if it means spending more $. I think either philosophy is correct but a backup for my backup sways me.
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BruceM

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Re: ST3 vs 5 for a 6/1?
« Reply #6 on: January 06, 2013, 06:30:01 PM »
I ended up with an ST-3 as that was all that was available at the time my 6/1 was to be shipped.  Much smaller, lighter.  It's adequate for my needs, and at 5600 feet elevation it's a pretty good match for my 6/1, which often has a parasite load of my air compressor, decompressed.  I have no motor starting loads bigger than 1/2 hp.  I usually run at 1000 -1500 watts load. A load of 2000 watts is rare, and only in the winter when I'm running my shop lighting/heat lamps.

The upside to the ST-3 is that with an AVR it has less flicker, as the rotor has less inductance than the ST-5, and so it is more responsive in correcting for the speed change of the compression/ignition stroke.

For near sea level applications, I agree the ST-5 is probably the best way to go, for bigger motor start capability, and especially if you expect to be operating well over 2000 watts continuously in the summer.  And especially if the freight is the same.  George B was kind enough to break down an ST-3 for me into two containers so it could be shipped UPS.  Saved me a bundle on my backup ST-3.




38ac

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Re: ST3 vs 5 for a 6/1?
« Reply #7 on: January 07, 2013, 02:27:40 AM »
Sorry, A bit more info would have helped you guys but you kind of hit a cord with the parts deal. Guess I'll order me up a 5KW. We have a farm property that is off-grid and we just need to be able to run a few lights now and then, maybe a drill, grinder. Main thing I need to do is run a battery charger for the tractors and such.

Thanks.
« Last Edit: January 07, 2013, 02:30:14 AM by 38ac »
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mike90045

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Re: ST3 vs 5 for a 6/1?
« Reply #8 on: January 07, 2013, 05:36:20 AM »
Sorry, A bit more info would have helped you guys but you kind of hit a cord with the parts deal. Guess I'll order me up a 5KW. We have a farm property that is off-grid and we just need to be able to run a few lights now and then, maybe a drill, grinder. Main thing I need to do is run a battery charger for the tractors and such.

Thanks.


Then I'd worry about under-loading the 6/1 with only a couple hundred watts load.   Might be better off with a little inverter genset for those times.

veggie

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Re: ST3 vs 5 for a 6/1?
« Reply #9 on: January 07, 2013, 03:16:50 PM »

You can match the ST3 to a 6/1 by slowing down the engine to about 550 rpm.
That would allow you to load the engine to 100% without exceeding the ST3 rating.
Then the pair would be properly matched.  :)

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BruceM

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Re: ST3 vs 5 for a 6/1?
« Reply #10 on: January 07, 2013, 04:32:29 PM »
I like Veggies plan.  Less is more.

38ac

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Re: ST3 vs 5 for a 6/1?
« Reply #11 on: January 07, 2013, 05:17:44 PM »
The engine is mounted on a cart and used to power several pieces of equipment via flat belt. Its loads are varied from nearly nothing to all it will pull.   The head will be mounted down and driven the same way. Not the ultimate plan for loadings but I rather imagine it will out live me.  ;)
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