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Three Phase to Single Phase via Transformer

Gunny

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gratis
Where can one find a 3 phase to single phase transformer?

Can you draw out the connections for one?
 

BTPost

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70
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12/29/2008
Re: Just bought a 2006 Onan 7.5HDKAL-3E Need some help

Actually in theory one could make, or wind one, but in practice NO ONE does, so it is just Theory. There is NO Practical difference between a Three Phase Genend, and a Three Phase Transformer Secondary. If one had a Three Phase Delta, or Wye, wound Primary Triple Core Transformer, and then wound what would be a 12 Lead Secondary with 2 Coils, on each of the Three Cores, you would have exactly what you are looking for... A Three Phase to Single Phase Transformer with all the same connection diagrams that a 12 Lead Genend can produce. This would include a Parallel Delta, or Double Delta Configuration. The math works out the same, in either case. Just Say'en.....
 
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Jim Rankin

Registered
Age
58
And the upshot of this exercise is that the single phase connected secondary will always have a lower capacity than when it's connected 3 phase.

The best you can do is to balance the load seen by the primary as well as possible which is what all the single phase reconnections accomplish.
 

Jim McIntyre

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Last Subscription Date
07/10/2019
I'm wondering what the original post is really asking. Is it that he wants to connect a single phase, say 120V load to a 480V 3-phase supply? Or is it that he has a 3-phase generator and wants use a transformer to 'convert' it for use with a single phase load? Is he hoping for a transformer-based circuit that somehow skirts around the 2/3 capacity reduction? Or something else? :shrug:
 

EricWood

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Last Subscription Date
10/15/2019
Jim,

I would guess :shrug: the question is related to something like this:

http://www.nuteckproducts.com/three-single-phase-transformers.htm


People seem to want a way to pump their 3-phase genset into a transformer and get the single phase 240V "house power" out of it, so the full capacity of the generator can be utilized. Transformer would need to be sized so single phase KVA output equaled that of the generator's capacity. A cost-prohibitive venture in my opinion.


This kind of transformer is not going to be on anyone's shelf in a warehouse I suspect; custom-built to your requirements.

eric
 

Jim McIntyre

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Last Subscription Date
07/10/2019
OK, well I'm curious about the connections for that "3-phase to single phase" transformer, too...
 

pegasuspinto

Registered
Final word-there is no 'simple' way to convert 3 phase to 1 phase without significant loss of KW capacity. It may be possible to custom tune something with large capacitors and load coils, but I suspect it would require the load to be in a very narrow window and could dramatically increase the generator load once the load fell out of specs, possibly enough to start letting the smoke out of everything. Other way would be to convert the 3 phase to DC and invert it back to the AC power you want, but that's certainly NOT simple, or cheap. The small inverter type portable generators (Honda and it's clones) work exactly that way. But price would get crazy once you were past 1-2kw.


Robert
 

BTPost

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12/29/2008
Final word-there is no 'simple' way to convert 3 phase to 1 phase without significant loss of KW capacity. It may be possible to custom tune something with large capacitors and load coils, but I suspect it would require the load to be in a very narrow window and could dramatically increase the generator load once the load fell out of specs, possibly enough to start letting the smoke out of everything. Other way would be to convert the 3 phase to DC and invert it back to the AC power you want, but that's certainly NOT simple, or cheap. The small inverter type portable generators (Honda and it's clones) work exactly that way. But price would get crazy once you were past 1-2kw. Robert
You miss- understand the issue here. If you can wind a Triple Core Primary Transformer with one winding per core, at the input voltage, and then wind twin seconday windings, on each of these cores. These secondary windings can be then configured the same as ANY Parallel Delta, or Double Delta, to make 120/240 Vac Single Phase output. The only real issue that needs to be designed into this transformer, is there needs to be enough iron designed into the cores, to carry the power from the three Phase side, to the single Phase Side. Much like an Extended Stack Genend.
 

Jim McIntyre

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Last Subscription Date
07/10/2019
...The only real issue that needs to be designed into this transformer, is there needs to be enough iron designed into the cores, to carry the power from the three Phase side, to the single Phase Side.....
Yep, and then after you did all that, you'd still be left with the 2/3 derating that kicks in when a 3-phase source powers a single phase load...
 

armandh

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Last Subscription Date
09/02/2010
yes the extended stack gen sets could [with enough engine] produce 50% more 3 phase power.
thus the windings can produce 2/3 of that higher amount in double delta or zig zag single phase configuration.

the only way to get full power is to divide the load into 3 parts.
this has some VR challenges.
 
B

BergmanJ

Guest
Folks,

There is a way to convert 3-phase to single phase; but, as BT indicated above, the efficiency is questionable, at best.

Here goes: Scott-Tee from 3-phase @ 120 degrees = 2-phase output @ 90 degrees; then series connect the two output windings with center connection isolated and insulated. Output from two "outside" leads at 240 volts (yes, need to "figure-out" the appropriate turns-ratios to obtain 240 here) to center-tapped auto-transformer (re-establishing "neutral" for 120/240 "split phase" from the center tap.

Again, not efficient; and, I have not figured-out the power-split ratios from all 3-phase windings; but, believe they are not evenly split. Don't know how this compares to derated single-phase use from 3-phase gen output, either. Guessing not a good!

This is more or less just an excercise for those interested in transformer phase conversion.

The direct opposite was used decades ago in 400 Hz aircraft power supplies to provide precision power to electro-mechanical gyroscopic navigation systems: Single phase to + and - 45 degree sources (provides 90 degree total differential outputs -- call one "zero" and the other "90") into two power amplifiers, then into scott-tee power transformers for three-phase power output to drive the gyro motors.

Regards, JLB
 

armandh

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Last Subscription Date
09/02/2010
getting the right voltage and phase relationship is NOT the same as getting the same power output.
the two [zig zag] legs in series use 2/3s the windings and power to produce half the output
 

BTPost

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Age
70
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12/29/2008
If you choose the right Transformers with enough Copper & Iron, then you will have your correct AMP thru-put in the conversion....
 

armandh

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Last Subscription Date
09/02/2010
generator too just like an extended stack

OK for a 240/480 delta or 380Y generator transformed to 120-0-120 single phase

but without enough Fe & Cu in the generator, problems still {IMHO}

there is always a weak link in the power chain. by design it should be the breakers or fuse.

no matter how it is configured.....

both the generator engine and the generator it self should handle more than the breaker,

or longevity will suffer.
 
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TomBall

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Last Subscription Date
12/26/2019
So in reading the responses, am I safe in concluding that if you had a three phase generator laying around and someone said you could easily wire it to run single phase power during outages, it is not that easy or efficient?
 

Vanman

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Last Subscription Date
07/10/2019
Many of them can be reconnected for 120/240 single phase, but all of them will be limited to 2/3 of their original three phase kva. That said there exist sets that are simply equipped with a larger generator, "extended stack" in Onan lingo, that have their three phase rating decreased such that they are rated the same kw for both single and three phase.
 

armandh

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Last Subscription Date
09/02/2010
Many of them can be reconnected for 120/240 single phase, but all of them will be limited to 2/3 of their original three phase kva. That said there exist sets that are simply equipped with a larger generator, "extended stack" in Onan lingo, that have their three phase rating decreased such that they are rated the same kw for both single and three phase.
"that have their three phase rating decreased"
[because the engine is smaller and matches the single phase output ability of the greater at 3 phase generator]
 
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