3-Phase or Single-Phase Supply
3-Phase or Single-Phase Supply
(OP)
I am in the process of purchasing laundry equipment that is now independent of the phase; it can now operate on either 120v/Single Phase or 208-240V/three Phase since the "motor" unit is an inverter drive.
In the past, from an energy cost and amperage perspective the prefer choice for this equipment would be 208-240V/three Phase. However, the equipment vendor states now that same cost and efficiency of operation can be achieved with 120v/1P.
What's the opinion of the experts: 208V/3P or 120V/1P?
In the past, from an energy cost and amperage perspective the prefer choice for this equipment would be 208-240V/three Phase. However, the equipment vendor states now that same cost and efficiency of operation can be achieved with 120v/1P.
What's the opinion of the experts: 208V/3P or 120V/1P?





RE: 3-Phase or Single-Phase Supply
RE: 3-Phase or Single-Phase Supply
Your vendor is correct, you really will not see much difference in machine efficiency. There are small percentage losses in the VFD, but now you have a VFD either way so the difference between the two input voltages is negligible. The technology that allows this is called a Voltage Doubler on the input side of the VFD. It is a passive device, i.e. no switching, so no additional switching losses. Only a very slight amount of extra resistance across the diodes involved.
It will take a larger circuit capacity on the input source for the end user and there may be some slight additional losses there, but not really enough to worry about, and technically that is not your "machine's" efficiency
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: 3-Phase or Single-Phase Supply
I believe the vendor states the equipment can operate at 120V/1P but recommends 208-240V/1P since the HP of the motors run between less than 1 HP up to 4 HP.
What's the preferred supply among manufacturers and the experts:
1. 120V/1P
2. 208-240V/1P
or
3. 208-240V/3P??
RE: 3-Phase or Single-Phase Supply
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I don't suffer from insanity. I enjoy it...
RE: 3-Phase or Single-Phase Supply
I don't understand the variation on HP though. Are they referring to different models? Because if they mean that this one model sometimes uses 1HP and at other times 4HP (i.e. multiple motors), then as far as you are concerned the total load is 4HP. You must always consider the worst case scenario, so you will need that 30A circuit.
If on the other hand you are reading a sales brochure that is common to several models, then base your decision only on the model you are going to buy. Their recommendation would (should) also be based on the worst case scenario. So if you are buying a 1HP model, either way is fine. If you are buying a 4HP model, go with the 208 or 230V input. 3 phase would be better all around, but if you don't have it, it's a moot point.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: 3-Phase or Single-Phase Supply
I've been debating making all the large washers use 240V/3P; my past training says 240V/3P is the right choice for heavy loads, especially over a 7-10 year period.
RE: 3-Phase or Single-Phase Supply
However, the cost of adding 3 phase when it is not needed will be excessive.
RE: 3-Phase or Single-Phase Supply
If you use a VFD to change 1-phase to 3-phase then you need more 1-phase input current that the required 3-phase output current. The input current would be 1.73 times the 3-phase motor current.
A 4hp, 120V, 3-phase motor would draw approx. 24A on 3-phase so multiply times 1.73 to give approx. 1-phase current of 40A on the input. On the other hand, 20V, 3-phase would draw about 14A.
Of course, the manufacturer should be able to provide you with the 1-phase and 3-phase currents of the machines you're looking at. When you get into the smaller motors the rated current can vary greatly between different motors so using a s"standard" current from a table means little. Use the manufacturers current values and determine which voltage and phase gives the cheapest, easiest and most logical installation.
RE: 3-Phase or Single-Phase Supply
Do you have 3 phase power in your plant already?
RE: 3-Phase or Single-Phase Supply
RE: 3-Phase or Single-Phase Supply