I bought a surplus fan/HEPA filter unit for using in a clean room. The wiring diagram is here.

enter image description here

I want to connect it to a power cord and plug it into the wall. I know basic electric, but I'm not sure about the issue of using 240v to run a 200v motor. Any advice would be much appreciated.

  • \$\begingroup\$ We'll need to know more about how your building is served, and if it's in a primarily residential area or if three-phase service is not an option for some other reason... \$\endgroup\$ – ThreePhaseEel Jan 9 '19 at 2:43
  • \$\begingroup\$ You need to check your mains voltage. It could be 120V/208V (2 phases) or 120V/240V (1 phase with center-tapped transformer). \$\endgroup\$ – StainlessSteelRat Jan 9 '19 at 4:33

The choice of 200 VAC is curious, I have not encountered this voltage before on a motor. 208 VAC is a reasonably common power standard in some parts of North America. This motor would probably be fine operating on that voltage as it is only 4% different.

Your options for running this motor are, from best to worst.

  1. Get 208 VAC power to your premises. Unless you have it already, this is cost prohibitive in most places.
  2. Get a transformer that converts 120 VAC to 200 or 208 VAC 60 Hz single phase. This should exist, although I haven't purchased one before.
  3. Run the motor with a series resistor in the high speed from 240 VAC single phase 60 Hz power. The motor would normally draw about 0.65 amps in high speed. This corresponds to an impedance of around 307 ohms. You can use a resistor of approximately 61.5 ohms in series to drop the 240 VAC to 200 VAC.

Option #2 is the most practical.

Option #3 is simply tolerated by most motors of this type, it is the least desirable option. The motor may have a very large startup time if you do this. Also note the resistor will generate around 25 watts of heat and need to be rated as such.

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  • \$\begingroup\$ 208/120 transformers do exist, so I think option 2 is the most practical if he's in an area where 208Y service isn't feasible, otherwise he might as well just use what's there and go for option 1 \$\endgroup\$ – ThreePhaseEel Jan 9 '19 at 4:12
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    \$\begingroup\$ Also, the choice of 200V is probably due to peculiarities of the Japanese electrical system... \$\endgroup\$ – ThreePhaseEel Jan 9 '19 at 4:14
  • \$\begingroup\$ An example 208/120 1ph distribution transformer... \$\endgroup\$ – ThreePhaseEel Jan 9 '19 at 4:19
  • \$\begingroup\$ @ThreePhaseEel Isn't 1 KVA a bit high? Would it get away with a 500VA? Some standard isolation transformers also offer taps to change the voltage, that might be cheaper than what you listed. \$\endgroup\$ – Jeroen3 Jan 9 '19 at 7:11
  • \$\begingroup\$ @Jeroen3 -- 1kVA was the smallest unit that was available through that vendor, I bet you could get smaller if you ordered through an electrical supply house \$\endgroup\$ – ThreePhaseEel Jan 9 '19 at 12:39

100/200VAC 50Hz or 60Hz is standard Japanese power.

If you could get a transformer that is ~40VAC and rated at the current of your appliance, you would wire that in a box to buck the incoming power. 1A should be sufficient. For example, this Triad part # FD8-48, about $20.

enter image description here

You connect the primaries in series (jump 2 to 4) across the 240V power, and connect 6 to 10 winding in series with the 240V mains. In one direction it will add, giving you about 288VAC, on the other it will subtract, giving you a reasonable 192VAC. Check with a voltmeter before wiring it to the fan.

It should be like this:


simulate this circuit – Schematic created using CircuitLab

Note: It might survive okay on USA-standard 60Hz 240VAC given the 50/60Hz compatibility, but personally I would not chance it without agreement in writing from the manufacturer.

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  • \$\begingroup\$ Thanks a lot for this advice. That Triad part is very cheap so I would definitely consider trying it out, but I'm not sure it I can understand the diagrams you've shown because they require quite a bit of circuit literacy. Meanwhile I'm not even sure which two terminals on the wiring diagram I attached represent Line-1 and Line-2 for the 240volt power cable. Can you tell me of the terminals shown (H,L,C) which are the terminals that should receive the hot wires from the mains? \$\endgroup\$ – Seth Friedman Jan 10 '19 at 2:36
  • \$\begingroup\$ Looks like a 2-speed setup, so apply mains from H to C or L to C with the unused connection left open. Not sure the purpose of the (static pressure?) switch. \$\endgroup\$ – Spehro Pefhany Jan 10 '19 at 2:55
  • \$\begingroup\$ Okay thanks! I guess when you say "from H to C", thats a more technical expression for "connect one hot wire to H, and one hot wire to C"?. \$\endgroup\$ – Seth Friedman Jan 10 '19 at 2:57
  • \$\begingroup\$ Correct........ \$\endgroup\$ – Spehro Pefhany Jan 10 '19 at 2:58
  • \$\begingroup\$ Trying to understand your diagram above, I think I know what you mean by "jump 2-4", what do you mean by "connect 6 to 10 WINDING IN SERIES"? \$\endgroup\$ – Seth Friedman Jan 10 '19 at 2:58

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