Rotary Phase Converters Sizing and Buying Guide

Rotary Phase Converter (or RPC) is a machine that is designed to change single-phase power into three-phase power. These converters could be used to run industrial machinery with three-phase motors or any 3-phase motor in your own shop.

Single-phase motors are known to produce no more than 15 hp (11 kW) with many of them producing up to 5 hp (3.7 kW). There is a great demand for three-phase motors because of the power they generate (15 hp + ), easier starting, and greater efficiency than ones that work on a single phase.

Phase converters are very popular among shop owners since it’s a bit pricey to get your own 3-phase power line. Rotary Phase Converters will allow you to use 1 phase power supply coming from your utilities and change it into a power source that could be used for any 3-phase motor (or series of motors), as long as the appropriate size is used and everything is connected properly.

static phase converter

Rotary Phase Converters also allow you to run smaller loads on the larger size converter without a problem (could be manufacturer-specific, check your manual first), which is great for future expansions! This little piece of machinery (converter) could be indispensable in deciding whether to expand your business by getting new equipment or even starting a business (woodworking shop, for example) in the first place.

As of now, there is a lot of different equipment out there that requires 3 phase power to operate at maximum efficiency and this is why phase converters became quite popular. If you need to use a three-phase power source for your business or hobby shop, the two most common options are:

Rotary Phase Converter. This one can constantly deliver 3-phase power to your motor.

Static Phase Converter.  It only gives 3-phase power at the start-up.

The difference between Rotary Phase Converter and a Static Phase Converter is that the Static  Phase Converter will only startup your 3-phase motor and then switch back to the single phase. On the other hand, the Rotary Phase Converter will keep on giving your device a full three-phase power to keep your engine running.

Not ALL devices could run on the Static Phase converters and you should use this system only for motors where the operator can control the load. Devices that use FULL horsepower for their motors should be used only with Rotary Phase Converters.

Rotary Phase Converter sizing

rotary phase converter

Before sizing your phase converter, you will need to find out the exact specifications that reflect your electrical power needs. You will see the numbers in:

  • AMPs. Ampers.
  • kWs. Kilowatts.
  • HP. Horsepower.
  • kVA. Kilo-volt amperes.

You will also need to know what type of voltage your equipment requires to run on in order to calculate your power needs properly.

Converting AMPs to HP

Amps x Volts = Watts

If you know your motor’s AMPs, use this formula to get HP:

With 1 HP being equivalent to 746 Watts, use this formula for final conversion:

Watts / 726 = HP

Converting kW to HP

If you know your kW, but need HP:

kW / 0.746 = HP

Converting kVA to HP

This is the formula for kVA to HP conversion:

kVA × Efficiency × Power Factor / 0.746 = HP

What size do you need?

When sizing a Rotary Phase Converter, the general rule is to get the converter TWICE THE SIZE of your engine. Look at the HP (horsepower) rating of your machine and a converter of HP rating that is double that.

Here is an example:

20 HP motor x 2 = 40 HP Rotary Phase Converter

** Very important! Check carefully if the manufacturer specifies the power of your converter or the size of the load that you can run on the converter (and does not mention the actual size of the converter).

If they DON’T mention the size of your converter, you may need to call them to figure this out. The information on the Rotary Phase Converter size is very important in order to plan your electrical setup and breaker size.

Buying Rotary Phase converters

So what to look for when purchasing a Rotary Phase converter? Before I get into popular RPC manufacturers, let’s check the important points:

  • Reputation. Talk to your friends and see what they recommend. If you never had any experience with Rotary Phase Converters, this is a good way to get some information.
  • Read reviews. Skip the good ones and go for the bad ones. This is how you know what problems people had and if they are insignificant or were quickly resolved by customer service, here is your winner.
  • UL-listed. Products that are checked by Underwriters Laboratories are usually the ones that could be trusted. There are good products out there that are not UL listed and you can try testing them out yoursel. But if you have limited resources and not so much time, go for the ones that were checked already by this organization.
  • Warranty. This is a key component to check before you decide whether to trust a company or not. Do they trust that their own products will not break prematurely? If they do, the warranty generally reflects that.

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