Well, you're not alone. Welcome to the "Internet phase converter jungle".
The first item to consider is the NEMA (National Electrical Manufacturers Association) HP rating of the converter. Converters manufactured in North America (both Canada and USA products), can be referenced in terms of NEMA frame sizes.
As a general example, consider a PhaseMAXX - 5T rotary converter. The 5T is supplied in a 215T frame (of which the NEMA equivalent is 10 HP), hence, it will generally be referred to as a "10 HP converter".
As you can see, while the 5T is commonly referred to as a 10 HP converter, the model number will not necessarily reflect the converter HP. So ask the converter supplier to provide the converter's NEMA HP rating.
Once you have the HP rating of the suggested converter for your application, check with a few other manufacturers for their converter recommendation and get the HP rating of these converters also.
If each of the various converter manufacturers you discussed the application with all
suggest the same HP rating for your application, then the rest is easy.
Having said all of the above, what if each of two converter manufacturers suggest a different HP requirement for your application? This is quite often where the confusion begins.
You need only be aware that certain loads require different amounts of starting torque to be brought up to their rated speed. When an electric motor driving a particular load is connected to a phase converter that is undersized, the motor's overload relay will trip before the motor has reached its rated speed.
Some converter manufacturers may fail to recognize the speed/torque characteristic of the motor and load for your specific application, and subsequently undersize the converter.. A few other factors also influence converter sizing. Each of these additional items to be considered by the converter manufacturer will also affect their suggestion for a particular phase converter HP rating.
When the converter HP ratings suggested by various converter manufacturers differ, then you must simply decide which converter manufacturer seems to have the best expertise on the subject. Having then selected the converter manufacturer you believe to have provided the best information, you may want to get pricing from other converter suppliers for the same HP rated converter, and consider the six (6) comparison points above.
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