Compressor Conversion Selection Guide

Compressor Conversion Selection Guide: Convert Your 3 Phase Air Compressor Motor to 1 Phase

Changing out the Three Phase Electric Motor on your Air Compressor can in many cases, provide the simplest, most cost effective solution to operation in a single phase environment.

We offer several options for operating three phase machinery on single phase.

The most common is the rotary phase converter. These are a simple to install, reliable method of supplying three phase power to machinery when only a single phase source is available. Due to the high demand during start up of Air Compressors and at full load, the phase converter to be used must be sized very conservatively (we call this a Hard-Load classification).

For smaller loads, Variable Speed Motor drives (VFDs) can serve as an excellent choice. They provide high reliability, high efficiency and integrated motor protection in a compact, low maintenance package. The downside is that they are more complex to install than other options of phase conversion and tend to lose their cost-advantage above 5 HP.

In the case of the conversion of Three Phase Air Compressors to operating where only single phase power is available, many users main goal is to find a reliable solution at relatively low cost. In many instances, second-hand three phase air compressors can be had at a significant savings to their single phase counterpart but when considering the cost of the relatively large Rotary Phase Converter or VFD needed for their proper operation, this advantage can be lost altogether.

Replacing a Start Capacitor in a Single Phase Motor

Which one's best for me?

Here's a simple comparison of factors. 3 stars being the most desirable for each category

★ = Less Desirable
★★ = Moderately Desirable
★★★ = Very Desirable

What you'll need to know

• What HP are you looking for? This guide is focused on Compressors requiring 1/2 HPup to 15 HP.
• What RPM does your existing motor run at?
• What is the Frame Size of your existing motor?
• What Voltage do you plan on using
• Do you need an Open Drip-Proof motor or a Totally Enclosed Externally Fan Cooled motor (referred to as ODP or TEFC)

What parts will be required?

Single Phase Motor: In many cases, this is all you will need.

Single Phase Magnetic Motor Starter: If the amperage of the single phase replacement motor is significantly higher than the original three phase motor or the control voltage needs to be changed, you may need a motor starter.

Specification Details

HP

You should always choose a motor with atleast the same HP rating as the original 3 phase motor for the replacement single phase motor. The only exception might be where a lower output rate of an air may be desired to reduce power usage or increase air pump wear life. In this case a smaller HP motor may be selected but must be used with an increased belt ratio. This is done to slow down the pump in compensation of the reduction in HP. A smaller motor pulley would be selected. As a general rule of thumb, by selecting a pulley with half of the diameter, you may reduce the required HP by half and so on. This would also cut air output by half.

SPECIAL NOTE: Some pumps may require all of the original HP and RPM to achieve a desired air pressure, and may not be reduced in RPM as the example above indicates. Use this recommendation as a general guide only. Exact performance of a given pump at different RPMs and HP ratings may be obtained from the original compressor pump head manufacturer.

RPM

Most 3 phase compressors operate on either 1800 RPM (4 pole motors) or 3600 RPM (2 pole motors). Many motors will show RPM accounting for "full load slip". You might see 1745 or 1725 RPM numbers indicated. This is due to the differing performance at full load each motor will exhibit. For simplicity, we will only show 1800 or 3600 RPM here. The actual variation in full load RPM from model to model will not have any affect on Air Compressors as long as the appropriate pole count is used; again, 1800 RPM for 4 pole motors or 3600 RPM for 2 pole motors.

Voltage

Most Single Phase motors are offered in one or both of two common voltages 115, 230 or 115/230. Most single phase suppliedin the US is either 120 volts or 240 volts. 220 volts is a commonly referenced voltage in the electrical trade but in actuality has not been in use much since the 1950s. When referring to 220 volts today, the reality is most commonly a 240 volt supply. Motors which are labeled 115 volts will operate correctly on 120 volts. Likewise, motors labeled 230 volts will operate correctly when supplied 240 volts. 115 and 230 are considered "nominal" voltages and motors will typically tolerate a range of up to 10% above or below these numbers.

If your Compressor was originally designed for a voltage other than 115 or 230, you may still convert to using a 115 or 230 volt single phase motor. Care must be taken in determining if any controls are present that may require a different voltage. A good example of this would be the conversion of smaller Rotary Screw compressor originally equipped with a 480 volt three phase motor. With a slightly more advanced control and monitoring system, there would usually be a control transformer that may need to be re-configured for the lower voltage on the input side or replaced entirely. Many reciprocating air compressors use a mechanical pressure switch or a simple magnetic motor starter to start and stop the motor. In the later case, the coil voltage of the magnetic starter may need to be changed to match the desired supply voltage.

Frame Size

Most air compressor motors will carry a NEMA standard frame number. This number describes the most important physical dimensions based on a standard set of measurements. The two most important dimensions that should be closely compared are the Shaft Diameter and Mounting Base Bolt Pattern.

Even if you do not have the original frame number, these dimensions may be compared to determine suitability.

Simply choosing a single phase replacement motor with the same frame number from your 3 phase motor is usually an adequate practice. In some cases, it may be beneficial to look at an actual drawing of the single phase replacement motor to verify that particularly the junction box and the tail end of the motor would not interfere with other attached components on the compressor. Neither of these are part of the NEMA standard of frame sizes.

The chart below describes NEMA "T" frame dimensions for common single phase motor sizes.

Drawings represent standard TEFC general purpose motors. Dimensions are for reference only. Contact your local Baldor office for "C" Dimensions.

Enclosure Rating

Motors are offered with several common types of enclosures (Shell Designs). These are ODP, TEFC and TENV.

ODP (Open, Drip Proof) motors, are fully enclosed but use vents in the ends and bottom for ventilation. These are commonly used in somewhat low dust environments with low risk of water intrusion. For environments which are more prone to airborne dust, debris or exposure to the elements, rain etc, TEFC and TENV motors are preferred. ODP motors are generally the least expensive option.

TEFC (Totally Enclosed Externally Fan Cooled) motors use an external fan to force air over the outside of the motor body to provide cooling. The main shaft will commonly have a "Slinger" seal as sometimes will the fan end of the shaft. The shell will have no entry points for non-pressurized particulate or liquid intrusion.

TENV (Totally Enclosed Non Ventilated) motors use an internal fan with a mostly sealed shell (similar to TEFC) but differ in that they rely on convection air movement over their exterior surface for cooling. Their is no external fan.

It is important to note that neither TEFC or TENV motors are water "Proof" they may not be submerged nor will the seals stand up to pressurized water spray.

Amperage and Conversion

A note on amperage and conversion of three phase machines: When converting any three phase machine to use a Single Phase motor, if the HP remains the same, the amperage will increase.

This is caused by two primary factors and has nothing to do with efficiency. It is due to the way circuit amperage is measured on any one of the lines at any time. What was once evenly divided over three lines (and offset in time) has to be re-distributed over only two lines and therefore, increases per line. The second factor is that single phase motors on average, operate slightly less efficiently than three phase motors. The actual difference in power consumption overall (kWh) will usually be negligible.

Magnetic Motor Starters

If you've determined that you will need a replacement magnetic motor starter either because the amperage will be higher than the original one or that the control voltage of the original on will no-longer work with the voltage you plan on using, we've provided a selection of Single Phase magnetic motor starters offered in both 120 and 240 control / operational voltages. These would be wired to your pressure switch to control the starting and stopping of your motor.

We recommend the use of a starter with integrated motor overload protection as a standard feature. These are adjustable and will need to be set for the rated amperage of the replacement Single Phase motor.

ODP Single Phase Motors, 60 Hz

HP				RPM	Frame	Voltage	Integrated Overload Protection
0.50	-	.5036OT1B48-S	E100184.00	3600	48	115/230	No
0.50	-	.5036OT1BW56-S	-	3600	W56	115/230	No
0.50	-	.5018OT1B48-S	-	1800	48	115/230	No
0.50	-	.5018OT1BW56-S	-	1800	56	115/230	No
0.50	-	-	100045.00	1800	S56	115/208-230	Manual
0.75	-	-	101433.00	1800	48	115/208-230	Automatic
0.75	-	.7536OT1B56C-S	E100340.00	3600	56	115/230	No
0.75	-	.7518OT1B56-S	-	1800	56	115/230	No
1.00	-	-	120044.00	1800	143T	115/208-230	No
1.00	L1309A	-	-	3600	56	115/230	Automatic
1.00	-	00118OT1B56-S	E113027.00	1800	56/56H	115/230	No
1.00	L1310M	-	-	1800	56H	115/230	Manual
1.00	-	00136OS1BCD56-S	-	3600	56	115/208-230	Manual
1.50	-	00156OS1BCD56-S	-	3600	56	115/208-230	Manual
1.50	L1313		-	3600	143T	115/230	No
1.50	L1313T	-	120107.00	3600	143T	115/230	No
1.50	-	00158OT1B56-S	-	1800	56/56H	115/230	No
1.50	L1319T	-	120042.00	1800	145T	115/230	No
1.50	-	-	110161.00	3600	56	115/230	Manual
2.00	-	00218OT1B56-S	-	3600	56/56H	115/230	No
2.00	L1322T	-	-	1800	145T	115/208-230	No
2.00	-	-	120106.00	3600	145T	115/208-230	No
2.00	L1405T	-	131515.00	1800	182T	115/230	No
2.00	-	-	131515.00	1800	184/184T	115/230	No
2.00	-	00236OS1BCD56-S	-	3600	56	115/208-230	Manual
2.00	-	-	113608.00	1800	56H	115/208-230	Automatic
2.00	-	-	116601.00	1800	56H	277	Automatic
2.00	-	-	113632.00	3600	56	115/208-230	Manual
2.00	-	-	120879.00	1800	145T	115/208-230	Manual
2.00	-	-	110232.00	3600	56	115/230	Manual
3.00	-	-	110222.00	3600	56Y	230	Manual
3.00	-	00336OS1CCD56-S	-	3600	56H	115/208-230	Manual
3.00	-	00318OS1C184T	-	1800	184T	230	No
3.00	L1406T	00336OS1D182T	131636.00	3600	182T	115/230	No
3.00	L1408T	-	131534.00	1800	184T	115/230	No
3.00	-	00318OS1C184T	-	1800	184T	230	No
3.00	-	00336OS1D182T	-	3600	182T	230	No
5.00	L1409T	00536OS1D184T	-	3600	184T	230	No
5.00	L1410T	-	-	1800	184T	230	No
5.00	L1508T	-	-	1800	213T	230	No
5.00	-	00518OS1CCD184T	-	1800	184T	208-230	No
5.00	-	00536OS1DCD56H-S	116523.00	3600	56/56H	208-230	Manual
5.00	-	-	120554.00	3600	145T	230	Manual
7.50	-	00736OS1C184T	-	3600	184T	208-460	No
7.50	L1509T	-	-	3600	213T	230	No
7.50	L1510T	-	140155.00	1800	215T	230	No
7.50	-	-	140680.00	3600	213T	208-230	No
10.00	-	-	140681.00	3600	215T	208-230	No
10.00	L1511T	-	-	3600	215T	230	No
10.00	L1512T	-	140311.00	1800	215T	230	No

TEFC/TENV Single Phase Motors, 60 Hz

HP				RPM	Frame	Voltage	Integrated Overload Protection
0.50	L3408	-	102020.00	3600	48	115/230	No
0.50	L3503	.5036ES1BB56	-	3600	56	115/230	No
0.50	L3409	-	100956.00	1800	48	115/230	No
0.50	L3504	.5018ES1BW56-S	-	1800	56	115/230	No
0.50	-	-	102906.00	3600	S56	115/208-230	No
0.50	-	-	102905.00	1800	S56	115/208-230	No
0.75	L3506	.7536ES1B56-S	-	3600	56	115/230	No
0.75	L3507	.7518ES1B56-S	-	1800	56	115/230	No
0.75	-	-	110017.00	1800	56	115/208-230	Automatic
1.00	L3509	00136ES1B56-S	-	3600	56/56H	115/230	No
1.00	-	-	110142.00	3600	56/56H	115/208-230	Manual
1.00	L3510	-	-	1800	56/56H	115/230	No
1.00	-	00118ES1RFD56-S	110023.00	1800	56/56H	115/230	Manual
1.00	L3510T	-	-	1800	143T	115/230	No
1.00	-	00118ES1RFD143T	120008.00	1800	143T	115/230	Manual
1.50	L3513	00156ES1B56-S	110094.00	3600	56/56H	115/230	No
1.50	L3513T	-	-	3600	143T	115/230	No
1.50	-	-	113333.00	1800	56/56H	115/230	Manual
1.50	L3514	00158ES1B56-S	-	1800	56/56H	115/230	No
1.50	L3514T	-	120026.00	1800	145/145T	115/230	No
1.50	-	00158ES1RFD145T	-	1800	145/145T	115/230	Manual
1.50	-	00152ES1E182T	-	1200	182T	208-230/460	No
2.00	-	00236ES1E145T	-	3600	G145T	208-230/460	No
2.00	L3515	00236ES1B56-S	110352.00	3600	56/56H,56T	115/230	No
2.00	L3515T	-	120036.00	3600	145T	115/230	No
2.00	L3516T	00218ES1RFD145T	121507.00	1800	145T	115/230	No
2.00	-	00218ES1RFD56H-S	-	1800	56	115/230	Manual
2.00	-	00218ES1RFD182T	-	1800	W182/4T	115/230	Manual
2.00	L3605T	-	131509.00	1800	182T	115/230	No
3.00	L3606T	-	131637.00	3600	182T	115/230	No
3.00	L3609T	00318ES1E184T	131533.00	1800	184T	115/230	No
3.00	-	00336ES1E145T	-	3600	G145T	208-230/460	No
3.00	-	-	116705.00	3600	56H	230	Manual
5.00	-	-	132042.00	3600	184T	230	Manual
5.00	-	00536ES1E184T	-	3600	184T	208-230/460	No
5.00	L3612TM	-	-	1800	184T	230	No
5.00	L3708T	-	-	1800	213T	230	No
5.00	-	-	131856.00	1800	184T	208-230	Manual
5.00	-	00518ES1E184T	-	1800	184T	208-230/460	No
5.00	-	00518ES1E215TZ	-	1800	215TZ	208-230/460	No
5.00	-	00518ES1DFD215T	-	1800	W213/5T	230	Manual
5.00	-	00518ES1DFD215Z	-	1800	W213/5TZ	230	Manual
5.00	L3708	-	-	1800	215	230	No
7.50	L3709T	-	-	3600	213T	230	No
7.50	-	00736ES1E213T	140684.00	3600	213T	208-230/460	No
7.50	-	00718ES1E215T	-	1800	215T	208-230/460	No
7.50	L3710T	-	140120.00	1800	215T	230	No
10.00	-	-	140685.00	3600	213T	208-230	No
10.00	L3711T	-	-	3600	215T	230	No
10.00	-	01036ES1E215T	-	3600	215T	208-230/460	No
10.00	-	01018ES1E215T	-	1800	215T	208-230/460	No
10.00	L3712T	-	-	1800	215T	230	No
10.00	-	-	140706.00	1800	215T	230	Manual
12.50	-	01218ES1E215T	-	1800	215T	208-230/460	No
15.00	L1177T	-	-	1800	254T	230	No
15.00	L3912T	-	-	1800	256T	208-230	No

Magnetic Motor Starter Selection

Alternate Conversion Options (Rotary & VFDs)