Compressor Electric Motor Prices: Complete Compressor vs Drive Motor Only

If the compressor's pump unit (block), tank and pressure switch are sound and only the drive motor has failed, replacing just the electric motor is enough instead of buying a complete compressor; what you pay for then is not a compressor but a single three-phase motor of the same power and speed. For example, a failed motor on a 5.5 kW, 4-pole belt-driven compressor is replaced directly by the DRG-132S-4 (1460 rpm, 10.7 A at 400 V). Compressor electric motor prices are driven less by the brand than by five technical features: power, number of poles, frame material and size, mounting arrangement and nameplate voltage.

Switching to a complete compressor only makes sense if the block is worn, the tank no longer inspires confidence because of corrosion or a pressure test, or the plant's air demand has outgrown the existing unit. Fitting a new motor without finding out why the old one burned simply moves the same fault to the new motor; read our article on what burns out motors on piston compressors for that, while screw machines are covered in the separate guide on screw compressor motor selection and replacement. Removing the motor, terminal connections and the direction-of-rotation check must be done by a qualified electrician. You can see suitable models and current prices among the 120 models on the Buy Electric Motors Online page.

Motor only or complete compressor? Decision table

The decision depends on the condition of the rest of the compressor, not the motor. The table below summarises the most common field situations and the usual decision:

The last row points to a common trap: on a compressor that runs non-stop because air consumption has grown, fitting a motor one size up does not solve the problem. As long as the amount of air the block delivers is unchanged, a stronger motor only means more current capacity; for more air, block and motor grow together.

How do you know the pump unit is sound?

Before deciding to replace only the motor, check the block and the tank. By removing the belt, turning the block by hand and a few simple observations you can tell most problems apart on site:

• Take the belt off and turn the block pulley by hand: it should turn smoothly, without catching, with similar resistance every revolution.
• Check the oil level and colour; metal particles or milky, cloudy oil point to internal wear or water ingress.
• Check for oil mist at the air outlet and excessive oil at the tank drain.
• Listen to the unloader valve: when the compressor stops it should really vent the discharge line, with a short hiss.
• Make sure the check valve does not let tank pressure leak back to the block side.
• Inspect the tank surface for blistering, rust marks at weld seams and the condition of the drain valve.
• Verify that the pressure switch and safety valve operate at the set pressure.

If only the motor-related items are faulty, replacing the motor is the right decision. If there is a defect in the block or tank, do not spend money on a new motor before that defect is fixed.

Which technical factors determine the price of a compressor motor?

When comparing quotations or models in the shop, knowing the factors behind the price lets you compare two motors that do the same job correctly. Without quoting figures, here are the factors themselves:

• Power (kW): The most decisive factor. Copper in the winding, the rotor and the frame length all grow with power.
• Number of poles: At the same power a 4-pole motor produces more torque than a 2-pole one and usually moves up to a larger frame. Most piston compressors run with a belt-driven 4-pole motor.
• Frame material: Cast iron and aluminium frames involve different material and workmanship at the same power.
• Frame size (standard / compact): In the compact series the same power fits in a frame one size smaller. The DRG-112M-4K delivers 5.5 kW in a 112M frame, while the standard DRG-132S-4 is in a 132S frame.
• Mounting: Compressors mostly use foot-mounted (B3) motors; a flange or foot-and-flange frame is a different product.
• Nameplate voltage: In the DRG range motors up to 3 kW are 230/400 V, 4 kW and above are 400/690 V. A compressor with a star-delta panel requires a 400/690 V motor.

The motor price is only one item in the total cost of a compressor; a complete unit also includes the block, tank, pressure switch, check valve, unloading system, belt guard and panel. That is why replacing the motor while the block is sound is the narrowest intervention that keeps the same air capacity.

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What information should you take from the old motor's nameplate?

The old motor's nameplate and a few measurements are enough to order the right motor. If the following five items are complete, the chance of receiving the wrong motor is very low:

On a motor with an unreadable nameplate, the shaft height (H, from shaft centre to the foot base) gives the IEC frame; all foot, shaft and flange dimensions of DRG motors are on the technical drawings page.

Can the old pulley be used on the new motor?

The pulley is the part most often overlooked in a motor replacement. Even with the same power and speed, the old pulley will not fit the new shaft if the shaft diameter differs. Shaft dimensions on DRG frames are:

The two 5.5 kW motors in the table are a good example: the compact DRG-112M-4K comes with a 28 mm shaft, the standard DRG-132S-4 with a 38 mm shaft. If your old motor is a 132S-frame 5.5 kW unit, your pulley has a 38 mm bore and will not fit the compact motor; in the opposite case the pulley must be re-bored or replaced with a bushed (taper lock) pulley. If you are thinking of changing the pulley diameter, check that you keep the compressor speed with the pulley and belt calculator.

Shaft length E matters too: the pulley hub must sit on the shaft over its full length. A pulley only half seated on a short shaft moves the belt force to the shaft end and strains the bearing.

Which DRG motor should you buy for a compressor?

The 4-pole models in the 3–11 kW range most often used on piston compressors are listed below. The exact power is the value on the block and old motor nameplates; use the table by matching it to the nameplate.

Example model data for a 7.5 kW workshop compressor:

• Model: DRG-132M-4
• Power: 7.5 kW
• Rated speed: 1460 rpm
• Frame: 132M · cast iron
• Voltage: 400/690 V (Δ/Y)
• Current 400 V: 14.3 A
• cos φ: 0.84
• Rated torque: 49.1 Nm
• Starting torque: 2 × Tn
• Starting current: 7.5 × In
• Shaft D × E: 38 × 80 mm
• Bearing: 6208-ZZ-C3

DRG Motor is a manufacturer, supplier and seller of electric motors; DRG MOTOR motors are guaranteed against material and manufacturing defects for 2 years from the delivery date (warranty certificate). Periodic instalment campaigns may be available with Halköde; for the current option message us on WhatsApp or see the payment options page. Shipping is by contracted freight and courier companies and is paid by the buyer; details are in the sales, delivery and return terms.

Motors in this power range

• DRG-100L2-4 – 3 kW – 1450 rpm – 100L cast iron
• DRG-112M-4 – 4 kW – 1450 rpm – 112M cast iron
• DRG-132S-4 – 5.5 kW – 1460 rpm – 132S cast iron
• DRG-132M-4 – 7.5 kW – 1460 rpm – 132M cast iron
• DRG-160M-4 – 11 kW – 1465 rpm – 160M cast iron

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Frequently Asked Questions

Should I replace the compressor motor or buy a complete compressor?

If the block turns smoothly by hand, does not pump oil and the tank and safety equipment are sound, replacing the motor alone is enough. If the block is worn, the tank is corroded or air demand exceeds the compressor, consider a complete compressor.

How many amps does a 5.5 kW compressor motor draw?

The DRG-132S-4 (4-pole, 1460 rpm) draws 10.7 A at 400 V and 11.2 A at 380 V. The compact DRG-112M-4K in a 112M frame draws the same current; the difference is the frame and shaft diameter.

What determines the price of a compressor motor?

Power, number of poles, frame material (cast iron / aluminium), frame size (standard / compact), mounting arrangement and nameplate voltage. Current prices are published on the product pages in the shop.

Will the old compressor pulley fit the new motor?

It will if the shaft diameter is the same. On a 4 kW 112M motor the shaft is 28 mm, on a 5.5 kW 132S motor 38 mm; if they differ, the pulley is re-bored or a bushed pulley is used.

Send us the nameplates of your compressor and old motor and we will select the right DRG model together: Phone +90 (542) 666 11 11, e-mail [email protected], contact page. For all models and current prices, see Buy Electric Motors Online.