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20 & 30 hp 1ph motors

howard d

Cast Iron
Joined
May 6, 2003
Location
Clinton, TN, USA
A friend who works at a salvage yard called and said he had gotten in new a 20hp and a 30hp single phase motor. I figured he had looked at the SF. Went to look and sure enough they are single phase motors. Each are 240v synchronous motors made by Precision Power Corp, Bradenton, Fla. The 20 is 3600 rpm, 67FLA, Fr 365Y, Model ME 210020, and the 30 is 1800 rpm, 98 FLA, Fr 326Y, Model MI 493630. They can be had for under $300.00 ea. If anyone is interested, contact me.

What would these motors be used for?
 
Howard, seems we touched on the topic of big single phase motors here a year or two ago. IIRC there used to be even industrial areas of the US that had only single phase.

The 30hp being 1800 would make an awesome air compressor motor but at 97FLA x 220v = 21kw so 21x .06= $1.26 per hr here. At 4hrs a day, 7 days a week = $141. a month roughly. Check my math.
 
These are synchronous motors, how do they start? I've only worked with a few synchronus, all fractional HP, and they all needed a second motor to bring them up to synchronus speed. Make sure you know this before purchase.

Ed
 
Yes, I know.. :nutter:I'm 8 years behind the ball but I did not see anyone post saying they were interested. Is there a snowball's chance that these motors are available still? I'm looking to get one but not pay retail ($2k-$4k):wall:
 
Synchronous motors start like squirrel cage motors, connect the field to a resistor start it, apply DC to the field at correct speed, apply load



Generally they ARE squirrel cage in part..... they have induction type bars on the poles to act as "dampers". Those will also generally start the motor as induction.
 
Yes, I know.. :nutter:I'm 8 years behind the ball but I did not see anyone post saying they were interested. Is there a snowball's chance that these motors are available still? I'm looking to get one but not pay retail ($2k-$4k):wall:

Talk about being late for the party!! The OP hasn't been back in over a year.
 
Howard, seems we touched on the topic of big single phase motors here a year or two ago. IIRC there used to be even industrial areas of the US that had only single phase.

The 30hp being 1800 would make an awesome air compressor motor but at 97FLA x 220v = 21kw so 21x .06= $1.26 per hr here. At 4hrs a day, 7 days a week = $141. a month roughly. Check my math.

This math is not quite correct. The only time an Air Compressor motor will draw full load amps is as it nears shut off. The pressure in the tank will have to be overcome by the compressor so t will start at a lower pressure, HP requirement will slowly increase as the pressure in the tank increases. Plus I doubt that a compressor designed to be used with a 30HP motor will need 30HP and that it is that big to help start. Therefore the motor will not use it's max amperage for all the time it's running. Multiplying FLA X Volts is not correct for motors, they are inductive, that calculation is for resistive load. Though it's somewhat a good reference if having a 30HP compressor it will be the cost. I am assuming you want to compare it to 3 phase in that the FLA will be much lower which is true but 3 phase has 3 wires, if using your calculation the KW must be multiplied by 1.732. If intended to use with some sort of converter such as an RPC then the RPC load must be included. The main advantage is a 3 phase motor with an RPC is they are lot cheaper for the motors, I would expect a 30HP single phase motor is quite expensive. In addition the 30HP single phase motor is much less to use than it's 3 phase alternative if the power connected to the building is not thru a Demand meter! All 3 phase meters I've seen are the Demand type.
 
giphy.webp
 
This math is not quite correct. The only time an Air Compressor motor will draw full load amps is as it nears shut off.

Not strictly true. As the back pressure rises, more of the air displaced by the piston will simply be pushed into the headspace and passages and will expand as the piston drops. When the back pressure equals the maximum pressure the compressor can generate, it is in effect compressing and releasing a spring and the only power required is for frictional, heat, and other losses. Of course, in a properly designed system, the compressor will not go to that extreme, but as it approaches its maximum pressure, the power requirement will peak, then diminish as the amount of bounce back increases. There always be some. A reason for multiple stages is to reduce that effect.

Bill
 
Though I'll be beating the ghost of this dead horse!!
I would think that a compressor requiring 20HP will be at least 4 cylinder. The amount of spring back will be for a very short duration as most compressors limit the volume above the piston at TDC. If not the spring or reed valves will be delayed in opening lowering the volume of air being pumped. Also offsetting the spring back will be the next cylinder advancing to TDC. Another indication I seen in a place I worked was as the pressure in the tank came near the shut off pressure the incandescent light bulb started to flicker, not much but just noticeable. Not to mention the sound.
 
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