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Old 08-19-2012, 04:18 PM
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Should I buy a new compressor?

Wanted to get everyones opinion which I should do. I have a 80 gal 5hp compressor at home that I'm thinking about using. It is an older compressor, probably early 70's, manufacturer is Wayne. It had a 3 phase motor on it already so that won't work for my home electrical. Here is my questioning should I buy a new single phase motor for the compressor for around $400 and have it wired or get a new compressor? As far as I know the compressor was in working order and the oil and everything else looked good on the compressor. I plan on using it for some bodywork at home, using a d/a, maybe some priming, possible painting. I also have a extra 60 gallon air tank that I'll pipe with the compressor. Money wise it would be cheaper to use what I have I didn't have to pay for the compressor or tank, obviously I'll be spending $1,000 + for a new quality compressor.

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Old 08-19-2012, 05:37 PM
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bigger motor ?

My experience is that when you switch to a single phase motor you will need more HP like go up to a 7 single phase. and using a bigger tank can over heat the pump and motor, they are rated for a duty cycle. and need a rest, A single phase rotory converter to power the 3 phase would probably cost more than a new compressor, I have a capacitator converter on my Milling machine and end up with 2/3 of the rater power, It wont run it full speed full, load.
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Old 08-21-2012, 09:57 AM
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I suggest you find a used 3phase 8+ hp electric motor and use it for a converter.

Spin the 8 hp with a drill motor to start it spinning, the rest is all magic and your 5 hp will run fine.
You should be able to accomplish this for less than $100.

Duty rating has nothing to do with tank size, it is how long the motor runs as compared to how long it rests in a given time period.
Use of air tools or paint guns may use enough air the compressor will not be able to get ahead and shut off, that is a 100% duty demand.

example of duty cycle:
8 minutes on, 2 minutes off = 80% duty cycle
10 minutes on, 0 minutes off = 100% duty cycle

To all the electrical experts, lets not get into a pissing contest about phase converting and efficiency. For the large majority of users a simple converter as suggested works in 1000's of applications daily and will work fine for the OP.
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Old 08-27-2012, 06:42 AM
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I've heard of this before ,how exactly does this work and how do you hook it all up? why 8 hp....
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Old 09-08-2012, 07:26 AM
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Simply using another 3 phase motor for a phase converter won't work very well if at all, especially for a high start load like a compressor motor! Three phase converters using another motor are very common and work quite well but they must be paired with a large capacitor bank to work properly, these converters can be quite expensive (one big enough for 7 HP will be around $800 to $1,000) so just to run one compressor it's probably not a good option. Trying to run a high start load by using just a second three phase motor is usually just an exercise in futility and at worst could smoke the compressor motor!


Here's a schematic for a common design,

Figure 1

The capacitors can be eliminated for a simpler design but they only work for light start loads and would be very problematical for something like a compressor which is almost always a very high start load situation.
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Old 09-08-2012, 02:59 PM
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Quote:
Originally Posted by oldred View Post
Simply using another 3 phase motor for a phase converter won't work very well if at all, especially for a high start load like a compressor motor! Three phase converters using another motor are very common and work quite well but they must be paired with a large capacitor bank to work properly, these converters can be quite expensive (one big enough for 7 HP will be around $800 to $1,000) so just to run one compressor it's probably not a good option. Trying to run a high start load by using just a second three phase motor is usually just an exercise in futility and at worst could smoke the compressor motor!


Here's a schematic for a common design,

Figure 1

The capacitors can be eliminated for a simpler design but they only work for light start loads and would be very problematical for something like a compressor which is almost always a very high start load situation.
Aren't the old Wayne air compressors a mechanical unloader type and do not require high starting currernt
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Old 09-08-2012, 03:10 PM
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I've heard of this before ,how exactly does this work and how do you hook it all up? why 8 hp....
Hey DBM, set down the 6 pack, get up off your lazy *** and go clean out your mailbox! How in the hell can I send you mail when it is stuffed full?

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Old 09-08-2012, 03:24 PM
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Originally Posted by Old Fool View Post
Aren't the old Wayne air compressors a mechanical unloader type and do not require high starting currernt


Almost all air compressors (except for the really small "tire pumper" units) have an unloader system otherwise the load would be too high even with a capacitor start, some are mechanical and some are a simple bleed-off system connected to the switch but they all serve the same purpose. An unloaded compressor is still a huge load at start-up due to the mass and inertia encountered when the motor suddenly kicks on and attempts to start all that stationary weight spinning. A simple unassisted motor type phase converter could work for something like a table or band saw or other very light start load if it's sized properly but those capacitor banks are needed for most applications.
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