|09-08-2012 04:24 PM|
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.
|09-08-2012 04:10 PM|
|09-08-2012 03:59 PM|
|09-08-2012 08:26 AM|
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,
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.
|08-27-2012 07:42 AM|
|deadbodyman||I've heard of this before ,how exactly does this work and how do you hook it all up? why 8 hp....|
|08-21-2012 10:57 AM|
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.
|08-19-2012 06:37 PM|
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.
|08-19-2012 05:18 PM|
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.