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Topic Review (Newest First)
07-05-2011 08:22 AM
oldred Even that rotary converter, while just fine for light start load equipment such as the lath in that video, would not work for a high load air compressor. That set-up would be a big improvement over a static converter since it would apparently allow full, or near full, power once the equipment is running while the static type would only allow about 2/3 of the rated power (which would destroy an air compressor motor ). The type of rotary converter that would be useful with a compressor would be the type that uses an idler motor in conjunction with a large capacitor bank for high start-up loads. Also since a compressor is automatic start the supply voltage MUST be wired so that power can not be turned on until the converter is running, it must be wired so that the converter has to be turned on first. If someone forgets to start the converter when using something like a lath, mill, saw, etc it's no big deal, just turn it off and start the converter, but automatic start equipment such as a compressor could be seriously damaged if it switched on unnoticed while the converter was not running. The motor would remain stalled and would most likely burn out in a couple of minutes.

This is what I was talking about when I said the compressor being discussed might be a good deal IF the buyer fully understands what he is getting into. While there are a couple of ways of making it work properly there are even more ways of seriously damaging it and use of the wrong converter, even the wrong type rotary converter, could result in a burned out motor.
07-04-2011 10:02 PM
richard stewart 3rd Hi
JohnnyK81

The link is to YouTube w/ a home made rotary phase converter
powering a lathe. It's pretty cool.
Rich

http://www.youtube.com/watch?v=BOPFdFgfH6E
07-04-2011 01:09 PM
JohnnyK81 I'm not familiar actually hooking up 3 phase motors with a slave motor, but if it's as I imagine.. It would totally not be worth it to me.
07-04-2011 12:05 PM
timothale
static converter

I have a static converter for the milling machine, a table top model with power feed 30 in travel I bought for $175 with collets, dial gage a few bits. a used converter was $ 100. I had a spare 3 ph motor t wired into the system. It will not run at full speed. turn on the system. start the slave motor, turn on the mill, turn off the slave, a rotory is nicer but more expensive. The motor is direct drive and a spline drive, not easy to change to a 1 phase.
07-04-2011 10:18 AM
oldred Honestly it is not that I am trying to just discourage the sale of this compressor it is just that I have seen people fall into this trap several times in the past. The OP seems to be disappointed that everyone did not congratulate him on finding a good deal but the fact is that compressor is not the "Steal" he seems to think it is. Is it a good deal? Probably, IF the buyer is aware of exactly what he is getting into and from the OP's comments, such as running on reduced power and using a converter in spite of having it explained why that won't work, it is obvious he does not fully understand what is involved. It's his money and his decision and he probably can make this thing work, others have, but it will most likely cost twice the selling price if he's lucky and that's for a 5 HP set-up. If it's 7 1/2 HP then the final cost gets to be questionable as to whether it actually is worth it or not. For a 5 HP two stage (I assume it is two stage) 80 gallon tank IR compressor $1000 is not a bad price if he can get it going PROPERLY for that amount but that is of course for a used compressor. Obviously his mind is made up and I wish him well, my comments were meant more for general discussion more than anything else since this subject has come up before.
07-04-2011 09:55 AM
JohnnyK81 I can't really add to what oldred said, but....

To sum it up.. It won't work.. It's not just that it will run at reduced power.. It just won't work!

BUT, (And also as oldred said) you can sell the motor, and buy a single phase motor.. But be warned nobody wants a 3 phase motor.

AND, as oldred was alluding to (Why did I even write this message, haha), buying the motor isn't the only cost here! If it's 5hp, you need to run 10 gauge wiring, which is pretty expensive.. If it's 7.5, you need bigger gauge, which, as you guessed, is far more expensive.

That doesn't mean much if the breaker is beside the compressor, but if it's not, be warned!
07-04-2011 09:22 AM
oldred
Quote:
Originally Posted by err
even running at less than optimal output, it is probably a cheaper solution than something else



i am getting it for 500 and its mint

im hard pressed to see a reason not too, and i can just sell the motor on my ebay store and swap for a different one, and have a banging ir 80 gallon thats mint, or get an inverter/converter

i wont be losing money, ill def be able to break even i think.

i am not saying you guys are wrong, im sayin just because i dont know much now doesnt mean its a problem for me


It seems your mind is made up already but you obviously are not listening to what you are being told! You CAN'T run that thing on a static converter so running it at reduced power like you mention will NOT work, it will for some light start load equipment like a lathe or mill but NOT a heavy start load air compressor! Besides even after starting a compressor motor reaches a much higher percentage of it's rated power before shut-down than most equipment so it will NOT operate properly on reduced power, if you don't burn out the converter then you will surely burn out the motor if you attempt to run it at reduced power on a compressor.


Quote:
Originally Posted by err
or get an inverter/converter

An inverter converts DC to AC is of absolutely no use to convert three phase AC power to single phase AC and a rotary converter will cost more than a new motor



Quote:
Originally Posted by err
i buy and sell **** all day long, its my job, if it doesnt work out for me nbd

If you are getting it for $500 then you will probably be able to buy a new motor and come out ok, just bear in mind that a three phase motor will bring only a small part of what a similar power single phase motor will sell for. You will also need an electrician to install the new motor and switch so that it is wired correctly. A new motor is going to be your only real option.

You still have not mentioned what the HP rating is and if it is more than 5 HP you may have more serious problems than just converting three phase to single phase. A 7 1/2 HP single phase motor is going to be very expensive to buy and to wire for and if it is more HP than that then single phase is just not practical. You can not run a lesser HP motor without also reducing the load by slowing down the pump with a pulley change but when you do that you MUST do it properly and even then your performance will be reduced accordingly.
07-04-2011 08:32 AM
err even running at less than optimal output, it is probably a cheaper solution than something else

it runs 24 cfm at full power

i am getting it for 500 and its mint

im hard pressed to see a reason not too, and i can just sell the motor on my ebay store and swap for a different one, and have a banging ir 80 gallon thats mint, or get an inverter/converter

i wont be losing money, ill def be able to break even i think.

i am not saying you guys are wrong, im sayin just because i dont know much now doesnt mean its a problem for me

i buy and sell **** all day long, its my job, if it doesnt work out for me nbd
07-04-2011 08:25 AM
oldred
Quote:
Originally Posted by timothale
A neighbor has 3 lathes in his shop, He has offered to sell me the big one,, 18, in by 8 ft bed with a 3 phase motor.

Lathes of 5 HP or less are much easier to run with a phase converter than an air compressor and in fact work just fine on the much cheaper/simpler static converters. Since a lathe is a light load start-up machine and is started only once during operation the static converters are an ideal solution to the three phase/single phase problem. The reduction in power that results from using a static converter is usually no problem on a machine like a lathe or mill and is a very simple and economical way of running these machines.


BTW, that's a good size lathe and would be VERY useful! I have a 14x40 (3 HP three phase on a static converter) and I still find myself needing more swing. With the gap removed from the bed I have a 21" swing but it is limited in length by the length of the gap and of course rigidity is also compromised when the gap is removed, you would have none of those problems with that big swing and bed length!
07-04-2011 07:44 AM
timothale
costs vs usage

My step son works for an oil dist-gas station Co. They replaced a big compressor in one of their locations so he brought the old one to the house. I has a 3 phase 8 hp 440 v motor, I haven't found a single phase 220 V motor yet that would handle it. . A rotary converter to run it would cost $ 2 k and require $ 400 in wiring. A neighbor has 3 lathes in his shop, He has offered to sell me the big one,, 18, in by 8 ft bed with a 3 phase motor.I still haven't decided if I want to get both the air comp and lathe set up in the 4 car garage at the house. .. We put in a 3 phase irrigation system on one of the farms last year. the power company charged us $ 4 k to install new transformers. a step son is an elect contractor and our cost with me helping was $ 1500 for the rest of the elect panel, breakers and wiring, WE have a $ 1000 a month basic electrical charge even if we don't use any power. the power companies don't like large loads being added in a residential area, It can cause problems with old transformers running 3 or 4 houses. interference from start up loads and HF tig welders etc.
07-04-2011 06:06 AM
oldred
Quote:
Originally Posted by err
it looks like the motor says it can be run at 2 different voltages

i will probably get it and if it doesnt work for me, sell it, or use it at the shop

thanks for the info

Sure it can be run at two different voltages but so can a lot of single phase motors, that has absolutely nothing to do with what we have been telling you! I know what you are looking at on that motor data plate but 240 volts single phase and 240 volts three phase are NOT the same thing! You can't run that thing on residential power no matter what voltage the motor is wired for, it's three phase and you don't have three phase power available. It's your money so do as you like but you have been warned it is going to cost a bundle to get that thing to run at home.
07-04-2011 04:59 AM
err it looks like the motor says it can be run at 2 different voltages

i will probably get it and if it doesnt work for me, sell it, or use it at the shop

thanks for the info
07-03-2011 07:19 PM
richard stewart 3rd oldred
Thank you for the information. I enjoy reading what you post, as they are always well written & informative.
Thanks again
Rich
07-03-2011 06:55 PM
oldred
Quote:
Originally Posted by richard stewart 3rd
Hi
Have you thought about how your going to run the compressor?
Anyway you'll need a phase converter of some sort, either home made or bought, they cost about $200. & up.
Rich

For $200 you will get a static converter that will only allow the motor to produce 2/3 of the power plus they don't work well at all with the frequent high torque start loads of a compressor. It is possible to build a rotary converter of sorts using a static converter and a three phase "idler" motor in addition to the compressor motor, this would be similar to a true rotary converter but probably not suitable for the high start loads of a compressor-plus combining the cost of the converter with the idler motor will cost more than a replacement single phase motor. If that three phase compressor is 5 HP then it will take a rotary converter in the $400 to $600 range to operate and if it is 7 1/2 HP he could be looking at upwards of $1000 for a converter that would handle the job, if it is 10 HP, well just forget it. Basically some three phase equipment runs just fine on a phase converter but compressors are usually a PITA to get to operate properly using a converter besides a replacement single phase compressor duty motor is MUCH simpler and in all likelihood a lot cheaper than a phase converter that would be suitable for the job, one of those little $200 static converters will not get the job done for a compressor even if it is the right power rating.
07-03-2011 06:49 PM
JohnnyK81 Yup.. I looked at them myself.. However, if it's cheap ENOUGH, and you can probably find a used motor on Kijiji or something (What is it, 7.5hp or something?) then I say go for it!
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