Is getting involved with 3-Phase Compressor worth it?

[wnstwolf]

Hi guys,
I know some of you have performed the needed conversions from 3-phase equipment to single phase to use at home but was it worth it?
I am looking for a new compressor and due to this one being 3-phase I can get it for a steal. $250 80 gallon 7hp but will need the conversion or replace motor. Any thoughts:

 

[koditten]

A replacement motor would be the way I would go. Install a single phase motor and you have a nice compressor. Offer them 150 bucks. There are not a lot of buyers for 3ph. You got them by the short hairs.

 

[Bob C]

Good luck with that! Before you jump on that deal, you better size a replacement motor correctly and then take a heart pill when you hear the price of the new electric motor!

 

[koditten]

That has a 3600 rpm motor. Those aren't too bad price wise. If it was 1750 motor, I would walk away.

 

[ny1]

A good 1750 rpm 1 phase motor is about 800.00 dollars. I've never priced a 3600 rpm one. You could try searching for a used one but they are kind of hit and miss as far as finding one. Keep in mind you might need a starter also.

 

[Falcon67]

7 HP gets into the pretty expensive VFD range. Just a quick search shows a 7.5HP Mitsubishi at around $700. 5 HP 220V single phase motor about the same. So you'd likely need like a 10HP static or motor/idler setup. STILL - even at total cost under $1000, that should be a decent buy for the whole setup. 7HP 3 phase must be a humper of a compressor. Searched on a 7HP IR and found a 230V 3 phase two stage for $2000.

 

[snorky18]

In general, for a single piece of equipment, I don't personally think used 3 phase is worth dealing with in many cases.

The exceptions would be: your POCO provides it for free and you know how to work with it, or you already have a single phase replacement motor for the equipment (b/c that is a big ticket item). Or you already have a phase converter.

Now if you're doing a shop full of equipment, that may be a different story

 

[LutzTD]

taht sure looks like a nice compressor. Like the others have said if you plan a shop full of 3ph equip Id jump on it. Could you get away with a smaller motor? , maybe get a smaller motor and redo the pully sizes?

 

[wnstwolf]

Quick search at Grainger has the 7hp single phase 220 unit and starter at $850 for one that matches the shaft size/base layout. $850 and $250 for the purchase has me walking away. Grainger does have a even free at this stage is no "deal" Seller failed to mention the 30phase issue until I got out there. he is moving and the rate he is going Free is almost the only way he will get rid of it..

grainger has a power converter but I am not sure the current motor on the compressor can be used with these? Any input would be appreciated

 

[LutzTD]

Quick search at Grainger has the 7hp single phase 220 unit and starter at $850 for one that matches the shaft size/base layout. $850 and $250 for the purchase has me walking away. Grainger does have a even free at this stage is no "deal" Seller failed to mention the 30phase issue until I got out there. he is moving and the rate he is going Free is almost the only way he will get rid of it..

grainger has a power converter but I am not sure the current motor on the compressor can be used with these? Any input would be appreciated

thats a static converter, I would stay away from those. Get one with an idler motor (rotary phase converter). there are some nice ones on ebay. they also pop up on craigs every now and then pretty cheap, just stick with the rotary phase converters.

 

[Falcon67]

That's why I'd put a $700 VFD on it - it'll work right and you have way more control over the motor with a VFD than a static converter. You'd have to read the fine print on the static to see if it's a 100% conversion from single to 3 phase or if you have to de-rate the thing - meaning, buy bigger than the name plate rating. You'd still have one hell of a compressor for a good price.

 

[larry_g]

Check out the pump head model number. A lot of pumps are rated for different horsepower's at different speeds. So it is entirely possible to drive the pump at a bit slower speed with a 5hp motor which will be quite a bit cheaper than a 7hp single phase. Just be aware of the minimum speed of the pump.

lg
no neat sig line

 

[wnstwolf]

Thanks Guys I will see if I can get a snap shot of the pump info and post it.

 

[930dreamer]

If it was rated for a 5hp-3 phase motor, do a motor swap and build a 10 hp rotary phase converter. Better yet add the 7 hp motor from the compressor to the converter and have a 17 hp converter.

 

[Zengineer]

Add a VFD, $200 and you are good to go.

 

[EOC_Jason]

You should almost certainly be able to run that pump with a 5HP at a lower RPM (changing the pulley on the motor)... Once you find the pump model (or even the entire unit's model), look on the IR website or a catalog to see if there is a 5HP with the same pump, then you can get the exact pulley and wallah!

Wish that was near me, my friend would love to have that as a backup compressor for his machine shop for only $250...

 

[maxspeed96ct]

Add a VFD, $200 and you are good to go.

Give us some more details, from what Ive heard VFD controller cost about $1000 and up

 

[930dreamer]

X2 on 7 hp vfd being expensive, I'm seeing the price from $700- $1400. I'll bet the motor is 7.5 hp.

 

[Diggers4life]

Damn. If you were closer, I'd make you a hell of a deal on a Dayton single phase 10hp motor. I've got an extra one sitting around waiting to go on a compressor... Shipping would be a ***** to NY though. It's pretty heavy.

 

[Norcal]

Quick search at Grainger has the 7hp single phase 220 unit and starter at $850 for one that matches the shaft size/base layout. $850 and $250 for the purchase has me walking away. Grainger does have a even free at this stage is no "deal" Seller failed to mention the 30phase issue until I got out there. he is moving and the rate he is going Free is almost the only way he will get rid of it..

grainger has a power converter but I am not sure the current motor on the compressor can be used with these? Any input would be appreciated

A static converter just starts a 3Ø motor & then it just single phases the motor, you lose 1/3 of the HP, which makes a static converter a bad idea. A 15 HP VFD would be required for a 7 1/2 HP motor as single phase input VFD's above 3 HP are rare & expensive, so a 3Ø input drive double the size of the motor one wishes to use & that allows the phase loss parameter to be disabled has to be used. Single phase input A/C drives do not need to be derated.

 

[amh]

At $250 it is a very good deal, at $150 you stole it.
Even if you cannot get a 7hp single phase motor (which I have not seen one in your run of the mill commercial applications - usually max out at 5HP), just get a 5HP single phase motor regardless of the RPM and then put a pulley on the 5HP that compensates for the loss in HP and increase in rpm - here is an off the top of my head calc: RPM x2 HP x 0.7 makes the new pulley on the weaker but faster 3500RPM 5HP replacement motor about 35% of original diameter.

This monster even when derated to the 5HP motor will huff and puff and blow the house down. If it is ~20cfm @ 90psi (check specs) at its current RPM just derate the RPMs for the appropriate HP and compensate for the drive motor RPM with appropriatr reduction in drive pulley size. For the calc above still gives you mid teens cfm at 90psi+. Better than anything at homedpot for that kind of money. Get the specs and do a worst case 3HP calculation for yourself.

Even if you derate to 3HP it is still a monster for the money. If you have a local HF and TSC you should be gtg for single phase motor & pulleys. (many lower HP single phase motors have built in thermal overload so you wont need to muck with the heaters in the switch box just use the old ones as shunts). And at low RPM the pump will live forever.

Cheapest way to get a single phase motor is to find a broken/needs-work large compressor on CL - they appear once in a while. You will also see 3phase 5HP motors often from people doing conversions

I would avoid phase converters - for this type of currents big & expensive.
reducing the HP will also avoid dimming the lights on your 220V service, a 7HP single phase ideal motor would draw a lot of AMPs -> 7HP=746W/HP*7HP= 4522W@220V or 4522/220=20.5A sustained, never mind startup inrush and the fact that no motor is ideal (probably more like 30A running under load).

 

[Norcal]

At $250 it is a very good deal, at $150 you stole it.
Even if you cannot get a 7hp single phase motor (which I have not seen one in your run of the mill commercial applications - usually max out at 5HP), just get a 5HP single phase motor regardless of the RPM and then put a pulley on the 5HP that compensates for the loss in HP and increase in rpm - here is an off the top of my head calc: RPM x2 HP x 0.7 makes the new pulley on the weaker but faster 3500RPM 5HP replacement motor about 35% of original diameter.

This monster even when derated to the 5HP motor will huff and puff and blow the house down. If it is ~20cfm @ 90psi (check specs) at its current RPM just derate the RPMs for the appropriate HP and compensate for the drive motor RPM with appropriatr reduction in drive pulley size. For the calc above still gives you mid teens cfm at 90psi+. Better than anything at homedpot for that kind of money. Get the specs and do a worst case 3HP calculation for yourself.

Even if you derate to 3HP it is still a monster for the money. If you have a local HF and TSC you should be gtg for single phase motor & pulleys. (many lower HP single phase motors have built in thermal overload so you wont need to muck with the heaters in the switch box just use the old ones as shunts). And at low RPM the pump will live forever.

Cheapest way to get a single phase motor is to find a broken/needs-work large compressor on CL - they appear once in a while. You will also see 3phase 5HP motors often from people doing conversions

I would avoid phase converters - for this type of currents big & expensive.
reducing the HP will also avoid dimming the lights on your 220V service, a 7HP single phase ideal motor would draw a lot of AMPs -> 7HP=746W/HP*7HP= 4522W@220V or 4522/220=20.5A sustained, never mind startup inrush and the fact that no motor is ideal (probably more like 30A running under load).

NEC tables list a 5 HP 1Ø motor 28A at 230V, & 7.5 HP 40A at 230V, 220V is a obsolete voltage, most motors are rated for 230V today for a 240V supply voltage, & 746 W per HP will only be a WAG, Wild A**ed Guess, as no motor is 100% efficient.

 

[Zengineer]

Give us some more details, from what Ive heard VFD controller cost about $1000 and up

Oops, I failed to notice the hp rating. I got my 3hp VFD from dealerselectric.com for less than $200, I see they are listed at $215 now. http://dealerselectric.com/item.asp?PID=4710

For the 7.5hp its a lot more money for sure, here is a 15hp for $836. http://dealerselectric.com/item.asp?PID=4574

 

[speadphreak]

Damn. If you were closer, I'd make you a hell of a deal on a Dayton single phase 10hp motor. I've got an extra one sitting around waiting to go on a compressor... Shipping would be a ***** to NY though. It's pretty heavy.

If you need to ship heavy items like that try Greyhound. Package it up. Take it to the bus station. They will put it underneath and take it to the closest bus station to your destination.

 

[wnstwolf]

You guys have me stoked to get out of here at Lunch and get motor spec info. The seller said I amd good to pop in for info but would not take a pick and e-mail. he is still a dial up guy. Hope to have some direction later today..

 

[Mandres]

imo it's worth $250 just for the tank and pump. There's no way you'll lose $ on it, even if you end up not using it.

 

[Todd.Brock]

Makes me appreciate the 5hp Baldor 1725 rpm motor for 80 bucks on c
CL

 

[wnstwolf]

All right fess up who drove out and bought it on Saturday AM. Snoose you lose.
Owner stated a guy with a home wood shop who already had a large 3-phase converter set up stoped by early on Saturday and bought it.
thanks for all the input and ideas guys..