3 phase to single phase - Page 3 - Electrician Talk - Professional Electrical Contractors Forum
CLICK HERE AND JOIN OUR COMMUNITY TODAY, IT'S FREE!
Go Back   Electrician Talk - Professional Electrical Contractors Forum > Electrical Trade Topics > PLCs, VFDs, Motors and Controls


Like Tree15Likes
Reply
 
Thread Tools Display Modes
Old 03-10-2016, 02:42 PM   #41
Wyome
 
Join Date: Jun 2007
Location: WY
Posts: 754
Rewards Points: 910
Default

Quote:
Originally Posted by telsa View Post
A single phase motor is a TERRIBLE match for this load.

It can't tolerate the incredible number of start-stop-start-stop... to be endured by a compressor loaded motor.

This performance cycle just about demands a three-phase motor.

As a stop gap he must install a separate blower motor to force cool the primary motor whether it's running or not. ( with temperature regulation akin to that found on European automotive radiator fans )

As it stands, it's cooking in its own juice.
Thanks for the input. About the start-stop-start-stop. I guess that makes sense to me, but I did not factor that in.
te12co2w is offline   Reply With Quote
Join Contractor Talk

Join the #1 Electrician Forum Today - It's Totally Free!

ElectricianTalk.com - Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it's the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you'll find that ElectricianTalk.com is a great community to join. Best of all it's totally free!

Join ElectricianTalk.com - Click Here JOIN FOR FREE


Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Sponsored Links
Advertisement
 
Old 03-10-2016, 02:45 PM   #42
Wyome
 
Join Date: Jun 2007
Location: WY
Posts: 754
Rewards Points: 910
Default

Quote:
Originally Posted by micromind View Post
Bad things will happen......lol.

If the start winding does not disengage, the current will be somewhere near locked-rotor (roughly 6X full-load), it won't come up to full speed, it'll trip the O/L in about 5 - 10 seconds (if properly sized), it might blow the start capacitor and if the O/L or breaker fails to trip, the motor will burn up in less than a minute.
it'll trip the o/l in about 5-10 seconds (if properly sized). The overloads are not properly sized. In fact they don't even have a proper starter. Every time I mention that, a just get head shakes. That's a work in progress.
te12co2w is offline   Reply With Quote
Old 03-10-2016, 02:47 PM   #43
Wyome
 
Join Date: Jun 2007
Location: WY
Posts: 754
Rewards Points: 910
Default

Quote:
Originally Posted by InPhase277 View Post
How about a hard start kit?
That was one of the things I first thought of. I haven't looked hard, but a short search leads me to believe that a hard start for a single phase, 7.5 hp motor is not easy to find.
te12co2w is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 03-10-2016, 02:51 PM   #44
Wyome
 
Join Date: Jun 2007
Location: WY
Posts: 754
Rewards Points: 910
Default

Quote:
Originally Posted by Galt View Post
China made capacitors suck . Get some better ones. If a capacitor start capacitor run motor fails to start for any reason the start capacitor will usually be ruined in 10 to 15 seconds the start capacitor normally is taken out of the circuit by a centrifugal switch or a potential relay . Take the end off the motor and examine the switch or sometimes 2 switches wired in series. You can also improve your odds by buying a capacitor with a higher voltage rating. However make sure the microfarad rating is very close to the original. Capacitors do not go bad sitting on the shelf.
I would not have considered changing capacitor ratings for fear of smoking the motor, but maybe I will look into that.

Last edited by te12co2w; 03-10-2016 at 02:52 PM. Reason: spelling
te12co2w is offline   Reply With Quote
Old 03-10-2016, 03:25 PM   #45
Wyome
 
Join Date: Jun 2007
Location: WY
Posts: 754
Rewards Points: 910
Default

Quote:
Originally Posted by JRaef View Post
I'd think the centrifugal switch is hanging up and not opening all the time. It only takes once to kill the start cap.

As others have said, a single phase motor sized at 1:1 against a 3 phase motor on a recip compressor is the likely root cause of this. It seems to me (hard to follow) that you said the original design ran all day and loaded/unloaded, then you changed it. That would likely have been hard on the 3 phase motor, let alone changing it to single phase. You have increased the duty cycle of the motor, which is part and parcel to the motor selection process on a recip compressor. Yes, HP is HP, but if you increase the duty cycle, you sometimes have to de-rate the motor size. So you may have needed to go to 10HP even if it was 3 phase, maybe 15 single phase, but that would be a rare motor at that point. Even then, the increased number of starts is still going to take a toll on that centrifugal switch. That's why you rarely see single phase compressors that large.

If its a belt drive, and you don't need as much air as it was originally designed for, you could consider changing the sheave ratio to reduce the load on the motor. That might increase the duty cycle however so because it's a single phase motor, would make it worse. A better plan may be to return to something closer to the original design, run the motor longer and just unload it when not being used. You can add what's referred to as a "minimum run timer" to the pressure switch circuit. It's an off-delay timer controlled by the pressure switch so when the pressure drops, the timer closes, then the timer energizes the starter for the compressor. When the pressure switch opens, it drops out the timer coil, but the timer contacts stay closed for the time value, let's say 10 minutes. After 10 minutes, if the pressure switch is still open, the timer contacts open and drop out the starter. If in that 10 minutes the pressure switch had closed again, the compressor kept running. What this does is minimize the number of start-stop cycles that motor is subjected to.

It will also increase the energy consumption. In reality, that might cost more in the long run than getting a compressor professional to come in and evaluate their needs to give them the correct compressor setup to start with. In a lot of areas, the power utility may even offer a rebate to help offset the cost of that! Here in my area of California, air compressor optimization can get you a nice rebate, sometimes enough to make the cost of changing pay for itself in under a year by the energy cost savings.
The original design was with a 3 phase motor. One of the mechanic/owners brought the compressor from another state. Plumbed it in and then realized 3 phase was not available. So he bought a single phase motor that would be an easy swap. HP, frame size, shaft size, rpm all the same as the original 3 phase motor. Then someone else wired the compressor motor. That motor lasted a little more than 2 years. Then, one of the start caps blew out. That is where I came in. Replaced both start caps and the single run cap. Things went well for around 2 weeks. Right now I am still waiting for more replacement caps.
This compressor has a switch up in the mechanic bay that controls the coil on the contactor. They turn it off when they quit for the day (supposedly) I know it does not run 24/7 even during business hours. It cycles on the pressure switch.
I like the idea that a 1:1 swap might not be adequate. That is what I wondered about in the first place. I don't know their air requirements. I did suggest that they could fiddle with different size sheaves to maybe help things out. The owner wasn't real receptive of that idea, and I certainly don't want to spend any more time doing that.
Thanks for the suggestion of "minimum run timer". I'll not suggest that yet.
The local power company does have some rebate programs in place that might help. At one time their policy was to require VFD or soft start technology of motors over 5 hp. I think that was the policy. Didn't want to talk to them about it because then maybe the owners would be forced to spend more money and blame me for their woes.
Long winded, I know. Thanks for your suggestions.
hardworkingstiff likes this.
te12co2w is offline   Reply With Quote
The Following User Says Thank You to te12co2w For This Useful Post:
hardworkingstiff (03-10-2016)
Old 03-10-2016, 03:31 PM   #46
Wyome
 
Join Date: Jun 2007
Location: WY
Posts: 754
Rewards Points: 910
Default

One more thing. The owner brought up the idea of going back to a 3 phase 7.5 hp motor and then putting a phase converter on it. I haven't followed up on that.

Thanks for all the help!!
te12co2w is offline   Reply With Quote
Old 03-10-2016, 04:24 PM   #47
Modérateur
 
frenchelectrican's Avatar
 
Join Date: Mar 2007
Location: Philippines
Posts: 8,630
Rewards Points: 16,772
Default

Quote:
Originally Posted by te12co2w View Post
One more thing. The owner brought up the idea of going back to a 3 phase 7.5 hp motor and then putting a phase converter on it. I haven't followed up on that.

Thanks for all the help!!
That can work but if this will be the only 3 ph load you may need one size larger uunit due the starts per hour...
__________________
Bleu est beau.
frenchelectrican is offline   Reply With Quote
Old 03-10-2016, 04:57 PM   #48
Senior Member
 
Join Date: Jan 2007
Location: Wilmington, NC
Posts: 12,167
Rewards Points: 14,714
Default

Quote:
Originally Posted by JRaef View Post
In reality, that might cost more in the long run than getting a compressor professional to come in and evaluate their needs to give them the correct compressor setup to start with.
THAT is the best idea yet.
__________________
Three vastly different enemies, but enemies who shared one common trait. ALL of them stifle free speech. All of them bully, degrade and terrorize those who hold opposing views and who peacefully express them. All of them are intolerant and demand “loyalty” to the leader. Michael Sand
hardworkingstiff is offline   Reply With Quote
Old 03-10-2016, 05:46 PM   #49
Registered Member
 
Join Date: Feb 2008
Location: Alabama
Posts: 11,885
Rewards Points: 1,360
Default

Just for the fun of it, hang an ammeter on the EGC and see if there's any current.
RePhase277 is offline   Reply With Quote
Old 03-10-2016, 06:47 PM   #50
Senior Member
 
NC Plc's Avatar
 
Join Date: Mar 2014
Location: Nationwide
Posts: 3,529
Rewards Points: 7,888
Default

How much cfm does an air compressor like that generate?

Is it really worth the hassle of all this instead of buying a proper AC like mentioned above?
__________________
I would rather ask a seemingly stupid question than not ask it and make a stupid mistake.
NC Plc is offline   Reply With Quote
Old 03-10-2016, 08:20 PM   #51
Modérateur
 
frenchelectrican's Avatar
 
Join Date: Mar 2007
Location: Philippines
Posts: 8,630
Rewards Points: 16,772
Default

Quote:
Originally Posted by NC Plc View Post
How much cfm does an air compressor like that generate?

Is it really worth the hassle of all this instead of buying a proper AC like mentioned above?
If i recall about 18 to 28 depending on pressure..

I know mine 15 hp compressor can kick out about 45 or more cfm ..depending on the pressure it discharge..
__________________
Bleu est beau.
frenchelectrican is offline   Reply With Quote
Old 03-10-2016, 09:10 PM   #52
Senior Member
 
NC Plc's Avatar
 
Join Date: Mar 2014
Location: Nationwide
Posts: 3,529
Rewards Points: 7,888
Default

I don't know, if it was my call I would just replace the unit with a single phase one. I know quincy makes a 17cfm ac @ 170 psi for 1300 or so.

Seems like a waste of effort and time. Though, when I make judgement calls about replacing equipment it's always time down troubleshooting vs cost of downtime, with if it's a critical asset or not also considered.
hardworkingstiff likes this.
NC Plc is offline   Reply With Quote
Old 03-10-2016, 09:28 PM   #53
Modérateur
 
frenchelectrican's Avatar
 
Join Date: Mar 2007
Location: Philippines
Posts: 8,630
Rewards Points: 16,772
Default

Yuh but make sure that the cusstomer get cast iron compressor they last much longer than the alauinm verison..

That something the customer have to make a choice of keep fix the compresssor or get a new one ...
telsa likes this.
__________________
Bleu est beau.
frenchelectrican is offline   Reply With Quote
The Following User Says Thank You to frenchelectrican For This Useful Post:
telsa (03-11-2016)
Old 03-10-2016, 09:43 PM   #54
Senior Member
 
NC Plc's Avatar
 
Join Date: Mar 2014
Location: Nationwide
Posts: 3,529
Rewards Points: 7,888
Default

Best way to determine if it's cast or aluminum is with a magnet I am guessing?
__________________
I would rather ask a seemingly stupid question than not ask it and make a stupid mistake.
NC Plc is offline   Reply With Quote
Old 03-10-2016, 09:48 PM   #55
Modérateur
 
frenchelectrican's Avatar
 
Join Date: Mar 2007
Location: Philippines
Posts: 8,630
Rewards Points: 16,772
Default

Yup and if you work around the cast iron just look at cooling fins plus the crankcase..
There is a difference between the two..
__________________
Bleu est beau.
frenchelectrican is offline   Reply With Quote
Old 03-10-2016, 09:51 PM   #56
Senior Member
 
NC Plc's Avatar
 
Join Date: Mar 2014
Location: Nationwide
Posts: 3,529
Rewards Points: 7,888
Default

When you say cast vs aluminum which are you referring to? Rotary, piston, etc?
__________________
I would rather ask a seemingly stupid question than not ask it and make a stupid mistake.
NC Plc is offline   Reply With Quote
The Following User Says Thank You to NC Plc For This Useful Post:
frenchelectrican (03-11-2016)
Old 03-10-2016, 11:02 PM   #57
Senior Member
 
Galt's Avatar
 
Join Date: Sep 2013
Location: Wis.
Posts: 566
Rewards Points: 977
Default

A capacitor losing it's charge is not the same as a capacitor failing. When used for motor starting they are quite often discharged with a bleed resistor to stop arcing of the start switch contacts. I do not know their purpose in a vfd but apparently bad things can happen if they lose their charge so they recharge them. they are a very simple component two conductive plates with an insulating material in between. what happens when you hook an ohm meter to the terminals is deceiving They are not conducting current rather the dc battery is stuffing electrons into one plate causing electrons to leave the other plate. Eventually the voltages equal and electrons stop making the ohm meter read very high.
Galt is offline   Reply With Quote
Old 03-10-2016, 11:28 PM   #58
Bilge Rat
 
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 6,468
Rewards Points: 2,546
Default

Quote:
Originally Posted by NC Plc View Post
How much cfm does an air compressor like that generate?

Is it really worth the hassle of all this instead of buying a proper AC like mentioned above?
A general rule-of-thumb is 4 CFM per HP at 100 PSI.

Reciprocating or rotary.
micromind is offline   Reply With Quote
The Following 4 Users Say Thank You to micromind For This Useful Post:
frenchelectrican (03-11-2016), guest (03-11-2016), hardworkingstiff (03-11-2016), NC Plc (03-10-2016)
Old 03-10-2016, 11:49 PM   #59
Bilge Rat
 
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 6,468
Rewards Points: 2,546
Default

In an electrolytic capacitor, there is a thin layer of oxide on the aluminum that is sandwiched between the electrolyte-soaked material. Aluminum oxide doesn't conduct so it insulates itself from the electrolyte, which does conduct.

With no charge, the electrolyte will dissolve the layer of oxide over time. With no oxide to insulate, when a high-energy charge is applied......boom.

Reforming involves applying a low voltage low power charge and ramping it up every so often. The time for each step depends on how long the cap has been uncharged. Figure an hour per year of non-use.

The oxide layer will build up when voltage is applied, but it's slow, so voltage needs to be applied slowly or the aluminum will bond to the insulating material and the oxide layer won't form.
micromind is offline   Reply With Quote
Old 03-11-2016, 12:22 AM   #60
Modérateur
 
frenchelectrican's Avatar
 
Join Date: Mar 2007
Location: Philippines
Posts: 8,630
Rewards Points: 16,772
Default

Quote:
Originally Posted by NC Plc View Post
When you say cast vs aluminum which are you referring to? Rotary, piston, etc?
Both piston and rotary..

That why the cast iron piston verison is best for hevay duty operatiio
For liight duty the alum will work fiine witth short duty cycle.. ( some may have castt iron sleeve )

For rotary it can be either way as long it have clean lube oil and not get overheated it willl be fine..
__________________
Bleu est beau.

Last edited by frenchelectrican; 03-11-2016 at 12:25 AM.
frenchelectrican is offline   Reply With Quote
The Following User Says Thank You to frenchelectrican For This Useful Post:
guest (03-11-2016)
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
220 single phase to 3 phase? TechieBecky Canadian Electrical Forum 16 02-19-2016 03:46 AM
3 phase panel (208) used for single phase (240)? CEC09 Canadian Electrical Forum 3 02-10-2016 02:35 AM
I need to run this motor on single phase. (with photos) Neanderthal General Electrical Discussion 1 01-29-2016 04:28 PM
Can be both a three or single phase motor just the cowboy General Electrical Discussion 2 01-21-2016 10:36 AM
single phase motor man Galt PLCs, VFDs, Motors and Controls 1 01-19-2016 07:11 PM


All times are GMT -4. The time now is 06:40 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Our Pro Sites Network
ContractorTalk.com | DrywallTalk.com | HVACSite.com | PaintTalk.com | PlumbingZone.com | RoofingTalk.com