Multiple Compressor motor problems

I have two separate problems. The first is my Kobalt 3 hp 60gal upright compressor, which seems to run fine most of the time, but it keeps eating capacitors. The one that keeps going bad (3 times in as many months) is a 161-193mfd start capacitor, the run cap seems to be OK. I am not sure why this keeps happening - any ideas? Can ambient temperature be a factor? The temp in the shop has been higher than normal, as high as 80 to 85, and the compressor is semi-enclosed to dampen noise. I have tried blowing air into the enclosure to cool the motor, but it is still going thru capacitors. The motor and compressor both turn over oK.

The second problem is my Worthington 100gal compressor with a Baldor 5hp single phase motor. It quit starting and would just growl and trip the breaker, even with no load, so I believed that the start caps were bad and ordered two replacements, 216-259 mfd. When I went to take out the old ones, the slip-on connectors were very difficult to remove. In the process of getting one wire off, I pulled the other end of it free from one of the other caps, either the other start cap, or the run cap. I cannot find a schematic that clearly shows how to place the wires and jumpers for TWO start caps and one run cap. No, of course, I didn't make a sketch before I went to pull the wires off. That would have been smart, right? And then I wouldn't be asking this dumb question. If anyone can make a simple sketch of how the jumpers and connections are supposed to go, I would be very happy. The 5hp motor spins over easily by hand and I can turn the compressor over also.

For the first problem, is the unloader working properly, so the compressor starts easily? How is the capacitor failing, letting the juice out? Or burning the terminals? What is the voltage rating of the start cap? Is the motor running on 120 Volt or 240 Volt?

For the second, what is the voltage rating of the start cap?
The problem may be the starting switch in the motor not closing when it is stopped.

So do you know how the other connections are made, with just one lead in question? Or do you have 3 wires going into the motor and several (2 or 3) jumpers, with no idea what goes where?

Most guys use their smart phone to get some pix while taking things apart, so going back together goes smoothly.

Bill

Voltages - for the Kobalt compressor, the voltage on the cap was 220. For the Worthington, the voltage of the cap was 330. I made sure to match not only the capacitance but also the voltage rating.
I don't know about the unloader, it does sound like the compressor is starting under quite a load, and it is popping a 30amp breaker.
When I last tried the 5hp motor on the Worthington, I turned it on at the breaker panel like I always do, and after a few seconds, the breaker opened. I waited for a few minutes, and tried again, but the same thing happened. I left the breaker off, walked the 75 feet out to the compressor, turned off the power switch there, and went back and turned on the breaker. My father was an electrician and wired this shop, so, i am sure the wiring is more than sufficient for the load, and we have been running this same compressor for over 30 years. We went thru 4 motors the last 10 years, and used to go thru electronic starters about every 6 months, so the last couple motors had conventional starters. Anyway, when I walked back out and turned the compressor on, itjust growled (Loud electrical hum) for a few seconds before the breaker tripped again. That sort of starting behavior was similar to the other compressor (which is supposed to be my "backup" compressor), so I assumed capacitors.
Addressingb how they are failing...good question. I have had capacitors that shorted and blew up, or let out a lot of smoke, etc, beu these just seem to quit working. Maybe I'm not as smart as I think I am (well, absolutely), but I "cured" the Kobalt the first time by replacing the capacitors. I will check the unloader - I don;t even know if it has one, but it stands to reason it would.
I also have a Marathon 5hp motor that quit working a while back (it was the last motor before the Baldor on the bigger compressor), that I'm going to check out to see if the caps are gone on that one too.

On the Worthington, if you are using a panel breaker for your ON/OFF switch, I would change that first. They are not rated to use as a switch and although if often done that way, they can fail, and do so in a strange fashion. They are pretty cheap and it would get that off your list of 'possibles'. I would also take my Wiggy or Ohmmeter and make sure the mag for the Worthington was passing power through both sets of contacts.

Stuart

Summary of symptoms: Burning up multiple 1Φ motors of varying sizes, and makers, along with, start switches, start caps, electronic starters. Been going on for 10-30 Years?

It sound's like a case of repeated low voltage during starting, increasing startup time, increasing starting current, stressing the starting components. Seems as though any compressor in this shop is destined for starting system problems.

But you assure us that there could not be a supply problem.

so, i am sure the wiring is more than sufficient for the load, and we have been running this same compressor for over 30 years. We went thru 4 motors the last 10 years, and used to go thru electronic starters about every 6 months, so the last couple motors had conventional starters.

Click to expand...

Did you ever measure the voltage and current at the motor terminals during starting, to quantify what the problem is?

What was passable 30 years ago, may not be in the same condition now. Age can take a toll on electrical installations.

If it were me, I would a least consider the notion that there could be a issue with the supply, before acquiring the 6th motor or capacitor/starter sets. Or at least quantify the conditions to assure myself.

Just a thought...

SAF Ω

Responding to several replies. trying to cover all the points - On the Kobalt 3hp compressor - the unloader valve seems to be doing its job. I have actually unhooked the bleeder tube just after the compressor shut off and had no residual pressure in the bleeder tube. Ergo, the unloader is working. It will start from an empty tank condition, but even at as little as 50 lbs pressure in the tank, the motor will stall and trip a 30 amp breaker if I turn it off (with the pressure switch at the tank itself)and then turn it back on. I have 115v on both legs of the single phase 220 supply. I have no good way to check the amp draw on any motor, but it is a good bet the Kobalt is drawing more than 30. On the 5hp, again, no way to check the starting amperage. In the winter, when it is really cold, it will trip the 50 amp breakers. Presently, I can't even try to start it until I get the capacitor jumper situation sorted out. Does anyone know if start capacitors used in pairs are hooked in series or parallel? On the issue of voltage, well, yes and no. We have always experienced some fluctuations because we are a good ways from the nearest substation, with a lot of farms on the line ahead of us, but the 3-phase converter that we use for the CNCs usually smooths them out for those machines and any of the single phase machines haven't seemed to notice anything if the voltage drops or surges a little. We have a 400 amp SINGLE PHASE service to the shop, but have always had a slight dimming of the lights when the compressor started. It was pronounced enough early on that we had to replace the original 3-phase motor with a single phase motor because the compressor put so much demand on the converter that the CNC's would quit. They only tolerate a maximum of about 10% voltage fluctuation. As for the wiring, the 5hp compressor is on a dedicated 50 amp breaker and fed with 6 gage wire to a sub box with 60 amp fuses. It also has a Cutler Hammer magnetic starter between the sub box and the motor. We called my father "Overkill Al" because of his penchant for going over and above what was necessary in most any situation. Maybe, as suggested, the 6-gage wiring is not heavy enough, but I would kinda doubt it. Philosophical discussions about the wiring aside, it has worked for a long time. I think the reason for going thru the motors (4 in 30 years isn't so bad a track record), is the compressor is running so much. For years, it pretty much ran continuously for 16-18 hours a day, but over the last few years, more like not so continuously for 10 hours a day. Anyway, my biggest concern at the moment is getting one of these compressors up and running again. LATE BREAKING NEWS - I think I found a clear photo of the correct setup for the caps on the 5hp compressor. I'm going to try to duplicate it and see if it will run, 'cause I'm dead in the water with no compressor and things are starting to back up. I will post an update when I know.

Here's a link to a Baldor internal wiring diagram for a 5HP 1Φ motor # L1430T. Not sure if it's the model you have but should be close, and from there you could search your model if it's different.

id - Baldor.com



I would suggest that you look into getting yourself an amp clamp meter so that you can quantify what is going on at your facility. They aren't that expensive today, and can be a huge benefit when your having problems.

SAF Ω

Hey SAF,
wondering if you can help me out here. I noticed on this and some other threads that you were one of the guys that seems pretty knowledgeable with regard to capacitor wiring. I have a GE single phase 5hp motor that I bought new in 2002 and never used very much. Currently I'm retrofitting it into a Sharp 17x60 tool room lathe. My problem is that I accidently disconnected one of the capacitor wires when I was removing the lines from last machine that I was using it for. I can't find any info on the motor as it has been long discontinued by GE. I think GE was making or subbing motors out of Korea at the time. The motor seems to be a knockoff of the Baldor L1430T that you show the diagram for above. Like the 1430T my motor has two plastic start caps and one metal run cap. I see the Baldor diagram only shows one start cap but has the note to run multiple caps in parallel. Most of the pics for the Baldor that I find online show it with the two start caps and one run cap like mine. Anyway, the attached diagram that I made is of my setup. There are 6 wires coming out of the motor as labeled. They all come out of the motor from one hole and three of them go to the caps as shown the other three go to the lines. My caps don't have any identifiers on the terminals but I numbered the terminals 1 through 6 just for reference. The wire I am trying to figure out is the very bottom one (terminal 6) on the run cap. Each cap has only two terminals but each terminal has 3 spade connectors so the disconnected wire could have come from any terminal. Wondering if you can tell by looking at my diagram where disconnected wire went to?
Thanks Much!
Manny

Looks like it should connect with motor wire #6

SAF Ω

Hi SAF,
You nailed it!!! I finally got back out to the shop today after a long battle with the Flu. I hooked up the mystery wire to the additional spade on the cap where the #6 wire is. it started right up and ran like the wind.
Thanks Again!
Manny