Electrical help needed -- Irrigation Pump - PeachParts Mercedes-Benz Forum

sunedog · #1 03-14-2007, 07:58 AM

I need some electrical debugging help:

I have a 2 HP 220V pump for my lawn irrigation system. I pull water out of a lake. The system is 15 years old and I am having a problem this season. The timer starts the pump, the pump gets power for a few seconds and then trips the 30 Amp breaker. I pulled the pump into my shop and verified that the motor is not bound up (I could turn the shaft with a screwdriver). One of the two hot wires possibly had a very small cut in the insulation where it passes through a hole in the motor, so I fixed that. Pulled the covers off of the large capacitors (I assume they are capacitors) on top of the pump. No signs of burning or other problems. Reinstalled the pump and get same result.

Anyone care to offer de-bugging advice? How do you test the capacitors? I think at least one of them is a jump start capacitor to help the pump overcome start-up load. I have a volt-ohmmeter, but only know the basics of electrical debugging.

You may be concluding (correctly) I know enough to be dangerous, so I treat this 220V appliance with great respect.

Thanks in advance.

wbrian63 · #2 03-14-2007, 08:06 AM

The motor you have is called (and I'm not sure about the actual phrase) capacitor start/capacitor run. One of the capacitors does exactly what you surmise, it gives a boost of electricity to the motor to overcome the load at startup. The other is there to help out during normal operation.

If you can, disconnect the motor from the pump and see if it starts up without an issue.

Also, if I'm not mistaken, there will be a centrifugal switch somewhere on the back side of the motor. When the motor spins down at shutoff, this switch engages, allowing the power from the capacitor to reach the windings of the motor at startup. When this device fails, the motor doesn't get the boost it requires to start up, and you generally just get a humming sound (and possibly a motor that will trip the breaker).

If you can get the motor to run (you can usually get a capacitor start motor to run without the aid of the capacitor by spinning the shaft and applying power before the motor stops spinning), listen for a tell-tale "click" when the motor winds down after shutoff. It should occur just before the shaft stops spinning.

I could be wrong about all of this - but most of the time the capacitors aren't the problem, either the aforementioned switch, or the windings of the motor itself.

Your safest and probably best course of action is to take the motor to a repair shop that specializes in things like this. You might be surprised at how cheaply the motor can be repaired.

sunedog · #3 03-14-2007, 09:35 AM

Quote:

Originally Posted by wbrian63

If you can, disconnect the motor from the pump and see if it starts up without an issue.

I tried this and believe the motor starts without a load and doesn't trip the breaker. The pump is down near the shore of the lake. The timer and breaker are in a closet in my basement. I reinstalled the pump without connecting it to the load (irrigation pipes). I turned it on from inside the closet. Quickly walked outside. Heard the pump running. Saw a wisp of smoke from a distance so I ran back inside and killed power. It only ran for a few seconds. I am concerned I was burning up the impeller, but hope it wasn't damaged in those few seconds. Of course, the smoke may also have been from the motor. It's 15 years old and I guess the windings may be shot.

I think I will try to examine the centrifugal switch you mention. Sounds like a simple yet ingenious set-up. If I can't isolate a problem there, I will try to test the capacitors. If that's not the culprit, I need professional help.

Thanks for your informative response.

dannym · #4 03-14-2007, 10:42 AM

You can check the windings by going lead to lead. You should have continuity.
Then go lead to ground, you should not have continuity.
If either if these tests fail you need a new motor.

You need a special tester to test capacitors but if it actually starts that's highly unlikely to be your problem.

Probably unlikely also but is there a screen inline? Probably at the pond. Is that clear? A good test would be to disconnect the discharge and run it and see if it still kicks out.

Have you actually ran it with an amp probe on it to see what's happening?

Danny

Zeus · #5 03-14-2007, 10:45 AM

Check to see if either the source lines or irrigation lines are clogged. If the pump can't draw or push the water, it could trip the motor.

My wife's grandmother had a similar lawn irrigation system, drawing from a lake. Always had problems with weeds and algae clogging the source line.

kerry · #6 03-14-2007, 10:46 AM

I agree, check the amount of amperage it is pulling. It's not beyond the realm of possibility that you have a bad breaker.

TwitchKitty · #7 03-14-2007, 11:30 AM

Get a book from the library or a supply house. The start capacitor shifts the phase of the power rather than boost it. Capacitors are cheap. You need a megger to check the windings. A quick check at a rebuilder should be cheap.

dannym · #8 03-14-2007, 12:03 PM

You DO NOT need a megger to test the windings. You test them the way I explained in my last post.

I don't know what your trying to say by "shift" and "boost". The capacitor provides a delay in power to one of the windings. This delay causes an unbalance and the motor to start.
The start capacitor starts the motor, that's all it does.

DAnny

Matt L · #9 03-14-2007, 12:49 PM

Starting capacitors are typically wired in series with the winding, at least in my memory. This causes a phase shift in the current on that winding. The run winding is active at the same time, and this "fools" the motor into thinking that it has more than a single phase coming in. The additional phase helps drag the rotor to get it started (and in the correct direction). Once the motor is turning, the additional phase is not needed.

Three-phase motors need no starting windings, but like single-phase motors, they often do have run capacitors. These are wired in parallel with the windings, and their sole purpose is to help correct the power factor.

TwitchKitty · #10 03-14-2007, 01:25 PM

Get a book or see a professional or both.

dannym · #11 03-14-2007, 02:10 PM

I like going to the library.

Anyone who thinks you need to meg a motor to test it should take a trip there too.

kip Foss · #12 03-14-2007, 07:58 PM

If the pump is 220 V check that both legs of the incoming power are good. Check that you have at least 220v between the two hot leads and at least 110v to ground.

sunedog · #13 03-15-2007, 08:14 AM

All good information. Thank you all.

Right now, I am focusing on the centrifugal switch. Please look at this pic.

Is that the centrifugal switch? If it is, it is obviously corroded but it appears to be intact. I can't figure out how it works becasue I can't see any electrical connections to it. It just seems to be connected to the motor shaft.

Any way to test it? How do you remove it to replace it?

Matt L · #14 03-15-2007, 01:19 PM

That piece would actuate the switch, which is presumably in the end cover. There are no wires in the rotor of that motor.

That corrosion visible on the wires in the bottom of the photograph is cause for alarm. It may not be your problem today, but it will eventually become one.

sunedog · #15 03-15-2007, 01:41 PM

Quote:

Originally Posted by Matt L

That piece would actuate the switch, which is presumably in the end cover.

Matt L: Here's a shot of the end cover:

The red wire from the white device goes to one cap and the orange wire from the black device goes to the other cap.

I'm betting the centrifugal switch is the white device. Any way to test it?

Thanks for your help!