Speedaire dayton 4b227 blowing fuses

by Mark

Greetings Bill, All,

When the tank is empty turn it on no problems fires up and runs great let the tank get too full and it will trip the breaker, anything over 80lb pressure in the tank. Try to start with a pressure in the tank over 40lb and it trips the breaker. I pulled the unloader valve and it's working fine, so went for the tank check valve and although very rusty outer case appears to be working fine. So nothing seized the breaker on the motor doesn't pop only my main breaker. I have tired a stand alone 15a outlet with the same results. Although it did get all the way to a full tank on the stand alone outlet. Am I dealing strictly with a power delivery problem or something else. Any help or suggestions would be greatly appreciated

Bill says....

Good on you for doing the checks you did, and for telling us all what steps you've taken so far.

Unless you have a mechanical issue overloading your motor, based on what you are saying, and the trend to flowing the breaker when the back pressure in the tank rises, I would suggest you next check out the capacitor. If it isn't performing, as your tank pressure grows, so too does the load, and the compressor may be relying on the added power supply from the capacitor that isn't there now, hence it pulls too much current and pops the breaker.d

Good luck, and keep us all posted if you would.



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Sep 30, 2011
capacitors... the rest of the story
by: Anonymous

A good capacitor charges up to that voltage, so when you connect the meter to a good capacitor, you'll see the ohms start kind of low and go up really high as the capacitor charges up to the 1.5 volts or whatever your meter uses.

This can happen in a few seconds, or as fast as a half second.

Step 4 - Here's the trick - switch your probes to the opposite terminals on the capacitor. Now the capacitor is charged the opposite way from what you're measuring, so the ohm meter will momentarily read a negative number! which will move through the range to zero and back to the high number or infinity like it did before (or if your meter is not digital, it'll slam the needle to the peg as it discharges the capacitor and recharges it the other way).

I usually switch the probes back and forth a couple of times to make sure I'm getting that capacitance effect that sends the number negative and slowly rises back up. Only a capacitor does that. And it won't do it if the capacitor is shorted or an open circuit.

That will give you about a 95% certainty that the capacitor is good... again, the value of a capacitor rarely changes significantly enough to affect the running of a motor. Also, most motors have a start capacitor, which is only used to START the motor. The capacitor and the start windings are only used to get the motor up to speed. A few motors (usually the bigger ones) also have a run capacitor. While the method of checking the capacitors is the same, this whole discussion is about run capacitors because it's about a motor not having the power to keep running under higher loads...

And one thing I would check if you're blowing breakers is whether you have too long or too light of an extension cord. You may be losing a lot of power across the cord, so your motor draws more amps to keep running, and that could be blowing your breakers.

To see if that's an issue, try to check your voltage at the compressor while it is running, especially when it is bogging down. If it is significantly below 110 or 220 volts, then you might get better power to your motor and see if it still does that.

Hope this helps someone!


Bill says... thanks a bunch. A lot of visitors will enjoy this post.

Sep 30, 2011
checking capacitors... part one
by: Anonymous

I'm probably too late to help the original poster, but someone might find this thread and be thankful for a little insight.

There are various ways to test capacitors, but for your average handy person, there's an easy way to tell whether they are good or bad.

Generally, capacitors themselves fail in one of two ways: they become an open circuit, or a dead short. When they're a dead short, usually they trip a breaker or explode, so most likely it's not dead shorted. I'll tell you how to test it after letting you know about the other "capacitor failure" that's just as common as the capacitor itself.

That's a connection failure. Look closely at the terminals where the capacitor connects. Are they rusty? Are the push-on connectors loose? Are they discolored, like they were overheating? Is there melted plastic around the area? All those things could mean a bad connection... I even had one where the terminals and wire connectors were fine, but the rivets that held the terminal (push on tab) on the capacitor were rusty enough that there was no connection. The electrical test to the rivet showed a good capacitor, but not to the connector.

OK, to check the capacitor you need a volt meter/ohm meter. Do not touch the terminals of the capacitor with your fingers or metal objects before you're sure there is no charge on the capacitor! It could have up to 1.4 times the voltage that the motor takes (the actual peak voltage reached by a 120V ac line is actually over 170! 120v is just the equivalent DC voltage, or the root mean square of the sine wave... but that's another story).

Step one - CHECK VOLTAGE on the capacitor with your volt meter set on DC Volts. Make sure to check all the terminals on your capacitors, and push your probes hard enough to dig in through the crud or surface oxidation. Does it read close to zero? Great. If you read that accurately, then it won't melt the tip off a screw driver that you will short across the terminals to make extra sure. Again, push it hard enough to make a good solid contact with both terminals, but no other metal (and make sure you are not touching the screw driver or anything that could lead to a shock). If you were wrong about the reading, or didn't have the voltmeter turned on, there will be a really strong "zap!" - a spark that might melt a chunk out of your screw driver.

Step 2 - now that you're sure there's no charge on the capacitor, if you haven't already unplugged the wires to it, note where they went and unplug them.

Step 3 - Switch your volt meter to the ohms range, maybe around the hundred ohm range if it isn't auto-ranging. Check the meter by touching your two leads together - the meter should go immediately to about zero ohms if everything is set right, and you have a good battery in it.

(I apparently typed too many characters, and I'm not into editing a lot, so I'll add a second comment with the balance)

Jul 21, 2011
Electrically Dumb
by: Mark

Hey Bill.
Thanks very much for the quick reply. Now I like to consider myself a fairly handy person however when it comes to testing the load on the capacitor.... I would have to say HUH? Would you be able to describe the best way to test the capacitor for somebody who isn't an electrician.


I am not an electrician either, and since a capacitor, by it's nature, holds an electrical charge that is rapidly released, you want to be careful.

I am researching the testing of compressor motors right now for a series of pages on them, and that will include testing capacitors. I cannot give you that data as yet, since there are conflicting reports on methodology, and I'm trying to decipher what does, and what does not, make sense.

Hopefully in the next couple of weeks I'll have some pages on compressor motors for you all.

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Compressor won't start when it's hot

by Dan

I have a Speedaire compressor model # 4B227C that will run fine when it's cold, but once the pump gets hot it trips the breaker. I had the motor checked, and no problems with it. Now I've taken apart the pump and no cracked pistons, no worn rings. Not sure where to go next.

Bill says...

Dan, in the absence of an motor or start/run capacitor failing issue, and if the mechanical side of the air compressor is working normally, then that only leaves your power supply.

An electric motor that is underpowered electrically will both run hot and fail sooner.

Make sure your power supply is not compromised by other devices pulling power from the same circuit at the same time your air compressor is starting or running, and that you are NOT using any extension cord except a heavy duty (12 gauge?) model.



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