I have replaced a 40amp 4 pole general contactor 120volt twice in the past year. I am puzzled as to why this is happening. It is turning on some bay lights in a carwash. A photocell is also hooked to it so that the coil becomes NO at dawn. The photocell is definitely not bad. It is the contactor. Am I overlooking something? Or do contactors normally go bad this quick?
Contactor keeps going out
- Thread starter Voltech
- Start date
- Status
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
What's going bad on the contactor (coil, contacts)?
Is this a definite purpose contactor or lighting contactor?
What is the amperage draw on the circuits?
Is this a definite purpose contactor or lighting contactor?
What is the amperage draw on the circuits?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
DP contactors... DP should stand for "Don't Purchase" instead of Definite Purpose.
DP contactors are ONLY to be used in engineered OEM systems where everything about them is specifically tailored to known quantities and qualities that are controlled within the OEM assembly. One big issue is that the coils do NOT have the same kind of voltage tolerance that you find in other contactors like NEMA or IEC. If the coil says 110V, they usually mean 110V, not 120V. If you feed it 120V it fries and vice versa; if the coil says 120V and you feed it 110V it fries. There are no NEMA design spec guidelines that apply to DP contactors, you get what you pay for.
That said, you should also observe the operation BY THE PHOTO CELL, not your over ride test. It could be that the photo cell is "chattering" between on and off in low light conditions and that chatter is going to fry your coil.
DP contactors are ONLY to be used in engineered OEM systems where everything about them is specifically tailored to known quantities and qualities that are controlled within the OEM assembly. One big issue is that the coils do NOT have the same kind of voltage tolerance that you find in other contactors like NEMA or IEC. If the coil says 110V, they usually mean 110V, not 120V. If you feed it 120V it fries and vice versa; if the coil says 120V and you feed it 110V it fries. There are no NEMA design spec guidelines that apply to DP contactors, you get what you pay for.
That said, you should also observe the operation BY THE PHOTO CELL, not your over ride test. It could be that the photo cell is "chattering" between on and off in low light conditions and that chatter is going to fry your coil.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
I think you should also check the voltage on the coil with the photo cell in the on position. There might be an unusually high VD across the photo cell.
Thanks for the information very useful. I am going to do as you guys suggested and test the voltage on the coil with the photo cell in the ON position. I didnt realize that "chatter" could be the culprit. That being said, what would your remedy be if "chatter" via the photocell is the issue?
On the initial visit my guys just tested to see if the power was going to the contactor when the photocell was covered but voltage readings etc was not documented or observed.
On a completely different topic, I called all the local supply houses in my area and NONE carry lighting contactors only definite purpose which they say are the same thing...go figure. I am wondering if the engineer that designed and spec'd this setup thinks the same!!
Again I appreciate the quick and informative responses. Glad I have a resource like you guys to turn to.
Regards,
CY
On the initial visit my guys just tested to see if the power was going to the contactor when the photocell was covered but voltage readings etc was not documented or observed.
On a completely different topic, I called all the local supply houses in my area and NONE carry lighting contactors only definite purpose which they say are the same thing...go figure. I am wondering if the engineer that designed and spec'd this setup thinks the same!!
Again I appreciate the quick and informative responses. Glad I have a resource like you guys to turn to.
Regards,
CY
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Have the photocell energize an Off-Delay solid state timer, the timer contact energizes the contactor. Better quality photocells have this feature built-in by the way.
They are wrong. Look at the label on the DP contactor. Is it UL listed? You will see that it is not, it is "UR" which means it is a UL Recognized Component. That means you can ONLY use it as part of another overall UL listed assembly and it's application must be investigated and approved by UL. That basically eliminates the possibility of EVER using them in the field for anything other than direct replacement of an exact unit in a piece of OEM equipment!
Most people don't understand that, including many supply houses. What happens is that some buyer with no knowledge or experience in such things makes a decision based on reading simple data like amps and volts, then says "We don't need to stock lighting contactors, these are the same thing and we can make more money!" That doesn't make it a valid decision.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
One difference is DP coils are not replaceable, at least none that I've seen, they are basically throw away when any part of them goes bad. Most lighting contactors have replaceable components. I've never had an issue with DP's not lasting because of voltage not being exactly what it's rated for, if this was true, many a/c units would constantly be burning out contactors, because thats what they use.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
An On-Delay would close only after a set amount of time. If the command signal is chattering, it basically will fail to close until the chattering stops because the chatter is constantly resetting your timer. I suppose that might work eventually though, but your delay time would have to be set for longer than the time it chatters, and you don't know what that is (yet). So let's say it is chattering for 15 minutes, your contactor would not energize then for 15 minutes as the photo eye voltage chatters.
An Off-Delay time would close immediately, then if the command signal chatters, it remains closed for a set time, let's say a second. As long as the chatter cycle is less than a second, the output never changes. But you don't have to worry about how long it is chattering, it doesn't matter.
By the way, I should have also mentioned that sometimes this can happen if the lighting you are controlling is bright enough to be detected by the photocell controlling it. In other words it gets dark, the cell turns on the contactor, the light hits the cell, it turns off. Repeat to destruction. it might be a simple as moving the photocell.
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