Contactor k ohm resistance  - Page 1
Forum section: electronics / beginners

author: wertyu
author_rank: Contributor
timestamp: April 30, 2022, 09:00:46 am
content: Is this faulty or am i missing something , measure across T to L on all contacts is in hundreds of kohm.Bought new is there something im missing here.https://ibb.co/4sBGnPyTIA

author: Siwastaja
author_rank: Super Contributor
timestamp: April 30, 2022, 11:50:35 am
content: I have noticed that contactors cannot be manually actuated like you show in the picture. I have read high resistance, too, with brand new contactors, which then work just fine to the specs with coil energized properly.Why manual actuation is made physically possible at all when it is not suitable for testing, I have no clue.

author: Per Hansson
author_rank: Unknown
timestamp: April 30, 2022, 12:22:11 pm
content: Yes on these large contactors you have to push down quite hard on the contact to engage properly, and push in the center, not the side.As the poster above mentioned it is best to not do it with a load: you risk damaging the contacts...

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 30, 2022, 01:09:45 pm
content: While it's best to test the contactor by energize the coil but I found when you push on the contactor manually like that you could make it read even lower resistance than when it's pulled in by the solenoid. Putting the test lead in the terminal and tighten the screws is a good way. I found if you only use the test probe to touch the screw sometimes the screws don't conduct as well and causes high reading.I would try pushing it harder. It should read less than 1 ohm. Or try to power the coil.

author: wertyu
author_rank: Contributor
timestamp: April 30, 2022, 01:51:53 pm
content: Thanks all excellent advice i tried to energise but still it is showing high resistance so i think it may be faulty or at least i dont like it , maybe i should not of bought the cheapest i could find.They are supposed to be in the microohms iirc.https://ibb.co/Dp9PV2VThanks all for replies

author: Siwastaja
author_rank: Super Contributor
timestamp: April 30, 2022, 02:06:25 pm
content: You can still try with mains voltage and an actual load, for example a resistive heater (carefully, of course). Power relays and contactors actually have minimum load requirement (often unspecified, though; might be discussed in a separate appnote) and do not work as "signal relays", as the contacts oxidize. That's why signal relays exist as a separate category. But when switching higher power loads, the sparking of the contacts cleans them.Of course, it's possible it's just defective.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 30, 2022, 04:52:43 pm
content: Just a question out of curiousity. How do you keep the Fluke meter so clean and yet you crack the screen. We have a good number of Fluke meters in use here and the yellow are all black with oil and grease but none with cracked screen.

author: IanB
author_rank: Super Contributor
timestamp: April 30, 2022, 05:58:44 pm
content: Quote from: wertyu on April 30, 2022, 01:51:53 pmThis reminds me of a test I did recently on my electric kettle. When I operate the switch and measure the resistance at the plug I see a very high and unstable kiloohm resistance instead of the expected 19 ohms. Yet when I plug it in and turn it on it works fine. It might just be a cheap switch, but it might also expect to operate with higher voltages and have a problem when measured with the low voltage from a test meter.

author: wertyu
author_rank: Contributor
timestamp: April 30, 2022, 06:47:35 pm
content: Yeah think ill try it on live curcuit and test for Volt drop across it.

author: wertyu
author_rank: Contributor
timestamp: April 30, 2022, 06:50:11 pm
content: I bought it with screen crack it was also black with oil and grime not sure how it was done as they are quite tough , I cleaned it best i could, i am gonna replace screen cover when i can but also the upper cover is cracked around screen, its not to bad but i may try to replace whole upper cover. But it was cheap enough and an excellent meter otherwise.

author: bdunham7
author_rank: Super Contributor
timestamp: April 30, 2022, 06:56:07 pm
content: A contactor like that may need a significant current to achieve a low resistance in operation, especially if it has been sitting around or riding around on a boat. If you energize the contactor coil with the appropriate voltage and then cycle it a few dozen times, your meter might start to read a lower resistance as well. But the appropriate test is under a real load.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 01, 2022, 11:29:06 am
content: So how hard did you actually push on the thing?In those big contactors, there is a light sping that separates the contacts far enough so they do not acr over when the contactor is off.When you push the contactor in, then at some point the contacts start contacting (in the contactor (could not resist), and each of the contacts has it's own spring.That means you suddenly have 4 extra springs to push down.From the photograph I can see you're holding the orange thing like a pen, and in that position you simply can not push hard enough for full contact.Take a screwdriver, hold it firmly in your hand and then push in the middle of the armature with several kgf (30N or so) until you notice the armeture moves deeper into the contactor and hits something solid.It is of course also possible that the contacts are damaged of dirty and do not work properly.

author: strawberry
author_rank: Super Contributor
timestamp: May 01, 2022, 04:55:34 pm
content: small contactor looks new, must be testing problemremove two bottom screws and take it apart