Identify value in ohms relative of coil relay - Page 1
Forum section: electronics / beginners

author: Jasonbit
author_rank: Regular Contributor
timestamp: November 08, 2018, 11:36:06 am
content: Hello folks,I need know how many resistance the coil of 40.31 relay finder has. Because I am calculating the schematic where I will use a simply transistor PNP to control this relay. I am trying identify the value in ohm relative to the coil of the relay. I am search around on the web and I found this article:https://na.industrial.panasonic.com/blog/how-measure-contact-resistance-relaysAfter I read the article (my level english it is not very good) but I don't understand how this test works. Because when I turn on the coil and the contacts close my power supply 6VDC/1A will short circuit, right?Anyway, how can I identify the value of this coil (in ohm's)? I use the test diode of multimeter (like this image:https://snag.gy/3lFeEU.jpg). My multimeter shows the value 81 in display. The unit of this value is ohms?Datasheet:https://docs-emea.rs-online.com/webdocs/138b/0900766b8138ba16.pdfThanks

author: PTR_1275
author_rank: Frequent Contributor
timestamp: November 08, 2018, 11:58:29 am
content: That document you linked to is measuring contact resistance not coil resistanceWhat relay are you using? Do you have a data sheet?

author: Jasonbit
author_rank: Regular Contributor
timestamp: November 08, 2018, 12:26:18 pm
content: Quote from: PTR_1275 on November 08, 2018, 11:58:29 amBut how can I measuring contact resistance? You're going to short-circuit, right?I intend using this relay: 40.31https://docs-emea.rs-online.com/webdocs/138b/0900766b8138ba16.pdfThanks

author: PTR_1275
author_rank: Frequent Contributor
timestamp: November 08, 2018, 12:42:33 pm
content: One way of measuring low resistances is with a known current (say 1.0000A) and measuring the voltage drop between 2 points. You may think it’s shorted, but if it’s 10mOhm, you will see 10mV across the contacts (at 1.0000A)The data sheet gives lots of info and variables on the coil.What voltage are you running the relay from? The data sheet says 0.65 watts for dc operation. That gives a current of ~54mA and should have a resistance of around 200ohms. This would be measurable with the normal ohms range on a multimeter. Keep in mind the tolerances will vary that figure.

author: Jasonbit
author_rank: Regular Contributor
timestamp: November 13, 2018, 11:17:26 am
content: Quote from: PTR_1275 on November 08, 2018, 12:42:33 pmThanks to your reply,I will study and do again this steps in laboratory. I will share the results in this thread.Thanks

author: PTR_1275
author_rank: Frequent Contributor
timestamp: November 13, 2018, 11:34:00 am
content: No problems.I forgot to mention in my previous post that those figures given were for a 12v coil. If you are running a different voltage, the figures will change

author: Jasonbit
author_rank: Regular Contributor
timestamp: December 02, 2018, 06:31:05 pm
content: On this link:https://www.finder-relais.net/en/finder-relays-series-40.pdfI can see the specifications about relay 40.31. On this board, page 1 of 8,https://snag.gy/QxL97M.jpg, I can discovery which the current I will need to energize the coil with 6VDC. Because the power necessary is 0.65W to 6VDC, this means which my current will be: 0.65/6=0.108A, right?Thanks

author: mansaxel
author_rank: Super Contributor
timestamp: December 02, 2018, 07:13:53 pm
content: Hmm.(what am I, a newbie, missing?)On page 7 in the document you linked to, there are all the data you need, in plain text.Code:Nominal Coil Operating range Resistance Rated coil DC: Releasevoltage code consumption resistance**UN Umin Umax R I at UN R DCV V V Ω mA Ω6 6.006 4.8 6.6 33 165 62So, 33Ω, 165mA and 6V. Don't forget the snubber diode!

author: sarahMCML
author_rank: Regular Contributor
timestamp: December 03, 2018, 02:30:11 am
content: Hi Jasonbit,If you are using the 0.65W relay #9006, 6V, the coil resistance is 55 ohms, giving a current of 109 mA, whereas if it is the sensitive relay #7006, then its resistance is 75 ohms, giving a current of 80 mA. These values are all given on page 8 of the second URL of your first post.Regards,Sarah.

author: vk6zgo
author_rank: Super Contributor
timestamp: December 03, 2018, 03:37:01 am
content: The coil resistance of a relay is simply that--- resistance!If you measured the thing with theohmsrange of your DMM, you would have known it a month ago!( It seems you already have the relay, because you talk about testing it with the "diode test" function of your DMM).