Having trouble with relays - coils drawing current, but never switching - Page 1
Forum section: electronics / beginners

author: HwAoRrDk
author_rank: Super Contributor
timestamp: November 21, 2016, 09:08:31 pm
content: I bought some of these micro relays to use in a board I designed:TE Axicom IME06TS. 12VDC, DPST-NO.Datasheet:http://www.farnell.com/datasheets/1717939.pdfI cannot for the life of me get these damn little bastards to work properly!The thing is, theyseemto be working. I can supply the coil pins with 12V, and they will happily sit there drawing 8-9mA. That appears to be within spec; actually measuring the resistance of the coils gives me about 1K, which matches the datasheet. But they don't switch the contacts!Rarely and randomly - and this only ever happens out of circuit on the bench, and I don't know what combination of circumstance causes this - theywillwork, and I can hear the 'click' and there will be good continuity between the switching pins. It can be working one minute though, and not the next. And I have not been able to get them to switch at all, ever, when soldered-in on my board.Is there anything I'm missing here? What else I can check before I declare these parts as faulty and try and get them replaced? Or is there perhaps some way I may have inadvertently killed these relays?

author: cvanc
author_rank: Frequent Contributor
timestamp: November 21, 2016, 09:27:49 pm
content: Quote from: blueskull on November 21, 2016, 09:13:27 pm^^^This.Page 2 of your datasheet shows pin 1 of the coil as positive. Please verify you are driving it thusly.(and if you feel like saying 'well that datasheet wasn't terribly clear about this', well, you're right)

author: Seekonk
author_rank: Super Contributor
timestamp: November 21, 2016, 09:31:25 pm
content: How old are they? I mean date code. Some relay contacts over time oxidize and don't make contact at low voltage. Apply a higher voltage and some minimal current the oxide layer breaks down. Assume you tried the obvious. I once spent a half hour on the phone with some guy trying to hook a see through plastic relay. Finally couldn't take aymore.

author: langwadt
author_rank: Super Contributor
timestamp: November 21, 2016, 09:35:19 pm
content: Quote from: HwAoRrDk on November 21, 2016, 09:08:31 pmdouble check number on the relay maybe you accidentally got the latching version ?

author: HwAoRrDk
author_rank: Super Contributor
timestamp: November 21, 2016, 10:19:28 pm
content: Quote from: cvanc on November 21, 2016, 09:27:49 pmSon of a *****!!!I just tried one with the 'correct' polarity voltage on the coil and it works consistently.And guess which ****ing way around I have the pins laid out on my PCB? That's right, the wrong way round.So much for that batch of boards...Before I go and drown my sorrows, someonepleaseexplain to me why polarised relay coils are a thing, and why the coil itself draws the same current no matter which way round the connection is made.And FFS, TE. Make it more bloody obvious on the datasheet! And an actual polarity marking on the relay itself wouldn't go amiss either.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: November 21, 2016, 10:34:18 pm
content: Ah, okay. I guess these relays might need a permanent magnet because of the small size. I suppose such a tiny coil may not have the holding power to make a secure switching contact, so it needs some assistance.

author: dmills
author_rank: Super Contributor
timestamp: November 22, 2016, 12:34:39 am
content: You might try subbing an IM06DTS which is not as far as I can see polarized.I think everyone gets stuffed by this at some point (Bit like SMT LEDs where the polarity depends on the colour even within a range)....73 Dan.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: November 22, 2016, 01:34:09 am
content: No, I don't think that'd help. The IM06DTS is just a 'high current' version of the DPDT plain-IM part, and the datasheet for those still shows the coil as polarised; not to mention it has an extra pair of pins for which my board has no holes.I think the entire IM series has polarised coils.Think Imightbe able to make good my current lot of boards by cutting some traces and soldering a few kynar wires. Gonna be a pain in the backside, though.

author: Cerebus
author_rank: Super Contributor
timestamp: November 22, 2016, 01:46:02 am
content: Quote from: dmills on November 22, 2016, 12:34:39 amWhen placing SMD LEDs I no longer use normal component tweezers, I use measurement tweezers with a multimeter on the diode setting.

author: JoeN
author_rank: Frequent Contributor
timestamp: November 22, 2016, 02:41:27 am
content: Make some tiny "adapter" boards that have a pinout on one side that matches your "wrong" PCB and then wires it into your relays correctly. Then it will look professional.OSHPark is perfect for this, they are very cheap for very small boards and if you send them the files tonight you have it in 10 days in the US at least. Not sure on how long to UK.

author: w2aew
author_rank: Super Contributor
timestamp: November 22, 2016, 03:16:45 am
content: Quote from: HwAoRrDk on November 21, 2016, 10:19:28 pmIf you used a through-hole version of the part, maybe you can mount the relays on the other side of the board. If so, you can save that batch of boards.

author: macboy
author_rank: Super Contributor
timestamp: November 22, 2016, 03:42:18 pm
content: Quote from: w2aew on November 22, 2016, 03:16:45 amI love this suggestion! Very clever

author: HwAoRrDk
author_rank: Super Contributor
timestamp: November 22, 2016, 04:00:14 pm
content: Quote from: w2aew on November 22, 2016, 03:16:45 amAha, yes! Great idea.Don't know why I didn't think of that.Not sure if the board will fit inside the intended enclosure once the relays are mounted on the underside, though - I'll have to see.

author: bson
author_rank: Unknown
timestamp: November 22, 2016, 06:53:10 pm
content: Quote from: HwAoRrDk on November 21, 2016, 10:19:28 pmWe've all done it. I remember when I discovered some Omron relays specify pinouts based on abottom-upview for TH while the exact same device in SMD have top-down pin numbering...I haven't checked the datasheet for your TE device, but if it's TH just mount it on the bottom side for further verification to help find any other board problems so you can fix as much as possible in a single update.

author: jitter
author_rank: Frequent Contributor
timestamp: November 22, 2016, 07:52:32 pm
content: Reminds me of when for some product we used polarised Omron relays and the things refused to work...Everything checked out fine, type and everything, polarity of the layout was correct (as proven in earlier runs). But then I noticed something odd in the printing on the relays that I couldn't find in the datasheets.The relays we should have gotten were Omron G6B-1114P-US5VDC, but instead we got the G6B-1114P-1-US5VDC.The difference was "-1" and I couldn't find its meaning in Omrons datasheets (still can't). Than I saw this description on the Mouser page for the "-1"-version: "General Purpose Relays SPST-NO 5VDCReversed Polarity" and all became clear.Edit: I think this version may have been a "special" by Omron, hence not finding their way into the datasheet. However, to this day, Mouser sell a reversed polarity version of the 12 Vmodelof the above relay.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: November 23, 2016, 01:07:28 am
content: I de-soldered all the relays and re-soldered on the underside of the board and everything works fine now.Definitely doesn't fit in the enclosure any more, though.

author: w2aew
author_rank: Super Contributor
timestamp: November 23, 2016, 03:21:10 am
content: Quote from: HwAoRrDk on November 23, 2016, 01:07:28 amAt least you can validate proper operation of the rest of your board.

author: JoeN
author_rank: Frequent Contributor
timestamp: November 24, 2016, 06:12:11 am
content: Quote from: blueskull on November 23, 2016, 03:24:53 amI have a pile of PC ISA boards from the old days and back then, mid to late 80s, early 90s, it was not at all rare to see bodge wires on boards that were sold into retail. It happens.