- Relays that don't work
- Posted by darkknight on March 21st, 2008
Anyone had any experience with relays that don't quite work - try to
turn a relay on and it sometimes does and sometimes doesn't, or turns
on for a bit and then drops out or oscillates intermittently. Seems
the coil is faulty or something. Anyone heard of relays that do this
and what might cause it.
Thanks
[Is there a better newsgroup for this question?]
- Posted by Moon Shine on March 21st, 2008
"darkknight" <darkknight.21@gmail.com> wrote in message
news:bn06u3t0qejuhha8u3o6sppq29o7k4t9qs@4ax.com...
I've experienced it on a production run.
Turned out the manufacturer's cleaning solution was bad.
The contacts would stick after a number of consecutive
toggles during test. Apparently there was a sticky
residue on the internal contacts. Happened often
enough to return the entire lot of relays.
Oscillation is bad firmware.
- Posted by Al on March 21st, 2008
On Fri, 21 Mar 2008 13:40:36 +1300, darkknight wrote:
Silly question, but is the sustaining voltage above the drop-out voltage?
Al
- Posted by Mark Borgerson on March 21st, 2008
In article <9996u311vhrq2rss7gvbfu9knri91jdp6b@4ax.com>,
speffSNIP@interlogDOTyou.knowwhat says...
Or the supply driving the relay can't sustain the output
current at DC. Depending on the coil inductance and
DC resistance, you can get weird voltage spikes accross
the coil. The oscilloscope is your friend in these
cases. Depending on the time scale, you might also
have a supply or driver going into thermal overload.
Mark Borgerson
- Posted by Spehro Pefhany on March 21st, 2008
On Fri, 21 Mar 2008 13:40:36 +1300, the renowned darkknight
<darkknight.21@gmail.com> wrote:
Sounds like the coil voltage isn't high enough...
Best regards,
Spehro Pefhany
--
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Embedded software/hardware/analog Info for designers: http://www.speff.com
- Posted by CBFalconer on March 21st, 2008
Spehro Pefhany wrote:
50 years ago we used lots of IBM relays that had a pick coil and a
hold coil. In those days computers were large monsters with many
vacuum tubes. But the relays were reliable.
You can make peculiar circuits involving diodes and capacitors and
multiple voltage supplies that can effectively supply the extra
'pick' effort. Repetition rate is limited.
--
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[page]: <http://cbfalconer.home.att.net>
Try the download section.
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- Posted by Paul E. Bennett on March 21st, 2008
darkknight wrote:
Herer is OK for this question. If you are having this problem with all of
your relays then you have a number of possible causes. Others have
alluded to Voltage or Current availability for the relay to hold in. You
can confirm this by test-benching a relay from a small bench power
supply that has current and voltage adjustments (the lab variety). See
what your relays really want by way of drive.
You usually need a good driver transistor powered from a supply rail that
has plenty of current drive behind it. Most relays (and solenoids) want
60% of their rated voltage to hold in but you need to give them their
full rated voltage to ensure the pick properly. Limiting the current
available from supply rails will also limit the voltage they see. This
sort of thing you will see on the bench test.
Bad batches like those alluded to by Moon-Shine do not happen that
frequently but they can happen. So try a number of relays from different
batches if you are able. If the relay has a removable cover, inspect the
mot
ion as it closes. If it is a DIL type or fully sealed type then check
them out thoroughly as suggested above and compare with their
data-sheets. Scopes are very useful for this type of exploration.
--
************************************************** ******************
Paul E. Bennett...............<email://Paul_E.Bennett@topmail.co.uk>
Forth based HIDECS Consultancy
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-811095
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
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- Posted by cs_posting@hotmail.com on March 21st, 2008
On Mar 20, 8:40 pm, darkknight <darkknight...@gmail.com> wrote:
Yes -
- Some that had polarized coils and I didn't notice that when I
designed the board. They'd make a soft clicking sound (being repelled
by the magnet I guess) but not close the circuit.
- Cleaning solvents, our own rather than the component vendors
(actually this was with PCB mount audio transducers)
- Posted by Andrew Smallshaw on March 21st, 2008
On 2008-03-21, darkknight <darkknight.21@gmail.com> wrote:
Do you have a protection diode to absorb the back emf when the coil
turns off? If not it is possible that your driver components are
being partially fried. As other posters have hinted at, my first
plan of attack would the to check the power to the coil, both in
terms of voltage and current.
--
Andrew Smallshaw
andrews@sdf.lonestar.org
- Posted by Jim Stewart on March 24th, 2008
Moon Shine wrote:
Aqueous cleaning non-sealed relays can
do the same thing.
