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Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
I have a relay switching a solenoid valve that won't turn off. It turns the load on OK, but instead of turning off, the relay just whines (oscillates).
For full disclosure, its a tiny little relay driven directly by the output of a 556, and the load is a 6W@12V solenoid. A 9V batt is switched by the relay, and the 556 and relay coil is running on regulated 5V.
I tried filtering caps in the power lines, but the 556 is not resetting. I tried diodes across the load, but it didn't help.
I know there must be a simple solution, I hope this doesn't constitute a revocation of my right to ridicule.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
You do have a diode in antiparallel with the coil on the relay, right?
Does it work if you just manually connect/disconnect 5v to the coil? And if you just connect a LED/resistor to the 556 it blinks like you expect it to?
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
AM wrote ...
I have a relay switching a solenoid valve that won't turn off. It turns the load on OK, but instead of turning off, the relay just whines (oscillates).
Peter has said just about everything appropriate, but I'd add, you couldn't have mixed up the relay terminals or made something common where it shouldn't be, right?
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
I checked the 556 output with a scope, its perfect.
..., I tried putting a diode in antiparallel with the coil, but it didn't help.
I triple checked my schematic to see how I might have wired up a relay oscillator, but its pretty straight forward. After work I'll unsolder the coil and put in a noninductive dummy load to see if that makes a difference.
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
I have no idea what was going on, but indeed the 556 was tossing its own cookies trying to flip that relay. Its a 5v, 250ohm, relay coil, so the 556 should be able to source more than enough current......
A big cap across the relay solved the problem... probably heats up the 556 when connecting power, oh well...
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Relay problem
