Rectifier output?

"Ross Herbert"

Both worked just fine with full wave rectified, 50Hz AC.

Both closed with just 30 volts rms supplied via a bridge rectifier = 26 volts DC average on the coil.

NO TRACE OF BUZZING NOISE WHATSOEVER !!

However:

With half wave rectification, both relays buzzed loudly and would not close at any voltage

Conclusion:

The OP simply has a faulty bridge rectifier.

BTW:

..... Phil

: :"Ross Herbert" :>

:> The relays, presumably, did not "buzz" when the system was first designed. :> Unless the spring loading on the armature has been increased then the :> relay :> should not buzz when driven from a non-filtered bridge rectifier output. :> Since :> the mains input period is 16.7ms there is only a very brief period :> (somewhere in :> the region of 3-5ms) between the 8.35ms half cycles when the voltage will :> be :> reduced below the holding voltage of the relay and the normal magnetic :> inertia :> of the magnet system should be sufficient to keep the armature from :> chattering. : : :** Just tried a couple of 48 volt relays: a Finder octal base type (DPDT :10A) :and an Omron PCB mount ( SPDT 16A) miniature. : :Both worked just fine with full wave rectified, 50Hz AC. : :Both closed with just 30 volts rms supplied via a bridge rectifier = 26 :volts DC average on the coil. : :NO TRACE OF BUZZING NOISE WHATSOEVER !! : :However: : :With half wave rectification, both relays buzzed loudly and would not close :at any voltage : :Conclusion: : :The OP simply has a faulty bridge rectifier. : : :BTW: : :110 volt DC relays are apparently designed to work from rectified US mains :with no filtering. : : : :..... Phil : : :

Thanks for confirming my hypothesis Phil. I concur the most likely reason for the OP's buzzing relay may be a faulty diode in the bridge.