[Boatanchors] Relay Repair - Demagnetization Question

[Carl]

My Scott 800B hasnt acted up yet!

Ive had a few 24VDC relays fail to engage after several years of RF use 
switching antennas on the towers. Nothing would restore them to service but 
they now work fine on 24VAC.

Some digging thru the P&B site and others gave info on how DC relays are 
actually created.

Vacuum relays as used on amps sometimes appear dead on receive. Reversing 
polarity sometimes works.

Carl
KM1H


----- Original Message ----- 
From: "Mark Foltarz" <Foltarz at rocketmail.com>
To: <boatanchors at mailman.qth.net>
Sent: Tuesday, February 02, 2010 12:00 PM
Subject: Re: [Boatanchors] Relay Repair - Demagnetization Question


I experienced the phenomenon with a Scott 800 radio. The mute relay kept 
sticking and by all appearances it was the coil and core
staying magnetized. Indeed the relay uses DC.

After a lot of head scratching I placed a piece of scotch tape across the 
coil assembly to prevent it from making contact with the contactor arm 
(terminology ? )

Has not stuck since.

de KA4JVY

Mark



----- Original Message ----
> From: Glen Zook <gzook at yahoo.com>
> To: boatanchors at mailman.qth.net; Ron <ronami at yahoo.com>
> Sent: Tue, February 2, 2010 11:31:22 AM
> Subject: Re: [Boatanchors] Relay Repair - Demagnetization Question
>
> In theory, yes. But, unfortunately, in reality, no! There are all sorts of
> relays "out there" that, when run from DC, definitely get magnetized. The 
> "fix"
> is to reverse the connections periodically. Now when run from AC the 
> problem
> doesn't exist.
>
> Glen, K9STH
>
> Website: http://k9sth.com
>
>
> --- On Tue, 2/2/10, Ron wrote:
>
> Relays are designed with very low coercivity (or remnance) cores. There is 
> no
> need to ever demagnetize a relay.
>
>
>
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