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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Replacing mechanical Latching Relays with dual coil relays...
Date: Mon, 26 Aug 2024 14:09:26 -0700
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On 8/26/2024 10:52 AM, John Robertson wrote:
> Anyone have experience with dual coil latching relays? I'm trying to replace 
> old (1950s) Guardian latch relays as used in 1950s style jukeboxes with more 
> modern two coil latching relays but have had trouble with some relays going to 
> an indeterminate state if the power to the coil is  below optimum.
> 
> What I actually need to do is a circuit that only allows the Latch/Reset coils 
> to trip when there is sufficient voltage and current available...
> 
> This somewhat plays into the discussion on DC relay latching voltage thread and 
> I'm wondering if the Zener diode across the windings or in series with the 
> windings might help my design.
> 
> As for the old original relays, the contacts are getting so pitted they can't 
> be saved and Guardian hasn't made this coil assy for decades. They don't turn 
> up on eBay either.

You're not trying to be "genuine"... so, why dot replace the relay with
a hybrid *circuit* that emulates a latching relay?

[No idea what yours are like; I used to encounter them in pin setters
("ten pin") -- two coils mounted on a frame at right angles to each
other.  Each coil being a DPDT relay with their armatures mechanically
interlocked.  Nothing to prevent you from energizing BOTH coils except
the actual design]

Depending on the number (and form) of the contacts being used, you
could design a little SR latch on a board, driving a single relay
(to give you volt-free contacts) with the appropriate number (and
form) of contacts.

One possible complication would be if these were used to maintain state
in a nonvolatile manner -- adding that to your circuit would require
a nonvolatile store.

Of course, the "easy" way is a tiny 6 pin MCU with a FET driving the
relay...  persistent state could be maintained in FLASH.