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From: piglet <erichpwagner@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: Replacing mechanical Latching Relays with dual coil relays...
Date: Tue, 27 Aug 2024 09:44:17 -0000 (UTC)
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John Robertson <jrr@flippers.com> 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.
> 
> Thanks,
> 
> John :-#)#

Millions of latching relays are still made. If the problem is under
voltages causing erratic activity I guess a driver with threshold detection
using LM339s or TL431s or whatever might be possible. Either to trigger
dual coil latch relays or single coil bipolar latch relays. 

Can you give numbers, like correct coil voltage and the troublesome
incorrect voltages ?

Something as simple as series SCR with zener anode to gate might be enough?

-- 
piglet