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From: John Robertson <jrr@flippers.com>
Newsgroups: sci.electronics.design
Subject: Re: Replacing mechanical Latching Relays with dual coil relays...
Date: Tue, 27 Aug 2024 07:06:03 -0700
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On 2024-08-27 2:44 a.m., piglet wrote:
> 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.

The problem is switch noise.

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

Correct coil voltage is 24VDC.

Modern latching relays don't have a mechanical interlock - at least I 
haven't seen any - like the original Guardians. So if the microswitch to 
trip the relay is noisy then the modern latch relays go into a middle 
indeterminate state and then we get jammed gears - blown fuses.

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

Yes, something like that may work, I'll have to post the schematic of a 
typical interlock relay when I have some time. Whatever is figured out 
has to not allow an indeterminate state.

Thanks!

John :-#)#



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