Re: Replacing mechanical Latching Relays with dual coil relays...

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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