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

On 2024-08-27 7:40 a.m., john larkin wrote:

On Tue, 27 Aug 2024 14:02:37 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Robertson <jrr@flippers.com> wrote:

On 2024-08-26 2:09 p.m., Don Y wrote:

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]

Yes, this sounds the same.

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.

There are two DPDT relays that change state together. 8A non-inductive
at 24VDC 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.

Ah, yes these MUST be non-volatile. The relay must stay set/reset until
the mechanical operation resets it, otherwise fuses blow after the gears
jam. Power interruptions can't change that state...

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

Now you are just getting fancy! (ducking)

John :-#(#

I’d be cautious about any solution that separates the physical state of the
switch from the logical state.

How about a nice small latching relay controlling a triac or SSR?  You can
do the UVLO function with a MAX809 or something like that to gate the
supply to the relay coil.

Or a small latching relay controlling a big ole relay?

We like the

FUJITSU             FTR-B3GB4.5Z-B10

Interesting that you reverse the coil polarity to release the single coil.

Gives me other ideas on solving the problem - use a small (2A contacts)
dual coil latching relay to drive a bigger relay. The small relay won't
be bothered as much by switch noise as the current required is much less
so is unlikely to get into an illegal state. Will read the product
literature on these and see what comes up as a good unit.

Like I don't have enough projects!

John :-#)#




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