Replacing mechanical Latching Relays with dual coil relays...

Oh, and Guardian called these latching relays INTERLOCKING RELAYs and they look like this (this is a 120VAC coil version):

Yes, this sounds the same.

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

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...

Now you are just getting fancy! (ducking)

John :-#(#

A little cmos flipflop circuit and a Tadiran lithium battery or a supercap would work too.

Two opposed solenoids and an arm on the spindle of a rotary switch.

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?

Or on an bank of opposed microswitches. I've seen that done except the solenoide were a telephone ringer hammer driver.

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.

Cheers

Phil Hobbs

The problem is switch noise.

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.

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 :-#)#

Or a small latching relay controlling a big ole relay?

We like the

FUJITSU FTR-B3GB4.5Z-B10

There is a large literature on electronic designs for interlocking safety-critical functions, like firing a rocket or detonating a bomb. This literature can be a source of circuit ideas and hazards to be addressed.

Joe Gwinn

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 :-#)#

We use a fiendishly clever dual NOR gate circuit to drive these. It takes basically one wire per relay from our uP or FPGA.

Depends on whether simply 'remembering' last state is as good as holding it, during power loss.

RL

What's with this dreck?

-- A host is a host from coast to snipped-for-privacy@panix.com & no one will talk to a host that's close.......................... Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433

No one else has commented on that bad data stream - I suspect your news host garbled it. E-S sometimes jumbles messages together I find, as an example

Enough people here would have mentioned if it was an actual post.

John :-#)#