Simple latching relay with momentary power trigger

Thread Starter

Raygunner

Joined Feb 9, 2024
2
I have a simple question that I cannot, for the life of me, solve.

The premise is simple: I need to turn ON/LATCHING relay using a momentary programmed switch that closes and supplies 12vdc for 25ms, and have it stay LATCHED until the same programmable switch closes again for 25ms, providing another 12vdc pulse. This would turn OFF/UNLATCH that same relay. The latch action shorts a gate circuit for 10 hours via the programmable switch, and then unlatches via that same switch. The shorting action keeps the gate open. The home development wanted a programmable system to open the gates automatically at 630am and close again at 830pm.

This is a remote solar powered system opening and closing gates so I went with a latching relay to minimize power draw. So after latch and unlatch operations there should be zero power draw. The only power used is twice a day for less than a second to latch/unlatch.

Problem is... I cannot find a latching relay that simply LATCHES on a simple closure that supplies temporary 12vdc for 25ms, and later UNLATCHES using the same 25ms closure. I've been through three boards and a latching relay from Amazon but ALL of them need a set/reset function that requires power during the duration of set or reset. A simple automotive latching relay that I thought would work requires REVERSE polarity through the coil to latch/unlatch.

All circuits are 12VDC. Again, this is a solar powered system driving the gate control board and an automated scheduler (Altronix PT2724A) that I installed in the box with the controller as part of my modifications. The gate control and the scheduler use about 54ma total in normal use and control (2) 3000XLS gate arms. There are (2)12v7AH batteries and (2) 10 watt solar panels that supply power 24/7 to the system. There are no local power options.

I've attached a PDF of my design and layout. The relay is to the right of the scheduler and shorts "SHADOW" to "COM" to hold the gate open, preventing the autoclose. This was recommended per GTO tech support.

If anyone has suggestions or could point me in a general direction I would greatly appreciate the help. This is the last thing holding me up from finishing. Thanks for reading.
 

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eetech00

Joined Jun 8, 2013
3,953
Seem like your looking for a single coil latching relay.
Relays of this type are set and reset using a polarity sensitive coil. They set with one polarity and the reverse polarity resets it. They also require a pulse a few milliseconds long to set/reset and cannot be left energized, or the coil will burn out.

Does this sound like what your looking for?
If so, what are the mounting requirements?
In a weatherproof enclosure?
How much current is required for the contacts?
 

vu2nan

Joined Sep 11, 2014
345
You need an 'impulse' or 'ratchet relay' that's available off-the-shelf.

It gets 'set' on application of a pulse input to it's coil and 'reset' on the subsequent pulse.

In other words, an impulse / ratchet relay alternately gets set and reset with pulse inputs to its coil.

Here's an animation, courtesy Homofaciens.de, that gives an idea of how the impulse relay works.

Nandu.
 

Thread Starter

Raygunner

Joined Feb 9, 2024
2
Seem like your looking for a single coil latching relay.
Relays of this type are set and reset using a polarity sensitive coil. They set with one polarity and the reverse polarity resets it. They also require a pulse a few milliseconds long to set/reset and cannot be left energized, or the coil will burn out.

Does this sound like what your looking for?
If so, what are the mounting requirements?
In a weatherproof enclosure?
How much current is required for the contacts?
Mounting will be either velcro (if a box relay) or stand-off's if a small PC board. Space is limited in the existing GTO control box. If an auto box-type relay I would use spade lugs for connection.

Enclosure is weatherproof.

No real current is used. It is a simple 5vdc line to common ground. Probably .01ma is my guess.

Many thanks for your reply and help! - Ray
 
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