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I'm working on a project involving single coil latching relays (specifically the JQC-3FF-S-Z relay modules), and I'm encountering some issues with maintaining the relay state when power is disconnected. Here are the details of my setup:

  1. Components:

JQC-3FF-S-Z latching relay modules: AMAZON LINK TO MODULE.
Battery Babysitter module providing ~5V power.
Pushbutton for toggling the relay state.
Breadboard and jumper wires for connections.
Note about the relays, they are not exactly like in the diagram below. I'm using a module with 4 relays, load sides of the relays are the same, but the entire module has the following pinout - 5V, G, T1, T2, T3, T4.

  1. Current Setup:

VCC (3.7-5V) and GND from the SparkFun Battery Babysitter are connected to the relay module.
The pushbutton is connected to the T pins of the relay module to send a toggle pulse.

  1. Issue:

When the pushbutton is pressed, the relays toggle correctly. However, upon disconnecting power, the relays switch back to their default state, which defeats the purpose of using latching relays.
I suspect this might be due to unintended reverse polarity effects or voltage spikes when power is removed. I tried using capacitors to help stabilize voltage and that didn't help. I also suspect these possibly aren't true latching relays, why does this module require 5V, G and T? How do these work exactly?

  1. Objective:

I need help understanding why the relays might be toggling back when power is removed and how to ensure they maintain their state.
Additionally, I would like to learn more about properly implementing reverse polarity switching for single coil latching relays using basic components like jumper wires.

Questions:

What could be causing the relays to lose their state/switching back when power is switched off, and how can I prevent this?

How can I manually achieve reverse polarity switching using basic components to properly control the single coil latching relays?

Are there better ways to configure my circuit to ensure the relays maintain their state without adding complex components?

Also, would THESE (UA2-5SNU) be a good alternative if the JQC-3FF-S-Z doesn't pan out? My requirements are simple for a latching relay, that the entire circuit can be powered off and only power on to toggle the relays and when powered off the relays will maintain their last position.

Diagram:

enter image description here

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3 Answers 3

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Based on the module image JQC-3FF-S-Z are not latching relays.

The control circuit uses trigger to change the state.

Could you please describe a task that you are trying to solve.

I used to drive latching relay using inexpensive motor driver DRV8833 and I2C I/O expander MCP23017.

When I wrote code for the relay control I issue 100ms impulse to switch relay to the desired state and then turn the current off.

DrivingLatching Relay

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  • 1
    \$\begingroup\$ What a waste of money, i got bamboozled. Will double check datasheets from now on. Thank you for the educational notes on the timing. Im not really driving anything right now, just LEDs for learning how these work. I think they are a good fit for a circuit i want to build to run various motors. \$\endgroup\$
    – RobbB
    Commented Jul 11 at 5:22
  • \$\begingroup\$ You can use motor drivers instead of using relays. I had a very specific application where I have to use relays and I/O expander doesn't provide sufficient current to drive such relays. Each relay has specific timings to activate. I usually add some margin to this time and it works very well. \$\endgroup\$
    – zoonman
    Commented Jul 11 at 20:48
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It appears to me that the relays are normal non-latching DPDT relays, with the toggling function produced by the six pin ICs by each relay. In that case,the relays WILL go to their NC position when the power is removed.

There are relays that will maintain position when power is removed, but these are not that type.

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The Amazon listing uses flip-flops and non-latching relays to achieve a "latching effect"; remove power to the board and the relays revert to their unpowered state. I would argue that a latching relay that requires power to maintain its state doesn't deserve the name but you can put anything into an Amazon listing.

Your battery might be able to maintain power to the board, but the true latching relays you've linked will do the job without the exorbitant current consumption of relay coils.

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  • \$\begingroup\$ Yes, clearly i fell for the silly self-locking statement. Will try the other relays, two channel will grant me more space anyway. Thanks. \$\endgroup\$
    – RobbB
    Commented Jul 11 at 5:24

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