# Suitable Replacement for a Dual Coil Latching Relay

After questioning about my broken thermostat there Debugging an old Thermostat: What component is this? (3 pins SMD IC), thanks to @JRE I could find that it was actually the relay on the board that was broken. Now I'm looking for a replacement of this relay, but I didn't think it could be so difficult to find it... I need either to have a correct naming of this component so that I can find it, or a website + specific component to buy would be so much better. I already checked mousers, digikey, rs etc but couldn't find a suitable replacement. The main reason is that I can't find one with the same pin out (I've got 3 input pins due to the dual coil, and also 3 output pins. The output pins are not aligned, also see picture below)

Here is the detail of the component (from my understanding, please also check the picture below): Dual Coil Latching Relay, 3Vcc 21 Ohm coil, 8A 250Vac contacts, SPST (not sure this is the actual acronym because it's dual coil).

• Update: What's wrong with the broken relay?

The relay "clicks" both ways (i.e. whatever coil I supply, the relay clicks), but only two of the three output poles are connected (i.e. one position doesn't work even if the relay clicks when it turns to that position).

• that is a SPDT (single pole double throw) relay ... it is the contacts that determine the name ... same as a SPDT switch that is manually operated ... what is wrong with the bad one? Apr 4 '20 at 16:39
• you could try taking off the cover and cleaning the contacts Apr 4 '20 at 16:53
• @jsotola Added an update about what's wrong with this one! You mean to keep it soldered to the pcb and take off the cover? Can I just pull the cover with pincers?
– Elia
Apr 4 '20 at 19:06
• yes, the cover may be held on by tabs ... wiggle it with your fingers to see if the cover moves ... if you can get the cover off, then try to polish the contacts with a piece of paper ... paper is actually abrasive, that is why it dulls scissors Apr 4 '20 at 19:50
• also, if the thermostat uses only one set of contacts, then you could switch the wires in the screw terminal strip and reverse the relay coil connections by cutting traces and jumpering them Apr 4 '20 at 19:55

 M15=range
|  M=3.5mm pitch
|  | R2=2 coils
|  | | I=reverse coil polarity
|  | | | A=Ag CdO
|  | | | | H=sealed
|  | | | | | 001=SPDT
|  | | | | | |   8=contact current in amps
|  | | | | | |   | 3VDC=coil voltage
|  | | | | | |   |
M15M-R2I A H 001 8 3VDC


Datasheet at an Italian supplier Cimee https://www.cimee.it/gavazzi/23M15MR1IAH0018eng.pdf which might be able to help you.

It appears that the part is discontinued, and that perhaps this was a Feme part, a company bought by Gavazzi in 1988.

## Possible replacements

I haven't seen anything which is electrically equivalent and also mechanically with the same pinout.

Searching on Digikey for dual-coil latching with 3V coils gave four with adequate current and contacts:

Perhaps you can find one which is small enough, mount it sideways with glue and solder some flying leads to the PCB holes?

## Possible Panasonic Part

For example, perhaps Panasonic

 Range
|   Contacts: 1 Form A (NO) 1 Form B (NC)
|   | Latching dual coil
|   | |  3 VDC coil
|   | |  | Reverse or not
|   | |  | |  Contact material
|   | |  | |  |
DSP-1-L2-3-??-Any


I confess I'm not clear what the "Reverse Polarity" means on this part or your orginal one.

## Possible TE Part

RT314F03

Or this pinout from TE looks close enough you might be able to make a few extra holes and solder the leads bent over.

From TE Datasheet

• Wow, thanks! Any chance to find a suitable replacement? @jsotola aslo suggested to open the relay and clean the contacts, but from what you said and also the datasheet, the relay is "sealed". Is it possible to open it? At the end of the datasheet it's explained that the case is filled with gas, and also how to open the case. Of course the gas would go out (no risk, it's inert), but wouldn't that compromise the component functionality? It's not clear to me for what cases the datasheet explains how to open the case.
– Elia
Apr 4 '20 at 19:16
• Hi ... updated with some thoughts on close potential alternatives Apr 5 '20 at 14:28