dual coil relay coil polarity

[VEGETA]

Hello

I want to use a dual coil relay and found these two to be suitable:

https://www.digikey.com/en/products/detail/same-sky-formerly-cui-devices/PRL3-5V-DC-1A/26833116
https://www.digikey.com/en/products/detail/panasonic-industry/ADW1205HLW/6012615

I want the activation or set coil to receive a positive pulse to ran, and the reset or turn off coil to receive a similar positive pulse to turn off the relay.

However, I looked at the diagram of these and other similar relays, and they draw the common pin of the 2 coils as positive while the coil pins themselves are negative.

So, is the plarity here gonna work like I said? hooking the middle pin to ground, put pulldown resistors on set and reset coils, then wait for a positive signal on either of them.

thanks!

[xvr]

I want the activation or set coil to receive a positive pulse to ran, and the reset or turn off coil to receive a similar positive pulse to turn off the relay.

No, that's not possible. It's a single-coil relay. To activate it, you need to apply a positive pulse to the coil, and to reset it, a negative pulse.
But this can be done using a full-bridge driver. Simply connect the coil to the bridge output, then apply a pulse to one input to set it, and to the other to reset it.

[VEGETA]

I want the activation or set coil to receive a positive pulse to ran, and the reset or turn off coil to receive a similar positive pulse to turn off the relay.

No, that's not possible. It's a single-coil relay. To activate it, you need to apply a positive pulse to the coil, and to reset it, a negative pulse.
But this can be done using a full-bridge driver. Simply connect the coil to the bridge output, then apply a pulse to one input to set it, and to the other to reset it.

I saw some of them having a single coil as you mentioned.

however, I want the dual coil ones. check the drawing in their datasheet to see the types. I attached a picture from Panasonic DW type.

[Psi]

Hard to say, yeah, it's annoying

It's only an issue if they put a diode on the coils or are using a secondary magnet to push/pull against based on the magnetic pole you generate.
They don't say anything about how they work inside, but they both have polarity markings which is suspicious

You could email Panasonic with the part number and ask.

[VEGETA]

Hard to say, yeah, it's annoying

It's only an issue if they put a diode on the coils or are using a secondary magnet to push/pull against based on the magnetic pole you generate.
They don't say anything about how they work inside, but they both have polarity markings which is suspicious

You could email Panasonic with the part number and ask.

i checked multiple ones and they seem to be the same way of marking.

I hope someone really knows how it is done and actually tried it. worst case i will try one board and see if it works in real testing.

[Psi]

They make latching relays with 4 terminals, 2 totally separate coils.
I've used a few of those.


Another thing you could try is ask Digikey to check for you. They do have technical support chat
I've not tried asking them to do something like this, but might be worth a try.

[VEGETA]

They make latching relays with 4 terminals, 2 totally separate coils.
I've used a few of those.

I believe this is one of them: https://www.digikey.com/en/products/detail/same-sky-formerly-cui-devices/PRL2-5V-DC-1A/26833103

[Psi]

They make latching relays with 4 terminals, 2 totally separate coils.
I've used a few of those.

I believe this is one of them: https://www.digikey.com/en/products/detail/same-sky-formerly-cui-devices/PRL2-5V-DC-1A/26833103

na, still has a common terminal between the two coils

Check out this one, bottom 3 diagrams
https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/2477/DE%20Relays%2C%20ADE.pdf

[Zero999]

Here's a cheap and cheerful way of driving a latching relay. It's not very efficient because some power is lost in the resistors, but the coil doesn't need to be driven for long.


EDIT: The above is only needed for the single coil relay. I would recommend using the dual coil relay linked to in the original post.

[PGPG]

I hope someone really knows how it is done...

I don't really know, but I believe there are partially magnetized cores and if you drive coil with reverse polarization you will need higher voltage to switch relay then when driving it as datasheet says. Just check it.
Whenever I used relays I always was using OC npn transistor to drive them so having common '+' and separate '-' seems for me logical.

[VEGETA]

Here's a cheap and cheerful way of driving a latching relay. It's not very efficient because some power is lost in the resistors, but the coil doesn't need to be driven for long.


EDIT: The above is only needed for the single coil relay. I would recommend using the dual coil relay linked to in the original post.

well, looks like you made the simplest one... I can use this with PRL3-5V-DC-1A or PRL6-5V-DC-1A even without series resistors with the coil. I attached a simple schematic, on and off pulses are 3.3v and npn can be something like 2n2222. maybe it needs a pulldown on "ON" and "OFF" transistor gates?

however, i want to know if the relay will actually stay latched for a very long time... like, how exactly? the coil will have a constant 5v at one side but the pulse only briefly complete the circuit.

[Zero999]

Here's a cheap and cheerful way of driving a latching relay. It's not very efficient because some power is lost in the resistors, but the coil doesn't need to be driven for long.


EDIT: The above is only needed for the single coil relay. I would recommend using the dual coil relay linked to in the original post.

well, looks like you made the simplest one... I can use this with PRL3-5V-DC-1A or PRL6-5V-DC-1A even without series resistors with the coil. I attached a simple schematic, on and off pulses are 3.3v and npn can be something like 2n2222. maybe it needs a pulldown on "ON" and "OFF" transistor gates?

however, i want to know if the relay will actually stay latched for a very long time... like, how exactly? the coil will have a constant 5v at one side but the pulse only briefly complete the circuit.

That circuit is fine for a dual coil relay. You forgot the back-EMF diodes. My circuit doesn't need them because the current flows through the resistors, when the relay turns off. Your circuit interrupts the current through the relays, which produces a high voltage spike. The base resistors are also far too lower value. They can be increased to 1k and still provide sufficient base drive.

A latching relay only needs a brief pulse to latch on. It will stay in the same state indefinitely. If you want to ensure your circuit always starts in the same state then, you need to apply a pulse to the same relay coil on start-up. If you want to know the state of the relay, then the easiest way is to use a spare pair of contacts, but note that the contacts might not be well enough isolated from one another to have a hazardous voltage, i.e. mains on one set of contacts and the other connected to a control input.

[VEGETA]

i found that using 2N7000 mosfets is best for me, now with just 22R gate resistors and 10k pulldown should be ok. the coils have resistance of 100 ohms, is it a must to add more?

[Zero999]

i found that using 2N7000 mosfets is best for me, now with just 22R gate resistors and 10k pulldown should be ok. the coils have resistance of 100 ohms, is it a must to add more?

You probably don't need the pull-down but it's not a bad idea, if it's an MCU and there's a chance it could boot with the IO pins set to inputs, leaving the MOSFET gates to float and randomly power the relays.

Just treat the two coils as though they're separate relays. Use the standard transistor, resistors and back-EMF diode circuit.

[floobydust]

A latching relay only needs a brief pulse to latch on. It will stay in the same state indefinitely. If you want to ensure your circuit always starts in the same state then, you need to apply a pulse to the same relay coil on start-up. If you want to know the state of the relay, then the easiest way is to use a spare pair of contacts, but note that the contacts might not be well enough isolated from one another to have a hazardous voltage, i.e. mains on one set of contacts and the other connected to a control input.

"It will stay in the same state indefinitely."

No, a latching relay can change state when bumped. A multimeter product I supported had them coming in for repairs due to bad readings.
I found it was the range relays changing state from when people bonked the thing.
On start-up, the firmware did not pulse (initialize) the relays and assumed they were in the previous state.

I advise, on start/power-up ALWAYS pulse a latching relay to a known state, never assume it's where you left it.

[Psi]

And some latching relays have a manual slider on the top so you can change their state with your finger.

Here's something i made 30 years ago that has lots of manually adjustable latching relays.

[Zero999]

A latching relay only needs a brief pulse to latch on. It will stay in the same state indefinitely. If you want to ensure your circuit always starts in the same state then, you need to apply a pulse to the same relay coil on start-up. If you want to know the state of the relay, then the easiest way is to use a spare pair of contacts, but note that the contacts might not be well enough isolated from one another to have a hazardous voltage, i.e. mains on one set of contacts and the other connected to a control input.

"It will stay in the same state indefinitely."

No, a latching relay can change state when bumped. A multimeter product I supported had them coming in for repairs due to bad readings.
I found it was the range relays changing state from when people bonked the thing.
On start-up, the firmware did not pulse (initialize) the relays and assumed they were in the previous state.

I advise, on start/power-up ALWAYS pulse a latching relay to a known state, never assume it's where you left it.

Even, then if it's bumped whilst powered up, the device will malfunction. It won't happen if the mechanical shock ratings aren't exceeded. Mechanical damping the PCB will be necessary if there's a risk it could be thrown around and dropped.

[VEGETA]

i found that using 2N7000 mosfets is best for me, now with just 22R gate resistors and 10k pulldown should be ok. the coils have resistance of 100 ohms, is it a must to add more?

You probably don't need the pull-down but it's not a bad idea, if it's an MCU and there's a chance it could boot with the IO pins set to inputs, leaving the MOSFET gates to float and randomly power the relays.

Just treat the two coils as though they're separate relays. Use the standard transistor, resistors and back-EMF diode circuit.
(Attachment Link)

your circuit is basically like mine but more complete and polished, I will use it for sure. thanks. however, i put 7000 instead of 7002 thinking its Vgs_th is better suited for my 3.3v pulse signal (coil is 5v though) but looks like they are the same. 7002 seems less Id but more common part, 50mA max Id makes it very suitable. Having TO-92 is also good as I plan to make the board open source where many people can make it themselves, so i searched and found 7002 does not come in to-92 which will force me to 7000.

I initially planned for 10k pulldown and 22 ohms series resistance since i already have 22 ohms elsewhere... will keep the 22 ohms and maybe just use your 100k suggestion. but isn't it better that 100k is after the series resistance?

"It will stay in the same state indefinitely."

my application will not have any movement or so, just put there and stays there.

however, I originally wanted to know how it retains its position with just a pulse? like, internally... i know regular relay needs magnetism in the coil to keep attracting the metal contact... but this one??


 

Mechanical damping the PCB will be necessary

in my case the PCB will be firmly installed using a screw, will be small too and inside a device.

[PGPG]

however, i put 7000 instead of 7002 thinking its Vgs_th is better suited for my 3.3v pulse signal

Yesterday I was reading your posts once more to find if your drive is 3V3 or 5V. As this information looked being secret I assumed that you probably know what you are doing and didn't wrote anything.
I'd never use 7000 with 3V3 source as:
- it is guaranteed to drive at least 1mA with Vgs=3V,
- the minimum Vgs for which its Rds is specified is 4.5V.

[Peabody]

My memory is that (some) latching relays use permanent magnets, one at each end.  And the contact is also attached to a sliding magnet.  The coil overcomes the magnetism enough to get the slide moving toward the other side where it is again captured.

[VEGETA]

however, i put 7000 instead of 7002 thinking its Vgs_th is better suited for my 3.3v pulse signal

Yesterday I was reading your posts once more to find if your drive is 3V3 or 5V. As this information looked being secret I assumed that you probably know what you are doing and didn't wrote anything.
I'd never use 7000 with 3V3 source as:
- it is guaranteed to drive at least 1mA with Vgs=3V,
- the minimum Vgs for which its Rds is specified is 4.5V.

I did not really firmly decided on that but rather the preliminary choice, and then i will search for better parts which has same pinout and package.

I however checked its table and showed Vgs th to be max of 3v so I said it could work, at least a try. BS170 was my alternative, and irlz44n is the higher performance and size one but it is very expensive.

microchip VN2222LL-G/2N7008 seem very good and has even lower vgsth, don''t feel they are "generic" enough like the 7000 and have no alternatives. if going smt then bss138.

I did switch to mosfets to get away without using another resistor value like 1k for npn gate... but if no cheap mosfet is ok, then i may revert back to 2n2222 or 2n3904 but add 1k to its gate or so.

[xvr]

don''t feel they are "generic" enough

Check out the SI2302, my favourite.

[Zero999]

i found that using 2N7000 mosfets is best for me, now with just 22R gate resistors and 10k pulldown should be ok. the coils have resistance of 100 ohms, is it a must to add more?

You probably don't need the pull-down but it's not a bad idea, if it's an MCU and there's a chance it could boot with the IO pins set to inputs, leaving the MOSFET gates to float and randomly power the relays.

Just treat the two coils as though they're separate relays. Use the standard transistor, resistors and back-EMF diode circuit.
(Attachment Link)

your circuit is basically like mine but more complete and polished, I will use it for sure. thanks. however, i put 7000 instead of 7002 thinking its Vgs_th is better suited for my 3.3v pulse signal (coil is 5v though) but looks like they are the same. 7002 seems less Id but more common part, 50mA max Id makes it very suitable. Having TO-92 is also good as I plan to make the board open source where many people can make it themselves, so i searched and found 7002 does not come in to-92 which will force me to 7000.

I initially planned for 10k pulldown and 22 ohms series resistance since i already have 22 ohms elsewhere... will keep the 22 ohms and maybe just use your 100k suggestion. but isn't it better that 100k is after the series resistance?

I wouldn't bother with a series resistor in this case, because the output impedance of the MCU will be enough to dampen any oscillations, but I put one in there anyway because it's the norm.

"It will stay in the same state indefinitely."

my application will not have any movement or so, just put there and stays there.

however, I originally wanted to know how it retains its position with just a pulse? like, internally... i know regular relay needs magnetism in the coil to keep attracting the metal contact... but this one??


 

Mechanical damping the PCB will be necessary

in my case the PCB will be firmly installed using a screw, will be small too and inside a device.

I've never taken a latching relay apart. There are two ways to do this. Either two separate electromagnet assemblies, each attracting the iron lever, thus flipping the switch from one position to another, or a permanent magnet on the switch and the two coils wound in opposite directions on the former. In this case, since there are single coil variants of this relay, it will be the latter.

[VEGETA]

don''t feel they are "generic" enough

Check out the SI2302, my favourite.

seems nice and suitable, i just want to focus on getting a through hole first... if i can't, then i could go smt.

or maybe revert back to npn.

[PGPG]

I however checked its table and showed Vgs th to be max of 3v so I said it could work

Max Vgs th is defined by output current (typically very small, here 1mA).
Practically you need max Vgs th about 1V below voltage you will be using to drive it.