School me on relay latching, good articles welcome "how to make a relay latch"

[buildafriend]

Hi,

I'm experimenting with getting some relays going for the first time. I picked up 5 of them and I'm looking into my options for setting them up.

I chose to toy with panasonic DS2Y-S-DC24V relays.http://www.mouser.com/ProductDetail/Panasonic-Industrial-Devices/DS2Y-S-DC24V/?qs=HLLy2pIPwuueuYyfAMBQzQ%3D%3D

Now, I understand that in order to make a relay latch you have to power the coil so that the magnet draws in the switch but do you have to use a "latching" circuit or can you just just use a switch to either connect or disconnect the coil to power? is there a basic circuit or easy to understand literature that I should study?

How important is it to give your relay very clean and smoothed out DC? I'm just wondering what kind of power supply would work best without going overboard. You know, no hum/added noise without breaking the bank.

Thanks,
-JP

 

[JohnRoberts]

There are "latching" type and non-latching type relays.

The latching types will stay in place after you change state. The non-latching will relax to a normal state when coil current is removed.  IIRC from looking at spec sheet it takes at least 70% of rated current to insure a non latching relay will close, and current must drop below 10% to insure it will release.

JR

 

[abbey road d enfer]

Now, I understand that in order to make a relay latch you have to power the coil so that the magnet draws in the switch but do you have to use a "latching" circuit or can you just just use a switch to either connect or disconnect the coil to power? is there a basic circuit or easy to understand literature that I should study?

You can turn a standard non-latching into a latching relay by using one set of contacts to continue to energize the coil after the initial stimulus is gone. (See attached pic). Only problem is that it takes one set of contacts, so if you need 2-pole switching you need a 4 pole relay.

How important is it to give your relay very clean and smoothed out DC? I'm just wondering what kind of power supply would work best without going overboard. You know, no hum/added noise without breaking the bank.

Relays don't need a clean voltage source. There are a number of products where relays draw their power from a very poorly rectified winding with minimum smoothing capacitor. But you have to be very cautious to make sure that the return current is not injected in a noble ground. It is best to provide two completely separate wires for relay powering. You'll need to add a snubber on the switch(es).

 

[ruffrecords]

Here's something I designed a while back but never made:

http://groupdiy.com/index.php?topic=51356.msg652685#msg652685

Cheers

Ian

 

[peterc]

http://freestompboxes.org/viewtopic.php?f=13&t=13295&hilit=Latching+relay

 

[buildafriend]

Now, I understand that in order to make a relay latch you have to power the coil so that the magnet draws in the switch but do you have to use a "latching" circuit or can you just just use a switch to either connect or disconnect the coil to power? is there a basic circuit or easy to understand literature that I should study?

You can turn a standard non-latching into a latching relay by using one set of contacts to continue to energize the coil after the initial stimulus is gone. (See attached pic). Only problem is that it takes one set of contacts, so if you need 2-pole switching you need a 4 pole relay.

How important is it to give your relay very clean and smoothed out DC? I'm just wondering what kind of power supply would work best without going overboard. You know, no hum/added noise without breaking the bank.

Relays don't need a clean voltage source. There are a number of products where relays draw their power from a very poorly rectified winding with minimum smoothing capacitor. But you have to be very cautious to make sure that the return current is not injected in a noble ground. It is best to provide two completely separate wires for relay powering. You'll need to add a snubber on the switch(es).

Cool little trick there with the non latching to latching relay!

Good to know that I don't need clean power. Will 2 forward facing rectifier diodes coming from the high and low taps of a 12V transformer and a filter cap suffice? I'm guessing yes for 24V relays. Hey I just noticed that they make 48V relays in the same footprint. I could have probably bought those and used my phantom power rail. Right?

I'm noticing you're right about keeping the ground separated. It seems to be the way to go.

Looks like I have to get down with momentary switches. I've never had to hand select any of those before so that should be a whole new game. I have unknowingly selected a latching type relay, but that's no problem. I can work with that. I remember that the Orange 86 project used this relay (that's why I chose it) so I'll toy with the circuit from that schemo. Now I'm trying to figure out what all the parts around the relay are doing.

If you guys don't mind helping out, I have a few questions about what's going on with the attached schematic:

What is the BC560 doing?

Why is the .1uF cap in parallel with the 1n4148 also in parallel with the coil?

Am I seeing things correctly when I think I see a SPST momentary switch AND an on/off switch?

I think the resistors are just bias resistors, but R3 may also be a snubber coming from the switch.

Is there anything missing from this circuit (besides the PSU) and can the on/off switch be omitted?

 

[buildafriend]

Here's something I designed a while back but never made:

http://groupdiy.com/index.php?topic=51356.msg652685#msg652685

Cheers

Ian

Ian that looks awesome! I'll have to try breaking that down after I fully understand a basic single latching type relay circuit.

 

[buildafriend]

There are "latching" type and non-latching type relays.

The latching types will stay in place after you change state. The non-latching will relax to a normal state when coil current is removed.  IIRC from looking at spec sheet it takes at least 70% of rated current to insure a non latching relay will close, and current must drop below 10% to insure it will release.

JR

Got it. So if I went the non latching way then I would be able to use a regular old on/off switch. Latching seems to require the use of momentary switches.  Good to see some numbers there for the control voltages.

 

[pvision]

The diode is to stop the back EMF of the relay coil from spiking back into the transistor & the psu.  I imagine the cap is to further damp the back EMF?

Nick Froome

 

[buildafriend]

The diode is to stop the back EMF of the relay coil from spiking back into the transistor & the psu.  I imagine the cap is to further damp the back EMF?

Nick Froome

I hope you're correct because that's a pretty easy to grasp explanation. 

Now I just need to figure out what's going on with the extra switch and the transistor.

Thanks Nick,
-JP

 

[taram101]

Here's something I designed a while back but never made:
http://groupdiy.com/index.php?topic=51356.msg652685#msg652685
Cheers
Ian

It looks overcomplicated to me. Here is the solution I I have used it for years.

 

[abbey road d enfer]

Now I just need to figure out what's going on with the extra switch and the transistor.

Ther's no extra switch; it's just a connection and its label.
The transistor is there to allow the use of a low power switch. The inductive nature of relay coils generates high-current and/or high-voltage spikes that can prematurely wear out contacts.

 

[abbey road d enfer]

Here's something I designed a while back but never made:
http://groupdiy.com/index.php?topic=51356.msg652685#msg652685
Cheers
Ian

It looks overcomplicated to me. Here is the solution I I have used it for years.

Indeed there are easier solutions, particularly one that involves the use of 2-pole switches.
The NO contact energizes the coil in the normal way and the NC contact disarms the feed to the latching contacts.

 

[buildafriend]

Are you guys willing to show me some examples of your favorite relay circuits? Simple examples are probably better for those who are learning. I'm hoping other can learn from this thread.

Here's what I'm deducting(I'll edit this based on your feedback):

-There are two kinds of relays
Latching and non latching. Either way it is wise to not connect the relay coil to a noble ground because the coil causes spikes which can wear out contacts and cause pops. So, isolate relay ground somehow. And, diodes and caps can be used in parellel with the coil to suppress the spikes.

-Latching relays
Every time you send a latching relay it's required voltage it will latch and stay that way until you send it it's required voltage again and then it will unlatch going back to its original state. This requires the use of a momentary switch that rests on the NO position that kisses the closed position and then reverts back to the NO position.

-Non latching relays
require continuous power to keep the relay in its secondary position. Once power is taken away it reverts back to its original position.

Extremely clean power is not needed for relays. A basic full wave rectifier with only one or two filter caps should work fine.

Please correct me if I'm wrong.

Thanks a million guys. I always appreciate learning from you. This forum is a gold mine of information.

-JP

 

[abbey road d enfer]

-Latching relays
Every time you send a latching relay it's required voltage it will latch and stay that way until you send it it's required voltage again and then it will unlatch going back to its original state. This requires the use of a momentary switch that rests on the NO position that kisses the closed position and then reverts back to the NO position.

There are several types of latching relays:
http://en.wikipedia.org/wiki/Relay#Latching_relay

 

[sahib]

Are you guys willing to show me some examples of your favorite relay circuits? Simple examples are probably better for those who are learning. I'm hoping other can learn from this thread.

Google " toggle on-off switch cuircuits" or "push button on off circuits" you'll receive gazillions of options with good explanations.

Here's what I'm deducting(I'll edit this based on your feedback):

-Latching relays
Every time you send a latching relay it's required voltage it will latch and stay that way until you send it it's required voltage again and then it will unlatch going back to its original state. This requires the use of a momentary switch that rests on the NO position that kisses the closed position and then reverts back to the NO position.

The idea here is to provide a pulse to the relay. However, you have to be extremely careful as you may get a surprise. There is something called "contact bounce".  When you press a momentary (or any) button/switch the contacts will bounce more than once before they engage fully. The same will happen  on the way back before they disengage fully. That means there will be more than one pulse generated which will turn the relay off as soon as it turns on. To overcome this you have to use a  contact debouncing circuit after the push button/switch to make sure that only a single pulse goes out to the relay.

 

[Chuckles]

Latching action with a relay means that you want to actuate a relay with a momentary push button switch and have the relay stay on after you release the switch. To do this you need to wire a `normally open`set of relay contacts across the push switch. This is so that the contacts maintain the current flow to the relay coil after the momentary push switch is released.

To shut off the relay, a second switch is needed to interrupt the current to the coil.

In doing this, you lose the use of one set of the relay contacts.

ON THE OTHER HAND

You are not totally clear. If all you want to do is turn a relay on or off, a latching switch, when closed will energize a relay and pull in the contacts. Then when you open that latching switch the relay will shut off.

 

[JohnRoberts]

Latching action with a relay means that you want to actuate a relay with a momentary push button switch and have the relay stay on after you release the switch. To do this you need to wire a `normally open`set of relay contacts across the push switch. This is so that the contacts maintain the current flow to the relay coil after the momentary push switch is released.

To shut off the relay, a second switch is needed to interrupt the current to the coil.

In doing this, you lose the use of one set of the relay contacts.

ON THE OTHER HAND

You are not totally clear. If all you want to do is turn a relay on or off, a latching switch, when closed will energize a relay and pull in the contacts. Then when you open that latching switch the relay will shut off.

There are actually "Latching"  relays designed to be stable in both states so energy is only required to change state. Once changed they stay in the last state.

The link the OP provided, while called a latching relay appears to be the far more typical non-latching type. Conventional non-latching relays have NO and NC contacts for the relaxed state, opposite from the energized state.

JR

 

[ruffrecords]

It looks overcomplicated to me. Here is the solution I I have used it for years.

That is a nice simple solution but unfortunately it only works for small numbers of relays. For n relays you need n-1 contacts on each relay just to work the system. So for the three relays shown you need two sets of contacts to work the system just as in my scheme. However for 6 relays you would need five sets of contacts for the system whereas mine scheme still only needs two.

Cheers

Ian

 

[Andy Peters]

-There are two kinds of relays
Latching and non latching. Either way it is wise to not connect the relay coil to a noble ground because the coil causes spikes which can wear out contacts and cause pops.

The main reason for isolating the relay coil return (lazily called "ground") is to prevent the coil spike putting noise back into your more sensitive circuitry.

So, isolate relay ground somehow.

Easy. The most common way of controlling relay coils is to tie the + coil terminal to the positive supply. And remember that the spikes can go into that supply, too, so that's why it's OK if it is a "dirty" or unregulated rail.

Then you actually switch the - terminal of the coil. So one switch terminal goes to the coil - and the other goes to a net we'll call "coil return." Draw a thick trace from the switch to a ground point near the power supply. Yeah, this is a star ground, which is something we don't do on circuit boards, but in this case you're trying to manage ugly current spikes.

-Latching relays
Every time you send a latching relay it's required voltage it will latch and stay that way until you send it it's required voltage again and then it will unlatch going back to its original state. This requires the use of a momentary switch that rests on the NO position that kisses the closed position and then reverts back to the NO position.

Yes, exactly, but as noted elsewhere you should debounce the switch.

One more thing with latching relays: do you care what state they come up in?

-a