Wanted relay genius!

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CADMAX

274 posts

Ultimate Geek

#199239 9-Aug-2016 17:05

Help i’m in over my head.. I don't know crap about relays (other than the standard car horn type). So i’m working on a small project at home,
wast oil burner with pump and fan and i want a power cut off (safe cut out for the pump and fan) as well as a easy on off, for my homemade oil burner.

All 12V max load 10 amps

I want to use a push button switch to change over a relay to closed and have it open back up when the button is repressed or the power to the system drops out and comes back on.

The push button switch is this one from jaycar SP0656. Due to it being IP67 and a nice looking switch.

I think i’m after a latching relay?

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gregmcc

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#1607149 9-Aug-2016 17:47

a latching relay won't unlatch when power is removed, it stays latched,

ideally your are looking for a stop start type arrangement, this would involve 2 switches, 1 x N/O contacts for start, 1 x N/C contacts for stop and a 2 pole change over relay.

richms

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#1607150 9-Aug-2016 17:48

Doing it with one button is the problem.

If you can deal with 2 buttons then a normally open for the start and a normally closed for the stop wired to a relay set up as a no volt dropout will do what you are looking for.

Keep in mind with electricity open and closed are the opposite of what you expect.

Richard rich.ms

SATTV

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#1607154 9-Aug-2016 18:06

Using a std relay and a simple little circuit like this http://www.zen22142.zen.co.uk/Circuits/Switching/555toggle.htm is exactly what you describe.

You will just have to make sure the NO side is the power off state.

John

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CADMAX

274 posts

Ultimate Geek

#1607173 9-Aug-2016 18:43

gregmcc

a latching relay won't unlatch when power is removed, it stays latched,

ideally your are looking for a stop start type arrangement, this would involve 2 switches, 1 x N/O contacts for start, 1 x N/C contacts for stop and a 2 pole change over relay.

Lol i said this was over my head... so do you have a parts list for that?

richms

Doing it with one button is the problem.

This is where i came unstuck and could not find a solution.

SATTV:

Using a std relay and a simple little circuit like this http://www.zen22142.zen.co.uk/Circuits/Switching/555toggle.htm is exactly what you describe.

You will just have to make sure the NO side is the power off state.

John

Thanks!! i'm going to give that a shot!

The "NO" Side?
Sorry i don't understand...

Thanks all for the help :) you are Awesome!

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#1607182 9-Aug-2016 19:01

NO = Normally Open

NC = Normally Closed

richms

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#1607188 9-Aug-2016 19:09

CADMAX:

The "NO" Side?
Sorry i don't understand...

Thanks all for the help :) you are Awesome!

NO means normally open, disconnected, but because electricity is opposite, that means that power will not pass thru.

NC is normally closed, which means connected, which means power will pass. Person who decided on that naming needs a punch to the head.

Richard rich.ms

SATTV

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#1607237 9-Aug-2016 20:18

If your in Auckland and need a hand send me PM and we can jack something up.

I am a bit rusty but I am sure it will come back fairly quickly.

John

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pipe60

127 posts

Master Geek

#1607239 9-Aug-2016 20:22

simple 2 button circuit

Masterpiece

247 posts

Master Geek

#1607258 9-Aug-2016 20:50

I use relays to control stuff.

Some considerations;

1. Always consider safety and fail safes even with low voltage.

2. You might be low voltage, but short a 12vdc battery and you get unlimited amps and glowing wires. If you are using a switch mode supply, you can still cook the supply and cause fires with shorts, so...

3. Fuse the circuit, this protect the electronics, devices and everything else.

4. Consider safety of the devices you intend to operate, motors, just note that motors tend to have start up currents far higher than running current. This can pop fuses and or overload under designed circuits. If operating burners, really think about this.

5. Using two relays wired correctly you can latch with a momentary button then when the power drops the latch breaks. The latch in this case is activated via one relay powering the second relay which intern hold power to the first relay. Although you typically need a secondary button or third relay to break the power in this design.

6. Timer relays, slightly better than above, a bit more costly though as you get a single unit with one or dual relays built in, but also includes timer functions which can be set for purpose. I use some of these for a single button operation, hold for 5 seconds to turn on, hold for ten seconds to turn off. I could set longer or shortly on off periods, but 5 stops accidental button pushes to turn on.

7. You can get logic electronic relay's for this purpose as well, they tend to be a little costly like the timer relay's.

8. Cheap alternative with a little logic and home DIY fun is use an Arduino board and relay and momentary button switch. The advantage here is that there will be someone who has posted a design on the Arduino forums for a similar need already, so all the hard "I don't know" stuff has been done as they post instructions. I think the Australian Arduino maker actually makes a board with relays built in, but they all make attachable shields with relays to control motors and stuff.
Note with software logic you can get into controlling fan speed and other aspects.

9. Always consider fail safe, "What if?".

Me:"I'm not a robot!"

ET: "Maybe; you have some freewill, but you chose your path by arrangement"

Me "That sounds like a program with no freewill?"

ET: "We will catch up when you end this cycle"

Me: "Sounds like a 'KPI'!"

ET: "Did you read the terms and conditions?"

Me: .....

Technofreak

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#1607301 9-Aug-2016 22:37

To the OP,

SATTV's suggestion is a really good way to do what you want.

richms:

NO means normally open, disconnected, but because electricity is opposite, that means that power will not pass thru.

NC is normally closed, which means connected, which means power will pass. Person who decided on that naming needs a punch to the head.

It makes perfect sense to me. In the unpowered state the contacts are either closed (NC) or open (NO).

To follow on a closed contact means the contacts are touching (closed) and therefore conduct electricity. In an open state the contacts are not touching (open) and therefore electricity cannot flow across the gap. I don't see where the confusion lies. Anyone who works with electricity knows you close a switch to turn something On and open the switch to turn something Off. Simples.

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sir1963

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#1607404 10-Aug-2016 09:27

CADMAX:

Help i’m in over my head.. I don't know crap about relays (other than the standard car horn type). So i’m working on a small project at home,
wast oil burner with pump and fan and i want a power cut off (safe cut out for the pump and fan) as well as a easy on off, for my homemade oil burner.

All 12V max load 10 amps

I want to use a push button switch to change over a relay to closed and have it open back up when the button is repressed or the power to the system drops out and comes back on.

The push button switch is this one from jaycar SP0656. Due to it being IP67 and a nice looking switch.

I think i’m after a latching relay?

You are 100% correct. A mechanical latching relay has a cog in it, each time the relay is energised it shifts the cog 1 position, so it alternates between on/off.

You want a mechanical latching type.

Have a read here

http://www.omron-ap.co.nz/service_support/FAQ/FAQ02822/index.asp

mclean

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#1607447 10-Aug-2016 10:28

CADMAX: I want to use a push button switch to change over a relay to closed and have it open back up when the button is repressed or the power to the system drops out and comes back on.

The push button switch is this one from jaycar SP0656. Due to it being IP67 and a nice looking switch.

I'm not 100% sure what you're trying to do, but a rotary switch with an integral power failure release might be simpler and avoid a relay altogether. These switches return to the OFF position if the supply fails to prevent an auto-restart. Kraus & Naimer have one. I think the code is CA10-X, or something similar with an -X suffix. Not IP67 though, and not usually a stock item at most suppliers.

RUKI

1402 posts

Uber Geek

#1607460 10-Aug-2016 10:40

You may wish to look at utilising car alarm system:

- what you get in a common alarm design is: remotely controlled doors open/closed by [NO] relays inside the box. Those are 12V.

- another relay [NC] breaks the circuit (e.g. Ignition) triggered by external inputs shorted to ground (doors, boot, etc) - those are in parallel.

- at the same time when triggered you get 12V output to activate lights / horn.

Similarly you can utilise for your needs almost any home alarm system which works similarly with inputs/outputs/triggers of all sorts including magnetic, PR, flood etc

Home alarms even have back up power (12v battery)

For safety reasons you may use as input triggers extra temperature switches found in home appliances (microwave owens, oil heaters)

Rikkitic

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#1607467 10-Aug-2016 10:47

Why not just use a push-on/push-off switch from Jaycar? If you get a double pole (SP0743) you might not even need the relay. Switch also looks the same or similar as far as I can tell.

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