12v Switched Power

[rebelleader]

I need help from the mighty electronics Gurus.

I need to build a switch that will supply a constant 12v to multiple sources when it receives a 12v 'on' signal and turn off power when the 'on' signal goes away.

I thought about using an automotive StartUp/ShutDown controller, but the circuit is more complicated than I need.


Any help is appreciated, if any more info is need I will provide it

 

[agent420]

Sounds like all you need is a simple relay.

 

[Mohonri]

Sounds like all you need is a simple relay.

That's exactly the thought I had. A relay acting as a buffer (of sorts).

 

[Mysterae]

From your original post, I presume this is an automatic switch and not manual?

I would ask myself:

1. What kind of current load are you switching?
2. Do you need an override function to enable it when the on signal isn't present?
3. Do you need to isolate the 12V on signal from the feeding circuits?
4. How fast do you need the switching to be, i.e. less than a second?
5. Is the switching repetitive?

Sorry if I'm making this more difficult than it should be, but there are times when you wouldn't want a relay.

 

[rebelleader]

From your original post, I presume this is an automatic switch and not manual?

I would ask myself:

1. What kind of current load are you switching?
2. Do you need an override function to enable it when the on signal isn't present?
3. Do you need to isolate the 12V on signal from the feeding circuits?
4. How fast do you need the switching to be, i.e. less than a second?
5. Is the switching repetitive?

Sorry if I'm making this more difficult than it should be, but there are times when you wouldn't want a relay.

1. Max of 30amps
2. This function is not necessary for my application.
3. Not sure what you mean here. The 12v 'on' signal should only be used to trip the switch to another 12v source.
4. Time is not an issue. This is an automotive application, so I guess less than 5seconds would be desired.
5. Not to any significant degree. Again, this is an automotive application. I need power only when the vehicle is on, but don't want to be drawing the power through the stock wiring harness, but rather directly from the battery.

Thanks for you help.

 

[agent420]

Again, this is an automotive application. I need power only when the vehicle is on, but don't want to be drawing the power through the stock wiring harness, but rather directly from the battery.

A relay is exactly your answer; this is a very common use... Your local RatShack carries the one you need. These are also commonly available at auto parts stores. Make sure you use wiring that can handle the load. And if I may offer hard learned advice, use rubber gommets when feeding wire through panels, even though you think you may not need one; vibration can take it's toll much more quickly than you realise..

Just for future reference, I think it's often easier to provide help when you post the exact application or problem you are working on right off the bat.

 

[Frank4d]

For 30 amps I would use a solid state relay similar to the D1D40 here: http://www.crydom.com/userResources/productFamilies/39/crydom_1dc.pdf

They are kind of expensive: http://www.newark.com/jsp/Electrome...s/CRYDOM/D1D40/displayProduct.jsp?sku=80K9298 but input current is very low for the control input, and you don't have to worry about wearing out relay contacts from arcing.

 

[agent420]

...and you don't have to worry about wearing out relay contacts from arcing.

Yes, but automotive electrical environments are pretty brutal, you might have to worry about exceeding the 32V supply (spikes of 100V+ are not uncommon)... solid state stuff in a car really has to be designed for the application.

Relays are pretty hardy, and the contacts are designed to wipe over each other in a self cleaning action. They've been turning on headlights for decades...

 

[Mysterae]

I would agree, a relay is what you need. In fact, as agent420 implied try to get hold of an actual automotive relay and it's socket. These are designed for the harsh conditions and sometimes are protected from the back emf that the coil can create when power is removed.

Also, make sure the 12V on signal has enough current available to operate the relay, but I'd imagine you would be fine.

 

[rebelleader]

I would agree, a relay is what you need. In fact, as agent420 implied try to get hold of an actual automotive relay and it's socket. These are designed for the harsh conditions and sometimes are protected from the back emf that the coil can create when power is removed.

Also, make sure the 12V on signal has enough current available to operate the relay, but I'd imagine you would be fine.

I am having a bit of difficulty finding the socket

 

[agent420]

I am having a bit of difficulty finding the socket

The socket certainly makes life easier, but I've always had good success using common insulated spade lugs hooked directly to the relay.

I would think a local auto parts store has the sockets, but I bet they're cheaper at places like All Electronics.

 

[Crazy tech]

A plain starter relay would work the kind for tractor that use 12 volt in, not 5 or 7 like an cars.