I have an alarm with a orange grounded when armed wire and I currently have one relay attached to it for a starter kill and I now want to add a second relay for something else.
The thing is the installation manual for the alarm says "If more than one electronic device will be connected to the H3/5 orange wire,it will be necessary to isolate the connection of each device control wires with a diode",but I don't see why diodes would be needed for two relays...

So do I have to use diodes?
Also will it be ok to add a second relay or would it consume too much power(the wire is 200mA)?

 

bump

 

Bump cuz i had have almost the exact question in my "Rolling up your windows using your alarm" thread.

the answers i've received have been yes, you can connect as much as you want. but i would like to find out about the diodes. im running a tilt sensor and going to be adding a relay'd kill switch to the GWA orange wire.

 

I Don't know this alarm but here is why as and engineer I would recommend a diode.

When you hook a relay up you hook one end to +12V and the other end to your switched ground wire. When the switched ground is activated it switches the relay on. When the switched ground is off the relay turns off.

Now if you take a relay apart its just a straight wire. The part you "energize" is a coil of wire meaining +12V will pass right through it. So when you deactivate your switched ground your relay will now supply +12V to any other item attached to the same wire. If its just another relay it probably doesn't matter much. But if you have another sensitive electronic device attached to that wire sending +12V down it when its expecting a ground is not a good idea. A diode ensures the current will only flow in one direction.

Its easier to write instructions that cover every case then to write and expect everyone to understand specific cases.

 

You need to check the current demands of the relay you are using could be yes could be no.

 

interesting.
so would the diode go right before the relay, but after the sensor thats on the same circuit?

 

Each item connected would have its own diode.

 

If you are using relays, I don't think you will need the diodes since the relay will not affect the orange wire at all.

If you connect say the orange wire directly to something that gets grounded when it gets used THEN you will need to use a diode.

 

I would use a relay to make a high current ground. Depending on what relay you use. 200ma might not be strong enough ground to power both. Then follow nsxtreme advice on the diodes if needed.

 

i believe they are referring to a spike supression diode. if it is, its only there for safe reasons which i never use.

 

This application is not the same thing. Those diodes are asserted across the coil of the inductor. These diodes are put in series with the pulsed ground, entirely different purpose.

 

Use the diodes, it can't hurt, 12V+ through resistance, [relay coil] can act as a ground to low current demand electronics

Most automotive relays will need about 200mA to energize and about 125mA to stay energized, as mentioned, use a relay to change the low current, [200mA] ground of the GWA lead to a high current ground and use a diode on each line from relay to any other device, 1A diodes are cheap. 94

 

I haven't read anyone's posts so sorry if this is already stated.

With a mechanical relay, there is a coil that energizes a plunger which then moves a set of contacts to 'contact' another set (simply put). All inductors have a specific property that must be remembered... all inductors resist changes in current.

This is of particular importance because if one energizes a inductor coil (by connecting/energizing the control coil wires), the current will build slowly over time. Conversely, if you de-energize the coil, the energy doesn't just disappear. The energy stored must discharge through various means.

A coils discharge in an industrial environment has tendencies to crash microprocessors among other equipment. To reduce this tendency, one must install ferrite beads (to reduce the electric field produced), install across coil diodes (to allow a path for appropriate energy discharge), among other methods.

Hope this helps. Comments, questions, corrections welcome.

 

From the post in this thread if you were the engineer writing the instructions can you see how its easier to write a method that covers all cases instead of trying define each individual case?

 

Very good points here, while I wouldn't call a relay coil a "straight wire" it has a very finite resitance which allows it to act as a pull-up (or down if attached to ground) resistor, this won't hurt most things you attach though, lights, other relays configured in the same fashion, etc

Also a typical 30A automotive relay uses <50mA, using 2 or 3 on a 200mA alarm output should be fine. edit: although it is wise to check the current draw of the relay with a multimeter before you blindly add a bunch to the output wire just to make sure it is not drawing more than the 200mA.

 

Its a straight wire only because of the number of windings does it have any impedence at all. Take one apart and unwind the wire its one long piece of wire. Notice I said impedence and not resistance.

Same principal as your subwoofer. Your speaker coild is one long piece of wire with an impedence of 4 ohms (not resistance).

Take it apart and undwind the wire and measure the resistance it will be almost 0.

 

Maybe i wasn't very clear when I initially responded (english is not my strong suit). The diode is there for 1 severe purpose, to allow the inductor's Electro magnetic field an alternative exit escape point thereby protecting your peripheral circuitry. I.e. when power is pulled from your coil, the electro-magnetic field collapses under itself causing an intense "backfire" (going car terms, this is honda-tech). Unless I am misunderstanding how your setup is situated, this pdf is how I drew it and maybe help explain the purpose of the diode better (figure 2 and 3 in the pdf).

It seems most a lot are concerned about your floating high node. Once again, not exactly certain of your setup but I don't really see a problem with that (as shown in my quicky little schematic figure 1). The floating high is nowhere near as important as eliminating the significant voltage spike induced by the EMF of the coil.

Click here ---> Schematic.pdf

Hope that helps man, unless I am entirely missing something. Good luck. Oh, I'm using the conventional current method (for simplicity). Comments, concerns, corrections welcome (although I probably can't respond in a while).

 

You were clear I understood you, but that is not the question or use the original poster had.The use you are refering to is to put a diode in parrallel with the coil to discharge any stored energy when the magnetic field collapse.

The use the original poster is refering to is to put a diode in series with the switched ground lead to isolate the device from any other device.

The two cases are mutually exclusive. Far more information then the original poster requested.

 

Cool beans man. Thanks for clarifying that for me. I was obviously so looking at it a different way.