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Automotive relay

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kwijibo007:

Hi, I've been slowly building my first Mame cab (cocktail) for about six months. I've been lurking here for a while and have picked up a lot of great tips. Firstly, big thanks to this great community!

I've tried searching but can't find a clear answer to whether or not I can use an automotive relay safely in my cab.

I purchased a cheap 12v amp to drive my speakers with the intention of powering them directly off the PC power supply. When I did this I got a lot of very bad feedback through the speakers. I did some searching and found this to be a fairly common issue with PC power supplies and amps.

Therefore I decided to use this relay http://www.jaycar.com.au/productView.asp?ID=SY4045&form=CAT2&SUBCATID=979#1 by using the 12v pc rail to control power coming from separate 12v power supply I'm using elsewhere in the cab. The point of this was that the amp would only power on when the PC was powered on.

Everything works great but after reading this thread http://forum.arcadecontrols.com/index.php/topic,109029.0.html I'm concerned that I might be doing something stupid by using the wrong kind of relay. This thread suggests using a solid state relay for the knocker being used. The knocker would be triggered many more times than my scenario but my relay will be active for many hours at a time...

I only know enough about electronics to cause trouble... Is what I have done ok? Is the PC power supply too large to control the realy? If the relay fails will it simply stop working I could it cause some damage to the pc/power supply/amp?

mgb:

This should do you fine.
In the other thread about the qbert knocker, I assume you're talking about where someone said the relay would burn out quickly?
You're bassically just turning on a relay when your pc turns on, it should be fine.
Is the relay rated for continous duty?

though it may already be built into the relay (I couldn't open your link)
One good idea to do with a relay, though is to put a diode in reverse bias across the coil (where the 12 volts goes to). This helps to alleviate possible damage done by the collapsing magnetic fields when the relay shuts down. you can get an IN4001 diode at radio shack and install it at the diode coil across the red and black from pc so that the silver bar on the diode is at the red side and the other end is at the black side

and oh yes..... Welcome to the forums.

mgb:

another simple way to do what you're trying to do is use a 12vdc plug in transformer / power supply for your amp and use a smart strip (i use the belkin smart strip and it works great) with your pc in the control outlet so anything you want on when your pc is on, will foolow the pc.

kwijibo007:

Thanks mgb,

I think it's an MC2/012-1HRF.

Yeah, it was the burn out comment that caught my attention. I'm not worried about replacing it if it dies (it cost about $4) but whether it might cause other damage. I'll rack my head around diode and give it a go.

It has 'Extended operation range' so i assume that's continious duty? 

I considered the smart strip but thought I'd give DIY a go and save a couple of bucks!

Thanks for the advice.



DaOld Man:

I need to add that if you are switching the AC to the power supply with this relay then it might not be a good choice.
The relay you linked to is for switching 12 or 24 volt DC circuits. AC acts different when switched, also, the insulation in the relay may not hold up to higher 120 volts.
If you are leaving the power supply on all the time and using this relay to switch the 12 volt side of the supply to the amp, then you should be ok.
But if you intend to shut down the power supply when the cab turns off, you need to look at a relay that can switch 120 volts. Also, the 120 volt side of the power supply will be much smaller current than the 12 volt side.
Hope this makes sense.


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