Automotive relay

[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.

[mgb]

Good point on the ac or dc switching. But it really comes down to what the contacts are rated for and these appear to rated for 30A, assumably with 12 volt. The 12 or 24 volt mentioned are just what the coil takes.
I was under the impression he will be switching 12 volt dc for the amp power.

[Mysterioii]

I believe some (most? all?) solid state relays only conduct in one direction, in which case AC might come out half-wave rectified...  You are justified in your concern that there might be additional damage if the relay burns out though...  I had a relay on the controller board for my upstairs furnace/air conditioner burn out last year when it couldn't cool the second floor enough and basically ran all the time.  It scorched about an inch radius all around the relay and burnt a small hole through the circuit board including burning some traces.  Replacing the relay wasn't an option at that point and I had to buy a replacement board online for $130 (which would have cost me more if I got it through an AC guy and paid him to put it in).  However, any electronics COULD burn if a failure happens so just be careful and position things away from flammable materials, use standoffs, etc.

[kwijibo007]

I have a power brick that I scavenged from an old modem/router. It takes 240v in (I'm from Australia) and 12v DC out.

The power brick is always powered, even if the PC is off, as it also powers a small garage door opener circuit board that I bought of the net for $20. The garage door opener circuit board has a remote (the type you use to unlock your car). The remote has four buttons which correspond to four built in relays (nothing to do with the relay in question) on the board. I use one button to power on the PC and one to add Mame credits. I have a coin mech and internal power button also... It's just that access to the pysical power button is reached when unlocking the coin mech door. The idea was so that I can power on the PC without unlocking the door and I can add credits without inserting a coin.

The DIY relay is attached on the 12v DC side of the power brick.  Is the relay ok given mgb's diode advice? Or should I re-think?

[mgb]

Why not give it a shot, the worst thing that would more than likely happen is the relay burns out. This doesn't mean it catches fire, it just ceases to work.
I will say however though that the relay you got is not really rated for continuous duty but for extended duty. I thinks its more for air horns and that kinda thing but again the worst thing is that relay may die and if that happens just swap it with something hardier.

[Mysterioii]

Why not give it a shot, the worst thing that would more than likely happen is the relay burns out. This doesn't mean it catches fire, it just ceases to work.

Well, some times they catch fire.  I could show you a furnace control board where it did.  I've seen it happen elsewhere.  Happens sometimes, just think things through and don't put them behind the curtains.  I agree though, it is more likely that they will simply be stuck off or stuck on.

[mgb]

True, fire is possible with any electronics. But there's more going on going on with a furnace controller than just simply switching 12vdc   

[mcseforsale]

I hacked a wall wart and created a 12V block inside my speaker panel.  3 of the connections are (+) 12V and 3 are (-).  I have the LEDs from my speakers, 12V amp, and my CCFL lights for my marquee powered there.  Here's the block:




I use a relay to switch on the wall wart at the AC level.  So, the hard drive power header trips the 12V DC side of the relay, then the relay switches 120V AC up into a second dual-gang box.  The relay was 9 bux.

http://forum.arcadecontrols.com/index.php/topic,117977.msg1267034.html#msg1267034

AJ

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?

[Mysterioii]

True, fire is possible with any electronics. But there's more going on going on with a furnace controller than just simply switching 12vdc   

Well, not gonna argue since I feel that we're pretty much on the same page, but the relay in question was just switching 24V (I had the schematic at the time, it might be printed on the inside door of the furnace, can't recall).  It wasn't anything particularly complicated.  What I personally feel happened was:

1. Coil Layer Short

If overvoltage is applied to the coil, the coil's insulating film will be destroyed, and short-circuiting will cause high temperature. The color of the coil will change, and the resin around the coil will melt. It is also possible that an external surge was applied to the coil circuit, but this is often difficult to determine.

I don't feel that it was due to overvoltage, but in the dead of summer it was probably 120 degrees up in that attic.  Running constantly didn't help either.  Eventually the lacquer on the coil wire probably melted off a bit, shorted the coil, and burned it out.  Inside an arcade cabinet obviously the conditions are far less severe.

[MTPPC]

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.

I use the belkin smart strip in my pinball cabinet and the computer has a small draw making the strip undependable. If you go the smart strip route, be sure to buy the actual "Smart Strip" brand: http://www.amazon.com/Smart-Energy-Saving-Autoswitching-Technology/dp/B000P1QJXQ/ref=pd_bxgy_hi_img_b

It has an adjustment - the belkin does not.

[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.

I use the belkin smart strip in my pinball cabinet and the computer has a small draw making the strip undependable. If you go the smart strip route, be sure to buy the actual "Smart Strip" brand: http://www.amazon.com/Smart-Energy-Saving-Autoswitching-Technology/dp/B000P1QJXQ/ref=pd_bxgy_hi_img_b

It has an adjustment - the belkin does not.

That's good to know, too bad they don't all have adjustment. My pc is a little older (p4) so it draws enough that all works well off the Belkin.

[kwijibo007]

Thanks to everyone for your advice and comments. I think I’ll stick with what I’ve got (adding the diode for safety). I’ll report back once the cab/relay has had some mileage.