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If you are going to use your amp "on" signal lead from your HU, make sure you measure at the HU the amount of current you are loading this with various amps and relays as not to exceed it's current rating, or you can run the risk of damaging your HU. This generally is as little as 300mA. See your HU docs for this rating. A single amp can utilize more than half of the rating, and many relays can be well over 150mA for the coil. Multiple amps with multiple relays need to be addressed by a single reed relay providing a single 12v source as the buffer circuit for providing 12v to all of the devices like amps and secondary relays for fans or illumination.

It is much better to utilize the model shown and illustrated at the lower end of this page under the "Proper Fuse and Wire Selection" section;

Relays
 

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Curious why most HU remote turnons are not fused. The current is magnitudes lower than that of your amp's power wire from the battery, but still... if it gets shorted, it will likely draw more than what is considered safe and might damage the HU. The good news is, it's easy to wire an inline fuse at the HU for the turnon remote.

As for the relay use... the 30A automotive relay I assume you plan on using is epic overkill for a set of less than 1A fans, but spade connectors or a relay socket makes is easier to work with vs a surface-mount breadboard and project enclosure, so... no judgement.

Relays function by an electromagnetic coil (85 & 86) to actuate a switch (30- common, 87A- NC or normally closed, 87- NO or normally open). "Normally" being at rest or un-actuated. This electromagnet coil, since it's a coil, also acts like an inductor and stores a high voltage charge (1,500v is possible) while it's actuated/powered.

What happens when you deactivate the relay coil is this stored HV charge takes the path of least resistance, and if your HU is that path, then your HU will take the 1,000v spike. Maybe it will take a joke and not care for the first few hundred times. All you need to do to avoid this is wire a diode in parallel with the relay coil (85 / 86), also known as a spike suppressor or flyback diode. The anode should be connected to the ground side. The cathode side of a diode is indicated by the "|" symbol. If you get it backwards, the diode will be forward biased when the HU turnon is active and the relay will not trigger nor will your amps turn on. If you get it right, the diode will only be forward biased when the HU turnon is deactivated and absorb the HV spike.




It's pretty easy to implement, esp if you use a socket for the relay:


The only thing I would do differently here is use clear shrink tubing over the diode as a function of my OCD.
 

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Hi there, I recently upgraded my sub woofers and now it has been causing my amp to overheat, so i've decided to build an amp cooling rack to keep it cool.

I'm going make an enclosed rack made out of MDF with a plexi-glass lid with 4 80mm fans, 2 on either end, one side pushing the other pulling.

Since I don't have much experience with wiring and such I did bit of research on how to wire all of this together and have it turn on and off with a remote source. I found that I needed a relay for all of this to work. So I made a diagram for myself on what information I was able to find but none of the information I came across was really specific about the wiring.

Because I am not sure if the diagram I created is 100% accurate I would like anyone on here to take a look at it and correct me on anything that is wrong so I don't burn my car down or fry something.

Thanks in advance!

I think you
Hi there, I recently upgraded my sub woofers and now it has been causing my amp to overheat, so i've decided to build an amp cooling rack to keep it cool.

I'm going make an enclosed rack made out of MDF with a plexi-glass lid with 4 80mm fans, 2 on either end, one side pushing the other pulling.

Since I don't have much experience with wiring and such I did bit of research on how to wire all of this together and have it turn on and off with a remote source. I found that I needed a relay for all of this to work. So I made a diagram for myself on what information I was able to find but none of the information I came across was really specific about the wiring.

Because I am not sure if the diagram I created is 100% accurate I would like anyone on here to take a look at it and correct me on anything that is wrong so I don't burn my car down or fry something.

Thanks in advance!

Might be better to add separate relays protected by separate fuses for each fan, in case there's a short on one device the others are okay and protected.
 

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Although this thread is over 3 years old it s relevant to my current build. I m have a builder make an enclosure for all my gear, and incorporate 2 fans. I think the builder is going to re arrange stuff, but it will be similar to image.
302353

302354
 

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Hello guys.

I am using the old discussion in order to ask your opinion about my installation plan.
Could I use 1 x relay for delivering +12V to 2x amps REM In, 4 x fans and optional LED strip in my amp rack as in the photo? Or, could I use it just for the amps and the fans? LED strip is not planned to be installed now anyway.

I decided to use barrier terminal blocks in the sake of the easy serviceability of the system (huge fan of SIS masterpieces works, where they are using them frequently).

If there is a need to install a switch in order to turn on/off the fans, where should I plan to install it on the scheme? Would it be on the positive 12V wire between the "12v terminal block" and the fans?

relay wirring.jpg
 

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Why not just run a small sub panel with or without a relay? You can then run your fans (with or without a controller), your LEDs, etc. Everything can be fused separately as well.

 
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