Printer Friendly Forum Posts - temperature turn on for fans

I understand how to properly use a relay for wiring cooling fans near an amplifier. I would like to take this one step further and wire the fans to turn on after an amplifier reaches a certain temperature. How can I wire this? I would like to mount a device on the amplifier heat sink that activates the fans at a certain temperature.

I would like to use a relay to energize the circuit when the stereo is on and vice versa. I do not want the fans running when the radio is off even if amplifier temperature is above the "fan on" temperature.

Thank you

Why the added expense of the "temp sending unit" as far as wiring goes just use the "sending unit" as the relay coil trigger with another relay that sends 12v+ only when the headunit and amps are on. you could go so far as to make a latch that would keep the fans on till the amp has cooled down even if you have turned it off( i know you said you did not want it though)

#1 relay
85-        ground through "temp sensing device"??
86-        12V+ from blue amp remote
87-        12V+
30-        12V+ out to fans
pin 30 is used to prevent 87a from constant 12v+

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The RIGHT way is the ONLY way.

Hmm maybe I didnt word my post well.

I plan on using the remore turn on lead as you explained to energize and de-energize the relay. What I want to do is use 30 to another heat sensitive circuit that will power up the fans at a certain amplifier temperature.

In other words I only want the fans to turn on when the amplifer heat sink is above 115 degrees farenheit. 115 degrees farenheit is only an example.

What electronic devices opens and closes a circuit at a given temperature?

i think you worded it fine. if you wire it as shown it will do what you ask. the resaon 12v+ goes into 87 and "out" 30 is so that when de-energized pin 87a "sees" nothing. if you hook up the Temp device to the coil then the relay will only turn on when BOTH the radio is on AND the amp is at "115" this is a one relay setup. as far as the actual temp sensor....dunno yet but looking into it.

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The RIGHT way is the ONLY way.

Thanks resquchas. I am eagrly awaiting the best circuit design to build.

I would start with a thermister of some sort - a device whos resistance changes with temperature. You can use that device as one half of a voltage divider circuit to turn the changing resistance in to changing voltage.

You can then use an op amp set up as a comparator to control the on/off point. Ideally you would add hysteresis to give you different on and off points (ie turn on at 125F and turn off at 115F).

I would question, though, the necessesity of such a feature because most likely you will not have enough cooling capacity to actually drop the temperature. I would think that once the temp hits the fan threshold the fan would just turn on and stay on until the car is turned off. Which brings us back to just turning the fans on right away and trying to keep the temp as low as possible.

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Kevin Pierson

Kevin has a valid point. what enviroment is your amp to live in. is it class A/B, D. If you are thinking of multiple fans then there are 12 volt computer fan controlers between 25 and 60 bucks. but most i have experience with require noth 12 volt and 5 volt. this is doable but to what end?

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The RIGHT way is the ONLY way.

KPierson wrote:

I would start with a thermister of some sort - a device whos resistance changes with temperature. You can use that device as one half of a voltage divider circuit to turn the changing resistance in to changing voltage.

You can then use an op amp set up as a comparator to control the on/off point. Ideally you would add hysteresis to give you different on and off points (ie turn on at 125F and turn off at 115F).

I would question, though, the necessesity of such a feature because most likely you will not have enough cooling capacity to actually drop the temperature. I would think that once the temp hits the fan threshold the fan would just turn on and stay on until the car is turned off. Which brings us back to just turning the fans on right away and trying to keep the temp as low as possible.

Very good point. I do not have the knowledge base to design this circuit for one. I do agree that it probably would be best to have the fans on when the system is on. If there was a detailed schematic available for what I want I would build it.

I just right that it would be awesome to have "thermostat" controlled fans.

resquchas wrote:

Kevin has a valid point. what enviroment is your amp to live in. is it class A/B, D. If you are thinking of multiple fans then there are 12 volt computer fan controlers between 25 and 60 bucks. but most i have experience with require noth 12 volt and 5 volt. this is doable but to what end?

The amplifer is a class A/B 3500 watt mono amp. It is 33" long. It will be mounted in my trunk in the spare tire well. I would be using multiple fans in a push pull configuration.

Do you think external fans will help cool the amplifer?

in your application external fans are a good idea if you are going to confine the amp in that enviroment. push/pull or any configuration is acceptable as long as you account for laminar airflow. bay far the easiest way to do this is to just wire up the fans to run with the amp on. try COOLERGUYS.com. they specialize in stuff like this. let me know what you decide and/or come up with. the wiring should be pretty straightforward. but i can help if needed.

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The RIGHT way is the ONLY way.

I call the temp switches Klixons, but that is a trade name. They are typically ~$5 or less.

EG - https://www.jaycar.com.au/productView.asp?ID=ST3821 - use NO type.

resquchas wrote:

in your application external fans are a good idea if you are going to confine the amp in that enviroment. push/pull or any configuration is acceptable as long as you account for laminar airflow. bay far the easiest way to do this is to just wire up the fans to run with the amp on. try COOLERGUYS.com. they specialize in stuff like this. let me know what you decide and/or come up with. the wiring should be pretty straightforward. but i can help if needed.

Thank you! How can I wire the breaker below posted by oldspark to the relay?

oldspark wrote:

I call the temp switches Klixons, but that is a trade name. They are typically ~$5 or less.

EG - https://www.jaycar.com.au/productView.asp?ID=ST3821 - use NO type.

Perfect oldspark! How do I wire this to the relay?

ok i like old sparks source. here goes the wiring

since it is a normally closed circuit do it like this.

85-    12v+ from head unit blue remote
86-    ground
87a-
87-    12v+
30-    12v+ out to relay number2 pin 85
#2
85-    from relay #1 pin 30
86-    ground through st3821
87a-   12v+ out to fan/fans
87-
30-    12v+

this will do what you want. IF the headunit is on and the temp is low then no fan, when the st3821 gets hot and breaks ground then pin 87a gets into its resting circuit and will turn on your fans. use diodes to protect across coils.

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The RIGHT way is the ONLY way.

Thank you very much. I understand 85% of this. I am using st3821 as a ground circuit then right? When it is open the relay does not have ground and when it is closed the relay has ground. Right? One terminal on st3821 goes to pin 86 on relay #2 and the other terminal goes to ground, right?

I was also going to use pin 30 from relay #1 to a remote turn on distribution strip for my other amp and proccesor, is that ok?

How do I wire diodes across coils? I have no idea about this.

you can use relay#1 pin 30 to power up to 30 amps worth of stuff if you have a 30amp relay so no problem. the 12 volt wire into pin 87 should be fused if you STEAL it off of , like your amplifier main power wire through distribution block.ANYTIME you change to a smaller wire guage then you must protect that new section of wire with proper fuse. if 60amp fuse and 4 gauge wire goes to amp then you can not just TAP into that, with like a 12 gauge wire because it would still be on the 60amp fuse....BAD. you will not draw much with these fans but all circuits need to be protected. you have got the st3821 wiring correct, its just in the ground path to cut the relay off and on as temperature dictates. diodes across the coil will prevent voltage spikes, potenetially bad ones, sometimes you hear them as pops through speakers. can damage stuff easily. cathode side of 1n4004 goes to the side of coil with positive so that at REST no current will flow, this is called a reversve bised diode clamp. cathode side has the stripe.

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The RIGHT way is the ONLY way.

Thank you.

I do not understand "diodes across a coil". How do I wire that? I understand the side with the stripe is a cathode and the other side is an anode but that is it. What pins on the relay do I wire the cathode to? 87 on both relays?

Thank you very much for your help!

Ok I did some more research.

On relay #1 I solder the cathode to 87 and the anode to 85.

On relay #2 I solder the cathode to 85 and the anode to 86.

Is this correct?

diode only needs to be across the coil. this is going to be pins 85, and 86. cathode is toward the positive. relay 1 and 2 get same treatment.

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The RIGHT way is the ONLY way.

I got it!

Pin 30 relay #2 gets the same +12v battery as pin 87 relay#1?

I am going to draw up a schematic this weekend for your approval.

Thank you very much for guiding me through this I really appreciate it!

when you draw it up, on relay number 2 change pin 87a and pin 30. the reason for this is when the relay is activated it will then have nothing "live on pin 87" if you insulate or use a relay pigtail then no issue really but that way no empty terminals are ever sitting with 12v waiting to touch something.so......

85-    12v+ from head unit blue remote CATHODE
86-    ground            ANODE
87a-
87-    12v+
30-    12v+ out to relay number2 pin 85
#2
85-    from relay #1 pin 30              CATHODE
86-    ground through st3821             ANODE
87a-   12v+
87-
30-    12v+ out to fans/fans

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The RIGHT way is the ONLY way.

Got it.

I included a small diagram of my electrical set up to better understand. I have a DC Power 270XP alt, D3400 starting battery and D3400 auxiliary battery in trunk.

Relay I planned on using

Dual relay socket

Diodes

Electrical overview
posted_image

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Relay wiring
posted_image

[/IMG]

Does everything look good? Correct fuse ratings?

Thanks!!!!!!

I could not edit my post. Here are the diagrams, sorry.

Electrical overview
posted_image

Relay diagram
posted_image

My links didn't work either!!

Relay https://www......com/item_5635_Bosch-BRLY1.html
Dual relay socket https://www......com/item_8400_Bosch-RS2-Dual-Relay-Socket.html
Diodes https://www......com/item_5909_400V-1A-Micromini-Silicon-Diodes-2-per-pack-Diode1.html

only thing i would change is i dont feel comfortable running 30amps on 16 gauge. the relays will do up to 30a but you have nowhere near that kinda load. my chart says you can go up to 24 amp on 16gauge. 30 amp requires 14gauge. i would leave 16 gauge and put 20amp fuses on the relays. i could not get my browser to the website where you are looking to purchase from sorry. but the wiring is spot on.

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The RIGHT way is the ONLY way.

resquchas wrote:

only thing i would change is i dont feel comfortable running 30amps on 16 gauge. the relays will do up to 30a but you have nowhere near that kinda load. my chart says you can go up to 24 amp on 16gauge. 30 amp requires 14gauge. i would leave 16 gauge and put 20amp fuses on the relays. i could not get my browser to the website where you are looking to purchase from sorry. but the wiring is spot on.

Great. I wil make the changes you noted.

I do not know why the web address is being blocked. Where the "...." is type s o n i c e l e c t r o n i x without spaces. I think the forum is blocking due to spamming but this isn't the case.

As soon as you review the hardware I am making the purchase.

I can not thank you enough!

you are good to go. checked it out and you have the right gear. let me know if you need anything else. happy wiring.

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The RIGHT way is the ONLY way.

resquchas wrote:

you are good to go. checked it out and you have the right gear. let me know if you need anything else. happy wiring.

I owe you resquchas, thank you for guiding me through this!

If you are interested in what I am doing with this you can see my build log here.

Have a good new year!

oldspark wrote:

I call the temp switches Klixons, but that is a trade name. They are typically ~$5 or less.

EG - https://www.jaycar.com.au/productView.asp?ID=ST3821 - use NO type.

I just noticed that this item is normally closed. It opens at 60 degrees. Doesn't this mean that the way I have it wired it will break the ground at 60 degrees turning the fans off?

NO. and yes. the way the relay works 87a is normal closed. 87 is when relay coil is triggered.

ok....... so when the amp turns on it will ground relay 2 shutting off the power to the fans because they are wired to 87a.

when st3821 is heated up and "opens its circuit" relay 2 is no longer grounded and the 87a pin will se power and voila....fans come on.

aren't relays great. if you wire it like the diagram and fuse it with diodes and all you will have a reliable system.

hope this clarifies. if the st3821 was the other way around...then we would switch it to pin 87. you are good to go.

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The RIGHT way is the ONLY way.

its a different concept that something turns OFF and turns another ON. but thats a relay for ya

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The RIGHT way is the ONLY way.

resquchas wrote:

its a different concept that something turns OFF and turns another ON. but thats a relay for ya

I should have studied the relay design more before I posted. I was not doubting you I was confusing myself.

I have all the parts ordered (need to research and order fans) with extras. I am very excited to get this project competed!

THANK YOU

Just saw the post...Remember this from another site... Thought i would throw it out there(i didn't read through all the post's...sorry)... https://bcae1.com/coolfans.htm ...Think what you're looking for is near the bottom...

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M.E.C.P & First-Class
Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!

yeah that set up is always on with the remote wire. the set up in this post is using a klixon at 60deg c. so only on when needed.

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The RIGHT way is the ONLY way.

tommy... wrote:

Just saw the post...Remember this from another site... Thought i would throw it out there(i didn't read through all the post's...sorry)... https://bcae1.com/coolfans.htm ...Think what you're looking for is near the bottom...

I refer to that website often. Very well written and diagrammed.

Unfortunately his "Thermally Controlled Fan Switch" diagram is way beyond my electrical understanding. I am sure that this circuit works wonderfully. He charges $14.95 for his "full version" of his circuits and other diagrams.