Subject: indicator led for temp controller
By: tim (IP: 192.250.34.*)
Written on: 08-03-2006 16:58

I am attempting again to build the temp controller circuit for controlling cooling fans in Home Theater Equipment Cabinet. Using a 12v 1500mA DC power adaptor from Radio Shack. Putting all of the components into a project box with plug-ins for Power in, 12v relay power switch for power on in sync with Stereo receiver, and plug for thermistor connection. Also have a 12v 30mA LED which I would like to indicate power on. Where in the circuit would this be placed? Fan-on indication would be best, but indication of power to the box based on relay activation from 12v trigger would be acceptable. Any issue with using the power adaptor I am planning on using?

By: aks (IP: 202.62.117.*)
Written on: 09-03-2006 13:12

It is not clear from your mail what exactly you are making . If possible please give the wiring deatils .


By: tim (IP: 192.250.34.*)
Written on: 09-03-2006 15:02

Sorry for confusion.

I am building a cooling system for my stereo equipment cabinet, as opposed to a PC. Instead of a PC power supply, I am planning on using a 12v 1500mA DC adaptor to provide power.

I am using a relay to make/break connection from power supply to fan controller circuit from the 12v trigger from A/V Receiver.

One question is should make/break connection through the relay be on the + or - side of the power supply, or does it matter?

Second question is whether a 12 v LED power indicator could be put across the +/- out to fan to indicate fan on condition, or would this always be on due to low voltage constantly being present even if fans aren't running. Perhaps brightness would be indicative of fan speed? Or am I better off running the LED across the post relay side of the +/- power feed to the controller circuit.

By: Tillmann (IP: 84.58.114.*)
Written on: 09-03-2006 20:56


here are my replies:

- It doesn't matter if you break at the + or - line. However, please observe precaution when using Radio Shack power supply; see other threads in this forum - some users had problems with it (overvoltage), though I'm unsure about the cause.

- If you have 12V from the AV receiver in first place, why use an additional power supply at all? If you have a low power fan, why not connect it directly to the AV receivers's 12V? (But be careful with large/strong fans, maybe it's too much for the receiver's power supply).

- You can connect a LED in parallel with the fan alright. This will not interfere with the temperature controller (but make sure that you make the temperature controller adjustment with the LED already connected).

There is no such thing as a 12V LED. I suppose you're referring to some LED assembly where there is a resistor in series with a LED? Anyways, the result you will get is that the LED brightness will indicate fan speed. Sounds pretty cool. However, it may be possible that the LED will still provide (dim) light even if the fan is not spinning.

By: tim (IP: 192.250.34.*)
Written on: 09-03-2006 22:37

Thanks for the advise. I am one of the folks that had the overvoltage issue with the Radio Shack supply and have a newer one that seems to be fairly accurately 12v.

The max amperage rating on the receiver trigger is something like 25mA. So not enough to run the 6 fans I am planning on, ergo the power supply.

I don't know anything about electronics, the led assembly I bought says 12v on it. That's all I know.
By: tim (IP: 24.63.20.*)
Written on: 17-03-2006 03:10

Just an update. Completed my project box. 2 zone fan control using Radio Shack power adaptor for 12v supply, relay for power on from 12v trigger from receiver. Works like a charm. Cooling DVR / DVD on one zone , Receiver and Amp on zone 2. Couldn't figure out any way to post picture of setup here, but it sure is sweet. Great site !!!!!!
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