This exactly what I am talking about! Several different good ideas here, some just adjustable speed, some temp control....like the one I posted in first post.
Would appreciate you ideas how you have done this AudioSan.
Russellc
Russellc: i would build the sitter in a base under the amp, as ZM and others have done. but with multiple smaler fans right under the sinks. Each raw af fans Connected to there own thermal switch (that goes on at 65c) mounted on the center of the sink (inside the amp). and use a smal LM317 based regulated PSU. if i have a 12-18VAC sec left over on your transformer, you can use this to power the fans.
Reviving this somewhat musty thread to get some ideas for the ultimate cooling fan control. Here is my wish list, in no particular order.
1) Adjustable turn-on temperature
2) Adjustable minimum fan speed (Vout)
3) Adjustable maximum fan speed
4) Start-up boost
5) Does not require PWM fans
6) Made from readily-available discrete components
I've scoured the web and while there are a lot of simple circuits out there (including in this thread), I have found none that can do all of the above. I'm guessing the circuit I've described would include both a MOSFET and an LTxxx, but working out the details on how those would work together is beyond my capability... Any pointers on getting started?
BTW the Pass schematic posted by WalterW in post #6 lacks a thermistor or other sensor, or am I missing something?
1) Adjustable turn-on temperature
2) Adjustable minimum fan speed (Vout)
3) Adjustable maximum fan speed
4) Start-up boost
5) Does not require PWM fans
6) Made from readily-available discrete components
I've scoured the web and while there are a lot of simple circuits out there (including in this thread), I have found none that can do all of the above. I'm guessing the circuit I've described would include both a MOSFET and an LTxxx, but working out the details on how those would work together is beyond my capability... Any pointers on getting started?
BTW the Pass schematic posted by WalterW in post #6 lacks a thermistor or other sensor, or am I missing something?
Nice circuitOr build a real Pass fan controller, with Mosfet of course
You could add a thermistor in there too get some thermostat fan control.
Now that my dumb brain thinks about it, using irfp240 in that circuit would actually perform the same function (no need for thermistor) given it's tendency to turn more on with increasing temperature.
Circuit has gone from just nice to VERY NICE.
Brainy Papa.
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Nearly all of that can be achieved with Nelson's circuit with simple adjustment.
Why do you want start up boost?
I would want the amp to get to operating temp as quickly as possible and for fans only to turn on once heatsinks start approaching 60 C
2pD: I presumed the single pot in Papa's circuit is to set the turn-on temp. I don't see where the min/max fan speeds can be adjusted.
By start-on boost I meant a little extra voltage at fan start-up if the minimum fan speed (Vout) is set to less than, say, 6V. I think Papa's circuit provides this.
By start-on boost I meant a little extra voltage at fan start-up if the minimum fan speed (Vout) is set to less than, say, 6V. I think Papa's circuit provides this.
Current through mosfet increases with increasing temp also Vgs threshold is also affected by heat.
You might set up Vgs for 10mA Id at 50 degrees. Then as temperature increases on heatsink Id will increase to 20mA then to 30mA etc (fan speed increase) as heatsink cools the Id reduces (fan speed reduces). Maybe you want 100mA at 50 degrees, that will depend on fan specs, I'm just throwing out hypothetical examples.
Min max can be adjusted with some tweaking after playing with basic circuit.
You could add different levels of source resistance to change max fan speed (maybe some pot arrangement at mosfet source pin output)
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Or maybe a pot at drain to get some voltage drop with increasing Id.
Or combination of both source and drain pots.
Or you might get lucky, and it works good enough exactly the way Nelson has designed it.
The pot adjusts the fan speed. There is no thermal turn on. The transistor boosts the start-up voltage so you can run the fan(s) at low speeds that normally would not allow the fans to start. I built the circuit right on the solder lugs of the pot. Works perfectly. I don't think it will work with the super high speed industrial Noctuas, but it works great with the grey Noctua. Silent.
The pot adjust Vgs.
There is thermal turn on if you use IRFP240 mounted to the same heatsink of the output stage
If you look at the graph of Id vs Vgs, Vgs threshold is very much affected by temperature.
It also provides some thermostat control.
At 25 C with 4V Vgs current is virtually zero, with increasing temperature Id rises significantly (ie the fan turns on). At 150 C Id of Irfp240 jumps to approximately 1A.
So there is definitely thermal turn on using IRFP240 if mounted to same heatsink of output stage
There is thermal turn on if you use IRFP240 mounted to the same heatsink of the output stage
If you look at the graph of Id vs Vgs, Vgs threshold is very much affected by temperature.
It also provides some thermostat control.
At 25 C with 4V Vgs current is virtually zero, with increasing temperature Id rises significantly (ie the fan turns on). At 150 C Id of Irfp240 jumps to approximately 1A.
So there is definitely thermal turn on using IRFP240 if mounted to same heatsink of output stage
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I was finally able to put Pass's circuit together on a breadboard & test it out. Mosfet was IRF521. Ran 4 fans connected in parallel. Was able to adjust the Vout to as little as ~2v. The circuit provided enough start-up boost to start the fans even at this low running voltage. I didn't have a heat source to heat up the mosfet, but the mosfet produced enough heat itself to test Pico's theory, and there was no appreciable rise in Vout. Still, even though it lacks all the bells and whistles I was asking for earlier, it should be fine for my ACA project...
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