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Author Topic: Fan Speed Control  (Read 1041 times)
VE8EV
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« Reply #15 on: November 07, 2017, 01:03:04 PM »

You may find the cap has to be rather large to hold a charge for any length of time to drive that  TIP at a reasonable gain. In the past i have used a 1/4 of 324 op amp (voltage follower) to drive LM317ts , if you can get a gain of 50 a 324(20 - 30 ma out)  might drive your TIP .  

Assuming a gain of 1000 for the TIP125, a 1A collector current, and 12-0V, I'm thinking 5000uF should give me about a minute of ramp time.  Do those numbers sound reasonable?  I've got lots of capacitors around, op-amps not so much...
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KM1H
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« Reply #16 on: November 07, 2017, 02:07:22 PM »

Headphones would be much easier Grin
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AE5GT
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« Reply #17 on: November 07, 2017, 02:43:53 PM »

Your gain for the TIP may be a bit optimistic . Usually for stability reasons the gain is reduced from the ideal . hfe can vary with temp of the device . as the device heats up the gain can increase , in this case it appears to a least double from 25 C to 150 C . So it might runaway when it turns on (DC gain graph on the datasheet).

 Bottom line is it may turn on and then not want turn back off. Something you want to keep in mind (if it doesnt behave the way you expect) . If no op amps are handy a FET or Bipolar buffer amp could be used, if needed.


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VE8EV
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« Reply #18 on: November 07, 2017, 02:50:05 PM »

Headphones would be much easier Grin

That's what I thought too until I started using this amp on the air.  I'm sure it was just fine in the electrical room on a ship but in a smallish ham shack it is deafening.  Even noise-cancelling headphones probably wouldn't help.  My tube amp (also a CCS monster) had the same problem but I replaced the one noisy axial fan (the blower was fine) with a quiet-rated fan and it was much better.  Quieter fans are "plan B" for this one if the speed control doesn't help enough.
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VE8EV
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« Reply #19 on: November 07, 2017, 02:50:53 PM »

Your gain for the TIP may be a bit optimistic . Usually for stability reasons the gain is reduced from the ideal . hfe can vary with temp of the device . as the device heats up the gain can increase , in this case it appears to a least double from 25 C to 150 C . So it might runaway when it turns on (DC gain graph on the datasheet).

 Bottom line is it may turn on and then not want turn back off. Something you want to keep in mind (if it doesnt behave the way you expect) . If no op amps are handy a FET or Bipolar buffer amp could be used, if needed.

Excellent info, thanks!
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AE5GT
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« Reply #20 on: November 08, 2017, 07:12:35 AM »

Headphones would be much easier Grin

Thets what i use , I have air conditioner that is very noisy . I found a vendor that was selling RS20's for less than $40 . I then modified them slightly . I also have a set of Shure 440 s for back up .
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AC2RY
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« Reply #21 on: November 08, 2017, 09:45:47 AM »

You may find the cap has to be rather large to hold a charge for any length of time to drive that  TIP at a reasonable gain. In the past i have used a 1/4 of 324 op amp (voltage follower) to drive LM317ts , if you can get a gain of 50 a 324(20 - 30 ma out)  might drive your TIP .  

Assuming a gain of 1000 for the TIP125, a 1A collector current, and 12-0V, I'm thinking 5000uF should give me about a minute of ramp time.  Do those numbers sound reasonable?  I've got lots of capacitors around, op-amps not so much...

Actually it would be easier to do with Arduino. You can use PWM regulation and likely no need for switch transistor cooling.
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