Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Fan Speed Control  (Read 1122 times)
VE8EV
Member

Posts: 322


WWW

Ignore
« on: November 07, 2017, 07:26:59 AM »

So this commercial-grade SS amp I'm using has temperature-controlled two-speed fans.  When the amp gets warm enough (which it does eventually even at idle) the fans will switch from "tolerable" to "full take-off thrust".  They usually only stay on full for four or five seconds and then it goes back to low.  The fans are fed +28VDC and the "ground" is either 0V (full speed) or +12V (low speed).  I didn't check the current draw but all 6 fans have a 5A fuse upstream and there are 3 fans on each speed control output from the main power board. 

What I want to do is add in a circuit so that when they switch from low to high the fan speed will slowly ramp up over 2 or 3 minutes instead of coming on full blast right away.  Does anyone have any ideas for the simplest way to accomplish this?

73
John VE8EV
Logged
W1VT
Member

Posts: 2489




Ignore
« Reply #1 on: November 07, 2017, 07:52:33 AM »

You could add high side PNP switches, with a capacitor between the base and collector, to ramp the voltage to the fans.  Three minutes is long enough that you may need to heat sink the transistors.

Zack W1VT
Logged
N4MQ
Member

Posts: 139




Ignore
« Reply #2 on: November 07, 2017, 08:45:57 AM »

Why not make the low speed higher ?

Might be as easy as adding a parallel resistor to shunt more current to the motors. Enjoy, Woody
Logged
VE8EV
Member

Posts: 322


WWW

Ignore
« Reply #3 on: November 07, 2017, 08:57:35 AM »

You could add high side PNP switches, with a capacitor between the base and collector, to ramp the voltage to the fans.  Three minutes is long enough that you may need to heat sink the transistors.

Zack W1VT

That sounds like it would work.  I've got some TIP125's in the parts box that'll fit the bill.  Any guesses on a capacitor value and possibly a circuit sketch to save me a bunch of experimenting time?

Thanks
John VE8EV
Logged
K6AER
Member

Posts: 4671




Ignore
« Reply #4 on: November 07, 2017, 08:58:28 AM »

You could use Selco thermistor snap switches 9N/O) and have them short out current limit resistors. Two resistors for low and medium speeds. The resistors would short on higher temps. increasing fan speed.
Logged
VE8EV
Member

Posts: 322


WWW

Ignore
« Reply #5 on: November 07, 2017, 09:06:35 AM »

Why not make the low speed higher ?

Might be as easy as adding a parallel resistor to shunt more current to the motors. Enjoy, Woody

I think if I find the answer for speed control I might even make the low speed lower.  It's barely tolerable in the shack as it is.

You could use Selco thermistor snap switches 9N/O) and have them short out current limit resistors. Two resistors for low and medium speeds. The resistors would short on higher temps. increasing fan speed.

I kind of want to stay out of that side of the equation.  The amp is all computer controlled and (mostly) made from unobtainium.  If the computer decides it wants more cooling (there are temp sensors in each of 10 modules plus who knows where else) I'm not going to second guess it, just make it wait a couple of minutes before the fans really start screaming.  Shocked

John VE8EV
Logged
W1VT
Member

Posts: 2489




Ignore
« Reply #6 on: November 07, 2017, 09:08:45 AM »

The QRP Three-Bander
QST October 1989, pp. 25-30
This low-power, direct-conversion CW trnsceiver covers 18, 21 and 24 MHz, and includes sidetone, spotting and relay-less full break-in --- all on one circuit board!

The Q7 circuit could be scaled for higher power,  which means more bias current and an electrolytic timing capacitor

http://www.arrl.org/files/file/protected/Group/Members/Technology/tis/info/pdf/8910025.pdf
Logged
VE8EV
Member

Posts: 322


WWW

Ignore
« Reply #7 on: November 07, 2017, 09:52:51 AM »

The QRP Three-Bander
QST October 1989, pp. 25-30
This low-power, direct-conversion CW trnsceiver covers 18, 21 and 24 MHz, and includes sidetone, spotting and relay-less full break-in --- all on one circuit board!

The Q7 circuit could be scaled for higher power,  which means more bias current and an electrolytic timing capacitor

http://www.arrl.org/files/file/protected/Group/Members/Technology/tis/info/pdf/8910025.pdf


Wow, your memory is excellent!  

So something like this?  I think I need a diode somewhere.


« Last Edit: November 07, 2017, 10:05:26 AM by VE8EV » Logged
KM1H
Member

Posts: 2499




Ignore
« Reply #8 on: November 07, 2017, 10:20:12 AM »

Quote
Wow, your memory is excellent! 

So something like this?  I think I need a diode somewhere.

Zack sorta has the edge on those things as he works in the ARRL lab since birth it seems Grin

Carl
Logged
VE8EV
Member

Posts: 322


WWW

Ignore
« Reply #9 on: November 07, 2017, 10:24:14 AM »

The schematic I posted is rubbish but I think I can figure it out.
Logged
VE8EV
Member

Posts: 322


WWW

Ignore
« Reply #10 on: November 07, 2017, 10:37:39 AM »

This...

Logged
W1VT
Member

Posts: 2489




Ignore
« Reply #11 on: November 07, 2017, 10:48:50 AM »

The capacitor connects to the base and collector.  When the base resistor is shorted to ground, the transistor won't deliver full current to the fan until the capacitor is charged.

Zack W1VT
Logged
AC2RY
Member

Posts: 282




Ignore
« Reply #12 on: November 07, 2017, 11:01:03 AM »

The QRP Three-Bander
QST October 1989, pp. 25-30
This low-power, direct-conversion CW trnsceiver covers 18, 21 and 24 MHz, and includes sidetone, spotting and relay-less full break-in --- all on one circuit board!

The Q7 circuit could be scaled for higher power,  which means more bias current and an electrolytic timing capacitor

http://www.arrl.org/files/file/protected/Group/Members/Technology/tis/info/pdf/8910025.pdf


Do not forget that this pass transistor will need cooling on its own.


Wow, your memory is excellent!  

So something like this?  I think I need a diode somewhere.



Logged
VE8EV
Member

Posts: 322


WWW

Ignore
« Reply #13 on: November 07, 2017, 11:05:01 AM »

The capacitor connects to the base and collector.  When the base resistor is shorted to ground, the transistor won't deliver full current to the fan until the capacitor is charged.

Zack W1VT

So like this.  Much simpler!  (yes, the transistor will need cooling, np).

Thanks so much for your help!
73
John VE8EV

Logged
AE5GT
Member

Posts: 43




Ignore
« Reply #14 on: November 07, 2017, 11:15:36 AM »

You may find the cap has to be rather large to holld 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 .  
Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!