A brushless fan needs to be powered from a brushless motor controller.
Google could not find a datasheet for your Chinese fan. AliExpress again?

 

Hadn't even crossed my mind...

You have a life outside of being my mentor?

Now add the TIP31 to the circuit:

Now I get the following:
into circuit: 40V
2N3904 Base: 40V
TIP31C Emitter: 39.8V

I tried it with two different TIP31C's. Same results.

 

A brushless fan needs to be powered from a brushless motor controller.
Google could not find a datasheet for your Chinese fan. AliExpress again?

No, this one was from Ebay. I think it's a computer fan. What is a more appropriate fan?

 

You have a life outside of being my mentor?

I limit the amount of time I spend on AAC...

Now I get the following:
into circuit: 40V
2N3904 Base: 40V
TIP31C Emitter: 39.8V

I tried it with two different TIP31C's. Same results.

Are you certain you're using the correct pinout?

 

The 1N5240 is a 10V zener diode that drops 10V. Then with a 40V input to it, the base of the 2N3904 is 30V and its emitter is 0.7V less at 29.3V.
The TIP31 base is 29.3V so its emitter is 0.7V less at 28.6V.
The circuit posted has 39V input and 27.6V output:

 

No, this one was from Ebay. I think it's a computer fan. What is a more appropriate fan?

ebay and its sellers know nothing about English or electronics. Fakes and defective items are common.
Repeat: A brushless motor has 3 wires and must be powered from a brushless motor controller.

 

Are you certain you're using the correct pinout?

I am using the ones in your picture. I've triple-checked all my connections....
I'm going to take the TIP31C out and go back to where I had good numbers and try again.

Thanks!

 

ebay and its sellers know nothing about English or electronics. Fakes and defective items are common.
Repeat: A brushless motor has 3 wires and must be powered from a brushless motor controller.

I learned something new today about brushless fans, thanks!
Repeat: what is an appropriate fan I can put into my PSU box? type or model?

 

I am using the ones in your picture. I've triple-checked all my connections....
I'm going to take the TIP31C out and go back to where I had good numbers and try again.

When you verify that the single transistor configuration works, substitute a TIP31 for the 2N3904.

You could also stay with the two transistor circuit and replace the TIP31 with a 2N3904. With a 27.6mA load current, about 10mA will be through R1 and the rest mainly in Q2. Q2 will disipate P = IV = 17.6mA*11.4V = 200mW. The transistor is rated for 625mW.

 

Now I can't even get the single transistor setup to work. I get 39.8V at every test point. I swapped out fresh Zener and 2N3904. I also tested the Zener and get a .671V reading. The 2N3904 shows an hFE of 184 on my meter. I've rechecked my wiring 10 times. Getting almost hopeless. I can afford any PSU I want. Just wanted to learn. I feel guilty about all the time I've taken up (especially Dennis). Don't know what to do....

 

Now I can't even get the single transistor setup to work. I get 39.8V at every test point. I swapped out fresh Zener and 2N3904.

If you treat every failure is an opportunity to learn, and learn from it, you won't have wasted any time.

For the one transistor circuit, use the expected voltages to determine what isn't working properly.

I also tested the Zener and get a .671V reading.

You're reading the forward biased voltage. A DVM can't test a 10V zener.

The 2N3904 shows an hFE of 184 on my meter.

Beta doesn't really matter; especially when you're using a DVM at some unknown collector current and collector-emitter voltage.

I feel guilty about all the time I've taken up

Most of us who don't create many threads are more interested in helping/teaching than learning; though we can learn by teaching. I realized I was applying the common mode input voltage range for opamps incorrectly (at times) while trying to help another member learn how they work.

 

If you treat every failure is an opportunity to learn, and learn from it, you won't have wasted any time.

Most of us who don't create many threads are more interested in helping/teaching than learning; though we can learn by teaching. I realized I was applying the common mode input voltage range for opamps incorrectly (at times) while trying to help another member learn how they work.

I appreciate your encouragement, Dennis. It's just that I've been trying to make a fan run for 3 months of Fridays and I'm not used to being the slowest learner in the land.

You really have been very patient.

I will try to isolate the problem.

 

My first hypothesis is that the Zener is not doing it's expected 10V drop. I read some on Zeners and tried the test circuits in the attached. Even isolated like this, I am not getting the expected 10V or 16V drops. What am I doing wrong?

 

My first hypothesis is that the Zener is not doing it's expected 10V drop. I read some on Zeners and tried the test circuits in the attached. Even isolated like this, I am not getting the expected 10V or 16V drops. What am I doing wrong?View attachment 229044

Ground is supposed to be 0V (the black voltmeter's lead), not the same +40V as the red voltmeter's lead.

Use ohm's law to calculate the current and heating in the 1N5240 10V/0.5W zener diode. Its current is (40V - 10V)/400 ohms=75mA but it is rated at 20ma. its heating is 10V x 75mA= 0.75W so it will smoke and burn out. the resistor will heat with 30V x 75mA= 2.25W.

The current in the 1N4745 16V zener diode is (40V - 16V)/10k ohms= 2.4mA but it is rated at 15.5mA so it is barely conducting.

 

Ground is supposed to be 0V (the black voltmeter's lead), not the same +40V as the red voltmeter's lead.

Use ohm's law to calculate the current and heating in the 1N5240 10V/0.5W zener diode. Its current is (40V - 10V)/400 ohms=75mA but it is rated at 20ma. its heating is 10V x 75mA= 0.75W so it will smoke and burn out. the resistor will heat with 30V x 75mA= 2.25W.

The current in the 1N4745 16V zener diode is (40V - 16V)/10k ohms= 2.4mA but it is rated at 15.5mA so it is barely conducting.

Thank you! Back to the books........

The workshop is closed. I'll be back next Friday (my only day to play)

 

Even isolated like this, I am not getting the expected 10V or 16V drops. What am I doing wrong?

In the first circuit, the zener current will be 75mA. The zener diode would be dissipating 750mW, but the zener is only rated for 500mW.

Before throwing components at a circuit, you need to consult the datasheet and do some rough calculations to pick some sane component values.


In general, you don't want to operate components at their maximums; so you'd want the zener current to be less than 50mA. Another consideration is that you need to be far enough beyond the knee that you'll get decent voltage regulation.

For 1N5240, the knee current is 0.25mA. But notice that the knee resistance is 600 ohms. That tells you that you're not on the steep part of the IV curve. I've been designing for a zener current of about 10mA.

For a 10mA zener current, you need a series resistor of 3k ohms. Calculated as follows:
\(R = \frac{V}{I} = \frac{40V-10V}{10mA} = 3k\Omega\)

You should do similar calculations for the 16V zener.

 

Here's something from Motorola that will define things like zener impedance and knee current.

 

I am using a new 12V .16A fan. It is 2 wire only. First experiment today I used my switching power supply set at 12V. The fan works great and the meter shows it's delivering exactly .16A to the fan. Question: Without the fan's load, the volt meter on the supply shows 12V. With the load, it shows 8.7V. I am thinking about Ohm's law as the answer why but I can't figure out the principle. Ideas?

 

The power supply should be able to supply 12 volts at any current up to the power supplies rated output. (Or the set current limit if it has an adjustable current limit.)

Les.

 

The power supply should be able to supply 12 volts at any current up to the power supplies rated output. (Or the set current limit if it has an adjustable current limit.)

Les.

Does that mean I should adjust it up to 12V after it's running? I set it to 12V before starting the fan. Thanks!