What is the voltage on the input of the LM7809 with and without the fan connected to the output.

Les.

 

What is the voltage on the input of the LM7809 with and without the fan connected to the output.

Les.

without fan: 33V in, 9V out
with fan: 33V in, 3.3V out

 

without fan: 33V in, 9V out
with fan: 33V in, 3.3V out

The input to the regulator should be more like 26.4V. If the regulator had been able to maintain an output voltage of 9V, it would have been dissipating over 5W. So if you don't have a heatsink on it, it's throttling to stay in a safe area.

 

The input to the regulator should be more like 26.4V. If the regulator had been able to maintain an output voltage of 9V, it would have been dissipating over 5W. So if you don't have a heatsink on it, it's throttling to stay in a safe area.

I went up to a 12V regulator and put it on a heat sink. The L7812CV outputs 12.2V without the fan connected. With the fan connected, the voltage out of the L7812CV, at the anode of the cap and at the fan connection are all 3.3V.

I don't understand why I get 33V coming out of the TIP31C since it's supposed to be 26.4V

Putting the customary zero in front of the decimal point might have caused it to be read it as 0.3A.

You have no idea how much I'm learning from you that book-reading doesn't provide.

Thanks!

Carlo

 

And the fan runs great on the buck controller set to 12V.

 

In post #78 it says the output voltage of the LM7809 drops immediately to 3.3V when the fan is connected. This suggests to me that the drop is not due to thermal shutdown. I think the problem may be oscillation as there is no decoupling capacitor on the input of the LM7809. I suggest adding a non electrolytic capacitor there. Try a capacitor 0.33 uF or larger film capacitor. To work out why the transistors zener are not dropping the voltage correctly you need to understand how it should work. This is how it should work. The voltage on the end of the zener that connects to the base of the 2N3904 should be 10 volts less than the input voltage as it is a 10 volt zenner. So if the input voltage is 38 volts the voltage on the base of the 2N3904 should be 28 volts. The voltage on the 2N3904 emitter will be about 0.6 volts less than that. (27.4 volts.) Note most of the emitter current comes through the collector of that transistor. The same reasoning applies to the TIP31C so the voltage on it's emitter is another 0.6 volts less than on it's base. So the voltage on it's emitter is another 0.6 volts less. (26.8 volts.) The resistor is to provide enough current through the zener so it is within it's normal operating point. By measuring the voltage at these points you can get a good idea which component is faulty.

Les.

 

I went up to a 12V regulator and put it on a heat sink. The L7812CV outputs 12.2V without the fan connected. With the fan connected, the voltage out of the L7812CV, at the anode of the cap and at the fan connection are all 3.3V.

With a differential voltage (input - output) of 26.4V-12V=14.4V and 300mA, the regulator would be dissipating 4.32W. If you don't have an adequate heatsink on the voltage regulator, it's going to go into safe mode.

I don't understand why I get 33V coming out of the TIP31C since it's supposed to be 26.4V

If the regulator is throttling, it's dropped the current too low for the zener to drop 10V.

When you probe nets with your voltmeter, you're drawing enough current to give erroneous readings.

And the fan runs great on the buck controller set to 12V.

A buck regulator is a switching regulator. It has lower power dissipation than a linear regulator.

 

In post #78 it says the output voltage of the LM7809 drops immediately to 3.3V when the fan is connected. This suggests to me that the drop is not due to thermal shutdown. I think the problem may be oscillation as there is no decoupling capacitor on the input of the LM7809. I suggest adding a non electrolytic capacitor there. Try a capacitor 0.33 uF or larger film capacitor. To work out why the transistors zener are not dropping the voltage correctly you need to understand how it should work. This is how it should work. The voltage on the end of the zener that connects to the base of the 2N3904 should be 10 volts less than the input voltage as it is a 10 volt zenner. So if the input voltage is 38 volts the voltage on the base of the 2N3904 should be 28 volts. The voltage on the 2N3904 emitter will be about 0.6 volts less than that. (27.4 volts.) Note most of the emitter current comes through the collector of that transistor. The same reasoning applies to the TIP31C so the voltage on it's emitter is another 0.6 volts less than on it's base. So the voltage on it's emitter is another 0.6 volts less. (26.8 volts.) The resistor is to provide enough current through the zener so it is within it's normal operating point. By measuring the voltage at these points you can get a good idea which component is faulty.

Les.

Les,

Thank you for the explanation. Iread up on Darlington pairs but your explanation makes things clearer. Looks like the cap I have after the L7809CV (and the L7812CV) is too small (.1uF). I'll give these ideas a try, test the individual points of the circuit as you suggest and report back.

Thanks!

Carlo

 

The workshop is closed for the day. It's been fun and great learning once again. With Christmas and New Years being Fridays (my only play day), I should be back with things to report in 3 weeks.

Thanks so much to Dennis and Les!.

 

No rush. Enjoy your holidays!

 

No rush. Enjoy your holidays!

You too, Dennis!

 

I'm finally back to the project. I ordered the capacitors and this morning tried out the suggestion in #88. This produced progress as the fan stays running longer but always stops. I tried .33uF, .68uF, 1uF, 2.2uF and .15uF. The fan ran various lengths of time (sorry, I didn't collect full data). The longest was 50sec for .68uF before the fan stopped. What's a smart troubleshooting step? The voltage regulator is heat-sinked.

 

It seems like the part of the circuit that drops the voltage before the 7809 is not functioning correctly. Here are my voltages:

At zener cathode: 39.0V
2n3904 Base: 38.8V
2n3904 Emitter: 38.4V
Tip31C Collector: 38.4V
TIP31C Emitter: 38.2V
L7809CV Input: 38.4V

This is too high a voltage for the L7809CV to operate correctly, right?

The L3809CV Output starts at 12.3V but after some seconds, drops in the 3V range (and the fan stops, of course).

I've double-checked my wiring and the Zener doesn't appear burnt.

Thanks for any help!

Carlo

 

Remove the TIP31 and voltage regulator from the circuit, so you'll have this:

R2 needs to be 1W.

 

Nobody uses a voltage divider or a voltage regulator for a 12VDC fan. Instead they use a transformer that produces 12VDC when its output is rectified and filtered. A 9VAC transformer will produce a full-wave rectified and filtered 10.7VDC when fully loaded or 12VDC when it is moderately loaded.

You have a European L7812 but do not say the letters that say its size and maximum allowed heating.
You did not look at its datasheet to show that your 39VDC voltage is higher than its max allowed voltage of 35V so maybe you have destroyed it.

Other people replying in this thread are talking about different regulators like an LM7812 and an LM78L12.

 

Remove the TIP31 and voltage regulator from the circuit, so you'll have this:
View attachment 229019
R2 needs to be 1W.

Happy New Year, Dennis! Did you think I had given up?

I came pretty close to your figures:
Into circuit: 39V
2N3094 Base: 30V
after 2N3094 Emitter: 29.3V

Now how do I get it to fan voltage?

Thanks!

Carlo

 

Happy New Year, Dennis! Did you think I had given up?

Same to you. Hadn't even crossed my mind...

Now how do I get it to fan voltage?

Now add the TIP31 to the circuit:

 

Nobody uses a voltage divider or a voltage regulator for a 12VDC fan. Instead they use a transformer that produces 12VDC when its output is rectified and filtered. A 9VAC transformer will produce a full-wave rectified and filtered 10.7VDC when fully loaded or 12VDC when it is moderately loaded.

You have a European L7812 but do not say the letters that say its size and maximum allowed heating.
You did not look at its datasheet to show that your 39VDC voltage is higher than its max allowed voltage of 35V so maybe you have destroyed it.

Other people replying in this thread are talking about different regulators like an LM7812 and an LM78L12.

Hi, there and thank you for trying to guide me. I am a really humble novice who's enjoying learning and the help here is incredible. I have no formal traning and have read and am reading several books on electronics including the Forest Mims book and I'm working through "PRactial Electonics for Inventors". So I've got a very large learning curve but I'm really trying! I should carify a few things:
- I had almost thrown in the towel on this 24V 2A transformer early on but wanted something that could charge at up to 10A. Others encouraged me to continue with it.
- The charging / power supply part is working fine but I have really struggled to have a branch that can power the fan.
- I did read the datasheet and understand that I'm starting way too high in voltage for it. I have been trying, with help, to correct that (not yet successfully).
- I've got the blood of a number of parts on my hands. I accept that I may have murdered the L7809CV.

I may once again get discouraged and go to a smaller transformer but I'm not there yet. So, anything you can do to help me salvage this project and get a fan running will be greatly appreciated!!

Thanks for your time and expertise!

 

The charging / power supply part is working fine but I have really struggled to have a branch that can power the fan.

Your fans are Chinese from AliExpress and have no details. You showed Brushless fans with 3 wires but you did not show their controller. Didn't the fans come with a brushless motor controller? It should be labelled with the current needed.

 

Your fans are Chinese from AliExpress and have no details. You showed Brushless fans with 3 wires but you did not show their controller. Didn't the fans come with a brushless motor controller? It should be labelled with the current needed.

I switched to a larger single fan. It is: Minebea brand. Model 2806FL-0.4W-B59 It says it is brushless.
12V DC 0.30A