I am having trouble with voltage regulation

Discussion in 'The Projects Forum' started by wallaby, Feb 21, 2016.

Jul 26, 2011
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I am working with a wind-powered generator that only needs to light up some LEDs when the wind blows.
I rewound my generator to make enough voltage at low RPM, but as expected, it provides too much as the wind speed picks up.
I figured a voltage regulator would cure the problem, but I can't seem to get it to work. I get it dialed in at a certain shaft speed, but then as the speed rises, so does the output. I'm using a simple LM317 adjustable regulator.
Isn't the regulator supposed to supply a constant output regardless of input? What might I be overlooking?

2. ericgibbs AAC Fanatic!

Jan 29, 2010
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hi W,
Please post your circuit diagram, the LM317 should give a regulated Vout, not a constant Iout.
E

3. ScottWang Moderator

Aug 23, 2012
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If you used LM317 then the Vout will be as Vout = Vin - 3V and the Vin must be ≤ 40V.

4. ronv AAC Fanatic!

Nov 12, 2008
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What are you using for a generator? If it is brush-less you may need to rectify and filter it to get DC.

Jul 26, 2011
34
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Not brushless. It is a 2 pole permanent magnet motor driven to act as generator.
I used a diagram and chart to wire the LM317. It shows a resistor between the ADJ pin and Vout pin, and another resistor between Vout and ground. I had it mocked up on a breadboard and by altering the value of R2 I was able to get the desired output. The problem is it can't hold it there.
It WILL drop the output.. right now it has 17.5 going in and 8.5 out at 171 rpm. If I step up the shaft speed it has 28.7 in and 15.4 out at 280 rpm. It's a drop, but clearly not regulated.
Would the circuit be any easier if I went with a fixed 5v regulator? My ideal target is 6v

6. ScottWang Moderator

Aug 23, 2012
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If your generator output is ac then what do you expect the Vout of LM317 (dc ,ac) ?

7. ian field Distinguished Member

Oct 27, 2012
4,447
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You can make a 317 regulate current, by adding a single resistor.

The problem is more likely feeding the 317 too much input voltage at high RPM.

A shunt regulator set just under the maximum input voltage for a 317 would probably sort things out.

Jul 18, 2013
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You should be regulating the field or excitation rather than the output!!
Max.

Jul 26, 2011
34
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anyway, it's generating DC.
What I thought would be a simple project has turned into an electronics lesson. I am at the part of the learning curve where the slope is straight up.
At first, my generator had to be spun very fast to get any output. Not ideal for a windmill, so I rewound it. I then had a generator that topped out (in the wind) at a level that was safe for the LEDs. All simple and straight forward, except nothing happened until the wind was really blowing... So I rewound the armature again. Now I get instant results; the generator outputs enough for the LEDs almost as soon as the propeller begins to rotate.
The downside to this is as speed increases, it quickly overpowers the LEDs and I need a circuit to keep them safe with minimal impact on the low speed operation.
I am open to another route to get the job done.

10. ScottWang Moderator

Aug 23, 2012
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If the input voltages of generator is not stable then you could adding the bridge rectifier and capacitor filter, at least adding a big capacitor filter.

11. Alec_t AAC Fanatic!

Sep 17, 2013
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For a LEDS only load, have you considered using a constant-current circuit, rather than a voltage regulator?

Marcus2012 likes this.
12. Marcus2012 Member

Feb 22, 2015
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There should be one resistor between the ADJ and Vout to set the reference voltage at 1.25V and then the second resistor (R2) goes between ADJ and GND NOT Vout and GND and this will set your required output voltage. LM317 should work fine with varied input, it has an application described in the datasheet for AC regulation.

Jul 26, 2011
34
4
It's confusing trying to describe a circuit without a picture.
Don't know how to grab the diagram I was using.. it's here: http://www.reuk.co.uk/LM317-Voltage-Calculator.htm
I see the confusion with my description. The ADJ terminal becomes the output after the R1 connection.
Anyway, I had it wired right minus all the capacitors and diodes.

If you think the 317 is a good basis for the job, I will get some that are "known to be good" and try again.
I switched brands and pin outs were reversed..

Marcus2012 likes this.
14. ronv AAC Fanatic!

Nov 12, 2008
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So your motor looks like this? Where the coils rotate?
Or are the coils on the outside and the magnets rotate?
Maybe a picture of it????

absf likes this.
15. Marcus2012 Member

Feb 22, 2015
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Yeah that's a good calculator so should be ok if you followed that but any linear regulator will need an input at least 3V greater than the desired output so I think Alec_t might have the more efficient idea of limiting the current rather than regulating voltage.

16. Marcus2012 Member

Feb 22, 2015
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Jul 26, 2011
34
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That's it. Coils rotate.

18. ronv AAC Fanatic!

Nov 12, 2008
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Maybe this is just a mistake, but there should be a resistor from ADJ to Vout and another from ADJ to ground, not Vout to ground.
You could also try adding the capacitors Ci & Co shown in the data sheet. It might be a good idea to add a 1.0uF in addition to Ci.

Jul 26, 2011
34
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the lights for this thing are from a pre-engineered kit for RC airplanes. It is designed to be run by batteries, but I am using the generator instead. I don't have data on the individual LEDs. The setup has 8 LEDs, 3 colors, and blinking pairs as well. The info on the control unit states 30mA at 4-6v.
If I were to control current, would I also need to control voltage?
My generator ramps up output with RPM, but a practical max is around 25v with 65mA. That is at 280 RPM. Guesswork here...who knows how fast it actually spins in a wind gust.

20. Alec_t AAC Fanatic!

Sep 17, 2013
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In that case I think you do need voltage regulation. Looks like the control unit handles current control internally.