Capacitor charging

Discussion in 'The Projects Forum' started by hubble, Dec 28, 2014.

Jun 17, 2009
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Hello, is there a good way to charge a 10mF 63v capacitor to, say, 50v using a small 4 wire 200 step 2-phase stepper motor which generates around 6Vrms at each of the two coils when rotated at around 350 rpm?

Thanks.

2. #12 Expert

Nov 30, 2010
16,257
6,762
No.

You could make a 7 stage voltage doubler with capacitors and diodes, but I don't think that's a, "good" way to get to 50 volts.

Last edited: Dec 28, 2014
3. #12 Expert

Nov 30, 2010
16,257
6,762
Yes.

All you need is about 7 or 8 diodes and a similar number of capacitors to do that!

See? It depends on how you feel about the word, "good".

Jun 17, 2009
22
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Thanks for you so quick response. System like Cockcroft Walton voltage multiplier or is there some other type of arrangement?

5. #12 Expert

Nov 30, 2010
16,257
6,762
Absolutely!

Jun 17, 2009
22
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I would love to hear from you on this as to why is it so bad or not good?

Last edited: Dec 28, 2014
7. wayneh Expert

Sep 9, 2010
12,093
3,033
I think the most "bad" thing for folks new to the subject is that no extra power is generated in increasing the voltage, and in fact a significant fraction is lost. Most, in fact. But you do get the higher voltage, and that's the good part.

Another "bad" factor is the sheer number of parts required.

#12 likes this.

Jun 17, 2009
22
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Thanks wayneh for your reply. Actually, the purpose of increasing the voltage is not to increase the power but to increase the charge storage of the capacitor. I was supposed to use low voltage supercapacitor but these are very costly here if available at all. So the only way to store more energy is to increase the voltage. I do understand there will be considerable energy loss to the circuit. I have to have somehow minimum of 10J of energy in the capacitor.

Thanks.

9. wayneh Expert

Sep 9, 2010
12,093
3,033
You might be able to find a DC-DC converter on e-bay that will give you much higher efficiency. They're cheap and simple. A 50V output may be tough to find but if you could find one to efficiently boost to 24V, for instance, you'd only have to double that with an inefficient voltage doubler. Your overall efficiency would be much greater.

Jun 17, 2009
22
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Can it really be done using boost converters? I was thinking of using them to achieve this but was not sure about it. Also, is it possible to use two of them in series instead of going for the doubler?

11. Bernard AAC Fanatic!

Aug 7, 2008
4,170
395
Is there any time limit to charge the cap? Have you tried a 6.3 V filament transformer or a 8 ohm output audio transformer on one coil? If you convert the 6 V AC to DC there are forms of buck converters or flyback converters that will give 50 V DC. Once made a flyback 3 V? to 120V. with 4.5 mH choke converted to transformer.

Jun 17, 2009
22
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I don't know what the current will be when the voltage is raised to 50 V. Let's say it provides 1 mA, the time for charging will be 500 sec. In fact I am still looking for a practical way so I am yet to try anything. 6 V AC can be converted to DC using FW rectifier and a smoothing capacitor. After that I really don't know the next stage in the circuit. Is it possible to use two boost converters in series to get the required voltage? Also, can you provide a circuit which you designed?

Last edited: Dec 30, 2014
13. MrChips Moderator

Oct 2, 2009
12,421
3,357
If the 6V is already AC then a voltage multiplier as already stated seems to be your best bet.

14. Bernard AAC Fanatic!

Aug 7, 2008
4,170
395
Step motor driven with 1/2 drill motor, 6.47 V AC, 277 Hz. Loaded with 33 ohm, 4.29 V AC @ 130 mA.
Transformer step-up; RS 273-1380, 1 k input, 8 ohm out. 80 V PP with 2.2k load; fullwave rectified in to 220 uF @100 V, took 15 sec.
Transformer- RS 273-1385, 120 V, 60 HZ, sec, 12.6 V, 300 mA; fullvawe rectified into 220 uF. took 6 sec to reach 50 V DC.

Step motor: Clifton, type 23, SHAB,- 16BU/H105, 5.1V, 1.8 deg. One coil used for test.

Last edited: Dec 30, 2014
15. #12 Expert

Nov 30, 2010
16,257
6,762
One experimental result is worth a hundred educated guesses.

Jun 17, 2009
22
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Thanks all for your informed responses. I am going with voltage multiplier circuit. I need some help with component selection though. Is 1n4007 okay for this application? What should be the voltage rating of 10nF cap? Also, shall I directly connect this multiplier across the 10mF capacitor? Or, do we need some zener?

Thanks.

Wish you all a very happy new year!!!

Jun 17, 2009
22
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EDIT: 12.2 mF (10 mF + 2.2 mF) cap got charged to 3.5 V using 1n4007 based rectifier with one pull stroke (<1 sec duration) - since it is a pull string type generator.

Jun 17, 2009
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After trying to charge for more than 30 sec with 1n4007 and 10 nF cap system, the 10 mF cap got charged to only 500 mV. I think I have chosen wrong value cap. Here, I tried to simulate with 7 VA 800Hz source, and different stages of 10 uF cap and 1n4007 in TINA, got this result as shown in the attachment. Where am I going?

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19. Bernard AAC Fanatic!

Aug 7, 2008
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395
I connected coils in series & to V multiplier, about same RPM as before. Takes 5 sec to charge C6 to 50 V DC. All componets rated @ 50 V or greater.

20. crutschow Expert

Mar 14, 2008
12,991
3,227
Do you have a ground in your circuit?
Spice simulators generally won't work without a ground point.