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 12/120V inverter again
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YS
Nobel Prize Winner

USA
1132 Posts

Posted - Mar 05 2004 :  10:13:25 PM  Show Profile  Visit YS's Homepage  Reply with Quote
Very popular topic.. Looks like people have problems with this device.

I was wondering about this schematic. Just a mental exercise, you know. What caught my attention is the fact that both tantalum caps showed in - as I think - reversed polarity.
Look at the schematics: the base of the transistor never gets more than 1V above emitter voltage - when the transistor is opened; when the transistor is closed, the base voltage may go well below 0.
The other side of the cap is connected to collector. When transistor opened, it goes to almost 0; but when it is closed, it goes well above 12V (without a diode; 13V with a diode in place).
Therefore, I would connect minus of the caps to bases and plus to collectors. BTW, blowing caps may be just a sequence of wrong polarity..

So, my advice would be - change caps polarity.

Opinions are welcome.


Edited by - Aaron Cake on Feb 02 2007 09:46:32 AM

phoenix
Apprentice

Canada
54 Posts

Posted - Mar 10 2004 :  08:52:33 AM  Show Profile  Visit phoenix's Homepage  Send phoenix a Yahoo! Message  Reply with Quote
HEY! Thanks 4 the advice...


T-boss
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Aaron Cake
Administrator

Canada
6702 Posts

Posted - Mar 10 2004 :  09:57:22 AM  Show Profile  Visit Aaron Cake's Homepage  Send Aaron Cake an ICQ Message  Send Aaron Cake a Yahoo! Message  Reply with Quote
Uh oh...If I made a mistake, I would like to correct the schematic. But what's odd is that the circuit has always worked for me...unless I was mentally switching the capacitors without realising it...

Anyone else found this as a solution to inverter problems?

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YS
Nobel Prize Winner

USA
1132 Posts

Posted - Mar 10 2004 :  9:31:38 PM  Show Profile  Visit YS's Homepage  Reply with Quote
What is the most intriguing to me - the fact that aluminum caps blow up and tantalums are not. I used to think that tantalums do not survive reverse polarity well - aluminums are better on that. With reverse polarity, a tantalum cap usually acts almost like a diode.
Interesting..


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tim
Mad Scientist

198 Posts

Posted - Mar 13 2004 :  3:33:12 PM  Show Profile  Reply with Quote
with all the questions about that 12v-120v inverter , ive been working on it for months and the circuit does work with the diodes in place. however the problem is with the caps, i tried 100ohm 1watt in place of the 180ohm 1watt with same result and also tried 10watt 10ohm in place of 5ohm 10watt again with same result,low voltage.i tried 25v 68uf tantalums and they instantly exploded , i tried polarized caps and got full power for only about 30 seconds befor they blew.i also tried various transformers , same result. so now im using the 24v ct transformer and the circuit is again complete but still dont have the correct caps to run this thing. now i put a cap bank together that has 5 50v 10uf caps and 1 50v 1uf cap in paralle, thesecaps are all nonpolarized to settle the discussion about caps being in backwards.the 2 caps that go to the circuit i used 50v 68uf nonpolar which by themselves you only get about30-40 volts not acceptable, so i took the cap bank which has 2 sets of the above values and cris-crossed the polaritys from the base to collector and wound up with about65 volts just enough to light a 75 watt bulb but not bright. so if someone tells you that the circuit works with tantalums i think its bull, unless they are not using dipped caps and it calls for something other then dipped tantalums.does anyone out there know what they are doing?

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YS
Nobel Prize Winner

USA
1132 Posts

Posted - Mar 16 2004 :  11:32:09 PM  Show Profile  Visit YS's Homepage  Reply with Quote
Yes. For instance, I do know what I am doing, so I am very cautious about using somebody else's schematics, especially if they seem too simple. The simpler schematic is, the more chances that you will need lot of adjustments and experimenting.
BTW, Aaron mentioned several times in this forum, that this inverter is very critical component-wise, and in my understanding that means you need some good luck with it.
Quote from schematic page: "This circuit can be tricky to get going. Differences in transformers, transistors, parts substitutions or anything else not on this page may cause it to not function."

OK, couple of thoughts to add:

1. Use thick and short wires. It is necessary for such a device.
2. Caps should be reversed IMHO.
3. Caps have certain max current rating. You need caps capable at least 0.2A. So I would use caps designed for switching power supplies. Try Panasonic FC series; for instance, 68uF 50V, available at DigiKey. Part number P11252-ND.
4. I would consider using Darlington pairs instead of transistors. Or, add another two transistors - either medium or the same 2N3055 - to existing ones to produce Darlingtons. That will put great relieve on the caps. There may be other issues though so this is consideration only. And if you doing that do not forget to add base to emitter resistors.






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Aaron Cake
Administrator

Canada
6702 Posts

Posted - Mar 17 2004 :  3:02:48 PM  Show Profile  Visit Aaron Cake's Homepage  Send Aaron Cake an ICQ Message  Send Aaron Cake a Yahoo! Message  Reply with Quote
I think I'll link to this topic via the Inverter page. Should help answer a lot of questions.

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tim
Mad Scientist

198 Posts

Posted - Mar 18 2004 :  09:17:22 AM  Show Profile  Reply with Quote
well if anything the 68uf 50volt nonpolar caps i tried should have worked but they didnt. this circuit i tried 3 times with all said to use including the tantalums but they explode.another site said dont use dipped because they explode, but they did say to use 68uf 50-60volt tantalum but these are can type and grey or silver color but it didnt say if it has to be solid or electrolytic so i dont know.

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YS
Nobel Prize Winner

USA
1132 Posts

Posted - Mar 18 2004 :  09:39:53 AM  Show Profile  Visit YS's Homepage  Reply with Quote
May be I was unclear? Or were you too disappointed to read it through? :)

The caps in this circuit have to pass relatively large current through them and not every capacitor is able to do that. There are special types. a bit more expensive, designed for high pulsing currents. Tantalums generally are more current-capable, but not all of them. See my previous post for the rest.

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tim
Mad Scientist

198 Posts

Posted - Mar 18 2004 :  4:20:19 PM  Show Profile  Reply with Quote
Aaron or YS -- could you please tell me what the next higher power transistor than that of the 2N3055 is? Amperage and voltage. This is to use in this crazy 12V-120V inverter. Thank you...Tim.

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YS
Nobel Prize Winner

USA
1132 Posts

Posted - Mar 19 2004 :  12:44:47 AM  Show Profile  Visit YS's Homepage  Reply with Quote
Tell you the truth, I do not know :). I usually deal with smaller currents.
For me, 15A seems to be pretty good and I do not think your battery will like the bigger currents anyway. 60V is more than enough for this circuit. Well, if you want more, search manufacturer's websites. Start with www.onsemi.com


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Epsilon!
Mad Scientist

Canada
276 Posts

Posted - Mar 23 2004 :  5:42:10 PM  Show Profile  Reply with Quote
Would i need to change any resistor values to use darlington transistors,. What if i use a smaller transistor to drive the 2n3055?

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YS
Nobel Prize Winner

USA
1132 Posts

Posted - Mar 23 2004 :  7:06:22 PM  Show Profile  Visit YS's Homepage  Reply with Quote
I wold use something smaller but not too small, not 2N2222. Something with 1A collector current at least.
As for resistors, I would think that as base current will be about 100 times less, you can try to increase R3,R4 maybe to 10K or more and get rid of tantalums. Try 1uF ceramics or film caps..

But that is only my guess, remember that! No responsibility on my part... use it on your own risk :))

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tim
Mad Scientist

198 Posts

Posted - Mar 24 2004 :  6:43:46 PM  Show Profile  Reply with Quote
boy ill tell ya, this inverter circuit has alot of people by the %@@*%#$ you know even me but the first one to get this thing up and running deserves a medal. my latest with this circuit is, a capacitor bank that consists of 10-50volt 10uf nonpolar caps 5 per side with a 100 ohm 1 watt resistor paralled with the caps 1 each side also 2 50volt 68uf nonpolar caps , one is put across both collectors and the other one is put across the bases . im getting 67 volts and it almost turns my 19 inch tv on. so now im waiting for 100volt transistors that might do the trick. i figure the 2n3055 transistors are only good for 60 volts these ones im waiting for is good for over 100volts and there rated for 20 amps not much more then the wussy 3055s. well what the hell its worth a try. and so far nothing is running hot, good sign, and finally this is with the diodes in place like the schematic shows, they have to be otherwise transistors would burn left and right they do shunt back currant.

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YS
Nobel Prize Winner

USA
1132 Posts

Posted - Mar 25 2004 :  9:47:56 PM  Show Profile  Visit YS's Homepage  Reply with Quote
I do not think 60 V is not enough.. on that side of transformer you have only 12V of power, and diodes should protect from flyback voltage.. just a comment :)

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plutonium233
Apprentece

16 Posts

Posted - Apr 12 2004 :  10:51:02 PM  Show Profile  Reply with Quote
Should the resistors be wirewound, metal film, or what? What would a good Qx be that could carry 30 + amps. Also, this is a simple squarewave inverter, I think it would be a good idea to work with some PWM and amplitude modulation to at least modify the wave to a rudimentary sine wave for any serious use of this circuit. What voltage should the caps be rated for.? Has anyone verified whether the caps were reverse polarity?

plutonium



Edited by - plutonium233 on Apr 12 2004 10:53:25 PM
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