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 12/120V inverter again
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Feb 26 2007 :  08:27:58 AM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
Tim, Yes you can put resistors in parallel to achive an uncomon value. The formula for parallel R is:

Rt = R1 X R2 / R1 + R2 = Rt

K
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tim
Mad Scientist

198 Posts

Posted - Feb 27 2007 :  07:44:02 AM  Show Profile  Reply with Quote
does the same apply to putting resistors in series as well to get a value?
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Feb 27 2007 :  10:19:04 AM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
No, Resistors in series add their value for ex. one 10 ohm resistor in series with a 20 Ohm will equal 30ohms in the circuit. The same with inductors (coils). The Henry value adds together in series. Capacitors are the opposite. Caps in parallel add together the (uf rating) and in series they divide. You can probably find a write up on Google about it if you want to actually read it for yourself. I like studying this stuff I like knowing how things work so happy searching!

Ken
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omleje
New Member

Nigeria
1 Posts

Posted - Mar 02 2007 :  08:52:13 AM  Show Profile  Reply with Quote
how long do the inverter works and can the circiut be made to produce 220v,5000w,50-60Hz?
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Aaron Cake
Administrator

Canada
6702 Posts

Posted - Mar 02 2007 :  09:23:05 AM  Show Profile  Visit Aaron Cake's Homepage  Send Aaron Cake an ICQ Message  Send Aaron Cake a Yahoo! Message  Reply with Quote
quote:
Originally posted by omleje

how long do the inverter works and can the circiut be made to produce 220v,5000w,50-60Hz?



Please at least take a quick look over the topic before you post a question. This circuit does not work very well in most cases, and building an inverter of that size is completely impractical.
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CATWHISKER
New Member

1 Posts

Posted - Mar 07 2007 :  12:12:24 AM  Show Profile  Reply with Quote
quote:
Originally posted by omleje

how long do the inverter works and can the circiut be made to produce 220v,5000w,50-60Hz?



JUST TAKE THIS AS A SUGGESTION.IF U HAVE TO BUILD AN INVETER, FIRST,BE SURE THAT IT IS PRACTICAL IN THE VERY SENSE!SECONDLY,CHOOSE A CIRUIT[DESIGN]THAT IS SURE TO BE 100% EFFICIENT.

THANKS, GOOD LUCK!
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Mar 07 2007 :  09:02:59 AM  Show Profile  Reply with Quote
It is impossible to make an inverter circuit that is 100% efficient. The transistors in an inverter pass many Amps of battery current and therefore get hot. The heat is wasted and reduces the efficiency.

If an inverter uses very good Mosfet transistors to switch the current then it would be about 90% efficient.
If it uses power transistors in a good design then it is about 80% efficient.

The inverter circuit on this site is about 40% efficient.
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Mar 07 2007 :  5:51:07 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
Not to mention that it takes a lot of engineers (elite, "smarter" then the normal person) a lot of thinking, prototyping, and research to get a circuit that is near 80% efficient! This is not something that the average electronics guru (not implying our audioguru on this site haha) can just put on paper and come up with it.

Why is this inverter thing so popular anyway? Even on other forum sites people always ask about inverters, wanting to build one!? WHY?

People, save your time and money. If you want a 1000W+ inverter buy one! Tripp-Lite makes really good ones for $300US.

K
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Mar 07 2007 :  7:03:29 PM  Show Profile  Reply with Quote
It is easy to make a fairly efficient square-wave inverter. The ouput transistors switch on and off so they hardly get a chance to get warm.

We are in Canada where electricity is nearly everywhere, is cheap and hardly ever fails. Some countries with billions of people don't have any electricity so they use inverters and car batteries to make their own.

In The Phillipines there are guys who pickup your dead battery and exchange it for a charged one, then they take the discharged one back to the big city for recharging.

In India there are rolling blackouts because they can't make enough electricity for everyone.
In Africa I don't know what they do.
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Mar 09 2007 :  6:19:12 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
Oh that makes sense, I'm a typical westerner (take things for granted).

Thanks for the info guru :D

K
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junkfunkydude
New Member

3 Posts

Posted - Mar 22 2007 :  9:48:07 PM  Show Profile  Send junkfunkydude an AOL message  Click to see junkfunkydude's MSN Messenger address  Reply with Quote
Hi, this might have been mentioned earlier, but I'm too lazy to look it up.

I am attempting to use this inverter circuit to make a 120vdc to 12vdc converter. I was planning on inverting the 120vdc ,and converting it to 12vac by means of a transformer. This could then be rectified.

I ran into some trouble finding tantalum caps rated at 120V, any suggestions?

BTW, I don't care what frequency the inverter runs at. It could be 10hz or 10khz for all I care.
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Mar 23 2007 :  12:04:48 AM  Show Profile  Reply with Quote
This inverter circuit doesn't work.
Besides, its parts are rated for 12V, not 120V.
Where are you going to find 120VDC?
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junkfunkydude
New Member

3 Posts

Posted - Mar 23 2007 :  4:36:39 PM  Show Profile  Send junkfunkydude an AOL message  Click to see junkfunkydude's MSN Messenger address  Reply with Quote
quote:
Originally posted by audioguru

Besides, its parts are rated for 12V, not 120V.
Where are you going to find 120VDC?



First of all, I know they are rated for 12v, not 120v, this is why I am searching for higher voltage rated components. I have been successful in locating replacements for all the components accept for the capacitors.

Second of all, if you really want to know the application for a 120VDC inverter circuit, here it is:

I recently purchased a 900MFD 125V electrolytic capacitor for the bargain price of $2.50 US. I did the math and found out that 900MFD at 120V is a capacity ruffly equal to 3aHr at 12V. This means that large capacitors at high voltages have higher capacity to weight ratio than any battery including Li-Ion cells. This astonishing capacity to weight ratio is only attainable at high voltages, so in order to make a virtual battery pack from a capacitor, voltage must be converted from the low voltage that would be used to charge the pack to high voltages before it goes into the capacitor, stored at high voltage, and then get converted back to a manageable voltage for use. If I can get this system to work with my 120V cap, I will attempt to build a virtual battery around a 400V capacitor.

This project is still on the drawing board, so if anyone has a suggestion on how to build an inverter based voltage converter, or any suggestions about how to do this efficiently without using inverters and a transformer, please let me know either in the forum, by e-mail, or by IM.
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Mar 23 2007 :  6:53:29 PM  Show Profile  Reply with Quote
A capacitor is not a battery. Its voltage begins to drop immediately when current is drawn and drops very quickly. 900uF at 125V is not a high capacity. Super capacitors are measured in FARADS. 10,000 times more capacity.

Charge your capacitor to 120VDC. Then it can supply 120mA for only 1 second. Then its voltage will be only 44V.
Invert the 120VDC down to 12V then it can supply 100mA for only 10 seconds when its voltage will drop to 4.4V.
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junkfunkydude
New Member

3 Posts

Posted - Mar 24 2007 :  10:09:01 AM  Show Profile  Send junkfunkydude an AOL message  Click to see junkfunkydude's MSN Messenger address  Reply with Quote
You apparently misread the unit of measure of my capacitor, I is 900MF, not 900uf. This makes a huge difference. Also, this specif is project is just to "test the waters" if all works well, I'm thinking about getting a 2F 400v cap and doing the same thing.
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