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 12/120V inverter again
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atul_jangle
New Member

India
3 Posts

Posted - Dec 14 2005 :  06:46:39 AM  Show Profile  Reply with Quote
Sir thans for suggestion
does their is any special technique required for recovery of primery side inductor when i will drive that from power mosfet and its driver ic.or does the flybac diode work.

A.M.Jangle
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 14 2005 :  1:45:32 PM  Show Profile  Reply with Quote
All power Mosfets I've seen have a powerful diode as part of their construction from drain to source that will arrest any flyback voltage from the transformer's primary if the load is suddenly disconnected. The diode is slow to operate so add a 0.01uF capacitor in parallel with the primary to slow down the rate of voltage rise.

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abc
New Member

1 Posts

Posted - Dec 22 2005 :  3:46:34 PM  Show Profile  Reply with Quote
the caps ar inveted in polarity

ther is de original osilator

http://www.interq.or.jp/japan/se-inoue/e_ckt7_1.htm

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 22 2005 :  5:16:09 PM  Show Profile  Reply with Quote
quote:

the caps ar inveted in polarity

ther is de original osilator

http://www.interq.or.jp/japan/se-inoue/e_ckt7_1.htm




The Japanese engineer shows the capacitors with the correct polarity and explains how the circuit works.
He also explains that the circuit's power supply voltage is limited to the 5V Veb rating of the transistors.

The transistors in the inverter project on this site are operating from a 24V supply due to center-tapped transformer action, but the 2N3055 transistors have an absolute max Veb voltage rating of only 7V. I've never seen a silicon transistor with a higher voltage rating. The circuit would operate fine with old germanium transistors.

Therefore when the emitter-base junctions breakdown due to overvoltage, then a massive current flows in the capacitors which blows them up!

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Gus B
Apprentice

USA
149 Posts

Posted - Dec 23 2005 :  08:26:16 AM  Show Profile  Reply with Quote
Neither of the inverters from that site run on 24V. True the push-pull primary transistors will have 24V on their collectors when they are off, but that's it.

MOSFET body diodes...... this diode is a parasitic diode with the substrate, it wasn't put there by design!! For the most part, you don't want to turn this diode on because it's reverse recovery characteristic "sucks". It is very common for designers to put a schottky in parallel with it so that it NEVER turns on.


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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 23 2005 :  09:54:52 AM  Show Profile  Reply with Quote
[quote]
MOSFET body diodes...... this diode is a parasitic diode with the substrate, it wasn't put there by design!! For the most part, you don't want to turn this diode on because it's reverse recovery characteristic "sucks". It is very common for designers to put a schottky in parallel with it so that it NEVER turns on.
Hi Gus,
The long reverse recovery time of the body diode is bad for a high frequency SMPS, but for this 60Hz inverter would be neglegible.

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John Doe
Apprentece

Mexico
14 Posts

Posted - Dec 26 2005 :  6:47:52 PM  Show Profile  Reply with Quote
One question... What happens if I have a 12/125 volts 500 watts transformer, also somewhat like an electronic multivibrator, can be a transistor, a mosfett, or a platinum system as the one that uses the old cars. This is for, to trigger transformer and induce 125 volts in the other winding. What would happen if I use an old relay voltage regulator as the vibrator (because they disconnect if a specific current travels it); also, with this disconnection, I could make a system that inverts polarity to simulate a square wave.
Thanks!

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Dec 26 2005 :  9:05:57 PM  Show Profile  Reply with Quote
Relay vibrators were used in cars long ago because IC square-wave oscillators and high current power transistors weren't invented yet.

You are thinking about re-inventing the wheel.

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John Doe
Apprentece

Mexico
14 Posts

Posted - Jan 01 2006 :  10:51:58 PM  Show Profile  Reply with Quote
Yes, that is right. In fact, I already have an UPS working as my car inverter; but I was just wondering about if what I told before, would work or not.

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jan 02 2006 :  12:20:02 AM  Show Profile  Reply with Quote
Using a mechanical vibrator instead of a solid-state oscillator will work only until the vibrator wears out. A few minutes? A few hours?

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jreld
New Member

2 Posts

Posted - Jan 10 2006 :  02:02:20 AM  Show Profile  Reply with Quote
Hi, new to the forum, this is just a little off-topic. I just got a catalog with some inverters (12V-120V) in it (for auto/boat/RV). The biggest is 5000 watts. By my crude calculation, that is over 400 amps coming out of the battery. How the heck could you keep the battery charged with that much drain? Thanks

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jan 10 2006 :  05:25:07 AM  Show Profile  Reply with Quote
A 5kW inverter is for a big sailboat. It has a huge wind-generator and the inverter is used when there isn't wind. A single battery would explode from the high current so many batteries are in parallel and used as ballast in the keel.

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naseerak
New Member

2 Posts

Posted - May 22 2006 :  01:40:42 AM  Show Profile  Reply with Quote
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.





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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - May 22 2006 :  06:40:08 AM  Show Profile  Reply with Quote
Hi Naseerak,
Yes the capacitors are shown with backwards polarity.
But they charge to a voltage that is nearly double the supply voltage due to center-tapped transformer action. Then when one side of the capacitor is driven very negative, the base-emitter junction of the transistor has its max reverse voltage rating of only 7V far exceeded. The junction behaves like an extremely high current zener diode when it has avalanch breakdown and the extremely high current pulses in the capacitors blows them and wastes a lot of power.

The transistors don't have enough base current to develop much power anyway.

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anton
New Member

1 Posts

Posted - Jun 14 2006 :  3:57:02 PM  Show Profile  Reply with Quote
hi i have builde this inverter and powerup a 100wat bulb with 4.5ampere battery. just use this cuircut http://www3.telus.net/chemelec/Projects/Inverter/Inverter.png it is similar to the cuircu that posted on aarons page but the caps are conected with the minus together to make one biopolar cap with lower capacience .for the transformer i use a 700va transformer from burned UPS so good luck and sory about my englihs im Russian

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