"Power?" Inverter

[audioguru]

Hi Ante,
Without a load in this circuit, or if the transistors had enough gain and drive, the capacitors will have a brief reversal of polarity of only about 0.6V, with a collector at 0.1V and a base at 0.7V. Electrolytics can handle that with no problem.

[ante]

Yea well you are a terrorist

[MP]

I have merged this one with your original posts. They are now all here in this thread.

MP

[audioguru]

Many other members tried to get this project to work by using electrolytic capacitors instead of tantalum. They even tried it with the capacitors connected with the correct polarity.

Onix says his project is "successful". He didn't say how many Watts, volts or amps is its output. The text in the project says only 15A but a whopping 300W. How?

[MP]

Since this old thread was started, I have gotten feedback that others have built this Inverter. No one has reported to me that anything has burned or exploded. No injuries and no damaged devices connected to it. This could mean that Aaron's site has more newbies or people who should not be sitting behind a soldering iron, or it could be a number of other things. One thing that is very clear is that others have built this project and posts warning of injuries etc., are just rumor. Posts stating that the project will not work have also been proven wrong. I do not understand a member repeatedly posting scare posts on a project he has not built or had experience with, other than what he has read on the Internet. I think this subject is dead and should not be beaten into the ground further. However, I understand that this is not going to happen, so knock yourself out and complain all you want in this thread about this Inverter project.

MP

[audioguru]

This project has its capacitors backwards!
Tantalum and Electrolytic capacitors blow up if the polarity is backwards and the current is high.

The 180 ohm base resistors supply hardly any base current and the power transistors have low current gain, so the output power is very low, less than 36W. The text in the project says 300W!

For this inverter to make 300W, the current in the transistors must be 300W/13.5V= 22.2A. The absolute max current for 2N3055 transistors is only 15A. Their current gain isn't spec'd over 10A where the min current gain is only 5. At only 10A, the typical current gain is only 12.
High power darlington transistors might work if they didn't have avalanche breakdown, but their max emitter-base voltage rating is only 5V like ordinary transistors, so of course they will breakdown.

[Cvscam]

      I have built this circuit using a radio shack transformer and it worked so I did a little testing.  I was using a full charged car battery and I measured 109 volts with no load and I tested it with a 60 watt lightbulb and the voltage dropped to about 105 volts.  I didn't have a way to messure the frequency but it sounded close to 60 hertz.

[audioguru]

Hi Cvscam,
If your voltmeter is not "true RMS" then it reads the output voltage of the square-waves with an error of about 1.414 times high. Therefore its 105V is really only 74V and the 60W bulb draws only 25W.

Did you connect the capacitors backwards like in the schematic? Did they get hot?

[Cvscam]

      I have a cheap meter so I would guess it is not true R.M.S.  The 60 watt bulb was not at full brightness, I was using a Radio Shack transformer part number  273-1512 it shows rated at only 3 amps on the low side.  The only parts that heated up was R1 and R2,  the transistors just got a bit warm but I had heatsinks on them.  I tried a 100w bulb and then I could hear the freq. go way and up and the circuit stopped working.  I checked and one of the transistors is now bad. I used 69-206s for Q1 and Q2 I have a bunch of them that I got somewhere.  I have a couple of old Microwaves and I am going to look into a better transformer. 

[audioguru]

The max input to your RadioShack transformer is 2A. It is overloaded if the output power is more than only 19.2W.