500W 12v to 220v Inverter

[audioguru]

Hi Doron,
Something must be wired wrong for the CD4047 to get hot.
It is Cmos which has an extremely low operating current at such a low frequency and its opamp load draws nearly no current.
Didn't you make an oscillator like this one that is on the modified version?

[doron]

I fixed the problem on the oscillator so evrything is working ok now.
I mounted the 4 2N3055 on one heatsink for each cycle,say when we have 1 cycle so i was curious as to how much heat they are  going to dissipate.you last said you need the specs for the heatsink so i was wondering what you were talking about
What exactly are you talking about when you say "Heat Specs" and can you give an example in relation to the 4 mounted transistors knowing their characteristics?

[audioguru]

The "heat spec's" for a 2N3055 transistor are that it will be at its absolute max temp when it has a PERFECT heatsink that keeps its case at 25 degrees C. Then it can dissipate 115W.
A REAL heatsink also has "heat spec's" that are its thermal resistance. Insulators also insulate heat, so should not be used. 4 2N3055 output transistors plus the 2N3055 driver transistor plus the pre-driver transistor can be mounted on one heatsink per side without insulators, then insulate each heatsink from each other and from the chassis.

With a load of 500W on the inverter, the total heat is estimated at 100W. So each heatsink will dissipate 50W.

[doron]

thanks audioguru for that piece of info. So are you saying that the 4 paralled transistors though each has a power dissipation of 115W alone when the are put together we get  only 50W dissipated,how come?

[audioguru]

Hi Doron,
A 2N3055 transistor will reach its absolute max internal temp and can dissipate 115W only if it has a PERFECT heatsink that is impossible to have. The heatsink gets hot because it isn't isn't a PERFECT heat radiator. When the heatsink gets hot then you must reduce the power in the transistor. The transistor's case gets hotter because its mounting to the heatsink isn't PERFECT. The chip inside the transistor also gets hotter than its case because its mounting isn't PERFECT.

Another problem is that you will have 6 transistors on each heatsink making it hot.

[photoar]

Hello !

i'm trying to build the same project,
seems like i have the same problem - no wave output from cd4047 - just continuous juice....

checked all wiring, but it's fine
what can i do to solve it ?

[audioguru]

i'm trying to build the same project,
seems like i have the same problem - no wave output from cd4047 - just continuous juice....

checked all wiring, but it's fine
what can i do to solve it ?

Did you make the WRONG circuit or my corrected one? My corrected circuit was recently replaced by the wrong one. I don't know why.

[photoar]

oh, now i see your attachment, and i guess it's the same as mine...

something is still wrong there...

i built this one....

[photoar]

do you have an idea how can i control the transistors with a 555 timer creating the wave ?

Thanks a lot !

[audioguru]

My schematic is correct.
Check the pins numbers on your CD4047 carefully and if it doesn't work then replace it.

[MP]

Photoar,
I got several complaints about the circuit you built. It is built like an audio amplifier and does not apply the same rules as all other square wave inverters. Other members have gotten better results by removing some of the power robbing and heat generating parts, making it more like the one which is now posted on our site.

However, if you are not getting a data stream from the CD4047, you have either pulled too much current through it or you have connected it wrong.

MP

[photoar]

Thanks MP !!

can you please attach or tell me the difference between the one i did and the one on your site ?
i found it on this site of course.... 

[audioguru]

The "500W" inverter schematic now on our site does not have enough output transistors for 500W output. Also its output transistors must be matched.

500W output.
83% efficiency is an extra 100W of heating. Total= 600W.
600W/12V= 50A.
The output transistors must conduct 20A-25A each but their absolute max rating is 15A and they operate poorly at 10A and above.

My corrected inverter had twice as many output transistors so that their current was 10A-12.5A each.
The output transistors used emitter resistors to reduce the current gain of high gain ones for better matching.
It had diodes to arrest voltage spikes.
It had resistors to turn off the transistors.
It had correct values for the frequency determining R and C.

[photoar]

Thanks, I see.

but hey, isn't it this attached schema ?
this one i'm building ! not the one on the site currently !