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 12/120V inverter again

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YS Posted - Mar 05 2004 : 10:13:25 PM
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.

15   L A T E S T    R E P L I E S    (Newest First)
Sun Dog Posted - Apr 13 2014 : 8:29:54 PM
Unfortunately I only have one of these batteries and at ~$1400 each I won't/can't be adding any more. I have tried to find a single 2V cell locally so that I could at least deal with a 6V system. Bumping it up to 12V would obviously make everything much easier, but I haven't had any luck sourcing the required batteries. I wonder what would happen if I connected it in series with a regular 12V automotive battery and then tried to charge it with a high quality MPPT solar charge controller? Wonder how long the 12V battery would last?
Aaron Cake Posted - Apr 13 2014 : 10:33:55 AM
Originally posted by Sun Dog

The 4V source is a large (1350Ah) lead acid battery and the manufacture's specs include a draw up to 459A http://rollsbattery.com/public/specsheets/4KS25P.pdf I didn't realize the efficiency of the inverter would be so low but I could live with it. I suppose it wouldn't be any more efficient, but would it be simpler to build a 4VDC to 12VDC converter and then just use a standard 12VDC to 120VAC inverter?

You need to build a high frequency switching inverter to convert your 4V to 120V to avoid 200 LBs of transformer and massively inefficient circuit. Your battery will last only a few hundred cycles at that kind of discharge. Peukert effect will eat into your AH capacity significantly.

I'd suggest connecting these batteries in series to get the voltage as high as practically possible before bringing it up to 120VAC. If you can get 120VDC or higher then so much the better.
audioguru Posted - Apr 10 2014 : 9:18:17 PM
This inverter project does not work. Its maximum output is about 45W at low voltage because the transistors have hardly any base current and they have avalanche breakdown of their emitter-base junctions which are reverse biased far more than the maximum allowed reverse voltage (7V) listed on the datasheet.
Find a better circuit.
Sun Dog Posted - Apr 10 2014 : 7:38:20 PM
The 4V source is a large (1350Ah) lead acid battery and the manufacture's specs include a draw up to 459A http://rollsbattery.com/public/specsheets/4KS25P.pdf I didn't realize the efficiency of the inverter would be so low but I could live with it. I suppose it wouldn't be any more efficient, but would it be simpler to build a 4VDC to 12VDC converter and then just use a standard 12VDC to 120VAC inverter?
Aaron Cake Posted - Apr 10 2014 : 09:36:02 AM
The current required at 4VDC would be enormous. Do you want to feed the thing with inch thick solid copper bars? Not to mention that voltage is way too low for the 2N3055s to bias properly. Basically, the circuit would need to be redesigned with a separate oscillator driving a set of more modern IGBTs. But that still doesn't help the current issue. Do you have a 4VDC source which can produce the approx 175A necessary to make 400W (accounting for inefficiency) at 120V? Such a system is best done as a high frequency switcher anyway so you don't need 200LBs transformer.
Sun Dog Posted - Apr 09 2014 : 1:18:03 PM
Would it be possible to change this circuit from 12VDC-120VAC to 4VDC-120VAC? I don't expect it to output 1000 watts (although that would be nice), but even 300-400W would be very useful.
audioguru Posted - Apr 25 2013 : 2:25:14 PM
This project works very poorly. The transistors have avalanche breakdown and waste most of the low output power.
A mains transformer is designed to operate at 50Hz or 60Hz and might work poorly at 400Hz.
hsh_4321 Posted - Apr 24 2013 : 07:36:51 AM
I'm trying this inverter in proteus simulation
I wanted to know does it work properly with high frequncies too? I want a frequency between 200 to 400 Hz
when I calculate the R and C for 200 and something Hz It kinda works with 18k ohm and 22uF but when I connect the transformer (P:834 ohm,5.4H and S:9 ohm , 0.8mH)the voltage becomes almost zero
is there any calculation that includes all the measures?!
tired of trial and error!!!!
audioguru Posted - Sep 03 2012 : 12:45:50 PM
Hi Rhonn,
I still have some new CD4017 ICs in DIP and surface-mount packages.
I would send you a few but you are too far away on the other side of the world.
Come here to get them.

I still have never needed and have never used an inverter.
kasamiko Posted - Sep 02 2012 : 08:05:21 AM
I'm back! and to my surprised this inverter topics never ends..:P

The inverter I made about 8 yrs ago suddenly stop working...upon circuit tracing, i found out that CD4047 is fried..:( don't know what's the reason but my suspect is voltage spike since I never put any zener/decoupling caps on IC Vcc line...

The sad part is it's not available anymore in my place, have to order it online cost about 3.5 US$ in bag of 5.

I got this PWM inverter using SG3524 with feedback using photo-coupler..Got all the stuff and will assemble and assessed its performance later..




audioguru Posted - Jun 26 2012 : 08:50:33 AM
If the transformer is not designed properly then it is probably saturating.

Try the circuit with a 24V center-tapped to 120V power transformer made by a power transformer manufacturer rated for 100W to 300W.
seb27 Posted - Jun 19 2012 : 10:09:27 AM

I made the circuit for testing, exactly as described, I just used my home made center tapped tranformer (in order to get an ouput of 12VAC)
It works (I mean I get well 12VAC output) but @ 3000HZ!! and the circuit consumes 3.5A without load , very strange isn'it!?

Did you have an idea of what I could doing wrong?

pebe Posted - Apr 27 2012 : 10:36:46 PM
Why use tantalum caps? Electrolytics with a 50V working voltage would do as long as they are fitted with the correct polarity - positive to collector.

But like I said - that's not the problem. Ths bases need to be proteced with diodes. The circuit using 2N3055s is rubbish!
guruji Posted - Apr 27 2012 : 4:16:07 PM
Then what one should use instead of those tantalium caps? cause these are not easy to find
pebe Posted - Apr 27 2012 : 08:07:51 AM
Putting two caps in series will double the voltage rating, but that is not the problem.

When the multivibrator flips state, the collector voltage of the ON transistor will drop by about 25V. That voltage is transferred to the base of the other transistor, trying to take the base voltage down to about 24.5V. As that is more than the 6V maximum negative voltage of most transistors then the BE junction will zener and the transistor will probably fail.

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