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 12/120V inverter again
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jul 28 2004 :  12:27:24 PM  Show Profile  Reply with Quote
SupraGuy,
Many electronic devices use the peak of the mains AC voltage to develop their DC supply voltage. That inverter will not supply enough voltage to them. The TVs that are used with it are international and work from 85VAC to 250VAC.

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marius
Apprentece

Israel
11 Posts

Posted - Jul 28 2004 :  12:40:44 PM  Show Profile  Reply with Quote
Thanks.
I have two additional questions, with your permission:
1. Do you know if most of the commercial converters (30$ to 100$) which do similar tasks uses square wave or sine wave ?
2. CD4047 is not easy to find. Is there a special reason for choosing this one or can I switch it with a 555 and a NOT gate ?
Thanks in advance!
quote:

Marius,
That 500W inverter is used to power TVs and flourescent lights.



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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jul 28 2004 :  7:57:19 PM  Show Profile  Reply with Quote
Marius,
All cheap commercial inverters have square wave output. Sine wave ones use either a big, special "tuned" transformer or a lot of hot and expensive transistors on a big heatsink

The 4047 was chosen because it has a built-in digital divider that gives exactly 50-50 duty cycle, and has opposing outputs. A 555 and inverter will be OK.

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marius
Apprentece

Israel
11 Posts

Posted - Jul 29 2004 :  06:53:22 AM  Show Profile  Reply with Quote
Thanks again.
Now, since 500W on the secondary winding are more than 40 amps on the primary winding (of the transformer), and since we're dealing with such huge currents, it'll be very interesting to see how have you implemented it - diameter/types of wires, heatsink for the transistors (which cannot be mounted on the box for cooling, since there are two square waves with a series of transistors for each of them. Meaning you can't short the collectors by mounting them on the box).
Since it's working for you, maybe you have a photo of this inverter so we can see how did you choose to implement it (if not, that's ok too, you've been very helpfull already).
Thanks.

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jul 29 2004 :  11:08:33 AM  Show Profile  Reply with Quote
Marius,
I have never built an inverter. I just helped re-design that one, since the original project had errors and didn't work.
All the guys who built the modified one didn't post pics yet
Of course it needs a big output transformer, heavy primary wiring and big heatsinks with proper insulators..

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phoenix
Apprentice

Canada
54 Posts

Posted - Jul 31 2004 :  12:02:08 PM  Show Profile  Visit phoenix's Homepage  Send phoenix a Yahoo! Message  Reply with Quote
I'm finding it really difficult finding large transformers...
Does anybody know how (wire diameter) I could rewound an old transformer? I've already tried it once ... not so good...
Thanks...
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n/a
DELETED (Inactive)

2 Posts

Posted - Aug 12 2004 :  7:08:36 PM  Show Profile  Reply with Quote
Hey, I was wondering where I could find those specific diodes mentioned on the schematic? If I can't find them anywhere, what are there specifications?

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Aug 12 2004 :  8:14:28 PM  Show Profile  Reply with Quote
Hi Drummerman,
Which inverter are you building? We have been talking about many different circuits here.


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n/a
DELETED (Inactive)

2 Posts

Posted - Aug 15 2004 :  11:08:59 PM  Show Profile  Reply with Quote
I was talking about the schematic that arron cake made. I want to find those HEP 154 diodes. I can't find them anywhere. If anyone could help me find them that would be great. If they don't exist, can someone tell me the specs that a diode would have for that particular circuit? Thanks.

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Aug 18 2004 :  8:31:24 PM  Show Profile  Reply with Quote
That project doesn't work. Read this thread.

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n/a
DELETED (Inactive)

1 Posts

Posted - Sep 14 2004 :  4:51:14 PM  Show Profile  Reply with Quote
so would i be able to use this inverter to power a PS2 and an LCD monitor? does the fact that the inverter outputs 220V make a difference?

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Sep 14 2004 :  9:44:17 PM  Show Profile  Reply with Quote
Bloodlust,
Which inverter outputs 220V?
If an inverter project works, you can build it to give nearly any output voltage by your selection of its output transformer. Many electronic products don't work when powered by an inverter that has a square-wave output.

The only difference that will happen to a product when you to apply a power supply voltage that is much too high, is that of course it will simply blow-up!


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n/a
DELETED (Inactive)

9 Posts

Posted - Sep 27 2004 :  4:42:14 PM  Show Profile  Reply with Quote
Well your correct. This circuit only uses 1/2 of a 24 Vac secondary used as a primary. This was wound with a ratio for 24 Vac to 120 Vac, not 12 Vac to 120 Vac. 60 to 65 Vac is all it will and can produce! To get the required 120 Vac, you need a 24 Vac C.T. transformer with a 240 Vac primary. This will give the correct ratio amd a 120 Vac output. =)


quote:

I do not think 60 V is not enough.. on that side of transformer you have only 12V of power, and diodes should protect from flyback voltage.. just a comment :)







-=Will Matney=-

(Edit...Remove email notification due to bad address...)

Edited by - Aaron Cake on Nov 25 2005 09:10:59 AM
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Sep 27 2004 :  6:37:10 PM  Show Profile  Reply with Quote
Hi Will,
If the inverter works properly (I don't know which circuit that you are talking about), the 24V winding's center tap is connected to +12V, so when a transistor grounds one side then the other side will swing to +24V. Select a 24V center tapped transformer that has a high voltage winding that is rated for whatever output voltage that you need, not double what you need.
To get 120VAC output, choose a 120V to 24V ceter-tapped transformer, which is also written as 120V to 12-0-12.

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n/a
DELETED (Inactive)

9 Posts

Posted - Sep 27 2004 :  7:13:25 PM  Show Profile  Reply with Quote
By analyzing the circuit, there's a few problems, One bad, and the other not that bad. First, the capacitors polarity is wrong. The + side goes towards the collectors. Next, the frequency is a little too fast. It will run at 102 Hz. Also, 100 ohms I think is a shade too small for the base current needed. Using a 47 uF capacitor and a 220 ohm resistor will give you about 67 hz which is close enough.

I read, but forgot from whom, mention about transistors matching. This is aboslutely what you do not want. Fot the circuit to oscillate correctly, one transistor has to start to conduct before the other. Two exactly matched transistors would lock the circuit up. Another thing that can help this circuit is simply adding a 10 ohm resistor in one of the transistors base leads between the base and the 220 ohm resistor which replaces the 100 ohm ones. This will cause a slight mis-match and help the oscillation start. Next, Remove the other two reisitors and diodes. Then, place some 24 V, 5 Watt zener diodes across the transistors collectors and emitters. This will kill any spikes from the transformer that may be generated. That's how the spikes were killed in the old days.

You might think of changing the 2N3055 to a 2N3772. This will raise the collector current up from 15 amperes to 20 amperes. The 2N3772 is good for about 9 -10 amperes for this type of switching and the 2N3055 about 5 amperes. Those ratings higher are for a 5 Vdc collector voltage and drop off as the voltage raises. You need to look at the spec sheets and see the de-rating charts for power verses voltage.

The formula for the frequency is; f = 0.7/R x C
R in ohms and C in farads.

Will Matney

PS,
One last thing. You might make an astable multivibrator up like this using a couple of 2N2222's then drive the 2N3055's or 2N3722's. The RC value will stay the same.

-=Will Matney=-

(Edit...Remove email notification due to bad address...)

Edited by - Aaron Cake on Nov 25 2005 09:11:47 AM
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