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 12/120V inverter again
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kasamiko
Apprentece

Philippines
6 Posts

Posted - Feb 25 2008 :  01:21:07 AM  Show Profile  Visit kasamiko's Homepage  Send kasamiko a Yahoo! Message  Reply with Quote
I think i should be shifting to MOSFET now..

I'll start with IRFZ44...

cooler..more efficient..

rHoNnZ
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WilliamW1979
New Member

USA
2 Posts

Posted - Mar 09 2008 :  8:23:01 PM  Show Profile  Send WilliamW1979 an AOL message  Send WilliamW1979 a Yahoo! Message  Reply with Quote
Was is he math formula to compute how many Watts can be handled based on the changing of the components of T1, Q1, and Q2? This is obviously for a 300 Watt system so lets say I want to create a 5,000 Watt system, how would I go about doing that?
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Mar 09 2008 :  11:58:02 PM  Show Profile  Reply with Quote
Changing T1, Q1 and Q2 in this simple circuit has nothing to do with increasing its output power because the circuit doesn't work. Its output power is only about 25W with a low output voltage, not anywhere near 300W.

The polarity of the capacitors are backwards and the transistors have avalanche breakdown. The transistors don't have enough base current.

You want the math? It is difficult to determine how much power is wasted by heating the backwards capacitors with the very high current pulses caused by the transistors avalanching.
The transistors have base resistors that are 180 ohms so the base current is only (13.2V - 1.0V)/180= 68mA. The typical current gain is 50 so the collector current is 3.4A. The output power is 13.2V x 3.4A= 44.9W minus the wasted power. The transistors saturate poorly unless the base current is much higher. If your transistors have minimum gain then the output power and voltage will be much lower.

For an output power of 300W then the power from the battery must be about 360W. Then the current in each transistor must be 360W/13.2V= 27.3A. But the absolute max allowed current for the 2N3055 transistors is 15A and they work poorly at 10A to 15A. I don't know of a power transistor that has a good current gain with a current of 27.3A.

Kasamiko's inverter is 500W and uses 8 2N3055 output transistors, 2 2N3055 driver transistors plus pre-driver transistors. It has a separate oscillator so its transistors do not have avalanche breakdown and its capacitors use low power.

5000W is rediculous from a 12V battery. The current would be 500A!
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mrservn
New Member

1 Posts

Posted - Apr 23 2008 :  03:47:43 AM  Show Profile  Reply with Quote
Dear Mr Audioguru.
The Chinese, Indian, Vietnamese,... will very thank you, if you were designed a inverter 12VDC to 220V Ac sine ware, with more effect than this http://www.aaroncake.net/forum/topic.asp?TOPIC_ID=2996&whichpage=24. Because it very heavy, expensive (the transformer) .
Did you know they living in very hot environment (34oC to 39oC)but electric company cut electric two or three times a week (6AM to 22PA). So that a 350W to 500W inverter is very important for a small family, to Fans, TV, lights,..
PS. I am sorry about my English skill.

Edited by - mrservn on Apr 23 2008 03:50:08 AM
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 23 2008 :  12:03:42 PM  Show Profile  Reply with Quote
I don't know why 3rd world countries are full of poverty, have no education and have unreliable electricity.
I can buy a modern inverter that is made in a 3rd world country much cheaper than I can make one. But I don't need one because my electricity is reliable and is cheap.
Why can't people over there buy a cheap inverter that is made over there?

I didn't design the very old inverter circuit that uses a heavy expensive transformer. I just fixed the circuit so it could be used in The Philippines where many people have no electricity. 2N3055 transistors are available there but not Mosfets.
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kivdenn
Nobel Prize Winner

Uganda
535 Posts

Posted - Apr 24 2008 :  07:26:47 AM  Show Profile  Reply with Quote
Audioguru why dont you give them this circuit, you helped build it and I have used it to make 15 DC-AC inverters and now they are working very well with no side effects. The problem is that its abit hard to get the 0.1uf electrolite capacitor but the rest of the parts are readily available on any market.
Just feed the 12VDC into the centre tap of a 12-0-12 5Amp transformer and connect each of the other two transformer wires to the drain of a mosfet transistor and connect their sources to the ground. The gates of the two mosfet transistors should be connected to pin 10 and 11 of the oscilator respectively.(Do this after ensuring that the oscilator realy produces oscilations r you will fry the fets). You should now be having a DC to AC inverter with a low current power on switch and a simple but practical low battery disconnect option that shuts down at 10VDC. The circuit shown was desined to run on 24V but iot can very well be adopted for the 12 configurations. Just change the 18v Zenner to 10V and omit the two 10K and the 100 Ohm resistors and connect the emiter of the TIP31C to a 100 Ohm resitor and then connect it to 13V zener in paralel with a 1uf,25 capacitor and then to pin 14 of the cd4047

Download Attachment: OSCil.jpg
55.59 KB


Edited by - kivdenn on Apr 24 2008 07:38:21 AM
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 24 2008 :  10:22:59 AM  Show Profile  Reply with Quote
The 0.1uF capacitor in the oscillator must not be an electrolytic type. Electrolytic capacitors are polarized for DC but in the CD4047 it has AC. An electrolytic capacitor has a horrible tolerance of -20% to +50%.

Use a metalized plastic film type of capacitor with a tight tolerance of 5%.

Why do you use a TIP41C power transistor in the circuit that has very low power. An ordinary little transistor will be fine.
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kivdenn
Nobel Prize Winner

Uganda
535 Posts

Posted - Apr 24 2008 :  10:35:11 AM  Show Profile  Reply with Quote
Actualy I drew the diagram above some time back but now I use BC546 instead of the TIP41C. Talking about that, Is it posible to convert the low battery disconnect part of the circuit into a battery over voltage disconnect circuit.
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 24 2008 :  12:18:48 PM  Show Profile  Reply with Quote
I think a window comparator using both comparators in an LM393 will be a good overvoltage cutoff and an undervoltage cutoff circuit.
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kivdenn
Nobel Prize Winner

Uganda
535 Posts

Posted - Apr 25 2008 :  07:57:33 AM  Show Profile  Reply with Quote
I have always pleaded to you Audioguru to help me with that kind of circuit but all in vein so I think talking about it here is useless because at the end we shall never have it. Lets go with the cheap one that we have, rermnber a bird in hand is better than two in the bush.
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 25 2008 :  09:03:31 AM  Show Profile  Reply with Quote
Please look at Window Comparator Circuit in Google. You will find some good circuits with explanations about how to set the threshold voltages.
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kivdenn
Nobel Prize Winner

Uganda
535 Posts

Posted - Apr 25 2008 :  09:53:57 AM  Show Profile  Reply with Quote
I have to done all that but all in vein. All I find are fan speed control circuits and the rest but not low battery disconnect circuits
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 25 2008 :  11:16:51 AM  Show Profile  Reply with Quote
I entered Window Comparator Circuit into Google. The very first link has this good circuit.

The output is low when the input voltage is higher than reference #2 and the output is also low when the input is less than reference #1.
The output is high (but with low current as determined by the LM393 dual comparator IC) when the input voltage is in the designed window.

Download Attachment: window comparator circuit.PNG
6.47 KB

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kivdenn
Nobel Prize Winner

Uganda
535 Posts

Posted - Apr 26 2008 :  05:45:36 AM  Show Profile  Reply with Quote
quote:
Originally posted by audioguru

I entered Window Comparator Circuit into Google. The very first link has this good circuit.

The output is low when the input voltage is higher than reference #2 and the output is also low when the input is less than reference #1.
The output is high (but with low current as determined by the LM393 dual comparator IC) when the input voltage is in the designed window.

Download Attachment: window comparator circuit.PNG
6.47 KB




I have also seen the same circuit before but it is incoplete. The resistor values are not shown and also I dont believe it can drive a relay directly, it needs a current amplifier circuit which is not added it also doesnt indicate the exact voltages it was built for either 12v or 24V. Lets trey to solve those problems then it can serve its purpose. Otherwise thanks forall your effort.
Dennis
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 26 2008 :  09:18:46 AM  Show Profile  Reply with Quote
quote:
Originally posted by kivdenn
I have also seen the same circuit before but it is incomplete. The resistor values are not shown

The datasheet for the comparator shows that its input current is extremely low so just about any resistor voltage dividers or zener diodes can be used.

quote:
I dont believe it can drive a relay directly, it needs a current amplifier circuit which is not added

Its datasheet shows that its minimum output current is only 4mA so a darlington transistor or Mosfet must be used to drive your big high current relay.

quote:
it also doesnt indicate the exact voltages it was built for either 12v or 24V

The voltage dividers or zener diodes are simple to calculate for any threshold voltages from 0V to 34.5V.
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