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 12/120V inverter again
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CurrentOverflow
Mad Scientist

Canada
311 Posts

Posted - Jan 10 2007 :  7:34:44 PM  Show Profile  Click to see CurrentOverflow's MSN Messenger address  Reply with Quote
I was just wondering how .1 ohm resistors take a load of transistors thx :)

~Mike~
Theres 10 kinds of people, those who understand binary and those who don't
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jan 10 2007 :  9:49:23 PM  Show Profile  Reply with Quote
Are you talking about the 0.1 ohm emitter resistors on the 500W inverter? They help make the paralleled transistors share the current.
Transistors with the same part number are different. At a collector current of 12.5A three could have a base-emitter voltage of 2.0V while one has a base-emitter voltage of 1.5v and it would be turned on hard but the others would not be turned on much. A 0.1 ohm resistor adds 1.25V to the base-emitter voltage of the one that conducts the most so the others can turn on and share the current.
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bala
New Member

India
2 Posts

Posted - Jan 11 2007 :  12:14:03 AM  Show Profile  Send bala an AOL message  Reply with Quote
i tried that transistor based astable multivibrator circuit in the inverter. there is only two transistor ,but one transistor get heated always, the another transistor doesn't work. so i just confused. how can i check the oscillation?

boobalan
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jan 11 2007 :  10:10:44 AM  Show Profile  Reply with Quote
Hi Boob,
Both transistors must work in a transistor multivibrator oscillator. Replace the transistor that does not work.
Then the capacitors will blow up.
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tim
Mad Scientist

198 Posts

Posted - Jan 13 2007 :  9:26:08 PM  Show Profile  Reply with Quote
ok guys ive got a better idea pick up a cheap chinese inverter then desolder every conponent then put it back together. this might be less stressful, lol, ......
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Nnamdi
New Member

Nigeria
1 Posts

Posted - Jan 15 2007 :  08:54:40 AM  Show Profile  Send Nnamdi a Yahoo! Message  Reply with Quote
quote:
Originally posted by pprabhu

Can anybody tell me how to obtain a 500W,12vdc to 220vac circuit diagram with output current of about 3Amperes.

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gcarson
New Member

USA
1 Posts

Posted - Jan 17 2007 :  10:05:04 PM  Show Profile  Reply with Quote
I have a 400amp pipeline welder that has no inverter for 120/240. Is it possible to purchase such a addition and is it practical. I am looking for a source of power when the power grid goes down.
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jan 17 2007 :  11:20:44 PM  Show Profile  Reply with Quote
If the welder's output voltage is 48V, then a 12V battery inverter will take about 1,920A from the battery. It would be a battery the size of a bus. The wires would be as big as your wrist. Ridiculous.
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Aaron Cake
Administrator

Canada
6702 Posts

Posted - Jan 18 2007 :  09:14:54 AM  Show Profile  Visit Aaron Cake's Homepage  Send Aaron Cake an ICQ Message  Send Aaron Cake a Yahoo! Message  Reply with Quote
I think he is referring to using the generator powered welder as a backup power source. At least, I hope he is.

Depending on how the welder is configured, it may be very easy to get a 120V or 240V output as most generator welders already have this capability built in but don't necessarily connect it to the output of the case.

Your welder's output is going to be pure DC so just connecting a transformer to it's output isn't going to work, and an inverter is bit impractical.
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Jan 20 2007 :  4:47:12 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
quote:
Originally posted by audioguru

The wires would be as big as your wrist. Ridiculous.



1920A WOW! you'd have to find a few huge cables each like 1500mcm or more. By that time you might aswell use a heavy duty buss bar! HA-ha! OUCH!
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Jan 20 2007 :  9:36:17 PM  Show Profile  Reply with Quote
A guy on the web made the world's most powerful audio amplifier with vacuum tubes from a high power radio transmitter. He blew the mains transformer for his whole neighbourhood while testing the amplifier with a railroad track as its load resistor.
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CurrentOverflow
Mad Scientist

Canada
311 Posts

Posted - Jan 21 2007 :  12:07:26 AM  Show Profile  Click to see CurrentOverflow's MSN Messenger address  Reply with Quote
Ha! Now thats a story to pass on :)

~Mike~
Theres 10 kinds of people, those who understand binary and those who don't
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Binary 1011001101
Nobel Prize Winner

United Kingdom
569 Posts

Posted - Jan 21 2007 :  03:40:24 AM  Show Profile  Reply with Quote
Sounds very intresting, got the website address?
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baniru1983
New Member

Uganda
1 Posts

Posted - Jan 25 2007 :  10:08:12 AM  Show Profile  Send baniru1983 an AOL message  Reply with Quote
hi mr james could u plz give me achance that i can tok 2 u?
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Jan 25 2007 :  5:47:38 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
Is that for real!? The average pole mount transformer in consumer areas are rated at 25KVA and if the transformer are in a bank (like most are in the states because their system is better) it would be in three phase so 75KVA thatís allot of amps! He would have been taking more then 208A thatís insane! The average size of customer service lines is 6AWG... how did he pull that much power? It must have happened in Canada because our system is known for being designed dumb and having unbalanced loads on the power grid! Thatís insane! Can you give us the article??

K
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