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 12/120V inverter again
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Dec 07 2006 :  3:34:57 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
Hey, I'm new to this forum and donít know who to talk to or anything. However, I am wanting to build a power conditioner like one of the high end audiophile ones you can buy like PS Audio but you pay an arm and a leg for them. I'd rather spend an arm and leg on parts to build my own because that is just more fun. What I want to do is take both phases (red and black) like a dryer, this way the current draw on whatever is up on the circuit is balanced. I want to run this 3 wire system to a DC power supply to step it down to 24 or 48 volts then use an inverter to make it ac 60hz again then step it back up to 120. This would give the best isolated power. I want some control over the out put ac frequency. I want to be able to adjust the ac sine wave from 60hz to 120 or even 400hz... some of the best conditioners do this because the current required is less and your frequency is still low enough not to cause problems with the skin effect of any conductors.

So if any one has any idea how to build an inverter that can supply 20 amps of current and about 2400W with adjustable Hz that would be great because I donít know where to find the parts or how to even start... hey if any one knows what kind of power supply I would need to deal with kind of wattage and current that would be great too I'm a little lost so if anyone has good ideas send them to me. If you think this is a dumb idea then tell me that too I'm a musician and good with constructive criticism haha. Thanks to whoever has an idea.

Kenny
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audioguru
Nobel Prize Winner

Canada
4218 Posts

Posted - Dec 07 2006 :  4:03:50 PM  Show Profile  Reply with Quote
Power conditioner? Isolated power? Step it down then step it up? Why?
My stereo works perfectly when it is plugged directly into the mains. No problem with my TV too.
Do you use a lousy generator instead of a stable mains?
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tim
Mad Scientist

198 Posts

Posted - Dec 08 2006 :  4:14:29 PM  Show Profile  Reply with Quote
is there anyone out there that may have designed or has an idea on how to use mosfet transistors for a simple inverter useing the radio shack 24v 2 amp ct transformer rather then aarons inverter using 3055 transistors. only have to get the right HZ in the mosfet driver circuit.
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audioguru
Nobel Prize Winner

Canada
4218 Posts

Posted - Dec 08 2006 :  7:35:11 PM  Show Profile  Reply with Quote
Hi Tim,
The transformer is too small for an inverter. The input power will be 12V x 2A= 24W so the output power will be only 20W. It will power less than 3 little night lights.

A pair of Mosfets can be driven by a CD4047 oscillator and drive a 24VAC ct transformer rated for 50A for a 550W load.
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tim
Mad Scientist

198 Posts

Posted - Dec 09 2006 :  4:50:42 PM  Show Profile  Reply with Quote
hi again, that transformer from radio shack is the one that aaron said could use instead of winding a microwave trans .
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tim
Mad Scientist

198 Posts

Posted - Dec 09 2006 :  4:53:18 PM  Show Profile  Reply with Quote
i guess what matters is using 3055s as opposed to mosfets , ok i got it .

thanks
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audioguru
Nobel Prize Winner

Canada
4218 Posts

Posted - Dec 09 2006 :  8:48:46 PM  Show Profile  Reply with Quote
Your little 24W transformer will smoke if you load it with more than only 24W.

2N3055 transistors have a very low current gain. R3 and R4 supply them with a base current of only about 70mA so their typical collector current is about 3A. Then if the transistors didn't waste power by breaking down and if R1 and R2 didn't waste power, the output power would be about only 36W. If the 2N3055 transistors have their minimum rated current gain then the output power would be less.

Mosfets would not work in the oscillator circuit and would need a completely different design.
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tim
Mad Scientist

198 Posts

Posted - Dec 10 2006 :  1:01:40 PM  Show Profile  Reply with Quote
hmmm , thanks , back to a drawing board for something different as a winter project.
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Dec 12 2006 :  3:43:27 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
Hey audioguru its ken again.

I guess i was a little unclear on what i was asking about so I'll clean it up a bit. I'm taking an electrical class and for it i have to build a circuit for a project (not for marks but for something to do in class to utilize our skills). I want to make a power inverter just for fun. I want to make it able to supply about 3000 watts and a current of about 20A on the AC side of the circuit. I want to team it up with a 3kva transformer.

the next thing i want to do is be able to control the frequency of the AC output wave. I want to be able to select a frequency between 60hz (standard ac) and maybe up to 400hz AC output frequency. I'm doing this for a project and I want some help with the idea. I would like to see if anyone on this site has any ideas for an inverter that would supply this kind of current and what the circuit should look like.

that is my question. So does anyone have a schematic for this?
and
Does anyone know what type of SCR,TRIACS, or transistors i would need??

thanks Ken

ps. How do i reply to just my post?
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audioguru
Nobel Prize Winner

Canada
4218 Posts

Posted - Dec 12 2006 :  6:56:39 PM  Show Profile  Reply with Quote
A 3kW inverter will use about 3750W from a battery. The current will be 3750/12= 312.5A which is ridiculous and will cause a car battery to explode.
The circuit will heat with about 750W.
How expensive will its custom-made huge and heavy transformer be? 32 power transistors?

There was a monster inverter like that on the internet. The prototype exploded and set the house on fire.
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Dec 12 2006 :  10:06:08 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
could it be done if I built a power supply?

what would the circuit be like if it was rated at 15 amps standard?? could it be done then? I already have the prototype for the toroid power transformers they are about $400. what about 15 amps can it be done? can i make the inverter with a selectable frequency?
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audioguru
Nobel Prize Winner

Canada
4218 Posts

Posted - Dec 13 2006 :  08:39:07 AM  Show Profile  Reply with Quote
Hi Ken,
You don't need a battery operated very high power inverter. You need a mains operated 3kW audio amplifier fed from an oscillator. If it is a linear circuit then it will make about 2000W of heat. If it is a class-D switching circuit then it will be cooler but will be extremely complicated.

Since you talk only about Power and Amps then you don't care about its output voltage. 3kW at 20A is a voltage of 3000/20= 150V. 3000/15= 200V.

What are the voltage ratings for the transformer you have?
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tim
Mad Scientist

198 Posts

Posted - Dec 13 2006 :  2:47:34 PM  Show Profile  Reply with Quote
well i found a winter project fixing a 3200 watt inverter, few mosfets , 4 zeners , 3 resistors, op amp ic, pwm control regulater ic, pwm control ic, and 1 lm339n ic. but it really was not worth it but only paid 10.00 for it and the power goes out all the time where i am .
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Dec 13 2006 :  4:16:30 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
Hi Tim,

Where did you get that power inverter from? Do you have any ideas on what the schematic would look like or have any idea where i would get one from. I was thinking of just buying one and taking it apart.. but hey if you have ideas that would be great.

Audioguru,

Thanks for your help so far. I was thinking of using a DC power supply to supply voltage for this. I realize at 12V the amps would through the roof so i ruled out batteries already. I was going to maybe use a power supply voltage around 48V that would bring down the amps alot.

How do i make this 3KW amplifier if that is best way to do it. I've have only built simple audio circuits before so if you have any pointers that would be great!

As for the transformer the 3KVA was meant for the current the transformer would have to take. 3kilo volt amps is VA=E X I so 120V X 20A= 2400VA or 2.4KVA With transformer you always want to supply a cousion of 120% incase of a fault. so 120V X 20A X 1.20= 2880VA So i stepped it up to 3000VA just because that is a standard size... I think that is right anyway... I double checked this with
http://www.unitedhomeproducts.com/id171.htm
they make high end audio stuff. The two boxes side by side house 3KVA isolation transformers check it out.
http://www.purepoweraps.com/
this one keeps the 120VAC 60hz at 120VAC 60hz no matter what and there are others you can change the frequency on.

How does a class D function differently to produce less heat?

Thanks guys!

Edited by - cyclopsitis on Dec 13 2006 4:43:10 PM
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tim
Mad Scientist

198 Posts

Posted - Dec 13 2006 :  4:40:05 PM  Show Profile  Reply with Quote
hi cyclopsitis, i find these inverters on ebay some just need fuses and others need alot more. i bought one on ebay for 99 cents and it only needed 3 fuses because the polariry was hooked up wrong.
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