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Old 13th September 2006, 08:04 PM   #1
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Default new kid has a power supply idea

well i'm thinking about rectifing the main line and getting 170V and using PWM with a few MOSFETs straight through a filter to get 14.4V at 50+ amps. no transformer, just PWM and a filter. will it work?
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Old 13th September 2006, 08:13 PM   #2
SY is offline SY  United States
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If you like danger and death, yes. Otherwise, NO!!!!!!!!!!!!!!! This is potentially lethal, and we like to keep the Forum members alive.

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Old 13th September 2006, 08:15 PM   #3
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Quote:
well i'm thinking about rectifing the main line and getting 170V and using PWM with a few MOSFETs straight through a filter to get 14.4V at 50+ amps. no transformer, just PWM and a filter. will it work?
No. don't do it!!!
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Old 13th September 2006, 08:20 PM   #4
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Default Aaaaaaaaaaaaahhhhhh ...

That is why they call 'em Isolation Transformers .... so that stupid DIY types won't stick their fingers into the box and kill themselves.

(FYI: anyone older than the age of 55 already knows this: one hand on the "rail" and one hand on the "ground" makes Jack a very, very dull boy. )

I am a long time electrician and can assure you that I have taken enough jolts from the light sockets that the next one will probably kill me for sure ... No kidding. ... and my insurance would probably call it suicide and cut my wife outta da bennies.
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Old 13th September 2006, 08:27 PM   #5
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Default There is a way ...

... to do this, but you should use a one to one torrid transformer and quick blow fuses and/or circuit breakers ... for no other reason than the results will be vastly improved, audio wise, and ... who knows, you might actually live through the experience.

(Most of the States' building codes insist that any alternating current voltage greater than 70.7 VAC be enclosed with shielding or at least 600 Volt resistant insulation ... cause that's usually the "threshold of death". ... and another thing: for DC volts, the "threshold of burn" is just over 28 VDC, ... ~30 VDC = nasty burns.)

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Old 13th September 2006, 10:22 PM   #6
gmarsh is offline gmarsh  Canada
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a 170V to 14.4V buck converter? please don't.

- safety, isolation, death, blah blah blah
- your input FET will have to switch 170V at 50A.
- your input capacitors will have to handle 50A of ripple too.
- you'll need a hell of a lot of input filtering to keep switching noise from heading back your AC cord.
- at 8.5% duty cycle, your output inductor will be massive. Have fun winding a gate drive transformer for that too.

etc.
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Old 14th September 2006, 12:44 AM   #7
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I have to ask the question - why? What are you trying to accomplish? by going this route?
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Old 14th September 2006, 12:47 AM   #8
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Most likely to power a large car subwoofer amp.
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Old 14th September 2006, 12:53 AM   #9
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Quote:
Originally posted by astouffer
Most likely to power a large car subwoofer amp.

More specifically, though, I meant why try this approach?

For simplicity's sake, there are plenty of off the shelf AC/DC modules that will give you a nice clean multi-hundred watt DC output with minimal external circuitry available. That would definitely be easier then what is mentioned above.

Internally, all of the isolation and filtering is in, but all the user sees (and has to work with) is a brick with some posts sticking out.
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Old 14th September 2006, 08:53 AM   #10
mrjam is offline mrjam  Italy
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There's a much direct (and safe!) way to use a car amplifier at home.

Why using a smps to reduce line ac to 14.4V and, internally, a smps which raises the supply to 35-50V?

Let bypass the supply section of your car ampli. In this way you don't need a huge 50A psu!! ..only few Amperes!
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