I bet there's some electrical engineers here, or at least someone with enough knowledge

I bet there's some electrical engineers here, or at least someone with enough knowledge.

Will this work, or will I burn down my house?
I'm planning to modify an old microwave transformer to get from 230V to 12V and drive a car amp with it.
I would need around 500W RMS from the amp and the amp will be either Class D or AB (~90% vs ~50% efficiency). So I would need 47-84A to it, and that should I easily get from the transformer unless I'm totally wrong with the transformer calculation.

So:
Will an old AC transformer work for DC(maybe a retarded question)?
Does the idea look ridiculous, or do you think it will work?

Other urls found in this thread:

ebay.com/itm/Bridge-Rectifier-Single-Phase-Diode-QL100A1000V-QL100-12-SMS-/162039017923?hash=item25ba4731c3:g:pIwAAOSw1DtXEJkH
ebay.com/itm/2PCS-50A-1000V-Metal-Case-Single-Phases-Diode-Bridge-Rectifier-KBPC5010-/221950605426?hash=item33ad497872:g:L~wAAOSwbdpWVV53
twitter.com/AnonBabble

try /diy/ if no can help here

Pretty sure you need to regulate that 12v.

DC cannot into a transformer.

>84A
Holy shit thats like more than everything in my house ccombined. Dude a normal circuit in a house won't even be able to handle that.

Usually the transformers are step down anyway, at least here in the USA, but your amps are way high bruh

It's not constant current.

Oh, too bad. Guess I would need to buy a more expensive rectifier bridge then,
ebay.com/itm/Bridge-Rectifier-Single-Phase-Diode-QL100A1000V-QL100-12-SMS-/162039017923?hash=item25ba4731c3:g:pIwAAOSw1DtXEJkH
instead of
ebay.com/itm/2PCS-50A-1000V-Metal-Case-Single-Phases-Diode-Bridge-Rectifier-KBPC5010-/221950605426?hash=item33ad497872:g:L~wAAOSwbdpWVV53

Power in would be 230V 10A at the most, after the transformer 12V 190A(if it were 100% efficient)

> Will an old AC transformer work for DC(maybe a retarded question)?

That's a super retarded question. Transformers ONLY work with AC. First transform down, then rectify. It also means you need smaller diodes.

When you are a noob at electronics, you shouldn't be working with mains voltage.You will probably kill yourself.

...

>thinks DC power is measured in RMS
>thinks transformers work with DC
>thinks a DC appliance can be used with un-regulated filtered AC

just stop, you have no idea what you're doing

>step down
?
>your amps are way high bruh
Which amps?

Put a capacitor after rectifier to reduce ripple

47-84
Step down transformer.

this.
only diode bridge is kinda ghetto. invest in a proper stabilizer and good capacitors to filter that shit.

in the end it might be cheaper to just get some computer PSU for it desu

This, you need to rectify it after having gone through the transformer.
Car equipment tends to be pretty robust because there's a lot of variation in the electrical system. A lot of the time you're actually getting closer to 14v.
Why do you want to do this yourself? Why do you want to take apart a microwave, a device that can easily kill you? Why do you want to use an automotive amp with a wall socket? Why won't you just buy a 12v power supply? Are you aiming for a Darwin award?

Theres so much wrong with this that im not even gonna start. Just get a cheap used amp and don't set your car on fire with this.

>Oh, too bad. Guess I would need to buy a more expensive rectifier bridge then,

Since you're working with such high power stuff you should really just forgo the whole thing and use a switched-mode power supply instead. This linear supply is going to be horribly inefficient.

>12V 190A

wew lad that's a lotta amps
enough to fuck over most electronics

Just get a wall wart for your 12V or an old desktop PSU. I don't fuck around with mains if I can avoid it. Also your circuit won't work.

>not wanting OP to kill himself

Oh right derp.

>mixing AC and DC
OP is going to fucking die

>Transformers ONLY work with AC
Forgot about that
>It also means you need smaller diodes.
How would I need smaller diodes, they would be able to handle much more Ampere?
>When you are a noob at electronics, you shouldn't be working with mains voltage
Actually have a electric education, but it was a few years ago. So the saftey bit I'm quite used to, just have forgotten some theory.

>Why do you want to take apart a microwave Why do you want to use an automotive amp with a wall socket? Why won't you just buy a 12v power supply?
Already have that transformer lying around, because they can deliver 500W RMS, thought about a computer PSU too, thought I would check out this solution too.

Car audio use a lot of power for some reason. Friends car amp have 3x40A fuses.

Just calculated the max, amp will draw around 47-84A(still much I know)

They are kind

>It also means you need smaller diodes.
In this case it means the exact opposite. OP is working with such high amounts of power that the diode bridge will have to be even bigger, there's simply too much current involved.

OP actually has the right idea(whether he realizes or not) but his device wouldn't work. What he actually wants is a switched mode power supply. SMPS sorta do what OP was trying to do but there's way more steps involved in the process.

>thinks DC power is measured in RMS
Not the DC power, the power from the amp to the speaker.

I hope you're trying to kill yourself instead of just pretending. This not only won't work but it'll fry your retarded ass to a crisp. Take it to /diy/ and prepare for the same response. 120vac is not a toy, stick to licking 9v batteries and fingering your butthole

>SMPS sorta do what OP was trying to do but there's way more steps involved in the process.
So basically it wont work without lots of fine electronics?
>120vac is not a toy
European baby, rocking that 230V

>thought about a computer PSU too, thought I would check out this solution too.
That's probably your best bet. It's much simpler, easier and doesn't carry the risk of screwing up something terrible. You'd also have a supply that will filter out a lot of the noise that would leak through your DIY transformer. Remember, thick wires, short distances, just to minimise the chances of things catching fire.
>Car audio use a lot of power for some reason. Friends car amp have 3x40A fuses.
Probably because higher number = better!!!
Idiocy aside, you'd get a considerably better setup if you bought something actually made for this. There's much more to audio than just the wattage value but a whole lot less than audiophiles believe. Car audio is a bizarre middle ground of audiophile tier bro science with focus on high numbers with no regard to what the numbers mean.

>So basically it wont work without lots of fine electronics?
Yes. A computer power supply(which is a kind of SMPS) might actually be perfect for this because the do happen to have high current 12V output(for graphics/PCIe)

I actually have some decent bookshelf speakers and a subwoofer, but the subwoofer is pretty small and I want something with more power. Since I have an 12" car subwoofer that's just collecting dust so I wanted to use that.

Why do car audio use so much power though? I mean there must be something else to it than just "higher number = better!!!" I feel. How do a 12" 500W RMS subwoofer compare to a whatever Wattage home audio one?

Yeah, had thought about it too, but if this would have worked it would have been much cheaper.
So it wont work(good) since there's a lot of "impurities"?

>Yeah, had thought about it too, but if this would have worked it would have been much cheaper.
Your device wont accomplish anything, it might just short out if it does anything. DC doesn't have any effect on a transformer.

The basic way that a SMPS works is it takes high voltage AC and rectifies it so it becomes higher voltage DC. Then the HVDC is switched between positive and negative at a super high frequency which creates a higher voltage "simulated" AC. The higher the frequency and the higher the voltage the smaller the transformer can be so this saves a lot of money. The simulated AC is then stepped down to the desired low voltage(s) and then rectified again. When it reaches its destination the voltage is fed into a voltage regulator and filtered with a few passive components like capacitors and inductors to keep the output consistent.

>How do a 12" 500W RMS subwoofer compare to a whatever Wattage home audio one?
You can really do a direct wattage comparison as they may well both be equally loud but the quality is probably going to be quite different. All amplifiers distort sound, no matter how neutral they claim to be. The question is how much and at what frequencies. Also, from general experience, car audio systems sound like ass when they're pushed to near what they're rated at.

230 means you pull less amps dumb ass. Amps are what will kill you, not voltage

>You can really do a direct wattage comparison
*can't

>DC doesn't have any effect on a transformer.
I of course meant after switching the rectifier bridge to after the transformer.

Well it was worth checking out the idea at least, but I guess it will be a PSU then, or maybe a car battery with a charger plugged in.

Car audio is mostly for producing much sound, and that they usually succeed in.

Never disagreed with that, just saying it.

>Car audio is mostly for producing much sound, and that they usually succeed in.
Exactly what I was getting at. The quality of the sound goes right out the window as a result and we're not talking audiophile "I can hear the difference between ALAC and FLAC" quality here.

Op, a microwave transformer is not meant for continuous use. After about 5 minutes it will overheat. They don't have enough copper or iron, so it operates well into saturation lowering efficiency. This type of transformer will probably burn down your house.

>or maybe a car battery with a charger plugged in.
You might get around an hour of useful operation at a time, just so you know. Depends on the size of the battery and the size of the charger but if you want much more then you'd have been as well off buying a power supply.

actually the amps you pull when something shocks you are relevant to your's body resistance, and thus more volts means more amps means, which in turn means more deader you. Relate to ohms law, your resistance is the constant. Ofc there are more factors but in a basic "if you're happy and you know it close the circuit with your hands" scenario with you being the receiver more volts mean more amps to you.

Well it usually sound decent imo, and when I ride in cars I'm not exactly looking for HI-FI sound. That's why I only planned to use a subwoofer as a compliment to my other speakers, to get some punch.
I usually listen with headphones normally.

>You might get around an hour of useful operation at a time
Yeah, now that I think about it that was the reason I ditched that idea in the first place.

Already ditched the idea.

>when I ride in cars I'm not exactly looking for HI-FI sound
Good because you won't be getting Hi-Fi sound. You also won't be in a car but I suppose that's another matter.
>That's why I only planned to use a subwoofer as a compliment to my other speakers
You'll probably still be able to hear it quite clearly, especially if you turn the sound up. If you're not familiar with clipping, you will be.

>I bet there's some electrical engineers here,

W E W
E
W

SOMEONE WANTS TO LOOSE SOME MONEY!

Well if you get clipping it's simply set up wrong.

>Well if you get clipping it's simply set up wrong.
Were it so simple. Car audio systems are made more compact and often more cheaply than other systems. Most often, this means cutting corners.

You can set it up right though, by setting the gain levels on the stereo and amp so that it avoids clipping. Preferably measure it with at oscilloscope but you can also do it just by listening, of course it will be harder then since you can confirm if it's truly free from clipping.

>You can set it up right though, by setting the gain levels on the stereo and amp so that it avoids clipping.
Cheaper and smaller designs very often have clipping at ALL levels. You can try what you want but there won't be any way to eliminate it. It's not just something that happens at high volume.

Might be a problem with cheaper stuff then, saw some instruction video about it some years ago, maybe they used better equipment.

Technically if OP did kill himself on the advice of a professionally licensed EE, said EE could lose his license.

Not just cheaper stuff but especially smaller stuff. Car audio systems cut corners to reduce their physical footprint. Even if they don't clip, the distortion can be a little interesting to say the least.

I dont know in what country, but no, everything you do without a said license is on your own responsibility, also you cannot officially prove you are an EE on an anonymous board

Sup, OP. I resurrected this Harman/Kardon sub after its internal transformer went down. You just need to short the main plug of a PSU, the one that goes in the motherboard. Watch the output ratings of the PSU.

How did you resurrect it?
I have one that makes a whining noise and the 12v rail is only 6-7v, everything else checks out though. I want it to stop whining and work right :(

>Amps are what will kill you, not voltage
adhering to the """amps is what kills""" meme are we now Cred Forums?
>putting both your fingers across a 12v battery
>nothing happens
>but that shit is capable of delivering 100+ amps
get your shit straight nigga, its neither one or the other, its a mix of the two, once it passes a threshold (skin/tissue conductivity, ac "permeates" better) you start to feel its effects (skin tingling, muscle spasms, skin burning) and eventually die

Can't be bothered to read the comments, so don't know if it's been said, but the easiest way to do this is a decent quality car battery charger, the type you can use while starting a car, then a car battery, then the amp.

if(voltage >= voltage required to permeate human skin){
its the amps that kill you();
}
else getfucked();

The big problem with car speakers is that they have piss poor efficiency. A 100W car audio system would be "loud" but a 100W guitar amp will cause hearing damage. You trade efficiency for flat response, but you can also trade efficiency for power handling. Just because your sub is rated for a kilowatt doesn't mean it's any louder than a well engineered 300W system. You could hook up a coathanger to your amp and break it; just because you have a big number system doesn't mean it's good.

Also, even though it takes more wattage in general to get bass volume, a 500W bass guitar amp would be loud enough to gig with and far louder than a 500W car sub system.

TL;DR you care about dB/watt, not just wattage.

Used this setup for years
Can be used for hours straight with no problems, sorry no pictures but I was running 500wrms through two 12" subs, 1200 peak

Professional 12v installer of 15+ years here, thanks for the laugh man. As you've gathered it's not a good idea. But fuck, I'll be dammed if you make it work without killing yourself, post pics.