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Possibility of an 80 amp 12 volt power supply? Answered

I'm just wondering about the possibility of me building one of these? I basically want to power a car amp inside a house. If its possible, how much money would I be looking at? How hard would it be to find the parts? And would I be better off paying $500 for a good home receiver, vs $200 for a good car amp plus whatever the cost of the power supply would be?


What kind of speakers are you trying to drive? Car speakers? In the house? Sounds like a car battery and trickle charger is in order.

Typically car stereo equip is spec'd very loosy goosy, as in barely complies with the ratings. Car amps are designed for low impedance speakers since theyve historically operated on 12V DC. Home stereo amps typ use +/- 40V or so rails to drive 6-8 ohm loads. (100W into 8ohms > 28.3V RMS or 40V peak)

Having read down the comments etc, two points come out to me.

They are right about the power supply needed, if you're a little cautious then a 750 PSU would be fair enough.

Second is that if you're using even sort of efficient speakers then 1000W is far more than enough for a house.

Find a 100W stereo and turn it all the way up... It'd be double that.

As an example, for smaller bars and places I'd often use a 1200W head with linked bins and tops to do the job of a PA...

If you wanted another option altogether a power amp from the likes of thaumann at 500W/side is less than £150 and would likely be a better bet overall, though it only takes XLR or Jack (1/4") in.

Of course the speaker set up you intend to use would also affect this a fair bit, as to what makes the best option for you.

By the way the efficiency of speakers makes a big difference, if you're not sure, EV don't steer you wrong.

well, you could mod a couple microwave transformers (like 2) and just get some heavy duty rectifiers. But it wouldn't be regulated. By mod I mean cut off the secondary windings and wrap heavy gauge wire around for the secondary.

thats not a safe option, especially for 80 amps of power. there is a big risk of fire. also, how would you cram on the needed windings in very thick wire? to make it work, the primary and secondary would need re-winding. and diodes with 20V 80 amp PIV? sounds like several in series. you could never really regulat a power supply like that, but i would never attach an unregulated source to my expensive stereo

woops, didn't know it was for a stereo (must of skipped that) According to various DIY microwave welders you can get about 50 amps out of a 1000 watt microwave.

oh, and I was considering moding a microwave transformer to output like 5 or 6 volts at like 100 amps to create hydrogen and oxygen from water extremeley quickly. Even if I use circuit protection such as a circuit breaker or a fuse, would this be a bad idea?

yes, and for a good reason. as youve noted, i have little fear of high voltages. respect yes, but fear no. this is because you can survive very high voltages safely. on the other hand, 20 ma, the amount of power an led draws, is a fatal current. a cattle prod transformer is several kv, but 5ma. also, why would you want one of the most dangerous substances on earth (pure oxygen) in your house?

I forget, it was a projet for when I was messing around with fuel cells. Actually, it wouldn't be that dangerous, right? touching the 2 secondaries with your finger would be no different than a nine volt battery. The only danger would be touching the primary, but that can be solved with stuff like heatshrink.

1) touching the secondary on a hv transformer could give you electrical burns. touching high amperage leads would have several consequences
  • your central nervous system would be blocked, making extricating your fingers hard
  • you could get severe electrical burns, as the fats and water in your body boiled under the resistive heat.

2) the primary would be safer, as its current limited to a lethal 15 or 20 amps. the primary, unlimited, can draw several hundred amps before something blows. also, i would not trust heatshrink above 1 amp, and not above 50 volts.

right, but when the transformer is modded the secondary is only several volts. The heatshrink shouldn't be a problem either, the voltage is too low.

several volts, but considerable amps (lower volts=more amps. simple law of physics. nothing created, nothing used, everything transformed). and id never use heatshrink on high amp applications

right, but lets say touching both ends of the secondary wouldn't result in anything, nor would touching the water when the leads are in (inless you have a cut, or you are extremeley sweaty, or if you put both hands in and something wierd happens)

uhh, yeah. lets say you wont be poisoned by drinking motor oil, so its perfectly safe. high amperage unprotected outputs, re-wound transformers and oxygene are a recipe for disaster.

as long as you go about it not dumbly then everything should be fine.

as long as you drive not dumbly, you could drive nascar right? no. there are NO safety guards on what you suggest. not even a circuit breakers. most nascars are very safe. i would not be my life on not making a mistake. id bet it on a safety function engaging.

I don't see whats so not safe about this, the ony way I see getting hurt (or dying) is touching the primaries (protection will be there, it'll be in it's own seperate container), or putting the modded secondaries on my tongue, which I won't do.

the risks are: o2 is one of the most dangerous stuff on the planet. anything non oxidized, including iron, can burn in pure oxygen. if you touch the primary, up to 15 amps will flow through your body. this is lethal. even if the breaker cut power before you die, a lot of people suffer heart failure within 48 hours of electrocution (if it makes you feel better, this is probably the second most painless way to die) you may also have a muscular spasm, which could cause you to spill the water. now, a very high amperage is flowing around you. and the breaker will not protect you from the secondary side. if you manage a shock from the secondary, you will almost certainly get electrical burns. if you take a shock across the heart, you will almost certainly die. the ac spasms will block the natural nerves that control the hearts valves. soon after, the valves break. there is no way to save someone like that, not even a defibrillator. youd actually be safer using a neon sine transformer than a moded mot

so are you saying the main saftey risk is the water? neon sign transformers are different, they are HV at low amps. I want low voltage at high amps.

hv at low amps is a lot safer. the main risk is the high amperage. the water near the electricity is also a big risk though

I understand all of that, it's just that the voltage is soooo low (like 9 volts) that it couldn't possibly do any harm (such as a nine volt battery couldn't).

One volt at one amp can kill. The old Electricians rhyme of "it's the volts that jolts, but the Mils. that kills." is true. The voltage will make you quiver, the amperage will kill you. If only one volt with one amp can kill, can you imagine one volt at many more amps? Think of it this way. A tiny tiny drop of water shot at you at the speed of a rifle shot, will put a hole in you like any lead bullet would. The drop of water is the voltage, the power because of the speed of the drop, is the amperage. It doesn't matter how small the droplet of water it, if it has enough power behind it, as it is with voltage, enough amperage and it is lethal.

ok, well I'll use the same analogy then.

It'd be the same as a misting you with a garden hose. A lot of water, next to no force.

in order to die at nine volts my skin resistance would have to be:
9/0.2 = 450 ohms.
Maybe if you cut yourself open and put the electrodes in.

For 10mA
9/0.1 = 900 ohms
still to low

for 5 mA
9/,005 = 1800
getting closer, but still really low

the point is that yes nine volts could kill, it's just highly unlikley. Goodhart, it's like that multi meter myth, exactly the same.

i know i'm coming in 4 years late on this one, but:

low volts, high amps safe. soldering gun. the copper wire that makes the tip is part of the secondary winding. it has hundreds of amps, low volts. i've been burned a few times from solder gun contact, but never thrown into heart stopping spasms.
high volts, deadly. i've forgotten to turn off breakers before, or turned off the wrong one when doing mundane electrical jobs like changing an outlet or switch. i've taken 110v 60 amp ac at least 6 times. tingles the whole body, scares you, burns the finger tips. not so serious. i've seen a guy working on a 3 phase, 480v 60 amp motor. he forgot to lockout. he was thrown into a wall 12 feet away, and supposedly dead before he left the ground.

dude, if you make it, make an instructable! i've got a microwave parted down, and have been wanting the coolest project to use the transformer for. i've considered it, and the spot welder would never be used.
how much energy do you think you could recover using the hydrogen and oxygen in an internal combustion engine?

Unlikely or not, I know of cases; we are just giving warning to be cautious. I have personally been "burned" by voltage, but have never been on the receiving end of anything with any amperage in it.

Any source of low frequency that (can) pump 0.7milliamps through you for some period of time is going to generally be lethal. Water, direct wounds, and several other factors can make our "resistance" much lower then we are at other times. We are just concerned. And refer to TK's answer, below mine too.

5 ma is the threshold for pain, 20 causes permanent damage. 50 is fatal. 10 causes your bladder to let go, above all else. and its not higly unlikly. a mot is current limited to 1 amp. it will continue giving 1 amp until either an emt pulls the plug, or the circuit blows (not gonna happen, as the secondary is isolated from the primary. i would try this. if you need oxyegen, use a standard 9 volt wall wart or somthing similar. those things are current limited

im replying to gmoon, but i think the comment thing broke. anyhow: 1) transformers like neon sign and oil burner ignition transformers are almost perfectly current limited. otherwise, the neon tube would burn out earlier, and the oil burner transformer would soon burn out. the microwave oven transformer, on the other hand, is badly limited, and can give upwards of 1 amp of power. 2) hv is more dangerous if you dont know what your doing. the odds of a hv accident are slightly lower, as people are well aware of the danger. the odds of surviving a hv accident are much better than a high amperage accident 3) at least we agree a modified transformer is not a safe option.

"I'm with you fellas..." (from O, Brother where art thou?)

Seriously, I agree with guyfrom7up.

It may be amps that kill, but it's the voltage driving those amp through a specific resistance that dictates the current draw. Since just about any battery I can think of (even AA) is capable of supplying > 50 mA (our "fatal" benchmark), a well-designed 1V 80A supply isn't any more dangerous....The amps are there, waiting if we need them, but don't push--the volts do the pushing.

Or should we really be that paranoid about 1.5V D cells? (anybody here under 15 yrs old even seen a D cell? ;-) )

On top of that skin conductance isn't linear--it increases with voltage. I.E., the amperage which would increase due to the higher voltage increases even more--as the resistance itself drops.

A higher voltage supply is safer only if was specifically designed to limit current, to a very minimal amount. Some are, many aren't.

Not that I'd trust a home-made transformer as far as I could throw it.... Or that it's impossible to be harmed with low voltage (just that HV is more dangerous, hands-down.)

think of it this way: one amp at one volt can kill. Ramping up the amps makes matter's worse. Raising the voltage while lowering the amperage makes is safer.

sorry to be nit pick but you made a typo on the last line

I am sorry if I barged in on your conversation :-( , but I was getting frustrated watching it, and I wasn't even posting :-) I was hoping putting it really simply might get the point across.

yeah, wrong finger correct hand...... IT safer, instead of IS safer

yes, but thats not with any real control over the voltage youd produce

Yeah! My I.T. teacher built one of these but at 90 amps. On the other side it cost him about... £200-£300. And a heafty electricity bill.

I have an 800 watt car amp in my dorm. To get the power you need, connect 2 580 watt computer power supplies that you can get from newegg.com for around $20 each. They each put out about 25 amps at 12 volts.

Do you mean 80 Amps ? Or 80 watts?

. A 1KW amp will not pull 80A @ 12V unless you are driving it REAL hard with a test signal. A PS half that size, with plenty of reserve for the drum kicks, ought to do the job.

Yeah, it's probably pulling less than 45A, normally. I looked up the specs of a 1KW amp--it has three 20A fuses. Probably wired in series, so the fuses blow when pulling a continuous 60 Amps.

They don't offer much real info in the specs (hint--the manuf's are always fudging the numbers on amps.)

And I wouldn't want to shell out for an honest 40 or 50 amp 12V transformer. Be cheaper overall to buy the home amp.... I guess you could operate several transformers in parallel, but they'd need to be nearly identical, or one would run "hot" (didn't we have a similar thread once before?)

20A fuses in series would blow at 20A. 20A fuses in parallel... I didn't think you could do that; fuses aren't that tightly controlled WRT resistance, so one would blow first, quickly followed by the next two. (it'd work as long as total current was well below 60A. heh.)

As you say, they're probably playing fast and loose with the specs. No one needs 1000W of sound in a car, or a home for that matter. Audiophiles might "want" 1000W peak (that's 30+V waveforms on each of 4 speakers simultaneously) for "accurate reproduction" (hope you have 300W speakers!),
but that won't end up needed an 80A power supply...

(I did find some 1000W 12V switching power supplies online. That's about at the top-end of off-the-shelf supplies.. :-)

Yeah, duh, you're right--fuses in parallel are like resistors in parallel... Odder still--they claim 1000W RMS, which would actually be ~1400W peak! And many of the new car amps are Class D amps, which is PWM-- so the amps would be much more likely to reach peak (with square waves.) (I think the RMS is B.S. in this case.) 1000W isn't completely crazy-- Subjectively, twice as loud is 10X more audio watts, so 1000W is only twice the volume of 100W....

80 amps? Yikes! How often do you plan to use it? If you are using it intermittently, with 6 hours or so in between uses of 1 hour or less, I would say just get a honking big marine-grade/deep-cycle lead-acid battery, and keep a charger nearby to top it off between uses.