Electrical Question. (more PSU modding)

[Nataku]

I my last post about using a PSU for alternative reasons, You were shown a picture of a 10" Car sub being powered by a PC power supply. The thing was It was put togerther in a hurry, PSU was just setting outside with wires run to the sub. and the wires were spliced together really poorly. So I decided to re do it.

I first starting by replacing the PSU (4 amp on 12v) with a smalling sized PSU for space reason (2 amps on 12v).

I put everything together (nicely this time) turn it on and it played for about 10 seconds and then shut off, wouldn't turn back on either. Turned out that 2 amps just wasn't enough to push the 200watt car amp and 10" sub (plus neons I through in for looks).

So I took out that power supply and replaced it with a larger 10 amp on 12v PSU (I still didn't want to reuse the old PSU do to the crapy wiring).

Put it in and it worked just fine... until I switched on the neons. It then ran for about 15 seconds +or- 5 seconds, then shut off. But this one would come back on by a flick of the reset swtich so it wasn't burnt out.

So, my first thought was I was trying to pull too much current through one 18 gauge wire. So I took 3 of the yellow 12v wires and twisted them together, as well as 3 black wires for the ground.

This time tested without the neons on, it would run until the first "thump" (technical term) then shut off.

so my conclusion is this powersupply can not handle the power draw from this setup. But, why could the older 4 amp PSU work without a problem?

[PCgeek]

Maybe the old PSU was just of higher quality? It really doesn't make any sense, unless the newer PSU is just malfunctioning...

[Dizzious]

So wait, you're trying to replace a 4 amp psu with a 2 amp psu? sounds to me like that's the problem right there.... if you need 4 amps, then 2 probably won't cut it.

...although i might be reading that entirely wrong.

[Rudegar]

some psu's shut off when the volts get too low
and the more amps is being drawn the lower the volts gets
as the psu struggle to feed enough amp

[Nataku]

So wait, you're trying to replace a 4 amp psu with a 2 amp psu? sounds to me like that's the problem right there.... if you need 4 amps, then 2 probably won't cut it.

...although i might be reading that entirely wrong.

you are, Read again. You missed the whole part about the 10 Amp.

[NotMyBest2Day]

It sounds like the responsibility of capacitors and the surge rating. If you want your troubles to go away, just like you would do in a car that has a huge system but you're still running the 45-amp alternator, get a capacitor for the positive power going into the amp. Then when the first thump hits, it'll drain the cap and not overload the PSU.

[Nataku]

I agree! although I'm not trying to spend $50+ on this.

Any suggestions for a cap (I wouldn't think it would need to be automotive grade) that would work? or does anyone have one lying around I could take off of your hands?

[NotMyBest2Day]

It might be possible to go to an electronics store (sort of like Radio Shack) and get the biggest caps you can find (some are the size of D-cell batteries), and make sure they're good for 12v, and just pick up two or three of them (you'll probably want at least 250mF (milli-farad), and most, if not all of the small ones for electronics are measured in µF (micro-farads), which it takes 1,000,000µF to make a farad. So find what you can to get at least 100KµF and then just do a few minutes of soldering and do them in parallel, and that should end your woes.

[Nataku]

It might be possible to go to an electronics store (sort of like Radio Shack) and get the biggest caps you can find (some are the size of D-cell batteries), and make sure they're good for 12v, and just pick up two or three of them (you'll probably want at least 250mF (milli-farad), and most, if not all of the small ones for electronics are measured in µF (micro-farads), which it takes 1,000,000µF to make a farad. So find what you can to get at least 100KµF and then just do a few minutes of soldering and do them in parallel, and that should end your woes.

nice! thanks. I'll keep you posted on what happens. and thanks for the info on the wood too. this is all the same project.

I wont have the money to play with this for 2 weeks. :-(

Edit: So to make 250mF (as you suggested), I need 250,000µF. Right?

Edit2: most of the ones I see on radioshacks website say they are rated at 35v or some time even 50v. would these still work in a 12v application? And the biggest they had was 4200µF... i'm going to need quite a few of those! unless I find something bigger.

[NotMyBest2Day]

Yeah, the 50v ones should be plenty fine. Just need something that is rated for at least 12 since that's what you're using. Yes, 250mF is 250,000µF. As I said though, just getting to 100KµF should be all you need. You might even be able to get away with half of that. If it doesn't work, it's easily expandable.

This is what I had in mind for hooking them up in parallel, by the way:
http://www.lifelessempathy.net/pics/pcstats/capacitor.gif

I'm pretty sure parallel would work better than series though, since it'll just act like a bigger cap and share the load equally across all of them instead of in series where you drain the first one and the second has to recharge the first, and the third has to recharge the second, etc.

Also, there's a store locally here called Wholesale Electronics and they've got a much bigger selection than radio shack does. They've got caps there the size of Pepsi cans. :eek:

[Nataku]

there's a store locally here called Wholesale Electronics and they've got a much bigger selection than radio shack does. They've got caps there the size of Pepsi cans. :eek:

where do you live?

[Nataku]

ok another question.

http://www.alliedelec.com/Search/ProductDetail.asp?SKU=507-0290&SEARCH=&ID=1640277&MPN=53D113G025JP6&DESC=53D113G025JP6

On that capacitor it says it is rated at 11000muf. What is muf?

and if you look at the datasheet on it it says it is rated from 15uf to 220,000uf, but it is so small?

[NotMyBest2Day]

I'm in Charleston, SC. Not sure what muf is. I'm thinking it's still just micro (µ), but they didn't know how to make the u with a leg. *shrug* µ is easy to make. All it takes is this: µ and it parses as HTML.

[Joe]

nataku ... check this site out http://www.hosfeltelectronics.com ... i used to live about 5 minutes from this place and they have everything you could want for projects such as this. .. i have also ordered from their online store and the shipping is fast and cheap.

[NotMyBest2Day]

Nice site Joe. I found a 22KµF. Just under $2. It's probably about as good as you're going to get.

[cracklingice]

http://cgi.ebay.com/1-5-Farrad-Capacitor-for-Stereo-Systems-upto-750-watts_W0QQitemZ290007484611QQihZ019QQcategoryZ1493 2QQrdZ1QQcmdZViewItem

Or you could always try bidding on one.

[Nataku]

Thanks joe!

I don't trust that ebay post too much, no name brand, no markings and it's 25? that's really cheap for what it "is".

So should I do 5 or 10 22KµFs in parallel?

Edit: it says it is 22000µF @ 16v. And is there a way to find out what it will be at 12v? or will it be the same?

[NotMyBest2Day]

I'm not sure if the farad rating works like watts/amps though. I think if volts goes down, then farads go up a proportional amount, so 22kµF @ 16v should be 27.5KµF @ 12v. 22,000 / 16 = 1375 * 4 (since you want to subtract four volts) = 5500 + 22000 = 27,500 @ 12v.

Or is it 16 / 12 = 4/3 then times 22000 = 29,333. I'll just call it 28K since that's about halfway between both methods.

I think four would be fine. Gets to the minimum of 100K that I suggested. 250K shouldn't have any problems at all, but I think 100K is a good minimum to start at.

[Nataku]

I think four would be fine. Gets to the minimum of 100K that I suggested. 250K shouldn't have any problems at all, but I think 100K is a good minimum to start at.

keep in mind that this is going to be powering 2 amps (50watt and 200watt) for the 10"sub and 2 6x9 speakers.

[Nataku]

anyone here electrically inclined enough to show me how to make a display showing how much charge I have in the caps?

[NotMyBest2Day]

Well the 1.5F caps are good for about 750 watts, and you're only running 250, so a third of 1.5 is 500KµF. I guess you should probably shoot for 250K to start with then.

As far as the displays, I don't know anything about those. I wish I did.

[Nataku]

I think I've found something.

Notmybest2day, check this out.

http://www.evilmadscientist.com/article.php/SuperCaps

I wonder If they make these rated at 12v

it doesn't look like they make anything bigger then 5.5v

[NotMyBest2Day]

Hm. Looks pretty interesting. To make them handle 12v, you'd have to do a hybrid of series and parallel. In the diagram I made that only had one cap, but it was hooked up in parallel, just make it five, but in the same design..::opens up paint...then photoshop to get a 2-bit palette GIF::

http://www.lifelessempathy.net/pics/pcstats/hybridcaps.gif

[JLAudioFan]

I would say that part of your problem is most car audio amps i've dealt with have at least 30amp fuses... The wattage may be close to the same but you need more muscle behind that wattage to have the PSU not shut down (or melt down...)

Adding capacitors might help but you're going to end up going over your 50 buck budget to really get it working like you want it to.

Just my 2 cents =P

[Nataku]

Actually only these new caps cost so much, the old ones we found were only 2$. and I would need 10 of them.

[Nataku]

Hm. Looks pretty interesting. To make them handle 12v, you'd have to do a hybrid of series and parallel. In the diagram I made that only had one cap, but it was hooked up in parallel, just make it five, but in the same design..::opens up paint...then photoshop to get a 2-bit palette GIF::

http://www.lifelessempathy.net/pics/pcstats/hybridcaps.gif

that would be a 37.5F cap! these caps are 1.5F each, not to mention 10$ a piece.

[NotMyBest2Day]

Well then you could power like a 2,000w amp with it then. :p

[Nataku]

something tell me that much current could be harmful.