User Guides [New Idea] Use SMPS to power your devices.. !!

I am using BSNL BB since 4-5 years With Type I modem

Recently my modem's adapter got burnt.. OK it served me for a quite ling time .... So I went to BSNL office to purchase new one.. Guy says we are not selling modems now go & get it from open market ... Checked 2-3 shops .. no luck...

searched all home appliance any one using same rating ... again no luck.... not a standard adapter 10 V 550 mA...

I dont want to use some cheep one may damage modem also .. so recalled some electronics & thought why not build one .... OK its not that difficult... but it requires time & .. work ...

Then while searching i got old SMPS in hand saw 12 V 40 A as a output .. Thought We can easily get 10V from 12 V just 2 v Drop ... Connected 3 diodes as 0.6-0.7 V drop per diode 12-2.1=9.9 V assembled some wires & go my modem is working w/o extra adapter .. wOw !!! . . .


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Connected this cable to my working SMPS to Modem..... Working since 1 month .... works great.. Side Benefit.. no need to switch on off modem .. Auto switching with PC ...
 
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1. Using a power supply that big to power something that small is a colossal waste of energy. I would think it may not be more than 20% efficient. In a few months, you will have spent enough energy to have justified the cost of an adapter.

2. Almost all power adapters below 2A output (and some above) available after-market, are internally SMPS, except much, much smaller and more efficient.

3. A 'Cheap' adapter and a 'cheap' PSU like the one you have are both equally and spectacularly prone to failure, so you have not mitigated the risk.

The +5 and -5 are a good idea but the -5V is not externally exposed except at the 20-pin connector. Also, most regulators except LDOs need a bit of headroom to operate, 2V is probably out of the domain of the cheaper 78xx series which one would use for applications like this one. Of course one can construct a small series regulator, but the diodes in practice work just as well.
 
I have absolutely no idea how you can get something to work on an SMPS that is not 'working'. I am assuming it is working. My point is that it is a suboptimal solution in your application. If you were running a higher-power device (for example, a watercooling array or even as a second PSU to power fans and lights) I would have accepted this as a good solution. People have been doing that for many years.

I don't understand where you got the word 'extra' from. I haven't mentioned it once. Neither can I understand what you mean by the word. 'Spare'? 'Additional'? 'External'? Please do clarify.

To be very clear, the fact that something does work does not always mean it is the best way to do things. It is not appropriate to be labelled as a probable solution for those missing a power adapter. Since you know enough to solder three diodes onto a veroboard, you will also know what I'm talking about.

And before I forget to mention, if that PSU can survive 20 seconds of you pulling 40 amperes through it, hell will freeze over.
 
cranky said:
I have absolutely no idea how you can get something to work on an SMPS that is not 'working'. I am assuming it is working. My point is that it is a suboptimal solution in your application. If you were running a higher-power device (for example, a watercooling array or even as a second PSU to power fans and lights) I would have accepted this as a good solution. People have been doing that for many years.

I don't understand where you got the word 'extra' from. I haven't mentioned it once. Neither can I understand what you mean by the word. 'Spare'? 'Additional'? 'External'? Please do clarify.

To be very clear, the fact that something does work does not always mean it is the best way to do things. It is not appropriate to be labelled as a probable solution for those missing a power adapter. Since you know enough to solder three diodes onto a veroboard, you will also know what I'm talking about.

And before I forget to mention, if that PSU can survive 20 seconds of you pulling 40 amperes through it, hell will freeze over.
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Actually, i think what he is trying to say is that he is using the SMPS to power his PC as well.
 
rdst_1 said:
Actually, i think what he is trying to say is that he is using the SMPS to power his PC as well.
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+1


surajspai said:
^thats still risky in itself.the contacts short out on any thing by mistake and the whole pc is at risk
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We r getting 12 v from yellow cable in my case supports up to 17 A. ok Now my modem adapter is 10 V 550 mA means lil more than 0.5 A. I am using 1A diode so this diode prevents reverse current as well as diode will burn if current increases (Fuse Action) ....

So can we say SMPS is protected from reverse current & over current....

Do we need any other protection ?

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I have 2 SMPS
1. CIL-Odyssey 450W - 12 v 17 A o/p - currently connected to pc & powering modem
2. Umax 450W - 12 v 25 A o/p - Spare


why such difference ? which is good one to use ..?


@cranky : I am not saying it is solution.. it is one way... may may not perfect ..
 
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not like that mate.i tried this before,with a psu,was using it as a bench supply sort of thing to run my arduino and other diy projects.it so happened that a unused molex cable,which was lying free came into contact with a metal tab on my table and it shorted.the psu had protection (some dell oem model) and it powered off.but a diy circuit,which was in the same path as the 12v molex line caught fire and it was nasty.so...

why not make your own adapter?something like this.adjustable too,so you can get decent output range for other uses too.
Tangent Regulator, Adjustable, plus Diode bridge

or,if the psu is good enough or you dont want to spend more,seal off the unused cables,to avoid my mistake.i think you would have already considered that
 
JPushkarH said:
diode will burn if current increases (Fuse Action) ....


I have 2 SMPS
1. CIL-Odyssey 450W - 12 v 17 A o/p - currently connected to pc & powering modem
2. Umax 450W - 12 v 25 A o/p - Spare


why such difference ? which is good one to use ..?


cranky : I am not saying it is solution.. it is one way... may may not perfect ..
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To your 3 points:

1. A single 1N4001 has an overload current rating of 30A (the current after which it is destroyed) and a maximum current rating of 10A. It is not any form of protection, it has not been designed to protect anything and indeed, it does not.

2. Both your power supplies have ambitious labels. That is the difference between them, both are equally pathetic. I don't even know if they have any form of protection installed.

3. I did not say you were, I was saying that to warn off other readers who will not know better. You have created the post and it is our duty to express what we feel. I feel it is without merit and risky for a very small gain. Added to that is how dangerous these no-brand power supplies can be, specially one that has its 'Hi-port' tested by Service 'Personal'. I would not trust even one of the ratings on that label, or its ability to keep things downstream safe. I have seen power supplies destroy graphics cards, hard disks, network adapters and other hardware. I have seen a few combust and explode, and one literally catch on fire. Fair warning.
 
Why attack the OP for experimenting on his own computer and sharing his experience here? The point of experimenting/modding is to learn and have fun. If his computer blows up, so be it, he'll learn, and so will the rest of us.

While this is a tech forum, the number of users actually doing something interesting is quite low.
I found @JPushkarH 's post interesting, and worth following.

JPushkarH - keep experimenting, and have fun. Mod, blow-up stuff, listen, learn, repair, improve.

Looking forward to reading about your other experiments.
 
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kudos for trying and the curiosity to try things out, (and of late we've been missing this sort of stuff on TE) but this is pretty risky IMO. the grounds may not match, and you might end up frying the modem/onboard lan chip or both.
 
the modem has a 0V (ground) for the adapter input and the outputs are often W.R.T to that. Same for the inputs on the motherboard. Ideally these should be the same. but since these are run off different power supplies, any DC offset is irrelevant, since the isolation at the adapter takes care of it.

But if you are running them off the same power supply, if there are any DC offsets somewhere, and the circuitry cannot handle it, there may be problems.
Then even if they match, there is the problem of ground loops that might happen
 
greenhorn said:
the modem has a 0V (ground) for the adapter input and the outputs are often W.R.T to that. Same for the inputs on the motherboard. Ideally these should be the same. but since these are run off different power supplies, any DC offset is irrelevant, since the isolation at the adapter takes care of it.

But if you are running them off the same power supply, if there are any DC offsets somewhere, and the circuitry cannot handle it, there may be problems.
Then even if they match, there is the problem of ground loops that might happen
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How to get out of this ..? this is sol ? Tangent Regulator, Adjustable, plus Diode bridge

My SMPS supplies power to 3 hdd, one dvd rom, & mother board ....in pc actually these are diff devices so ... Problem is here also am i correct ..?

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cranky said:
Since you know enough to solder three diodes onto a veroboard
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I have started soldering since i am in 7th std :)

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surajspai said:
not like that mate.i tried this before,with a psu,was using it as a bench supply sort of thing to run my arduino and other diy projects.it so happened that a unused molex cable,which was lying free came into contact with a metal tab on my table and it shorted.the psu had protection (some dell oem model) and it powered off.but a diy circuit,which was in the same path as the 12v molex line caught fire and it was nasty.so...

why not make your own adapter?something like this.adjustable too,so you can get decent output range for other uses too.
Tangent Regulator, Adjustable, plus Diode bridge

or,if the psu is good enough or you dont want to spend more,seal off the unused cables,to avoid my mistake.i think you would have already considered that
Click to expand...

nice one
but do I need variable .. ?
and i am using it on wooden table no metals aside except cabinet ...
 
in a PC, they are explicitly designed to run off the same PSU, so they would be designed with a common signal ground. but this is designed to run off a seperate PSU, so that assumption need not hold true.

I'll illustrate with an example. I tried to use the 12V off my music system that was supposed to drive a turntable to power my walkman via an LM317. When I plugged in the walkman to the amp, there was this huge noise (which wasnt there when I was running it off a seperate adapter). After checking with a multimeter, I found that the ground of the audio output of the walkman was around 1.5V above the 0V of the power input, and when you tried to connect it to the 0V ground of the input, it shorted.

I eventually solved it by adding a set of capacitors in between to block the DC offset, but there was still some interference.
 
remove disturbances?you mean like a filter?i guess it can but the input should be higher than what ever output you are taking.you cant add it to a 12v line and expect a full proper 10v out,as the regulator will have a drop of atleast 2v.
what i was thinking of is-make a all out adapter,starting from raw AC mains->stepdown transformer->rectifier cum regulator circuit->filtered dc output.you can vary the output supply as you like,so you can use it as a supply for your modem,and use it to power any thing you feel like making too.


as for removing disturbances from a computer psu supply,there will be no need for it at all,as the apparatus wont require so clean a supply.
 
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