modified computer power supply?

[soundman]

[QUOTEA bare transformet has no direct finger access to 240v if the primary is taken thru a terminal block......if the mains cord is joined in a covered terminal block and the primary windings have sleveing over the tails there is not even access to primary insulation
]

That is a lot of ifs! There is a vast difference between all your "ifs" and the solid metal case of my PS's. I am not saying you are wrong, but I suspect that the main issue is that they were not intended as being stand alone units and so did not get them rated as such. I cannot picture any risk that is different to some of the cheap import appliances I have dismantled and that are rated.

The only risk is electrical. This is not changed as the PS is screwed to the computer case. Structually, my PS's are far better than many applianced I have seen. It just seems hard for me to comprehend how there can be any further risk.

Dean[/QUOTE]

Solid metal case...don't make me laugh...flimsy tin box more like.

AND a tin box that was never designed to stand alone or operate other than screwed into an additional housing and to only supply power to circuitry entirely contained within that housing.

At no point does any power exit the computer case without further processing...unless it has been butchered

and it goes much further than that.

The fact that you cant comprehend the problems is a problem in its self.


THE worst factor is unqualified and untrained people working on switchmode power supplies.


In themselves switchmode power supplies can be very dangerous...far far more dangerous and far more complicated risks than working with transformers.


I have very little issue with unqualified, untrained, and unlicenced hobbists who have made sure of their facts, working with iron cored transformers......the issues are very straight forward and as long as you have managed to connect and insualate two wires and connect the third to a proper case earth connection......there is very little you can do to pose risk to yourself or anybody else.

But as we qualified technicians where drilled and plainly informed there are some very particular risks involved in working with switchmode power supplies.

These cheap nasty computer power supplies in particular are not something I believe untrained people should be playing with.

As they stand, they push every limit to the max and are barely compliant or adequate for what they where intended for.

the boards are crowded, the clearances are minimum and the components barely up to spec.

If you want a good bench power supply...yes you can buy quite nice chineese made supplies ready to go.

If you look on ebay you can buy some pretty respectable regulator boards both analogue and digital very cheaply.....and there are heaps of nice big transformers to be had.

I have a pile of these power supplies here...but i'm not using them as bench supplies.....there is a reason for that.

cheers

[Oldneweng]

The units I have. Pictures are from one of the links. The DC connections have been added by the modder. These get used to recharge batteries for RC Helicopters. They are used in pairs and that is the reason for the tape around the 2. There is a 12v and 24v connection fitted.

Power Supply 1.jpgPower Supply 2.jpg

These are Dell Server supplies, so the cheap and flimsy is not relevant and I would suspect that the internals are of very good quality. They are also as well protected from insertion as any in a computer case. The only vents are at the ends as shown. They cost me $36 all up. At the time I did an intensive search for suitable PS's and I can tell you that the lower price range was way above my budget.

They will need some form of protection tho as I want to avoid the risk of metal chips causing trouble. I have a metal case that I think they will fit neatly in. I was going to fold a shroud around them to cover top and side and extend out some distance at the ends. The other side will be attached to the cabinet of the mill. It will not be much more trouble to fit mesh to the ends of this metal case. It will add some protection against chips.

I think that many of the issues discussed would not be relevant to these PS's, but these are quite different to the average PS. This type would be a good one to use if available, but I suspect they may be hard to find now.

Dean

[Oldneweng]

The fact that you cant comprehend the problems is a problem in its self.


THE worst factor is unqualified and untrained people working on switchmode power supplies.

Please don't go getting your knickers in a twist.

I am trying to comprehend the situation.

I cannot say more than that.

Cheers Dean

[Ropetangler]

The only risk is electrical. This is not changed as the PS is screwed to the computer case. Structually, my PS's are far better than many applianced I have seen. It just seems hard for me to comprehend how there can be any further risk.

Dean

G'Day Dean and All,
I suspect that the electrical risk is vanishingly small, but the lawyer risk is somewhat higher. As Soundman says a computer case could be used to house the power supplies, and if common sense prevailed, they would make a fine and sturdy housing. However I suspect that if the lawyers got involved, nobody would be absolutely safe, after all the case was designed to house a computer, but legal types would probably argue that does not mean that it would be suitable for a power supply.
Rob.

[cba_melbourne]

Power Supply 1.jpgPower Supply 2.jpg

They look quite good Dean. Pretty sure these would cost new more than a complete home computer though. Fortunately these things become obsolete in very short time. So one can find "new old stock" maybe 5 years old quite cheaply. This is an example, slightly smaller than yours, 870W for $100 new: http://www.ebay.com.au/itm/Dell-870W...d=723089994450

If looking second hand professional lab power supplies, the Taiwanese Topward brand are an excellent buy. They also turn up from time to time on ebay Australia. The cheaper models have analog meters. These were made in the 90's. There are models with different voltage ranges and currents. Here a sample: http://www.ebay.com.au/itm/Topward-D...item27e129e48f Make sure its a 240V model though.

Linear power supplies are generally safer in a lab or workshop, than switch mode power supplies. This is because linear PS use a large transformer. However, if you need a small and light yet powerful power supply, switch mode is the way to go. This is a typical hobby model 30V/30A under $300 delivered: http://www.ebay.com.au/itm/0-30V-0-3...item58b73369e1 but its 110V input. I have also seen similar 240V models being offered on eBay Australia.

[Oldneweng]

I found the components including PS's. Just for fun I put one on the floor and stood on it with my full weight. That deals with the flimsy problem. These are rated at 41A max at 12 volts. This is not total output, it is max 12v output. The motor they will drive is a 24v geared motor which has a max input rating of 14A at 24v. I think this will work ok. Bear in mind that all of this has been discussed before on the forum.

The box I was thinking about is not long enough. It needs to be about 370mm long. I have found this box. It was housing one of my car tune-up meters. Guess how long it is since I used that.

Power Supply 3.jpgPower Supply 4.jpg

Rip out the junk and they will fit fine. The mesh at the rear of the first pic is stainless 3mm perforated. This will be used at each end for vents. Not this same piece. I have lots of scraps of this, some quite big , but bent for its original purpose. The box needs a clean-up and some paint. The PS's are from a server so they are designed to fit in a rack mount. They don't have seperate mount points. A couple of clamps will fix that.

Cba. A couple of points. I did an exhaustive search of every option I could think of at the time I bought them. Nothing else showed up in the right price range. The reason I chose these particular PS units was that this was the same model shown in the conversion/modify links I posted which made it easy to convert. I am sure I could work it out but at the time I found 2 only of these available in oz and decided that was good enough for me. There were no resonably priced bench power supplies available. This for a mill power feed. If I had the money to buy one of them I might as well buy the real thing. That is why I went this way.

In relation to others wishing to find a power source, your info is quite useful.

Dean

[Oldneweng]

G'Day Dean and All,
I suspect that the electrical risk is vanishingly small, but the lawyer risk is somewhat higher. As Soundman says a computer case could be used to house the power supplies, and if common sense prevailed, they would make a fine and sturdy housing. However I suspect that if the lawyers got involved, nobody would be absolutely safe, after all the case was designed to house a computer, but legal types would probably argue that does not mean that it would be suitable for a power supply.
Rob.

All quite true, but considering the purpose that these will be put to and the fact that they will not be left unattended I do not see much chance of a problem. I will probably switch them via the mill power supply. It has a 12v transformer. I would like to have a red light on top of the mill to remind me it is switched on. Same with the compressor. The lathe already has one quite visible. I do not like leaving my shed with stuff powered up.

Dean

ps I hope Ken has found out everything he needed to know.

[soundman]

Trying to comprehend the situation.....um well lets.

We started out talking about ..MODIFYING.....ATX...power supplies.

Now that typically infereers a power supply out of a typical home or office computer.......and it infeers that there will be changes made internally.....producing different voltages..was mentioned.

This is very different to just putting a pair of binding posts on an unmodified power supply of an entirely different construction.


There are still issues but far fewer.

Hmm interesting that you can afford to buy a helcopter, but not a propper power supply to charge the batteries.

cheers

[Oldneweng]

Trying to comprehend the situation.....um well lets.

We started out talking about ..MODIFYING.....ATX...power supplies.

Not specifically mentioned but implied. I will allow that. lol

Now that typically infereers a power supply out of a typical home or office computer.......and it infeers that there will be changes made internally.....producing different voltages..was mentioned.

This is very different to just putting a pair of binding posts on an unmodified power supply of an entirely different construction.

I do not know where changing voltages was mentioned. I was talking about linking 2 in series to get 24v but I don't think that is what you meant.

There are still issues but far fewer.

Hmm interesting that you can afford to buy a helcopter, but not a propper power supply to charge the batteries.

cheers

I guess that some people like to do stuff like this. Maybe they blew the budget on the heli. I don't know. There may be some clues on the forum I linked to about heli's.

Why do people on this forum and others spend huge amounts of money on machines and tools which they have no hope of recovering by the savings their projects create?

When I first posted about all this stuff including geared motor and control unit their were no problems brought up. Now some have been and I am just trying to comprehend whether or not any of these will affect my situation. I have decided to house the PS's which is a plus.

Cheers Dean

[BaronJ]

Hi Dean,

Those PSU are a very different beast from the cheap and nasty AT and ATX style ones used in domestic computers. They will do what you want them for just fine. You are right to protect them from swarf, cutting oil spray etc. Just remember that the fans are shifting air through them.

[Oldneweng]

Hi Dean,

Those PSU are a very different beast from the cheap and nasty AT and ATX style ones used in domestic computers. They will do what you want them for just fine. You are right to protect them from swarf, cutting oil spray etc. Just remember that the fans are shifting air through them.

Well I hope the fans are doing this because I won't be.

Dean

[Pearo]

No I am saying exactly what I said.

Computer power supplies are not stand alone appliances and in many ways are not fit for use as such.

There are many reasons for this.

That is before the relationship between mains earth and dc supply common is considered.

The use of a computer power supply can be compared to using a bare unhoused transformer from the point of view of legality, fitness for purpose and safety.

cheers

Just a heads up, this is not true.

I am now, but willing to debate in the morning.

A PC powersully is a full integrated powersupply and should be compliant to be used stand alone.

[Vernonv]

I have a PS here (from a run of the mill PC) and had a look at it with naysayers comments in mind. Here is what I've found:

1. The box is solid - unless you are the the Hulk, you won't be crushing it with your hands.
2. All air and fan openings are made up of collections of only small orifices, that are certainly no bigger than the vents found on some higher end electronics (I was comparing it to the vents on a Sony home theatre system). Come to think of it, on probably 95% of all of PC power supplies, the fan openings are exposed to the outside world, on the back of the PC. Kind of negates the reason to put it in a box.

[cba_melbourne]

I have a PS here (from a run of the mill PC) and had a look at it with naysayers comments in mind. Here is what I've found:

1. The box is solid - unless you are the the Hulk, you won't be crushing it with your hands.
2. All air and fan openings are made up of collections of only small orifices, that are certainly no bigger than the vents found on some higher end electronics (I was comparing it to the vents on a Sony home theatre system). Come to think of it, on probably 95% of all of PC power supplies, the fan openings are exposed to the outside world, on the back of the PC. Kind of negates the reason to put it in a box.

1. I am not a naysayer. I just recommend caution and common sense. It does never hurt to discuss the risks beforehand.
2. This is the ATX PS from my Aldi desktop PC, seen from below. I believe it is better built than the average no-name computer. I have certainly seen worse made power supplies.

Aldi_PC.jpg
It has the fan at the bottom, sucking the air in. For size comparison I added a metric ruler so you can compare the vent opening size. I can assure you that these vents are very fragile, I can push them inwards by 5mm with my small finger. With my thumbs I could break through. That is very soft and thin metal. This PS is definitely not intended to be used stand-alone. You can not compare a $30 ATX power supply to a $500 file server power supply like proposed by Dean.

Now have a look under the vents of your Sony home theater: you will find that the designers have been very thoughtful of kids playing with paper clips and needles. You will see that is impossible to insert such an object in a straight line and touch a life component without also touching a grounded metal shield. Sort of a labyrinth setup that lets air through, but not in a straight line )1. The openings by the way, are less than 2mm wide slits or 4mm holes on my Sony.

)1: that is what you should aim achieving, when you put a PC power supply into an enclosure.

[Oldneweng]

Now have a look under the vents of your Sony home theater: you will find that the designers have been very thoughtful of kids playing with paper clips and needles. You will see that is impossible to insert such an object in a straight line and touch a life component without also touching a grounded metal shield. Sort of a labyrinth setup that lets air through, but not in a straight line )1. The openings by the way, are less than 2mm wide slits or 4mm holes on my Sony.

)1: that is what you should aim achieving, when you put a PC power supply into an enclosure.

I think this is the main issue to consider. Last night I had a good look at my PS's and noticed there is a fuse just inside the AC input end. Now the mesh holes here are tiny (2mm?) but still big enough for a paper clip. This end will be mounted towards the rear and not far from the wall, but I am still considering ways to baffle this without restricting air flow. As you would have noticed, there is not a lot of room for air movement thru the PS's and only smallish vents. The top of each units has a "Hot Surface" sticker on it. This may only be because they are meant to be mounted in a rack in multiples and as such would be hot swappable tho.

They look as tho they have more room in the box than they really do as there is the DC output connection block sticking out one end which is visible at the bottom on the right side of the pic with the PS's in the box. The black bits.

Many years ago a mate had a problem with blowing fuses every time he used high beam on his 4WD. Eventually he found his little cute darling monster son had managed to poke a bit of thin wire thru the radiator fins and shorted onto the high beam connection on the righthand headlight. Convoluted? You bet. How did he do it? This was "Simon". He just does this stuff. He had a very experimental nature. He wasn't being naughty. He was a nice kid. He just wanted to investigate things. He got this from his father.

Dean