2 PC power supplies in series

[skiddz]

hey guys,

im only new so dont bite my head off if this has been covered, i did search but couldnt find anything of use.

i want to connect 2 atx PSU's in series go get 24v DC out to drive my motors (only need 3A) now i have hacked up 2 power supplies one of them is a "traditional" looking PSU the other is a long skinny thing.

i can get both to run seperately and give me 5v and 12v but when i try and connect them in series the long skinny one cuts out. My question is can i get it to run in series without too much hassle or am i barking up the wrong tree?


cheers
luke

[blackbeard52]

here ya go....

http://thedatastream.4hv.org/at_psu_hack.htm and http://www.antennex.com/preview/archive3/powers.htm

oopps:

2+ supplies is here but limited to 24v

http://www.procooling.com/index.php?...s&disp=52&pg=2

[albertsteptoe]

Hi Luke

You can series PC supplies but be carefull to isolate the first two power supply grounds from the chassis earths.
The negatives are connected directly to the chassis, you need to bring the negatives out from the first two supplies and ensure they are completely disconnected from any chassis.
The last supply negatives may remain connected to chassis.

So just to recap :

Lets say you want 36v in total.
Power supply No.1 with its negatives isolated from chassis will provide the 36v positive from its yellow wires and its negatives connected to the yellow wires of power supply No.2
Power supply No.2 also has its negatives isolated from chassis which connects to the yellow wires of power supply No.3
Power supply No.3 will already have its negatives connected to chassis.

The links provided in the previous post are very helpful, study them well.

Cheers!
AlbertSteptoe

[ger21]

The first thread at the top of this forum.

http://www.cnczone.com/forums/showthread.php?t=17548

[albertsteptoe]

Hi Luke

I like your term : Long Skinny Thing

The long skinny thing is most likely a switch mode power supply, same as an ATX PC supply.

Switch modes are not easy to series, its okay if you just have the bare bones PCB, then things will be simpler.

My advice is to keep an eye on Ebay, have seen many 24v supplies on there at low cost, well worth a look.

Good luck with what you decide.
AlbertSteptoe

[skiddz]

Originally Posted by ger21 The first thread at the top of this forum. http://www.cnczone.com/forums/showthread.php?t=17548

[embarassment] sorry next time i shall look harder [/embarassment]

Originally Posted by albertsteptoe Hi Luke I like your term : Long Skinny Thing The long skinny thing is most likely a switch mode power supply, same as an ATX PC supply. Switch modes are not easy to series, its okay if you just have the bare bones PCB, then things will be simpler. My advice is to keep an eye on Ebay, have seen many 24v supplies on there at low cost, well worth a look. Good luck with what you decide. AlbertSteptoe

the long skinny one is an atx.. or so it claims, given the relative weakness of the aussie dollar ill be steering clear of ebay for a little while but i did consider it, the PSU has only cost me $10 all up + a VERY nasty electrical shock, thank god for earth leakage switches(or i would be an ex-cnc-enthusiast)

thank you all for the spoon feeding and the help

cheers
luke

[der_fisherman]

As you seem to have asked the question (eg. you are not an electronics wizard!), may I advise you not to do this as I see only the possibility of a blow up and you could damage both yourself and other (expensive!) equipment. it is not a simple job and you really need TWO IDENTICAL UNITS for it to have a chance of working properly.....

May I suggest that you build your own power supply using (because I know it and it works beautifully!) the 17 volt Switched Mode Power Supply design from Elektor April 2003 (I think! But definitely 2003). (Voltage is "Programmable up to max 40 volts!)

I recently built it (with minor changes to give 25 volts instead of the 17 volts of the original design). It can be made to give up to 40 volts at a full 10 amps if needed! I can help and support you fully if need be......such a power supply will deliver the current you may need for years to come, and being very efficient (Switched Mode 85% plus efficiency) will not make any radical changes to the electricity bill as it only takes what is needed!!

The special chips used mean that the component count is also very small in comparison to most Switched Mode Power Supplies (especially those on Ebay that were designed in the 80s and 90s.....!!).

I can post pictures of mine, inside and out if anyone is interested, also copies of the article if needed as a pdf. Careful purchase of components should hold the cost to well under €100. As the supply is relatively simple yet very refined and really modern, any problems will be most easy to rectify, not that I expect any as it is fully protected against overheating and over current!

Even using quite a large box to house it (it was cheap!) it is still far smaller than many units available on ebay!! The box could have been at least 40% smaller if needed.

Output voltage is set by the values of only two resistors that are relatively easy to calculate the values of.... these could be replaced with two pots to make the output variable in theory, but I would not recommend that as setting up might prove to be beyond that of a non-electronics person.....but the fixed resistors are dead easy to calculate and use.....

It was originally designed for a top quality HiFi system, so the quality of the output is far higher than most CNC designs actually need......not a failure to my mind!

In the beginning, I also tried to buy a reasonably priced SMPS on Ebay, but I was unwilling to buy units of unknown quality (working or not who knows?) from Ebay for half the amount that mine cost to build!Also if they ever had a problem, I would probably be unable to fix it without full circuit details, as generally the circuitry is quite complex for SMPS, non standard components and unmarked inductors are a further possible problem....seldom available of course! I have had years of experience with such supplies in my previous job.....

I will help anyone on this forum to build this unit if needed. PCBs are available from a company in Belgium that supplies Elektor as well. PCB quality from them is really good, but one could make ones own PCB if required, the design is in the article, its only single sided with only one wire link.

I could probably help in the area of delivery too if needed.....cash up front of course!!

[kreutz]

Originally Posted by der_fisherman .................................. May I suggest that you build your own power supply using (because I know it and it works beautifully!) the 17 volt Switched Mode Power Supply design from Elektor April 2003 (I think! But definitely 2003). (Voltage is "Programmable up to max 40 volts!) ..................................... I can post pictures of mine, inside and out if anyone is interested, also copies of the article if needed as a pdf. Careful purchase of components should hold the cost to well under €100. As the supply is relatively simple yet very refined and really modern, any problems will be most easy to rectify, not that I expect any as it is fully protected against overheating and over current!...............................

Hello;

I would like to see the pdf file, it looks interesting...How about getting the ferrite transformer? Are there links to the distributors?

Thanks,

Kreutz.

[der_fisherman]

If I did it correctly, there should be a .pdf file as an attachment....

The inductors are all normal components 1 x mains transformer toroidal 240VA and 3 chokes 100mH at 5 amps.

Let me know if I can be of any further help.

Regards

Der_Fisherman

[kreutz]

Originally Posted by der_fisherman If I did it correctly, there should be a .pdf file as an attachment.... The inductors are all normal components 1 x mains transformer toroidal 240VA and 3 chokes 100mH at 5 amps. Let me know if I can be of any further help. Regards Der_Fisherman

Thanks a lot, It gave me a very good idea.

Best regards,

Kreutz.

[der_fisherman]

I spent some months looking for good reliable and not too expensive power supply on ebay, before giving up and making my own after I stumbled upon this circuit in Elektor UK.

The circuit is of exceedingly high quality output (actually higher than we need for CNC but who's worrying?), very efficient, simple to construct and if it ever went wrong (its properly looked after with regards temperature and current output), it should prove very easy to repair.

It took nearly 3 weeks for the PCB to arrive as they do not make that design every day (I bought 3 as it was a waste of postage to only get one and I know that I will build more in the future!)

Tests show that it works EXACTLY as designed after I built it and it also worked first time (but I am a very careful builder when its my money!).

Easily programmed for anything between 12 and 40 volts with just 2 resistors!!!

Upto now, I have not found anything negative in the way that it works.......

Regards

Der Fisherman

[kreutz]

Originally Posted by der_fisherman I spent some months looking for good reliable and not too expensive power supply on ebay, before giving up and making my own after I stumbled upon this circuit in Elektor UK. The circuit is of exceedingly high quality output (actually higher than we need for CNC but who's worrying?), very efficient, simple to construct and if it ever went wrong (its properly looked after with regards temperature and current output), it should prove very easy to repair. It took nearly 3 weeks for the PCB to arrive as they do not make that design every day (I bought 3 as it was a waste of postage to only get one and I know that I will build more in the future!) Tests show that it works EXACTLY as designed after I built it and it also worked first time (but I am a very careful builder when its my money!). Easily programmed for anything between 12 and 40 volts with just 2 resistors!!! Upto now, I have not found anything negative in the way that it works....... Regards Der Fisherman

It is not exactly what I was looking for, but the current share idea was a very good one. I really am interested into get rid of the need of the toroidal transformer too, that is why I was asking for the source of the magnetic cores. A simple 700VA to 1000VA transformer/bridge/capacitor type linear power supply, even without regulation, costs well over a hundred of dollars.

I looked into modifying the high power ATX power supplies for 48 Volts 15 to 20 amps output, but they are also expensive at that power range. What has proven a limit is the magnetic core availability in small quantities, and it will be required in my design, in order to separate the mains potential from the power supply output.

Vielen Dank und auf Wiedersehen,

Kreutz.