View Full Version : a question for our elecrical engeneers
dimmreaper
03-03-01, 01:56 PM
Dan- I'm clueless as to were to post this, so I put it in here knowing that you would know it's appropriate place in the forum :O)
I know a few of you guys are electrical engineers, and as such you could answer this.
Can I connect a regulated and unregulated powersupply in a series to booste voltage?
I want to build a simple non-regulated 9V powersupply, and connect it in a series with my PCs 12V PSU rail for a combined voltage of 21V. I want to do this to power a rather thirsty 24V peltier.
Will this work without damaging my PC's PSU?
I'm not an electrical engineer but I think what you would want to do is build a -9v ps with reference to ground on your comp ps, meaning no difference of potential between the two grounds. You would also have to make sure it can handle the current draw from the pelt, but it should be possible. Hope this helps
dimmreaper
03-03-01, 02:33 PM
How exactly does a negative voltage powersupply differ from a normal powersupply?
Will the transformer in the 9V powersupply need to be rated for the amperage of the peltier?
For example: The peltier in question has a maximum current draw of 11.3 amps. Will the 9V powersupplies transformer need to be rated for 9V@ 11.3amps, or would it be ok to use a transformer rated for 10V@3amps (very common open frame transformer) and use the PC's PSU to handle the rest of the amperage?
Because current flows from negative to positive I think the transformer in the 9v supply would need to Handel the current of the pelt. The reason I said a - 9v supply is because to get the same potential for the grounds the easiest way is to connect them together. I think if you build a +9v supply and connect the positive to the ground of your comp supply you will fry something, but if you build a negative supply and connect the grounds it should be ok. I will see if I can find some schematics. If this doesn't sound right would somebody with ckt. design knowledge please correct me.
I just thought of something, the AT ps has a +12v and a -12v led you can connect the pelt across those and run it at 24v. I don't know how long it would last though
dimmreaper
03-03-01, 03:41 PM
Shep (Mar 03, 2001 03:30 p.m.):
I just thought of something, the AT ps has a +12v and a -12v led you can connect the pelt across those and run it at 24v. I don't know how long it would last thoughIt won't work because AT PSUs have a voltage regulator :(
http://www.repairfaq.org/sam/samschem.htm#schslp2
here is a page that has several different ps schematics. Why does the ps need to be unregulated? I know nothing about pelts.
dimmreaper
03-03-01, 03:53 PM
So will something like this work?
That will get you 21v. I would try with some junk ps before putting it on your pc supply just to make sure everything will work also measure your ripple voltage before and after and compare the two too much ripple and your pc may not like it.
Daniel ~
03-03-01, 04:53 PM
I'll go with "General hardware". Why can't you ask questions that that fit neatly into my petty little vision of the O/Cing world? But for stumping the Moderator you get 1 free day (This is a first!) in "General Discussions" LOL
markedmundb
03-03-01, 07:06 PM
Daniel - (Mar 03, 2001 04:53 p.m.):
I'll go with "General hardware". Why can't you ask questions that that fit neatly into my petty little vision of the O/Cing world? But for stumping the Moderator you get 1 free day (This is a first!) in "General Discussions" LOL
(*CHEEKY MODE ON*) :¬]} Shouldn't it be stuck in cooling seeing as it to with Peltiers :¬]} ? LOL (*CHEEKY MODE OFF*)
Daniel ~
03-03-01, 07:20 PM
You just cost Jeff 3 hours of free "General Discussion" Time. It's one thing to stump the Moderator and quite another to confuse him with facts!":O} "Cooling" it shall be. LOL
I don't see why you couldn't stack the two supplies, provided the 9 volt supply is floating. If the negative rail is tied to chassis it will not be pretty... Personally I would go to the surplus market and get a dedicated supply and leave the computer supply for running the computer- but that's just the way I was taught- the right tool for the job kind of thing. 12 and 24 volt supplies can be had for reasonable cost that are much better designs than these cpu supplies- which tend to be kind of cheap and not designed for steady state loads like peltiers.
dimmreaper
03-03-01, 08:56 PM
Tim- (Mar 03, 2001 08:19 p.m.):
I don't see why you couldn't stack the two supplies, provided the 9 volt supply is floating. If the negative rail is tied to chassis it will not be pretty... Personally I would go to the surplus market and get a dedicated supply and leave the computer supply for running the computer- but that's just the way I was taught- the right tool for the job kind of thing. 12 and 24 volt supplies can be had for reasonable cost that are much better designs than these cpu supplies- which tend to be kind of cheap and not designed for steady state loads like peltiers.I don't want to use a dedicated 24V PSU for two reasons:
(1) I want to fit my entire computer in my mid tower for easy toteability.
(2) I'm cheap, I can make a simple 9V PSU for very little bread.
The only reall problem I have found with this arrangement is that I will need a huge PC PSU fro the project. My current 300W PSU (AMD approved, so most of the wattage is dedicated to the low power rails) only has 11.6A available on the 12V rail. So I need to find a PC PSU that offers at least 20A on the 12V rail (probibly a 450W unit).
You could probably find a switcher supply that is about the size of a HDD and mount it accordingly. (5.25" drive of course)
Something like this- it would go 150W
http://www.mpja.com/product.asp?product=12424+PS
dimmreaper
03-03-01, 09:53 PM
Tim- (Mar 03, 2001 09:32 p.m.):
You could probably find a switcher supply that is about the size of a HDD and mount it accordingly. (5.25" drive of course)
Something like this- it would go 150W
http://www.mpja.com/product.asp?product=12424+PS Yes, I am aware of that Tim.
But the peltier in question draws 271W (I said it was a big fellow!). So I will need something with a bit more "umph". This is why it makes since to use the PCs PSU for some of the power and add a small (120W) supplimental powersupply.
dimmreaper
03-03-01, 10:45 PM
Shep (Mar 03, 2001 03:48 p.m.):
http://www.repairfaq.org/sam/samschem.htm#schslp2
here is a page that has several different ps schematics. Why does the ps need to be unregulated? I know nothing about pelts.Well AT and ATX PSUs are regulated to only push 12V on the 12V rail. If you connect two regulated 12V PSUs in a series, they will automatically regulate themselves to only produce a combined 12V.
But since a PCs PSU only regulates the +5V +12V and leaves the "negative" circiutes as common grounds (~0V), from what I've been reading today (all over the net), one should be able to stick a non-regulated PSU in the loop and achieve higher voltage.
Another alternative would be to build the second PSU with components only capable of generating 9-12V and build the PSU with a 24V regulator. But this is really just a costly waste of electrical components in my oppinion.
klosters64a
03-03-01, 10:49 PM
I am not an EE. If this were my project, I wouldn't dream of involving my PC's PS with one for this Peltier. I don't know it for a fact, but I think your diagram is a recipe for disaster. If you need to run a monster Peltier, shell out the money for a dedicated power supply for the Peltier.
dimmreaper
03-03-01, 10:54 PM
klosters64a (Mar 03, 2001 10:49 p.m.):
I am not an EE. If this were my project, I wouldn't dream of involving my PC's PS with one for this Peltier. I don't know it for a fact, but I think your diagram is a recipe for disaster. If you need to run a monster Peltier, shell out the money for a dedicated power supply for the Peltier.It's not the money that I am worried about. I want to keep my PC as small and portable as it can be. This means stick with a mid-tower, and concealing everything inside of it.
I'm not 100% posotive that it will work either. But I have a few old PSUs kicking around that I can test this on. If it works, great! If it fries an old PSU, it was time and money well spent on an educational expirience.
klosters64a
03-04-01, 03:51 PM
Please keep us posted on your adventure! Surely, someone sells a PS that'll run your Peltier. If it won't fit in your case, you could build a support for it on the ouside rear of your case.
Richard
03-04-01, 09:50 PM
I think a DC to DC converter might be helpful. They're usually very small. Unfortunately they're hard to come by.
If I were you I'd call a large distributor (that sells DC to DC converters) and ask them if they carry the voltage and current you need. Make sure you know how many volts and amps your PS puts out when you ask them.
Jeff Evans (Mar 03, 2001 10:54 p.m.):
klosters64a (Mar 03, 2001 10:49 p.m.):
I am not an EE. If this were my project, I wouldn't dream of involving my PC's PS with one for this Peltier. I don't know it for a fact, but I think your diagram is a recipe for disaster. If you need to run a monster Peltier, shell out the money for a dedicated power supply for the Peltier.It's not the money that I am worried about. I want to keep my PC as small and portable as it can be. This means stick with a mid-tower, and concealing everything inside of it.
I'm not 100% posotive that it will work either. But I have a few old PSUs kicking around that I can test this on. If it works, great! If it fries an old PSU, it was time and money well spent on an educational expirience.
dimmreaper
03-04-01, 10:32 PM
Richard999 (Mar 04, 2001 09:50 p.m.):
I think a DC to DC converter might be helpful. They're usually very small. Unfortunately they're hard to come by.
If I were you I'd call a large distributor (that sells DC to DC converters) and ask them if they carry the voltage and current you need. Make sure you know how many volts and amps your PS puts out when you ask them.Won't work, as no PC PSU can handle the wattage of the peltier. And on top of that DC to DC converters are rather inefficient, which will require even more wattage.
LimeyGreg
03-04-01, 10:35 PM
AT and ATX psu -ve supply rails are usually low current, so, as the total current has to flow through both supplies it will either shut down or get fried.
A DC-DC coverter sounds good but will cost more than a psu, not to mention the fact your psu still hase to deliver all the necessary current - actually it will be more due to the inefficiency of the conversion.
A conventional psu will be quite large (see how big a 12v 10a battery charger is). Also, it needs to be -ve wrt chassis, unless you intend to operate it as a "floating chassis" - but that is a dangerous way to go.
Best solution is a dedicated swithching psu for compactness. :)
Richard
03-04-01, 11:04 PM
Radio Shack, has a book for sale that basically sounds like what you need. I can't remember what it's titled, but it's a HowTo on building Power Supplies.
Also, I did do some searching last night on DC power supplies, and found a pretty compact 24 v / 12 amp. I'll see if I can dig up the specs.
I will also ask for some guidance from the alt.engineering.electical group.
Jeff Evans (Mar 04, 2001 10:32 p.m.):
Richard999 (Mar 04, 2001 09:50 p.m.):
I think a DC to DC converter might be helpful. They're usually very small. Unfortunately they're hard to come by.
If I were you I'd call a large distributor (that sells DC to DC converters) and ask them if they carry the voltage and current you need. Make sure you know how many volts and amps your PS puts out when you ask them.Won't work, as no PC PSU can handle the wattage of the peltier. And on top of that DC to DC converters are rather inefficient, which will require even more wattage.
dimmreaper
03-05-01, 06:52 PM
Richard999 (Mar 04, 2001 11:07 p.m.):
Radio Shack, has a book for sale that basically sounds like what you need. I can't remember what it's titled, but it's a HowTo on building Power Supplies.
Also, I did do some searching last night on DC power supplies, and found a pretty compact 24 v / 12 amp. I'll see if I can dig up the specs.
I will also ask for some guidance from the alt.engineering.electical group.
I already have a book coming from the local book store called "The PowerSupply Cookbook", I have a friend who has it and uses it to build PSUs for his pirate radio projects quite frequently.
Richard
03-06-01, 01:49 AM
Jeff, here's a high powered power transformer.
http://209.149.176.131/pdf/acdc201.pdf
Lots of other great stuff there too.
dimmreaper
03-06-01, 02:12 AM
Richard999 (Mar 06, 2001 01:49 a.m.):
Jeff, here's a high powered power transformer.
http://209.149.176.131/pdf/acdc201.pdf
Lots of other great stuff there too.Naw, those are all wussy transformer. I need a transformer thats got high amperage as well as high voltage. I already know were to get good (hammond) center-tap transformers anyway. The transformer needed will cost well in excese of $50 (for just the transformer).
Richard
03-06-01, 05:24 AM
25 amps too low?
Did you look on page 2 of that page?
dimmreaper
03-06-01, 06:18 PM
Richard999 (Mar 06, 2001 05:24 a.m.):
25 amps too low?
Did you look on page 2 of that page?I really need a 24V transformer. I decided that it is not worth having to buy a high wattage PC PSU for the peltier. It is much cheaper to just build a 24V PSU and keep my 300W PC PSU for running the computer.
As such I need a 24V 12A transformer. But like I said, I already know were to get them (though they ain't cheap).
A 24V transformer will get you 33VDC after rectification and filtering. That will drop some under load but not back to 24VDC.
Hoot
dimmreaper
03-06-01, 06:39 PM
Hoot (Mar 06, 2001 06:29 p.m.):
A 24V transformer will get you 33VDC after rectification and filtering. That will drop some under load but not back to 24VDC.
HootWell I guess it's a good thing that I have not ordered any compnents yet. I decided to get a book first. The book is on the way, and I plan to buy exactly what I need after I know all the ins and outs of home brewed PSUs. So what do you recon I will be needing? An 18V transformer?
That's the ticket, or a 36V center tapped. That way you can run a full wave rectifier (not full wave bridge). It is a lower source impedance and given well to higher current. Either will fit the bill. Don't plan on regulating it as it is not necessary with a peltier. Figure on some stud mount rectifiers and a hefty filter capacitor.
Hoot
Richard
03-06-01, 06:57 PM
Damn man, sorry I keep coming up empty handed. It's amazing how hard it is to find prices on this stuff.
I am very interested in what you come up with though. Keep us posted on your progress.
Here you go guys and gals.
From Digikey http://www.digikey.com
1) HM539ND 18VCT 15A Transformer-----$56.77
1) MB2505 50V 25A Bridge Rectifier-------$ 2.36
1) P10017-ND 35V 50k Mfd Capacitor-----$14.82
That's all you need.
Hoot
dimmreaper
03-06-01, 08:10 PM
Hoot (Mar 06, 2001 07:53 p.m.):
Here you go guys and gals.
From Digikey http://www.digikey.com
1) HM539ND 18VCT 15A Transformer-----$56.77
1) MB2505 50V 25A Bridge Rectifier-------$ 2.36
1) P10017-ND 35V 50k Mfd Capacitor-----$14.82
That's all you need.
HootNow all I need is for you to show me how I'm supposed to wire it all together, and I can send the book back when it gets here :D
Richard
03-06-01, 08:27 PM
Heck I'll buy it from you when you're done with it.
[img="http://forums2.overclockers.ws/forums/Public/Images/Default/E28.gif"]
This is the best I could whip out on short notice.
Hoot
dimmreaper
03-06-01, 11:04 PM
Hoot (Mar 06, 2001 10:42 p.m.):
This is the best I could whip out on short notice.
HootWow thanks, if only I knew how to read it :( I got the switch and 5amp fuse and transformer down. But everything on the otherside of the diagram is confusing? (I'm not an engineer, wish I were) So could you please explain it better? Maybe something with color coding?
But if you would rather not, I can wait till my book comes. I should look for that book "Basic Electronics for Dummies". Is there one?
dimmreaper
03-06-01, 11:11 PM
wait, I think I get it now, thanks.
Yup, I get it now. Had to call my Dad on the phone to get him to explane how a rectifier works, but I get it.
Thanks Hoot. My Dad also sayed he has the book I ordered, so I'm sending that sucker back when it gets here.
Were would this world be without Dads.
schmidty
03-07-01, 08:28 AM
Hey hoot,
I never played with reticfiers when I did all my electronics messing, but how clean is the DC signal that you get from that powersupply? I remember much much larger power supply circuts - but then again it was 7+ years ago.
Just wondering
cheers!
With 50,000 mfd of filter capacitor, it will be clean enough for Peltier use up to the current limit of the transformer. The rectifier is not the deciding factor in the cleanliness of the DC. The amount of filtering capacitance is the deciding factor. If I was using that supply for a DC coupled Hi-fidelity stero amplifier, I might use more filtering capacitance, but then you run the risk of too much inrush current at power up. That is, without a soft start circuit.
Hoot
Jeff, I sent an email to your listed address that you may find interesting.
Hoot
The Faceless Rebel
03-07-01, 09:08 PM
I love the way this thread keeps on misspelling "electrical" in it's topic name.
come on guys :D
dimmreaper
03-07-01, 11:06 PM
The Faceless Rebel (Mar 07, 2001 09:08 p.m.):
I love the way this thread keeps on misspelling "electrical" in it's topic name.
come on guys :DYeah well I also misspelled "engineers" so sue me! :D
dimmreaper
03-07-01, 11:12 PM
Kurt Schmidt (Mar 07, 2001 08:28 a.m.):
Hey hoot,
I never played with rectifiers when I did all my electronics messing, but how clean is the DC signal that you get from that powersupply? I remember much much larger power supply circuts - but then again it was 7+ years ago.
Just wondering
cheers!Now that I have read a book on this PSU stuff. I can tell you that a rectifier does not filter the current. It isolates a polarity, which means it converts AC to pulsating DC. Then the capacitor "fills in" the low spots in the resulting current. You still don't end up with very clean current (it ripples about 2%), but a voltage regulator (or multiple regulators in a parallel circuit for high amperage) will make the single very very clean. But you will still should use a capacitor as a "pre-filter" to a voltage regulator.
Damn I learned a lot from that book Hoot :D I sound like a pro now :)
Jeff Evans (Mar 07, 2001 11:14 p.m.):
Damn I learned a lot from that book Hoot :D I sound like a pro now :)
Hang out with HAMs long enough and you become one!:)
73,
Colin
dimmreaper
03-08-01, 01:17 AM
Colin (Mar 08, 2001 12:59 a.m.):
Jeff Evans (Mar 07, 2001 11:14 p.m.):
Damn I learned a lot from that book Hoot :D I sound like a pro now :)
Hang out with HAMs long enough and you become one!:)
73,
ColinI don't know about that, but I had a crazy A$$ed idea about a half-hour ago. I'm thinking of taking on a bigger project latter. I'm thinking about building a 600W ATX PSU. I honestly have the needed skills now too.
You wouldn't happen to know were to get ATX PSU tech-specs would you?
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