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a question for our elecrical engeneers

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dimmreaper

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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?
 

Shep

Senior Member
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Location
Marshall, MO
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
 
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dimmreaper

dimmreaper

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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 [email protected] 11.3amps, or would it be ok to use a transformer rated for [email protected] (very common open frame transformer) and use the PC's PSU to handle the rest of the amperage?
 

Shep

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Marshall, MO
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.
 

Shep

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Marshall, MO
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
 
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dimmreaper

dimmreaper

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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 though
It won't work because AT PSUs have a voltage regulator :(
 

Shep

Senior Member
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Location
Marshall, MO
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 ~

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Seattle Wa.
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

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Kent, UK
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 ~

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Location
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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
 

Tim-

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Location
North Carolina
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.
 
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dimmreaper

dimmreaper

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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).
 

Tim-

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Location
North Carolina
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
 
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dimmreaper

dimmreaper

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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.
 
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dimmreaper

dimmreaper

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Shep (Mar 03, 2001 03:48 p.m.):
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

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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.
 
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dimmreaper

dimmreaper

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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

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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.