Peltier power Amps?

[Raul]

A PC ATx switching power supply will give me the 12 volts DC I need to drive a Peltier unit but what about the Amps.

Does it matter of the Amps available from the PS exceed the Peltier's needs by a substantial amount?

 

[Sceadwian]

No of course not, this is a commonly miss-perceived rating on a power supply, it would only be bad if it couldn't supply enough amperage, ATX power supplies (as most power supplies in general) are constant voltage.

 

[cr0sh]

No; the thing you have to remember is that devices (in this case, the peltier) -pull- current from a device (in this case, the ATX power supply) that -source- current (that is, it supplies current to a device); power supplies don't "push" current, so as long as the power supply is capable of supplying the current for the voltage rail you need to connect the peltier to (in this case, the 12V rail?), above the amperage needed for the peltier (you never want to run exactly "at" the current needed, because of possibly fluctuations), it should work fine. Note, though, that if a device says it can potentially pull more than what the power supply can supply, then you stand a chance of tripping the power supply's protection system (fuse or breaker, or auto-cutoff in a bench supply) if you exceed its current rating/setting. In the case of a supply that is not well designed, or not properly rated or whatnot (or has an improper fuse put in place), you can literally burn out the supply (up to and including starting a fire!). So read the spec sheet and everything for the devices you plan to hook up to the supply, and read the supply's spec sheet thoroughly too, to make sure you can hook up such a device to a single rail (ie - is the wire or connectors spec'ed properly for the current needed?). There's more to it than just slapping it together; make sure you read and understand everything. Once you have something together, carefully test and monitor it as part of your development effort, to make sure nothing that shouldn't be is overheating and presenting a fire hazard...

 

[chemelec]

A PC ATx switching power supply will give me the 12 volts DC I need to drive a Peltier unit but what about the Amps.

Does it matter of the Amps available from the PS exceed the Peltier's needs by a substantial amount?

What Really Matters is If your Peltier tries to Draws more Current than you power supply has Available.
Peltiers draw Considerable current and could easily Damage your supply.

 

[Raul]

Thank you so much for the information.
Mili Grazi.

 

[Sceadwian]

An ATX supply? Not likely chemelec. He stated plainly that the supply was capable of much more current than the peltier unit, aside from that ATX supplies have something like 4 failsafes. They're over current protected, short circuit protected, thermally protected, and DI/DT protected, they're nearly impossible to hurt even if you do something stupid. They can be damaged by large inductive loads and that's about it.

 

[Raul]

An ATX supply? Not likely chemelec. He stated plainly that the supply was capable of much more current than the peltier unit, aside from that ATX supplies have something like 4 failsafes. They're over current protected, short circuit protected, thermally protected, and DI/DT protected, they're nearly impossible to hurt even if you do something stupid. They can be damaged by large inductive loads and that's about it.

Is there a color code that lets me know which wires are the 12 VDC max Amp ones?
I know that the leads will be different.
The ATX I have in my hand has the following listing for Max output:
+5 VDC at 5 amps 200 watts
+3.3 VDC at 28 amps 200 watts
+12 VDC at 45 amps 540 Watts

Then there are some other call out I don't understand:
-12 VDC at 0.6Amps 7.2 Watts
+5VSB at 2.5 amps 12.5 Watts

 

[cr0sh]

The 12VDC wires are typically the yellow wires leading to the peripheral device (hard drives, floppy drives, CD-ROM drives) power connectors; there may be a couple on the ATX motherboard connector as well (but not necessarily colored yellow!!!). The 5V wires are typically the red wires to the peripheral device power connectors (and same with the ATX mobo connector - once again, maybe not colored same!), black wires are typically ground. The 3.3 VDC wires are typically on the ATX connector for the CPU and other motherboard devices. Best to get pinout for -all- the connectors (they are standard, plenty of websites out there show them), and figure out which is which with that, and a multimeter.

The 45 amps for the 12VDC is spread over all of those yellow wires (plus any on the ATX motherboard connector) - so you need to keep that in mind; one peripheral connector may only be able to supply so many amps of that 45 amp total. Sometimes you can parallel the outputs together to gain more current, other times you can't (depending on the design of the PSU). Since you don't have and can't get the needed information to know this (forget even trying), it will be a hit-n-miss operation; I've never seen it be an issue though on PC power supplies I have played with, though. If you can trace the wires back to a common point, you could remove the wires at that point, and solder one hefty gauge wire there instead just for powering the peltier...

Just realize that voids the UL listing (and a host of other things), so if it burns down your house, don't expect your insurance to pay out (or re-insure you!)...

 

[zipdogso]

There are quite a few things you need to consider here.

While PC PSU's can be used to power Peltiers they are not the best thing by any means.

Firstly I trust you know the modders trick to get the PSU working without a motherboard. You don't do this it wont work at all. Bear in mind if you power up the PSU with no load you will probably kill it.

2nd assuming it is a fairly modern PSU there will be several special coloured sense wires that will need to be grounded for it to work correctly.

3rd When installed correctly in a PC the PSU will use the 5v line for regulation so often to get it to work reliably you should have a load on the 5v (red) line you can provide this with a 10w resister.

finally both the molex connectors and the wires on a PC PSU are only rated at 8 amps, 7amps for safety. If your Peltier is say.... 15 amps you divide the current you want by the wire limit - 7amps so thus:- 15/7 =2.1 round it up to 3 for safety.
You can then use 3 yellow wires soldered together for the Peltier +ve and 3 Black wires soldered together for the ground. Make sure all the wires seperately trace back to the body of the PSU and of course cut off the molex.
Obviously you can see you you may be quickly limited to the Peltiers you can use due to the number of wires.


REF

Yellow.. plus.12v
Red.. plus.5v
Orange.. plus.3.3v
Purple.. plus.5V....standby
Blue.. minus.12v
White.. minus.5v

Sense wires
green - DC on
Grey
Brown
and there may be a very slim orange one in the same pin as another wire.

You need to leave the special sense wires connected but all the other wires your not using can be safetly cut off so long as you insulate the ends.


There are loads of pages about using PC PSU's. I actually turned one into a grossly overdone bench supply for my first attempts with Peltiers. It was only because I had the bits laying around I did it, otherwise it would of been far to expensive for such a simple project.
All I have done is bundled and connected the different wires to posts....simples..as they say.

**broken link removed**

**broken link removed**

Note:- I now only use it for low power undervolting experiments with peltiers. I was a bit concerned about the current limits of the posts when using big units.

On final point don't power up the Peltier without some form of cooling on the hotside as you may well burn it out.

 

[tcmtech]

Peltier coolers are not that fussy about their power source.
A second hand 12 volt battery charger with an amp rating above what the Peltier's require plus a good filter capacitor are all they need to work.

As long as you stay under their peak voltage rating at load and don't overheat the hot side of them they are rather robust and forgiving little devices!

 

[cr0sh]

There are loads of pages about using PC PSU's. I actually turned one into a grossly overdone bench supply for my first attempts with Peltiers. It was only because I had the bits laying around I did it, otherwise it would of been far to expensive for such a simple project.
All I have done is bundled and connected the different wires to posts....simples..as they say.

**broken link removed**

**broken link removed**

Note:- I now only use it for low power undervolting experiments with peltiers. I was a bit concerned about the current limits of the posts when using big units.

That's a pretty nice unit you've set up - got any more info on it, pictures of the inside?

I wish I knew of an easy way to make a PC supply adjustable, both for current and voltage - being able to have a preset and a cutoff would be really useful; right now I have a couple low-amperage ECI bench supplies; they were cheap, but they leave a bit to be desired in the amperage dept (the adjustable stage can go from 0-25VDC @ 0-1.25A)...

 

[Sceadwian]

Sometimes you can parallel the outputs together to gain more current, other times you can't (depending on the design of the PSU). Since you don't have and can't get the needed information to know this (forget even trying), it will be a hit-n-miss operation;

I have never seen an ATX power supply that has more than one 12V rail, and even if it did you'd still be able to put them in parallel safely. Simply popping the lid off the power supply and looking inside will tell you instantly. Every ATX I've seen or used has common connections for all the same voltage rails. I have heard of higher end power supplies that have multiple 12 volt rails but again there is nothing wrong with paralleling them.

None of this will void the UL listing if you don't modify the supply and simply plug it into molex based connectors, and route the power however you want from there.

While PC PSU's can be used to power Peltiers they are not the best thing by any means.

Firstly I trust you know the modders trick to get the PSU working without a motherboard. You don't do this it wont work at all. Bear in mind if you power up the PSU with no load you will probably kill it.

2nd assuming it is a fairly modern PSU there will be several special coloured sense wires that will need to be grounded for it to work correctly.

3rd When installed correctly in a PC the PSU will use the 5v line for regulation so often to get it to work reliably you should have a load on the 5v (red) line you can provide this with a 10w resister.

finally both the molex connectors and the wires on a PC PSU are only rated at 8 amps, 7amps for safety. If your Peltier is say.... 15 amps you divide the current you want by the wire limit - 7amps so thus:- 15/7 =2.1 round it up to 3 for safety.
You can then use 3 yellow wires soldered together for the Peltier +ve and 3 Black wires soldered together for the ground. Make sure all the wires seperately trace back to the body of the PSU and of course cut off the molex.
Obviously you can see you you may be quickly limited to the Peltiers you can use due to the number of wires.

I'm not sure why you say this isn't the best way by any means, the bulk majority of peltier coolers are meant to be run off 12 volt supplies, for either automotive (portable coolers) or CPU heat pumps.

The warning that powering up the PSU without a load will kill it is absolutely dead false, I've used two and they supply regulated voltage with no load at all, they generally have a small internal load to prevent this from happening, only the oldest or dirt cheapest supplies from the bowels of China will have problems with no load.

I've not seen any modern ATX supplies that have sense wires, from the ATX specifications they're optional, the last three or four I've seen didn't even have sense wires except for the 3.3V line on one of them, and you obviously wouldn't short this to ground you would attach it to the 3.3V line at the load so that it can properly regulate, it's there to compensate for line losses. Modern ATX specifications are moving away from this and relying on supplying massive 12V power lines and the motherboards themselves have additional switching regulators to get the highly precise CPU and memory voltages required, they don't just blindly rely on the power supply for proper regulation anymore. Grounding a sense line would very likely fry any device hooked up to line that required it, it's there for voltage feedback, if you ground it the supply is going to put out the maximum voltage it's capable of on that line thinking the voltage is low.

Cutting off the molex connectors and soldering wires from the supply is not required, simply buy female molex connectors, you will need multiples to allow for higher amperage's as stated, but this isn't that big of a deal, if you start needing enough amperage to justify 2-3 connections it's probably best to actually modify the power supply at that point with heavier gauge wire directly from the power supplies output connection.

 

[zipdogso]

That's a pretty nice unit you've set up - got any more info on it, pictures of the inside?

I wish I knew of an easy way to make a PC supply adjustable, both for current and voltage - being able to have a preset and a cutoff would be really useful; right now I have a couple low-amperage ECI bench supplies; they were cheap, but they leave a bit to be desired in the amperage dept (the adjustable stage can go from 0-25VDC @ 0-1.25A)...

I might have some photos somewhere....it was years ago.

Generally I dont think its worth the hassle to make one adjustable, just buy a decent PSU (not PC one.)
They will have a variable voltage but few if any wil have variable current it just isn't neccessary. So long as the PSU can deliver more than the peltier/s will draw that's it. If you had variable current and accidently set it low you'd blow the fuse or worse.

I'm not sure why you say this isn't the best way by any means, the bulk majority of peltier coolers are meant to be run off 12 volt supplies, for either automotive (portable coolers) or CPU heat pumps.

Peltiers aren't meant to be run at 12v at all....that's just what every Tom, Dick, Harry and his dog does....they don't know any better. Why would manufacturers bother producing performance charts at all input powers if this was the case ????? They are actually used in Industry far more than in automotive or computer scenarios.

If you are happy running Peltiers at the bog standard accepted input of 75% power (12v for a 127 couple Peltier.) then everythings good and dandy but if you really want to run peltiers and get better performance and efficiency and have a variable power supply is really the best way to go. You dont need to use 12v supplies strictly for 127 couple you could use them with 263 couple Peltiers (31.5v Peltiers.) and while I don't actually like meanwells you could use a 12v meanwell which has a +/- 15% output giving you the option to fine tune the performance of the Peltier. For most of my fiddling with Peltiers these days I use a 25A max supply with a 4 - 16v variable output. (not Meanwell.)

 

[Sceadwian]

What kind of efficiency improvement total do you get after tweaking? Not power handling, straight up efficiency, and how does that gain compare with the straight power handling of 12V on the same module? I'd love to see some graphs. The majority of peltier modules currently available on the market are already for most purposes tuned for 12 volt operation, under common conditions. If you want results, 12V is good enough, if you want to get every last eck of power transference before the ohmic heating overtakes it you analyze it. Show me some graphs.

 

[zipdogso]

No your wrong....TECs are not tuned for any particular voltage. You can run any TEC at any voltage from about 5% up to full power they AREN'T tuned for anything.....that's totally cow muck.

I don't need to show you any graphs you can get them yourself from any TEC manufacturer they are called performance charts...you know....performance. Admittedly some are better than others and some don't show COP charts. Run properly you can get a COP of 2 or 3 easily.... run at the standard 75% power it is about 0.8. Try running them at full power like some suggest and your down to 0.6. When Undervolted (properly.) half a volt either way can make a big difference.

 

[zipdogso]

Grounding a sense line would very likely fry any device hooked up to line that required it, it's there for voltage feedback, if you ground it the supply is going to put out the maximum voltage it's capable of on that line thinking the voltage is low.

The sense wires are for the motherboard after all that's what the PSUs are designed for.
The extra small orange one should be left attached to the wire it is connected with and neither wire should be cut off or otherwise removed so it is grounded. The Grey if not used (in my case for an LED indication.) should also be grounded. The brown should be grounded too. Occasionally there is a pink one too.
They are all sense wires for a motherboard which you aren't using !!!

 

[zipdogso]

Sorry it seems COP charts are not as common place as they used to be.

Here is one:- Module Graph Detail - - 1

The COP chart actually changes very little from unit to unit so the shape is relatively generic just think of the current across the bottom as % of Imax rather than specific values.

 

[Raul]

WOW~!! Thanks for all the Information~!

I was unaware that there were pinout charts on line. But then I didn't know the word "pinout" When I read it I thought it was a typo and thought it should have been "printout." Imagine my surprise after some efforts trying different words as search terms I stumbles across a "pinout" chart.
Off the first one I found was in English from a Russian site
ATX power supply connector pinout and wiring @ pinouts.ru
I think "ru" is Russia

I found Lazar Rosenblat's page here:
ATX PC Power Supply Pinout and Connectors
Which it pretty comprehensive. Though he's got it so you can't cut and paste to keep you gotta print it out.



I was going to follow the step by step instructions found here:
PCPowerSupply - RepRapWiki
There's a PDF of the same thing some where.

It talks about "sense wires." Are those the ones you mentioned zipdogso?

2nd assuming it is a fairly modern PSU there will be several special coloured sense wires that will need to be grounded for it to work correctly.

At any rate it all looks fairly straight forward.
And I don't even have to know what mossfets& zeniers do.

 

[Dr_Doggy]

don't forget also cpu power consumption goes up during overclocking too, some peliters go up to 6amps and over, 72 watts, so thats 18% of a 400watt power supply,

what i'd do in this situation, is:

1)Hook da shat up,
2)get your supply rating,
3)put an ammeter on your power cord,
4)FIrE IT UP!!

 

[cr0sh]

I might have some photos somewhere....it was years ago.

Generally I dont think its worth the hassle to make one adjustable, just buy a decent PSU (not PC one.)

Which is why I bought those ECI supplies; they were priced right, and I managed to get the service manual for them (due to their age and condition, they needed adjustment). A good dual-output adjustable bench supply isn't cheap, though - especially once you get past about 15V and 2A output (I would love to have a dual adjustable 0-100VDC, 0-15A bench power supply, but I can't afford it - not by a long shot).

They will have a variable voltage but few if any wil have variable current it just isn't neccessary. So long as the PSU can deliver more than the peltier/s will draw that's it. If you had variable current and accidently set it low you'd blow the fuse or worse.

Not on a bench supply; on my ECI supply, I can set it to say, 12VDC @ 1A max, and if the device exceeds that, it -instantly- shuts off the power, and an overload LED blinks. No fuse blown, nothing. You have to cycle the power on the supply to reset it. This is what is great about a supply that you can adjust both voltage and current on; they just aren't cheap when you buy them new.

But this is all kinda off-topic of the discussion at hand...