Peltier and voltages

right, go a simple couple of questions.

For my A level physics coursework, i am using peltier elements. This could be a 80W or 172W.

My first q is, if i took to seperate 12v lines coming out of the psu, and then put them together, would they make 12v or 24v. i think it would be 12v.

In conjunction with the first question, if they are taken of 2 seperate rails on a 12v, would they mae 24v. i think no again.

Then their is also the 12+5v = 17v?

And finally would two psus runnign be better to get 24v. o two completly seperate psus connected together where the peltier connects. Hope you can help me, cause i also wana use the peltier at home for a while after, and looking at a 172w peltier @ 24.6v

- Paul

I think the forums have a no-homework helping policy, so I can't really give you the answer, but...

Play with a couple of batteries. See if you can place them in such a way that having two doubles voltage. Also try to get them to output the same voltage. That should give you your answer right there for separate power sources.

You can also play with a power supply to see if you can get your 17V. After playing with the batteries, using what you have found with them, try the same on the PSU. Again, you should find the answer pretty quickly.

Hope I've been at least some help

yeah, i thought about this, and it goes down to needing two seperate psu's. This is because on my psu for example, the 5v is combined with the 12v. Also all psus are really just one rail split and then come back again. Thanks for your help. i had a quick search, and couldn;t get anything concrete. Then i checked my physics book about it, which leads to thi.

- Paul

you cant get higher than 12v by joining other voltages on a psu. if you connect gnd - 12 - gnd - 5v, you realise that all the voltages share the same earth! so you have just shorted the 12v lin to earth! if you connect them the other way you short 5v to earth. either way short circuit protection should kick in and the psu wont power up.

if you use two seperate psu's you have the same problem. both psu's are using the same earth! all earth's in every house on this planet is the same. if you have one psu on earth and one on say, the moon, then you can add the two voltages together.

the only way to connect the voltages is if at least one is isolated. if one of the 12v lines is isolated using a transformer than you can connect them together, but whats the point in that? the transformer would need to be able to supply 7a (172w/12v) and have a 1:1 ratio. dunno where you're gonna find that?!? would be much easier to either get a 24v 7a psu or make a 24v 7a psu.