A friend has a neat project (DIY PCR Machine) that uses relays that are really loud (there's a lot of switching that goes on). I am wondering if he could use transistors instead, and what their limitations are.

Currently he is using an ATX power supply for its 5v and 12v power. And uses peltiers that can go up to 9 amps, the more power the better in this case because it means faster heating and cooling times in his application. I would like to know if transistors are an option, or if he has to stick with relays, because of the amount of he's using.

Here are some photos of what he's got going on if you want to check it out.

Thanks for your help.

 

If we knew what a PCR machine is we might be able to give some sensible advice. A quick search for PCR brought up the following but how any item relates to relays is beyond me.

pedal-crank rates
pellicle cleaning ratio
Penile circumference responses
per cent regurgitation
peripheral chemoreceptor response
Philips Computed Radiography
Philips Computed Radiology
photosynthetic carbon reduction
photosynthetic carbon-reduction
Pickled Cabbage Railway

If you must use acronyms in your posts please give definitions so that others have some idea of what you are taking about.

 

Sorry for the acronym. PCR in this case stands for a "polymerase chain reaction". It is used by molecular scientists to amplify a piece of DNA across several orders of magnitude. These devices are very expensive to purchase. The idea behind this project is to make it cheap enough to have in high schools.

There is a picture of the machine (and the relays) are in the link above.

 

There is a picture of the machine (and the relays) are in the link above.

Switching 10A at 12V is not particularly difficult with MOSFET. However, a simple circuit diagram of how these peltier devices are connected in the existing project is needed.

How many independent current paths? Where does the control signal comes from and its level?

I would think the current need to be ON/OFF/REVERSE with current up to 9A for each path.

 

Penile circumference responses

More seriously, mostfet H bridges can easily commute several dozen amps for Peltier modules. You have half H bridges in SO-8 (by Siliconix, Fairchild...) that would fit the job.

But a too silent machine is so boring !

 

If you feel more comfortable with relays than transistors, look into the solid state switching variety. They are very quite, if you listen real hard, you can almost imagine some sound....