TEC cooled Diode testing station, suggestions?

Bionic-Badger said:

Yeah, with the Arduino, you an attach "shields" to them, for example this SD-card shield. I haven't used it myself, but there are links to a FAT file-system memory writing library for it, necessary for writing computer-readable files.

Edit: According to the comments, the board I linked to above is kind of iffy, so some other choices may be better.

Edit 2: They've updated the bad board with a new revision that supposedly fixes the voltage level problems. Not sure about card compatibility, etc.

Click to expand...

Thanks man

SO the peltier/heatsink/fan all fit together perfectly.

I ended up covering the hot plate of the peltier with arctic silver, then I fastened it to the heatsink using hotglue on the corners (not on the plate).

The problem I have, however, is powering the peltier. I am not getting the cooling I want with conventional powering methods, and I need to run it safely at like 4-5A and 10-12V. What should I use to regulate it??!?

Going to go cut out the project box now.

You'll want to PWM regulate a power transistor providing a current sink for your load (the peltier). Here's a page describing a pretty decent design.

Looks like a good circuit indeed. You can use a bipolar transistor instead if the mosfet if you want, but you'd have to reduce R1 depeding on its amplification factor.

Check out this beer chiller project someone worked on. Same kind of thing, only for cooling beer.

So with the arduino, can it actually power the peltier and send the desired current to the peltier based on input temp, or would I have to power it separately, then have the arduino control the resistance of the adj resistor connected to the regulator (i.e.) and have it adjust that?

And thanks for the links badger, I'm checking em out!


Also, I cut out the hole for the [Current] (I) LCD which came in the mail a couple days ago, and I'm thinking the large radioshack project boxes aren't gonna cut it. I can fit 2 LCD's on top of each other, but the third would be too close to the edge. Not to mention all the closeness would cause a shitton of clutter underneath...

I donno, I will see...

If you link in the program one of the analog inputs to one of the PWM outputs, then you can build a thermostat that detect the temp of the plate, and increase or decrease proportionally the duty cycle of the PWM for keep it stable ..... also, if you need to drive power transistor hooked to a different power supplies (for the LD and the peltier), i suggest you to use optocouplers, instead simple resistors, so you can keep the power sources totally separated, if you need this (like, having a 9V for the arduino, and separate high current 12V PSUs for the peltier and LD, without that the switching causes disturbs on the other power sources and influence the reading/controls section)

Transistors are really the best way to regulate the current going into those peltiers. The Arduino can't source much current or voltage; however, it can control the gate of a MOSFET or base of a BJT, which also isolates your microcontroller and other delicate electronics from the high-current electronics. The resistors (trim pots) used in laser driver circuits are really just there so that humans can adjust them; microcontrollers need an electrical input to affect. Furthermore, many microcontrollers do no have digital-to-analog converters (DACs) for outputs; this is why we use PWMs: you can bit-bang (change the digital state of the output) rapidly through a circuit like I linked above to change the voltages or currents. For your peltiers you'll want to use higher-frequency PWM to ensure that the peltier doesn't experience great changes in voltage which is bad for them (higher frequencies will look more like a continuous signal).

When you buy the parts, you'll probably want to get them through Digikey or Mouser so you can get the right transistors and other parts all from one source. They have a much nicer selection of enclosures, LCDs, and whatnot than your local Radio Shack (which really scrapes the bottom to be honest); they have better prices too. Sparkfun is good for specialized components or breakout boards, but for stuff like transistors, enclosures, and basic parts it is usually better to go through the big dedicated part stores like Digikey or Mouser.

Yea I use mouser frequently for parts, but I didn't wanna wait 2 weeks to get an enclosure and some shrink tubing when I could just get it next door .

But Yea, I guess I'll have to do some more shopping online.

amkdeath said:

The problem I have, however, is powering the peltier. I am not getting the cooling I want with conventional powering methods, and I need to run it safely at like 4-5A and 10-12V. What should I use to regulate it??!?

Click to expand...

I'd say use a computer psu and a 5 ohm 100w rheostat. However, a typical peltier needs more like 10-12 amps, not 4-5.

He won't be using more than 4-5 amps if he doesn't want condensation to be building up on his lens...

Meatball said:

He won't be using more than 4-5 amps if he doesn't want condensation to be building up on his lens...

Click to expand...

That and the ebay page says the I(max) of the peltier is 6A, but they could be wrong.

They were wrong about it's internal resistance, at room temperature it has roughly 5 ohms of internal resistance, not 1.3

So I did some more work on it last night, It's not gonna be preety, just a prototype to see if the idea works. Pics soon.

So I worked on a prototype PCB for the LD driver/Vregs/switches/ammeter/Vmeter:



The only problem is I realized I made it in one of those programs that requires you to order the PCB's from them, and I'm not paying 149.99 per PCB for 2 PCB's. It does get cheaper as quantity goes up, but the total stays around $300.
Time to do it all over again in another program lol


And also, I am still having doubts about temp-regulating the peltier, the arduino idea sounds plausible but I don't think I have the time or the readiness to learn to program the microcontroller. I could just keep pumping power into the peltier, but I have yet to find a 5A regulator lol. Another problem with no arduino would be the fact that I couldn't utilize the arduino's logging capabilities for graphs afterwards, which is something that I need...

Regards,

amk

Mark2:

Bionic-Badger said:

You'll want to PWM regulate a power transistor providing a current sink for your load (the peltier). Here's a page describing a pretty decent design.

Click to expand...

hmm, ok, sounds cool...

the part that says:

As the value of R2 is based on the transition emitter-base voltage of Q2, calculating it is easy: all you need is Ohm's Law and an idea what voltage to use. Most conventional silicon general-purpose NPN transistors switch fully at around 0.7VDC and start to transition from off to on at 0.56-0.58VDC. Assuming a transition voltage of 0.58VDC and a target load current of 750mA, the math is as follows:

R = V / I

R = 0.58VDC / 0.750A

R = 0.773 Ohms

Click to expand...

so what if I'm trying to run 5Amps? The "most.... NPN transistors switch fully at around 0.7VDC and .... 0.56-0.58VDC" applies to all transistors? I am assuming I will have to use a different transistor to run 5 Amps of current.

And also, if 0.58 holds true for the transistor I am using, that means the resistor (R2) will be dissipating ~3W of heat! I'ma need a giant resistor... lol

Dissipation through the MOSFET under operating conditions is calculated the same way, only the voltage used in the calculation should be the supply voltage so that the heatsink selection will account for the worst-case scenario of a dead-shorted load at the target current. In the above example, assuming a 12VDC supply and 750mA current limit, the math works out as follows:

P = V * I

P = 12VDC * 0.750A

P = 9 watts

Click to expand...

So if I want the peltier to be running around 12-13 VDC and 5A, I will need a good 16v of input.

In this case, worst case heat dissipation is 80 watts!! O_O That's a lot! Are there and mosfets that will run those numbers and not fry up?

The IRF520 listed in the schematic is rated to handle 9.2A @ 100VDC, and can dissipate 60 watts, so this part will work perfectly well in this configuration with a modest heatsink.

Click to expand...

Ok, ok, sounds promising. So I think I can find a variation (maybe in the same line?) that can do my numbers. I think I should just add this to the Board that I'm ordering.

The extra parts for PWM support include Q3, R3, and R4 - these are blue shaded in the schematic. Since Q3 is a PNP transistor and R4 biases its base to ground, Q3 starts up turned on and pulls Q1's gate to ground regardless of what Q2 is doing, and this forces both Q1 and Q2 to turn off. R3 limits current draw to the PWM signal source. Provide a positive voltage greater than ~0.7VDC to Q3 through R3, and Q3 turns off, which allows the rest of the regulator to function as described above. In this manner a PWM signal can be used to vary the brightness of a load of power LEDs, or a simple on-off switch effect can be implemented by merely pulling Q3's base to positive supply with a few milliamperes of current. In this manner it would be possible to use the circuit as a self-current-limiting switch that only needs a tiny little low-current button as its actuator even though the load could be an amp or more.

Click to expand...

So BB you said we can use the arduino as the so called actuator? If so this circuit sounds amazing!

Regards,

amk

BB would This work?