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Old 12-11-2007, 12:04 AM #17
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Default Re: Open Can with TEC

Thanks for all the good advice so far everybody...I'm leaning toward setting up some kind of a finned heatsink with fan now...
Gazoo, I don't know ohms law. Please tell me this, since I have a 1 watt resistor, but a 1/2 watt pot, does this mean I'm ok up to 500mA on this circuit?
Jay


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Old 12-11-2007, 12:06 AM #18
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Default Re: Open Can with TEC

Quote:
Originally Posted by wooooooolazer
Be sure to not give the peltier more than 5v, any voltage above that and it will alll be changed to heat not to cooling ability, with mine it can run on 5v for about 3min before the heatsink will start to get warm.

...lazer... ;D ;D ;D
Using DDLs circuit, isn't it similar to the LD in that the peltier will only take the amount of voltage it needs? Even If I have a 6 volt battery pack or more?
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Old 12-11-2007, 03:26 AM #19
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Default Re: Open Can with TEC

Quote:
Originally Posted by jayrob
Thanks for all the good advice so far everybody...I'm leaning toward setting up some kind of a finned heatsink with fan now...
Gazoo, I don't know ohms law. Please tell me this, since I have a 1 watt resistor, but a 1/2 watt pot, does this mean I'm ok up to 500mA on this circuit?
Jay
Use this link for ohms law:

http://www.the12volt.com/ohm/ohmslaw.asp

Working with the 317 is easy.

The sense voltage between the output and adjust is always 1.25 volts...... providing the regulator is not dropping out.

To calculate the resistor needed, take 1.25 and divide it by the current.

To calculate the wattage of the resistor needed, tale 1.25 and multiply it times the current.
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Old 12-11-2007, 12:41 PM #20
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Default Re: Open Can with TEC

For driving the TEC, i'd look at PWM control really. It can be done with a linear regulator like the LM317, but it's not very efficient.

This works best when the supply voltage is equal to the TECs rated voltage, or at least below it. Most TECs are built to operate from 12v or 15v max though, so that should be fine.
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Old 12-11-2007, 04:25 PM #21
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Default Re: Open Can with TEC

Quote:
Use this link for ohms law:

http://www.the12volt.com/ohm/ohmslaw.asp

Working with the 317 is easy.

The sense voltage between the output and adjust is always 1.25 volts...... providing the regulator is not dropping out.

To calculate the resistor needed, take 1.25 and divide it by the current.

To calculate the wattage of the resistor needed, tale 1.25 and multiply it times the current.
Hey Gazoo, using my DMM, I tested the circuit at over 600mA. Could it be that at the higher currents, the 10 ohm 1/2 watt pot is barely even being used by the circuit? Because even if I eliminated the pot, I should get around 625mA with the 2 ohm 1 watt resistor...
Jay
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Old 12-11-2007, 07:08 PM #22
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Default Re: Open Can with TEC

To me it means your pot is turned to the least resistance. With the pot at its maximum resistance the current should be around 100ma's. What are you using for a test load?
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Old 12-11-2007, 09:23 PM #23
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Default Re: Open Can with TEC

Quote:
Originally Posted by Gazoo
To me it means your pot is turned to the least resistance. With the pot at its maximum resistance the current should be around 100ma's. What are you using for a test load?
Gazoo, when I use the DMM just to see how well a battery holds up and how many mA it puts out, the battery gets warm to the touch very fast. So, isn't the DMM taking a load? This is why I just used the meter to check the current from the circuit. I can just turn the pot and watch the meter reading go up as I turn...
Jay
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Old 12-13-2007, 09:49 PM #24
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Default Re: Open Can with TEC

You are shorting out the circuit by testing that way. You need to use a load.
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Old 12-14-2007, 01:58 AM #25
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Default Re: Open Can with TEC

Quote:
Originally Posted by Gazoo
You are shorting out the circuit by testing that way. You need to use a load.
Ok Gazoo, I did some testing and I am scratching my head a little...First I tested one driver on a 5 volt fan that I bought for cooling. (both tests were done with two 3 volt lithiums - 6 volt supply) I used the DMM in-line on the positive lead and using the fan, I could only get a max of 155mA?? Then, I tested the current on the peltier using the same method. I was able to turn the current up to 593mA using the peltier as the load. Well, I guess I'll be ok for the peltier using this circuit huh? And, if the peltier can be run up to 593mA with this circuit, then the LD would probably also be able to get up to the level I plan on, which is probably going to be around 400mA. Maybe the fan was too much of a load? I wish I knew about these things...
Jay
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Old 12-14-2007, 08:23 AM #26
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Default Re: Open Can with TEC

Quote:
Originally Posted by jayrob
[quote author=Gazoo link=1197272621/15#23 date=1197586148]You are shorting out the circuit by testing that way. You need to use a load.
Ok Gazoo, I did some testing and I am scratching my head a little...First I tested one driver on a 5 volt fan that I bought for cooling. (both tests were done with two 3 volt lithiums - 6 volt supply) I used the DMM in-line on the positive lead and using the fan, I could only get a max of 155mA?? Then, I tested the current on the peltier using the same method. I was able to turn the current up to 593mA using the peltier as the load. Well, I guess I'll be ok for the peltier using this circuit huh? And, if the peltier can be run up to 593mA with this circuit, then the LD would probably also be able to get up to the level I plan on, which is probably going to be around 400mA. Maybe the fan was too much of a load? I wish I knew about these things...
Jay
[/quote]

Jay, I don't think you understand how the 317 works as a constant current supply.
The LM317 IS a voltage regulator, that's all it can do, regulate voltage.
How then, you ask, do we make regulate current? The answer is that we understand Ohm's Law, and how the LM317 works.

The LM317 always tries to maintain exactly 1.25V between the Vout and Adj pins. So if the voltage between those pins is less than 1.25V, the 317 will raise the voltage at the Vout pin.
Conversely, if the voltage is higher than 1.25V, the 317 will lower the voltage at the Vout pin.

Moving to diodes:
A LASER diode (or 'LD' in LPF slang) like any other semiconductor device, has a voltage drop which is dependant on how much current is flowing through it, as well as on the junction temperature. The catch is that at current levels near (above and slightly below) the laseing threshold, a very small change in voltage will make for a very large change in the current which will flow. So, we need something which can very precisely control the voltage while monitoring the current in order to keep the current constant.

Now to the LM317 as a constant current supply:
In the circuit we've all come to know and love for driving these LDs there is one resistor. Yes, I said one, only one.
But what about the potentiometer some may ask? Any series resistors (defined as: 'all, and only the current passing through one also passes through the other') in a circuit act as one resistor. In the case of a 4 Ohm resistor in series with a 100 Ohm potentiometer we have an approximately 4 Ohm to 104 Ohm variable resistor. This resistor resides between the Vout pin and the load and is called the sense resistor. Tapped just past the sense resistor is the Adj pin of the LM317, if you will recall, it is looking at the voltage drop across the sense resistor and causing the LM317 to raise or lower the voltage at the Vout until the voltage drop across the sense resistor is exactly 1.25V.

The voltage at Vout, provided the regulator is not dropping out (dropping out or regulation for the LM317 is defined as: Ďthe voltage across the sense resistor is less than 1.25Ví), will be 1.25V (the sense voltage) plus whatever the voltage drop of the load.

Back to the LM317:
The LM317 needs about 2V - 3V just to run itís internals; we call this the regulator Ďdropoutí
Again, the LM317 being a semiconductor device, needs a different voltage depending on how much current is flowing through it. This is why when a voltmeter is connected as the load it will show almost the supply voltage. The voltmeter is a VERY high resistance, so no matter how high the LM317 tries to raise the voltage, so little current flows that the 2V Ė 3V average dropout is in this case only a few mV.

Finally on to a few examples:
If I supply 7.2V to the circuit when driving a 16X DVD burner diode at 250mA (the sense resistor is set to 5 Ohms), about 2V is lost because of the regulator dropout, there is a 1.25V drop across the sense resistor, and letís say the voltage drop of the LD at 250mA is 2.8V. So thatís 2+1.25+2.8=6.05V the other 1.15V has to go somewhere, and this is where the LM317 goes to work by wasting it as heat.

Letís try that example again but with only four alkaline AAA cells to power it. When these cells are brand new, they provide 1.57V each for 6.28V.

If I supply 6.28V to the circuit when driving a 16X DVD burner diode at 250mA (the sense resistor is set to 5 Ohms), about 2V is lost because of the regulator dropout, there is a 1.25V drop across the sense resistor, and letís say the voltage drop of the LD at 250mA is 2.8V. So thatís 2+1.25+2.8=6.05V this time thereís only .23V for the LM317 to get rid of. But wait, when I applied the load to the battery the voltage began to drop. It seems that under load they can only provide 1.48V per cell. Thatís only 5.92V, which means that the LM317, no matter how high it tried to raise the voltage, can only get the sense voltage up to 1.2V and at 1.2V the 5 Ohm sense resistor will pass only 240mA. Our regulator is now dropping out, and this was with fresh cells!

Iím sure you can easily see now why when driving a red LD with a forward voltage drop of nearly 3V you must supply more than 6V to the circuit, and were you driving a Blurry LD which has a forward voltage drop of almost 5V, you must supply the circuit with at least 8V.

Now what would happen if I tried to attach a load to the circuit where the sense resistor had a range of 2 Ohms to 100 Ohms, was set to 2 Ohms, the circuit was supplied with 6V and the load was trying to take 5V? Well, that load sure wouldnít see 5V, but it might see 3.5V, and with the LM317 doing all it could, it could probably only get the sense voltage up to about 0.31V. 0.31V divided by the 2 Ohm sense resistor (thereís Ohmís Law again) would only give about 155mA. (Does that sound familiar?)

Anyways, I hope none of this sounded condescending. Itís late and Iím tired, so off to bed with me with one last wish. That all who read this will find great use of it, and ease of understanding in it.
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Old 12-14-2007, 01:34 PM #27
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Default Re: Open Can with TEC

a_pyro_is, hey thanks for the crash course! I might have to even print out a hard copy of that... Hey, I'm planning on trying to set this thing up with all the bells and whistles but still make it portable. I'm planning on using a 7.4 volt 1200 mAh Lipo battery to power the two DDL drivers (one for the LD and one for the peltier) Also, the 5 volt fan via a 5 volt regulator. I have room for two of these batteries in parallel if necessary and maybe even a third. I'll show some pictures when I get ready for testing. What do you think about the 7.4 volt Lipo?
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* FS: 405-G-1 Glass Lens Mod for Blu-ray! 31% increase in power vs AixiZ acrylic!

* FS: New! 1000 Lumen XML-2 Maglite Modification With Voltage Monitor! - Parts or Complete Light! Must see!

* FS: Polished Stainless Steel Green Kit! Easy assembly in minutes!

* FS: Large Maglite Monster Kits! Side Button Forward Clicky! Custom Head Option! Gnarly...


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Old 12-14-2007, 01:48 PM #28
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Default Re: Open Can with TEC

CAN WE GET THAT ADDED TO THE THREADS OF INTEREST! (Not that anybody reads them, but I'd sleep better at night knowing it was there )

Seriously - I've explained this stuff I dunno how many times now, but I never took that much time and trouble to spell it all out. Good job a_pyro_is!
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Old 12-14-2007, 03:01 PM #29
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Default Re: Open Can with TEC

Nice summary!

Now, everyone who does not understand how the LM317 (and kin) work, should read this 20 times before asking questions!!!!

Quote:
Originally Posted by a_pyro_is
Jay, I don't think you understand how the 317 works as a constant current supply.
The LM317 IS a voltage regulator, that's all it can do, regulate voltage.
How then, you ask, do we make regulate current? The answer is that we understand Ohm's Law, and how the LM317 works.

The LM317 always tries to maintain exactly 1.25V between the Vout and Adj pins. So if the voltage between those pins is less than 1.25V, the 317 will raise the voltage at the Vout pin.
Conversely, if the voltage is higher than 1.25V, the 317 will lower the voltage at the Vout pin.

Moving to diodes:
A LASER diode (or 'LD' in LPF slang) like any other semiconductor device, has a voltage drop which is dependant on how much current is flowing through it, as well as on the junction temperature. The catch is that at current levels near (above and slightly below) the laseing threshold, a very small change in voltage will make for a very large change in the current which will flow. So, we need something which can very precisely control the voltage while monitoring the current in order to keep the current constant.

Now to the LM317 as a constant current supply:
In the circuit we've all come to know and love for driving these LDs there is one resistor. Yes, I said one, only one.
But what about the potentiometer some may ask? Any series resistors (defined as: 'all, and only the current passing through one also passes through the other') in a circuit act as one resistor. In the case of a 4 Ohm resistor in series with a 100 Ohm potentiometer we have an approximately 4 Ohm to 104 Ohm variable resistor. This resistor resides between the Vout pin and the load and is called the sense resistor. Tapped just past the sense resistor is the Adj pin of the LM317, if you will recall, it is looking at the voltage drop across the sense resistor and causing the LM317 to raise or lower the voltage at the Vout until the voltage drop across the sense resistor is exactly 1.25V.

The voltage at Vout, provided the regulator is not dropping out (dropping out or regulation for the LM317 is defined as: Ďthe voltage across the sense resistor is less than 1.25Ví), will be 1.25V (the sense voltage) plus whatever the voltage drop of the load.

Back to the LM317:
The LM317 needs about 2V - 3V just to run itís internals; we call this the regulator Ďdropoutí
Again, the LM317 being a semiconductor device, needs a different voltage depending on how much current is flowing through it. This is why when a voltmeter is connected as the load it will show almost the supply voltage. The voltmeter is a VERY high resistance, so no matter how high the LM317 tries to raise the voltage, so little current flows that the 2V Ė 3V average dropout is in this case only a few mV.

Finally on to a few examples:
If I supply 7.2V to the circuit when driving a 16X DVD burner diode at 250mA (the sense resistor is set to 5 Ohms), about 2V is lost because of the regulator dropout, there is a 1.25V drop across the sense resistor, and letís say the voltage drop of the LD at 250mA is 2.8V. So thatís 2+1.25+2.8=6.05V the other 1.15V has to go somewhere, and this is where the LM317 goes to work by wasting it as heat.

Letís try that example again but with only four alkaline AAA cells to power it. When these cells are brand new, they provide 1.57V each for 6.28V.

If I supply 6.28V to the circuit when driving a 16X DVD burner diode at 250mA (the sense resistor is set to 5 Ohms), about 2V is lost because of the regulator dropout, there is a 1.25V drop across the sense resistor, and letís say the voltage drop of the LD at 250mA is 2.8V. So thatís 2+1.25+2.8=6.05V this time thereís only .23V for the LM317 to get rid of. But wait, when I applied the load to the battery the voltage began to drop. It seems that under load they can only provide 1.48V per cell. Thatís only 5.92V, which means that the LM317, no matter how high it tried to raise the voltage, can only get the sense voltage up to 1.2V and at 1.2V the 5 Ohm sense resistor will pass only 240mA. Our regulator is now dropping out, and this was with fresh cells!

Iím sure you can easily see now why when driving a red LD with a forward voltage drop of nearly 3V you must supply more than 6V to the circuit, and were you driving a Blurry LD which has a forward voltage drop of almost 5V, you must supply the circuit with at least 8V.

Now what would happen if I tried to attach a load to the circuit where the sense resistor had a range of 2 Ohms to 100 Ohms, was set to 2 Ohms, the circuit was supplied with 6V and the load was trying to take 5V? Well, that load sure wouldnít see 5V, but it might see 3.5V, and with the LM317 doing all it could, it could probably only get the sense voltage up to about 0.31V. 0.31V divided by the 2 Ohm sense resistor (thereís Ohmís Law again) would only give about 155mA. (Does that sound familiar?)

Anyways, I hope none of this sounded condescending. Itís late and Iím tired, so off to bed with me with one last wish. That all who read this will find great use of it, and ease of understanding in it.
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Old 12-14-2007, 04:55 PM #30
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Default Re: Open Can with TEC

Thanks for the encouraging words! When I have some time I think Iíll clean it up a bit, add a little more, and give it its own thread.
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Old 12-14-2007, 11:21 PM #31
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Default Re: Open Can with TEC

Excellent idea. It is a great writeup and does need its own thread..
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Old 12-15-2007, 04:12 AM #32
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Default Re: Open Can with TEC

Some updated pictures of trying to follow my plan of powering everything in a portable case... Heatsink out the bottom and a 'blower type' fan which will fit inside the (removed) peltier heatsink which I want to use as a base.

I have room inside for this 7.4 volt 1200mAh Lipo battery and can fit 2 of them if needed and maybe just connect them up parallel.

Block and module will be isolated, as well as the small heatsinks for the LM317s.

Has anybody used the Lipo batteries for powering these drivers or similar? Can I just go by voltage? Because these lipo's have very high discharge capabilities. But the drivers and the fan (which will have a 5 volt regulator) will only take what they need correct? I just haven't tested this battery yet and don't want to fry anything...
Jay


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