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Topic: 0 Voltage from power supply when connected to peltier (Read 5584 times) previous topic - next topic

shiznatix


But is the fan a 19v fan? Most of them are rated for 12v, so that may overheat and burn out too if left connected to 19v for a longer time. For powering a peltier your best bet would be a computer psu. I use a small desktop computer psu for mine, rated at 150w, and i still get enough extra power to use some fans, an arduino or other low power consumption electronics on the same psu.


I want to run more volts through the fan to increase the speed a bit but this is another thing. First I want to just make sure that I understand everything correctly  :).

jackrae

If the fan uses a brushless motor (and many of them do) then extra volts will not materially increase speed.  The 3phase module that converts the DC to an AC generally operates at fixed frequency ior at a frequency determined by an external temperature sensor.

magnetman

You would be better off by using a more powerful 12v fan and variating speed by using a transistor & pwm.

shiznatix

I thank you all for the advice with the fans and everything but I would like to know if my understanding of basic electricity is correct in the previous reply I had here:
http://forum.arduino.cc/index.php?topic=266999.msg1883753#msg1883753

Peter_I

#19
Sep 16, 2014, 03:39 pm Last Edit: Sep 16, 2014, 09:54 pm by Peter_I Reason: 1

.....
Is this correct or am I still lost in the woods over here?


It is absolutely getting better.
Ohm's and Kirchoff's  laws are your friends (but a pair of merciless friends!)

One for playing with the basics:
http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc
"Nothing is foolproof to a sufficiently talented fool"

polymorph

Yes.

Although for a device like a fan, we don't really assign a resistance value to them, because they are nonlinear. That means that the current draw is not based linearly on voltage. Loading the fan increases current, startup current is more, and as someone else pointed out, the circuits in a brushless computer fan may limit the power drawn even when more voltage is applied.

Although my experience is that I've applied up to 18 or 19V to 12V computer fans and they've run faster. However, you are taking the risk of overheating the internals of the fan.


Ok, I think I am getting it. The PSU values of 19V and 5.27A are just that it will push 19V out and the amp is a rating, not a constant value. Meaning that it can push out max 5.27A or less, just not more. No matter what the amp draw is (as long as it is below its rating), the voltage will always be 19.

If that is correct, then the resistance will vary across each device connected to it. So I have a fan that is taking 19V and drawing 0.25A meaning the resistace of the fan is 76 Ohms. The peltier would have to have a resistor set up infront of it to limit the voltage but at the same time it would limit futher the current available and pull even harder for that current, but would still have the same affect on the PSU.

The device itself will pull the amps out instead of the PSU pushing them in. If the device exceeds the PSU limits, then things happen that can be bad.

Is this correct or am I still lost in the woods over here?


Generally, when you overload a power supply, the voltage either drops as the load resistance goes down, or suddenly cuts off. It depends on how the power supply was designed.

Rather than use a resistor to limit current to the peltier, which will cause the generation of a lot of heat, I'd get a desktop computer power supply and modify it to work without a computer. The 12V outputs will generally put out a lot more than 10A.

Basically, you need a minimum load on the 5V line, and a way to turn on the power supply. This one does it as an external adapter:
http://makezine.com/projects/computer-power-supply-to-bench-power-supply-adapter/

I repaired a peltier junction cooler, replacing the rusted out fan with two 12V computer fans, and found a 12V 12A open frame power supply surplus, and put it into a case with a fan cooling the power supply so I could run it on AC.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

MarkT


If the fan uses a brushless motor (and many of them do) then extra volts will not materially increase speed.  The 3phase module that converts the DC to an AC generally operates at fixed frequency ior at a frequency determined by an external temperature sensor.


Brushless fans run at a speed proportional to the supply.  They are 2-phase, not 3-phase,
normally, and have hall sensors so the frequency is locked to the fan rotation.  The back-EMF
of the windings roughly balances the supply voltage at equilibrium so that the speed is
nearly linearly related to the supply voltage.  (Most 12V fans work from below 6V up to
15+V if you don't mind taking the risk of damaging them).
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

shiznatix

Thanks everyone. I have enough information now to continue learning more :) but at least I am moving in the correct direction.

With all the remarks about using a computer PSU, I have one already set to go that I have been using to charge LiPo batteries so that isn't really a problem. The problem is that the thing is a computer PSU so it is big and heavy and has a tangled mess of additional power lines that I just don't need.

I would like this peltier thing to be somewhat-portable so using a computer PSU certainly isn't optimum.

Peter_I

That is a classical problem.

You have something that needs a lot of power, and you want it to be portable.

Peltier based coolers can drain a car's battery if you are not careful.
"Nothing is foolproof to a sufficiently talented fool"

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