Cold DSLR Fan Speed Control

[glend (Glen)]

Most of the good CPU and PC case fans being used for DSLR Cold Finger and Cooler Box builds are PWM fans (meaning they are designed to run on pulsed power). They typically have a 4-pin connector, originally intended to plug into a CPU board header. The four pins are: Ground, +12V, a Pulse lead and a Tach lead (these are called other things some of the time). You can run your fan flat out at maximum rpm simply by connecting just the ground and +12V leads to your power supply. These fans draw next to no current (my biggest fan uses only 0.1amps) but they are voltage dependent. Some of the best fans are now using three-phase motors, meaning that they run smoother than previous fans which are two-phase.

Controlling fan speed, there are a couple of good reasons you might want to do this: reduce noise, reduce potential for vibration (which may migrate to the sensor if not carefully isolated), and avoid annoying breezes blowing the face or hands of you or others. I have lost track of the number of times people at Bretti have commented on the cool breeze coming off my fan. There is also less need for high fan speeds in winter and so seasonal control is feasible with a controller. Integration of fan speed control with TEC power and temperature setpoint management is a more complicated area and I don't want to get involved in that right now.

Typically, people building DSLR cooling solutions just wire the +12V supply up and run the fans flat out, and that's fine, but if you want fan speed control it gets more complicated. PWM fans (with onboard electroncis) should not be powered through a PWM themselves as this can introduce 'transients' and potentially affect the lifetime of the motor. It is best for these fans to be throttled through the 'Pulse' lead. Here is an article that discusses this, and circuit design (simple) for a fan controller circuit that you can build:

http://www.overclockers.com/pwm-fan-controller/

This article is a good introduction of PWMs and fan speed control.

Now I am not an electronics guru, but Rowland is pretty close (at least in the cooled camera area), and he has looked over the above link and has a few ideas on the subject and how it could be done. Rowland care to comment?

So for people buying fans for their cooling projects, think about whether you want to control fan speed, and how it can be done. Hopefully the link helped.

I will be building a 555 timer circuit for my mono cooled camera fan but it will be a month away at least. In the meantime if anyone spots a simple plug and play cheap small box solution let me know.

[Camelopardalis (Dunk)]

Glen, given the fan uses so little power there's so little to gain by controlling the fan speed...you might as well just have maximum air flow all of the time, and that in turn keeps your Peltier happy.

More importantly IMO is controlling the current to the Peltier, both to keep it in the sweet spot and to keep your system cooled adequately.

[glend (Glen)]

Absolutely Dunk, the TEC is the priority and the major factor in the success of the build and operation. My point with fans is that many of the good fans now run at speeds from 1500 up to 3000rpm and while that maybe wonderful for dispersing the heat of hot summer night, it is way over requirement for a cool winter's night when maybe 400rpm would be sufficient for the TEC. I have always run my fan at 100% by directly connecting it to 12V and never had a problem, but in winter when ambient is below 12C you don't need much fan push to keep the TEC working effectively down to your target. Especially if your only looking to stay above 0C, you don't need alot of air pressure. If your looking to run down below 0C then yes you need more flow for heat disappation (when talking about fans and heatsinks of equal size). If your objective is to stay above 0C then buy a smaller fan/heatsink combo that just has the pull down you need, but keep in mind that overshoot and undershoot around the setpoint will get larger the less capable your heatsink/fan at responding. No one needs a fan control circuit, you can get along just fine without it if you have nailed the selection of the heatsink and fan for your particular use; it just gives you some flexibility to use larger combo configurations at reduced settings.

[Camelopardalis (Dunk)]

Yeah the more I think about it, the more I wonder how much risk there is of it frosting over on cooler evenings