peltier cooling webcam - power problem

[theodore]

Hi,

following the previous threads on webcam mods, I was thinking of including a peltier cooler, mainly because I have a salvaged one. Its about 3cm square but has no other information on it. The problem I have is that it seems to draw a very high current. All the various power supplies I have can't handle the amps. I tried it briefly with a car battery charger and it drew 10 amps! It got very cold though!

So, it must be a very high power one. I don't need that much cooling but even at the lowest voltage I have available, 3V, it draws too much for the supply (2.5A, supply max is 1A so it starts to smoke!).

Has anyone had this problem? Is there a simple current limiter I can make? I'm sure at lower current it will cool enough for my purpose.

Thanks for any help,

Theo

[Photosbykev]

I can't help with a supply but be very careful you don't destroy the peltier cooler. It needs to have hot side of the cooler cooled with a heatsink and maybe fans or the core of the cooler will destroy itself.

Even the smaller peltier coolers can pull 5A or more

[theodore]

Hi,

yes, I already have a substantial heat sink on it.

I'm going to try adapting this circuit:

An Add-On Current Limiter For Your Power Supply

Thanks,

Theo

[theodore]

Well, that didn't work. either gave zero or 10 amps....

[Tom How]

An atx pc power supply will give 3.3v at more amps that you'll ever need. They can often be got 2nd hand for nothing.

[pete_l]

So, it must be a very high power one. I don't need that much cooling but even at the lowest voltage I have available, 3V, it draws too much for the supply (2.5A, supply max is 1A so it starts to smoke!)

Peltiers do draw a lot of current, several Amps is the norm - and as you've already discovered, all that power turns into heat on the "hot side" and has to be got rid of. The more effectively you remove that heat, the cooler the "cold side" will get.

If you're into building electronics, I'd suggest a small switch-mode supply based on an MIC4576 chip. Briefly, these supplies take a higher input voltage with a low-ish current and turn it into a lower voltage, but with a high current which would match your Peltier. So with this device you can get 3V at 3A (i.e. 9 Watts), but the power you put into the power supply could be (say) 12Volts at 1Amp (12 Watts, for a 75% conversion efficiency - not too bad).

[theodore]

Thanks Pete, the MIC4576 looks just the ticket - I can run that off my 12V 1A supply.

Theo

[George]

You might be able to regulate the amps drawn using pwm controller, this would also control the degree of cooling you could apply.

[rfdesigner]

Excellent project... cool a webcam, nice shortcut to a cooled CCD camera on a tight budget.

I've played with peltiers, and I'd like to put a couple of warnings your way.

1. Don't let the peltier frost up. The peltier device is essentially two ceramic plates with all the peltier elements sandwedged between them. If you let one face drop below ambient temp, you can get water condensing between the two faces of the peltier cooler.. if this water freezes you can snap one or more peltier elements, eventually it will fail.

I've seen peltier coolers with silicon sealant around the edge to prevent water ingress.. but this provides a thermal path between the plates and so you get less efficient cooling.

2. Be careful about water freezing on the CCD. I'm not sure about webcams.. but with more expensive cameras with microlensing, if any water at all gets onto the face of the silicon and freezes it can damage the microlenses and you end up desensitizing pixels randomly.

when you're ready to really cool the CCD make sure it's completely enclosed ideally with some dessicant.. I've also seen a design with a cold element deliberately exposed such that frosting occured prefentially there and not on the CCD, a nice simple improvement.

Also I would add a thermistor to the cold end, then you can add setpoint cooling after it's working. It's easy to design in from the beginning, difficult to retrofit.

You can also buy peltiers from uk.farnell.com you can set up a private account although it's really an industrial supplier.

Hope this is of some use

Derek

[theodore]

Thanks Derek, very useful advice.