DIY cooler for asi178

[ChrisLX200]

3 minutes ago, D4N said:

USB connectors work fine at -25°C, I have imaged with no problems at that temp.

I doubt the TEC could bring the casing down to a temperature that would damage it unless you have seriously over-specked your cooler.

It's not the temperature as such it is the ice collecting around it causing shorts.

ChrisH

[ChrisLX200]

2 minutes ago, Gina said:

I have built and programmed several automatic set-point coolers in the past.  I use DS18B20s for digital thermometers.

May have to call on your expertise in this area Gina!

ChrisH

[Gina]

Fine

[D4N]

2 hours ago, Gina said:

I have built and programmed several automatic set-point coolers in the past.  I use DS18B20s for digital thermometers.

Interesting, I put a DS18B20+ in my focuser.

I've not heard of the s, anything different about it?

It works great and a set point cooler would be fun to make but I don't think I have the time at the moment.

[Gina]

The s is just the plural.

[D4N]

Haha it's been a long day, I guess I should go go to bed.

[Icosahedron]

On 08/08/2016 at 19:28, D4N said:

I think the TEC isn't fussy about its supply but PWM is probably the most efficient way of having a manual control, a rheostat would be cheaper and smaller but inneficient so not ideal for battery powered setups.

Otherwise you can have a controller with feedback that will keep a set point but this would be a lot more complicated and more expensive.

 

I'm planning to just leave mine on full, if I find it gets too cold I will have to rethink this but the combination of dew heater and the heat from the sensor should be enough I think.

A few weeks ago I suggested to someone on this forum to utilise PWM for TEC control. This person pointed out to me that PWM is not recommended. Needing a controller for my camera project, I've investigated the reason for this and would like to share what I've learnt:

The cooling effect of a Peltier device is directly proportional to the average supply current. This current flow also results in resistive heating of the device which again is proportional to the square of the root mean square current. For a DC supply I_rms = I_average at all times, but for a pulse train I_rms > I_average and there lies the problem. As you reduce the PWM duty cycle you reduce the cooling effect more than the resistive heating which leads to poor control.

I'm not saying that PWM control won't work at all, but that power is being wasted by forcing the device to become inefficient. This may not be much of a problem if you're hooked up to a power station, but in my case I depend on a battery for power.

All is not lost for PWM control though. A better option is to convert the PWM signal to a DC voltage for the Peltier. This can easily be done with a buck converter.