Low amperage risk for cooled cameras

Hi Pablo,

 I guess with 5V/2.1A battery you mean a small power supply?

There are some things that could happen. I try to explain it in a short way. This is by far not a complete description…

The power supply for digital devices is key. Your camera needs 3 Amps as average current , if you run it at 12V and with 100% of cooling power. You could run it with less current, but there are some things that could happen.

Digital devices are basically little computers with one or more microcontrollers in it. They consist of thousands of transistors, that switches all the time. While they switch, they need a good amount of current for a short while. When you measure the current you are usually not measuring those peaks, but you are measuring the average current. Those are different things. If you draw more current than the power supply can handle, the voltage drops and you are not working with 12V anymore. This may have different effects.

At first, your power supply will probably heat up and in the worst case will be destroyed.

The second case could be, that your camera will not work safely. The voltage drop or the missing current can lead to errors while you are working with them. They may disconnect, deliver bad data or may not working well for other reasons. But the real issue is always a bad power supply. It is hard to detect the reason for those problems, because nobody thinks about the power in the first place.

With 5V and 2.1 Amps, the power supply can deliver about 10 Watts of power. Your camera needs with 12V and 3 Amps already 36W of power (worst case). No matter what you do, you will not get more than 10 Watts out of the used power brick. If your 12V converter is used, you loose something (mostly about 5 to 10% or more). But your Step-Up-Converter is made for only 0,875A. If you draw more current, the voltage will drop and your camera may probably not work correctly. Also the converter gets usually really hot if you even use it at the maximum possible current. Don't trust that value if it is a cheap converter!

As conclusion, I wont suggest a solution with such a drastic difference in values. It can work, but it surely is not reliable. If things go really bad, you can destroy your camera. I think, a 12V/3A power supply isn't that expensive. You can get them for under 10 Bucks.

If I misunderstood your question and you really want to use a battery, than this is another topic. Then we have to talk about other parameters like Amps per hour and how much current the battery can deliver or how long you plan to run your device.

I would suggest to buy a decent power supply. It really can be a small investment. If you are going the battery route, than do some more research and be careful. There are a lot of things that can go wrong. If you do not have much knowledge about electricity, than better ask for help and don't do it yourself!

I hope, this answer helps in any way.

Clear skies…

Christian

However, the TEC cooler and the camera draw power independently: TEC from the power supply, camera from USB.

So the discussion about what circuit gets damaged or malfunction applies only to the cooler. I believe it will work okay with reduced power input (it is a rather simple electronic circuit quite unlike the camera) except perhaps 25% performance might not be adequate. Also even though the camera is independent from the cooler, it might check wether the cooler has sufficient power and refuse to function. 

I would ask QHY support.

Cheers,

D.

OK, thats a good point I forgot about. Sorry. I am powering the camera (via an external USB hub) and the cooler from the same power supply. So for me there might be those problems. 

Thanks for the kindly reminder...

I don't think you need to run the camera so cold. If you look at the product page for the 294 on the QHY website, they show a graph of dark current vs temperature and it is quite flat up to around zero or even +5 degrees. The important think is to use temperature matched darks but read noise is more significant than dark current noise.

The TEC itself won't get damaged - the temperature differential it can generate is proportional to the current through it so you'll limit how much you can cool. The main but rare failure mode in the setup is going to be a voltage drop across a FET, particularly a power FET that might be found in a switched-mode power supply leading to a "latch-up". Those FETs might get destroyed if they latch up due to a low-voltage situation. It would be a particularly amateurish circuit to not include under and over-voltage protection and discrete components like the image sensor itself, TEC controller and the USB transceiver generally have their own internal latch-up protection. If something is going to burn, it will likely be the step-up convertor due to latch-up.