24h usage - dangerous?

Submitted by fxj on Sat, 06/20/2015 - 07:15

Forums:

Hi,

I just got my picoborg and it is working as expected. Great! But now my question.
I am using a 12V power supply for the picoborg which has to switch 2 fans (0.25A / +12V DV) consuming 5watts each when running. I have read this in the specifications:

"There is no thermal shutoff, keep an eye on temperature of the FETs and diodes
There is no current limiting, you must observe current restrictions
There is no short circuit or reverse voltage protection
This is primarily designed to be used with large resistance, low inductance motors and for learning and experimenting purposes. For commercial applications and control of larger motors and lower resistance coils etc, PiBorg or PiBorg nano may be a better solution"

I want to use the picoborg 24/7 to switch on fans if humidity is too high. It might occur that it has to switch often a day or that it has not to switch for long time.

Can something overheat then or is it dangerous and something can burn?

Shall i use another board with some protection stuff?

Thanks in advance.

piborg's picture

piborg

Mon, 06/22/2015 - 12:09

In most cases the fitted 2A fuse should blow if the fans short circuit in some way.
The concern would be if the fans stall when powered, for example if the bearings wear out.

Stall current is almost always a fair bit higher than the normal running current, sometimes drastically slow.
If the motors were powered and had stalled they could potentially draw 2A continuously without blowing the fuse.

In a worst case scenario the PicoBorg could draw 2A at 12V, making a little 24W heater from the transistors on the board itself.
Any draw higher than this should blow the fuse and stop the board working instead.

Whilst it is unlikely to manage this it is possible, we would recommend caution with running this 24/7.
In particular:

  • Make sure anything flammable is kept away from the board
  • Check the fans are in good condition and operating correctly on a regular basis
  • If there is ever any sign of a problem turn everything off immediately and fix the cause is before using again
  • Ensure there is decent air exposure to the PicoBorg
  • Ensure the fans cannot be blocked or stopped by anything nearby
  • We would ideally suggest using a board with overheating protection to be safe, for example a PicoBorg Reverse
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