[stephenb (Stephen)]

I am testing a cooling fan for the 8"dob project and I need some advice regarding the fan's performance.

I purchased a typical chinese-made slimline computer fan 70mm x 10mm thick. It has a 5vDC operating capacity. It draws about 200mA.

I plan to operate it on 'AA' rechargable Nickel Metal Hydride (NiMH) from a small battery back mounted on the bottom of the mirror box. Although these batteries are rated at 1.2vDC (nominal), when fully charged these batteries are at a peak capacity of 1.45vDC, which I assume, they do not stay at this high voltage for very long when in use.

(1) If I use 4 of these batteries, at start up when fully charged, the total voltage of 5.8vDC. Is this too much for a 5vDC cooling fan?

Obviously after about 30 minutes operation, this drops to under 5V and steadies for a while until they begin to constantly drop further.

(2) If I use 3 of these batteries, at start up when fully charged, the total voltage of 4.35vDC. Will under-voltage put any stress on a small fan like this for a long period of time?


I have run 3 x AA NiMH batteries on this 5V fan and I got about 4 hours operation out of it.