Re: [ATM] Gell cell batteries

[Mark Holm <mdholm@telerama.com>]

Treur, Harro wrote:
> Hello Tim,
> 
> I use small penlite-batteries to drive the electronics of my 12,5 inch
> Dobson. 
> 
> - There are four cooling fans. Three under the primary to cool down the
> mirror and one above to blow away the boundary layer. These fans are 5 Volt.
> I have 3 rechargable penlitebatteries (1,2 Volt) to feed those fans. The
> batteries can run for about 6 hours. Most of the time I only cool the
> primary for about one hour. After that I switch off the three coolingfans
> and let only the upperfan do its work. 
> By the way: Usually all cooling fans are 12 Volt. Finding 5 Volt
> coollingfans turned out to be a hard job: I have not been able to order
> those seperately (unless I ordered more than 1000 !!). I finally bought
> myself a cooling-pad for a laptop: these are 5 Volt fans and get their power
> from the USB-port.
> 
> - My secondary (2,6 inch or  63 mm) is heated by two penlites. These give
> 2,4 volt and about 0,4 Watt. The penlites work for about 15 hours and it
> works amazingly well.

These are very useful numbers for design estimating.  Especially, I
think nowing that a secondary heater can have such a low power and work
well is important.  You don't want to design any optic heater to be more
powerful than necessary.

The fact that your laptop cooling fans were designed to be powered from
the laptop's battery probably means they were chosen for high
efficiency.  Fans designed for line powered applications probably don't
get nearly the attention to efficiency.  That might be a good reason to
favor fans like this.

Mark Holm
mdholm@telerama.com



Mark Holm
mdholm@telerama.com

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