Fan Modding

[Darkplague]

Hi,

I have a 12" GS dob with cooling fan. I would like to mod the fan to run off a power source rather than batteries. However I can't see anywhere on the fan what voltage it runs at. Does anyone know what power source I should use? eg a standard 12 volt pack from diksmiths?

Has anyone performed this mod?

Cheers!

Clear Skies to you all

[ballaratdragons (Ken)]

Yep! They are a 12 Volt fan.

Be careful of Amps though! Any ol' power supply may pump too many Amps into it and cook it!!

Someone into electronics should be able to let you know your maximum allowable Amps.

[janoskiss (Steve H)]

You cannot cook the fan IF the power supply output does not exceed 12 volts, because amps and volts (current and voltage) are interdependent. At a fixed voltage the fan draws a fixed number of amps. The power supply cannot put more amps through the fan without increasing the voltage across it. So, the power supply just needs to be a 12 V and able to supply enough current to maintain the voltage (i.e., supply enough power = voltage * current); the maximum amp-rating of the p.supply should be greater than the amp-rating of the fan.

PS. Congrats on the 2k Ken!

[ballaratdragons (Ken)]

Thanks for clearing that up Steve. (and for the congrats)

The Amps bit always confuses me.

In that case, if 240V is nearby, a small car battery charger should work???? They are very cheap!

[RAJAH235]

Darkplague, The fans run on around 170 mA. with 12 volts applied. A little less with reduced voltages, but not much! L.

[janoskiss (Steve H)]

Originally Posted by ballaratdragons

The Amps bit always confuses me.
In that case, if 240V is nearby, a small car battery charger should work???? They are very cheap!

That's the tricky bit! A charger is not a constant voltage supply, but a current supply. Even though a car battery is 12V, you need to charge it at around 14V. The charger works by maintaining a constant current of 4, 8 or more amps. It will vary the voltage (up to some limit) if need be, to maintain the constant current. Now that would cook your fan!!

[RAJAH235]

Sorry to disagree Steve. The voltage out of an UNregulated battery charger will be somewhere near 17/18 volts, some are higher. This would possibly 'cook the 12 volt fan', because of the light load. But, It relies on the characteristics of the battery/load, to limit the current/voltage.
HTH. L.
ps. If you have 240 avail., why not use a 240/9volts @ 500 mA plug pack????? (probably enough voltage, speed wise). L.

[ballaratdragons (Ken)]

Oh well, at least I got one thing right.

The fan is 12 volts. LOL
and it spins around!!!

[janoskiss (Steve H)]

L. It doesn't sound like you disagree...

[RAJAH235]

Sorry. Misread or interpreted meaning......... L.

[ballaratdragons (Ken)]

Laurie & Steve,

It sounds like you are both saying the same thing 2 different ways!!!!

[RAJAH235]

Yeah. B****Y inglesch langaje.... L.

[janoskiss (Steve H)]

Darkplague, my point was that a car battery charger is not a constant voltage supply and the fan presents a small load and the charger is likely to overload it. Do not use! You need a half decent 12V supply with current rating above that of the fan.

[RAJAH235]

Ta, Steve.

[vindictive666 (John)]

i use one of those 12 volt 6 amp rechargeable gel cells they use in alarm systems works a treat

[slice of heaven]

It doesnt need to be a large power source either.
I use a 12v Makita rechargeable battery pack for a cordless drill. 1.2 or 1.5 amps. Only because I've upgraded to 18v and 14.4v tools.
These power the fan, the Telrad with a heater and a couple of LEDs and last for ages without having to recharge.
Check out whats available and choose what suits. A compact pack can be fitted to the base. The larger packs can be used for other things as well.