Fan amps and watts

[jaclaz]

I know the thread IS about fans, but I intentionally separated that big chunk from the post because it starts with "specific device (fan)" then goes on with things like "a load" and "a device". I'd like to point out that those consideration are in fact all for that "specific device (fan)" (or a DC motor) as for instance Ohm's law would say a big "well no" to the 4th example in case of a resistor. An AA battery would power a 220v radiator for few hours without burning (in fact you'd die of cold before it burns) .

Well, noone talked of a battery, we were talking after having expressly said "(simplified, and in order to let you understand)" of a PC power supply connected to mains and about a brushless DC motor, which is both a resistive load and an inductive one (actually essentially the second), and unlike the "will burn", "very likely to burn" was used instead for example #4.

Ohm's Law was cited AFTER the 4 examples and as an additional point, to exemplify how powering (within a bearable range) a device (still talking of an electric DC motor) connected to a PC power supply) with higher voltage will reduce the amount of current needed and how current absorption is linked to the voltage level supplied.

In the case of an electric radiator suited for 220 V , actually norms are about 230 V with some slightly different tolerances:

http://en.wikipedia.org/wiki/Mains_electricity#Standardization

labeled 1000 W, we can use:

W = V x I to get I=1000/230=~4.35 A

and then use

I = V / R to get that the resistance of the thingy is about 53 Ohms as 230/53=~4.34

But now, when we use the AA battery 1.5 V we have:

I=1.5/4.34 =~0.35 A or 350 mA

Since a normal AA battery (alkaline) has a capacity of roughly 2200 mAh, and without taking into consideration a number of factors, it will last 2200/350=~ 6h30 which, while NOT being accurate, it is still more accurate than "a few hours".

jaclaz

[Ponch]

You can't expect everyone to write 100 lines just to add a little precision. I had done a short calculation. The battery/power supply will not burn, nor is it very likely to. That was my point. 230v, 220v, 2500W, 1000W, alkaline 1.5v, rechargeable 1.2v, 2200mAh, 2500mAh, 6h30, 40h, a few hours, whatever, it will not burn.

Edited December 22, 2012 by Ponch

[jaclaz]

You can't expect everyone to write 100 lines just to add a little precision. I had done a short calculation. The battery/power supply will not burn, nor is it very likely to. That was my point. 230v, 220v, 2500W, 1000W, alkaline 1.5v, rechargeable 1.2v, 2200mAh, 2500mAh, 6h30, 40h, a few hours, whatever, it will not burn.

Sure it won't .

jaclaz

[Molly Dawn]

0.7amps @12 is more than enough to handle the average fan no problem. Only high performance fans like those made by delta electronics (the mini jet engines like I use on my FX9350 radiator) are going to draw more power than the motherboard can supply.  Thats why Delta fans come with molex power connectors or bare wires instead of 3/4pin fan headers (usually).  at any rate the fan amp ratings are printed on a sticker on the back of the fan, so its easy to see if one will work or not.  THere are a lot of good fans in your amp range, and even some of the lower powered Delta's are right at 0.7@ and thus compatible as well.  (the 25mm thick ones) the 35mm thick ones like the 9xxx series FX chips need pull anywhere from 1.5 to 4a each, and thats when you need to plug them into molex connectors directly.