Originally Posted by ginger_nuts
So I have started to leak check everything on my new build
But the pumps (Alphacool DC-LT Ceramic 12 Volt
) are very noisy, at a full 12v, at 5v they are only just turning.
I am wanting to know how can I run them at 7v or 9v without
Cheers for any help
Using the low speed fan adapters isn't going to work well, if at all, since even these little pumps draw more power than most common fans, which means the adapter will drop wayyyy more voltage than it would with a fan as the load.
I did a little quick math for you.
The pump is listed as drawing 0.408A which is right at 4.9W with 12V power.
That translates to an effective resistance of 29.4 Ohms.
To run at 7V, you'll need ~21 ohms in series with the pump with a power drop in the resistor of ~1.2W.
To get what you need with readily available resistors, (meaning RadioShack) . . . .
Get a pack of five 68 Ohm, 1/2W resistors . . . . Catalog #: 271-1106
By using appropriate combinations in parallel, you can get very close to what you're looking for with respect to overall resistance and power sinking ability.
Use 3 in parallel to get ~23 ohms for ~ 7V operation
Use 4 in parallel to get ~17 ohms for ~ 7.6V operation
Use all 5 in parallel to get ~13 ohms for ~ 8.3V
If you want to try ~9V to ~10V operation, get the 33 Ohm resistor pack too . . . Catalog #: 271-1104
3 in parallel will get you ~9V
4 in parallel will get you ~9.4V
5 in parallel will get you to ~10V
Be sure to put the resistors in the +12V lead. . . . If you put them in the Gnd lead, it could keep the tach signal from being readable.
Once you do some experimenting and determine a speed that fits your target of noise versus flow rate, then you can look for a more aesthetically pleasing options to a bunch of little resistors with the legs all twisted together.
DarleneEdited by IT Diva - 9/8/13 at 6:37am