Equation for CFM @ 12v .vs CFM @ 5v

[J-Mag]

Now I know that this is probably not possible for exact numbers due to variations in fan construction.

However, I really don't care if it is an approximation b/c most manufacturer's tend to lie anyway...

Essentially, I was wondering If I could take the rated 12v CFM or dba and convert it to what it "should" be at 5v.

Thanks

[Agr3sive]

If i understood your question right, I would imagine it to be just under half as there is no regulators, its just direct power, ie-
100cfm @12v
45cfm @5v
Just the same if you could manged to get 18v down one line i would guess the cfm to be 150, hope this helps

[Holst]

This will depend on the fan itself.

Some wont even spin at 5v....

Does it matter if you know?
I dont think you could work it out unless you do lots of maths. Better to just test it.

Dba is not a linear scale anyway so that definately wont work on a ratio.

[AMD-me]

I agree, I think fin design and motor efficieny need to be taken into account to get a accurate measurement.

[J-Mag]

This will depend on the fan itself.

Some wont even spin at 5v....

Does it matter if you know?
I dont think you could work it out unless you do lots of maths. Better to just test it.

Dba is not a linear scale anyway so that definately wont work on a ratio.

True but you could always keep the curve rate in mind...

It's not like marketing people don't do this all the time. I give my left nut if 90% of specs out there are altered, guessed, or rounded.

[jellybeard999]

I give my left nut if 90% of specs out there are altered, guessed, or rounded.

They ARE ... you owe me that nut :woot: :)

[rick_fx]

Lol!

[craig588]

Just some numbers here, I havn't done any measurements. Half voltage=half amperage = quarter wattage = quarter of the ability to move air. The formula goes like this VA=W You are using 42% of the rated voltage, so multiply the rated amperage by that and multiply the modifyed values and compare it to the fans rated wattage. That might be aproximately the % of the full CFM that the fan will push.

[Rippthrough]

Problem is that then fan blades won't be at peak efficency anymore, the motor porbably wont be either, so you need to take of a bit for that too, and even then you still only get an estimate.

[$a1Ty]

is the fan rpm a linear scale with voltage

[J-Mag]

They ARE ... you owe me that nut :woot: :)

Shipping Addy? :stick:

Btw, I had not had the ability to :rehab: before i made that post, which is why my thoughts were backwards...

Edit: I am not sure if you follow... the Ganja Banana Legacy...

[J-Mag]

is the fan rpm a linear scale with voltage

It seems so... until obviously the cutoff point...

[craig588]

is the fan rpm a linear scale with voltage

RPM != CFM

[J-Mag]

RPM != CFM

Definately the case, but after starting voltage i think RPM cales close to linear. However I believe the RPM to CFM scale is more like an "S" curve.