Panaflo L, M, H, and U: same noise/CFM at same wattage?

FishaOfMen · Post by **FishaOfMen** » Fri Jul 04, 2003 3:55 pm

I've seen that Panasonic has L, M, H, and U versions of their Panaflo fans. A "U" fan will operate at a much higher wattage and speed than an "L" fan. Thus, it will be much more noisy. My question is this, if I take an 80mm "U" fan and undervolt it to the same noise level of an 80mm "L", will it push the same CFM as the "L"?

miker · Post by **miker** » Fri Jul 04, 2003 6:23 pm

You will not be able to lower the voltage enough on a U to make it as quiet as an L. It has to do with the amperage, I believe. Those fans are just wired differently.

GamingGod · Post by **GamingGod** » Fri Jul 04, 2003 7:29 pm

I think hes asking if undervolting a high performance fan would be more efficent than a lower cfm fan.

miker · Post by **miker** » Fri Jul 04, 2003 8:00 pm

Excuse the crude "table"

Model# |SIZE |CFM |dBA |mA | Watts

FBA08A12L1A 80x25 24 21 68 0.82
FBA08A12M1A 80x25 32.1 28 124 1.49
FBA08A12H1A 80x25 39.6 32 173 2.08

Using the formula: Watts = Volts x Amps

L: 12V * .068A = .816 Watts
U: 6.5V * .124A = ~.816 Watts

So right off you have to run a U at 6.5V to be comparable to a L at 12

Let's say you want it to move like a 7Volted L (i.e. tolerable)

L: 7V * .068A = .476 Watts
U: 3.83V * .124A = ~.476 Watts

I think it unlikely the U would even start at <4V.

The mA column here is the important part, since it is the constant for the fan. Maybe we can get a EE or someone who plays one on TV to explain better than me (I slept through physics)

somebody · Post by **somebody** » Fri Jul 04, 2003 8:55 pm

How does wattage relate to decibels?

miker wrote:Excuse the crude "table"

Model# |SIZE |CFM |dBA |mA | Watts

FBA08A12L1A 80x25 24 21 68 0.82
FBA08A12M1A 80x25 32.1 28 124 1.49
FBA08A12H1A 80x25 39.6 32 173 2.08

Using the formula: Watts = Volts x Amps

L: 12V * .068A = .816 Watts
U: 6.5V * .124A = ~.816 Watts

So right off you have to run a U at 6.5V to be comparable to a L at 12

Let's say you want it to move like a 7Volted L (i.e. tolerable)

L: 7V * .068A = .476 Watts
U: 3.83V * .124A = ~.476 Watts

I think it unlikely the U would even start at <4V.

The mA column here is the important part, since it is the constant for the fan. Maybe we can get a EE or someone who plays one on TV to explain better than me (I slept through physics)

FishaOfMen · Post by **FishaOfMen** » Fri Jul 04, 2003 9:22 pm

miker, I like the table a lot. somebody hit the question I'm going for, though. Does equal wattage mean equal noise and airflow? That is, if I run the U at 6.5 volts, will it push the same CFM and create the same noise as an L?

cpemma · Post by **cpemma** » Sat Jul 05, 2003 6:11 am

If you plot the fan rpm or flow against noise, you get a pretty good relationship for most fan families. So yes, undervolting a Panaflo M to give the "L" flow will also roughly give the "L" noise.

Of more use, you can take most any decent 34cfm fan, undervolt to give 24cfm and end up with a quieter fan than the Pan L

Some graphs here

There is a formula for noise related to RPM, works providing you don't compare chalk & cheese.

N2 = N1 + 50log10(RPM2 /RPM1)

Or Noise difference (dBA) = 50log10(RPM2 /RPM1)

Riffer · Post by **Riffer** » Sat Jul 05, 2003 10:07 am

All I know is that the M is noisier at the same airflow than the L.

This was tested scientifically by running the L and an undervolted M at the same time, and sticking my hand in front of each to see how much breeze there was. I then tested sound level by putting each in turn up to my ear:)

SometimesWarrior · Post by **SometimesWarrior** » Sat Jul 05, 2003 12:55 pm

Riffer, I'm not sure if that scientific test would stand up to peer review.

There have been accounts from a couple people, Powergyoza being one, that the "H" versions make more noise at low voltages than the "L" and "M" versions. Not airflow noise, but motor/bearing noise. Here's the link. So apparently, if the H and L models are pushing the same volume of air, the L is still quieter. Combine this observation with Riffer's, and you can assume that the U will be noisier as well.

FishaOfMen · Post by **FishaOfMen** » Sun Jul 06, 2003 7:11 pm

Well, it looks like we have some differing opinions. I think I'm going to have to send Panasonic an e-mail inquiring about this.

miker · Post by **miker** » Sun Jul 06, 2003 7:40 pm

My guess, they'll tell you its bad to undervolt fans.

cpemma · Post by **cpemma** » Mon Jul 07, 2003 2:05 pm

miker wrote:Excuse the crude "table"

Model# |SIZE |CFM |dBA |mA | Watts

FBA08A12L1A 80x25 24 21 68 0.82
FBA08A12M1A 80x25 32.1 28 124 1.49
FBA08A12H1A 80x25 39.6 32 173 2.08

Using the formula: Watts = Volts x Amps

L: 12V * .068A = .816 Watts
U: 6.5V * .124A = ~.816 Watts

So right off you have to run a U at 6.5V to be comparable to a L at 12

Your theory's wrong, at 6.5v the M fan won't still draw .124A.

Work out the fan resistance, then power = V^2/R

So the L is 176.5R, M is 96.8R

If V^2/96.8 = .816, V^2 = 79, V=8.9v.

Actually you're better using the rpm or flow values, the M is 2450rpm, the L 1900rpm. So to rev the M @ 1900rpm, u need 12 x 1900/2450 = 9.3v, or working on flow, 12 x 24/32.1 = 9v.

All 3 methods are complicated by a diode and transistor junction in the Panaflo power path, losing about a volt, so really it's around (11 x 1900/2450) + 1 = 9.5v or (11 x 24/32.1)+1 = 9.2v.

The truth is somewhere between, probably.

FishaOfMen · Post by **FishaOfMen** » Tue Jul 08, 2003 8:30 pm

Thanks for the help on that, cpemma. Well, here's the response I got from Bob Drack at Panasonic:

Andrew;
As a "rule of thumb", you are correct. Be careful to give the fan the minimum required 7 volts, or, the IC may not work.
Bob

There's our final answer.

cpemma · Post by **cpemma** » Wed Jul 09, 2003 12:16 pm

If it's the U fan you've got, spec figures are 270mA, 3.24W, 3450rpm, 46.9cfm, so to knock it down to the L's 1900rpm I'd guess around 7v would do it, so it should start OK. And 7v is a nice easy voltage to find...

Panaflo spec 100g weight for all the 80mm range, but I'd have thought the U would have the heaviest motor of the 4 (more copper?)

which could account for the extra bearing noise at low speed commented on. It's not a fan I'd buy, TBH.

On GamingGod's comment

I think hes asking if undervolting a high performance fan would be more efficent than a lower cfm fan.

I'd turn it round a bit - if you need 50cfm to cool your system, it's quieter to use two 25cfm fans (or even four 12.5cfm) than one 50cfm. Though the 50cfm will produce more pressure and be more effective in a cramped case.

ez2remember · Post by **ez2remember** » Thu Jul 10, 2003 2:12 am

All this science is good, but until you live with these fans you will NOT know which fan is quieter by using calculations.

The L1a is STILL the best all round cooling/airflow/quiet fan and this is using them for nearly a year or so now and has come under heavy competition of other quality quiet fans.

The M1a is a good compromise for airflow and noise. I have found the H1a noisy even at 5v's. The H1a may push more air at the scientific noise/cfm, but this fan is just too rough, with lots of bearing noise.

If we use the manafacturer quotes and calculated the best cfm/noise when undervolted then we would be in trouble.