DC vs AC Fans

[winston77]

Lost my knowledge on DC vs AC.

How is the comparison of a DC fan vs an AC fan? In terms of power consumption, fan speed, etc?

I am currently using a 12x12 Profantec fan, AC240 0.12Amp. If I were to get a 12x12 DC Fan, which is typically 12v and ???amp, will it perform to the same level as the AC type?

[juggler]

Hope someone can verify my computations as I can't be trusted on such stuff...

I just look at the specs of my DIY DC Fan. It is about 8cm x 8cm size, rated 12v, 0.14A. It runs 24 hrs on my 2.5ft tank. So power consumpton = 12 x 0.14 = 1.68W. Using the electrical usage calculator, the usage per month is < $0.30.

Seems quite low assuming no heat loss from the ac/dc adaptor. It is sufficient to cool the tank 2 to 3 degrees below room temperature.

If I were to use your AC to compute, I get power consumption = 240 x 0.12 = 28.8W. Using the electrical usage calculator, the usage per month is about $4.30.

In our humid environment, we can only cool our tanks not more than about 3 degrees below room temperature as I heard. So if this is the case, there's no point using a high powered AC fan when a lower powered DC fan will do the job. By right, I should be able to increase the number of DC fans to improve efficiency without incurring as much running cost as a AC fan.

[valice]

Hmm... a small Eheim canister filter only uses 8W... A fan uses 28.8W? Are we missing something in the calculation? Can someone who still remembers his/her physics help?

[juggler]

Just checked my household equipment. My standing fan is 240v, 60W. A smaller table fan is 240v, 42W.

So an AC fan with 28W is not surprising to me.

[lEddyl]

think there's more calculation. AC to regulated DC should have some power lost. depending on efficiency of the adapter

AC item should have more power saving
thus stuffs for DC is cheaper

[juggler]

Surely there's power loss from the ac/dc adaptor. No idea how much though. It feels hot. Just like our magnetic ballast vs eBallast.

But I feel cooling with AC fan could be more expensive than DC. The wattage for AC fan is already higher than a Eheim pump.

I found 2 sites suggesting DC fans more energy saving than AC fans. Hope I am looking at the right things. Or these companies could be doing marketing talk?

http://www.controlres.com/inversion.htm
http://www.pelonistechnologies.com/fans_acdc.shtml

[tawauboy]

think there's more calculation. AC to regulated DC should have some power lost. depending on efficiency of the adapter

AC item should have more power saving
thus stuffs for DC is cheaper

assuming a 240vac to regulated 12vdc (varies with design), the conversion process will be
a) 240vac to 12vac through a transformer
b) 12vac has to be rectified and this may give ~18vdc
c) 18vdc regulated to 12vdc

losses:
a) 240vac to 12vac - quite a fair bit due to transformer core loss; heats the adaptor
b) rectification - insignificant losses, if any
c) regulation - quite a fair bit depending on load current; calculated by voltage difference between regulator input and output (in this case, 18-12) multiplied by load current.

[stephen chung]

Well, I think most of the time the rating stated on the products are MAX allow load. And I think they are in Peak to Peak power.

Actully, to calculate the power on a motor is pretty complex.

Its been 20+ yeard since I studied these during my university days. I might have forgetten alot of the stuff...

Motor are inductive device which means they have impedence (not pure resistive).

Noramlly, you just divide the power with 1.414 will give u the ture power or what we call if effective power.

Oh..Thomas..when we use a rectifier to convert AC to DC ..It will be like..

a) 240vac to 14vac through a transformer
b) 14vac has to be rectified and this may give ~14vdc
c) 14vdc regulated to 12vdc

Most of the losses are through heat especially the power regulator...They are very very hot...

Well, its been almost 20+ years since I have studied all these...So, I might be wrong..And I have try my best to explain it as simple as I can..

[celticfish]

erm... sorry but what would be the wattage?
i believe this is what counts with the power company, right?

[tawauboy]

b) 14vac has to be rectified and this may give ~14vdc
c) 14vdc regulated to 12vdc

Most of the losses are through heat especially the power regulator...They are very very hot...

Well, its been almost 20+ years since I have studied all these...So, I might be wrong..And I have try my best to explain it as simple as I can..

yeah! you are right with b.
a 240v to 12v transformer may provide an output of ~18vac due to winding tolerance. your 20+ "archive" still serves you well.

the voltage regulator does dissipate a lot of heat depending on the voltage difference between regulator input and output. thus, there is a need to minimize the voltage differential. this is typical for linear regulation.

you'll need a switching regulator to minimize losses. but these cost more that linear regulators.

[tawauboy]

erm... sorry but what would be the wattage?
i believe this is what counts with the power company, right?

the wattage will be according to the label on the device. else calculate "power = voltage x current". this is what you pay.

[celticfish]

so we would be using the 14 vdc in your example and not the 240v right?

[winston77]

a 240v to 12v transformer may provide an output of ~18vac due to winding tolerance. your 20+ "archive" still serves you well.

Based on the above assumptions, I would say that the power consumption would be as follow:

18V x 0.5amp = 9W

Will this promote the use of DC Fan instead of AC Fan? Are there any downside to using a DC Fan instead?

[stephen chung]

Based on the above assumptions, I would say that the power consumption would be as follow:

18V x 0.5amp = 9W

Will this promote the use of DC Fan instead of AC Fan? Are there any downside to using a DC Fan instead?

Actually, I don't think it make a difference that much. But to save myself trouble I'll just get an AC fan..

[tawauboy]

so we would be using the 14 vdc in your example and not the 240v right?

what you are paying to power companies are based on 240v. they don't care whatever conversion efficiency you get out of your devices. however, the difference in running cost calculated will be quite insignificant.

[tawauboy]

Based on the above assumptions, I would say that the power consumption would be as follow:

18V x 0.5amp = 9W

Will this promote the use of DC Fan instead of AC Fan? Are there any downside to using a DC Fan instead?

i don't think there are any significant downsides to using a dc fan. advantages are safety (water and ac don't mix) and simple fans speed controller (if you know electronics) when compared to ac fan speed controller.

[tawauboy]

Actually, I don't think it make a difference that much. But to save myself trouble I'll just get an AC fan..

you may save some trouble but make sure that the ac fan is securely fastened. and before tank maintenance, ensure that you switch off the power. ac and water don't mix.

[valice]

Yup... I totally agree with what Thomas say about AC and water after my fan dropped into the water with my hands in there... That's the biggest downside about using AC fans... But the simplicity of not needing to wire the fan to a convertor is also attractive..

A good wake up call...

[stephen chung]

you may save some trouble but make sure that the ac fan is securely fastened. and before tank maintenance, ensure that you switch off the power. ac and water don't mix.

Hahahaha...That is very true....