# Is this Amount of Wattage Correct?

Discussion in 'General Electronics Discussion' started by roonyroo, Sep 12, 2012.

1. ### roonyroo

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Jul 13, 2012
14000 mah at 12 volts is 168wh ?

I used an online calculator, but it doesnt seem right?

Im trying to run a fan, it states 230v 50hz & 30 watts

Im presuming the fan runs at 12v so this 14000mah battery gives me a headroom of 138wh minus the 30w from the fan?

2. ### Harald KappModeratorModerator

11,813
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Nov 17, 2011
1400mAh=1.4Ah
1.4Ah*12V=16.8Wh
At 30 W your battery will be empty after ~30minutes.

Why do you presume the fan runs at 12V? If it is specified for 230V (AC) operation it would be unusual to have a 12 V motor. This would require a 230 V / 12 V transformer (or step-down regulator) plus a rectifier. This is not plausible as these fasn usually are very cost sensitive.
Assuming I'm right, you'd need an additional 12 V to 230 V inverter which lessens the operating time for the fan because it will be at best 85% effective, meaning that the uptime of the fan reduces to 30 min*0.85=25 min.

3. ### GreenGiant

842
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Feb 9, 2012
Harald the battery is stated at 14Ah not 1.4

would increase the uptime to 5 hours*.85=4.25 hours

4. ### roonyroo

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Jul 13, 2012
Thnx greengiant, so the battery is more then powerful enough to run the fan .. great

I presumed 12v as everything seems to run at 12v here in the u.k? ie my pc power supply is rated at 12v

How do I found out what voltage it runs at here in the U.K. if its rated for 230v? ie 230v 50hz = 12v etc

One final question, the larger the ampage, the longer it takes for a battery to recharge to a specific level?

ie If I had a 10amp battery it would take longer for a 20amp battery to charge upto 10 amps, then the 10 amp battery?

thnx

Last edited: Sep 12, 2012
5. ### GreenGiant

842
6
Feb 9, 2012
The fan says on it that it is 230V rated, ergo it probably needs 230V to run

if you are charging them both at the same rate (amperage) then no, they will charge to 10A charge at the same time.but if you charge them at a 1C rate (amount of current needed to charge them to full in one hour, 10Ah 1C = 10A, 20Ah 1C = 20A etc) then the 20Ah cell will actually charge to 10A faster (in about half an hour) this is not an exact science, but its close enough for the most part

6. ### roonyroo

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Jul 13, 2012
Thnx greengiant,

I meant as in 12v, 3.3v etc., how do I work that out if it states 230v 50hz?

Basically how do I work out if its 12v 24v etc if it states 230v 50hz & 30watts?

thnx

7. ### BobK

7,682
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Jan 5, 2010
What are you not getting? If it states 230V why would you think it runs at any other voltage? It is possible, (though not likely) that a transformer is used and the motor runs at a lower voltage, but I would not assume that unless I took it apart and found that configuration.

Bob

8. ### Harald KappModeratorModerator

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Nov 17, 2011
Oops, thanks for the correction. I overlooked a zero.

9. ### davennModerator

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Sep 5, 2009
you saidiIt states 230V 50 Hz on the fan, thats 230V AC from the mains

It is NOT going to run on 12V, 24V or any other voltage DC
Your battery is 12V DC so it cannot run the fan

Dave

Last edited: Sep 13, 2012
10. ### Harald KappModeratorModerator

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Nov 17, 2011
Why do you think everything runs at 12V in the UK? As far as I know everything runs at 230 V in the UK. The rating on the power supply you cited only means that the output is 12V, But surely the input is 230 V 50Hz.

11. ### roonyroo

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Jul 13, 2012
Im a complete newb to electronics .. lol

So why does a battery state 12v while the fan states 230v?

Thanks for answering my questions ...

12. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,500
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Jan 21, 2010
That's a bit like asking "Why does my car have 4 seats when there are 43 people waiting for a train?"

The answer is that your car is not a bus, and the people aren't waiting for a bus anyway.

What made you think the battery would power the fan?

13. ### Harald KappModeratorModerator

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Nov 17, 2011
Why are there batteries rated 1.5V, 4.5V, 9V, 12V etc...?

14. ### davennModerator

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Sep 5, 2009
cuz a fan isnt a battery and a battery isnt a fan. they are totally different things

a battery supplies power as a certain voltage and current as stated on that particular battery eg 1.5V as in an AAA, AA, C or D cell or 9V as in those small rectangular batteries or maybe 12V as in a car battery. There are many different batteries and a number of different voltages.

A fan requires power to operate, the amount of voltage and current will be printed on the label of the fan you told us that your fan has 230V 50Hz on it so it requires 230VAC mains voltage, the 50Hz is the frequency of the AC mains in your country.

other fans may require different voltages 5V 12V 24V etc they will also state if its voltage needs to be AC or DC

Dave