• posted on January 7, 2004, 6:01 pm
Hi
My "theoretical" knowledge of electrics is next to nil., can anyone tell me how to calculate the load (in amps) for the following:
7 x 18w 2D Lamps 2 x 4" inline fans (wattage unknown)
I cannot determine the "wattage" or ? for the fans from the scant documentation with them but they are these...
http://www.tlc-direct.co.uk/Main_Index/Ventilation_Index/4_Inch_Fans_Duct/in dex.html
I have a IR time lag switch which is rated at 6 AMPs, hence the question. All this is hopefully being switched from it.
I have looked at the TLC Ohms law calcuator? 240v @ 6 AMPs = 1440 watts? Dowes this mean the switch will cope with 14 x 100w light bulbs attached? If so it should do what I need. I'm guessing at this point though.
Tony

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• posted on January 7, 2004, 6:17 pm

Your later fragment from the TLC website has it right: amps time volts = watts, so amps = 240 / wattage. Your itty-bitty inline fans will draw very little, maybe 30W each; your total wattage for this lot will therefore be around 200W, so 5/6th of one Amp. So, the switch ought to cope just fine.
As it happens, neither flourescent lamps nor fan motors are totally "simple" loads for switches: depending on the exact contact arrangements the switch might need to be derated to, ooh, 3A for such loads. You've still got lots of switching capacity in hand, so you should be just fine.
HTH - Stefek

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• posted on January 7, 2004, 6:26 pm
On Wed, 7 Jan 2004, enuff wrote:

current (amps) = power (watts) / volts (assuming linear load...)
therefore the current at 230 volts will be 0.55 Amps
However there will be losses in the control gear (ballast etc) and it is not a purely linear load and the mains voltage is unlikely to be 230 volts all of which make it very difficult to calculate an accurate figure.

there is no mention on that site - you might like to contact the distributor and enquire.

You'll probably be fine. If the circuit is fused at 6 amps or less then you will definitely be fine.
--
Alistair Riddell - BOFH
IT Manager, George Watson's College, Edinburgh

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• posted on January 7, 2004, 11:03 pm

Wattage of lamp * 1.8 = total wattage is the formula for all discharge lighting.
Jon.