wire length versus energy consumption
wire length versus energy consumption
(OP)
I'm looking for a way to calculate the additional energy consumption of an electrical device, if the same current used for the device has to run through a wire with a given length, diameter and resistance, before reaching the device.
As an example, take a lamp with an energy consumption of around 60W, 5 amps and 12V, when connected near the power source, then insert an additional wire between the lamp and the source, e.g. a copper wire with diameter=1mm and length=10m. The heat losses caused by the electrical resistance of the wire will lead to a current reduction in the device, so if I want tho have still 5 amps running through the lamp, more energy has to be consumed.
Is there a way to calculate the additional energy consumption?
Appreciate any help, tanks
As an example, take a lamp with an energy consumption of around 60W, 5 amps and 12V, when connected near the power source, then insert an additional wire between the lamp and the source, e.g. a copper wire with diameter=1mm and length=10m. The heat losses caused by the electrical resistance of the wire will lead to a current reduction in the device, so if I want tho have still 5 amps running through the lamp, more energy has to be consumed.
Is there a way to calculate the additional energy consumption?
Appreciate any help, tanks






RE: wire length versus energy consumption
r = rho/A where rho is the resistivity of the wire and A is the wire area.
rho = 0.01724 mm²·ohm/m for annealed copper at 20°C. (0.01724=1/58)
RE: wire length versus energy consumption
RE: wire length versus energy consumption
Watts per second is not a meaningful unit for everyday calculations.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: wire length versus energy consumption
xnuke
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RE: wire length versus energy consumption
xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: wire length versus energy consumption
Watts = I²·r·D
I=5 (amps)
r=0.01724 (mm²·ohm/m)
D=10 (meters)
=5²·0.01724·10
=4.31 Watts
Or do I have to adapt the effective diameter aerea (0.5mm·pi=0.785mm²) for the r value?
RE: wire length versus energy consumption
I=5 (amps)
r=0.01724 (mm²·ohm/m)/0.785mm²
D=10 (meters)
=5²·0.01724/.785·10
=1.1 Watts
xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: wire length versus energy consumption
Shoul;d be 5.5 W.
xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: wire length versus energy consumption
So, connecting a 60W-bulb to a wire descibed above will consume 65.5 Watts (theoretically). Correct?
RE: wire length versus energy consumption
An incandescent lamp is basically a resistance, so as the voltage goes down, the current goes down, and therefore, the voltage drop in the wire goes down. And power consumption goes down. Other types of loads can behave differently as a function of voltage.
RE: wire length versus energy consumption
I don't understand much of voltage drop, but it seems logic that the lamp manufacturers will rate the wattage of the active state rather than the initial energy consumption. The latter would be orders of magnitude higher because tungsten has a much lower resistance in the cold state than in the hot state.
RE: wire length versus energy consumption
And yes, this is ignoring the initial warm-up phase - I'm talking steady-state conditions.
In power systems, all voltages are NOMINAL, and variations of +/- 5% are normal and +/- 10% not uncommon.
For an incandescent lamp, operating at 90% voltage reduces the power consumption to 81% of nominal.
Utilities often take advantage of this by slightly reducing voltage supplied to customers to reduce peak demand.
RE: wire length versus energy consumption
Therefore exact values of power consumption will be easier to measure than to calculate. However, I guess the formula ist still usefull to estimate a relative increase in power consumption compared to the original device.
RE: wire length versus energy consumption
One caveat. The distance D has to include both the wires running to the lamp. So, if there are two 0.785 mm² wires, each 10 m long, then the total power is 71 watts.
RE: wire length versus energy consumption
RE: wire length versus energy consumption
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com