Posted: Mon Apr 12, 2010 7:45 pm Post subject: Info: Calculating Bus Cable length against voltage drop
Hi,
maybe for someone the following considerations are helpful:
I had the issue of having a given cable (given R/m) and bus
members connected to them in equal distance to each other.
Since taking the total current and muliplying it with the total R
leads to huge - and false - drop results, I evaluated the formula
for that:
dist_step/2 * (x^2+x)*I*R = Vdrop@x
with:
dist_step : is the distance between each member
x: is the member where the voltage drop is calculated
I: current consumption per member (all the same)
R: resistance per meter (cable)
E.g. having 50 members with 20mA each and 2m space between;
R = 80mOhm/m leads to a drop of 4.1V at member 50 (100m total
distance). Distance at x is certainly given by x*dist_step.
Compare: Itotal=1A, Rtotal(100m) = 8Ohm => Vdrop=8V,
which would be more than pessimistic.
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