.

European Commission project  for your Life & the Environment click here ISO 9001 quality  company	Oxygen Monitors & water quality monitoring Instrumentation Environmental & sustainable water treatment to save the planet	| Contact us  | About us |  Search |  Shop ||
Web  sites               | DrydenAqua |  AFM  |  Ozone | Membrane filtration | Swimming Pools |  Instrumentation       | Index for instruments | Oxygen probes | AquaTraul O2 monitors |  Refractometers | bacterial dip slides | Total Gas | Water test kits         | index for water test kits | Swimming pools | aquaculture & aquaria | drinking water | water treatment |

Voltage drop in 12v dc power supply cables

Norwegian version

The AquaTraul is powered by a 12v dc supply, it is important to insure that the cables used to connect the AquaTraul to the power supply are of a sufficient thickness to avoid a voltage drop.  The voltage required by the AquaTraul is 12vdc to 15vdc,  if the voltage falls below 11.7v dc then communication with the unit will fail.

Wire thickness is measure in several different conventions, AWG = American Wire Gauge, SWG is used in the UK or it my be designated by diameter in mils = 1/1000 of an inch.

When working in 12v dc the choice of wire should be determined in order to minimize voltage drop and its resultant high current. Although the effect of voltage drop.   The formula is as follows;

E =  (0.0164 x I x L) / S

E = voltage drop in volts

I = max current in amps  ( 1 amp for 1 x AquaTraul)

S = conductor cross section in square milli meters

L = total length in metres from the +ve source to the load ( or AquaTraul) and back again.

***************************************

Example.

I = Maximum current load of 1 x AquaTraul = 1 amp

E = voltage supply = 12.5 v

S = 1.3mm

L = 200m this is equal to a two core cable 100m in length

E = ( 0.0164 * 1 * 200)/ 1.3     =   2.52 volts

************************************

Example 2

If we take the above data,  how would you calculate the diameter of the 100m long wire to insure that the voltage drop does not exceed 0.5v.

if              E =  (0.0164 x I x L) / S

then     S = (0.0164 x I x L) / E

so        S = (0.0164 x 1 x 200)/0.5    = 6.56 squ.mm

******************************************

Additional Notes

The AquaTraul uses very little power,  the main component that requires energy are the alarm and control out-puts.  The actual power consumption by the AquaTraul is 0.8 amps when all relay out-puts are activated.  However if none of them are activated then the power consumption is approximately 0.2 amps.  The choice of cable therefore may not need to be as large as given in this page,  however if you base the calculation using the above equation,  you can be assured that there will not be a voltage drop issue.