EXPERT TIP #1: WEIGHT & LENGTH OF MAGNESIUM ANODE AFFECTS CP SYSTEM LIFE & PERFORMANCE

EXPERT TIP #1: WEIGHT & LENGTH OF MAGNESIUM ANODE AFFECTS CP SYSTEM LIFE & PERFORMANCE

Magnesium Anode Current Output & Service Life

Key Facts:

  • Longer anodes produce more current than shorter anodes.
  • Doubling the diameter of the anode will increase the volume (weight) by a factor of 4; yet, will only increase the current output approximately 15%. 
  • Greater anode weight (volume) increases the anode or system life.
  • Surface area of the anode is not as important as some people believe.
  • High potential anodes will always generate more current than a standard potential anode given the same resistance-to-earth.

Myths:

Almost a Myth - System life can be calculated by using the published deterioration rate of 17 lbs. per ampere year.  This is a good start but anodes, as they consume, will become physically smaller, therefore producing less current.  For that reason, we always include a "utility factor" when calculating anode life.  If basic calculations require 100 lbs. of anode material, specify a minimum of 130 lbs. of anode material, a 1.3 to 1 utility factor. 

Full Myth - Installing two anodes will double the current output.  Not true. In most instances, it will be less than double.  The distance between the anodes will effect how much total DC current the system can provide.  The farther apart the anodes are spaced from each other, the better.

The chart demonstrates the effect of various physical anode sizes to current output & service life.

                Anode Characteristics Comparison 
Dia.
 In.
Length
In.
Area
In2
Volume
In3
Res-to-Earth in
1000 Ω-cm Soil
Calc. Current Output Amps. 
13094.223.69.4Ω0.080 
230188.494.27.9Ω0.095 
330282.6212.07.1Ω0.106 
430376.8376.86.4Ω0.117 
160188.447.15.4Ω0.139 
260376.8188.44.7Ω0.160 
360565.2423.94.3Ω0.174 
460753.6753.64.0Ω0.188 
NOTE: The lower the Res-to-Earth, the higher the current output achieved by the anode

Example 1:

1" X 60" anode can generate 0.139 amps

2" X 30" anode can generate 0.095 amps

Note: The 1" anode is half the weight and twice the length of the 2” anode yet they have identical surface areas.

Example 2:

1" X 60" anode can generate 0.139 amps

4" X 30" anode can generate 0.117 amps

Note: The 1" anode generates more current and has 1/8 the volume (weight)with half the surface area of the 4” anode.


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4 years ago