Electric Starters
Cable Size
The start circuit between battery and starting motor, and control circuit between battery, switch, and motor solenoid must be within maximum resistance limits shown.
Not all this resistance is allowed for cables. Connections and contactors, except the motor solenoid contactor, are included in the total allowable resistance. Additional fixed resistance allowances are:
-Contactors (Relays, Solenoid, Switches)-0.0002 ohm
-Connections (Each Series Connectors)-0.00001 ohm
The fixed resistance of connections and contactors is determined by the cable routing. Fixed resistance (Rf) subtracted from total resistance (Rf) equals allowable cable resistance (Rc): Rt - Rf = Rc.
Battery Performance
Air Starters
Air Storage Tank Sizing
Many applications require sizing air storage tanks to provide a specified number of starts without recharging. This is accomplished as follows:
Where:
VT = Air storage tank capacity (ft3 or m3)
VS = Air consumption of the starter motor (ft3/sec or m3/sec) - see air starting requirements chart on next page.
T = Total cranking time required (sec). If 6 consecutive starts are required, use 7 sec for 1st start, (while engine is cold), and 2 sec each for remaining 5 starts, or a total cranking time of 17 sec.
Pa = Atmospheric pressure (psia or kPaa) - normally, atmospheric pressure is 14.7 psia or 101 kPaa.
PT = Air storage tank pressure (psia or kPaa) - this is the storage tank pressure at the start of cranking.
Pmin = Minimum air storage tank pressure required to sustain cranking at 100 rpm (psia or kPaa) - see air starting requirements chart on next page.
Air Starting Requirements
3600 Air Start Tank Sizing
