dauphin95 wrote:Hello,
How to calculate the necessary power of a 12V car alternator, to operate at 100%, 9 headlights of 130W.
Knowing that it will be a second alternator in addition to the one that is mounted.
I have two different calculations !!
The first 9x130 = 1170W output of 0.75 (1170x0.75 = 1560w: 12 = 130A
Le second 9x130=1170:12=97.5A
What is the correct calculation ???
I don't want to go wrong to order this second alternator!
Thank you to enlighten me!!!
Your calculations are far too optimistic.
An alternator has an efficiency close to 50% and its belt transmission has one of the order of 90%.
Electric power to be supplied: 130W x 9 = 1 W.
Power absorbed by the alternator: 1 / 170 / 0.5 = 0.9 W.
Alternator rating to be provided: 2 / 600 = 14 A.
Pay attention to the power taken from the engine:
1 CV = 736 W -> 2600/736 = 3.5 CV.
By taking a security of 15% which takes account of any misalignments and mechanical friction, the real practical power will be close to 4 CV.
The most powerful model we can offer you is a 12V 160A - see attached data sheet. It should suit you because its priming speed is quite low (1 rpm).
Public price incl.VAT = 522.65 EUR. 1 piece available to date. Delivered without pulley.
Rotation speeds of the engine and the alternator:
Minimum alternator speed> ignition point (1 rpm) = engine at idle speed.
Maximum alternator speed (approximately 15 rpm) <manufacturer data = maximum engine.
Diesel engine: 2000 rpm <cruising speed <4000 rpm.
800 rpm <Idle speed <1200 rpm.
Taking these considerations into account, the pulley ratio allowing to load correctly when the engine is idling and to obtain a maximum load at cruising speed brings us to a ratio between 2 and 3.
Advice: do not exceed a pulley ratio of 3.5 (premature wear of the belts).
Reminder: pulley ratio = diam. engine pulley / alternator pulley diam
Sincerely,
Frederic DESMONS
Electricity Product Manager for PROSHIP