I was diagnosing my alternator to find out if it is working properly. It seems like it is doing its job well. Anyway, interesting thing I found out was that the average voltage output from alternator varies with varying throttle / actions. Is it possible that one can model the engine load / torque based on the voltage output from alternator? The answer in my mind is No, unless we can relate the "Mechanical" torque and "Electrical" torque of a system with each other. Thoughts?

1 Answer 1


No is the simple answer. The voltage output from the alternator varies, as you found out, with engine speed. It also varies with the state of charge of the battery and, to make it more complicated with the type of charging control system - some have a very "intelligent" control fitted.

The best solution for engine load information is from the OBDII (if the vehicle has it or an equivalent) if you can get the information as the engine ecu is mapping fuel volume spark time and duration and lots of other parameters constantly.

  • - Thanks for the answer. I figured out OBD port and have started collecting data..lets see if I can co-relate. On another note, I believe heavy duty vehicles like truck or tractors may not have any "intelligent" control, as they generally don't even have a regulator at alternator o/p and have a simple shunt for charging control. Do you think , (assuming the SOC is not varying much within 5-10 mins) in heavy duty vehicles we may see any co-relation?
    – Pudi
    Commented Aug 14, 2017 at 6:42
  • Most trucks / agricultural tractors have controlled charging systems - some have or had external regulation, others have the regulation built-in to the alternator and only have two wires (one thick to battery and one sense), some have more... There will be no relation between torque and alternator output as explained above.
    – Solar Mike
    Commented Aug 14, 2017 at 6:48

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