AC Alternator Load Loss on Engine Performance

Click For Summary

Discussion Overview

The discussion revolves around the impact of an AC alternator on engine performance, specifically focusing on the load or power loss experienced by a theoretical engine when the alternator operates at maximum capacity for a very short duration (0.005 to 0.010 seconds). The conversation touches on theoretical calculations, efficiency considerations, and practical implications of alternator operation.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks to quantify the power loss from an alternator rated at 40 amps and 110 volts, questioning the engine's performance impact during brief maximum load conditions.
  • Another participant points out that power is a time rate, suggesting that the duration of load may not be relevant for calculating power loss.
  • A third participant provides information on typical automotive alternator specifications, noting that they usually output around 14 volts and can deliver between 100 to 140 amps.
  • Further calculations are presented, estimating that if an alternator generates 14V at 100A, the power delivered is 1400W, but due to inefficiencies, the engine would need to produce significantly more power (approximately 2600W) to account for alternator and belt efficiencies.
  • Concerns are raised about the continuous operation of the alternator and the associated losses that may occur outside the brief maximum load period, suggesting these losses could be more significant than the short-duration load impact.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of the duration of load in calculating power loss, and there is no consensus on the exact impact of the alternator on engine performance. The discussion includes various assumptions and calculations, but no definitive agreement is reached regarding the overall effect.

Contextual Notes

Participants mention alternator efficiency ranges and the efficiency of the belt driving the alternator, highlighting the complexity of accurately determining power loss. The discussion also reflects uncertainty regarding the operational context of the alternator beyond the specified short duration.

Brian James
Messages
8
Reaction score
0
I'm trying to determine the amount of load (power loss) a theoretical engine will suffer from an AC alternator, such as one you would find on an automobile engine, they produce something of 40 amps with 110 volts I believe? To be specific, I'm curious to know how much a theoretical engine would suffer from an alternator when it is at maximum capacity for only .005- .010 of a second. I understand a lot more goes into it but if anyone has a general idea of what I could expect that would be appreciated
 
Science news on Phys.org
Power is already a time rate, so the duration doesn't matter. You have specified volts and amps: do know how to calculate power from that?
 
Most automotive alternators are regulated to output 14 volts +/- 0.5 with a maximum current output in the 100 to 140 ampere range.
 
Brian James said:
I'm trying to determine the amount of load (power loss) a theoretical engine will suffer from an AC alternator, such as one you would find on an automobile engine, they produce something of 40 amps with 110 volts I believe? To be specific, I'm curious to know how much a theoretical engine would suffer from an alternator when it is at maximum capacity for only .005- .010 of a second. I understand a lot more goes into it but if anyone has a general idea of what I could expect that would be appreciated

If we assume the alternator generates 14V at 100A then the power delivered by the alternator is 1400W. An alternator isn't 100% efficient so the engine will need to produce more power than that. This paper suggests alternator efficiency ranges from 55% to 80% and the belt driving it around 97% efficient.

http://www.delcoremy.com/documents/high-efficiency-white-paper.aspx

So if we assume 55% the engine would have to deliver 1400 * 100/55 * 100/97 = about 2600W.

That's the power the engine would have to generate if the alternator was running continuously at 1400W. If it's just for 0.01 seconds that equates to 2600 * 0.01 = 26 Joules. For reference a AA battery might contain about 5400 Joules of energy.

However what does the alternator do the rest of the time? Typically it's still turning so the engine will still experience losses and these could be considerable and more important than what it's doing for the 0.01 seconds.
 
  • Like
Likes   Reactions: billy_joule

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 2 ·
Replies
2
Views
8K
  • · Replies 39 ·
2
Replies
39
Views
5K
  • · Replies 30 ·
2
Replies
30
Views
3K
Replies
2
Views
2K
  • · Replies 26 ·
Replies
26
Views
4K
Replies
5
Views
3K
Replies
9
Views
3K
Replies
23
Views
3K