Timeline for Calculating engine starter’s energy use
Current License: CC BY-SA 3.0
12 events
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| Aug 29, 2013 at 8:12 | history | edited | user6972 | CC BY-SA 3.0 |
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| Aug 29, 2013 at 8:06 | history | edited | user6972 | CC BY-SA 3.0 |
added 494 characters in body
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| Aug 28, 2013 at 19:22 | comment | added | user6972 | Does that matter? We're talking about a small difference 20kW-200kW (1.7 kA-Hr to 17 kA-Hr) vs a battery with loads at < 1 A-Hr. Your question of efficiency (how much energy is used to generate that engine's output power) is much harder to answer and is engine specific and I can't find any published info on that. | |
| Aug 28, 2013 at 19:00 | comment | added | theUg | Judging by some power curves for 4-cylinder engines, idling makes around 25-40 kW or around 20-25% of the max power. | |
| Aug 28, 2013 at 18:57 | comment | added | user6972 | We're really out of the realm of physics and into engineering. 100kW is only about average rpm for 30-40 mph for most 4 cylinder engines and less for 6. If I have time I'll make a spreadsheet with the numbers for you -- assuming I can find manufacturer's curves on an engine. | |
| Aug 28, 2013 at 18:31 | comment | added | theUg | Not really, no. But a good example with ubiquitous engine would be helpful. That very Civic, for instance. And I think important part in the calculations is to keep the engine power output realistic — nobody is going to sit on the red light with throttle fully depressed producing 100 kW. And I hope I don’t discourage you with my comments — I’m not being picky, but trying to crystallize the best answer it could possibly be. | |
| Aug 26, 2013 at 19:03 | comment | added | user6972 | It would take multiple days 24/7 of lights/AC running to compare to the engines power output. I didn't say it was possible with a 100 amp-hour battery, that would be silly. The power we are talking about for the engine is output power, not power consumed/used. Every engine has a different efficiency ratings so it is hard to give a specific example. Do you have a specific engine in mind? | |
| Aug 26, 2013 at 4:44 | comment | added | theUg | Not sure about multiple days. Headlights left on can kill the car in a few hours (still hours, so not a problem for start-stop). And what about any efficiency losses? For instance, 100 kW motor consumes so many joules per second — say, it makes 25 kW at idle, then it ideally consumes 25 kJ of energy per second, but how many Joules of fuel is consumed to produce those 25 kW? | |
| Aug 26, 2013 at 0:47 | comment | added | user6972 | There's really no comparison between the amount of energy used in a running engine versus anything else in a car unless you are running the headlights or a pure electrical AC system for an extended period of time off the battery (multiple days). Most standard car batteries only have 100 Amp Hours of capacity (1200 watts @ 12V), which is ~ 1/83 the power expended in this 134HP example engine. | |
| Aug 25, 2013 at 21:34 | comment | added | theUg | Good edit. Let’s see how people vote on that during the week, and if there are other comments or answers. Although there’s one more thing — what about consumption from lights, radio, electromechanical AC that would run while the engine is stopped? Would they be on the same level of insignificance as the starter’s use? | |
| Aug 25, 2013 at 18:35 | history | edited | user6972 | CC BY-SA 3.0 |
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| Aug 25, 2013 at 5:11 | history | answered | user6972 | CC BY-SA 3.0 |