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Old 05-27-2014, 09:17 PM   #1 (permalink)
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Measuring Charge Efficiency

There has been some discussion of replacing a lead-acid car battery with super capacitors and/or LiPoFe4 batteries to save weight and possibly eliminate the need to periodically replace the battery. Some sources place charging efficiency for lead-acid as low as 50% when charging near full capacity. Sources also claim charge efficiency as high as 90% for LiPoFe4 at near full charge, and >95% efficiency for charging capacitors.

Not only is there charge efficiency to consider, but also discharge.

I'm looking for a way to compare charge/discharge efficiency. My idea is to measure cumulative Wh or Ah output from the alternator for a given distance or engine running time, and compare the results to battery alternatives.

The problem is controlling for the many variables in electrical use. If the test period wasn't sufficiently long enough, a single trip at night running the headlights would significantly skew the results.

1. What device would I use to measure the cumulative Wh or Ah? I'm thinking the Watt's Up would do the trick, but don't know how it would work, or how to protect it from the large discharge of starting a motor.

2. How should I control my variables to get the most accurate efficiency results? Ideally I would measure the amount of power going into the battery, and the amount going out. Any idea how to accomplish this? Perhaps bench charging/discharging is a better way to control the variables, but I'm very curious of what the results would be in actual vehicle use.

I realize the impact on fuel efficiency is minuscule, but my curiosity must be satisfied!

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