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Directory:Bedini SG:Battery Characteristics:Hard to Measure

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Directory > Bedini "School Girl" > Battery Characteristics > Hard to Measure


Battery Characteristics are Hard to Measure

Contents

Hard to Measure

How to Measure

Basic Considerations by Dennis Turner

October 20, 2004

Hello Sterling,

I have been observing your recent data collection re SG Bedini. I think you are hoping to be able to draw useful conclusions regarding efficiency in/out by logging changes in battery voltage over time. I think you are discovering that it is very difficult, if not impossible, to draw accurate conclusions by this method. This is because of the potential variations in battery capacity among your different batteries. It's even hard to compare one battery to itself, because of the progressive capacity changes over the life of the battery.

A graphic example is a worn out, damaged, or highly sulphated car battery (or solar system battery). It can show a normal voltage at rest, but the voltage will drop abnormally fast under a load (as in load testing). Likewise, the voltage reading will go back up abnormally fast under a charge. This, as you know, is because of a reduced battery capacity.

The only way to know how much energy is actually stored in a battery is to drain it dead and measure the work done. But even this is difficult, because your rate of discharge will affect your results. A high rate of discharge will show less total work than a low rate, because of proportionately higher losses due to resistance at higher current draw.

Even brand new batteries will have some variations in capacity and, therefore, varying rates of voltage change under equal charge/discharge conditions. These hidden variations can lead to erroneous conclusions

I believed you mentioned the need to test specific gravity. You are on the right track, but I doubt even that would suffice to accurately measure energy in vs. out, unless you are measuring fairly large differences. But even then, you don't really know how much the hidden variables are contributing to the measured results.

This difficulty in accurately measuring energy is why so many well intentioned people initially think they have something when they don't.

My background is in AE systems, construction, and mechanics, mostly of a practical nature. I'm not an electronics specialist, but I thought I would offer my observations based on my experience with batteries.

Keep up your experiments and sharing. It's nice when we can all learn together.

Regards,

Dennis Turner

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