I'm working on a physics experiment where I have to investigate the effect of temperature on a battery's internal resistance. I know how to measure the internal resistance, but the problem is in changing the temperature. I need to heat the battery in a safe way so that it doesn't explode. I thought of decreasing the temperature instead of increasing it (for example, working on temp. from 25 degree C to -5 degree C). Is it better? If not, how can I heat the battery in a safe way?
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1$\begingroup$ You need to ensure that the battery has good temperature uniformity throughout its volume when you measure each resistance point. If you don't have the appropriate lab equipment for controlling temperature, you can try just leaving the battery outside your house in the shade and taking data points throughout the day and evening as the air temperature slowly changes. $\endgroup$– user93237Commented Feb 26, 2018 at 18:46
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$\begingroup$ Just use a sand bath: no messy oil, no possibility of ignition, etc. Check with a chemistry friend or colleague. $\endgroup$– Ed VCommented Apr 18, 2023 at 2:13
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2 Answers
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Submerse the battery in Mineral Oil. It is non-conductive. A few notes on safety however:
- Make sure you have a fire extinguisher rated for electrical fires (any household fire extinguisher should meet this requirement).
- Mineral oil burns, so take extra care if you use an open flame to raise the temperature of the oil bath. It's flash point is 160 C / 320 $^\circ$F, and boiling point around 260 C.
- Mineral oil quickly loses it's non-conductive properties if you contaminate it with water, so don't do that.
- Don't forget to stir your mineral oil bath to ensure uniform heating of the battery, and remember #2.
- Suspend the battery; you don't want the sides of your container touching the battery as they may not be in equilibrium with the mineral oil. Better yet, don't put the battery in the oil until after it is heated. Then stir and allow the battery to come up to temperature.
If you have the resources, transformer oil is a non-flammable version of mineral oil and would be safer. But anyone that can safely fry fish on a stove top could do this experiment safely.
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Given the three considerations of safety, uniformity of temperature throughout the battery, and convenience, I would suggest using the smallest battery practical. A small, say 9-volt, battery like those in smoke detectors, will change temperature faster than a car battery. The refrigerator and freezer in you kitchen may be fast enough. On the other hand, measurements will have to be made rather quickly and carefully, because handling the small battery will change it's temperature back quickly as well. Overall though, I'd say it's worth a try to just use the fridge. Maybe even hearing-aid batteries will work. Of course always protect the terminals from contact with anything conductive.
