![]() We would get more heat (power across the load), but less running time. If we dropped the load down to 0.4Ω, the same battery would be drawing 2.5A, and the battery would last 1 hour (that’s its rating). If our circuit drains current at a rate of 1A per hour, then we can expect to continue at this rate for 2.5 hours. The nickel metal hydroxide battery above has a capacity of 2,500mAhour or 2.5Ahour. This “heater” will have a constant current of 1A per second as long as the voltage remains the same. ![]() Going back to our 1Ω resistor example above, this is pretty straightforward, because the load does not change. We must therefore know the amount of current our circuit needs, to be able to calculate how long the chosen batteries will last, based on their advertised capacity. ![]() It is every designer’s dream to never have to change or recharge batteries, but with the technology of today’s batteries, that just isn’t possible. When multiple cells of the same type are put in parallel, we get twice the capacity. When multiple cells of the same type are put in series, we get twice the voltage or potential to push electrons through a circuit. Batteries usually have ratings tattooed on their skins describing their capacity-numbers such as “1.2V NiMH 2,500mAhour” or “3.7V Li-ion 5,800mAh.” ![]() The chemistry and size of the battery determine the energy it can store. The volume/weight is inversely proportional to how long it will power your equipment before it must be changed (or recharged). ANALOG 12V BATTERY METER PORTABLEWhen you choose a battery to power your portable equipment, you will most likely make a compromise on the size of the battery. This was named after him as Coulomb’s law. His later work in physics led to the discovery of the inverse relationship of the force between electric charges (and magnetic) and the square of their distance. During his decades of military service, he was continuously involved in engineering fields, including structural and soil mechanics. I do, however, want you to think about the gas tank in your car, because it does relate to the “coulomb.” First, like many terms, the coulomb is named after its discoverer, French military engineer and physicist Charles-Augustin de Coulomb. In the near future, I foresee an environmental tax to offset the damage we’ve done, and to help pay for what is necessary to reverse it. It’s hard to guess the real reason for such swings-politics, reserves, auto industry and the like. While they are now rising slightly, 20 years ago I thought I’d never see those prices ever again. Long lines and prices approaching $5 a gallon seemed like the “new normal” (a pandemic of another kind).Įventually, the pendulum swung back and we saw gas (and heating oil) prices below $2 a gallon. ![]() ANALOG 12V BATTERY METER DRIVERSWhen gas shortages hit, rationing meant assigning drivers to odd or even days, on which access to the pumps would be granted. Often, they would check the fluid levels under the hood, and even add air to your tires while their gas pump was adding fuel to your tank. In the past, these service or gas stations would fight for your business by giving away premiums like beverage glasses, for the privilege of pumping your gas for you. We’ve also lost the “service” from service stations. Throughout my lifetime, gas prices have really fluctuated. Note that this project is designed to be more of a theory-lesson than a real practical unit.One thing the COVID-19 pandemic brought on was lower gasoline prices. The maximum current is recommended at 5A, however with a few minor tweaks you can easily change that. This device is a simple current meter, set up so you can use it while camping to see what sort of power your 12v devices are using. This is more of an electronics lesson than anything else, We go over the fundamental electronics for building a complete circuit idea, discussing Ohm's law, Kirchhoff's law, analog and digital values, and the difference between website and embedded-C code. ANALOG 12V BATTERY METER CODEPlease see the attached Camping-Power-Meter.zip for code files. ![]()
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