I am preparing to test a battery-powered device and I am interested in determining its load on the battery. The load is periodic, but not constant, varying from about 11 watts to about 65 watts depending on what it is doing.
A web search for battery simulators located the Keithly 2302 and 2306 instruments. Does anyone have esperience with those, or can recommend a similar or better instrument?
I guess what I really need is a low-voltage DC watt-hour meter.
You can pretty easily make a watt-hour meter by using an analog multiplier (such as AD534), which will give you an output proportional to watts, and a voltage-to-frequency converter, which can be connected to a counter to give a watt-hour reading. There are also battery "fuel gauges" made by Maxim, and maybe TI, Linear, and Intersil, that can be matched to the battery chemistry.
For a battery, you can probably get a good enough idea of the load by just monitoring current, and converting that to ampere-hours, which is how batteries are usually rated.
Paul
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Good idea.
One challenge I have is that the load is so spiky that the battery cannot fully deliver the current needed, which is seen as a drop in voltage during the worst part of the current spike. Since the battery is essentailly current-limiting, base, I guess on the limits of its chemistry, it is difficult to measure the power being consumed.
Good idea.
One challenge I have is that the load is so spiky that the battery cannot fully deliver the current needed, which is seen as a drop in voltage during the worst part of the current spike. Since the battery is essentailly current-limiting, base, I guess on the limits of its chemistry, it is difficult to measure the power being consumed.
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It's always good to add a low ESR capacitor across the battery, close to the load that is drawing such spikes. That will smooth out the current from the battery, and keep the voltage steady, making it easier to read it. You may also want to add a small inductance from the battery to the capacitor, to keep the current spikes from being drawn through the battery.
Paul
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