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I have a friend who is getting into quadcopters and being the good techie buddy, I'm trying to find the right technology for battery monitoring so his expensive machine does not fall out of the sky unexpectedly.

So far the only technology for hobbyists that I am seeing is voltage monitors, which aren't really useful for this battery chemistry. With the flat voltage curve LiIon has I'd expect a voltage monitor to falsely report a low battery when you draw extra current and indeed I'm seeing exactly this when my buddy does fast maneuvers mid flight.

In my day job we use charge counting battery monitors (BMS) for this battery chemistry. Usually custom designed for the battery pack (just like for laptop batteries, etc). Sometimes built into the battery pack, or sold by cell suppliers.

Have I missed a product for electric aircraft? Are hobbyists in the battery dark ages?

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  • $\begingroup$ It looks like 3D robotics has a smart battery that might be using proper tech. $\endgroup$ – hauptmech Jan 2 '16 at 23:10
  • $\begingroup$ Modern batteries used in smartphones have a builtin Battery Management System (BMS). If you have access to an Android device, open a terminal and check the values in /sys/class/power_supply/*battery/*. $\endgroup$ – ott-- Jan 3 '16 at 3:48
  • $\begingroup$ @ott-- Are you saying that hobbyists are wiring their android phones to quadcopters somehow? $\endgroup$ – hauptmech Jan 3 '16 at 4:51
  • $\begingroup$ The idea is to use a Li-Ion battery with a builtin BMS. In the Android source you could check how to extract the values. $\endgroup$ – ott-- Jan 3 '16 at 16:20
  • $\begingroup$ @ott-- Ah, I get you now. Use the System Management Bus. Yes, I do this with a research UGV I designed using the 2590 packs I linked above. At $350 a pack they are a bit pricy for a hobby and I haven't seen any indication that hobbyists are using them. The 3D robotics smart battery linked above is the same. I have not checked if DJI's smart battery (or the 3D robotics one) use a security protocol.... $\endgroup$ – hauptmech Jan 3 '16 at 20:36
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Proper Lithium Ion battery fuel gauging and management is not really used in the hobby world. System specific batteries (3DR Solo, DJI Phantom) exist but generic components for people building their systems from components do not.

Probably not worth the cost for mini-quad racing type stuff. Possibly a business opportunity for prosumer systems.

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  • $\begingroup$ If you think this is the best answer, you can accept it as correct. $\endgroup$ – Chuck Jan 7 '16 at 21:56
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Texas Instruments makes a line of "battery fuel gage" IC's. I don't know that they come in a standalone solution, but it shouldn't be too big of a deal to poll it with the microcontroller that runs the flight controls.

Read more here, but highlights include:

The fuel gauge provides information such as remaining battery capacity (mAh), state-of-charge (%), runtime to empty (minutes), voltage (mV), current (mA), and temperature (°C), as well as recording vital parameters throughout the lifetime of the battery. The device also supports interrupts to the host to indicate detection of a variety of important battery conditions to the system.

I think the link I posted is to one particular chip, but there's a family of them. The one you (your friend) will need specifically depends on capacity, current, etc. Hope this helps!

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  • $\begingroup$ Yup, I know the ti chipsets pretty well. this is what we use professionally. But what do hobbyists do? $\endgroup$ – hauptmech Jan 2 '16 at 22:35
  • $\begingroup$ @hauptmech - I'm not sure what more you're looking for. I would say that a "hobbyist" either uses an off-the-shelf aircraft and gets whatever comes with it (undervoltage low battery warning like your friend has) or they build their own circuit with chips like the ones I linked. Otherwise, how would you update that you replaced a battery, or update parameters like chemistry, capacity, nominal voltage, etc.? To answer your question exactly, hobbyists wait for the low battery indicator to alarm. $\endgroup$ – Chuck Jan 3 '16 at 14:13
  • $\begingroup$ What seems to be available are raw cells (which I knew) and voltage monitors which are not very useful when there is power fluctuation. I'm not seeing any indication that boards for hobbyists using a battery fuel gauge like you linked exist. No generic smart batteries. No raw PCB's. (The BMS PCB stays with the battery, not the main system, re updating parameters). $\endgroup$ – hauptmech Jan 3 '16 at 20:49
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Depending on the cost of your aircraft and the installed autopilot, there may be an approach, though, as @hauptmech mentions, industry doesn't have come down to a feasible solution, regarding the remaining charge in a Li-Ion battery.

For example, if your aircraft uses the Pixhawk or APM autopilot, they include a battery module which has a current sensor.

If you calibrate the current sensor adequately, you may use the reported mAh consumed to estimate the remaining battery life. Keep in mind, though, that as the battery ages, the total mAh it can store are reduced.

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