[simplechamp]

Here is an excerpt from a review of the Castle Phoenix ICE controller, which can measure voltage ripple as part of it's data logging feature. The context is from the airplane/heli side of things, but regardless it sheds some light on voltage ripple and how low-spec and low quality batteries can cause problems.

"Battery Ripple Voltage: This is a really cool feature that no one else has implemented in an ESC. If you wanted to try and measure this any other way you’d need a lot of high-end lab equipment to do so. Basically, if you could graph the battery voltage between the pulses of the controller which happen tens of thousands of times a second, you’d be looking at a ripply line, not a flat line. As the controller allows energy to flow from the battery, the internal resistance of the battery affects (causes) the voltage to drop, even in that millisecond. This isn’t necessarily a bad thing when the battery and motor are properly matched, but it is a very good way to determine if, indeed, the battery is up to powering a particular application.

Generally speaking, higher discharge batteries will provide better performance and have less voltage fluctuation with changes in load, so lower ripple voltage. Let’s take this a bit further. The big capacitors on the controller are used to smooth out that ripply voltage. This is important because the FETS need to have a stable voltage or bad things can happen. The capacitors can only smooth out so much of this ripple. If the ripple exceeds the capabilities of the capacitors, you have a much greater chance of the controller letting go. This isn’t a defect of the controller, it’s just the physics. Use the ICE’s ripple voltage readings as a relative number. Try different packs in the exact same machine with the same gearing. Those with lower ripple voltage are the ones best suited for that application. The others may simply not be up to running that particular setup.

So, the ripple voltage measurements finally give you a scientific way to compare the C rating of a battery pack with other packs. This is something that consumers have needed for a long time. You are no longer at the mercy of the marketing guys’ declarations of C ratings. You’ll now have the ability to produce graphs that prove which packs are better!

If you happen to have a charger that displays battery internal resistance, this is also indicative of C-rating. Combined with the ripple current data you can determine if a particular battery is either up to the task for your application or starting to age.

Say you have a 500 size model and you’re running a 20C pack and have a 3D setup. You may very well see a big ripple. If you were to change the battery to a 40C rated pack, the ripple will decrease and the flight efficiency will increase. That 20C battery could be old, or just not up to the task for the kind of demands your power system is putting on it. It may fair better in an airplane application that draws less current, thereby allowing you to get some more life out of it.

The ripple will be more pronounced with a lower C‐rated pack in a high demand application, whereas the higher C-rated pack will reduce the ripple. To get a baseline, log when your battery pack is new and then check it periodically to monitor its health. You can also look at the wattage data and determine when the battery starts to head south, since the wattage will drop."