Mercane single motor 8.8Ah battery range test

This post is a follow on from my repair post here. Well, looking at all this I'd say that my scoot has passed its battery test. and is pretty much "up to spec" despite nearly a year of use and some problems with the BMS and construction.

Introduction

To test the battery in the scoot I took it on this course:

So while I didn't tackle any significant hills (read mountains) I did indeed do some long uphill slogs. Here's the GPS data

When I got it home it was pulling Volts down to 44.2 or so on the milder hills, but still pulling better than it ever did on hills, and note how steady the speed was almost to the end.

Analysis

The interesting thing was the recharge: It took 271Wh to recharge (using my 150A meter to count that), and as the battery is rated at 422Wh this means I've used up about 60% of the battery total rated capacity. Now as anyone who knows much about batteries would know, getting that last part of the energy may be hard to get to and even predictable about how far you can go, perhaps even may damage the cells if getting to it (if you don't have a good BMS). Here is why: the discharge curve.

Looking at this test discharge of Volts vs Ah working out the area under the curve (using a near approximation and I've chosen to be a bit conservative) gives me 7.11Wh per cell. So with 13S4P that gives me 13 x 4 x 7.11 = 369.72Wh of actual usable Watts. Note how quickly that last bit of voltage at 3.4V per cell just dies off.

So while my cells are 2200mAh the difference will be small (if indeed it is any different and not just "rebadged").

For all intents and purposes I'm willing to call the 271Wh I put into it (on recharge) to mean that my ride took out 271Wh Effectively 75% depth of discharge. Given also that rapid fall off at the end that last unit may be quite unpredictable (and depend on hills), its best to not be relying on that being available. Meaning I won't get much more out of it than that (as you can see how the voltage plummets towards "out of juice" and I'm walking levels.

So a real world range of 20km "flat stick" on cruise control is reasonable. The less you do stops and starts of course the better because re-establishing speed will suck more energy than just maintaining it.

Thoughts

Knowing this curve you can more accurately use your Volt meter to understand how voltage (while riding) reflects your actual remaining range. For instance, when you see certain voltages under load (you'll note that flat road cruising voltage is different to that going up a hill, because of the load). To get the chart below I used the 2A discharge measurements of the Parkside battery (because I expect its pretty close to what I've got having observed my own discharge and the battery markings) and simply altered the scale on the Volts axis by multiplying cell voltages x 13 (because I have a 13S4P pack)

So seeing anything dropping down to 45V while under load means you're getting close to the end. If you're seeing 48V you've still got at least half your power left.

Next interesting thing is that if one considers that I needed (to supply to the scooter) 271Wh to travel about 19km that works out to about 1.4kWh/100km which (as mentioned previously in the article about my dual motor variant) is stunningly good efficiency and no electric car gets anything like this. Supporting my view that for short distance frequent trips a scooter is far more the efficient transport solution for cities.


It remains to be seen if I need to give this pack any more attention, but hopefully this shows how resilient they are and how easily rebuildable they are.

For how this started please refer to this post here