Two years in: Testing Dreifels 51Ah Pack Capacity

How time flies – it’s already been 2 years since I installed my 51Ah 17.7kWh LiNiCoAlO2-Cell-based battery pack.

For better battery health and less ageing my daily charge is only to 3.8V cell charge, I never discharge below 3.3V and balance the cell packs from time to time. As my daily commute is only around 11% of the total pack capacity, I never see what the real capacity of the pack is and if it has lost any capacity.

Using ‘Tesla-speak’ I drive in trip mode only 1-2 weeks total per year. And there, I never really drive the pack to full capacity. I charge the pack to capacity to get 350+ km trips for my longer daily stages.

This is why I – from time to time – plan a full day worth of driving as a one-day trip with the expressed goal of driving the battery to the very last Wh. (like here, where my pack still had 17.722kWh capacity)

And, yes, I could just use my high-tech battery workstation to extract the capacity of one string and extrapolate from there (which I do every single time I balance my pack) but driving the full pack to capacity is sooo much more fun! 🙂

Let’s see how much my pack has lost in 2 years and ~45,000 km.

One very important part is to charge the battery pack very, very slowly to a OCV of 4.20V. In TW560’s case this means to charge normally until Dreifels’ DFC3.0 controller cuts off the charge and then change the discharge depth. With this, the controller will add another x Ah and I do this at 230W for many hours – ideally until just an hour or so before I start my trip.

With this done, the next morning, I enter today’s discharge profile and am greeted with a very interesting range prediction:

Overly confident range indication

Overly confident range indication


 
Let’s do this! I’ve mapped out a route taking me from my home to Strasbourg and back via southern Germany. The route itself is around 440km with a multitude of possible extensions at the very end to add 20-60km depending on how the DOD looks like.

Ready for the test!

Ready for the test!


 
It’s a beautiful day and even if I shouldn’t take a route that involves any big climbs I have decided to drive across the black forest because it’s just a very nice place and the small roads wind their way up and down the hills 🙂

Leaving early gives me one nice side effect – a sunrise!

Driving on sunshine :)

Driving on sunshine 🙂


 
Not much to report from driving across the Black forest except…I drive very carefully and get as much energy back as possible. Consumption is very bad, as I’m going from 400m to 1100m.

Black forest, Germany

Black forest, Germany


 
When low consumption is the goal, driving across the black forest hills isn’t really the best thing to do – but the views and empty roads are totally worth it.

Up, up, up - munching into my range!

Up, up, up – munching into my range!


 
I finally make it to the plateau on ~1100m altitude. Consumption is at a staggering 56Wh/km and does not bode well for any distance record 🙁

On the plateau

On the plateau


 
At least I can see the Rhine valley and Voghese Mountains in the distance and a 35km drive down to 320m altitude, hoping to get back to an acceptable overall consumption.

France in the background - time to recuperate

France in the background – time to recuperate


 
As every EV driver will confirm, there is nothing more satisfying than driving downhill and see your range grow whilst covering distance at the same time! I got my consumption back down to 39Wh/km and am hoping that the flat Rhine valley will help lower my consumption even further.

France, flat, flat, flat

France, flat, flat, flat


 
As there is a light breeze, driving through forests shield me from the wind and allow me to go at even lower levels of energy consumption.

Protected from the winds

Protected from the winds


 
Time to look at how the voltage levels are – OCV is a very good indicator of how much the battery has been discharged – I’m very happy with the current levels and believe that a range record is still possible!

176km in and still at 381V - not bad!

176km in and still at 381V – not bad!


 
I really want to reach Strasbourg, not only is this a beautiful city worth a visit anytime, it’s where the Black Forrest has ended and allows me to drive eastwards without too many hills to cross. I’ll have to drive across another hill range later – we’ll cross that bridge when we get there. 🙂

Driving along the Rhine

Driving along the Rhine


 
TW560 and I arrive in Strasbourg with a growing confidence that this is a very good drive and the battery is still in very good shape. With the new seats, this drive is not only very economical, but also very comfortable!

Strassbourg - not stopping!

Strassbourg – not stopping!


 
About an hour after crossing back into Germany and on my way to Villingen-Schweningen, the controller thinks we’re halfway: Wow, just look at those numbers: You’ve gone 249km and there is still enough charge in the battery to go another 249km? (I will always remember my first TWIKE adventure 2008 crossing the Swiss Alps on a 40km-range battery!) We’ve come a very very long way!

Halfway - 370V!

Halfway – 370V!


 

Fast-forward 175km and I’ve crossed another hill-range taking me from 130m up to 800 and back to 400. The battery’s voltage is dropping ever so slightly faster than expected but I’m not yet worrying if I’m going make it back home.

Hohentwiel and Switzerland in the background

Hohentwiel and Switzerland in the background


 
Eventually, I get very close to the maximum capacity of the battery and only get to do one of my 5k add-on laps close to my home which I know really well.

The good news is that today I broke the existing record for TW560 on one charge – I upped it from 460km to 472km. This gain was fully and only achieved by driving much more efficiently as last time, because my feeling regarding the capacity wasn’t wrong – the battery has lost some capacity: 21km or ~4% less. (I’m going to forget the the 0.66% margin of error the controller is making over a 472km distance!)

Really proud of my consumption today!

Really proud of my consumption today!


 
Next year I’m going to try to drive even more careful and choose a better route that will allow me to go below 34Wh/km…stay tuned!

471.9km on 16.6kWh

471.9km on 16.6kWh


 
In this last picture the 10% corresponds to the Ah discharge model which is notoriously difficult to configure and I am still trying to get to be as accurate as the Wh model with 4%.

16.6kWh capacity left

16.6kWh capacity left


 
For those interested in some more data – I’ve started to keep a tally of all my capacity tests and will eventually start an own page tracking this pack’s capacity decline.

Date Wh Capacity Yearly loss Total loss 38.5Wh 55.5Wh
11.08.16 17,722 460 319
01.05.17 17,172 3.10% 3.10% 446 309
10.09.18 16,601 3.33% 6.33% 431 299
16.03.19 15,916 4.13% 10.19% 413 287
17.07.19 15,873 4.39% 10.43% 412 286

 
I’m happy with the current decline it means that it will take about another 6-8 years to get to a trip-mode 200 km range which is still very far if you are sitting in a TWIKE! This was one of the design goals for the new battery pack: 10 years at a minimum range of 200km – goal achieved! 🙂

Now to some data-driven visualization of today’s trip – elevation & GPS track!

Elevation model for today

Elevation model for today


 
All on one charge!

All on one charge!