Waynemarlow said:
Can I ask a question, why the need to run a 15S battery, it pushes the voltage up into the realms of having to replace the capacitors on the controller, serves no real purpose now that the field weakening is starting to give good cadence up to about 120 rpm and basically makes the batteries more expensive as you have to use specialised BMS’s and chargers.
Wouldn’t the simplest thing be to simply use 48 volts or even 52 volts that most use ?
I will try to answer quickly, as the answer is not simple.
1 - Before making the 15s battery I asked people who were developing the firmware if there was any problem. Casainho told me that, from the firmware point of view, there was no problem, and that it would even be interesting to have someone test it.
2 -
I do not advise anyone to make a 15S battery. Only if you are a person with a lot of knowledge of electronics. I am a telecommunications and electronics engineer.
3 - I make my batteries with BMS at home. DIY. They have bluetooth management. If I have a problem, I can always redo the battery. I just have to buy a new BMS.
4 - When I decided to make a battery with 15S, there was still no talk of "field weakening". At that time, the hypothesis that existed to have a good power, at a high cadence, was to increase the voltage.
5 - As you may know, the higher the current the motor consumes, the greater the heating. The higher the voltage, the lower the current, to obtain the same power. So we consequently have less heating.
I usually do off-road mountain trails. With quite a few climbs. In summer, the temperature is easily between 30 and 40 degrees centigrade in Lisbon, Portugal. Therefore, the engine easily reaches high temperatures.
The decreased heat in the motor was also a very important reason.
6 - If I have 15 cells instead of 14, I can have more than 7% energy, which allows me to have a lighter bike, with more energy. I use samsung 50E, 21700, 5000 mAh batteries. With a 2.1 KG battery (2P15S) I can have about 550 Wh of energy.
I take long trips on autonomy, bikepacking, and for me weight is important. Also for making mountain trails, weight is important. I like agile bikes.
7 - The battery, effectively never charges up to 63V. Generally, when installed on the bicycle, it never exceeds 62.5V.
The controller capacitors are 63V. But the manufacturer's specification always gives a tolerance of 5 to 10%. So we can get to 66 or 69V.
If we start with 62.5V, after a few kilometers the battery is already below 62V.
I've ridden more than 1000 km, and I haven't had any problems so far.
Another user of the forum has also ridden more than 1000 km without problems, with a 15S battery.
When I connect the battery to the motor, it is always without voltage, because it is turned off by bluetooth. It is to avoid voltage spikes when making the physical connection.
8 - BMS and chargers I buy on Aliexpress, and are a little more expensive than for 14s batteries. They are 5 to 10% more expensive, or even at no additional cost.
9 - As the nominal voltage is 55.5V, I almost always have voltages around 50V, which allows me to have a good performance most of the time.
10 - Finally, according to what Casainho says, the "field weakening- FW" removes some performance from the motor, although it allows a better management of the cadence / power.
What I noticed, in practice, is that with 15S, I don't need the FW, to have a good performance at high cadence. I also have a short time above the 100, 110 cadences.
Conclusion:
I am very pleased, so far, to have taken this option.
But I know I'm taking a little risk, as I am one of the few users of the TSDZ2, which uses 15S.
I hope I have answered your question.
Azur
Thanks also to all the other participants in the development. 
