Oberon,
Thanks for creating and updating this document. Seems some people find this useful and are willing to read such a long document (it is a surprise for me as no many people read even the first few pages of the user manuals).
I see you used appropriate fonts :)
I should read the entire document and provide feedback but I feel to lazy to do that and still have a lot of work with the PCB's on the DSSR50 and even some small adjustments to SBMS0 before ordering new batch.
Just started to read first pages.
In Overview point 2 the reason PWM is not needed or any other form of constant voltage charging is because Lithium hates constant voltage charging and for the particular case of LiFePO4 (what most people use) it is not even helpful since at most you may be able to push another 1% SOC by using some form of constant voltage charging.
PWM chargers where created as a simple charger for Lead Acid batteries. They will be fully ON for the constant current part of the charging so panels directly connected to battery same as DSSR20 is doing but that sort of charging will only get the Lead Acid to maybe 70% or 80% SOC depending on charge rate and battery characteristics and so from that point constant voltage will start and to active that in the simplest way possible they use PWM. They are basically turn OFF the charging for a small interval of time and turn it back ON in order to keep the battery voltage around 14.4V (or whatever the absorption voltage is for the specific battery).
The thing is that Lead Acid batteries hated being at any other SOC level other than 100% fully charged but in offgrid solar PV installations this was not possible due to the short day especially in winter so people where forced to use gasoline generators to at least once a week give the battery a proper full charge.
An MPPT also uses PWM but in a different way an at much higher frequency as it has a small energy storage device usually in the form of an inductor and also large electrolytic capacitors and so this allowed better utilizing a PV panel not matching the battery voltage for the constant current part of the charging but for the longer part the constant voltage charging MPPT offers no advantage as there only part of the available PV power is utilized so there is no advantage form MPPT over PWM.
Now the type of Lithium battery in your cellphone or most other portable electronic devices also uses constant voltage charging when it gets above around 70 to 80% SOC depending on charge rate (usually charge rate is fairly fast on portable electronics from 0.3C to above 1C). This constant voltage is the most detrimental part of the charging but for those applications it is considered that the extra 20 to 30% SOC is worth the reduced life of the battery. Most people will prefer a mobile phone that lasts for say 6h of gaming and has a dead battery after about 3 years than having the exact same phone but battery only charged with constant current so just 4h of gaming and 12 yeas of battery life.
The reason for that is that battery cost is not significant part of the phone cost and in 2 or 3 years a new phone will be more powerful and desirable not to mention likely no phone will have support for 12 years.
In solar applications things are different as you will not want to replace a super expensive battery every 3 years and there is no advantage or incentive to do so thus if you where to use those types of Lithium batteries you will not want to constant voltage charge them thus there is no point in having a PWM or any other method of constant voltage charging. For the special case of LiFePO4 there is no even any capacity to gain as with the 0.1C to 0.2C charge rate with solar battery is already 99% of real SOC with just constant current and just using PWM or similar constant voltage charging method to gain an extra 1% SOC at most will not make any sense.
The most common mistakes people make are.
1. Incorrectly connecting the cell balancing wires. Especially since the blue EVE, CALB type cells with black terminal for positive quite a few have connected the cells competently backwards and that results in a broken PCB fuse (PCB trace) and in some instances the 33V TVS next to the fuse may get damaged as that is the one that clamps the voltage to about 1V reverse polarity and so fuse will usually be the one to fail and nothing else but there where cases where TVS also failed as a short circuit so it will need to be removed if failed before repairing the fuse and reconnecting things with correct polarity.
2. Incorrect shunts wiring. I see you have point 9.3 talking about this What it is burned there is the current shunt amplifier (not the cell voltage sensor). The example you show is a fairly extreme one in most case the fault is not visible or much less visible under magnification. The PV fuse or breaker should also be close to the PV shunt.
3. Use of the SBMS0 or DSSR20 in high humidity condensing humidity environments. This is usually for those that use it it mobile applications like RV, Boats and usually in colder climates where the SBMS0 or DSSR20 get close to or below freezing over night then maybe the space is heated with propane or something similar fairly fast so that water will condense on all cold objects including the SBMS0 / DSSR20 PCB's
Neither SBMS0 nor DSSR20 and future DSSR50 are designed for outdoor use of condensing humidity type environments so in this applications they should be installed in a sealed box so they stay dry at all times.
I do not have plans to build a version that is waterproof as that is not easy to do will increase the cost and make things much harder to repair or modify.
Next time when I will work on my webpage likely end of April I will add a link to this document.