If you are going to make your own charging/balance setup, don't set it for 4.2v. Set it for 4.125v peak. Yes, you sacrifice 10% of the potential to store energy. However, your number of life cycles extends by about 10x (yes, 10 times the cycles) according to most manufactures cell life graphs.
Charging from a switching power supply works fantastic. They do the perfect CC/CV curve ideal for charging LiPo.
LiPos are really not a hazard when shorted. A proper LiPo battery is designed to harmlessly vaporize it's cell tab in the event of a serious short, and it vaporizes that tab well before the cell even gets warm. The packs are designed like this so it's as if each cell has its own fuse protection built into the pack design.
I run a 20s, and I made the packs in 20Ah 10s cell groups. I run these cell groups 2s 2p if I want a 74v 40Ah pack, or 2s1p if I want a lighter weight 74v20Ah pack. When I charge, I split the pack into 10s sections if I'm going to balance, or I leave it 20s if I'm not going to balance. My cells never go out of balance, so I generally just charge as a 20s pack.
I set the charger for 82.5v. This brings each cell to ~4.125v.
There are a couple things to be careful about with LiPo. If you over discharge a cell, it's damaged. It will have higher Ri, and it's a hazard to have in your pack the next time you charge. You are not in any danger as you are over discharging, it's when you go to recharge again that you are taking the risk of fire. The second is to not let cells go over 4.3v. Yes, you can generally raise a cell to 4.5v-4.8v before it starts to vent, but exceeding 4.3 is when you begin to damage the cell, and you are risking a venting event.
I think a potentially slick and simple and reliable way to deal with LiPo would be 5w 4.2v zener diodes with a 0.1ohm resistor in series across each cell. Then set your power supply to only charge to 4.125v/cell average, and if a cell were to get out of balance for some reason, the zener would clamp it at 4.2v during charging. You could very easily build this tiny cell level over-charge protection right into the pack.
I just did a quicky search on digikey, and found some 5w 4.3v zeners for $0.14/diode. They have an excellent temp/v change curve of about -0.4mV/degC. So, even if your pack got 40defC above room temp during charging, it would LOWER the clamping voltage by ~16mV, which would actually just make things slightly more safe I supose. lol. 10uA leakage current at 1v, does not list a spec for 4.1v leakage current. I would take a wild guess it might be around 100-2,000uA at 4.1v. That would mean it would be safe to stay on a 5Ah cell for months (maybe years) with out leakage current being a danger to draining the cell. It would be a good idea to disconnect it if you were going to store your pack for months, but that's not much of a hassle or concern for most folks.
Unless there is some critical flaw that I've missed seeing, it seems like you could setup indivual cell level over-charge protection for a pack for about $5 in parts.
Does someone see a flaw in my logic here? Any critical flaw that makes it a poor choice to use a simple zener clamp for cell protection? If the 2Ohm impedence seems too high, or 5w limit too low, it would be easy enough to connect 4 or 8 in P, and get that down to 0.5Ohm-0.25Ohms with a 20-40w limit. They are only $0.14 each from rip-off-key, so I'm sure I could do a 1,000 quanity buy on them for like $0.05 each from a real parts supplier.