That was strange. If you run the multiple channel charger into a circuit simulator program, the highest voltage cell will be charged at the proper rate. The next one down gets the top cell and its own cell, the third one down gets higher charge rates. And so on.
By the time you get to the bottom cell, the charge rate was over 1/2 amp, and overloaded the 3.6 volt regulators. It just didn't work.
The same thing would happen if you took six individual power supplies with 3.6 Volt DC outputs, and connected them all to each cell of the 6S battery pack. The bottom one will get far to much charging current. That's what the circuit simulator showed me, and that's exactly what I got in real life.
The isolation is so that each cell in a series pack can be charged individually. The goal is to get rid of the standard runabout method of charging the battery normally and then dissipating charge from cells that are too high. It slows down the charge time (sometimes making the overall charge time actually take longer at faster charge rates because the cells need more balancing), and there is debate of the ineffectiveness of dissipative balancers due to the flat discharge curve of some types of cells now allowing the cell voltage to be used as an accurate indicator (and instead requiring a current method which can only be done during the charge top-off).
I did consider eight isolated chargers each containing it's own isolation supply and buck switcher. The main reason I'd prefer a a single large multi-output winding transformer is to reduce the parts count. Eight isolation supplies seemed like quite a few parts that could be replaced with fewer number of parts. Individual isolation supplies does have the advantage of modularity though...no inherent limit on the number of cells, just add on another charger. And it would make frequency issues less of a crapshoot. Of course, going the individual transformer route, it might be possible to simplify things by replacing the isolation supply and buck charger in each channel with just a flyback charger (though getting voltage and current feedback is the main difficulty there).
So it's soley for frequency purposes? Sort of like how in motors they wind everything with very thing solid wire and then run the wires out and twist them into 3-bundles to form 3 regular looking pieces of wire?
Efficiency isn't my top concern here. I'm more worried about overheating due to saturation or skin effects. Sendust cores are so cheap compared to those PMM cores. From staring at material spec sheets it seems they're fairly similar...nowhere near worth the 400% difference in price for my application. Or get 4x as large lol, but with 8 transformers...that's pretty big heh. I'm more likely to be conservative with my core selection and just wind a 1:1 with a comfortable number of turns to be mechanically stable and spread itself evenly amongst the toroid. I'm not sure how important inductance is in this case though.
I obviously have something wrong with my conceptualization of magnetic cores since I would have though more turns would increase the flux density but apparently it decreases it. Hmm. I should realy get a book on transformers and switching power designs. They're just so expensive lol.
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