About a year ago, I built one made with 4 Meanwell 24 volt, 30 amp PSU's. It outputs 82 volts right now, but can go as high as 96 volts. I had to run a dedicated power circuit for it. 30 amps is 2X higher than typical household wiring and breakers in the USA. I couldn't run it at close to full power because I was always popping the breaker. This charger cost a good bit more due to the expensive PSU's used, but it does a great job charging my blue scooter and will do a great job on the moped too when I get back to completing that. The current limiting resistors on it are 100 watt, 3 ohms. They get quite hot! Enough to make you really regret touching them. If I did the current limiters again, I would go with 10 ohm 100 watt and parallel more of them for better current and heat dissipation. I think I have 10 resistors in parallel or .3 ohms.
Here's a rough schematic of how it is wired up. All the PSU's are identical isolated output units. If you can't get enough voltage from 3 PSU's, then run 4 or more in series until you get the voltage you need. Adjustable output PSU's almost always are rated for some voltage, but they will adjust up or down by quite a lot. These are 24 volts each, but they will go down to about 19 volts and up to 30 volts. This charger was built from $25 PSU's. Including the watt meter and resistors, I have less than $100 in a 20 amp charger. I have 19 100 ohm resistors in parallel or 5.26 ohms. I really need about 2 ohms total. More resistors are on the way. The problem with calculating this out is that the batteries and BMS's have resistance and I can't really measure that since I don't have a battery meter that can handle 16S to tell me the IR. I can calculate based on the current and voltage or 66/20 = 3.3 ohms. This isn't really what I need however as that will probably get me about 10 amps charge current at most. As a result, I have to add resistor banks in parallel until I get close to 20 amps. At 100 ohms, that will be probably 3 of these resistor banks.
*****USE isolated output PSU's ONLY!!!****
1. The power supplies in series add their voltages together. That means 22v+22v+22v=66v.
2. Current is NOT additive. These are 20 amp PSU's in series. Current is still 20 amps max.
3. If you parallel the outputs, you get the additive current of all the PSU's in parallel. If you run them in series, you get the additive voltage of all the PSU's.
4. In my schematic I show a limited number of resistors. If you use lower resistance for each one, then you need fewer resistors, BUT you also need higher wattage resistors. More higher resistance resistors in parallel means the total amount of current they each needs to dissipate is less. That means each resistor gets less hot.