Take a motors rating and triple it's wattage for surge at start up. So the above 1500W could do close to 4000W on initial start. That'll drop quickly as the torque lowers as the vehicle is moving. So you will need to calculate at a higher amp draw than 2A/cell with your current setup. Take that 25A/pack and size it as you'd you pull 75A/pack. So if you still want to pull 2A/cell (which isn't recommended with used cell), then you'd need close to 40p to handle the amp load. Might even go to 60p just to make sure the energy requirements are met.
so based on your 4000w max load i would take 4000/48v=83.33amp. then divide by 16 to get 5.2A on a string level. would it also then by divided by 8 to get .65A per each 18650 battery or does it not work like that? I see several pre buit packs that are usually 14s4p. I figured 8P would reduce strain on the individual 18650s.
You didn't mention what "type" of cells you are using. Are they powertool cells or other types? Are they LiFePO4's or other lithium based cells?
Cheap laptop packs. This is more of a experiment on the cheap and if it works even for short distances then I will look into higher amp and higher storage.
Currently they are an average of 2.35ahwith a total or 19180mah per stringof 8. I am uncertain of C rating on these cells but I would not feel safe pulling more than 2c for only short bursts of time.
Fusing between packs is not needed and doesn't really serve much of a purpose. You only need a fuse (except for cell level) at the ends of the string. So if you plan on pulling a continuous 25A, with a possible 75A surge, then 100A fuse would probably cover it. If your motor will only surge up to 40A, then a 50A fuse would be fine as well.
Remember, a fuse is only needed for dead short protection. A 20p pack can do at least 40A dead short, if not closer 120A or even more, depending on the cell types.
When you say end ofstring do you mean right between the electric controller and the XT90battery junction or between each 4s8p battery? 100Amp fuse would trip if i lost connectionto one of the 4s8p batteries because it would essentially be 14.8V less or 12v if it was 1/4 of 48v. 4000w/36v =111Amp. I think I would even want something closer to 80Amp maxi fuse since I am overvolting the motor. or would it be 20amp fuses on each 4s8p battery? Sorry I am sure there are some videos I can watch on this but most people are just build 15s packs with BMS and iI want something that will just fit evenly over the back wheel saddle bag and I could remove the saddle bag when I park the bike somewhere in the public to charge or just for protection sake of theft.