Ryzen said:
Would you suggest removing 2 of my batteries to keep them under 80v?
No, your controller, if actually built correctly as a 72v controller (which it should be, but some sellers lie), can handle 84V just fine.
However: The Vevor controller is marked as a 48v controller, and could have (probably does) have parts that can't handle higher than say, 60-63V. So I wouldn't put any bets on it working with a 72v pack.
See this post about considerations on what parts in a controller need to handle battery voltage:
https://endless-sphere.com/forums/viewtopic.php?f=35&t=117411&p=1734433#p1733690
Do the resistors need to be on the positive side?
Doesn't actually matter--they limit inrush current, and so can be anywhere in the loop from battery to controller.
However, they need to be able to handle the total power dissipation (watts) created during precharge. Ohm's law and Watt's law will help you calculate what you need.
Let's say you have a 200ohm resistor. At connection, it has 84v across it. 84v / 200ohms = 0.42A. 84v x 0.42A = 35.28W. So for that initial burst, you'd need a resistor capable of dissipating at least 35W of heat. LIke these 50w resistors:
https://www.amazon.com/LM-YN-Wirewound-Electronic-Industrial/dp/B076W87ZT8
The current (and power) will drop at the rate the capacitors charge. The time this takes depends on how much capacitance there is, vs how much current is flowing. Big controllers have a lot of capacitance.
http://www.learningaboutelectronics.com/Articles/How-long-does-it-take-to-charge-a-capacitor
Call it 5 times the T=RC to essentially fully charge them, where T is in seconds, and R is the precharge Ohms, and C is the uF of the caps. 1x that to get 63% of the way there.
Let's assume you have 10,000uF of caps in there (there's probably only 2000, cuz everybody's cheap, but for worst-case math....). 200ohms x 10000uF (which is 10mF, or 0.01F) = 2s (200 x 0.01). So after 2 seconds, the current will have dropped dramatically, and heat will be way less. After 10 seconds, they'll be pretty much fully charged. (realistically, you only need the precharge for the first portion of time, 2s in this case).
If you only have 2000uF of capacitors in there, it'll take 1/5 of that time.
That means you might get away with a much smaller resistor, like say 10W...it'll get really hot during inital inrush, but not much heat will be generated after that so it might be able to dissipate that heat, if it's in open air.
If it's enclosed where there is no airflow, you should probably stick to a resistor with a much higher wattage rating, higher than you need, to be sure it doesn't overheat. Keep in mind also that it will be shedding that heat into whatever is next to it, surrounding it, so don't put it somewhere it will melt or damage things--even though the intense heat is only there for a few seconds, if there's enough energy over enough time in a confined enough space, it can melt or damage stuff if it's sensitive to such temperatures. It really depends on how much total heat there is, and how long it is there for.
A higher ohms resistor will create less heat (current is lower, so watts are less), but it will take longer to precharge.