# eRPM, Voltage, and Speed Limits

Could I get some input on the effects of limited top speed via eRPM. I’m wondering how it affects the operation of ESC and the battery. I understand that as the speed rises the voltage to the motors increases. In the FOCBOX tool, limiting eRPM lowers the max duty cycle.

I need a new battery and am contemplating different configurations. I am mainly wondering how limiting eRPM on 12s config to the speed of a 10s config would affect battery performance? In other words, is their any advantage to spec’ing your battery for 35mph and only using 25mph. I hope this makes sense.

1 Like

I would simply do 10s battery. Because all electronics have a possibility to fail. So this eliminates one variable and saves your ESC.

1 Like

I was using a UNITY with 11s3p but I am leaning towards a 10s4p. I like riding at top speed since I don’t have too many hills and I’m slightly worried how slow it will be towards the end of the charge.

That’s an interesting question I really hope the more technical members could chime in.

If your going to be going near top speed a lot, the motor efficiency will be better if it can operate at a higher rpm or voltage. Which is more a factor of lower kv and or higher gear ratio.

As for the battery, a higher voltage battery pack will require less amps to output X wattage, but if the lower volt pack has more P’s it may draw less amps per cell. Less amps per cell is going to be better for your battery life.

You need to math it out. Just as a rough example if your system needs 1000w. 12s3p 1000w/43.2v =23.15 amps /3p = 7.7 amps per cell.

1000w 10s4p 1000w / 36v = 27.8 amps / 4p = 6.9 amps per cell.

So in this example 10s is better for your battery.

Higher p count will also keep balance better.

12s3p is 36 cells while 10s4p is 40 cells. 40 cells is better than 36.

If the cell count was the same then it’s really marginal either way.

As for the feeling of eprm limited top speed, I find it feels a bit unnatural when going over small crests as when you hit the down hill portion you expect a slight increase in speed but you loose some power on the down part. I would rather limit top speed with voltage/kv/gearing.

3 Likes

Set the voltage cutout to the 12s value. I’d be skurd to be able let the esc draw a 12s to 10s low voltage.

Thank you for the details. I will likely build a 10s4p 30q. 28mph is good enough for me especially on a flex 2 vanguard. Ideally, I’d try to cram an 11s4p in there but that might not be feasible. As for eRPM limits, since I have Meepo hubs my only options are to switch to the 90mm sleeves or change the voltage, no gearing unfortunately. I’ll probably just build the 10s4p and leave the limit open.

Should have gone with the 12s4p eBoosted enclosure

1 Like