Voltage sag is one of the issues I’ve seen many complain about with the Evolve CGT. It’s an issue I think is pretty prevalent in the DIY community. the easiest way to escape voltage sag shutting down your board is simply to using a bigger battery pack. But sometimes, that’s just not an option.
So I wanted to start a discussion about things that some in our community have done to deal with voltage sag. I also want to see how much people can sag their battery.
So how low can you go % wise before you sag your way down to 0% (in the worst case scenario)?
- less than 10%
- higher than 35%
And to those with more knowledge about voltage sag and solutions, please post away your thoughts and advice for the community
To mitigate sag, you have to leave as much buffer room as you can between maximum actual current under load and maximum rated discharge current. Best way to do this is to use prismatic cell lipos. Otherwise building a huge parallel pack would work as well. I don’t sag much on my route 5~% and I never go too low to prolong cycle life. I put 10-19% for now, but I’m sure it’d be a lot higher if I went up insane hills.
Hubs, I imagine, would sag worse since they need more current than belt drives.
I have a lot of hills on my route. I sag very little on flat ground, but when I go to tackle some steep hills, it can easily sag 25% or more, depending on the hill.
That’s pretty crazy. My Evolve GT sagged pretty bad, but I’m pretty sure they designed the throttle to be too aggressive on their ESC. Also, pretty sure they’re using bad cells for their battery.
Well, I am using 4wd with hubs, and I pull 80 amps (which is the max for my 12s4p battery) on steeper hills. Mind you, this is on a hill that was 25% grade… But still… I think 12s6p or maybe even 12s8p would be the perfect battery for my board, but that’s a bit too much, haha/
Will you get less sag from say A123 26650 cells like in the boosted?
I have A123 cells in 12S1P config and I still get decent sag up hills. From Nominal voltage per cell of 3.3v, I drop to around 3v per cell while going up decent hills.
A 12S2P pack of these cells would be great.
Yeah I was thinking about a 12S2P for my next build with A123.
Do you have any boards with different battery setups. Just trying to get an idea of what a A123 26650 12S1P setup is like. In terms of sag would it be like 10S3P with 18650’s roughly?
I only have the A123 setup so far. I’m thinking of 12S2P 18650 cells for my next build too.
Yea since 26650 A123’s have 70A discharge, you’ll have sag similar to something between 10s3p and 10sp4 18650’s.
Thanks for confirming. Just wondering if anyone in practice has some real world experience to see if it actually behaves like that. All makes sense from a theoretical perspective.
You could ask anyone with a boosted board. They’ll have to look at their mobile app while riding.
i build my packs to handle 80 amps continuous and i use a BMS that handles 60 amps continuous. Because of that, i’ve not seen one of my boards shut down due to voltage sag yet. I’m not saying it couldn’t happen, it just hasn’t.
So yeah, there’s something to the “big pack” approach that works. I use 12S 4Ps made from sammy INR-18650s.
What are the max con amps you’ve drawn using your board @longhairedboy ?
I am using essentially the same pack but I sag a lot on hills, because I get close or hit my 80 amp limit on super steep hills. Most of the time, I sag less than 10%…
What voltage are you running if you are pulling close to 80A?
50.4v 12s about as high as the vesc can do…
i’ve got my abs max set at 130 usually.
I mean like, what is the most amps you’ve recorded drawing from your vesc from your battery?
I’ve had the Carbon GT since a few days after the U.S. launch date and I haven’t had the voltage sag causing the board to shut down issues ever. I never knew that was even an issue. The voltage sag does makes the battery life percentage unreliable to look at while on the throttle as it does drop. I just look at the trip meter a lot to see how much longer I can ride.
Good thing I live in a non hilly area, the voltage sag hasn’t slowed me down on flat roads so far.
hat’s exactly why you haven’t had issues. They seem to be fine on flat ground. But steep hills apparently make it sag down to 0% from 30%.