6v sag too much?

just installed @Ackmaniac’s bluetooth monitoring, this thing is awesome.

i noticed my 12s4p pack of LG HG2 cells is sagging roughly 6v under max hard acceleration.

should i be alarmed by this amount of sag? reading other posts it seems people are seeing 4v with the 25Rs…

I’m not surprised by the amount of sag. I would say I see similar sag on with 25rs. Thats why I want to build a bigger pack with 18650s. I have 4p pack also but considering 5p for my next board for this reason (30qs). I would say you’re cutting down range by a lot though as you might reach cutoff sooner than if you were pulling less amps. How much range you get?

Looks pretty standard. Check the two squares I highlighted. In the first pic your at about 3.64v/cell resting. After you pull load (74A, rounding to 80A) that’s about 20A/cell which gets to about 3.1-3.15v/cell at the same mAh which is about what you’re seeing with 37.8v/12 = 3.15v/cell

EDIT: I actually did the wrong color 25R, but the 25R green shows even worse sag, so you’re actually getting better results than the tests!


Good god! I get up to 1V sag with my Li Pos and I get concerned - time to relax haha.


Seems like a lot, but if you look at discharge charts, it is exactly what you’d expect

You’re drawing about 75A, which is almost 20A/cell. Your cells drop to 3.64V nominal voltage under this load. Comparing the 0.2A line to the 20A line, you see a voltage drop of 0.5V/cell. At 12s this equates to a 6.0V drop at 80A total

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ok, so let’s say i have lower cutoff set at 35v in the vesc. then let’s say the pack is drained down to 37v, close to but not at cutoff yet.

at 37v, and i hit the throttle and voltage sags down to 33v, will the vesc cut out? then come back on when voltage returns to normal?

just redid this pack with @yummyblobs spot welder and officially finished last night.

so far drained pack down from 49.2 to 43.2v, so drained total of 6v. out of that i got 13.9 miles so far, a mix of real-world riding and hard test riding.

that means i’m getting 2.3 miles per volt. i have cutoff at 2.9v per cell, or 34.8v for the pack, and if the drain is linear (and i know it’s not), i’m looking at 33 mile range with this pack.

when people used to ask me range and speed on my previous 10s4p build, i would just tell them “20 + 20.” now i can bump that up to “30 and 30” haha.

The vesc won’t cut out it will just reduce power. That can actually be a problem though because it won’t cut power and you can still throttle very slowly under your cutoff end. It’s pretty obvious you should stop though.

That’s really good range I would say I only get about 16miles on 25r 12s4p pack the way I like riding.

That is why I went back to Lipos. 1v total sag with 10s/1p charging up a steep hill. Only 0.5v total sag or less accelerating on flat ground


Do you have ackmaniacs vesc monitor to see the numbers?

Loved my lipos too… for 6 months

Now two or three of the cells have as much as 0.8V/cell voltage drop, while others only drop 0.05~0.10V/cell under the same load :cry:

(Zippy 40c 6200mAh Lipos. If I go with lipos again, I will only buy Turnigy 60C+)

I have my inline volt meter mounted through the top of my deck so I can watch it realtime.

I’m using Turnigy 60/120C 5000mah They have been going strong for one year. No change in capacity or performance

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I really should do this at some point with my 30Q 12S5P packs.

behaviorally they seem to give you serious load support all the way up until the BMS shuts down but i’d love to see the actual numbers in action (meaning video overlays like this) without having to move to the android ecosystem.

if anyone else has a similar config and can do so please post it.

not to keep throwing money at things but there are cheapass android phones out there you could use just for this purpose?

that’s an idea… maybe i’ll just find a used phone somewhere. thanks!

I recommend

Works very well on iPhone, i use it all The time to keep an eye on the sag :wink:


does this record pack voltage over time?

getting telemetry is great, but scope of this discussion is sag.

I’m more curious about your power consumption. Wh/AH there can be huge difference between riding style. For example slow cruising for me its 15 and normal riding it’s 23 and going a little faster I’ve seen 30 wh/ah per mile so power consumption is a huge factor

How much range/miles do you get minimum or average with the lipo packs you have?

i’m curious about this too because on the packs i use i get over 30 miles at what you consider normal riding speed, which is kind of fast for a lot of people.

sag in very high discharge packs vs sag in lower discharge packs of higher overall power is a neat topic because the higher the cell count in the lower discharge packs the closer you get to being a higher discharge pack while simultaneously eliminating more sag.

except the battery weighs 5 pounds by then.

You can compare sag on various cells pretty easily from the real world tests here.


Use .2a as a baseline discharge curve and compare to what you can pull (20a for example). You can check the difference to see the sag on a particular cell.

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