Do you have more details on that? Whats cells are used in the GT and what is their discharge rating?
4wd hub motors. Hubs eat up more current, on steep hills, I can pull 80a across the 4 motors (which is the max continuous of my pack). The reality is, on flat, I sag very little. But on hills, it’s another story.
Part of me is thinking I might be better going back to lipos so I can do higher amps again. 80a max is not always enough for me, even at 12s.
Higher C rating and better IR in cells will give you what you seek.
** deleted because wrong **
Could you provide and example?
I guessing this is due to the fact you have a wider voltage window, but how can you define Vs = Vw*N, for N is the number of cells (and number of cells in the entire pack, or the number in series?)? That doesn’t make much sense. For example, I run 12s, so my usable windows is 38.4v to 50.4v, so 12v is my usable window for my entire pack. According to your formula, it’s also my sag. But I sag at most 3v under high loads if I’m in the right part of my battery pack (fully charged for example, because that first 2 volts or so drop off quickly). I never sag 12v, so I don’t get what you formula is telling me, other than the range of my batter’s voltage.
Maybe we are talking about different sags… We are talking about the sag under load, not from using the energy out of the cells through normal discharge.
From another forum, I found this:
For instance if the internal resistance is 50 milliohms (0.05 ohms), then the voltage sag on a 6 A load would be 6 x 0.05 = 0.30 V.
Which seems more like the sag we are after. So…
sag = load * resistance
Can anyone confirm or deny this formula? My understanding prior to finding this was that resistance directly affects sag, which is true in this formula.
Sorry… Misquoted a conversation with our tech guy Kilian (again): Max SOC window was the formula described as voltage windows * number of cells.
Should have written “There will be more sag in longer serial configurations (comparatively). Max SOC window is the usable voltage window of a cell times the number of cells. Draw from a 2p setup with have much less sag than from a 1p, since the draw is distributed over 2 cells and thus resistance will be significantly lower.”
So your saying a 6s1p will have less sag than a 12s1p, since the 6s has a smaller serial configuration?
And that the resistance is less in say a 12s2p than a 12s1p, which is why we experience less sag?
So say a cell has say a 20 milliohms of resistance. If I run it in a 1p, I would have 20 milliohms of resistance, while in a 2p, I would have only 10 milliohms of resistance?
Sorry, forget the serial length statement. There’s a monkey at the keyboard.
As Sorrentino put succinctly and you earlier correctly surmised, it’s all about internal resistance. Your formula is correct.
As in your example, more cells in parallel will distribute the current and experience less IR.
OUCH! 10 CHARACTERS
Hey,
I have serious voltage sag when going up medium hill and pretty much just stops on steeper inclines. Im running 10s4p 30Qs with Vesc and 6374 200KV motor.
I think it might be because Ive got conservative settings in my Vesc but I could be wrong. Here is a bit of a screen grab from the Metr app. Any ideas whats going on!?
When I pushed it up the same hill for 20 secs then jumped on and gave it power, it starting pulling really well… for about 15secs then starting bogging again.
These readings are from a 15min ride with some flat areas and down hill in parts too. The last 5 mins was a significant hill but I felt the bogging even on a slight incline.
Post the full Metr log. If you paste in the URL, it will load automatically
Even conservative battery settings should yield 60a continuous. What are your settings in the VESC. What’s your battery cutoff start and end? Also I see you’re close to 80C on temp and somehow only pulled up to 27a Max. Also what are your Max and min settings? Seems like you could post some more data to get a better idea.
I also have some voltage sag. 12s6p 30q dual setup. If I have 30% left and I accelerate hard I can see it drop to 0 %. But I don’t have any conservative settings either
Data is from one FocBox. I have two but it only have data from one so double the amp and wh
Check the welds. May only be running on a10s2p
Interesting… I have actually wondered about the % drop after my last ride (maybe 7km). It did seem to use more battery than I was expecting. Im wondering how it could be 10s2p instead of 4p. Im trying to think, where in the welds could break to give less p while also still functioning?
You will not experience 100% p failure. One p might lose a cell, which would decrease your range. But it would be easy to spot because one p would keep getting lower than the rest of the pack. You balance it, and ride till empty again, you would notice 1 of the p lower than the rest always. So something like that is not too hard to pick up on. I would start by checking the voltages of each p when the battery is below 25% full. The reason being in a 4p, 1 cell is 25% of the battery, so if your at 25% left on most p’s, and on 1, you have 0% or around that, then you’ll know one cell has broken lose.
everything @evoheyax said.
also, if you have not done so already, pick up a set of dental picks from the local flea market or online somewhere. You can use those to tug upwards on the nickel to see if any of the welds are loose.
second hand dental picks? Think I need to buy a board from you to help support you !
@cliofreak look for something like this
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