So to set the scene, i run 4 5s 4500mah nano techs in a 10s2p config.
Usually with hard riding, I’ll get about 19-20km out of it with dual 6374’s.
On Thursday, i rode 19km no problem, with cells all relatively close to each other voltage wise (within 0.15 of a volt of each other). Yesterday, i rode 16.5km, and my bms shut down as one of my cells dropped to 3.3v when the others were just hitting 3.55.
Now what I’m thinking is, due to differing internal resistances, some cells discharge faster than others. This really shouldn’t be the case… right?
So I’ve swapped 2 lipo packs so one pack from the 5s2p is now with the other (swapped pairs). This should help shouldn’t it? it would help keep the voltage somewhat similar i believe?
Seriously calling all electro experts here (@b264 & @namasaki you guys especially) as i know i dont have dead cells, i just feel like the internal resistance differences have an effect on a linear discharge.
I have a 12s 4.6Ah 90c Graphene pack running 80 battery amps, 44V (3.66v/cell) soft cutoff and 42.6V (3.55v/cell) hard cutoff in my esc. I have monitored my cell deviation at lower cell voltages and as long as I stay at these voltages or above my deviation stays within 12mv or 0.012V if I discharge deeper with high amperage the deviation increase quick. My voltage sag at high amp is around 1v according to HUD.
Yeah its just weird how temperamental it is. like one day i ride 19km with room to spare, next day i ride very similarly, and only get 16 and it dies. one of the cells were still at 3.65v and the other at 3.25v. Im discharging through a bms so shouldn’t it really help with discharging more evenly? or is the balance current not enough to keep up with the drain?
I try not to go below 3.7v/cell and I always balance charge with icharger so I can monitor deviations and internal resistance. Have you set a low voltage cutoff in your esc? most bms’s cutoff are very low for lipo. My internal resistance range from 2-2.3 mΩ /cell.
was perfect weather. got the board in germany atm and it was like 22 degrees so defs not warmth related. on top of that, my enclosure has no heat dissipation so after 5-10min my enclosure sits at about 35 degrees anyways
yeah low voltage cutoff is at 3.5v start and 3.3v end as that last bit of juice is often what gets me home. My esc still said it was at 36v, but as one cell was so much lower the bms cut out. the bestech HCX-D223V1 i have is for lipo so it’s hard cutoff is 3 2v
yeah i mean i know when i get to that point so I back off, but yes probs a bit low. full battery when i pull 70a (35a batt max each) i get about 0.8v sag. when near empty it goes to about 1-1.5v. I’ve made an “eco mode” on my metr so it’s limited to 50a total. that’ll probs help a bit
I agree about the point that lipos low end voltage gets tossed around quite a bit…
From general experience Ive had with lipo on friction drive ebike, it does get bad below 3.55v per cell.
At 3.6-3.7v it is ‘manageable’ but below these 3.55v the voltages ‘get tossed’ around quite a bit and it gets quite visible that battery is close to its last remaining capacity.
Some good tips from Deckoz about internal resistance and how to look after when battery starts to get bad. Truly an insider info not everyone gets to witness themselves when starting out with lipos/batteries in general.