Low voltage.cutoff

[ebike11]

Hi guys
I have a 18s lipo pack and charge it up to 4.1v per cell so 74V or so hot off the charger. I then ride until 3.6v per cell which is around 64V.
My question is..of course going below the 64V wouldnt be good..but when voltage drop happens then it can go under 64V but will return back up to 64V+
Is voltage drop below 64V in this case ok if the voltage sits at 64V+ when I disengage the throttle and its sitting voltage OR should the minimum safe voltage AFTER voltage sag/drop be no less than 64V?
Thanks!!

 

[john61ct]

SoC when you stop is what counts

Only resting isolated voltage can be correlated to SoC, and even that is very rough.

A wattmeter counting coulombs with a shunt is good to calibrate for your situation.

You keep tweaking your LVC under your load levels C-rate

until you get to your target DoD%

 

[goatman]

I take my full throttle volt sag down to 3.0v. 18s=54v. im running 25r at 17s4p and 5v sag down to 51v. when I consider my battery dead its 56v/3.3v-cell

 

[DogDipstick]

I use 66v for a 20s so that is like 3.3v / cell. I can still wack it full throttle for the most part 90% of the battery capacity and wont hit the lVC.

Classic electric RC fail... setting up a high power setup.. and going hard ( climb? acrobatics?) into the load at 3/4 empty battery and you hit the ESC LVC and fall out the sky. Lol. Or set LVC so low that you burn up your cells by going to low to much.

I mean, any way, pretty sure you will know when the capacity is gone, and the "shelf" or "cliff" that your cells have in capacity giving.... I try to set LVC right above that.

 

[ebike11]

A wattmeter counting coulombs with a shunt is good to calibrate for your situation.

Would a cycle analyst be able to do this?

 

[ebike11]

I take my full throttle volt sag down to 3.0v. 18s=54v. im running 25r at 17s4p and 5v sag down to 51v. when I consider my battery dead its 56v/3.3v-cell

Curious..why run one pack down 3.0v sag and the other 5V?

 

[ebike11]

Classic electric RC fail... setting up a high power setup.. and going hard ( climb? acrobatics?) into the load at 3/4 empty battery and you hit the ESC LVC

I would never go hard on a low or semi low battery up hills etc...i only do street riding on flats mainly so i would be pushing my battery on straight flat stretches
Im assuming getting close to 75% of battery cells/pack would be "less risky" on flat rodes compared to hills?

 

[goatman]

I take my full throttle volt sag down to 3.0v. 18s=54v. im running 25r at 17s4p and 5v sag down to 51v. when I consider my battery dead its 56v/3.3v-cell

Curious..why run one pack down 3.0v sag and the other 5V?

18s is your pack,
5v is the sag my pack has
if my battery is dead at 56v and I hit full throttle itll sag 5v to 51v.
51 divided by 17s=3.0v per cell

from 3.2v to 3.0v theres not much capacity and heat will rise.

I consider 56v dead but ill run my pack down to 51v if im trying to get home, so that's like 1/4 throttle and slow speed

 

[john61ct]

A wattmeter counting coulombs with a shunt is good to calibrate for your situation.

Would a cycle analyst be able to do this?

Yes but dunno how accurately, prolly pretty good knowing Justin.

Cross-ref with resting voltage measurements.

You build up an intuitive sense as you gain experience.

Do not trust your battery Ah rating.

 

[ebike11]

A wattmeter counting coulombs with a shunt is good to calibrate for your situation.

Would a cycle analyst be able to do this?

Do not trust your battery Ah rating.

What range do battery makers usually use to determine the Ah of a cell? From 4.2V to 3.0V?
Id like to do a range/Ah test from full charge but i dont know at what voltage should be stopped at? I know every cell is different. Mine is an LG lipo..i think its an EV cell. They are 30cm long and flat..about 1cm thick

 

[DogDipstick]

What range do battery makers usually use to determine the Ah of a cell? From 4.2V to 3.0V?

Most LGX Chem cells I have seen are 2.8v/cell standard or 2.5v/cell on high power discharge test... or even lower dependent on temp.

Any battery manuf might do it (rate) a little different than.. another.. ( to their advantage, usually, lol. ).

You really need to know the sheet. Mine really run out of capacity at about 3.0v-3.2v. They fall flat there.

Snip from a random sheet I got floating around on my desktop. LGX C1.5 S 25.6Ah cell,. Generally brand new ( beginning of line life) they report a safe margin above what they rate on the sheets.. say 5-10% more... Brand new. When empirically datalogged through discharge / charge cycles.When they are not old, or old stock.

The hotter the environment, better a higher LVC. Cut current draw at a higher voltage, for longevity, in the desert, If you happen to be riding your ebike through the desert.

Undervoltage limit on this cell ( where the cell is irreparably damaged upon reachingZ) is 2.0v.
Overvoltage limit (1) is 4.3v.. ( you are allowed to reach limit "1" without damage.. ) and ...
Overvoltage limit (2) is 4.45v. ( where the cell is irreparably damaged, limit "2".)

OCV.

 

[john61ct]

The spec sheet data is "do not approach" stressful maximums.

Going there for cap testing NBD so long as rare.

But not part of day by day care for longevity.

______
These are absolute stress ratings only, functional operation of the device is not implied at these or any other conditions in excess of those given in the operations sections of the data sheet. Exposure to absolute maximum ratings for extended periods can adversely affect the device reliability.

 

[DogDipstick]

The spec sheet data is "do not approach" stressful maximums.

Wut? Lol. The sheet i have doesnt say (the sequence of those three words) that ("?do not approach?") anywhere on it. Could you reference your quote?

.. Also; what does .... "cap testing NBD so long as rare." mean? I do not quite get at what you're trying to relate here.

 

[ebike11]

What range do battery makers usually use to determine the Ah of a cell? From 4.2V to 3.0V?

Most LGX Chem cells I have seen are 2.8v/cell standard or 2.5v/cell on high power discharge test... or even lower dependent on temp.

Any battery manuf might do it (rate) a little different than.. another.. ( to their advantage, usually, lol. ).

You really need to know the sheet. Mine really run out of capacity at about 3.0v-3.2v. They fall flat there.

Snip from a random sheet I got floating around on my desktop. LGX C1.5 S 25.6Ah cell,. Generally brand new ( beginning of line life) they report a safe margin above what they rate on the sheets.. say 5-10% more... Brand new. When empirically datalogged through discharge / charge cycles.When they are not old, or old stock.

The hotter the environment, better a higher LVC. Cut current draw at a higher voltage, for longevity, in the desert, If you happen to be riding your ebike through the desert.

Undervoltage limit on this cell ( where the cell is irreparably damaged upon reachingZ) is 2.0v.
Overvoltage limit (1) is 4.3v.. ( you are allowed to reach limit "1" without damage.. ) and ...
Overvoltage limit (2) is 4.45v. ( where the cell is irreparably damaged, limit "2".)

OCV.

If Im not hurting my battery by going under the LVC with battery sag and if my battery still reads around my LVC when i let off the throttle, then I think it will good. I was worried when my voltage dropped into the high 50s on an 18s pack a few times when i gave full throttle on short bursts testing my top speed