Electric bike: diagnosis of a lithium-ion battery 24V

[bamboo]

Ah, that's much clearer! Thanks Pitt!

http://dilbert.com/strips/2011-07-11/

Otherwise nice editing Pitt. Too bad that it is not associated with the water heater

[Christophe]

Hihihiih not cry Indy, you put us on the way!

I do not have access to 1 elements by 1, I need to explode the battery for that
For the moment I do not want ...

Finally zavié reason, I'm afraid my ohmmeter took a blow yesterday: he can not measure stable resistance values ​​(it moves constantly)

[dirk pitt]

I do not have access to 1 elements by 1, I need to explode the battery for that

the same electricity that you did empty on the BMS socket but maybe you can not access it anymore because you would have to unplug it and the BMS would cut off the discharge

[Christophe]

That's all you understand ... the connectors of this plug once plugged are far too small to make a measurement.

In fact, the simplest solution would be to strip a little bit each cable in order to place a multimeter tip ... and tap later ...

I will do it.

[bamboo]

Finally zavié reason, I'm afraid my ohmmeter took a blow yesterday: he can not measure stable resistance values ​​(it moves constantly)

Try to change the battery (she could also make a lot of head), but I do not believe it too much ...

[I Citro]

Finally zavié reason, I'm afraid my ohmmeter took a blow yesterday: he can not measure stable resistance values ​​(it moves constantly)

Philippe BORGES, the excellent webmaster of forum VE once pulled 60 times the rated current of a Lifepo battery ...
Imagine what it can do in a multimeter like yours ...
doctorBass of which I already spoke, has fun to solder with the arc with lithium batteries ...

[Christophe]

Imagine what it can do in a multimeter like yours ...
doctorBass of which I already spoke, has fun to solder with the arc with lithium batteries ...

I promise you it hasn't smoked or heated (not even the cables) !! I had doubts (later confirmed) so I went "cautiously" !!

I am going to make measurements of other resistances known to be sure that there is a problem ...

Internal R measurements of Lithium and lead batteries

Lithium battery according to this method (voltage stabilized on 2 or 4 bulbs 20W).

Vacuum voltage V0 = 27.9V

40W:
I1 = 1.71A
V1 = 26.6V
Power1 = 45.5W

80W:
I2 = 3.18A
V2 = 25.5V
Power2 = 81.1W

R = (V1 - V2) / (I1 - I2) = 1.1 / 1.47 = 0.75 Ohm.


Same measurements on a lead battery 7Ah 12V, I took half the power to be about in the same conditions of (de) charge compared to the nominal capacity (the lithium makes 8Ah 24V):

V0 = 13.55V

20W:
I1 = 1.62A
V1 = 12.36V
P1 = 20W

40W:
I2 = 3.22A
V2 = 12.15V
P2 = 39.1W

R = (V1 - V2) / (I1 - I2) = 0.21 / 1.6 = 0.13 Ohm.

The lithium battery is more discharged than the lead battery.

Measurements with ITC-777 (voltage) and ITC-920 (current)

Uh and so? After what can we conclude?

[dedeleco]

At my heart, for batteries that have to 150 200W coast is a lot!

It is necessary to see the threshold in tension of safety trigger, 3,6V by elements ???
And see if it is achieved well to have the necessary power, as observed.

Follow a ball in this area,

What do they learn in engineering school ??
What gears ???
and not the Ba ba power resistors and their measurement ???

more tolerant if you plug in parallel

very very little recommended, even if "more tolerant" !!

[dirk pitt]

750mohms, it's a lot !!
a "normal" value would rather be around 250mohms

in my opinion, the BMS is a non-negligible part of it but I can be wrong. the battery itself may have an internal resistance that is too high.

short, it's not too much the problem, it means that it will be more tolerant if you plug in parallel with another of different voltage. (unless the other has a very low internal resistance.

on the other hand for the diagnosis of your problem, I insist: find how to measure the tensions of each element when you draw the current. that's what will tell you which element is weak. the vacuum voltage is only unrepresentative.

a solution that would work at least for not too high currents would be to draw juice by the famous balancing act, element by element. since it is small children, it will limit the current.

[Alain G]

Finally zavié reason, I'm afraid my ohmmeter took a blow yesterday: he can not measure stable resistance values ​​(it moves constantly)

Look inside there is a fuse on the Ohms scale