Trying to Salvage a 48V, 20Ah Battery

[Phantom]

Hello All!

I'm hoping to salvage a battery. It's a 48V, 20Ah LiFePO4 battery that worked exactly once. It powered my bike for about 2-1/2 hours (35 miles), when the motor abruptly died. I pedaled home and plugged the battery into the charger (a cheap "dumb" charger [not a smart balancing charger] that came with the battery). The charger's light remained green, indicating a full charge.

This could not be. I'd ridden for over two hours. Even if the battery weren't fully drained, surely it must be depleted enough to receive a charge. Hmmm . . . .

Over time, I tried three different chargers, all of which work properly. The battery refused to charge. Always a green light, never red. Since the battery did work (once) I concluded that the cells themselves were probably good, but that the battery's BMS was probably faulty. I took a deep breath and opened the battery, and here's what I found (see pictures 1 thru 4):

Picture 1: the naked battery on left, stripped of its shrink-wrap covering on right. My hopes of finding 18650 cells were dashed as I believe these are "pouch" cells, no?

Picture 2: close up of the BMS (sorry for the blurry quality). I count 16 small charging leads connecting to the battery: 1 black, 1 red, and 14 white.

Picture 3: a 3/4 view showing the battery and BMS.

Picture 4: a close up of the top of the battery, showing all 16 leads soldered onto the cathodes/anodes. I took voltage readings at various points and the voltage progressed at each tab, indicating a series connection, no? Since I see no parallel connections anywhere, I conclude that the entire battery is wired in series only, as a 16S1P battery.

My questions for the forum:

Are my assessments/conclusions correct? If not, how so?

I'm willing to buy a new BMS since they're relatively inexpensive and I could get a working battery if it fixes the problem. It must work with a 16-cell, LiFePO4-chemistry battery with these specs:

• 
  * Voltage : 48V
  * Capacity: 20Ah
  * Cut-off voltage: 40V
  * Max. discharging current: 100Amp
  * Max Continuous Discharging Amperage: 50 Amps
  * Rated Discharging Amperage: 40 Amps
  * Charging Current: <10 Amps
  * Charging Voltage: 58.4 Volts

Can someone post a specific link for a BMS that would work?

Thanks in advance to all who can help!

 

[Street Ryderz]

Hello All!

I'm hoping to salvage a battery. It's a 48V, 20Ah LiFePO4 battery that worked exactly once. It powered my bike for about 2-1/2 hours (35 miles), when the motor abruptly died. I pedaled home and plugged the battery into the charger (a cheap "dumb" charger [not a smart balancing charger] that came with the battery). The charger's light remained green, indicating a full charge.

This could not be. I'd ridden for over two hours. Even if the battery weren't fully drained, surely it must be depleted enough to receive a charge. Hmmm . . . .

Over time, I tried three different chargers, all of which work properly. The battery refused to charge. Always a green light, never red. Since the battery did work (once) I concluded that the cells themselves were probably good, but that the battery's BMS was probably faulty. I took a deep breath and opened the battery, and here's what I found (see pictures 1 thru 4):

Picture 1: the naked battery on left, stripped of its shrink-wrap covering on right. My hopes of finding 18650 cells were dashed as I believe these are "pouch" cells, no?

Picture 2: close up of the BMS (sorry for the blurry quality). I count 16 small charging leads connecting to the battery: 1 black, 1 red, and 14 white.

Picture 3: a 3/4 view showing the battery and BMS.

Picture 4: a close up of the top of the battery, showing all 16 leads soldered onto the cathodes/anodes. I took voltage readings at various points and the voltage progressed at each tab, indicating a series connection, no? Since I see no parallel connections anywhere, I conclude that the entire battery is wired in series only, as a 16S1P battery.

My questions for the forum:

Are my assessments/conclusions correct? If not, how so?

I'm willing to buy a new BMS since they're relatively inexpensive and I could get a working battery if it fixes the problem. It must work with a 16-cell, LiFePO4-chemistry battery with these specs:

• 
  
  
  • 
    * Voltage : 48V
    * Capacity: 20Ah
    * Cut-off voltage: 40V
    * Max. discharging current: 100Amp
    * Max Continuous Discharging Amperage: 50 Amps
    * Rated Discharging Amperage: 40 Amps
    * Charging Current: <10 Amps
    * Charging Voltage: 58.4 Volts

Can someone post a specific link for a BMS that would work?

Thanks in advance to all who can help!

http://www.batterysupports.com/images/48V 16S 100A BMS LiFePO4.jpg

All those white wires are the balence leads and the battery wont charge through the bms unless the balence plug with all leads are connected and reading.It is a series circut with pouch cells looks pretty small for 20ah what are the diamentions and weight of the pack?Also the nominal voltage of that pack is too high for a regular 48v charger since dead (completly discharged) is 51v and peak voltage being 57.6v ,What does the current voltage read?

 

[Phantom]

http://www.batterysupports.com/images/48V 16S 100A BMS LiFePO4.jpg

All those white wires are the balence leads and the battery wont charge through the bms unless the balence plug with all leads are connected and reading.It is a series circut with pouch cells looks pretty small for 20ah what are the diamentions and weight of the pack?Also the nominal voltage of that pack is too high for a regular 48v charger since dead (completly discharged) is 51v and peak voltage being 57.6v ,What does the current voltage read?

Street Ryderz --

Thank you so much for the link; that looks like just what I need.

The info. you requested:

Battery weight: 15 pounds
Dimensions: 10 x 7 x 3.75 (inches)
Battery Voltage: Highest I recorded was 57.2 volts; now it's 47.2
Charger Voltage: All three chargers are rated as 58.8 volts, and measure between 58.2 and 58.5 volts

You bring up a good point about the battery's capacity, and I had wondered about that myself. After riding until the motor stopped (presumably fully discharging the battery) the battery took nearly three hours to fully recharge, using a 5-amp charger. That suggests a 15 Ah battery. Do you know how I can measure that exactly? (I don't have a Cycle Analyst)

Thanks again for your help.

-- The Phantom

 

[Street Ryderz]

Street Ryderz --

Thank you so much for the link; that looks like just what I need.

The info. you requested:

Battery weight: 15 pounds
Dimensions: 10 x 7 x 3.75 (inches)
Battery Voltage: Highest I recorded was 57.2 volts; now it's 47.2
Charger Voltage: All three chargers are rated as 58.8 volts, and measure between 58.2 and 58.5 volts

You bring up a good point about the battery's capacity, and I had wondered about that myself. After riding until the motor stopped (presumably fully discharging the battery) the battery took nearly three hours to fully recharge, using a 5-amp charger. That suggests a 15 Ah battery. Do you know how I can measure that exactly? (I don't have a Cycle Analyst)

Thanks again for your help.

-- The Phantom

If it's at 47.2v now you may want to look for a bad cell or it got discharged below its cut off some how,if each individual cell reads 3.2v or better your good and the nominal v should be 51v thats the lowest discharged voltage, your controller should have a low voltage cutoff at 51-51.5v to avoid damage to the cells from over discharging.As for the capacity of the pack with out an analyst or charging system that shows the miliamps put in you would have to know your constant average draw and do the math against the milage sorry dont know of any other way,Its very hard to tell by the charge time because even with a 5 amp charger for three hours doesnt mean it put in 15ah,as the voltage climbs during charge the resistance also climbs and limits the amount of amprage accepted by the cells and by the midway point and beyond the actual amperage in is usualy quite low so as not to over heat and damage cells.