Battery issue

[JK71]

Hi, built my first ebike but having an issue with the battery power.
All items are new.
3000watt rear motor with 72volt controller, a 72volt 20ah, 3amp charger.
Have charged fully (green light on) the LCD reads 83volts, fully charged.
However, only able to ride for about 4mins before battery goes down and shuts off. I can turn back on and shows about quarter power left.
When recharging it only takes about half hour before lighting up charged which I feel should need more.

Could it be that the hub is pulling the battery down?
If I go light throttle it goes further but half to full it powers down.
Or even battery is faulty, it's a triangle shaped one.

Thanks and appreciate any guidance

 

[KirstinS]

Hmm , that's a very powerful set-up. I'm wondering if the battery is powerful enough. This could cause battery sag and cutoff as you describ when it sags below the lvc.

So two questions

1. What's the controller amp rating ?
2. What's the battery cell/bms peak and constant amp capability ?

If you tells us more about where you bought we might be able to find out ?

If, for example a 72v 40a controller is paired with a 72v 20a constant (30a peak) battery you will run into trouble

Such a mismatch can knacker the battery in relatively short order...

 

[JK71]

Thanks,
Best I could read without removing:
Model: KT72ZWSRKD-ZC14L
Rated voltage: DC72v
Rated current: 30A
Low Voltage Protection: DC 60 [+ with - underneath] 0.5v
Speed setting: 1-4.2v
Max current: 60 [+ with - underneath] /a

This is the link to the battery: https://www.aliexpress.com/snapshot/8319473699.html?orderId=79660401991208&productId=32650043622

 

[Deleted member 4366]

Set the display to show volts (power button), then watch what happens to the volts when you ride.

 

[KirstinS]

Thanks,
Best I could read without removing:
Model: KT72ZWSRKD-ZC14L
Rated voltage: DC72v
Rated current: 30A
Low Voltage Protection: DC 60 [+ with - underneath] 0.5v
Speed setting: 1-4.2v
Max current: 60 [+ with - underneath] /a

This is the link to the battery: https://www.aliexpress.com/snapshot/8319473699.html?orderId=79660401991208&productId=32650043622

I can't seem to follow the link - it might be to your own order page which needs a password

 

[JK71]

Sorry, hopefully this link works:
https://www.aliexpress.com/item/Triangle-style-60V-1800W-electric-bike-battery-60v-20ah-electric-bicycle-battery-60v-20ah-lithium-ion/32650043622.html?spm=2114.01010208.3.1.xZfDm1&ws_ab_test=searchweb0_0,searchweb201602_3_10065_10056_10068_10055_10054_10059_10078_10079_10084_10083_10073_10080_10070_10096_10082_10081_10060_423_10061_10052_10062_10050_424_10051,searchweb201603_8&btsid=a894b254-fa3b-4704-8f38-b6f8753d8fdd

 

[JK71]

Hi, thanks for the interest.
Done some tests today as weather was dry.
Battery fully charged at 83v, I then took off at half throttle which was all good, soon as I hit full throttle all the voltage drops to 15volts the LCD & bike shuts down & turns off.
However, within a few minutes with a multi meter connected to the battery it reads 74volts but when ignition is on it drops to 13volts.
If then left for half hour everything reads above 80volts....

The wiring diagrams (Chinese) says wire battery to control unit.
I have wired battery to 40amp fuse to an on/off switch & then onto control unit.
I am a engineer not electrical but was advised to fuse it with on/off switch.

Will continue testing, readings etc
Any advise would be appreciated & thanks again

 

[Danidl]

Hi, thanks for the interest.
Done some tests today as weather was dry.
Battery fully charged at 83v, I then took off at half throttle which was all good, soon as I hit full throttle all the voltage drops to 15volts the LCD & bike shuts down & turns off.
However, within a few minutes with a multi meter connected to the battery it reads 74volts but when ignition is on it drops to 13volts.
If then left for half hour everything reads above 80volts....

The wiring diagrams (Chinese) says wire battery to control unit.
I have wired battery to 40amp fuse to an on/off switch & then onto control unit.
I am a engineer not electrical but was advised to fuse it with on/off switch.

Will continue testing, readings etc
Any advise would be appreciated & thanks again

Hi do you note that there is a discrepancy between the specs you quoted and the specs listed in the aliexprress listing. Your earlier post indicated a rated discharge of 30a and the Ali more like 50 a when you close the throttle for full power you are demanding at least 41 amp . 72v at 3000w ... Actually a lot more as the motor is not rotating so probably closer to 150a. This is much above the ratings for the battery and it's protection circuits will kick in. When you use 50% of throttle the bike starts indicating that you are below these protection thresholds.
The fact that voltage recovers off load and then drops is indicative of discharged cell s creating a high resistance within the battery pack. A 20ahr battery of your spec should have 140 cells arranged in 7 parallel sticks of 20 . All it requires for failure would be for the BMS to lose contact with any of the 20 cells

 

[Deleted member 4366]

The dropping to 15v means that the BMS is shutting off. That will be because:

• The BMS is faulty
• The voltage in once cell group is falling below 3.0v
• You're drawing more current than the BMS limit.

The controller is 30A and the battery is rated at 50A so that should be OK.

One thing I would check is whether you have a false positive on your phase/hall connection. That can cause higher current to flow than the controller's rating.

The coming on at 74v is a bit worrying. That implies to me a problem with the cells - maybe some of the group not connected properly.

Another thing you could try is to put your voltmeter on the charge socket, which might give a better indication of what's happening to the pack voltage.

 

[mountainsport]

Hi there, KirstinS had asked you a very good and important question which you had forgotten to answer regarding the controller rating. Every bit of information from you counts.
The issue that you are experiencing needs to be rectified quickly because this is so annoying and frustrating. And people on here are willing to help you all the way.

MS.