48V 20Ah LiFePo4 question

[E-Chopper]

Hi again

i read the the Battery FAQ but im not sure ......

Last week the weather was fine, so i take the chance to make another short Testride with my D.I.Y Bobber .
I only drive a distance of 5 kilometer to see how it works and check the bike (most under full load "mountainclimbing") .
While i was driving back to my workshop i check the Voltmeter is shows 44Volt (+-1Volt) at full throttle .
Without push the throttle the Voltage goes immediately back to 52,6-52,3 Volt .
Back in the workshop i recharge the battery .
The batterycharger reload the two batterys simultaneously with 2 Amps (i measure it) .
After 4 hour the Charger stop´s... the Batterys was full (56,8 Volt) .

So now my question... if these Batterys were charge with 2 amps 4hours long that means i took 8Ah power from the 40Ah batterypack´s .
Is this thought more or less right

Next question ... how deep can i handle the Voltage ,if 2,5 volt per cell is the bare minimum i must stop driving and recharge at 40 Volt ( measured at full load ) ?!?
I had an Voltmeter on board so i can check the Voltage while drive so is a minimum Voltage of 2.5v per cell *16 = 40v under load ok !??


i dont want to injure the batterys .
What´s our opinion !

My data:
Batterys: 2 pice - pararell(40Ah) -the BMS rechargecable was connectet togehter - 48V 20Ah LiFePo4 - 960Wh- 280*180*110mm- Factory:Wolong
(i think inside one pack there are 16 cells includet BMS)
Motor:HPM3000b- 3KW
Full load amps : my controller gives the motor only max 70 amps .

thanks in advance

Martin

 

[999zip999]

2.8v lower than that is zero 45 -46 volt. Meaning there's no power and with lfepo4 flat discharge curve when it starts dropping it very late. Charge.

 

[dogman dan]

First of all, the stopping point is when you reach the voltage you decided on, while not under load. BTW, your sag under load is big enough to be pushing your battery pretty hard, despite it's large size. Less than 5v sag would be easier on the cells.

However, once it's showing below that cut off voltage under load, the battery will appreciate it if you lower the load some, and lower it some more when really in that last mile.

Bottom line, if your battery is getting really hot, much beyond just warm, back the hell off that throttle.

You'd likely be happier if you get full data on your discharges, using a watt meter. Sounds like you have enough invested in the project to get the best, a cycle analyst. Likely just a stand alone type, but still very nice to get all that data. You'll know exactly what your usage is, and know exactly what your real total capacity is. It's not 40ah under heavy loads. It will be somewhat less.

 

[E-Chopper]

Thanks for our respond .

So next testride i check the temperature of the Lifepo cell´s ( under full throttle) .
If they getting to Hot (above 45 C) i will reconfigurate the shunt or i controll myself and dont push the throttle to hard .
Now the Bike max.speed is 49mph .
I think i will lower the Amps for not torture the Lifepo´s .
Less Amps means lower speed but thats no matter i only drive inside the City (30mph allowed) :wink:
May a buy a cycle Analyst must think about it !!!! ............ in the ex-gastank there was enough space.............

grettings
Martin

 

[DAND214]

What motor are you running that you can do 49MPH not kph on 48v battery?

Dan

 

[E-Chopper]

Hi again
Thats my miscalculation .sorry .
According to the speedometer the Bike actually drive 70kph that´s not 49mph ...74km/h is around 43mph
The speedlimit for this bike in the city is not 30mph it is 27mph that around 45kph !!
my mistake........

The motor is a HPM3000b from GM connected to a Gearbox with five gears .
Its difficult for me to say whats the top speed on a normal straight street because my testtrack had a slight ascending or slight incline so the speed varies !!
Next time i will drive a long straight street to determine the real kph According to the speedometer and post it .(and check the temperature of the Lifepo )


Greetings
Martin

 

[DAND214]

Thanks Martin, I thought it was a bike not a Motorcycle. That was a large voltage drop for a ebike.

Dan