CEF50 External battery build

mike_kelly

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Aug 11, 2022
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Not possible. The Bafang charge connector is only designed for 2amps, the wires are not big enough to handle the current to drive the motor.
 

hamncheez

Member
Mar 9, 2021
28
5
USA
Not possible. The Bafang charge connector is only designed for 2amps, the wires are not big enough to handle the current to drive the motor.
My proposal is to leave the frame completely unmodified, and the auxiliary battery would connect directly to the charging port, which is again unmodified, so the power goes into the main battery.
I've tested mine with the supplied charger, the motor still turns on and runs when external power is supplied.
 

mike_kelly

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Aug 11, 2022
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All you are going to do is charge the main battery from the external, slowly, from the external battery. Not going to help much in a ride. For a 360whr 36v battery 360/36= 10amps 10/2=5 hours or more considering the external battery voltage will drop and as soon as it is lower that the main battery it will stop transfering energy.
If the charge port is simply in parallel with the main output port you risk all the dangers, with the exception that the small 2 amp charge wires would probably act as a fuse as they catch fire and burn.
 

hamncheez

Member
Mar 9, 2021
28
5
USA
All you are going to do is charge the main battery from the external, slowly, from the external battery. Not going to help much in a ride. For a 360whr 36v battery 360/36= 10amps 10/2=5 hours or more considering the external battery voltage will drop and as soon as it is lower that the main battery it will stop transfering energy.
If the charge port is simply in parallel with the main output port you risk all the dangers, with the exception that the small 2 amp charge wires would probably act as a fuse as they catch fire and burn.
So what you're saying is I should have ordered the 700wh battery!
 

mike_kelly

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Aug 11, 2022
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yep. If you are riding for two hours after work every day the 360whr is fine and lighter. if you want to do epic all day rides you need more juice.
 

hamncheez

Member
Mar 9, 2021
28
5
USA
yep. If you are riding for two hours after work every day the 360whr is fine and lighter. if you want to do epic all day rides you need more juice.
I got the custom 410wh battery, which sounds fine compared to the competition, but I ride at 5am and on my natural bike I like to do at least 2,400 feet of climbing, sometimes over 3,000. I was hoping to go even bigger on an ebike, but this motor in B mode reports a consistent 580+ watts, so if you do the math you aren't even getting 45 min before you hit the 20% cutoff to Eco mode. At first I was a bit frustrated, but physics is physics.
 

mike_kelly

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Aug 11, 2022
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I got the custom 410wh battery, which sounds fine compared to the competition, but I ride at 5am and on my natural bike I like to do at least 2,400 feet of climbing, sometimes over 3,000. I was hoping to go even bigger on an ebike, but this motor in B mode reports a consistent 580+ watts, so if you do the math you aren't even getting 45 min before you hit the 20% cutoff to Eco mode. At first I was a bit frustrated, but physics is physics.
Yes the motor is not designed to be used in boost except for short steep climbs. Bafang warns against using it for continuous boost riding and 700whr or larger batteries designed to enable this type of riding. Just not the right motor.
 

Freda

Active member
Feb 5, 2023
132
116
Vaasa
Off-topic, but I finally built an extender for my LCE930. It is a 13S1P battery with 2170p cells. Connected with a battery balancer between main- and extender battery to motor.

I didn’t want to make additional holes in the frame and connecting via charging port seemed too complicated, so I made a hole in the battery cover. Might well work on the Cef50 as well, it has been a lot of discussion about those!

Cable could be a few centimeters shorter for perfect fit. One benefit from a smart bms on the main battery is that I can switch it off and run only extender if I want to.

IMG_4041_Original.jpeg IMG_4043_Original.jpeg IMG_4042_Original.jpeg
 

patdam

Well-known member
Jan 17, 2019
837
573
france
Who really needs range extender ? with 480W i doing 21km with 1300m D+ and i have 50% of the battery left. As physically with the M820 help i will not try more 1500 D+ with my 100 kg weight. I whould like understand who needs range extender and for doing what ?
 
Last edited:

Freda

Active member
Feb 5, 2023
132
116
Vaasa
Who really needs range extender ? with 480W i doing 21km with 1300m D+ and i have 50% of the battery left. As physically with the M820 help i will not try more 1500 D+ with my 100 kg weight. I whould like understand who needs range extender and for doing what ?Who really needs range extender ? with 480W i doing 21km with 1300m D+ and i keep 50% of the battery.

Good question! I have two main batteries, on ~480Wh and one ~720Wh. Summertime I use the small one. I can ride around 3h and 40km on that one. I use mostly S assistance. Extender is nice when riding to my local hill, 30 minute journey, leave it in my backpack when going up and down the hill and then connect it again when going home. No need to worry about battery saving mode.

Big battery is for below zero Celsius riding temperatures, it takes a lot from the battery. And I also found building batteries very interesting, so I just need to come up with reasons to build them.

Also 50% battery left on bafang display is really not much at all.
 

patdam

Well-known member
Jan 17, 2019
837
573
france
Good question! I have two main batteries, on ~480Wh and one ~720Wh. Summertime I use the small one. I can ride around 3h and 40km on that one. I use mostly S assistance. Extender is nice when riding to my local hill, 30 minute journey, leave it in my backpack when going up and down the hill and then connect it again when going home. No need to worry about battery saving mode.

Big battery is for below zero Celsius riding temperatures, it takes a lot from the battery. And I also found building batteries very interesting, so I just need to come up with reasons to build them.

Also 50% battery left on bafang display is really not much at all.
you would mean that with 50% left for example, i couldn't doing 5km with 300 m D+. If i already done 1200 m D+ in 21 km for the first 50% ?

For the moment, i never emptyed the batteries with the M820,. but with the 15Ah i consumme at most 40% to doing 1700 m D+. (i can't do more phisically). it's my first use of the 10 Ah, but consumtion seem in line.
 

Freda

Active member
Feb 5, 2023
132
116
Vaasa
you would mean that with 50% left for example, i couldn't doing 5km with 300 m D+. If i already done 1200 m D+ in 21 km for the first 50% ?

Of course I cannot say exactly but seems correct. Comparing rides is hard with so many variables. I just really dislike the battery percentage shown and battery saving mode starting early. The extender is one way to have a light bike with enough energy normally and then add it when the need is greater.
 
Last edited:

temon10

Well-known member
Feb 8, 2022
663
547
Malang, Indonesia
Of course I cannot say exactly but seems correct. Comparing rides is hard with so many variables. I just really dislike the battery percentage shown and battery saving mode starting early. The extender is one way to have a light bike with enough energy normally and then add it when the need is greater.
agree
 

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