Get another 36V and connect it to the charge port on my present battery, or swap to a 48V higher AH battery?

NotHungry

New Member
I bought a ready made e-bike just to get my 'feet wet' if you will.

It has a bafang RM G020.250.D rear hub motor

a X866-AA003A 36/48V controller (cut off 27/38v, current limit 15a)

display: KD58C

the motor is pretty good actually, just the battery is horrible 7.8aH .. need to upgrade so i can go on long rides..

i was doing my research online and learned that i have two options

A) get a 36V higher aH battery, and hook it up to the battery charge port on my existing battery (make it act like a power bank for mobile phones, just for bikes)
B) get a new battery..


now this is where i am not sure.. is A possible? i've read it on many places, what are the pros/cons?

when it comes to B, taking into consideration my 'hardware' i believe this motor/controller supports 48V battery as well, does it? can you guys please help confirm?

if yes, what is better, to just trash this 7.8aH battery and get the biggest aH battery at 36V or to upgrade to 48V (i am looking for RANGE, not for speed increase thats not the focus)


looking forward to your answers

thank you so much!!

A from Budapest, Hungary
 

Timpo

Well-Known Member
yeah over volting is common, as long as your controller can handle 48V, it's fine.

 

Timpo

Well-Known Member
I bought a ready made e-bike just to get my 'feet wet' if you will.

It has a bafang RM G020.250.D rear hub motor

a X866-AA003A 36/48V controller (cut off 27/38v, current limit 15a)

display: KD58C

the motor is pretty good actually, just the battery is horrible 7.8aH .. need to upgrade so i can go on long rides..

i was doing my research online and learned that i have two options

A) get a 36V higher aH battery, and hook it up to the battery charge port on my existing battery (make it act like a power bank for mobile phones, just for bikes)
B) get a new battery..


now this is where i am not sure.. is A possible? i've read it on many places, what are the pros/cons?

when it comes to B, taking into consideration my 'hardware' i believe this motor/controller supports 48V battery as well, does it? can you guys please help confirm?

if yes, what is better, to just trash this 7.8aH battery and get the biggest aH battery at 36V or to upgrade to 48V (i am looking for RANGE, not for speed increase thats not the focus)


looking forward to your answers

thank you so much!!

A from Budapest, Hungary
Also, if range is your focus, Wh is what matters.

48V x 12Ah = 576Wh
36V x 16Ah = 576Wh

So in theory, 48V 12 Ah battery and 36V 16Ah will give you the same range, assuming that you're consuming same amount of wattage.
 

NotHungry

New Member
Thanks for the replies, should I just get another 36V battery and connect it to the chargeport of my existing one ? What do you think about that?
 

tomjasz

Well-Known Member
Thanks for the replies, should I just get another 36V battery and connect it to the chargeport of my existing one ? What do you think about that?
Gosh NO to connecting batteries to charge ports!! You could mount two batteries and switch between them.
BE993B61-47C5-46DF-916E-6E2B7FF1DFDB_4_5005_c.jpeg
 

tomjasz

Well-Known Member
BTW that is an old design. Some newer Bafang GD hub motors can run 36V and 48V. I wouldn't attempt it with your motor unless you can hold the watt input. The Bafang G310 from Grin can run 36v and 48v.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
Agree with Thomas. Using a battery's charge port to hook up a second battery is a really bad plan. That charge circuitry leads directly to a battery management system (BMS) that will likely smoke immediately.

Next time you're looking for an e-bike on the cheap, focus should be kept on the motor and on the battery of this potential purchase. Get those right and about anything else can be replaced/upgraded inexpensively.
 

harryS

Well-Known Member
It seemed counter intuitive to me to connect batteries via charge ports, but I tried it. If they are at the same voltage, it's reasonably safe and does work. The aux battery only supplies charging current, so if the first pack is starving the controller, it continues to do so.

As Micah said in his video, he loses efficiency because of losses from charging, i.e., the total AH doesn't add like it would if you just connected in parallel. So why not connect in parallel? Your current is now shared, so that's better longevity for both packs. No efficiency loss.

So I do wonder he he did it that way. Maybe it was to simplify the wiring for the DIY novice. And if you charge thru the remaining charge port on the aux battery, they will always be at the same voltage, so the novice won't be connecting unequal voltage packs

I have a few smaller 36V 4AH and 36V 5AH packs. I run them in parallel all the time, although I only parallel packs with similar cells.
 

tomjasz

Well-Known Member
It seemed counter intuitive to me to connect batteries via charge ports, but I tried it. If they are at the same voltage, it's reasonably safe and does work. The aux battery only supplies charging current, so if the first pack is starving the controller, it continues to do so.

As Micah said in his video, he loses efficiency because of losses from charging, i.e., the total AH doesn't add like it would if you just connected in parallel. So why not connect in parallel? Your current is now shared, so that's better longevity for both packs. No efficiency loss.

So I do wonder he he did it that way. Maybe it was to simplify the wiring for the DIY novice. And if you charge thru the remaining charge port on the aux battery, they will always be at the same voltage, so the novice won't be connecting unequal voltage packs

I have a few smaller 36V 4AH and 36V 5AH packs. I run them in parallel all the time, although I only parallel packs with similar cells.
In my experience that’s an accident waiting to happen for many new riders.
You are more the exception. You are one of the most experienced posters and hobby builders here. In my years of support I’ve seen several near disasters. But only gutted garages.(rolling eyes)
 

NotHungry

New Member
Thanks guys, i have the RM G020.250.D motor and a controller that supports both 36v and 48v so ill just buy another battery with more capacity and replace the one i have on right now
 

tomjasz

Well-Known Member
Thanks guys, i have the RM G020.250.D motor and a controller that supports both 36v and 48v so ill just buy another battery with more capacity and replace the one i have on right now
The motor is NOT capable of 48V . 43V max! 36v battery is 42v fully charged. Sorry if you already under stand that .
 

CityExplorer

Well-Known Member
Agree, do not try to use the second battery connected to the charge port of the first. Really bad idea!!

Keep it in a backpack or Pannier and swap it when necessary. You may find just using the larger battery is enough and you don't need two batteries. As long as the second battery is plug'n'play I'd go that route.