Battery Connections

[Tom Wrigley]

Could anyone help please regarding battery connections. I have recently bought an old Transx Eagle 250 which has a duff battery , I am thinking of buying a battery pack to fit inside the original case which appears to be of a similar output but the original battery is the LiPo type and has 4 connectors Red Black then 2 more thinner wires Blue and white. The new battery only has the + and - wires plus the charger input. I have stripped down the original battery pack to find out where the extra wires are from on the BMS and they come from the SDA and SCL points on the circuit board.
My question is, would everything work ok without these 2 connections or should i find the location of the points on the new BMS board and solder these two wires in.
I am a novice regarding electric bikes but quite technically minded.
Thanks in anticipation of any help offered.
Tom

 

[amberwolf]

Some OEM bikes (prebuilt vs DIY) use communications between system components (like the battery and controller) in a way that means the system will not operate correctly or at all with anything other than the original model-specific components. SDA and SCL are serial data and serial clock signals; if these go from battery to controller the system may not work without hte original battery. There's nowhere you can connect them on any new part that would do what is necessary, even if the new part has the same labelled pads, because the new part (if it's not the same as the original, from the bike manufacturer) won't have the right software in it to know what data to send, or how to respond to data from the controller.

You can still test the system without these connections, with only the main + and -, and if it works you're ok, but if it doesn't work, you'd probably have to find another brand-specific battery to make it work (assuming that is the only thing keeping it from working). It's often cheaper to replace the OEM controller/display/sensor system with a generic one (or one that fits your specific needs in how it responds to you); sometimes this also means replacing the motor especially for middrive systems (motor at the pedals) vs those with the motor in the wheel, because the middrive usually has the controller and sensors all integrated into the motor housing) but often that will work with most controllers, once you figure out the wiring required.

 

[Tom Wrigley]

Thanks Amberwolf for your very comprehensive answer to my question.
I have connected a 12v car battery which lit up the display ok but obviously as it was only half the voltage it shows low battery but at least it shows that there is a circuit.
A new battery is unavailable for my bike so I was thinking of trying to replace it with a generic battery of a similar spec.
I think my best bet would be to borrow one to try and see if all the functions work before the expense of buying one which would be useless if it doesn't work.
Thanks again for your help.
Tom

 

[E-HP]

Thanks Amberwolf for your very comprehensive answer to my question.
I have connected a 12v car battery which lit up the display ok but obviously as it was only half the voltage it shows low battery but at least it shows that there is a circuit.
A new battery is unavailable for my bike so I was thinking of trying to replace it with a generic battery of a similar spec.
I think my best bet would be to borrow one to try and see if all the functions work before the expense of buying one which would be useless if it doesn't work.
Thanks again for your help.
Tom

Do you have more than one 12V battery? If so, you could wire 3 in series and test the system without having to borrow a 36V battery.

 

[Tom Wrigley]

I connected 2 car batteries in series to try it and everything seems to work except the voltage display which is fine.
I could get a separate small display and wire it in to the battery.
The blue and white wires from the battery obviously just powered the voltage display.
Thanks for your help.