Using 2 Batteries ??

[davey_b]

Apologies if this has already been discussed on here, I did search but couldn't find anything.

I'm adding a second battery to my bike - both are 5.5kg, 36v 12Ah running the 250w motor.

Firstly, what is the best way to mount both batteries that gives me easy access (for charging off bike) but maintains security. I was thinking of a pannier style bag dropped over the back but as close to the seat, without interfering with the pedals, as possible. I already have a pannier bag which is normally pretty full on my long treks.
Do these even exist or will I have to get them made?

Secondly, is it possible to link the batteries so I don't have to switch between them or charge them separately?
This isn't a massive problem but it is a bit of a pain.

 

[daniel.weck]

Apologies if this has already been discussed on here, I did search but couldn't find anything.

Welcome to the forum !

I'm adding a second battery to my bike - both are 5.5kg, 36v 12Ah running the 250w motor.

What kind of bike is this (26" wheels, diamond frame ?), and what type of batteries (elongated shape, or squat parallelepipedic type ? Aluminium case or just exposed cell wrapping ?)

Firstly, what is the best way to mount both batteries that gives me easy access (for charging off bike) but maintains security. I was thinking of a pannier style bag dropped over the back but as close to the seat, without interfering with the pedals, as possible. I already have a pannier bag which is normally pretty full on my long treks.
Do these even exist or will I have to get them made?

Given the weight, I would definitely pursue having the batteries as low as possible, for example at the bottom of the pannier bags on each side. Are you able to customize the battery wires so that they reach higher up nearer the opening of the pannier bags ?

I assume you have strong panniers with some kind of integrated frame to protect against shocks with the bike frame. Otherwise you'd need to make such frame to spread the load and points of pressure. (it really depends on your type of batteries)

Secondly, is it possible to link the batteries so I don't have to switch between them or charge them separately?
This isn't a massive problem but it is a bit of a pain.

Two batteries in parallel should be linked with an ideal diode to avoid one pack displacing current into the other. Tiberius sells them on the Pedelecs and Endless-Sphere forums:

http://www.pedelecs.co.uk/forum/electric-bicycles/4140-ideal-diodes.html#post53493

Endless-sphere.com • View topic - Ideal Diodes - New High Current Version

Each of your batteries probably comes with its own BMS ("Battery Management System" electronic circuit) designed to protect the cells against over-charging and discharging (LVC Low-Voltage-Cutoff, etc.), and to balance the pack.

Using a diode for discharging the 2x paralleled packs is probably just fine, but I would have thought that your 2/3 Amps charger would work better by charging the packs separately.

Cheers, Dan

 

[davey_b]

Hi Dan,

thanks for the welcome and the reply.

The batteries are the elongated, aluminium case. they have BMS
Bike is 26" wheel - has no make on it but works really well.
I'm changing the frame, about to purchase a new one.

I can customise the wiring - I'm so not used to dealing DC, willing to learn though.
The pannier has a 30kg weight limit, bolted to the bike frame.

Using a diode for discharging the 2x paralleled packs is probably just fine, but I would have thought that your 2/3 Amps charger would work better by charging the packs separately.

The only probably with this is when charging overnight I'll either need 2 chargers (extra stuff to carry) or get up in the night to switch the units. This isn't really a major hassle and if it's the only way then so be it.

Thanks for all the information and the link to the ideal diodes.