Ebike, battery splitter to backup battery

[edlog20]

Hi I would like to add a second battery to my bike to extend range. Could I just add a splitter to the battery cable? Both batteries have switches built in, so when one battery drains, I'ld turn it off and then turn the back up on. Any thoughts on whether this would work? Would charge them both separately. Both batteries are the same voltage but the back up is much smaller ah. Thanks

I would like the back up battery to go in a seat bag, its a 40v xgt Makita battery. Im In the trade so I have a lot of these. When I do shorter technical rides would be able to use just the Makita batteries to keep weight down. When I do longer distances I'll be able to use both. Any thoughts or help on this would be great. Thanks!

 

[Chalo]

The packs will either need to be diode protected to prevent uncontrolled rushes of current between them, or you'll need to join them when they are at the same voltage (for example, both fully charged) and leave them both turned on to work together. Using the two packs in parallel is healthier for the batteries because it reduces their individual discharge rate.

 

[Diggs]

Agree with @Chalo above that batteries in parallel last longer and perform better.

There are battery combiners that are made for this. Here's one from Area13 -

Dual Battery Parallel connector

area13ebikes.com

 

[E-HP]

I agree with Chalo, but since it provides good performance benefits while sort of foolproof safety-wise. The scenario of running with only the small pack may kill it prematurely, so I’d adjust the controller current limits if you do that. Personally I can’t see where the weight difference would matter unless you do a lot of bunny hops.

Leaving them connected while using diodes or ideal diodes is going to be the safest and perhaps the least hassle. The third option is to direct parallel without diodes. That will combine their max current output for high peak current, however that creates more risk, so you should have a repeatable routine for safely charging them so you don’t burn down the house.

 

[edlog20]

Thanks guys, I'll get a proper battery connector like the one linked.
E-HP, does an ideal diode stop any current from travel back towards the batteries? If I install one of these on the positives cables to each battery will I still have to worries about each battery being fully charged when installing? I'll probably also install an online fuse one each line just be safe.

Cheers

 

[E-HP]

Thanks guys, I'll get a proper battery connector like the one linked.
E-HP, does an ideal diode stop any current from travel back towards the batteries? If I install one of these on the positives cables to each battery will I still have to worries about each battery being fully charged when installing? I'll probably also install an online fuse one each line just be safe.

Cheers

An ideal diode isn’t a diode, but a circuit that emulates a diode but without a voltage drop (fewer losses). Just look for one that can handle the current and voltage the battery can provide. It will have Both a + input /output as well as a ground input (for the circuit to work). You could use regular Schottky diodes, but you’ll have a voltage drop and losses.

 

[edlog20]

Any wiring diagrams for them? Cheers

 

[JackFlorey]

does an ideal diode stop any current from travel back towards the batteries?

Yes. Note that you can't use them with regen braking, but it looks like that bike is a mid-drive and thus cannot regen brake.

If I install one of these on the positives cables to each battery will I still have to worries about each battery being fully charged when installing? I'll probably also install an online fuse one each line just be safe.

No. The "high" battery will support 100% of the load until it reaches the voltage of the "low" battery, then both will supply the load.

A fuse is a good idea in any case if you are modifying the power runs.

 

[edlog20]

Thanks, is the grounding for the ideal diode a metal point on the bike?