Battery Configuration

[gullarm]

Is it better to have multiple battery's or keep the number to a minimum.

The reason I ask is I'm looking at building my battery pack for my bike and after seeing the multiple configuration options that can be made ( price very similar )

For example

2 x 18.5V 8000maH - wired in series
or
4 x 18.5v 4000maH - wired in parallel and series

 

[trex]

it depends very much on whether the packs have individual BMSes built inside. If you buy lipo (from hobbyking), they don't have internal BMSes then 2 x 18.5V 8AH is easier to control and alarmed, if you buy Lithium ion (from aliexpress) then 4 x 18.5V 4AH are more resistant to shock damage.

 

[OldFart]

Personally its down to the money. I required a 10s pack to get 36 volts which is the same as you. But my charger only does upto a 6s pack.

I went for a pair of 5s 4Ah packs and plan to add another pack giving 8Ah or 2 more giving me 12Ah.

Already ordered some volt meters for them. I found the 4Ah (£45)?to be £15 cheaper than the 5Ah battery. I thought an extra £30 and i can have 8Ah. Where the 5Ah wouold be £60+ delivery costs.

Also i think the advantage is that if one cells goes down i should be able to remove it and still have some power left to get me home.


trex. The BMS in the aliexpress batteries you mention. What is that exactly?
I bought the 4Ah HK ones and they have balance leads that i plan and have ordered volt meters for.
How do the aliexpress ones differ?

Thanks.

 

[trex]

@ OF: I gave Aliexpress as the popular source for Lithium ion batteries. These packs have BMS with over voltage charging protection, undervoltage protection, temperature cutout and output fuse as standard, some have anti-arcing switch as standard. Connecting them together is safe and easy because you do not need to monitor the voltage of individual cells, this is done by the BMS. With HK lipo, you need extra hardware to monitor the cells. By the time you factor in the BMS, charger, PSU, cell alarm and about 10%-15% reduction in nominal capacity due to the obligatory 3.2V low voltage protection, the cost benefit of HK lipo vanishes.

 

[OldFart]

Ahhh, Thanks i just learnt something new (again)

I assumed when people mentioned BMS they were talking about balance leads etc.

What are the capacities like from Aliexpress? Variable? Knowing my luck i would order some 20Ah batteries and get 2Ah.

I chose the HK ones because they came from the UK so quick delivery and obviously didnt know any better.

I have ordered some voltage meters with alarms. So part way to a BMS, I think? They were £1.30 each.

Thanks.

 

[trex]

@OF:
Most members who buy from China buy batteries from bmsbattery.com with their motor wheels to reduce shipping cost.
I did not mean to denigrate HK lipo - they are good choice if you want the lightest possible batteries, although new high tech Lithium ion batteries are quite light, like this one on the Woosh Zephyr-B 36V 10AH weighs only 1.5kgs:

Building the same with HK lipo would take two 10S 5000mAH blocks. Add wiring loom and a bag, would end up weighing more than that and still can't be locked to the frame.

 

[OldFart]

Thats another point i guess. Although this bike has plenty of underseat space for the batteries. where the original SLA's are/were. And the top box. I dont have a decent case for the batteries.

Just thinking about that tonight. I butchered an old computer PSU to get the socket to build a case, Added some 30A wiring to the pins.

I could reuse the old SLA case i guess, But i will need a lot of batteries to fill it or a lot of packing.

Choices choices...