Low Capacity Battery

[jerrysimon]

Paul,

No I am not going to use a BMS. I think for the cost its worth seeing if they work without one. I guess I will have to make sure that the controller shuts off before the cell voltage drops too much as this in the long term will certainly damage them.

There is a lot of stuff on line and mixed views of whether they need a BMS and or balancing or not.

The balancing tabs will allow me to measure the cells after a few charges to see what is happening. I can then use a cheap RC model charger like the Turnigy Acurcle to charge/balance them.

When not using that I will use a standard cheap 36v 1.6a charger when they are connected together.

I am not expert though have played arround with Ni-Cads, NiMh and Lithium Polymer batteris in my model aero/heli hobby, so I can make up a basic pack or two. I have ordered ones with welding tabs as this makes it easier and I won't have to solder directly onto the battery which can damage them.

I am not really into the detailed techy stuff and more an enthusiastic amateur. Its all going to be an experiment really and just for fun, as I like messing around with this stuff

Regards

Jerry

 

[emissions-free]

Fair play jerry

I'd say as long as you are careful they should be ok. Maybe you could knock up a resistive load and check it on the bench before fitting it onto the bike. You wouldn't want to trash the cells. A resistive load can be done in many different ways and they don't have to cost the earth. I bought a pair of 2ohm 750 loads and they weren't so expensive (custom made) but would imagine their a bit pricier in the UK. I'd say you'd want to put a load of say 3 ohms which should result in about 12A. I've found 250W controllers to be typically 15A.

Also a BMS isn't so expensive if you are running fairly sensible current levels and it would happily control a much bigger pack also, plus you could use a much simpler charger so it'd probably pay for itself. If you're gonna run parallel packs I think you'll need isolating shottky diodes to prevent any problems with packs that have different charges. I'd recommend a BMS for sure, it will keep the cells safe and remove all the faffing around. I can find out the price for the unit that I have in some of my packs which hasn't missed a beat even with far bigger motor than recommended? I'll be getting a few of these anyway, so it's no bother to pop 1 in the post

 

[jerrysimon]

Ok thanks Paul I will give you a shout later maybe.

Its gonna be a couple of weeks at least before I have all the cells together.

I don't plan to run them in parallel as its only for short trips.

Regards

Jerry

 

[daniel.weck]

I'm keeping an eye on eBay's DeWalt 36V 2.2Ah packs, and I just stumbled upon this video and documents:

YouTube - How to Dissassemble Dewalt 36V battery

Dissecting DeWalt 36V Packs (A123 Systems)

Disassembly of a DeWalt 36v Battery - RC Groups

How To Build a Battery Pack from A123 Cells - RC Groups

(further research on this forum revealed even more info...it's just new to me as I never really looked into battery options)

 

[jerrysimon]

Dan I have been through most those videos too. Dewalt packs here in the UK are really expensive even second hand. You can buy much cheaper NEW A123 sells from HK with solder tabs on them.

Regards

Jerry

 

[daniel.weck]

Yes, they are very pricey indeed !!

I just came across this video of the pack-macking process, involving a nice soldering job that doesn't cover the vent holes of the A123 cells:

YouTube - Hyperion A123 Cell Assembly Video

YouTube - 13 a123 Systems LifeP04

Nice to know that you can get the cells with tabs on already though !

 

[emissions-free]

What is the approximate cost for the A123 cells from HK? Be interested to see how these cells behave under load but you'll need a very low resistance to get the kind of current they can deliver. Be very interested to see how the voltage sags under different loads. Getting a few of these is also on my ever expanding ist of things to do and spend my money on

With a single cell you would need about 0.1 ohm to get 30A out of them. I would have thought that is quite achievable by just using a length of thick copper cable and you could use a shunt resistor or current clamp to measure the actual current flow. Maybe don't start with as low a resistance as that, just to make sure the cable is sufficient for the power being dissipated. Just have to make sure you monitor the voltage, as you do not want to run them below the specified minimum voltage and they do drop very quickly at the end of the discharge. Wouldn't recommend using more than 1 cell to do the tests as the power output would start to become quite serious

 

[daniel.weck]

What is the approximate cost for the A123 cells from HK?

fleeBay is your friend:

a123 cells, Consumer Electronics, a123 battery items at low prices on eBay.co.uk

 

[daniel.weck]

Foil-pouch cells are are a little bit more expensive than the cylinder form, with an impressive C-rate. Has anyone here tested these ?

A123 Systems M1, 2300mAh 1s1p Einzelzelle, 11,50 € - Lipopower Der Akkuspezialist, Lipo, LiFepo, LiFePO4, FePo, Balancer, PCB, Lithium, Akkus, Adapter, Steckverbinder

LiNANO 2,5 Ah 3,2V LiFePo Einzel-Zelle SL-FHC (5C), 14,00 € - Lipopower Der Akkuspezialist, Lipo, LiFepo, LiFePO4, FePo, Balancer, PCB, Lithium, Akkus, Adapter, Steckverbinder

 

[emissions-free]

Foil-pouch cells are are a little bit more expensive than the cylinder form, with an impressive C-rate. Has anyone here tested these ?

A123 Systems M1, 2300mAh 1s1p Einzelzelle, 11,50 € - Lipopower Der Akkuspezialist, Lipo, LiFepo, LiFePO4, FePo, Balancer, PCB, Lithium, Akkus, Adapter, Steckverbinder

LiNANO 2,5 Ah 3,2V LiFePo Einzel-Zelle SL-FHC (5C), 14,00 € - Lipopower Der Akkuspezialist, Lipo, LiFepo, LiFePO4, FePo, Balancer, PCB, Lithium, Akkus, Adapter, Steckverbinder

14euro a cell for 2500mAh, 3.2V, so for 36V, 10Ah, you'd need 12s 4p, 48cells. So 536 euro before you get a BMS and put it together into a pack Rather expensive for a self build.