batteries

[steveH]

Has any one made up a battery using dewalt lith iron batteries stripped down, and do you have to had a bmu. thanks

 

[jerrysimon]

Yes have been using one for years now. No BMS required especially in the small configuration I use.

The cells are known as A123.

See my long thread here

After three years use my view is these are great if you want a small capacity light battery. If not just buy a ready built LifeP04 battery which are available from suppliers on here for as little as £200.


Jerry

 

[Deleted member 4366]

Has any one made up a battery using dewalt lith iron batteries stripped down, and do you have to had a bmu. thanks

Yes and no.

You can also use recycled laptop batteries as well, but the same applies: Unless they're new you have to do discharge tests to measure their capacity and check that you've got no self-dischargers. If you're lucky enough to get the 2000maH cells, you need about 50 to make a 10aH battery. You can't make it smaller because they don't give enough current like that.

Whether you use Dewalt or laptop ones, you have to be careful when soldering them not to damage them with heat, so leave as many strips/tabs on as you can and use them to solder your wires to.

You should make two 18v 5S or 22v 6s packs with balance leads, then you can use an R/C charger to charge and balance them, but you need a voltmeter or alarm to make sure that you don't over-discharge them.

You could use a BMS out of a knackered 36v battery, as long as it came from a battery with similar type cells. Many batteries have similar cells in 10S4P configuration for 36v 8, 9 or 10aH or they have 12S if Z
LiFePO4. The Dewalt ones are often high discharge, so you can make a lighter smaller battery. Whatever cells you get, read the designation on them and look up the datasheet so that you know what you're dealing with. They all look the same, but you get different chemistries, different voltages. different capacities and different discharge rates.

I think Dewalt use A123 cells these days, but you'd need to check. A123 are only 3.3v, so you need 12S to get 36v.

 

[jerrysimon]

Of course A123 has now gone out of business and as far as I know cell production has ceased. Actually I don't think the latest Dewalt batteries use them any longer.

DIY battery building is not for the faint hearted and although savings can be made (though remember your time has a cost) and you know you can repair them its certainly easier to buy something off the shelf.

One of the reasons I went down the DIY route was because I wanted them a certain shape and size to fit in the Brompton rear pocket and I only required a low capacity for my short commute.

Jerry

 

[steveH]

Thanks for the info, if i double up two 18v 3ah batteries do i then get 6ah, ie if i put then in parrallel.

 

[Alan Quay]

In parallel the Ah will double, in series the voltage will double.

 

[Deleted member 4366]

Thanks for the info, if i double up two 18v 3ah batteries do i then get 6ah, ie if i put then in parrallel.

You need four of them for 36v 6aH or six for 9aH.

 

[jerrysimon]

Salvaging that many cells will get expensive/very labor intensive. Again IMHO if you want a larger battery you are better off buying ready made/new.


Jerry

 

[Alan Quay]

BMS Battery will do you a 10 Ah bottle battery delivered for about £190. I think you'll be hard pressed to beat that with drill packs.

 

[Scimitar]

Has any one made up a battery using dewalt lith iron batteries stripped down, and do you have to had a bmu. thanks

I used Bosch Fatpacks, six of them, to give me a 36V 15Ah pack.
The cells are Konions, which are relatively fool-proof to charge /discharge without running the risk of fire, venting, or explosion.
I keep a careful eye on rate of discharge though, and don't stress them too much.
It's only worthwhile using toolpacks if you get them at a knock-down price; paying anywhere near the market price is pointless - you may as well just buy a Ping pack.

 

[jerrysimon]

Again salvaging cells from used tool packs is a lottery in terms of how many good cells you harvest.

After getting individual cells with tags which I had to solder together myself for my first DIY built pack I subsequently purchased my A123 cells new ready spot welded/tagged together in 6s1p packs. They also came with power/charge/balance leads. I then made up series connectors for the packs and added a fuse.

http://www.ebay.co.uk/itm/6S1P-19-8V2300mah-A123-systems-original-Li-RC-battery-/200531656688?pt=US_Rechargeable_Batteries&hash=item2eb09e3ff0

or

http://www.a123rc.com/category-65-b0-A123+Batteries.html

Again as stated probably easier buying a ready made battery pack if you want higher capacity.

My latest 36v,6Ah battery is made up of Konion cells 2 * 5s4p, the blue pack shown below. Again like the A123 cells Konions are becoming harder to source new. A123 of course will support far higher current draw without voltage sag.

Again these where made specifically for my Brompton conversions for a short 10 mile round commute, small footprint size to fit in the Brompton bag back pocket and low weight to keep overall carry weight of my conversions portable. Small packs of Konions will not support the kind of current draw that A123 packs of a similar size will. Again not a problem for my light assist low current draw conversions.

Regards

Jerry