I have been thinking about taking my DeWalt battery packs apart and adding one more cell to each string to get 36.3 volts. I will need to have some type of bank charging system. I thought I had seen some on the site but I can't seem to find them. What I would like to do is connect 5 or 6 strings of 11 batteries each together in a parallel buddy configuration and charge each set of parallel batteries with a it's own charger so I would have 11 small chargers to charge the pack. Has anyone done something like this?
Thanks to all in advance for your help,
Chas S.
Chas, I have a lot of links to A123/DeWalt battery information here: a123systems DeWalt batteries
The stock charger won't handle the situation you're describing -- the charger works through their BMS and their BMS only knows how to deal with 10 cells, not 11. That means coming up with a different BMS and charging system.
The R/C guys have developed a charger that with an adapter (the lipodapter) can charge A123 cells. You can find a link through the above link. However I never found any decent documentation on how to actually accomplish it, plus the charger pictures I saw looks more suitable for charging in a workshop/bench rather than being carried on a bicycle and being used to charge out in the field somewhere.
On the old V (V.com) there was an interesting post by Aerowhatt discussing how to safely charge lithium batteries. He was writing this when li-poly was the only game, as the A123 cells hadn't come on the market yet. IIRC he said it was best to, for charging, put all the cells parallel to each other and charge off one charger. In essence that is bank charging, and the pack will be automatically balanced. But it would mean disconnecting the normal pack wiring and reconnecting a different wiring that puts all the cells on one charger.
What I started to do with my dewalt packs (before I got frustrated dealing with all the fiddly bits) was to wire the existing packs such that one BMS could charge several packs at once. In this case you don't change the number of cells in the pack, because you're reusing the DeWalt BMS. It does mean building a wiring harness that bridges the BMS-pack connections in parallel across several packs. That was where I got frustrated with fiddly bits.
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
Thanks for the info but the chargers I found in the links are all string chargers and I want to charge parallel strings which are in a series string.
Maybe a picture would help.
I am looking for some chargers which will allow me to build a charging station to charge a pack like this to help keep the cells balanced.
Thanks,
Chas S.
How do you figure a 36.3 volt pack? The stock dewalt pack is really 33 volts, and when they claim it's a 36 volt pack they're lying. Er.. fudging. If you had an 11 cell pack then, yeah, 36.3v is probably the right value. But a 36.3v pack would not be chargable by the dewalt charger or manageable by the dewalt BMS.
What I tried to do is pretty close to what you're asking for. Namely.. inside the dewalt pack, between pack and BMS, there are two five-conductor cables that end in specific connectors. These connect to every cell in the pack and let the BMS sense/control/charge each of the cells. Where all the fiddly bits come in is to build sufficient extra cabling so that the BMS connections go to multiple packs in parallel. I lacked the patience to do this but I know others have done this.
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
Oh, um... http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3285 is a 1 cell LiFEPO4 charger which should be suitable for an A123 cell. It has only a 1/2A charging current though.
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
The endless-sphere forum has a discussion going about using banks of single-cell chargers to charge up multi-packs:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=2586&st=0&sk=t&sd=a
One way to do it is to use a full voltage charger to charge the whole series/parallel battery pack up fast, and then to balance using the single-cell chargers.
Regards,
Brian
Thanks that is in interesting link. I had never considered using individual chargers with so many cells, but they seem to make it work. By reading the link, I also realized that the way I did bank charging on my 5 battery 60v system used more wires than was necessary. I used 10, but really only needed 6 wires to the chargers.
Like those on ES, it would be nice to find a charger that was more than 2 amps that could charge LiFePo4 batteries. I will check with mountain to see what he has found. If it is appropriate for TS LFP batt's with 19 or 20 cells, then it makes an EFUN-D or Paladin much more appealing in my eyes. I need to do more research, but it seems like you don't need a BMS if you have a charger for each cell - just need to monitor the batt's periodically and worry about cut off voltage? So much to learn here.
ZEV 7100 Alpine
Fort Collins, CO