The connector thing would work fine in theory. I can't imaging how hard it would be to pull apart a 24 pin Anderson block though. Finding the right kind of connector would be the trick.
Similar ideas have been bouncing around in my head too. From connectors and switches to a completely flexible array of cells connected by solid-state relays. Rearrange cells in any configuration on the fly ... even take exhausted cells out of circuit.Malcolm said:...
Am I right in thinking that if I could find a fairly simple and practical way of switching cells in a pack from series to parallel that A123 cells and LifeBatt cells should balance themselves perfectly well without any help?
The idea is to run wires from each cell to a multi-pin socket (possibly two). The cells themselves would not normally be connected to each other. Instead, you have two plugs that fit each socket; one is wired with jumpers to give a parallel (balancing) configuration, and the other wired to give a series (run) configuration. If you fit the parallel plug whenever the pack is not in use you can keep the pack perfectly balanced until you need it.
You also have the option of charging the entire pack as a single parallel string at 3.7V, although I'm not sure how useful that would be.
Granted it's not a very practical idea for A123 cells, but for LifeBatt cells with their screwed terminals it seems workable. For a 12s pack I could use two 12-pin trailer plugs and sockets. As long as I use 10 gauge cable, solder the connections to the sockets and keep the runs as short as possible it shouldn't add too much resistance.
In my limited experience with A123/Dewalt packs a common out of balance scenario seems to be one cell lower than the rest. So balancing via resistor shunts is going to bleed all cells in the pack but one.fechter said:If you use the shunt regulators on each cell and one full voltage charger, the shunt resistors won't dissipate any power unless a cell is out of balance. Normally, I think the shunts wouldn't be doing much since only a slight difference in current should keep the cells in balance.
Charge current will likely be different for different folks. Being able to charge in 15 minutes is wanted by most everyone, but not necessarily needed. The cost of fast charging versus overnight, or somewhere inbetween will probably make the difference.Jozzer said:I think 10 amps is more than enough for most Ebikes, and more to the point, it is more than most of the chargers that are suitable for our use (old SLA/NiMh chargers) put out.
For motorcycle type applications, where more charging current would definitly be desireable, the board could be fitted with a heatsink, and mounted in open air or fanned, or a new board made with components chosen for higher loading...
Or if you hope to realize most of their discharge potential.John Reid said:Basically you only have to balance the cells well if you are charging them without any individual cell protection.
Malcolm said:Stupid question for the day:
I've bought a 30A/5V power supply (originally used for LED lighting systems) and trimmed the supply voltage to 3.8V. What will happen if I connect a pack of 10 parallel-wired DeWalt cells direct to this supply? Will the cells stop charging when they reach 3.8V, or will they carry on charging?
I guess what I want to know is whether a lithium pack acts as a self-limiting load, which would make things nice and easy.
I know Richard and Beagle have put together a little circuit for switching off a power supply automatically,
http://endless-sphere.com/forums/viewtopic.php?t=278&postdays=0&postorder=asc&start=150
but could I just replace this with a timer plug that I set for roughly the length of time that will be needed to recharge the pack?
Trying to keep things as simple (and cheap) as possible.
fechter said:You might want to put some load on it when you are adjusting it.
There should still be a way to trim it lower.