DeWalt DC9000 36V charger
For a balancing charger, we have been investigating the DeWalt DC9000 36V one hour charger,
using an adapted DeWalt battery case to connect it to our packs.
Converted the empty case from a DeWalt DC9360 battery to allow the connection
of a built-up pack to the DeWalt charger. Do not connect the first and last balance wires. The DeWalt charger uses the main
connectors for those.
Never connect or disconnect any of the leads between the battery case and
the pack while the battery case is plugged into the charger.
This will damage the electronics module inside the case, as I have found out several times!
Some graphs of the cell voltages during charging with the 36V DeWalt charger. In the first two,
I had deliberately added some charge to one or two of the cells before the charge started, to see how it handled imbalanced cells.
The charge appears to be in three phases:
- Main charge at around 3 Amps, pulsed. First and then second lights flashing.
- Peak at 1.6 Amps, pulsed. Third light flashing.
- Balance at 150 mAmps, pulsed. All lights on solid.
The balancing does not start until after the first cell has peaked, which is the best way to do it. If you start balancing significantly before peak, you risk
making the balance at peak worse.
However, I'm not sure if these chargers are suitable for our purposes. They have a very effective balancing system, but unfortunately
they do not seem to carry on balancing for long enough.
Quite often it does not even bother balancing the pack, unless the cells are quite far out. While they ensure that no cell is overcharged,
they may not do a good enough job of balancing the cells to enable the pack to be charged with a simple (non-balancing) pack charger safely.
The pulsing is presumably just so that it can get accurate voltage readings from the cells, without being affected by voltage drop across the balance wires i.e. it only measures the cell voltage when the current is switched off.
The balance wires within the DeWalt pack are made of spring steel wire, and therefore have rather high electrical resistance - up to 300 mOhms each.
that the balancing only occurs AFTER all three lights on the charger come on solid, so you should leave the battery
connected for at least 20 mins after the three lights come on.
It is not clear how it decides to stop balancing, but it rarely seems to get all cells perfectly balanced.