Dennis Miles wrote:
When utilizing DUMP Charging, the particular cell chemistry makes a difference, the PbSO4 Lead acid can be charged with a heavy current but, lithium can not.
Agreed. What I wrote applies to lead-acid batteries. You can connect other chemistry batteries in parallel, but they are not as safe or foolproof as lead-acid.
Nicads can be discharged in parallel, but won't charge properly in parallel. Their voltage reaches a peak just before fully charged, and then *drops* as you finish charging. The first cell that peaks brings the voltage down so the cell in parallel with it won't fully charge.
Nimh have a similar problem, though not as severe. There is also a problem if the two cells are not at the same temperature. You can get a "thermal runaway" situation where a hot cell's voltage falls, so it draws current from the colder cell in parallel. This makes the hot cell even hotter, so it pulls even more current etc. until both cells are dead.
There are so many different lithium chemistries that it's hard to say what will happen. Small cells are routinely paralleled in laptops, which has resulted in some spectacular fires when things go wrong. But it's not clear what exactly is safe, and what is not safe. There is a great deal of hearsay and ignorance-is-bliss.
If you are charging from a much higher voltage pack you must limit the charging current, an ideal unit to do this is a DC motor controller.
No! A motor controller *depends* on the motor to provide an inductive load. The motor's inductance is an essential part of the circuit. If you want to use a motor controller as a battery charger, you *must* include a sizable inductor in series with its output. Without it, a motor controller can't limit current or regulate its output voltage.
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