I have found a cordless vacuum cleaner which had no plugpack/power supply. It has a battery pack of 18650's, 29.5v worth, and the charging "smarts" are all in the battery pack, so there is only a D.C. input jack on the side. I have set up another bunch of 18650's in series, with an ammeter and voltmeter to work out what I need for an input voltage to charge the vac. battery pack.(I don't have a variable power supply which can supply a couple of amps at this voltage). If I go more than about 5v over (around 35V), it looks like it "pulse charges" the batteries e.g., it goes to around 1.5amps for 2 seconds every 10 seconds. If I go down a bit in supply voltage (say 31V), it will charge steadily at 1.5amps , then the current slowly reduces to zero after a couple of hours. I am trying to work out if this "pulse charge" mode is an over-input voltage protection type set-up, or is this how these chargers start out, then go to a steady-state charge after a while. I fixed the original mechanical problem with the vac. (the reason they threw it out = jammed housing, so could not empty it), and the unit is less than a year old, so I am assuming the batteries are OK. I can charge the batteries with my manual "increase the voltage by adding another battery" method, but I would like to find/make a constant voltage unit for charging.
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