discharging batteries

[adwt2004]

I have some power tool batteries i want to re-condition. If i was to take a standard bulb and solder wires to it and connect to the batt i know that would drain it.

Am i right in thinking that if i connected a 40watt bulb to an 18v battery i'd be drawing over 2amps?

How fast would it discharge an 18v 1.7ah battery?

I'm interested in the above and will most likely use a much smaller bulb but any answers would be interesting!

 

[ericmark]

A 40 watt 18 volt bulb would draw 2.2 amp but a 24 volt bulb at same wattage would be 1.2 amp and this will drop as it discharges.

Although it is good to completely flatten a cell it is not good to reverse charge a cell so when cells are connected together and we have a battery of cells than one should avoid going to 0 volts as this may cause some cells to reverse charge.

Also the heat of a soldering iron is unlikely to help the battery and I would not solder but find another way to connect.

It would take around 1.6 hours to discharge using a 24 volt 40 watt bulb but I would not take below 14 volt on an 18 volt battery.

It seems a lot of effort rather than just using the drill?

Also note when old Ni-cad batteries are completely discharged you can get crystal growth which will make the battery useless. On new batteries storing a 0 volts is a good idea but not with old ones.

 

[bernardgreen]

Am i right in thinking that if i connected a 40watt bulb to an 18v battery i'd be drawing over 2amps?

If it were a 20 volt bulb then at full brilliance it would be approx 2 amps

But it it were a 230 volt bulb then the current would be far less. Measured current for 18 volts into a 40 watt 240 volt candle bulb was 52 milliamps which is 0.05 of an amp.

The 20 volt bulb ( approx 2 amps ) would empty the battery in about 3/4 of an hour.

The 240 volt bulb (0.05 amp ) would take around 35 hours.

BUT completely draining the battery may do more harm than good to the battery. To re-condition one normally takes the battery down to its end point voltage and then re-charge.

How fast would it discharge an 18v 1.7ah battery?

as a rough guide Time = Amphours divided by amps