0
\$\begingroup\$

I have a 12 volt Ni Cad Screwdriver battery (to be exact, it is a Black & Decker Firestorm) I would like to find the amp-hours of the battery. The battery doesn't say anything on it (except that it is 12 volts), and I couldn't find any info online. I have no amp meter for testing amps drawn/time, but I tested a 12 volt 21/5 watt bulb and it lasted around 45 minutes. I did the division of (21/5)/12 and got .35 amp hours if it lasted an hour, but it was only 45 minutes and that would be less than .3 amp hours. I don't think this is true. So am I doing anything wrong and if so, what should I fix, and how can I find the amp hours?

edit: The model number of the pack is ps160 12v type 3 power pack

edit 2: I just figured out that the 21/5 means there is 2 filaments and doesn't mean "21 divided by 2" so I probably used the 21 watt because I used the brighter one.

\$\endgroup\$
  • \$\begingroup\$ Working backwards through your math, you had 0.35Ah with a 1 hour discharge, suggesting 4.2W. This is neither the 21W filament, nor the 5W filament. Which filament did you use in your discharge test? \$\endgroup\$ – HikeOnPast Dec 3 '12 at 4:26
  • \$\begingroup\$ oh I thought it 21 divided by 5! silly me!! \$\endgroup\$ – skyler Dec 3 '12 at 4:30
  • \$\begingroup\$ I used the brighter one, which was probably the 21 watt \$\endgroup\$ – skyler Dec 3 '12 at 4:31
  • 1
    \$\begingroup\$ Bingo. 21W, 12V, 45min = 1.31Ah \$\endgroup\$ – HikeOnPast Dec 3 '12 at 4:32
3
\$\begingroup\$

The Black & Decker Firestorm 12 Volt drill / screwdriver FS1202D seems to match your description, I have the same product. This model uses a 12 Volt NiCd 1.2 Ampere-hour battery pack.

If your experiments indicate a much lower ampere-hour rating, that could be due to battery aging, charging issues or the battery being loaded beyond the current / continuous operation parameters it is rated for.

If you could provide the screwdriver model number, a more definitive answer could be obtained.

\$\endgroup\$
  • \$\begingroup\$ +1. Good bit of detective work, and 1.2Ah matches nicely with the rough calculation in comments for the 21W bulb. \$\endgroup\$ – Brian Drummond Dec 3 '12 at 10:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.