On 19 Dec 2001 at 10:28, Brendan wrote: > When I was doing those Nimh tsts I also mesured the > amperage of the cells, the best alkaline battery testd > at 1.6V 40~50 ma, a 1600 mah nimh battery was 1.3v > 130-140 ma, now remember your puttting 4 of these in a > fg battery pack, so 4 regular or rechargable alkalines > will provide 160-200 ma to the camera, now 4 nimh or > nicads are powering 560 ma to the camera, if they > built it to be powered by a higher voltage lower > amperage source and you double/triple the apmerage it > is only a matter of time before you burn something in > it. No rechargables in my MZ-3, the flashes can use > them all they want, since I change the AA's in the > MZ-3 every 3 months but the flahses nightly
Hi Brendan (and whomever else is interested), Sorry it doesn't work this way, the batteries are in series, consider voltage as the ~potential~ pressure available to push electrons thorough the circuit, stack the batteries (ie put them in series) and the potential pressure increases (in fact the voltage adds ie 4 x 1.2 for NiMH, 4 x 1.5 for Alkaline or 4 x 1.25 for NiCd) The current flow in any circuit is determined by the potential of the source (ie battery voltage), the internal resistance of the battery (determined by it's short circuit current potential) and the resistance of the circuit which is the load (ie camera, flash, motor etc). The battery and load resistances are always in series (resistances in series add ie create a higher resistance) so the maximum current that can be supplied is governed by Ohms law which is current (amperes) = voltage (volts) / resistance (ohms). Therefore the current can't be forced and usually in any device (excepting a very badly designed one) the current flow is less when used with rechargeable cells as the terminal voltage is lower. Generally (given the same sized cell) the internal resistance of a NiCd cell is lower than a NiMH which is lower than Alkaline which is lower than the old carbon cells, but the difference should only be noted under very large load current requirements (ie a low resistance load approaching what is effectively a short circuit). In short if any electronics engineer designs a circuit that factors the internal resistance of the battery into the design deserves to have a fried circuit on their hands, so it doesn't happen very often (and it would be very apparent in the field as not may users ever RTFM). There might be potential in a badly designed flash gun or motor drive for over-heating due to excessive current flow but it's not common. On the other hand there are now a range of devices on the market (mostly digital cameras) where they are designed specifically for use with NiMH or NiCd rechargable AA cell in which conventional AA Alkaline cells will fry the devices due to their comparatively high terminal voltages (hence they can cause excessive current flow). The battery rating in mAh is simply the absolute charge holding capacity of the battery like MB of hard disk, it has little to do with current flow in ordinary circumstances (ie AA use in photo equipment). It can be used to determine the potential life of the batteries charge for a given current drain, ie if you have a 1600mAh battery supplying a circuit which draws 100mA then the battery should theoretically last for 16hours before it is discharged. BTW the formula for power dissipated in a load is voltage (volts) x current (amperes) = power (watts) therefore power = voltage(squared) / resistance so a small change in terminal voltage has a large impact on power dissipated by the circuit. Sorry about the OT rant but there is no point discussing these sorts of things when there are fundamental misunderstandings of the laws. Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications.html - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
