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Forum: Lens Clubs
08-01-2011, 10:19 PM
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I took my new DA 18-135mm F3.5-5.6 ED AL [IF] DC WR out for a test at the Buffalo Bill Days parade in Golden this weekend. I got there relatively late and had to be satisfied being a few people back.
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Forum: Troubleshooting and Beginner Help
01-23-2012, 07:59 PM
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A smart charger is one that senses when the battery is fully charged and terminates the charge. In contrast, a dumb charger is one that just charges for a predetermined period of time. If the battery is not fully discharged, a dumb charger will overcharge it. Smart chargers look for signals like a very slight drop in voltage that occurs when the cell is fully charged, or a rapid rise in temperature that occurs once overcharging begins. For either of these signals to be reliable, the charge rate must be fast enough that a full charge takes 2 hours or less. Charging faster than about an hour is also bad. By the time the terminating signal is received, a substantial overcharge may have already been delivered. So 1-2 hours charge time is the sweet spot.
A good charger will also charge every battery individually, instead of in pairs. Sometimes one battery goes bad, and if you're always charging in pairs this will either undercharge one battery or overcharge the other or both.
It's cheaper to build a dumb charger that charges in pairs, so most places that cater to unknowing customers who select the cheapest charger on display (including big stores with even less knowledgeable sales staff) will only have non-ideal chargers to pick from.
See here for an overview of suitable chargers.
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Forum: Troubleshooting and Beginner Help
12-13-2011, 09:19 PM
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I thought couple of images to illustrate this couldn't hurt. I rummaged around and found an ancient Energizer 1850 mAh battery that has somehow managed to escape being recycled. This was a decent enough battery in its time, but that was long ago. Now it exhibits high internal resistance.
The first photo shows the open circuit (unloaded) voltage: 1.271 volts.
The second photo shows the voltage a few moments later, very soon after I connected a 1.0 ohm resistor in parallel to the battery. It now reads 42.3 millivolts, or 0.042 volts. Ouch.
After the load was removed, the battery quickly recovered to a high open circuit voltage.
This is a very high load, probably somewhat higher than what the K-x actually draws, but you get the idea.
An eneloop (not shown) maintained a voltage slightly over 1 volt.
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Forum: Pentax Camera and Field Accessories
12-07-2011, 01:49 PM
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Good charger. It charges cells individually and has smart cutoff.
Looking at the typical charging times on the manual, 320 mA is the rate it charges AA cells and 140 mA is the rate it charges AAA cells.
If charging was 100% efficient (it's not), charging a AA battery at 320 mA for 6 hours would add 320x6 = 1920 mAh of charge to the cells. For fully discharged typical LSD batteries of approximately 2000 mAh capacity, this seems like a reasonable fit, since I would rather slightly undercharge the cells than overcharge them (which can damage them and reduce their life). For fully discharged high-capacity 2700 mAh cells, a single 6 hour charge would not be enough. You would need about 8.5 hours total (2700/320).
It appears from the online manual that the charger is dumb with just a timer based cutoff. That is one reason why it instructs you to use fully discharged batteries and to manually remove the charger after the indicated charging time.
320 mA is a high enough charging rate to damage your batteries if your overcharge them, but not high enough to exhibit a reliably detected overcharge signal (so a dumb charger is all you can safely do).
If you don't want to fully discharge your batteries before charging them everytime, you could estimate how discharged they are and use a pro-rated time. Err on the side of under-charging. Don't rely on your camera's battery level, it's not accurate enough. You will still need to periodically fully discharge and fully charge your batteries, because they're not identical and will otherwise develop charge disparities over time.
Hope this helps. Hope also that you can get yourself a new charger soon.
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