I've been measuring voltages..........
I hadn't really tried out AAs yet despite having a cheap Hong Kong adapter, so I thought it was time I tried it out. This was partly because of Zafar's experiences but also because I have yet to find a decent cheap D-Li109 alternative. I've bought 2, one 1100mAh at £5 and one 2000mAh at £9 and both measure more like 4-500mAh and charge up in half the time of the Pentax one which is a bit of a giveaway. So, the AA measurements......
I chose my oldest most used 6 yr old 2100mAh Uniross Hybrios which seemed about the same as my 2yr old Eneloops a couple of years back when I compared them in my K100D, not quite as good if I remember correctly but they were 4yrs old at the time. I think recent Hybrios are made by Sanyo, but these look different so may not have been. They were last charged 2 weeks ago. Straight off the charger they were about 1.45v each. After 2 weeks they were all 1.36v which is typical for all NiMh although low self discharge types would be slightly better than ordinary NiMh at this stage but a lot better after 6 months. I started taking shots in approx 10 minute sessions spread over 4 hrs, with little LCD usage (1 sec review) and using AF on a 35/2.4 on a different subject each shot, no bursts, turning on the display occasionally to check the battery monitor which was set on Auto. I couldn't see any difference by setting it to NiMh by the way. I used the flash once at the end of each session to see if it would kill the camera (it never did). I took the batteries out and measured their voltage on a DVM at the end of each session or if any warnings came up or if the monitor reading changed.
zero shots .........fully charged display........ 1.35v
200 shots ..........half " ........ 1.29v
300 shots ..........zero " ........ 1.24v still working fine.
Now this is where it gets a bit messy as NiMh cells do tend to recover with a short rest.
328 shots.........battery depleted warning.........1.23v (but see later, cleaning affected this reading)
In the light of previous K100D experience I took the batteries out, cleaned the contacts of the batteries and holder with a residue free switch cleaner, and reinserted, spinning each battery (it helps).
328 shots (cleaned) ........ half charged display.......... 1.24v
350 shots..........................zero " .......... 1.23v still working fine
400 shots..........................zero " .......... 1.23v still working fine
450 shots..........................zero " .......... 1.23v still working fine
500 shots..........................zero " .......... 1.23v still working fine
At this point I've had to release myself for full time Xmas festivities. I'll continue another day with the same batteries but I won't repeat this exercise ever, I've no desire to wear my K-30 out. Preliminary conclusions? The meter is useless but it's not easy to get these right with NiMh, they vary too much. Clean contacts are essential, there's so many of them with 4xAAs (10 contacts). I would expect loads more shots before a zero display shows if I were to use freshly charged batteries, but they would carry on and on same as these 2 week old ones have. Bear in mind that technically speaking NiMh are still good at 1.20v and their voltage doesn't really fall off the cliff until about 1.15v so preliminarily I think Pentax are being a bit conservative - we'll see.
Edit update:-
After 24 hr rest, the batteries had all recovered to 1.25v each from 1.23v the day before (the wonders of NiMh)
500 shots..........................half charged display.......... 1.25v
550 shots..........................zero " .......... 1.23v still working fine
There started to be a small difference between battery voltages, so from now on I just measured the total of the 4xAAs
650 shots..........................zero " .......... 4.87v still working fine
700 shots..........................zero " .......... 4.86v still working fine
1hr rest here before measuring so the batteries recovered a bit
760 shots..........................zero " .......... 4.89v still working fine, about 48hrs now since I started
950 shots..........................zero " .......... 4.85v still working fine, nearly 4 days now since I started
1000 shots........................zero " .......... 4.84v still working fine, nearly 4 days now since I started
At this point I thought 'enough's enough'. 1000 shots is enough for anything surely, so I then put the K-30 into playback showing an image and turned power saving off. Every 20 mins approx I tried out Live View for one shot to see if its high current would shut the camera down. It did, but not for another 2 hours!
so, finally:-
1006 shots + further 2 hours of playback --> SHUTDOWN ........... 4.64v
This, I would say is just about optimum shutdown voltage in the K-30 running on AA NiMh rechargeables as their voltage will start to fall quickly below 1.15v and we're almost there (4x1.15v = 4.60v). AAs do vary a lot in their mid-range plateau voltage, and ones with the highest voltage should be chosen to get maximum life. Eneloops are a good choice. There's loads of AA graphs on the candlepower forums if you feel like googling. The K-30 battery meter is useless but the camera's use of AAs isn't but you definitely need clean contacts so as not to waste those precious tens of mV that make all the difference. The length of time the camera is powered up is definitely a factor though, the 0.21A lowest current means you have a maximum of a theoretical 9hrs with 2000mAh batteries, but will obviously be less in practice. Use the power saving timer, it will help a lot.
Last edited by SteveB; 12-29-2012 at 06:51 AM.
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