Tuesday, February 09, 2010

Better K-x Rechargable Solution? Is the NiZn Safe?

In my last K-x review, the "battery issue" of K-x is confirmed. But after I have used my two different units of K-x for even longer, I found that the original firmware is not buggy, it is just more *accurate* and thus actually more sensitive! (My last Navy K-x was replaced owing to the minor technical problems I found, e.g., Slight Underexposure and Back Focusing etc., which I have already overcome anyway, see my last review and this previous blog article, respectively. But anyway I am very glad that my brand new replacement unit is totally trouble free and is very accurate, for both the metering/exposure and the focusing! :-D)

Well, now the best usable NiMH set of mine are measured actually of higher voltage over 1.3V each when fully charged, which just shows a green battery indicator in my K-xes with Firmware V1.00. With latest "debugged" Firmware V1.01, the battery indicator is de-sensitized, i.e., more tolerance is added and allowed. So, I opted Not to Update the Firmware as such as I just want a more precise and accurate battery meter rather than a battery indicator with more tolerance!

Now, here comes the headache again, as usual with any Pentax DSLRs powered by AA batteries: Rechargable NiMHs are of significantly lower voltage and just the camera's actual performance is affected and the camera is slowened. The most obvious thing is the less powerful AF motor drive and slower speed of it when NiMH is used, which is very obvious when it is compared against the AA Lithium. In fact, I have measured the continuous drive mode frame advance rate of my K-x, which is of just 4.0 fps with freshly charged Eneloops and yet is considerably less than what is specified in the K-x Specs, i.e. 4.7 fps. (Also, to see how different battery types could affect the AF motor speed, see my last experiment with the K-m).

( P.S. Just discovered that my shared file links in my test reports are not working with my Google Docs, as I have to assign the emails of persons whom are allowed to download my files but it is not possible to share my files openly. As I have cancelled my Yahoo Web Hosting account, grateful if anyone could advise me of any Free Web-hosting account that I can register for hosting the small non-image files that I had in my reviews, e.g., the sound files and also some old html tables. TIA! )

Now, here comes the latest battery technology and solution of Ni-Zn rechargeables, which is now newly available in AA form factor by the PowerGenix. The battery is of 1.6V nominal voltage as specified and as seen in the above link, the Internal Resistance is marked as less than 4.5 mOhms whereas more than 5 Ohms for both NiMH and NiCd.

Next, people are concerning about If the Ni-Zn is Safe when using in the K-x (or any other Pentax AA DSLRs)? Well, as in the last paragraph, I have actually already mentioned the two key important battery parameters that we should know before that a conclusion can be drawn.

First, the Ni-Zn is very similar to the Energizer AA Lithium (L91, datasheet here). I measured the starting voltage of my L91s is roughly at 1.70V and will gradually decrease to just below 1.50V before they die. Similarly, as some new users of Ni-Zn reported (search those at the DPR Pentax SLR Forum), the initial voltage of the Ni-Zn is something around 1.72/1.73V and the battery will run out of juice at around 1.56V. So, the voltage discharge curves/characteristics of both types of battery are very similar.

As our K-x can use L91 quite safe as it is official certified (and bundled new in the box as well), what left to be concerned is the Internal Resistance of the new type battery..

From the above L91 datasheet, it is found that the Internal Resistance of the L91 is actually relatively much higher than that of the NiMH rechargables, which is specified at 90 to 150 mOhms for the L91.

So, how we have two choices that is known to be safe and official, i.e., Either a Low Voltage at 1.2V nominal with a Low Internal Resistance at about 5 mOhms, Or, a Higher Voltage at 1.6V nominal with a *Much Higher* Internal Resistance at about 90 to 150 mOhms! (As for AA Alkalines, the voltage is just lower than the L91 and the Internal Resistance is just higher, rated at 150 to 300 mOhms (See this Datasheet). So, it can just be ignored in this case.)

The Ni-Zn is a new type battery with *Both* a Higher Voltage and a Very Low Internal Resistance. I just wonder if it is safe to use in our K-x, as the battery do not limit current itself at a relatively (much) higher operating voltage (in 33.3%+).

Do also note the simply Physics Equation of Power is that: Power is equal to the Square of Voltage which is to be divided by the total Resistance of the circuit, the final Power dissipated could be tremendously different if the circuit is designed to limit the current somehow by taking account into the (High) Internal Resistance of the batteries at higher voltage (in case of the L91).

There was once a report that a Pentax user just fired his Pentax 360 Flashgun with the Ni-Zn batteries, just within a few second during charging. So, I think I should warn that the Ni-Zn batteries should not be tried in our DSLRs after my research and analyses above! In particular, I bet the new-type batteries could damage the flash circuitry, similar to the 360 burnt flash case as reported.

But then, after all, the battery issue of the Pentax AA DSLRs remains unresolved - after so many years: We, Pentax AA battery DSLR users, could Either use Disposal L91 which provides Higher Performance for our cameras, Or, Rechargeables which provides Lower Performance and also a persistent "half-depleted" Yellow battery warning and indicator for a prolonged period of time, which just defeat the purpose of the battery warning but it does actually reflect the truth (i.e., the battery voltage level is usually at the border line)!

All in all, we just CAN'T get the Best of Both World. If you want to get it, the risky way is only the Ni-Zn, which from the battery specifications, as compared against the L91 and the NiMH's, is actually not recommended by me, as a Professional Electrical/Electronics Engineer, at least!

P.P.S. I am glad that I might be the first person on the Web to do this might be simple research and quick analyses and then to conclude that the Ni-Zn is NOT Safe for our Pentax DSLRs, after so many people are wondering or even trying if the Ni-Zn is Safe to use or Not. :-) =V=

Asking Pentax Technical Support is useless for this case, I would say, as what they would tell you is they are unsure and that it is not told by their principal! (Search also those user reports at the DPR just in case if you want to see them.)

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