Battery performance in the cold - D5300/D5500, D7500, D500 - test challenge

[Øivind Tøien]

I'm monitoring your posts with much interest, Øivind!

That said, I would concern about the super capacitor: wouldn't the initial current pouriing into the empty cap damage the battery?

Yes, you identified the problem Akira - that is what I meant with "I will just have to figure out how to dampen the inrush current on first power up." A solution is to charge the super capacitor though a current limiting resistor and then discharge it though a diode connected in parallel with the resistor. However the charge rate will then be relatively low when the capacitor is recovering from the current draw between mirror movements. I might just order the super capacitor, power resistor and diodes to see if it works. Other solutions will requite more circuitry and require me to design a print, so a slower process.

[Akira]

Yes, you identified the problem Akira - that is what I meant with "I will just have to figure out how to dampen the inrush current on first power up." A solution is to charge the super capacitor though a current limiting resistor and then discharge it though a diode connected in parallel with the resistor. However the charge rate will then be relatively low when the capacitor is recovering from the current draw between mirror movements. I might just order the super capacitor, power resistor and diodes to see if it works. Other solutions will requite more circuitry and require me to design a print, so a slower process.

Oh, yes, I failed to find the English term "inrush current".  Sorry for my redundant post.

[Øivind Tøien]

No problem Akira, good to have it explained several ways. 

I have now posted some results from the Geminid meteor shower here:
http://nikongear.net/revival/index.php/topic,8225.msg133663.html#msg133663

[Øivind Tøien]

The super capacitor arrived and so far it seems to be a success in capping the current draw with a peak only slightly beyond 1A. As there is a conversion from 5V to only 9V with >95% efficiency this should be OK. The 1F super capacitor (SCMR22L105SRBB0) is rated to 9V which is a bit marginal, so if it is to be used in very hot environments perhaps a capacitor with higher voltage rating should be selected. The attached graph shows current draw  with D7100 at the end of an exposure, followed by the beginning of another exposure (I believe I used continuous shooting mode on this one).

The bench test indicated no problems powering any of the bodies from the battery banks as long as the exposures are not to frequent. As this is written it has been sitting outside for about 8h at -25°C powering the D7100 to record the Quadrantid Meteor Shower. We will see if there are any problems once I stop acquiring images and get them downloaded. The connections are shown below.

A limitation of this construction is that recharging the capacitor is relatively slow, so for instance 1/2 second exposures in continuous mode eventually failed, while 10sec exposures in continuous mode or 1/2 sec exposures with 10 sec pause between seemed OK.

[Birna Rørslett]

No images show, Øivind ...

[Øivind Tøien]

No images show, Øivind ...

They show both in an incognito window in Chrome and an old IE version here, none of them should have special permission to my zenfolio account (and IE would not share cache with Chrome). Perhaps a temporary problem with connections?

[Birna Rørslett]

Using Firefox 64 bit here and no images show. However, if I copy the URL inside your IMG tags into another browser tab, the pictures show? strange. Perhaps your image hosting company doesn't like hot linking?

You can attach the images directly to your post instead.

[Akira]

Using Firefox 64 bit here and no images show. However, if I copy the URL inside your IMG tags into another browser tab, the pictures show? strange. Perhaps your image hosting company doesn't like hot linking?

You can attach the images directly to your post instead.

Are you talking about the schematics in the reply #48?

My 64bit Firefox can display them with no problem.

[Øivind Tøien]

I have edited the post now and attached the two images. Except for one or two specific very strange hiccups in the past on a DPreview post I have never had problems with hotlinking from Zenfolio.

[Øivind Tøien]

I just rigged down and downloaded the images. The D7100 lasted for 8 hours and 37 minutes (846 exposures, each 30s) at -25°C before image data collection stopped due low power.

[Birna Rørslett]

That is a nice achievement, in terms of power supply to any digital camera.

[Akira]

I just rigged down and downloaded the images. The D7100 lasted for 8 hours and 37 minutes (846 exposures, each 30s) at -25°C before image data collection stopped due low power.

Nice!  Do you activate the dark frame subtraction (long exposure noise reduction)?  Or, is it not necessary for 30 sec. exposure in such a cold environment?

[Hugh_3170]

I agree.  This is good work - I have no doubt that there will be others here that will benefit from what you have achieved.

That is a nice achievement, in terms of power supply to any digital camera.

[Seapy]

Yes indeed, I for one am watching and learning.

[Øivind Tøien]

Thanks for the enthusiastic comments all of you. Retrospectively it would have been easier and simpler, if slightly more expensive to choose the battery bank that is capable of outputting 2A at 9V, linked to earlier in this thread if it had been possible to have it shipped to me. However this was a possible solution and much more fun figuring out. Besides I like the fact that the bank also doubles as a charger for my Convoy S2+ UV nichia 365 nm LED light that I recently acquired and is currently running on on old salvaged laptop cells. The Panasonic cells I use for the bank itself are supposed to be the same running in Tesla S models, so it not surprising they perform well. After warm up to room temperature the unloaded voltage of each cell was 3.63V so it will likely last quite a bit longer at room temperature.

Akira, I turn long exposure noise reduction off when doing tracked night sky imaging for stacking, so there is no overhead while acquiring the image data. I do a separate series of dark exposures at the same ISO and exposure time (I am actually acquiring those data while writing this). As long as temperature is the same (still -25°C here) and no light is allowed to enter the sensor, it does not matter to wait until the next day. In addition I do a number of bias exposures at very high shutter speed at the same ISO.

The super capacitor was for this test just connected up on a screw terminal protected in an antistatic ziplog bag. Now on to find the best way to place and solder components on at perf board and get it all potted (hot glue is usually my friend for this, but I need to check if it will be too warm for the super capacitor first).