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02-15-2017, 11:34 AM   #1
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Pentax external power supply voltage tolerances

fyi

We had a recent discussion on how to design a cheap external battery for Pentax cameras.
One forist did some tests and now we know that using the DC in connection there is a very nice wide tolerance for input voltage:
  1. The camera works from 5,5V to 9V
  2. Power required was from 450mA in LV up to 1,100 mA when using autofocus
So DIY building an external large capacity battery (e.g. for astro shots) seems really easy.

02-15-2017, 11:51 AM   #2
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Tolerance <> safe

It might be possible to cause damage over time with a tolerated voltage.

How do we verify that it is safe over the long haul?
02-15-2017, 11:59 AM   #3
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Would be good to know if the lower end of that voltage range takes into account every possible operation of the camera. Depending on the load and resulting current draw, the voltage will drop to different levels (continuous shooting, SD card formatting, firmware updates, flash operation etc. would likely draw more current than simply taking a shot, for instance).

Interesting, though
02-15-2017, 12:22 PM   #4
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QuoteOriginally posted by beholder3 Quote
The camera works from 5,5V to 9V
you can't know the range unless doing some reverse engineering or getting the spec from ricoh

02-15-2017, 12:47 PM   #5
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Just look at the output spec from one of the AC power adapters. There is a adjustable pre-built voltage regulator based on the same voltage regulator that the Pentax AC adapters use that I've posted links to before as well as to the connector that is used on Pentax bodies. I don't recall the input voltages but it take will take 12v DC. Just hook it up to a 12v sealed Lead Acid battery and you're good to go.

Board like this one:
http://www.ebay.com/itm/5-Amps-1-5-to-32V-Adjustable-Voltage-Regulator-Modul...gAAMXQqdhR6A69

And you need a Hirose H10485 connector.

Last edited by Not a Number; 02-15-2017 at 01:27 PM.
02-15-2017, 02:51 PM   #6
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Under-voltage runs the risk of lock-ups and data loss. Just because it seemed to work at 5.5 VDC doesn't mean it will be reliable at that voltage. All it takes is one ill-timed voltage drop to corrupt the SD card. Over-voltage runs the risk of burn-out of the power electronics.

IIRC, the specs for external adapter call for 8.4 VDC @ 2 A. That adjustable regulator + lead acid batteries looks like a good solution.
02-15-2017, 06:41 PM   #7
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Running on prolonged under-voltage could make things hot if there are any buck-boost regulators on board.
Better off sticking with design voltage if possible.
02-15-2017, 10:20 PM   #8
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I can't believe in the 5.5 Volts as the lower bound. When you are using the d-Li90 they camera says low at 7.1V with the K3 and 6.8V with the K1. I consider Voltages below 6.8 as dangerous, there may be accidental picture / function loss, switching of of the camera. Therefore I would set the lower bound at least to 7.2 Volt.

The external power supply which can be connected ist 8.4 Volts roundabout 2 Amps ( Dot.Foto-Netzadapter ersatz für Pentax K-AC50: Amazon.de: Elektronik ). The Pentax Input specification is 8.4 Volts

There are smaller and cheaper Voltage regulators available at ebay, there ist one with adjustable outputvoltage ( Input 3,3-40 V Output 1,25-35 V DC/DC with an LM2596S) which should fit LM2596S Einstellbarer DC/DC Step Down Spannungsregler Modul für Arduino ESP8266 | eBay Your Input should provide more than 2.4 Amps continuously to the regulator - therefore some USB Powerpacks won't fit, because the clamp near 2 Amps. I would set the voltage to 8.4 Volts. You could easily modify a batterie grip, especially the Battery-Pack, I would feed it with 6 external Batteries D-Type (roundabout 5 Ah 3 times the D-Li90 capacity) or a bike Batterie (12 Volt 18 Ah) with an voltage regulator.

There is a thread at a german photoforum Netzadapter mit 8,4V bauen - DSLR-Forum


Last edited by joergens.mi; 02-15-2017 at 10:33 PM.
02-16-2017, 12:13 AM   #9
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Since Pentax specifies a range instead of a fixed input voltage, I presume that a regulator is already built within the camera.
02-16-2017, 05:56 AM   #10
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QuoteOriginally posted by joergens.mi Quote
I can't believe in the 5.5 Volts as the lower bound. When you are using the d-Li90 they camera says low at 7.1V with the K3 and 6.8V with the K1. I consider Voltages below 6.8 as dangerous, there may be accidental picture / function loss, switching of of the camera. Therefore I would set the lower bound at least to 7.2 Volt.

The external power supply which can be connected ist 8.4 Volts roundabout 2 Amps ( Dot.Foto-Netzadapter ersatz für Pentax K-AC50: Amazon.de: Elektronik ). The Pentax Input specification is 8.4 Volts

There are smaller and cheaper Voltage regulators available at ebay, there ist one with adjustable outputvoltage ( Input 3,3-40 V Output 1,25-35 V DC/DC with an LM2596S) which should fit LM2596S Einstellbarer DC/DC Step Down Spannungsregler Modul für Arduino ESP8266 | eBay Your Input should provide more than 2.4 Amps continuously to the regulator - therefore some USB Powerpacks won't fit, because the clamp near 2 Amps. I would set the voltage to 8.4 Volts. You could easily modify a batterie grip, especially the Battery-Pack, I would feed it with 6 external Batteries D-Type (roundabout 5 Ah 3 times the D-Li90 capacity) or a bike Batterie (12 Volt 18 Ah) with an voltage regulator.

There is a thread at a german photoforum Netzadapter mit 8,4V bauen - DSLR-Forum
Nice, however other DIY determined that 3 amps wasn't sufficient which is why they settled on the 5amp LM388. I have the schematics if you want to build a smaller board from scratch. The board I linked to is larger because of the heat sinks and it is dual input taking AC as well. You can remove the heat sinks as 12 v to 8.4v shouldn't produce much heat.

If you're a lugging around a 12v SLA battery a slightly larger power suppy isn't going to matter. Just Velcro it to the side of the battery.
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