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02-03-2012, 12:32 PM   #1
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Battery vs AC Adapter Voltage Difference?

Anyone have an idea why the K-5's D-Li90 battery is rated at 7.4vdc output, but the jack on the camera where an AC adapter would plug in says 8.2 vdc? Why the difference of almost a full volt?

02-03-2012, 12:47 PM   #2
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You usually charge with a higher voltage as the charger/device itself may need extra power, and to guarantee the fastest possible charge.

For example, my laptop charger sends out 19.5v, but the battery is only 14.5v. I believe the higher the voltage, the faster it charges, but voltages that are significantly higher may damage the battery.

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02-03-2012, 01:07 PM   #3
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Yes, but I'm not referring to the output of the battery charger. I'm talking about the input jack on the camera body where you plug in the AC adapter (KAC-50) to run the camera itself instead of using a battery. So you aren't charging anything, just running the camera.
02-03-2012, 05:41 PM - 1 Like   #4
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Electronic devices are designed to operate at a voltage less than full supplied voltage, they have voltage regulators inside to protect the circuits. This is a requirement to compensate for the battery/power supply voltage dropping during its life and the loads applied. Think of a car battery, it is a 12.6 to 12.8 volts when fully charged, but drops instantly to 11 or so during the cranking period. Somewhere near nine to eleven volts is the required voltage for the starter, not the 12.6 to 12.8 volts at rest, or the 13 to 14 volts during charge while the engine is running. Nothing is constant.

Power supplies must also be designed the same, that is reasonable cost and size must play into their requirements. Example, a power supply that must operate at a 100% duty cycle will need a higher power ratings at a given voltage than one with a 10% duty cycle. Higher duty cycles add cost and size to the unit, thus engineers decide what is the typical duty cycle. One way to get a higher power rating out of smaller power supplies that do not operate at 100% duty cycles is to increase the voltage at rest, and accept that under load it will drop. Again, the voltage regulators in the camera protects it.

A digital camera consumes little power when at rest, a little more when awaken and getting ready to take a photo, a lot of power during autofocus, and a less during the display mode. If the power supply had to supply a constant voltage and current during this cycle it would be much larger and more expensive, and again not needed because of the voltage regulators in the camera.

Do not worry, your camera is fine. But, this is the reason some equipment manufactures warn you to not use the wrong type of battery in their devices. The expected voltage drop of certain types of batteries is taken into consideration when engineers design their circuits, and the wrong types of batteries may damage some equipment. You camera is not one of those.


Last edited by toooldtocare; 02-03-2012 at 05:47 PM.
02-08-2012, 05:26 AM   #5
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>Anyone have an idea why the K-5's D-Li90 battery is rated at 7.4vdc output, but the jack on the camera where an AC adapter would plug in says 8.2 vdc? Why the difference of almost a full volt?

@Steve,
There can be a handful of reasons, some of which are mentioned above by tooldtocare.

Nowadays, nearly any voltage can be converted to any other voltage by electronics.
But it is very difficult to tell from outside the device what it is doing internally with the incoming energy / power / voltage.

@Adam
>You usually charge with a higher voltage as the charger/device itself may need extra power, and to guarantee the fastest possible charge.
Not necessarily

>For example, my laptop charger sends out 19.5v, but the battery is only 14.5v. I believe the higher the voltage, the faster it charges, but voltages that are significantly higher may damage the battery.
NO!
02-08-2012, 06:51 AM   #6
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QuoteOriginally posted by toooldtocare Quote
Electronic devices are designed to operate at a voltage less than full supplied voltage, they have voltage regulators inside to protect the circuits. This is a requirement to compensate for the battery/power supply voltage dropping during its life and the loads applied. Think of a car battery, it is a 12.6 to 12.8 volts when fully charged, but drops instantly to 11 or so during the cranking period. Somewhere near nine to eleven volts is the required voltage for the starter, not the 12.6 to 12.8 volts at rest, or the 13 to 14 volts during charge while the engine is running. Nothing is constant.

Power supplies must also be designed the same, that is reasonable cost and size must play into their requirements. Example, a power supply that must operate at a 100% duty cycle will need a higher power ratings at a given voltage than one with a 10% duty cycle. Higher duty cycles add cost and size to the unit, thus engineers decide what is the typical duty cycle. One way to get a higher power rating out of smaller power supplies that do not operate at 100% duty cycles is to increase the voltage at rest, and accept that under load it will drop. Again, the voltage regulators in the camera protects it.

A digital camera consumes little power when at rest, a little more when awaken and getting ready to take a photo, a lot of power during autofocus, and a less during the display mode. If the power supply had to supply a constant voltage and current during this cycle it would be much larger and more expensive, and again not needed because of the voltage regulators in the camera.

Do not worry, your camera is fine. But, this is the reason some equipment manufactures warn you to not use the wrong type of battery in their devices. The expected voltage drop of certain types of batteries is taken into consideration when engineers design their circuits, and the wrong types of batteries may damage some equipment. You camera is not one of those.
One might also add that nominal voltage and the expected voltage drop (in particular when the camera is being powered up) is only part of the full sory. The current ("the Ampere") that the battery viz. power supply can supply under various situations of load also plays an important role. Power supplies are designed with limits as to how many Amperes you can draw, and I think the K AC-50 adapter cannot just be replaced by "any" ca. 8V supply with a low current output.
02-08-2012, 07:21 AM   #7
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I get that battery operated devices can work with lower voltages. They have to as the battery declines.
I also get that chargers may provide higher voltage to charge batteries.
My question arose because it seems to me that given all that, the voltage label on the camera might have been the same or possibly even lower than the battery voltage. I would think the AC adapter (KAC-50) would have a regulator circuit and so have no problem maintaining voltage within a tight tolerance as well as providing all the current needed to operate (not charge) the camera given it is powered by an AC power supply source. So I wouldn't expect a AC adapter to experience much of a voltage drop while operating a camera.
02-08-2012, 09:02 AM   #8
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Just curious, is that 8.2v an error or typo? I just noticed that my K5 says 8.3v.

Edit: For what it's worth, I just checked the no-load voltage of the battery in my K5. It's 8.3v.


Last edited by KyPainter; 02-08-2012 at 09:26 AM.
02-08-2012, 04:04 PM   #9
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Good catch on the typo. Camera label on my K-5 does indeed say 8.3V.
You solved the question by doing what I should have done myself. Didn't think to measure no load voltage of battery! Knowing that, it all makes a little more sense now.
02-08-2012, 05:18 PM   #10
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All good speculations, here is mine.
The external DC input voltage is higher in order to compensate for the voltage-drop, caused by the in-series reverse current protect diode. Usually around 0.7 volts for a silicon device.

Last edited by Ex Finn.; 02-08-2012 at 05:29 PM.
02-09-2012, 06:42 AM   #11
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FYI, Pentax support provided this answer:
The PENTAX K-5 is designed to operate within the range 7.2v 1.86A (D-Li90 battery) to 8.3v 2A (AC Adapter Kit A-AC50U).
06-19-2013, 11:34 AM   #12
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K-01 shutting down

Allow me to quote a post in another thread:
https://www.pentaxforums.com/forums/pentax-k-01/210111-k-01-shutting-itself-d...ml#post2425078
Maybe my problems with the K-01 are related to what has been discussed here.

What is the voltage output of your batteris when fully charged?

Cheers,

QuoteOriginally posted by slocant Quote
My K-01 has been shutting down unexpectedly when I trip the shutter.
It doesn't happen when filming or in playback mode.
It has happened with three Pentax batteries. One came with the camera (Amazon) and the other two I bought from B&H.
After the camera shuts down, the battery's voltage is 1.7v or 3.5v (can't recall the exact values).

However, after a few seconds in the charger, the battery's voltage output is reset. Maybe some sort of switch is in action here.

But then I measured the battery's output after being charged and it was 8.34v. Is this normal? The batteries are labled 7.2v.

I see the AC adapter for the K-01 outputs 8.3v (I don't have it) and the camera itself is labeled 8.3v. The battery charger outputs 8.3v or 8.4v.

Does anyone have a clue on what may be going on here?

Did anyone have this problem solved?

I've also downgraded from firmware 1.03 to 1.02 and back, to no avail.

Cheers,
06-20-2013, 09:29 AM   #13
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The batteries in your camera are made of 2 cells with a nominal (before being charged) voltage of 3.6v. (they will tell you 3.7v for marketing purposes).

When charged, each cell should be no more than 4.2v (100%) . 4.2x2 = 8.4 (When new, charge capacity lessens the further the cell is cycled).

The open circuit voltage (OCV) attained varies according to the metals and acid solutions (electrolyte) used. Applying a charge or discharge places the battery in the closed circuit voltage (CCV) condition; charging raises the voltage and discharging lowers it.

Full info about Lithium batteries here:

Battery Voltage Information ? Battery University
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