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02-10-2010, 11:03 AM   #1
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A dumb electronics (DC IN) power question

Electronics has never been my strong suit. Can someone explain to me how I can run my K200D on four 1.2v Eneloop batteries (presumably wired in series which would be 4.8V) but the AC adapter connection says "DC IN 6.5V" ?

Wouldn't it be possible (pretty easy) to create a DIY external battery pack that would plug into this? (I'm thinking of one with long wires that would fit inside your clothing to power the camera during extreme cold weather shooting.) If so, I'd like to know how many eneloops one would use. (5 in series would get you to 6V).

Can't find mAh output on the K-AC76U AC adapter, but in this thread it is discussed that the Pentax K-AC10U AC Adapter for DS/DL has output current of 3000 mA.
https://www.pentaxforums.com/forums/camera-studio-accessories/33730-ac-adapter-k200d.html

It also appears from the thread above that there is a range of input power that works. Also, can someone tell me the official name for the plug used in the DC IN connection?

This guy did something similar for a DV camera:
5 Hour External Battery for DV camera

Thanks in advance!

02-10-2010, 11:36 AM   #2
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If it would work as you descirbe (and I see no reason why it wouldn't), then you might as well make multiple banks of 5 NiMH batteries. Two or three banks of 5 in parallel (with the batteries in each bank in series), would multiply your capacity but keep the right voltage.

The only concern I see with matching voltage with an external system is the discharge curve of the batteries themselves. A freshly-charged NiMH battery rated for 1.2V has more like 1.45-1.5V. Five of those and you're nearing 7.5V total. If you drop it to four cells to avoid overvoltage, then after just a little use you start dropping into the range where they're at about 1.3V each, for a total of 5.2V. That may not be enough for the external connector if it expects 6.5V.

Personally, I woudn't expect the slight overvoltage of 5 fresh cells to be a problem. It's only a volt at most, and in my experience the input margin on most consumer electronics will be able to take that. Just don't hook it up to a car battery.
02-10-2010, 11:41 AM   #3
graphicgr8s
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QuoteOriginally posted by cheekygeek Quote
Electronics has never been my strong suit. Can someone explain to me how I can run my K200D on four 1.2v Eneloop batteries (presumably wired in series which would be 4.8V) but the AC adapter connection says "DC IN 6.5V" ?

Wouldn't it be possible (pretty easy) to create a DIY external battery pack that would plug into this? (I'm thinking of one with long wires that would fit inside your clothing to power the camera during extreme cold weather shooting.) If so, I'd like to know how many eneloops one would use. (5 in series would get you to 6V).

Can't find mAh output on the K-AC76U AC adapter, but in this thread it is discussed that the Pentax K-AC10U AC Adapter for DS/DL has output current of 3000 mA.
https://www.pentaxforums.com/forums/camera-studio-accessories/33730-ac-adapter-k200d.html

It also appears from the thread above that there is a range of input power that works. Also, can someone tell me the official name for the plug used in the DC IN connection?

This guy did something similar for a DV camera:
5 Hour External Battery for DV camera

Thanks in advance!
But wouldn't you need to leave the door open do plug in? To me that would be a problem.

1/8" miniplug. The larger ones are 1/4" phonoplugs. IIRC
02-10-2010, 11:50 AM   #4
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couple of points here

first of all, there will be a power converter and regulator probably in the camera for the 6.5 V input, but you need to check, that is why there is a different voltage than from the batteries when you add up the cell voltage. ALso, it is probaly higher, so that when using it, you do not discharge partially the batteries at the same time.

the two outputs could be connected VIA diodes to insure only the higher output feeds the camera and to insure no charging of the batteries through the external supply.

with respect to putting batteries in parallel NEVER do this. a fault in one battery can be fed by all other batteries and get very very hot.

connecting batteries in parallel requires each string to have a diode in series also, to insure no back feeding. Use a low voltage drop schottkey diode for this.

You also need to look at the capability to deliver current. If you gang up a bunch of batteries, they can deliver almost unlimited current. The camera may not like this. What ever yoou do should be current limited to the power ratings on the camera's supply.

02-10-2010, 01:40 PM   #5
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One more ignoramus here:

Isn't the current flowing the lesser of that which the device is capable of drawing or that which the supply is capable of providing? In other words, the device may overdrive the supply but the power supply will not deliver more than the device will draw. A 500 mw supply will do no harm to a device requiring 200 mw.

I hope.

Voltage, of course, is different. Over or under voltage can harm the device quickly or slowly.

And that's where I'd worry about batteries. The DC input system is designed for a constant voltage and may not be happy with one that varies over the life of a battery charge. The battery input system can compensate for that and will turn off the camera before the voltage is low enough to do damage, for example.

Not sure what happens if a system built for a constant voltage is presented with a highly variable voltage.

And we won't find out on my K-7!
02-10-2010, 04:32 PM   #6
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QuoteOriginally posted by glanglois Quote
One more ignoramus here:

Isn't the current flowing the lesser of that which the device is capable of drawing or that which the supply is capable of providing? In other words, the device may overdrive the supply but the power supply will not deliver more than the device will draw. A 500 mw supply will do no harm to a device requiring 200 mw.

I hope.
you'd better hope. actually some electronics is designed to use specific power supplies, this was a big issue with flashes a while back, where the different battery types had considerably different internal impedances and could deliver power at a much higher current,. the flashes were designed to use a specific battery and part of th elimitation of current was the internal impedance of the battery. changing batteries caused the flashes to draw higher current and fail.

It all depends on the design and the intent. This does not mean it can't be done, but you need to be careful.
Tim Allen is my hero but, Bigger is not always better
QuoteQuote:
Voltage, of course, is different. Over or under voltage can harm the device quickly or slowly.

And that's where I'd worry about batteries. The DC input system is designed for a constant voltage and may not be happy with one that varies over the life of a battery charge. The battery input system can compensate for that and will turn off the camera before the voltage is low enough to do damage, for example.

Not sure what happens if a system built for a constant voltage is presented with a highly variable voltage.

And we won't find out on my K-7!
As to stability, one would assume that the supplies people build to hook up are somewhere stabalized. but like you, even though I can figure it out it is not really worth my time. I see no difference any way in having a bank of batteries in my pocket feeding a cold camera, than I see with multiple sets of batteries keeping warm in my pocket waiting to replace the cold one in the camera when it dies,
02-10-2010, 10:00 PM   #7
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DC in

Hi all,
Could spend alot of time on this, but these guys have offered excellent advice
and I certainly couldnt improve on what theyve said.
Would like to stress,and reinforce what others have said, Input voltage is CRITICAL
design of body is inherently self regulatory in regards to current

I'm working on a system that will serve as auxillary power supply, I will post
a thread in DIY to let you see whats going on in a couple of weeks.Right now
I'm going to use 2-6vdc gel cells, in series, gives me approximate (no load)
14vdc@24AH. Those will feed inverter, like what is used for any number of
different portable appliances. AC output from inverter will feed pentax power supply
for my K20D, obviously output from P.P.S. feeds body. This is just an abstract
and prototype. A point to start from. Will get more sophisticated as consideration
for things like heat dissipation from inverter, housing for cells, weather proofing
and many other issues are addressed.

P.S. ( wont need 5th cell)
if you connect 4 cells in series(as you decribed with 5)check battery no load voltage
youll see what I mean, same happens will your power supply

Last edited by BillM; 02-10-2010 at 11:57 PM.
02-11-2010, 07:47 AM   #8
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QuoteOriginally posted by BillM Quote
Hi all,
Could spend alot of time on this, but these guys have offered excellent advice
and I certainly couldnt improve on what theyve said.
Would like to stress,and reinforce what others have said, Input voltage is CRITICAL
design of body is inherently self regulatory in regards to current

I'm working on a system that will serve as auxillary power supply, I will post
a thread in DIY to let you see whats going on in a couple of weeks.Right now
I'm going to use 2-6vdc gel cells, in series, gives me approximate (no load)
14vdc@24AH. Those will feed inverter, like what is used for any number of
different portable appliances. AC output from inverter will feed pentax power supply
for my K20D, obviously output from P.P.S. feeds body. This is just an abstract
and prototype. A point to start from. Will get more sophisticated as consideration
for things like heat dissipation from inverter, housing for cells, weather proofing
and many other issues are addressed.

P.S. ( wont need 5th cell)
if you connect 4 cells in series(as you decribed with 5)check battery no load voltage
youll see what I mean, same happens will your power supply
Good luck on your project. Probably heavier than it needs to be, but definitely safe.

Glad you mentioned the cell voltage, and the difference between rated voltage and open circuit voltage . for the poster asking about 4 or 5 cells, the 1.2 volt rating is at load.

Had you not mentiond this, someone would ask you how 2 x 6 = 14 God I love new math

02-11-2010, 04:23 PM   #9
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New and Expanded Math

As a cosmologist friend once noted, 2 + 2 can equal 5 .......... for large values of 2.

Falk? Are you listening?

PS: I think that 2 X 6 does in fact = 14. In base eight. I think.
02-11-2010, 06:00 PM   #10
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DC

Honest folks,
connect 4-1.2vdc cells in series and you should see no-load sum higher
than series cell term (as calculated) if not, replace cells.
Good example is something like a battery for 60s era Ford mustang(289)
ignition off(no load) voltage higher than ignition on(load) voltage
02-12-2010, 09:00 AM   #11
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No dont use them in parallel. You could easily damage the camera that way if you had batteries of different voltages. Better read up on ohms law there.
02-12-2010, 09:29 AM   #12
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QuoteOriginally posted by -Joe- Quote
No dont use them in parallel. You could easily damage the camera that way if you had batteries of different voltages. Better read up on ohms law there.
read my point above, never put batteries in parallel it is a fire hazard.

if one cell fails, all other cells will discharge into it.

the only safe way to parallel cells is to use a diode in series with each string, to insure no back feeding of failed cells.
02-12-2010, 09:32 AM   #13
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QuoteOriginally posted by BillM Quote
Honest folks,
connect 4-1.2vdc cells in series and you should see no-load sum higher
than series cell term (as calculated) if not, replace cells.
Good example is something like a battery for 60s era Ford mustang(289)
ignition off(no load) voltage higher than ignition on(load) voltage
but note both are lower than car running, and the battery sitting on a 14.5 volt regulated supply (from the alternator)

as a general point, batteries are not a regulated supply, their output voltage drops as a function of charge state, although the newer bateries have a relitively flat discharge curve, until they are discharged, then it bends down rather quickly. This is why the camera meter is so inacurate. most like K10D for example show fully charged until almost the end, show half charged for about 20 shots and then are dead.

Since battreries are not regulated there is probably a power supply between the camera battery and the electronics inside
02-12-2010, 10:59 AM   #14
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DC in

Hi all,
Hi Lowell, you have no argument from me on that, got married for all that arguin stuff
might mention 2-6 volt batteries, one measures 6.8vdc other 7.0vdc, fully charged,
no load.
Tried to explain apperent over voltage in laymens terms,muffed it up.

Lowell, you have a wealth of expierence, when you talked of past issues
with flash units, in regards to replacement batteries, would you say that
this something that has been "designed out" of the equation, with the course
of time? might be able offer explanation
02-13-2010, 03:21 AM   #15
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I'm only new here so I hope you don't mind if I try an answer.

Just a thought.

How would it go to use 5 or 6 batteries in series and a LM1085IT-5.0. ?
It's a 5volt 3 amp regulator. About $5.00 from RS Components.
Should let the batteries last a lot longer.

Chromo
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