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DC power input?

Discussion in 'Olympus Cameras' started by RobWatson, Sep 1, 2011.

  1. RobWatson

    RobWatson Mu-43 Hall of Famer

    The E-P1 has no such option. A recent thread showing how to use anti-shock and rubberband+coin has got me itching to do time lapse work. I want to make a time lapse of a whole day and night but the battery will not last. Can just change the battery but then the framing shifts (gotta demount from the tripod) and I don't want that shift.

    So, hack a DC power adapter .... OK, Einstein, what about the third contact? My multimeter shows two contacts at the same potential so just short then together call it the negative supply and carry on! Er, let's try your camera first ...

    So maybe I'll ask, why are there three contacts on the battery? What do they do? The charger only has two contacts so what is with that middle oddball? Why is it even there?
     
  2. RobWatson

    RobWatson Mu-43 Hall of Famer

    Found some internet blather that suggests the middle contact is a thermistor ...
     
  3. harrysue

    harrysue Mu-43 Regular

    164
    Mar 12, 2011
    I would agree, but it could be some other function. My OEM Oly charger is three terminal and it won't charge the battery if the middle terminal is not making contact. My PEN will power up that way and take pix, but since the terminal is inside the camera, it probably reads battery temperature. If tied to ground, I suspect that would signal the PEN that the battery is red hot.

    If you run a DC supply into your EP1, don't have the battery connected at the same time. That could lead to overcharge and a fire. Maybe a dummy battery out of wood with copper contacts. I've done this to run a Sony Handycam back in the 80's. Powered it with a small lead-acid battery in a shoulder bag. That was heavy.

    You could also take apart a $3 ebay knockoff for the plastic case and terminals, but be careful, as the internal cells are a fire hazard. Google lithium polymer batteries and search youtube for some videos of what happens when a battery is mistreated. I once took apart a tiny NP-22. Thought it was dead but the internal cell was charged. Accidentally shorted it out and wires melted. Lots of power there.
     
  4. RobWatson

    RobWatson Mu-43 Hall of Famer

    So I put a strip of tape over the middle contact of the battery and loaded it into the camera and everything works just fine. Maybe that thermister is used while charging or with DC power to the camera (those cameras that have it) to monitor the battery temp while charging? E-P1 seems not to care.
     
  5. harrysue

    harrysue Mu-43 Regular

    164
    Mar 12, 2011
    I'm pretty sure it is a thermister. I just checked the resistance between middle terminal and negative on my Olympus BLS1 battery and got a nominal 10000 ohm resistance that went up if the battery was cooled, and went down if it was warmed up. That's how thermisters behave.

    In contrast, I checked one of my BLS1 clones. It shows a constant 10000 ohms regardless of battery temperature. I conclude they stuck a resistor in there to save a few pennies and there is no temperature sensing.

    In any case, neither is needed to run the camera per your test.
     
  6. thearne3

    thearne3 Mu-43 Top Veteran

    807
    Jan 28, 2010
    Redding, CT USA
    Assuming you create a dummy/blank battery with leads that go to a power source, the battery door must be open. How do you plan to mount the cam on a tripod with the battery door open? Or is the door removable??
     
  7. RobWatson

    RobWatson Mu-43 Hall of Famer

    Hack it, Jack!

    So I had some spare parts laying about and built a voltage regulator to output 8.25 volts DC (my fully charged battery gives 8.4 VDC) and it can deliver up to 900 mA no problem. The output is very clean and rock stable ... LD1117 is very nice regulator.

    P9025892.JPG

    Whittled a dummy battery out of Delrin and 'mounted' the output of the voltage regulator to it ...

    P9025891.JPG

    Slide that sucker into the battery bay with a nice friction fit ...

    P9025893.JPG

    Turn on the juice (a 12VDC supply laying about) and turn on the camera .... Presto!

    P9025894.JPG

    For the tripod I'll make an 'adapter' ... basically a tongue to fit with the battery bay door open. Drag out my deep cycle marine battery (use that for remote astrophotography work) and away we go for days on end. Even a 'dead' battery will be >10VDC and still have plenty of capacity to run the camera for hours!
     
  8. thearne3

    thearne3 Mu-43 Top Veteran

    807
    Jan 28, 2010
    Redding, CT USA
    Nice project! How much current is the E-P1 drawing? That's a pretty hefty heat sink on your regulator...
     
  9. harrysue

    harrysue Mu-43 Regular

    164
    Mar 12, 2011
    The old electronics worrywart in me thinks you might want to crank the voltage down a bit. That's 8.4 volts open circuit. A battery is likely to be maybe a volt lower with a load?

    If the camera doesn't have an internal regulator, the lens motor is going to spin really fast and you might be worried about the components in the flash getting close to their max ratings.
     
  10. Sammyboy

    Sammyboy m43 Pro

    Oct 26, 2010
    Steeler Country
    Bob, I think you should be at 7.2 VDC. I'd be curious to know how many mA it's drawing. If we knew that, there's a simple regulator that can be made using a zener diode and a resistor.
    My charger indicates 400 mA @ 8.35 VDC, the battery is rated at 7.2 VDC.
    Sure hope you didn't fry any circuits.
    Sam
     
  11. RobWatson

    RobWatson Mu-43 Hall of Famer

    I didn't measure the current draw. Not sue exactly how to do that without changing the circuit ... I suppose I could measure the power going into the circuit and the voltage drop across the regulator and infer the current draw of the camera. Don't really care as the camera draw will vary depending on how it's used, lens, etc. Considering 1100mA-Hr battery capacity and ~4 hours run time over my last time lapse session figures to ~ 275 mA current draw on average.

    The heatsink is way over-kill but it was already epoxied to the regulator!

    8.25 VDC is probably not required as that is actually the battery charging voltage. Something in the 7.2-7.8VDC range is probably more like it but I'd bet even 9VDC would be fine. If I had a variable supply (or a suitable potentiometer) I could just lower the voltage until warnings or shut-down to find the bottom end ... Easier to just measure the battery volage after the camera says it is discharged too low to use!

    I'm going to repackage the circuit and give it a run overnight ... now if the weather will cooperate, fog you now.

    Zener and a resistor would work but I don't have one with anywhere near the right voltage. I've got a massive pile of surplus components so I'm not too keen on buying even more if I can make do with what I have. Scottish blood and all.
     
  12. RobWatson

    RobWatson Mu-43 Hall of Famer

    Dropped the voltage down to 7.0VDC and still get registered as fully charged battery and everything works fine. I suppose the lenses might draw different power levels but I've only got the 17mm F2.8 ... no problems there.

    As for the tripod/wires issue I found a 1/4"-20 stand-off that is 1/2" long and that fits the bill just fine. Good thing I hardly ever through anything away (I'm not a hoarder!) as I remember that stand-off left over from a little project from 1996!
     
  13. Sammyboy

    Sammyboy m43 Pro

    Oct 26, 2010
    Steeler Country
    To measure the current draw in mA, just hook up a multimeter (set to mA) in series on the positive side. Power up the camera and focus the lens. Your power is at a stable 7.0 VDC, so I don't think there should not any voltage drop. I would be interested to see what the current is.
    Sam
     
  14. RobWatson

    RobWatson Mu-43 Hall of Famer

    The meter internal resistance makes that method tricky as there will be a voltage drop across the meter and the camera will run at an even lower voltage.

    I put a low value resistor on the positive input in front of the voltage regulator and got 311 mA for camera + regulator. I think the regulator only draws 10's of microamps so most of the current is going to the camera.

    That power level is just the camera doing nothing but LCD on maximum brightness in live mode.

    ~60 mA extra pulled by the 17mm F2.8 while performing AF.