CHDK Forum
CHDK Development => General Discussion and Assistance => Topic started by: gtrecordings on 19 / November / 2008, 22:07:45
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I have an sd550 it uses a 3.7v battery and has no external power option. I was looking at the bottom of the camera and noticed a rubber cover on the battery door.
My plan was to make a wooden block the size of the battery and run wires from the power contacts in the camera out the whole in the door.
I noticed that the battery has 3 contacts, +, T, and -. My idea is to make two of these blocks, one for the camera and one for the charger. Then I would put connectors on either end for cable extensions.
Idealy, i would just make a bigger battery pack, but i don't know how to wire up the contact with the T symbol.
Is that the ground?
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Idealy, i would just make a bigger battery pack, but i don't know how to wire up the contact with the T symbol.
Is that the ground?
T=thermistor (usually) to measure battery temperature:
http://www.electronics-lab.com/articles/Li_Ion_reconstruct/ (http://www.electronics-lab.com/articles/Li_Ion_reconstruct/)
(https://chdk.setepontos.com/proxy.php?request=http%3A%2F%2Fwww.electronics-lab.com%2Farticles%2FLi_Ion_reconstruct%2Fpack.gif&hash=4ee84dd99391b17cba46dd89b9b00c23)
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I have an sd550 it uses a 3.7v battery and has no external power option. I was looking at the bottom of the camera and noticed a rubber cover on the battery door.
well, this rubber cover IS for external power adapters. for the small ixuses you get an AC together with a "fake battery". the cable then is led through this rubber cover. the canon acs are very expensive though.
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thanks for the diagram.. i am wondering if target/bestbuy/walmart booths has tons of those things laying around... maybe getting used one that way could be an option.
I wonder if i ran 3.5v to the camera and bypassed the temp circuit altogether. My camera is pretty trashed already, so I am willing to experiment. If this is reasonably safe to do, i think i might try it.
I wonder how i could recreate the temp fuse...
I thank you guys for responding, you have both been very helpful.
gt
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(https://chdk.setepontos.com/proxy.php?request=http%3A%2F%2Fwww.three-rings.com%2Fmedia%2F5%2Fmms-625526801.jpeg&hash=76d1333753e65af4128827bd8abc491b)
(https://chdk.setepontos.com/proxy.php?request=http%3A%2F%2Fwww.three-rings.com%2Fmedia%2F5%2Fmms-486323548.jpeg&hash=8eefc17ddc31985104f8e1d144ccaa46)
I just completely bypassed the temp circuit and it powered up with 4.5v and shot a timelapse for about an hour.
It go kinda warm, but nothing harmful. I plan to lower the voltage with a volume pot, or a resistor if i can find the right one.
The fake battery has two halves.. the picture shown is the middle.
more updates soon.
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You may know this, but you can enable battery temperature reading visibility on CHDK OSD menu to check your resistor choices. Many cameras don't have all 3 sensors, though (I believe in that case they give equal readings).
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I plan to lower the voltage with a volume pot, or a resistor if i can find the right one
I think that's a bad idea!
I am not an electronics guru, but a resistor will heat, and decrease its resistance. This might go on and on until it "melts"
Use a voltage regulator instead.
there are a few threads about this, for example:
external Battery - connected to DC-IN (http://chdk.setepontos.com/index.php/topic,341.0.html)
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Resistance goes *up* with temperature, not down, so you're safe :)
But you definitely want a regulator instead of a single resistor or pot, as the voltage drop across the resistor will vary with the current draw from the camera.
But since the camera hasn't died with a 4.7v input, it's probably already got some voltage regulation hardware already.
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oops, I stand corrected: I told I wasn't a guru :-)
All I remembered was along the lines of "regulating voltages with a resistor makes Santa Claus cry" ...
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Use this
Zener diode:
Also sometimes called avalanche
diode or Zener. A semiconductor diode (usually
silicon) specially fabricated to take advantage of
the effects of avalanche breakdown. It is available
in a wide variety of configurations and ratings; it
is commonly used as a voltage regulating device
in low-voltage power supplies.
George
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If the voltage dropping thing idea really was for dropping the supply voltage and not for putting a divider to the temperature measurement to fool the camera, then a proper regulator is the only way to go.
E.g. for my A570IS (a dual AA cell cam) the nominal required external PSU output is 3,15 V, 3 A if my memory serves. That's almost 10 W to dissipate in PLAY mode or camera OFF mode if you go with a zener (you don't, really).
A resistive divider is not possible either, for the same reasons and more.
Whatever you do, if you use too high impedance in your external PSU and you manage to power on, your camera will shut down when it operates a motor due to high current causing a voltage drop and brown-out protection shuts the cam down.
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thanks for the ideas... i am going to measure the voltage and try used the zoom motor tomorrow. My LCD is cracked so i usually have a preview monitor plugged in... that should save some power.