Battery packs have a trigger button on them so you can them to take a shot. I think this third contact is used exactly for that reason.
Mon Jun 21 13:41:49 PDT 2004
On viewing your website I have come across an article relating to the Canon dummy battery and power cord. I suspect the extra, seemingly redundant, ground connection on the dummy battery is used to allow the camera to determine that a battery/dummy battery is connected. The camera registers a voltage between the + power terminal and the dummy terminal - this allows the camera to determine if the power source is a dummy battery or a real battery (the dummy having one less connector than the real battery).
This is only a theory, but I hope it sheds some light on the matter?
Mon, 04 Oct 2004 20:17:57 +0000
You have a very good article on Canon adaptor and battery "DR-400 pinout". In that article, you asked about the B and D pins on the battery. The missing information can be found from a generic battery supplier such as GP Battery: GP Rechargeable Speciality Batteries
Keep up the good work.
Mr. LIN Yih . . . Singapore
Mon, 29 Nov 2004 00:19:37 +0800
That was a very good web-site, Mr. LIN Yih. They even have technical handbooks on Lithium Ion, Nickel Metal Hydride, and Nickel Cadmium.
I managed to find the B and D connector schemetic and specification (attached below) from the GP VCL002 Data Sheet.
I am not sure what it means exactly.
BP-511 Connector Specification.gif
Sun Nov 28 13:05:04 PST 2004
Usually one of them is connected to a thermistor - a temperature sensing variable resistor to sense the battery temperature during charging. For example, see
Since Canon has two pins D and B, I suspect the D pin is the thermistor, and the B pin is either obsolete or for Identification (tell the charger that "I am connected"). See
Of course, I have not confirmed the above. If I have more information, I will let you know.
My quest started because I was looking for a compact size charger for my Kodak battery pack (for SLR/c). The Kodak charger is large - AC/DC adaptor plus charger combo. Since I also have a Canon compact charger (for BP511) and both batteries are 7.4V lithium-ion, I wondered if I could use the Canon charger for the Kodak. But so far, I have found that the thermistor values are different - Kodak about 8.2K ohm and Canon about 74.5K ohm (D pin). Furthermore I cannot use the Canon charger by tapping the + and - pins only. Something needs to be connected to D (or B). Details to be confirmed.
Mon, 29 Nov 2004 08:58:28 +0800
That's quite interesting. Which Canon charger do you have?
My Canon CS-PS400 charger does not have an interface to B or D . . . It charges the BP-511 battery pack by interfacing to + and - only. My Lenmar Mach 1 charger is also the same way. Yet, both are able to detect that the BP-511 is fully charged.
I am quite surprised to hear that your charger interfaces to the B or D pin.
Mon Nov 29 20:29:03 PST 2004
Thanks for the tips. My Canon CB5L charger definitely senses D but B has no effect. I tested by tape masking away D and B pins in different combinations. Yes, I have a X-brand charger too, and works with only + and -. However, that charger is not compact (compared with CB5L). I have not tested X-brand with Kodak. Canon CB5L came with the 300D.
Thanks for the tips. I will be out of Singapore for the rest of week (work). Will revert back to the Kodak when I am back.
Tue, 30 Nov 2004 19:34:55 +0800
Ahhh . . . Yes . . . I can see the B and D pins on the following picture of the CB-5L charger:
How interesting . . . What kind of effect did you see when you mask away the D pin?
Canon CB-5L Battery Charger.gif
Tue Nov 30 11:47:10 PST 2004
If you take a look into camera's (20D)battery compartment you'll find that neither B nor D pins are connected :)
So they don't play any role in feeding up the camera.
Sat Feb 5 11:30:01 PST 2005
You guys rock! Sharing your knowledge with people who care enough to learn is awesome. Our throw it away society has a lot to learn about the value of things. Knowing how to do something well and teaching it to others is one of the most valuable resources we have. Rock on.
Mon, 19 Feb 2007 21:54:17 -0800
The 2 extra contacts are used when charging. 1 is the thermistor, its a variable resistor that changes with temp, it lets the charger know the battery temp, if the temp is outside a certain range, it will not charge the battery (to hot or cold). The other is serial data communication. This allows the charger to talk to the battery and vise versa.
Li-Ion batteries can be dangerous is not cared for during charge and discharge. The pack has a saftey chip. Each of the 2 cells is monitored for correct voltage range (4.20v is max and the min is around 2.5 to 3.0). If either cell is out of the range, the saftey chip will shut the output of the battery pack off, like wize to hot or cold. There are other parameters this saftey chip preforms, like max charge and discharge current, if to hi, it shuts down, max charge time, ect.
Mon, 08 Oct 2007 04:45:43 +0000
Did anyone ever find out what the connector is that goes from the DC-coupler DR-400 to the ac-e2 power supply? I'm hoping to make an extension that runs between the two but I can't find that connector.
Thu, 04 Mar 2010 19:07:02 +0000
Just splice into the middle of the cable with common power connectors. I've shown this trick in the "Hacking Digital Camera" book.
Thu, 04 Mar 2010 20:56:55 +0000
Just had to say that this was very helpful, I had ordered an adapter for the 60d (I have a 50d) but with a soldering iron, older battery and a few min I was able to retro fit the components inside the older battery shell and its working wonderfully now. I needed everything working by tomorrow and like hell if I was going to pay 50 for overnight shipping.
Wed, 08 Aug 2012 21:56:19 +0400
I actually have a BP-511 battery.
It didn't charge (when I put it inside CB-5L charger red light blinked once, then twice then three times then full in just 10 seconds and it didn't charge the battery).
So: at first I tried taping the B-D contacts. No success. Then I short circuited B-D and the charger blinked twice every 5 seconds. So I short circuited + and - contacts and the battery started charging (I checked after 30 mins putting it inside my camera: it was now a semi-charged battery.
After 10 minutes that way I completely removed the short circuiting piece of metal and connected the battery the standard way... It's now charging!
So probabily something works in a different way. Don't know how the battery could charge on a short circuit.
Sun, 03 Mar 2013 14:23:25 +0300
Did your message disappear? Read the Forums FAQ.
TrackBack only accepted from WebSite-X Suite web sites. Do not submit TrackBacks from other sites.
Title: cameras sense that the DR-400 is inserted vs. a regular battery
Weblog: Camera Hacker
Excerpt: The cameras sense that the DR-400 is inserted vs. a regular battery using a microswitch, not using one of the B/D contacts. You'll see a raised bar in a BP-511 charger that stops the DR-400 going in. In the cameras this location is occupied by a switch. Take a regular battery, cover over the matchin . . .
Tracked: Thu, 25 Aug 2005 02:10:57 -0700
Title: make a DC adapter for Digital Rebel XT
Weblog: Camera Hacker
Excerpt: I have a D rebel XT and would like to make an DC adaptor using an old NB-2LH battery case with the batteries stripped out) but don't know what the 3rd T contacts is for, it seems to be a negative connection by my volt meter. I already have a Canon power supply with the proper voltage and terminal wh . . .
Tracked: Wed, 28 Dec 2005 13:22:25 -0800
Title: DR-400 disassembly
Weblog: Camera Hacker
Excerpt: Does anyone know how to open the DR-400 without damaging it? I want to put a switching regulator module inside it so I can run the 20D and 5D from 12V. BTW - The AC adapter that came with states the output is 7.8V at 2.0Amps. This was for my 20D.
Tracked: Wed, 3 May 2006 02:35:40 -0700
Spam Control | * indicates required field
Messages, files, and images copyright by respective owners.