DIY EOS 12V power supply

[Davey-T]

Just rounded up all the bits to make 12v power supply for my camera, bought a 240v one and chucking the innards to fit a buck converter.

One question, does the buck converter generate much heat ? do I need to drill some ventilation holes in the enclosure ?

Dave

[malc-c]

Dave, how are you powering the camera, using a dummy battery or using some sort of motor drive port ?

My 400D doesn't have an external power input, so I removed the cells from a battery and used the casing  to connect to an 8.5v supply.  Are you sure the camera runs off 12v ?

[Davey-T]

Bought the 240v one and using the dummy battery from it and the enclosure / cables etc, the buck converter is adjustable and reduces 12volt to camera voltage 7.0 something need to check.

Following this site

http://www.deepskywatch.com/Articles/Canon-dslr-power-supply.html

Dave

[Alien 13]

The standard DC-DC buck convertors run cold with the Canon but a recent post has highlighted that they can sometimes fail outputing the input voltage i.e. 12V, my suggestion would be to add a crobar circuit on the output or use two devices one 12V to 9V (which the camera opperates on if using a battery grip with AA cels) the scecond converter would then go from 9V to 7.4V for the camera. The use of two converters would require multiple failures to cause any damage to the camera.

Alan

[Davey-T]

Thanks Alan, will do more research.

Dave

[Alien 13]

I have thought long about this and indeed have used down convertors in the past but recently have bought a few cheap USB power banks ranging from 4.8AH to 12AH for just a few quid and found that my EQ3-2 runs fine from the 5.2V provided, so am looking to use one with an up converter for my camera again protection will be the key and only the Dual output 12AH version has the 2A socket that would be required.

This method could provide cheap power to a DSLR when used out and about and is lightweight too.

Alan

[Davey-T]

Further to this project I have now purchased MC3423 IC to add a crobar circuit, looking at the spec it seems to support increasingly complex circuits to achieve the end result from just a thyristor and a couple of resistors to more sophisticated protection.

Question is will the simplest version suffice or ?

Dave

[Alien 13]

Further to this project I have now purchased MC3423 IC to add a crobar circuit, looking at the spec it seems to support increasingly complex circuits to achieve the end result from just a thyristor and a couple of resistors to more sophisticated protection.

Question is will the simplest version suffice or ?

Dave

I am looking at the motorola datasheet and I think fig 3 would suffice I would add a LED indicator across the fuse or in/out so you know if the circuit fired.

If you are handy with a soldering iron it might be worth replacing the pot on the convertor with fixed resistors which should offer better stability if using the unit in cold dewy conditions.

Alan

[Aphophis]

I"m going to add a crowbar to the EOS output of my next power box. Currently it runs from a regular DC-DC converter. I've never seen one failing at 12V. I had 2 fail open on me till now, but not on the EOS circuit. 
I've ordered the MC3423 as well for the project. I think the simplest design with 2 resistors and a SCR should be enough (I've seen people do it with a simple zener diode, but I think it may be a bit too slow to react). One thing to note about this circuit is the vaues for the resistors, as they set the trigger voltage, if you run at 7.4-7.8V, I'd aim for ~9 to trigger. Also, note that battery voltage drops a bit over the course of the night.

Currently my powerbox has 4 2.5mm connectors for the Computer and mount (at battery voltage, I'm thinking of adding a buck-boost converter to supply a constant 12.5V), EOS (at 7.4V) and a general plug, currently at 5V but will add an external pot to the panel in parallel with the one on the converter, to set voltage from the box itself. The box connects to the battery compartment via GX16 connectors on the box and the battery compartment. 
 

[Davey-T]

Further to this project I have now reached this stage and "designed" this crobar circuit to go between the buck converter and the camera.

Could some electrical savy person check the resistor values, am I right in thinking that no resistor is needed connected to the gate for the proposed voltage as per the spec sheet ?

Mounted on a bit of Vero board as pic.

Dave

http://www.onsemi.com/pub_link/Collateral/MC3423-D.PDF

[Alien 13]

The spec sheet does say that RG can be zero with voltages less than 11V however a fault condition could see the input rise to 12.5 V (if powered from a lead acid cell) in which case it might need to be around 5.6 to 6.8 ohms. 

Looking forward to see how it performs.

Alan

[Vox45]

The standard DC-DC buck convertors run cold with the Canon but a recent post has highlighted that they can sometimes fail outputing the input voltage i.e. 12V, my suggestion would be to add a crobar circuit on the output or use two devices one 12V to 9V (which the camera opperates on if using a battery grip with AA cels) the scecond converter would then go from 9V to 7.4V for the camera. The use of two converters would require multiple failures to cause any damage to the camera.

Alan

I already have 5 of those that I bought cheap. I stopped my project when I read that a faulty converter could output 12v ! I like the solution you are proposing. I could leave the one already in my box to output 9v and then follow the tutorial cited above and add a second one in the AC box (that I already own) to output 7.5v

Thank you for this brillant idea

P.-S: anyone knows if a 'good' DC-DC convertor would have protection already built in ? I see such a wide price range on these convertors.. from x5 for 4€ to 9€ a piece !