Digital Camera Power Supply

** See disclaimer at the end of this page **

This little project came about due to the purchase of my first digital camera - a Fuji MX1200. A Minolta DiMage 5 and digital video camera later saw the metamorphosis into the abomination presented below....

As most digital camera owners probably know, these wonderful devices have a rather unpleasant appetite for batteries. This isn't a problem if you have lots of rechargeables to hand and actually remember to charge the things prior to use. Me, I'd had enough of all the aggro and decided to make up my own power supply that would enable me to power the camera from any 12v DC source. As I had a few 12v alarm panel lead acid batteries available, these could (and do) provide enough juice for an entire days shooting. In addition, I picked up a 12v 3A mains supply from a car boot sale. Now the camera could be powered from the mains, a 12v portable battery or the cigarette lighter socket from the car.
Oh yes, the other reason for making a DIY power supply? A Fuji adapter costs £80, a Minolta power pack costs £180+ and a battery pack for the video camera is similar money. This one cost a grand total of £5 (I already had the 12v batteries, CPU cooler and DAT tape box). If you were to buy all the bits brand new, it would cost less than £40. That includes a 4Ah lead acid battery (£22) and the charger (£12) from Maplin electronics.

As mentioned above, since acquiring another digital camera and a digital video camera, I wanted all 3 to be powered from the same source. The only downside was that the Fuji wanted a 5v supply, the Minolta wanted a 6v supply and the DV camera wanted a 7.9v supply. As it turns out, a single supply producing 6.9v would work for the entire lot.

The Circuit
The circuit is based around a KA350 variable voltage regulator (the package has LM350 printed on it). This reg will provide upto 5A of current so was ample for the needs of the cameras. The reg was bought from RS for the princely sum of £0.97 (RS stock code 267-9917). I had tried other variable regs from Maplin but success was not on the menu - this since turns out to be that I had the output voltage too low.....the Minolta needs a 7-7.2v supply to run it.
circuit diagram

The Design
The output voltage from the regulator is governed by the formula Vout = 1.25 [1+ (R2/R1)] + IadjR2
Iadj is typically less than 100uA and was ignored in the design, so, Vout = (1.25 * 5.5) = 6.9v

Capacitors can be added to filter out noise on both the input and outputs if desired

Not having a single 4k5 resistor for R2, the closest I could make out of the resistors I had floating around was 4k55 from two 9k1 resistors in parallel. This effectively upped the output voltage to 7v. As the supply for the circuit will (in my case at least) be 12v lead acid batteries, I added a pair of zener diode driven LED's. Zener diodes only pass current when a certain threshold voltage has been reached. I could therefore use a red LED with an 8.2v (or 9.1v) zener to show when the circuit was suitably powered and a green LED with a 12v LED showing the health of the lead acid battery. When the green LED extinguishes, the supply voltage has dropped below 12v, indicating that the battery is at about 15% of it's capacity and therefore needs recharging. The zener diodes, LED's and associated resistors R3 and R4 can be omitted if you don't have the need for these.

As anyone who owns digital cameras knows, they tend to draw a fair amount of current. Anticipating this, the regulator was mounted onto a fan cooled CPU heatsink. The fan was wired directly to the input supply. If you intend using different voltages for the input, you'll need to add another 12v regulator to power the fan. I'm not sure if the fan is required, but it's never overheated yet. My design was mounted into an old DAT tape box, with suitable holes being cut to mount the fan and various power sockets. A 2nd DAT box was cannibalised to form a cover for the fan, preventing foreign objects from stopping the thing turning. If desired, a switch could be easily incorporated to allow the fan to be controlled manually.

The photos below show the finished article. As with all of the mini projects on this site, they are purely functional and will not win any design awards. There is a single input socket (that's the one with the resistors soldered directly to it), an output socket for the video camera (the one at the 'top')and a fly wire for the digital stills camera(s). Having the two power outlets lets me happily run both the digital stills camera and the video camera at the same time - both with full functionality (LCD displays on etc etc). Handy when my mate drives the video camera leaving me to the stills.

photo of finished circuit  cooling of the PSU

Using the Power Supply
This turned out to be a laugh a minute....
The Fuji camera worked no problem. It was quite happy running off a 7v supply even though it says it only wants 5v (this is a fallacy based on prior incarnations of the PSU, 6v supply minimum to get it working) Presumably the Fuji has it's own regulator built in.
The Panasonic digital video camera worked fine, albeit with the low battery indicator showing. Full functionality was maintained with the camera. According to the manuals etc the supply should be 7.2 - 7.9v. I guess 7v is OK!
The Minolta digital camera....thought I'd destroyed it! Plugged PSU into camera while batteries were still in the compartment - low battery indicator lights up, camera won't do anything. Remove PSU, low battery indicator remains on, camera still won't do anything despite switching the camera on and off several times. Cold sweat starts at the thought of having just fried £500 worth of digital camera. Removed and reinserted batteries, all back to normal. Removed batteries and try PSU, all works OK, full functionality from camera. Guess the batteries need to be out to use this supply.

Neither myself,, my family, my friends, my pets or my monkey take any responsibility whatsoever for any damage caused to anything or anyone by duplicating what I've done. If you feel confident in not destroying your expensive digital imaging equipment by trying this PSU, that's your choice and not mine. And, no, the unit will not be made commercially available - it's just not worth the aggro!

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