Power to Canon DSLR - L7808/capacitors

[DIYman]

Hello all

I want to run my Canon 20D from a 12 Volt battery and also from a mains AC through a 12 volt transformer/rectifier for AP. I need 8 volts output for the camera so the L7808 voltage regulator fits the bill.

Since I plan to run the camera from a transformer/rectifier I will need to fit capacitors to the input and output sides of the L7808 and this is where I need advice.

I checked the Internet etc and keep finding different values and types of capacitors in circuits using the L7808. It’s a bit confusing as electronic theory is not my strong point. I want to do what is correct for my application as I do not want to bugger up the camera’s electronics by using the wrong capacitors (transient spikes etc) especially when using the transformer/rectifier setup.

Some sources show 0.33uF capacitors being used on the input side while others show 220uF. That’s a huge difference - how can this be? On the output side, some sources show a 0.01uf ceramic being used while others even show the use of a (0.01uf) electrolytic capacitor. ????

I looked at the L7808 I bought from Jaycar and apart from a couple of meaningless numbers there is no manufacturer’s name so I cannot search for their datasheet. One web page warned strongly against relying on recommendations from one manufacturer and applying them to another’s device saying this could lead to failure of the regulator and associated circuitry (my camera).

I would really like some practical advice on this issue so I can get on and start using the camera.

Thanks in advance.

DIYman (does not include electronics)

[wasyoungonce]

Hi Doug

the Canon will require around a 1.5Amp (peak) psu, maybe even slightly more (depends on if you use a lens on it and auto focus etc etc), so the 7808 will be running very very hot. A few users here have built varying camera PSU's using various methods, see here (http://www.iceinspace.com.au/forum/showthread.php?t=34209&highlight=canon+power), here (http://www.iceinspace.com.au/forum/showpost.php?p=856699&postcount=12) and here. (http://www.iceinspace.com.au/forum/showthread.php?t=54153&highlight=canon+power+supply)

further to this voltage regulators device mfgrs recommend around 2.5V head room (in-put) voltage above their regulated voltage to regulate efficiently. In experience I found you need around 2V min above regulated voltages. You can get low drop-out regulators (LDO's) that will operate ok from a lower headroom voltage.

A better method is to use a high efficiency switch mode regulator (see links). They operate with far less heat waste and are very stable. I saw a few gents obtained cheapish regulators from fleabay and they said they work ok. You need to look on CN for info on this, I'll see if I can find the posts on this.

Lastly typical voltage regulators like 7808, 7805 require around a .01micro farad ceramic bypass capacitor on input that helps filter high freq noise oscillations and fix what is called Equilivent series resistance (ESR). Linear regulators don't like capacitive loads. This bypass capacitive value is usually listed in the OEM part data sheets. Sometimes a small electrolytic is used as well lets say 1.0 microfarad.

Hope this helps.

edit:

Here (http://www.ebay.com.au/itm/New-LM2596-DC-Buck-Step-Down-Voltage-Adjustable-Converter-Power-Module-Regulator-/140779718169?pt=AU_B_I_Electrical_T est_Equipment&hash=item20c7200619)is one of the cheap fleabay DC converter modules. 4 to 35VDC in for 1.2 to 30VDC out (adjustable)...2Amps for $2.14.
Another (http://www.ebay.com.au/itm/DC-DC-Converter-Buck-Step-Down-Voltage-Module-4-75-24V-0-93-18V-2-5A-Output-/270940113628?pt=AU_Gadgets&hash=item3f154a0adc) rated to 4A for $3.39. I like this one.

[2stroke]

don't they just sell these on fleebay? or are they plug pack just into a fake battery?

[wasyoungonce]

I've never seen a DC/DC converter with DSLR battery adaptor on fleabay...could be wrong though.

Plenty of cheap AC/DC converters available on fleabay. (http://www.ebay.com.au/sch/i.html?_trksid=p3907.m570.l1313&_nkw=canon+ACK&_sacat=0) I even have a knock off one. But this is that badly designed and built I won't use it.

[DIYman]

Thanks Brendan

I found this site which I thought is good value. http://www.berndmargotte.com/technical/external_power_en.html

This guy simply powers a camera with a 7808 without heat sinks or caps.

Even if I take the advice you and others have posted, I am still interested in knowing why there is so much variation in the cap values used with a 78xx voltage regulators - particularly when drawing power from similar sources.
Cheers
Doug

[mswhin63]

I have used this and now modified it to work on 12V battery power. Has been working well and now I have decided to replace the switching regulator with a linear regulator to make limited electrical noise.

[wasyoungonce]

Putting the linear regulator in the battery pack just places a heat (thermal) source in the camera. Moving the regulator out of the battery reduces thermal noise in the DSLR.

The variation in requirement for input caps is due to how each OEM device responds to the capacitive load on the input pin. Since each OEM has their own manufacturing process and quality of dies and taking each others design then variances are common.

Malcom, I made sure I used the appropriate "PI" input and output bandwidth filters as specified by the OEM for my switching regulator (PTN78060WAH)...no issues with noise that I can see. I used their exact specified parts as they were very particular on what to use....maybe I got lucky...maybe I cannot see the noise (more than likely)?

A 7808 will just suffice to power lets say a 450D since higher power usage spike ups and down with the demands of the camera operation...I remember testing one with loads of 500mA and damn they get quite hot! Placing the device on a good heatsink is required.

The Daniel McCauley pdf (http://www.easternvoltageresearch.com/dan/equipmods.html) on this shows the expected current draw and transients. he suggested using a metal case placing a 7808 against the case (with thermal pad) to dissipate heat.

[DIYman]

Thanks Brendan
Thats the sort of info I was after.
Well done.
Regards
Doug:)

[tlgerdes]

I put 2 of these in a box

http://search.jaycar.com.au/search?p=R&srid=S2-USWSD01&lbc=jaycar&w=voltage%20regulator%20kit&url=http%3a%2f%2fwww.jaycar.com.au% 2fproductView.asp%3fID%3dKC5446&rk=1&uid=971537174&sid=2&ts=custom&rsc=AfXpaSb62j-9QvaY&method=and&isort=score&view=list

On one, I replaced the regulator and diodes with 3A equivalents (I think LM350K) and it worked a treat. You can adjust the voltage to any value from 1.5v up. I had them set for 5v (USB Hub) and 7.5v (for Canon 1000d). Dont forget your heatsink.