Electronics help, 7.4v from 12v.

[Daz69]

Afternoon all.

I'm stuck. I need to get 7.4v output from 12v supply to power my Canon 60D. I have a 7809 voltage regulator and the required capacitors, but this will only get my to a steady 9v. I know I'll need a resistor to get me close to 7.4v, but which one? My next question, well maybe just a confirmation, will it need to go after the last capacitor,  and before the output socket?

Thanks peeps

Daz

[Gina]

No, that won't work as the camera current will vary.  You need either a variable voltage regulator chip which uses two resistors to set the output voltage or an off-the-shelf "buck converter".  The latter uses switch mode and emits negligible heat.  Available for very little from the usual auction site.  Has a multi-turn pot to set the output voltage.  These have over-current shutdown and regulated output voltage.

Edited February 6, 2017 by Gina

[Daz69]

My first capacitor before the voltage regulator will be a  100uF-25V electrolytic, the second one after the reg will be a  10uF-25V electrolytic, and the third one before the output sockets will be a  100nF-63V ceramic or polyester capacitor. Was also going to fit a diode before everything tor reverse polarity protection. I can get a 7808, but have some 09's in the workshop. 

Hi Gina, what sort of range would the voltage be likely to go from and to? 

[RayD]

+1 for Gina's suggestion of a simple pre-made buck convertor like this one which cover all angles and are pretty neatly packaged for a pretty reasonable price.

[Uplooker]

I used exactly what RayD linked to achieve the correct voltage to power my Canon 450D from a 12V leisure battery. Took a couple of weeks to arrive from China, but worked a treat

[Daz69]

Never knew they existed, thank you. Would certainly save some time. Umm, might get a couple installed in my power box.

[Davey-T]

Might be worth incorporating a crowbar circuit to protect your camera in the unlikely event of something failing and the camera receiving 12 volts.

Dave

[Gina]

52 minutes ago, Daz69 said:

Hi Gina, what sort of range would the voltage be likely to go from and to? 

I use ones like THESE

Quote

Specifications:

• Input voltage: 3-40V
• Output voltage: 1.5-35V (adjustable)
• Output current: Rated current is 2A, maximum 3A (if the output power more than 10W, the heat sink is needed.)
• Item size: 48 * 22 * 12mm / 1.9 * 0.9 * 0.5in
• Item weight: 12g / 0.4oz

 

 

 

[Daz69]

Just now, Gina said:

I use ones like THESE

 

 

 

Sorry Gina, I should have explained that a bit better. I meant the camera. What sort of differences are likely? 

[Gina]

I forget now - it's several years since I used a DSLR for astro imaging but I think it was something like a few milliamps to half an amp.  The voltage needs to be between 7.4v and about 8.2v as I recall.  8v is a good voltage to use.

[mapstar]

If you use a cheap buck converter buy two and feed one with the other in a serial chain.

If one fails then it wont then pass through 12v to the camera. Its cheap to do. 

Set the first to 7.4v and feed it into the second straight through at 7.4v. 

Edited February 6, 2017 by mapstar

[101nut]

You can use a 7808 and an output diode to drop 0.6v and give 7.4V output over a fairly good current range ... how accurate has it got to be bearing in mind the camera probably has power regulators on board to cope with the battery voltage varying?

AndyG

[Gina]

I found 7.4v was marginal for Canon DSLRs - APT indicated that the power was low.  In fact I found the cameras failed when the voltage was reduced below 7.3v.  I would definitely recommend using 8v.  When fully charged the Lithium Ion battery gives 8.2v and reads 7.4v when the battery display shows low battery.  I did a lot of testing on this when I was making PSUs for my EOS 1100D and earlier models.

[Dr_Ju_ju]

Canon's usually run on 8.4 volts (all mine do) & I run them off a buck converter e.g. http://www.ebay.co.uk/itm/1-3-5-x-LM2596-DC-DC-Buck-Converter-Adjustable-Power-Supply-Step-Down-Module-UK-/161818793869?var=&hash=item25ad26d78d:m:mfnqbLbvaO6JOj7AXxfgPMQ with no issues..

[Daz69]

1 hour ago, 101nut said:

You can use a 7808 and an output diode to drop 0.6v and give 7.4V output over a fairly good current range ... how accurate has it got to be bearing in mind the camera probably has power regulators on board to cope with the battery voltage varying?

AndyG

I presumed 7.4v as that's what's in the specs, but it seems that is not the case. I ordered a couple of the buck converters to see how good they are. I have some small red LED voltage displays that I'll use on the outside of the box, but I'll check the outputs firstly with my multimeter. 

Thanks for all of your replies, really helpful, especially as I'd never seen these converters!

[Alien 13]

If you have a Canon battery grip it comes with an adapter to use 6 AA cells which equates to 9 V so I have taken that to be the upper supply limit, more voltage does mean that the on board regulators in the camera get warmer though.

Alan

[Daz69]

1 minute ago, Alien 13 said:

If you have a Canon battery grip it comes with an adapter to use 6 AA cells which equates to 9 V so I have taken that to be the upper supply limit, more voltage does mean that the on board regulators in the camera get warmer though.

Alan

I don't, just have the standard battery. It's all good info so thanks for taking the time to assist me.

[JonC]

I use one of the buck converters to run my Canon. If you go for one with a display on it , double check the output voltage with a DVM, my one was reading a bit low.

[Juicy6]

I too use a Buck converter set to 8,0 volts on my current 550D. But I know for sure upper voltage is not critical. On my previous setup a converter failed and delivered 12 volts to the camera. Camera didnt complain about this so I used it at 12 volts for long time. Maybe it got a bit hotter, which noise-wise is not good for astro photo, but at least it showed that camera over-voltage protection worked fine.

Christer

[Daz69]

Moving on, @Davey-T has given me a good idea in incorporating a seemingly obvious safety net of a so-called crowbar circuit, ensuring the voltage doesn't suddenly spike or rise should the buck converter fail, and saving my camera. Here is a 9.1v crowbar circuit diagram, but I'm stuck (again) on some of the values.

I read that the circuit should be around 1v more than the operating voltage requires, so going with what others have said so far, this 9.1v circuit should fit the bill nicely. My issues are with the Schottky diode and the thyristor values. Also, would the 0.25a (250mA) fuse be enough?

Here is a link to the page where I found it: https://en.wikibooks.org/wiki/Practical_Electronics/Crowbar_circuit

Thanks again guys n' gals.

Edited February 8, 2017 by Daz69

[Xplode]

Like Alan wrote The Battery grip on these cameras make it possible to use 6xAA batteries @ 9v so it's totally safe to run at 9v.

I used 9v on my 6D and your 60D should work ok too since it uses the same battery.

 

 

I did actually run it accidentaly on 12v for months too, i had several battery dummies and thought i used one with a voltage regulator on it...but nope! 

[Juicy6]

Here is a simpler circuit:

Use zener 1N2974B. It will conduct and break fuse if it "feels" 10 volts. Rated for 1 Ampere, so choose a 1A fuse too. More here:

http://www.learningaboutelectronics.com/Articles/Overvoltage-protection-circuit.php

[Alien 13]

Another way of adding some protection is to use two of those switching regulators in series, the first would drop the voltage to 9 V the second would then output the required 7.5 V, this will ensure that no single failure will stress the camera.

Alan

[Davey-T]

I made a posher version using one of these.

Dave

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

[Daz69]

14 hours ago, Xplode said:

Like Alan wrote The Battery grip on these cameras make it possible to use 6xAA batteries @ 9v so it's totally safe to run at 9v.

I used 9v on my 6D and your 60D should work ok too since it uses the same battery.

 

 

I did actually run it accidentaly on 12v for months too, i had several battery dummies and thought i used one with a voltage regulator on it...but nope! 

I see that the recommended external battery pack is exactly as you say, 9v, so I have gone for a circuit that will shut down at 9.1v as shown in the above link (now fixed!). Having had this bought for me a couple of years ago by Mrs Daz as a "get well" present, and then finding the receipt (she also got me 2 extra lenses 18-135mm and 70-300mm), I want to protect it as much as possible, as I know I won't be getting another one in a hurry  

I went and bought the components from Maplin, luckily I got a nice chap who knew what I wanted to build, as sometimes it can be a bit of a gamble with their staff. Hoping that all of my other bits n' bobs will turn up before Sunday as I have 5 days off and want to get the whole project built. 

Thanks again.