Powering camera for longer

I have a wireless rear view camera in my bumper that currently draws 120mA @

8V DC (in the paper specifications) from a 9V PP3 battery - attachment is a PP3 clip. I tested it out with some of those (cheapo no-name crap) super heavy duty batteries and it lasted for about 30 minutes, which is OK for a quick trip, but any more and it means I have to have a load of batteries with me and keep opening the boot to change the battery over.

I tried one of those more powerful (and more expensive) alkaline batteries (Duracell Ultra) - I dunno what their capacity is, I googled and found its about 570 mAh, so I figured I should get a good 5 hours or so, but after just over two, I guess the battery ran out as it stopped working and I had to change over the battery again.

So I guess my problem is capacity - I ordered some 2650 mAh AA rechargeables and a battery block with PP3 connector - I suppose 6 x 1.5 is going to give me the 8V that I need to power this thing for a reasonable amount of time.

I was looking at running this thing from the car electrical system, but I don't have any reasonable convertor and I don't want to cook it with too high a voltage/current.

I have a multimeter and I am finding I am getting 12V DC from a pair of wires near the rear, which will probably be too much, but it says 0 amps? How do I get the 120 mA that will run the device?

I am able to solder and am handy with DIY well enough, so could add in a resistor or two to get it down to 8V, but I'm gonna maybe need some tips on how to do this right without blowing the camera.

It was cheap enough, but repeated learning experiences can get expensive! Please point out any misconceptions or probable pitfalls I am likely to encounter on this project - and any suggestions are very much appreciated!

Reply to
Jake
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In message , Jake writes

Yeah - what's wrong with your rear view mirror

better resolution, no batteries required

If you insist on playing with toys, just power it from the 12 v supply, they all seem to work off 12v in my experience - or you could put some diodes in series to drop some volts and a capacitor to smooth out the crap

Reply to
geoff

Maplin sell an LM317 type variable voltage regulator,

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uses a single variable resistor to set the output voltage as neeeded from 1.25 Volts to just under the supply voltage, or 37 Volts, whichever is lower. One of the 1.5Amp rated versions, (Order Codes UF27E and N61CA) with a variable resistor will fit into one of their small plastic boxes, add a 0.25A fuse in a holder in the side of the box or inline on the input cable, and that will do it. There's a sample circuit on their website, and it will all fit on a 6 terminal tag strip. Total parts cost about the same as a set of Duracell AA cells and a holder. The last one took me an hour to make, including searching for the *&^%& soldering iron.

Reply to
John Williamson

Thanks for your comments Geoff! Shows me the view from the bumper and is very handy when slowly reversing close to walls and other objects.

And yeah, each to their own toys :)

Reply to
Jake

In message , Jake writes

Dunno about you - I learned to drive and understand where my car is can you really not see the border of your metal box ?

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Reply to
geoff

You need a voltage regulator to reduce 12-16v down to 8-9v. Current draw is determined by the camera.

The gotcha is that most regulators will not cope with the load dump transients you get on car systems, and will simply kill the camera at some point.

Do not connect the cam to the 12v car supply, load dump will send it into orbit at some point. And 12v car supplies arent 12v, they're upto

16v in normal operation, and down to under 10v.

NT

Reply to
Tabby

Hi John, this looks just like what I need - have a few questions.

On

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they have a number of circuit diagrams - which is the one that I want? Adjustable current limiter or precision current limiter on page 5?

Which type of variable resistor should I have?

Anything else

Reply to
Jake

You need a voltage regulator to reduce 12-16v down to 8-9v. Current draw is determined by the camera.

The gotcha is that most regulators will not cope with the load dump transients you get on car systems, and will simply kill the camera at some point.

Do not connect the cam to the 12v car supply, load dump will send it into orbit at some point. And 12v car supplies arent 12v, they're upto

16v in normal operation, and down to under 10v. ************

Yeah, had an idea that might happen. Think I'll just go with a block of 9Vs in parallel and a on off switch to reduce the time it's in use.

Reply to
Jake

Depends on your vehicle. I can see the borders of my metal box but more often than not when reversing I can't see the other metal box I'm about to hit in any of the three mirrors or out of the windows.

The OP seesm to be hung up on current, that's not particulary relevant provided the supply can deliver it. The voltage is important several solutions posted but pick up the 12v from the feed to the reversing lights.

Reply to
Dave Liquorice

In message , Jake writes

What's a 'load dump transient'?

Reply to
Ian Jackson

The effect of poor regulation in the alternator. When a big load gets switched off the volts shoot up until the regulator notices.

Worst case can be spectacular. On a TV Outside Broadcast, a Songs of Praise I believe, many moons ago the generator used was a "good price". Unfortunately the main bus bar output was bare open terminals in the back of the wagon (think "fairground"). OK not the safest but no one should be clambering about in the back anyway...

Trouble is a spanner fell across the bus bars, that made the genset "work a bit hard" and eventually said spanner acted as fuse. When in did, the volts shot right up and blew every single lamp in the church... This was a while back when TV needed lots of light so most of the lamps were 2kW each and there would be in the order of 30 or more of them.

Reply to
Dave Liquorice

For your purpose, ideally, you could use the circuit labelled as "Adjustable regulator with inproved ripple rejection", using Maplin part number N52BR as the adjustable resistor. However, the basic circuit configuration on page 3 using a 220 Ohm resistor as R1, and the N52BR resistor as R2, with the slider connected to the adjustment pin on the IC, and either of the ends of the track connected to earth will probably work fine.

You are trying to get a stable voltage to the camera, if you do this, it will work as designed, drawing only the current it needs. The 1.5Amp capacity of the IC I suggested is only to save problem with the smaller one overheatingnd shutting down to protect itself.

In fact, checking the Maplin catalogue again, now I've had some sleep, there is a Velleman kit:-

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comes complete with a nice fibreglass circuit board and instructions for a tenner.

Add a box and a fuse, set it to 8 Volts, and you are, as the Yanks say, good to go. If your camera only draws 120mA, then you won't even need a heatsink. You could even use a PP3 battery clip, such as:-

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carry the power, so not having to modify the camera, but make sure the polarity is correct, comparing it with a PP3 battery.

Reply to
John Williamson

When you start the car, the battery voltage drops to 9 volts or less, then, when the starter motor is disconnected, it generates a relatively high spike voltage in much the same way as a contact breaker type ignition coil work. The spike can kill badly designed electronics.

Reply to
John Williamson

Urban myth. I've got loads of home brew electronics on my SD1 which has a non standard 100 amp alternator - and I've had no problems whatsoever using standard regulators. Of course if you do something stupid like disconnect the battery with the engine running you might fry something - but why would you?

Reply to
Dave Plowman (News)

Assuming competence, you could build a 9 volt 1 amp regulator for about a quid.

But I'm sure such things can be bought off Ebay etc ready made.

Reply to
Dave Plowman (News)

Well, as we don't have lots of dead car radios, CD players, satnavs etc, such problems would appear not to be insuperable. I would have thought that a smidgen of spike-removing decoupling at the input side of the regulator should prevent anything disastrous happening.

Reply to
Ian Jackson

And seeing the amount of electronics in Motah's nowadays they must be well designed;)..

Reply to
tony sayer

Yes, and the kit I mentioned elsewhere has worked well for me in the past. In the case under discussion, if the power feed is taken by connecting the dropper in parallel with the reversing lights, the problem won't arise anyway, unless the car is started in reverse gear.

Reply to
John Williamson

The alternator is inductive, so if a large load is removed, a transient overvoltage occurs. If a poor connection to the battery ever occurs, the voltage can be fairly extreme. Car appliances are designed to cope with it.

Yes, you can get away without any protection, its just not a reliable approach, and your appliance may die.

For the op, PP3s or AAs are entirely the wrong battery type for 120mA, you need something much bigger.

NT

Reply to
Tabby

Imaging the short term splashback you'd get from depositing a very large turd down the pan, It's the electrical equivalent usually caused by the alternator charging into the electrical system with no battery connection.

Reply to
The Other Mike

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