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5v DC feed anywhere ?

anthony1956

By anthony1956
in TechTalk

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Ben Willis

Ben Willis

Posted
Posted

If you were feeling lazy you could use a cigar lighter adapter. Maplin do a 1A version with 4.5V or 6V outputs for £5

http://www.maplin.co.uk/Module.aspx?ModuleNo=37423&doy=11m8&C=SEO&U=strat15

You could easily break open the case and wire the inards directly. Probably as cheap, and somewhat easier than making your own if it would do the job.

 

If you need exactly 5V, there are other, more expensives, versions out there. e.g.

http://www.pixmania.co.uk/uk/uk/135117/art/archos/5v-car-adapter.html

 

Ben

Ben Willis

Ben Willis

Posted
Posted

Not if, as I suggested, you break it open, throw away the unwanted casing and just use the guts. I bet 80%+ of the volume is for the connector and lead. The bits you need to keep will be very small - you could even lose the voltage adjustment knob when you have it set. I also doubt you would make anything yourself that is smaller than the mass produced internals of this device.

 

I suspect your device would run fine from 4.5V. If not, you could alter it to give a 5V setting pretty easily when you have split it open. Whatever, at £5 it isn't going to break the bank if it doesn't work out

dazula

dazula

Posted
Posted

It would help to understand more about the application?

 

FYI: I am in the process of fitting a couple of USB style sockets under the dash for 5volt devices such as SatNavs and Ipods.

 

Darren

anthony1956

anthony1956

Posted
  • Author
Posted

exactly Ben.

 

- and as it happens I have been wondering about the USB 5v spec and whether I might borrow from it in some way. How are you achieving the 5v feed Darren?

 

Anthony (I await current/amps spec)

 

 

 

Edited by - anthonym on 11 Aug 2006 16:00:53

dazula

dazula

Posted
Posted

opps. Brain not taking it what I was reading *confused*

 

I will end up designing or buy a suitable circuit. However I did start to use and take apart a cig light USB device like suggested. The only issue that I have suffered is current draw. A USB2 device will source 500mA at 5volts. The “cheap” cig lighter device claimed this, but produced less. Which sometimes caused charging problems with my 4G ipod, this was a surprise as the DC/DC converter in the iPod has a very wide operational voltage range. The SatNav worked fine.

 

A converter also needs to be able to supply a stable 5volts even whilst cranking the engine for a few seconds. It can be quite frustrating to wait for say the sat nav to reboot after starting the engine just as you intend to drive away. Maybe this also applies to your video recorder?

 

I could not see anything on the site that gave any power requirements for the mpeg device, other that the mains adapter?

 

Darren

 

 

 

 

 

 

 

 

 

 

anthony1956

anthony1956

Posted
  • Author
Posted

I'm curious (Norman?) why not take the 5v from the ECU? Current draw? Unregulated? Risk to the ECU?

 

or ..?

 

and anyway how does one take 5v from the ECU? A nice convenient terminal?

 

Anthony

 

Edited by - anthonym on 11 Aug 2006 16:52:29

mav

mav

Posted
Posted
I would strongly advise against trying to take the power from ECU. It seems sensible and easy to add a power outlet elsewhere...
anthony1956

anthony1956

Posted
  • Author
Posted

Here's an idea to create a nice smooth 5 volts..

 

"here’s what you need to scrounge up:

5.1v zener diode.

100ohm or slightly greater resistor. all i had was a 330ohm which works. don’t try anything lower than 100ohm.

9v battery connector and 9v battery."

 

here http://www.hackaday.com/entry/1234000520028239/

 

except he uses posh bits of plastic with holes in, we used to use copper backed bakolite and acid a in tray!

 

Anthony

 

Edited by - anthonym on 11 Aug 2006 20:52:19

 

Edited by - anthonym on 11 Aug 2006 20:52:40

anthony1956

anthony1956

Posted
  • Author
Posted

so, any regulator can be made variable by applying a resistance, if the resistance is variable, then so is the regulator.

 

A 7805 regulator outputs 5 volts, from at least 7 volts input (the dropout voltage). Dare I wonder if it will happily handle 12 volts input (maybe an inline fuse in here)? Screw it to something metal (as a heatsink), take 12v from the battery or wherever and the output 5v feeds my device. And insulate. Cost 2 quid. Space used, zilch. For up to 100 milliamps.

 

and yes I still need to know the current draw... seems to be a military secret.

 

I think I just reached Colin Mills' point of question... ho hum.

 

Anthony

 

Edited by - anthonym on 11 Aug 2006 21:20:46

dazula

dazula

Posted
Posted

A voltage regulator alone will not be enough. A car’s electrical system will have spikes and noise (At all frequencies) that will affect any system that requires a clean supply. Suitable filters and suppression must be used. At best you may simply crash the micro in the device you are powering; at worst you will destroy it. *thumbdown*

 

Taking the 5 volts power from the ECU also risks destroying the ECU and the reverse of the above can happen if you do not protect the ECU from the device you are powering.

 

There are suitable 12v – 5volt kits from companies such as www.cpc.co.uk or www.maplin.co.uk – don’t forget to fuse the circuit. *smile* Some curcuits have current limiters so even if you short the output you will not damage them or risk a fire.

 

I see that the company that produce the mpeg device have a cig lighter cable for just 14USD. Could be a good starting point. (Even if you take it apart and hard wire it)

 

Regards

 

Darren

 

 

 

Colin Mill

Colin Mill

Posted
Posted

If the load is less than 1 amp I would use the 7805 as the basis of the regulator. It is thermally protected and current limiting. A fuse is still a good idea as is a diode for reverse connection protection. The line regulation of the 7805 will take out most line noise. Its normal to have input and output caps on the chip anyway. I small inductor could be added to remove high frequency noise on the 12v line.

 

If you find that 1 amp will do the job I can easily chuck all the bits onto a small bit of vero for you as I have everything needed in my bit boxes.

 

Colin

anthony1956

anthony1956

Posted
  • Author
Posted

thanks Collin.. maybe I can come and watch! It's remotely possible I have to collect a car from Frodsham - which in my terms is near Derbyshire.

 

My thanks for explanations about the ECU - it was the bit about spikes that I was looking for and protection from the device - both ways presumably. Kind of you to worry, I won't attach anything to my ECU.

 

A fuse as a diode? I thought current can go both ways (no pun intended) through a fuse? Doubtless I am confused... *eek* I'd better read the messages again..

 

later: ah, you mean a zener diode? I seem to recall that does limit voltage. No, that's not what you mean. You mean a diode to protect against reverse polarity... I'm literally scratching my head here :-)

 

aargh! I can't read! You said "as is" not "as" - so both a fuse and a diode. Penny droppeth. 😬

 

d'y'know? I dream about having bit boxes like that.. one day.. when I'm old... *cool*

 

Anthony

 

 

p.s. mav congrats to you and your new wife! I read it in LF last month.

 

Edited by - anthonym on 12 Aug 2006 01:21:39

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