Car power supply

[krypton_john]

This has been hotly debated in the past - in particular the risk of spikes etc blowing up your circuit.

My question is this: what about the cheap cigarette lighter power units that abound for powering everything from cellphones to gameboys? I've never had an electronic device connected to one of these things blow up. Are the adapters spike proof? Given the phones etc were not designed to be car powered I don't see they have protection form 1000v spikes.

So are the adapters suitably protected or is the risk from car power overstated in modern cars?

<ducks for cover>

 

[mikie_121]

Those adaptor power supplies are well protected and consist of switchmode power circuits. In my opinion they are a good design and I too have never had a device blow up while connected to it. They are tricky to design so people (like us) tend to stick to the 7805 regulator which isn't well protected against the small spikes present in car power circuits.

 

[MFB]

There are many alternatives to the old 7805 regulator that are especially designed for automotive operations. They are available in low-drop versions and protect against reverse and over voltage spikes. A good place to start is looking for such devices is the National Semiconductor web site.

 

[hippy]

The advantage of such plug-in adapters should be that they've been designed for the job, by competent engineers who know what they are doing, and, most importantly of all, rigorously tested to verify that they work, are resistant to automotive electrical events and usually certified to some documented standard -- Assuming they aren't some cheap knock-off simply pretending to be that.

However, you will undoubtedly find that there is some 'all bets are off' clause when not used with the recommended product. You will usually have to second guess what the PSU is actually capable of. It may claim and actually deliver a certain output, but under what circumstances and for how long ? Something designed for use with some equipment will be designed to match its operating characteristics so a PSU permanently connected or used other than the manufacturer designed for may have problems.

While such a PSU may be better designed when it comes to input protection than the usual 7805 or many homebuilt circuits it isn't necessarily up to the job required of it.

 

[demonicpicaxeguy]

just out of morbid curiosity what exactly is the application here.? picaxe mpg guage?,keyless remote starting

depending on the application it might be better simpler and easier to use a battery instead,

somthing i've found that can be a good automotive powersupply is those mobile phone chargers, i've used several in the past and havn't had any problems, some of them filterout the noise very very well and there are other that don't also some of them can deliver some decent current

another option is to obtain a workshop manual for your car and see if the ecu has a 12V or 5V output on it that is usable,

what is the make and model of the car?

 

[Michael 2727]

My question is this: what about the cheap cigarette lighter power units that abound for powering everything from cellphones to gameboys?

"cheap" being the operative word, you get what pay for.
Many cheapie units are just a 78XX Reg in a plastic cigarette lighter adapter.

Once I was driving at night and the regulator on my car developed an (earth lift) failure, this
allowed the full regulator voltage (whatever that was 30V, 40V, 50V ?) into the system.
The Hi Beam headlights were on at the time and they lit up the road like a scene from
a Si Fi movie. I actually saw the shadow of the lamp filaments as they vaporized on the
road in front of me, then nothing but black. On a narrow, winding, hilly road @ nowhere.
Luckily the normal headlights switched out when the Hi Beam engaged so I gto home.
The fault cleared itself after the event (a known fault in the early Magna ).

Unless you design/build it yourself you may never know until a fault occurs.

EDIT: Some notes from Dallas/Maxim -
http://www.maxim-ic.com/appnotes.cfm/an_pk/4240

 

[Dippy]

Thats a very good point Michael. But it requires the use of the eyes and brain to make something good.
I never use the cheapest stuff, but I have got a couple of S/M ciagr lighter plug-ins for 12V to 19V for notebook. Bought from Maplin. Work fine.