12V car cig lighter adapters - safe?

te:

There's lots of good comments here and several concerns that are based on urban myth. Just as much as there will be filtering on the inputs to car electronic boxes, there will be powerful filtering across the likes of the starter motor, etc. EMC/RFI testing looks at the response on the inputs to surges, spikes, etc, but also makes sure that supply lines and the likes do not generate and propagate interference. So testing is a two way activity - in and out.

The real cruncher is that no-one at all has made a statement about experiencing any such failures - or knowing anyone who has, or hearing of any such failure through the likes of this inter-webby thing. The conclusion surely is therefore that it just doesn't happen.

I quite happily have my satnav and mobile on charge while starting and driving - I would really doubt that anyone would want to have a laptop running while starting the car, but as they too have a dirty great 'capacitor' across the supply I wouldn't have thought problems would have occurred.

Rob

I gave the figure of 40 volts for a bog standard regulator - but of course that's the differential. So if regulating to 9 volts the peak would be 49. And of course it's simple to increase this if needed.

My opinion would be that most stuff without a particularly fragile voltage regulator would be fine running on 12V from the cigarette lighter socket. OTOH, devices which have sensor wires running all over the car (not your general in-car entertainment devices, etc.) may have problems. They have to be designed to withstand a lot of noise on any signals and potentially harmful induced voltages on inputs.

The real cruncher is that no-one at all has made a statement about experiencing any such failures - or knowing anyone who has, or hearing of any such failure through the likes of this inter-webby thing. The conclusion surely is therefore that it just doesn't happen.

I quite happily have my satnav and mobile on charge while starting and driving - I would really doubt that anyone would want to have a laptop running while starting the car, but as they too have a dirty great 'capacitor' across the supply I wouldn't have thought problems would have occurred.

Agreed. I have used all sorts of vulnerable equipment in all sorts of cars going back 30 years and never had any hint of the car causing spikes that could damage anything. I've been building all sorts of electronic stuff for years and long before regulators were available in a single 3 pin package so most of the stuff didn't have a regulator and was designed to run straight off the car. The only time you would go to the trouble of actually building a regulator was if it needed a fixed voltage for stable operator as in an oscillator for instance.

I'd find it difficult to list all the equipment I've used in the car, but it goes from valve transmitters, through to home built transistor transmitters and receivers, transistor RF power amps, boards with switching and logic and god knows what else. Never has the car enviroment been problem beyond the slightly varying supply voltage, possible RF interferrence from ignition and protection from reverse polarity of the supply leads. Never has anything gone bang when starting the car due to the starter motor back emf. I have never encountered any mention of that in all the electronic/communications/broadcasting companies I have worked for and frankly think it gets sinked back into the battery long before it could do any damage. Its just never been an issue anyone has ever mentioned as it is not a problem anyone has had.

Graham

My experience too.

I didn't. I simply don't go around disconnecting alternators with the engine running. I try and design stuff to be foolproof, idiot proof even - but not c**t proof.

Assumptions contradict well proven standards. Load dump is defined up to 270 volts on the 12 volts. All car electronics includes designs to make load dump irrelevant. But some appliances selling on the cheap may simply forget that option.

Most all semiconductor manufacturers make power supply chips so that

12 volts can supply regulated voltages to electronics. Then they make special versions for automotive use due to higher voltages such as load dump. National Semiconductor has a specific line just for automotive use. Does you adaptor manufacturer used the standard and cheap voltage regulators - or those designed for automotive use.

Standards that define load dump including SAE J1455 and ISO

7637-1. Load dump can be defined by:

Some designs call for a protection circuit that can withstand up to

270 volts and 50 joules. Why do some manufacturers sell the equivalent 12 volt power source for more money? What does the manufacturer spec say about load dump?

Very often, there's f*ck all difference between parts supplied for normal or other environments. It's just not economical to do otherwise. Look at the way the supply of "military" grade silicon virtually disappeared.

Selling into the automotive market relies on implementing, and being able to prove you've implemented very strict QA processes. Another aspect is traceability of supply. Don't even mention the liability terms that automotive manufacturers will try to apply.

MBQ

That would explain your failure to see the spikes. Try repeatedly switching off the rear window heater while measuring next time. Then try it for real: switch off all accessories and waggle the loose battery connection. Dont have your laptop connected :)

If the op wants to play chance games with their lappy they can, but at least they're more aware of the problem now.

If these events didnt occur IRL no-one would write about them, and car electronics designers wouldnt design equipment to withstand them. They do.

NT

Disconnection of the starter motor is not the problem. The inductive current source is the alternator, and this is producing more or less nothing during starting.

NT

Most of us here don't have loose battery connections.

Disconnection of the starter motor is not the problem. The inductive current source is the alternator, and this is producing more or less nothing during starting.

So as previously stated, there is no problem. You carry on with your bad self and I'll carry on without the problems I've not had.

Graham

And if we did the car wouldn't start which means 'current dump' into an accessory couldn't happen...

And last night I started my Renault Premium which had my Satnav plugged into the 24V socket and a 300W Mains Inverter plugged into the 12V socket and my lappy plugged into that. Apart from them cutting out momentarily as the ignition key changed positions, they kept working throughout. It's not the first time I've done it either. At one point, it was happening several times a night when I was doing a night trunk for a pallet company. Lappy is still working fine, inverter is still working fine. So is moby and Satnav.

And I can guarantee that any back EMF you'd get from a 24V starter motor on a 12 litre diesel engine is going to far exceed anything you'd get from a poxy car one.

Fuck all happened. Difference is I had the night heater in the truck instead of a heated window. A night heater is a bit of kit which has an electrode which heats up diesel and a fan to blow the resulting hot air into the cab. Works like central heating in the fact that you set a temperature and it comes on and off to maintain that.

A night heater draws more current than a window heater and the electrical noise from the fan far exceeds that of the window heater to the point where it can be seen as RF interference on a TV.

And my laptop still works.

So again, you're talking out of your arse.

I use my laptop in my lorry. Its exposed to far more electrical noise and far higher potential back EMF than you'd get in a car yet my lappy is working fine.

Yeah, Eberspächer. Got one in my campervan. Brilliant things. Even during -6 nights I was almost too warm. and had to turn the themostat down.

Graham

That's the jobbie. Only downside to them is getting them to fire up for=20 the first time after a summer being unused.

--=20 Conor

I only please one person per day. Today is not your day. Tomorrow isn't=20 looking good either. - Scott Adams

Can you read ok Conor? 'Dont disconnect the battery with the laptop connected' is what was said. Tell you what, since theres no problem why dont you try it and prove it to us.

NT