12V car cig lighter adapters - safe?

[Lobster]

My family have a fair number of electrical devices ranging from mobile phones to electronic games to fridges, all of which lend themselves to being able to be powered or charged on the road by a 12V cigarette lighter adapter.

My question is, how safe are these adapters in terms of risking possible damage to the device in question? I read about 'surges' in power from the car; if so, is it down to circuitry built in to the device in question to protect itself from that? Or should such protection be built into the actual adapter?

Is it risky to buy a 'cheapo' aftermarket adapter in place of the device manufacturer - might that be a more dangerous proposition than buying an 'original' item? If so, how can you tell what's safe, other than by spending as much cash as possible? Can an existing adapter be tested for this?

Thanks David

[George (dicegeorge)]

i think the biggest danger with 12volt devices is of fire, if a wire is too thin it can get hot and burn plastic - it happened to me with my car second battery charger- i had a fuse on one battery but not on the second- whooops

[Chris Whelan]

[...]

Unless the battery terminal to cable connection is poor, of course!

;-)

Chris

[Graham]

That is why there should always be a fuse as close to the battery as possible. Close to battery so there is only the smallest length of wire unprotected from a short should the insulation chaff and touch the body. Its surprising how often long lengths are left completely unprotected or naively fused at the far end. By all means fuse at lower amperage at the far end, but there must always be a fuse at the battery end to blow if a short to the body along the cable run. These days cars have a fusible link next to the battery terminal, but this is designed to stop wiring catching fire and a very high current rating, so not to be relied on for protection. Pick up power after the fuse box or if for some reason its needed to connect directly to the battery, say because its a very powerful piece of equipment like an inverter or ridiculously powerful car audio system, then put a fuse within an inch or two of the battery.

Graham

[Geo]

The main source of surge/spike is when the starter motor stops turning - all those amps used to create the magnetic field have to go somewhere fast... On light aircraft, the rule is all avionics OFF until the engine has started. I neglected to turn off one item once and was rewarded with a fascinating display of random numbers/symbols (luckily no permanent damage) Just checked my car - the radio and cigar lighter power is disconnected from the supply while the engine is being started. I think you would probably be ok but if in doubt, just pull the plug out until engine running - this assumes you don't have any unusual heavy electrical items connected e.g. motors, large solenoids etc.

Geo

[Rod]

But would that apply if, for example, you were trying to restart the engine in flight?

[Geo]

Yes - the only supply required from the battery is the starter motor - ignition is from two independent magnetos (2 plugs per cylinder).

Geo

[Rod]

I meant, would it be OK to turn off all avionics while struggling to get the engine running again. I imagine that would include altimeter, radio, etc.?

I know nothing about aircraft but am thinking that the systems will be broadly similar to cars - when the engine is not running, all ancillary equipment will run off battery?

[Geo]

Yes - I am talking small (say 4 seat) aircraft in good weather. The aircraft will fly with basic instruments without battery power. Altimeter, airspeed and compass. Generally only two flight instruments are battery powered (in common Cessnas/Pipers) the direction indicator gyro and the turn/slip indicator. The other (avionics)stuff is mostly for flying when you can't see anything out of the window.

That is correct - in the event of alternator failure (for example) all unecessary stuff is switched off to conserve battery power for a couple of radio calls before landing at the nearest airfield.

Geo

[Duncan Wood]

Across the switch contacts unless you've wired it oddly.

That's to maximise the available current though :-)

[Gel]

:

My past satnav had definite instruction that not to plug in, until car started. My current Tom Tom has no such request.

[robgraham]

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

[Graham]

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

[Dave Plowman (News)]

My experience too.

[w_tom]

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?

[Man at B&Q]

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

[meow2222]

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

[Graham]

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

[Dave Plowman (News)]

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

[Conor]

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.