12V car cig lighter adapters - safe?

Really all that you can deduce from that is that nothing bad happens in your environment. It doesn't give the data to say that it can never happen in other cases.

In my early engineering career, I designed electronics, control and communication systems that were often fitted into military vehicles of various types.

In general it was necessary to incorporate various filtering and protection into the DC supplies to the electronics, because of electrical spikes and noise from the vehicle systems. Primarily, this was to avoid damage to certain sensitive semiconductors in the equipment and did so successfully.

The far harder problem was dealing with the sensitivity of the radio receivers, that were working in the 2-30MHz range from being swamped by the general electrical noise.

For example, on a tank, when the turret was rotated, one could find sharp rising spikes of 600-800v on some of the wiring.

I suspect that in a typical domestic car and possibly even a commercial truck, the potential for problems is not as great and certainly electronics has been improved from the EMC perspective over the last decade. Nonetheless, the mechanisms for bad things to happen are certainly present in a motor vehicle.

Because if the elctronics inside the car failed at that point then a loose battery lead would write the car off. Which would be highly embarassing to have to explain on watchdog & have enormous liability issues for anything safety critical. & it's most likely to occur during initial startup & subsequent servicing, your laptop/pda etc. are orders of magnitude more likely to be stolen because they didn't fit laminated glass to the windows.

"Dave Plowman (News)" gurgled happily, sounding much like they were saying:

Umm, cobblers. Many's the time I've come to remove a battery terminal only to find it's loose - and the thing's been running fine.

Ever heard of passengers? My lot are fiddling with countless gadgets while on the move. Some connected to car. The wife has been known to bid on ebay while we are travelling.

Graham

Maybe for a new laptop, just in case the old one fries due to loose battery terminals :-) Oh, wait a minute, can't happen, the car would never start, not with a loose battery terminal - the electrons would go on strike..... what a load of twaddle people spout.

Julian.

People have too much time on their hands. It's simply not a problem in practice.

That's a different matter from the topic under discussion.

So you don't use that wiring as pickup points for accessories.

What you're implying is that laptop makers who supply leads for car use are unaware of this?

Well if if it's capable of handling starter current it's not going to cause problems with the much lower currents from an alternator...

Of course. I'm simply making the point that conducted spikes in a vehicle do have the potential to cause damage.

In a tank you don't get a lot of choice.

I would say that that depends on the laptop maker and the accessory. If the accessory comes from the manufacturer of the laptop as an adaptor specifically for the purpose, then I would expect them to have done diligent engineering and if it breaks they get to own the problem. If I were to buy a cheap Chinese generic accessory, I would have little confidence in the engineering and not expect redress. Ergo, I would not buy cheap Chinese car accessory lead.

The car is rarely moving when the starter is being used.

So you're saying you have a battery connector which rattles loose when the car is moving but magically tightens itself so the car can start?

Do you write for CSI?

No, I am not.

I currently am as I'm posting from that very laptop.

It returns 31500 for "Andy Wade is a Wanker".

A Challenger or Chieftan Tank is not a car.

Conor wrote in

Oh yes, smartypants, it's alright you saying that now.

Next time you're using your laptop in a Chieftain tank, I know what will happen. You'll forget to ask them not to rotate the turret...

...and then we'll see who's so clever.

I know.

I am simply pointing out that the possibility exists for poor performance and failure of electronics if the engineering isn't done properly.

A single anecdote of "works for me" does not mean that it's impossible for issues to happen.

How about its been working fine for me over 35 years, using all sorts of delicate equipment in all sorts of crap cars and vans. That seems a fairly good test to me. These spikes are undoubtedly present, but are they of sufficient power to cause electronics to blink? My experience and many others says no.

Graham

It says that in your experience no. It doesn't say that therefore there can never be an issue. Correct design involves proper measurement and having a margin rather than hoping for the best.