Blowing fuses?

Andybtsn · 17 Oct 2012 at 09:37

Hi all,

I had a charger for my phone plugged into my cigarette lighter which continuously blew the 10a fuse after working for over a year, I presumed the charger was broke and borrowed one to test in my car, this one worked fine. I then bought a new charger and the amp is continuously being blow again..

Is there a specific thing I should look for or should I just refer to an auto electrician. I don't understand why one charger would work but the other two don't.

I presume sticking a higher amp fuse won't rectify this?

Cheers

Scania · 17 Oct 2012 at 09:45

Do NOT put a higher capacity fuse in, this is an easy but very imo foolish thing to do.

The fuse is doing its job by blowing, it's common in the trucking community to fit a higher capacity fuse to the cigarette lighter circuit for powering 24v kettles etc, trouble is, the wiring overheats and the truck goes up in flames!

Get it to an auto electrician, something is wrong.

MatteH Oxford · 17 Oct 2012 at 13:52

What car is it, what are you trying to power?

You've either got some crap in the socket, a minor wiring short, connections crusted up somewhere in the circuit or the feed/earth wires are just too skinny for what you're trying to power from the socket. It depends on the vehicle, the majority are o.k. but some are a bit inadequately wired for anything much more than a mobile, gps or cig lighter from experience.

Scania · 17 Oct 2012 at 15:12

You underline my point mate, he may well have a short somewhere, a phone is not going to draw much power, certainly less than the cigarette lighter itself I'd think - OP, does the cigarette lighter work? Or does it still blow fuse when you use it?
Either way, I stand by my advice to consult an auto electrician.

MatteH Oxford · 17 Oct 2012 at 18:06

It would have to be a very minor short, it doesn't take much of a drop in the resistance to up the current draw & fry a whole wire clean through. Hopefully O.P. might be lucky and find that the fuse in the circuit is lower rated than what it should be, i.e. due to a previous owner replacing the fuse incorrectly perhaps.

I am a qualified technician myself, it's very hard to give specific advice to people without knowing basic & critical info such as the make/model/year of manufacture. In this case, without knowing the gauge of wire, it's hard to even say the max current that the 12v socket wiring can supply either (wiring should be slightly higher than the fuse rating obviously, so the fuse always melts first).

MatteH Oxford · 17 Oct 2012 at 19:02

forget what I wrote earlier, build one of these for a few £ and you can test for dead shorts on any circuit really easily

http://www.crookedriverwriter.com/index.php?/Automotive-Topics/the-old-headlight-trick.html

Note that you can only dead short the live feed, if the earth shorts then most of the time you won't notice (unless it affected a separate circuit's wiring, the earth shorting on a live feed for example).

Tom_ed1987 · 17 Oct 2012 at 19:35

Does it repeatedly blow no matter what you have plugged in? Or just with this specific brand of charger.

MatteH Oxford · 18 Oct 2012 at 13:10

You can check this with a multimeter (the cheap bulb tester is much simpler to use though), you'd need to know which side of the fuse is the pin that supplies the 12v feed to the socket.

What you do is test for continuity between this pin & earth with the ignition switched off, there should be an open circuit. If not there's your short.

You haven't had anything spliced into the cig lighter feed, like some lovely interior LED strobes?