I was charging a car battery in situ using my bog-standard B&Q
extension reel on Saturday and its thermal cutout tripped.  The
charger was giving about 4 amps, which makes it about 50W.  I had
always presumed that the thermal cutout would trip because of high
current passing through it, but am I missing the point?  It was quite
warm and it may have got a bit warmer than you would expect in the
car, but I was a bit surprised.  It reset OK and worked later on with
a drill.  I just wondered whether some of the experts in these things
would know whether it's something trivial (too warm in the car, faulty
trip etc) or whether I'm just misunderstanding how these things work.

On 15/07/2008 10:33, GMM wrote:

> I was charging a car battery in situ using my bog-standard B&Q
> extension reel on Saturday and its thermal cutout tripped.

Had you un-coiled the extension reel?

"Andy Burns"  wrote in message 
news:BZadnSilyeIB7-HVnZ2dnUVZ8vKdnZ2d@posted.plusnet...
> On 15/07/2008 10:33, GMM wrote:
>
>> I was charging a car battery in situ using my bog-standard B&Q
>> extension reel on Saturday and its thermal cutout tripped.
>
> Had you un-coiled the extension reel?

It shouldn't make any difference - they are rated coiled and uncoiled but I 
don't recall seeing a coiled rating that wouldn't drive a battery charger! 
Call it 100W load, that's ~400mA.

It sounds like it was in the car and got hot in the sun.


-- 
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

On Tue, 15 Jul 2008 02:33:11 -0700 (PDT), GMM 
wrote:

>I was charging a car battery in situ using my bog-standard B&Q
>extension reel on Saturday and its thermal cutout tripped.  The
>charger was giving about 4 amps, which makes it about 50W.  I had
>always presumed that the thermal cutout would trip because of high
>current passing through it, but am I missing the point?  It was quite
>warm and it may have got a bit warmer than you would expect in the
>car, but I was a bit surprised.  It reset OK and worked later on with
>a drill.  I just wondered whether some of the experts in these things
>would know whether it's something trivial (too warm in the car, faulty
>trip etc) or whether I'm just misunderstanding how these things work.

Mine was doing it yesterday. It just gets hot with use and shuts
itself down to cool.

Yes, it was uncoiled, although I wouldn't imagine that would make a
great deal of difference at those current.  If mine's not the only
one, perhaps it's not the end of the world....it doesn't seem
permanent.  I was just wondering why it should happen!

Thanks chaps