On Sun, 17 Mar 2019 15:00:41 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Clive Arthur wrote:
On 17/03/2019 14:18, Dave Plowman (News) wrote:
Old car needed the battery charged.

Plugged that in via an extension lead from an outside socket - which has
an historical RCD just inside the house - from before when I fitted a
modern split load CU with RCD.

Charger was working and showing a charge, so left it to get on.

About an hour later, the house RDC tripped.

Unplugging the charger got things back to normal.

5 amp fuse in the charger plug had blown. Charger is an all plastic
type with a two core mains lead.

What sort of fault inside the charger could have caused the RCD to
trip?

Leakage from live or neutral to earth via the battery charging side
through the car body to ground? If it's an old charger, then
transformer breakdown could be the issue.

It's an SMPS type - no large transformer.

Of course the negative side of the DC output goes to the car bodywork.
Could enough current flow through the tyres?

If you unplugged only the charger to get things back to normal, it,s
the only explanation.

An SMPS invariably uses a fully wound transformer though, they are
pretty cheap when running at kHz.

If the charger was blowing the RCD with the plug fuse blown, it limits
the possibilities a bit.

A damp plug/ extension, miswiring and damp or an event elsewhere and
sheer coincidence that the fuse blew at some point during the charge.

Repeat the scenario and observe.

Of course if the car is very old it might only be suitable for
charging via ELCB's :-)

AB