On 08/02/2019 12:31, Paddy Dzell wrote:
Dave Plowman (News) formulated the question :
In article ,
** Paddy Dzell wrote:
Google for 'starter motor current'.* If a car wont start, I either
put it on* charge or just go an buy a new battery using a different
vehicle.

A normal starter motor draws upwards of 300A when cranking the engine
but there's no starter motor in a hybrid and all the 12V battery does
is power the entry/exit system and boots the computers to get the
hybrid system to the READY state, a draw of less than 20A.

How does the IC engine start without a starter motor? it may well be a
combined generator and starter, though.

The traction battery is located under the back seat and is around 288V.
There's an invertor/convertor that changes that to 650V to feed the two
motors (well, motor/generators) underneath and it's MG1 that acts as a
starter motor for the internal combustion engine.

There is also no alternator and both the power steering and the aircon
compressor are electric, driven from the traction battery. Because the
internal combustion engine (ICE) doesn't run all the time, you can't
have anything that in a 'normal' car would be belt-driven from the
engine. There's no reverse gear either - reverse is achieved by turning
the electric motor in the opposite direction to normal.

Because the 12V battery doesn't have to provide a big cranking current
they tend to be smaller and less capacity than usual and if the car is
stood, say, in an airport car park while you're away on holiday for a
couple of weeks, it's not common but not exactly unusual either, for the
battery to be flat and the car won't start, hence why I fitted this
convenient jumping point.

If there was ever an accident or something caused a short-circuit on
these two new wires that I've run to the new socket, the potential
short-circuit current could run into the hundreds of Amps, and those two
wires won't handle that current for long before they melt and perhaps
start a fire, which is why I need an overcurrent device in there. But I
also need said device to allow current to pass the other way too, when
or if I ever need to jump start the car, which is why I'm asking if a
circuit breaker will be alright or should I just use a fuse?

Thank you for the explanaion. I suppose an overcurrent device might not
trip if it was damaged in an accident. So maybe a fuse and spares.

--
Michael Chare