240V in a moving behicle? Really a safety issue?

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Background; A common question amongst various types of people is about
using mobile fridges/freezers and rechargers off 240V whilst driving
their car. The basis isthat most fridge/freezers run better on
240V(thermostats work) than they do on the 12V setting, plus a lot of
portable appliances still only ave mains rechargers.

Commenting on lists usually get someone squarking about danger to first
responders(emergency services people) if there is a crash.

Is this a realistic or theorectical(sp?) danger?

Would runnng it through an isolator/relay(drop out when engine stops)
reduce the risk?

Is a safety device also recommended?
Earthing the inverter to the car body help?

T.I.A.

Re: 240V in a moving behicle? Really a safety issue?
Would definitely recommend a safety system of some kind.
I use a 1500W UPS powersupply that feeds off a 24V bank
and the nice thing is that if so much as a bee farts the UPS
detects an ''error'' and shuts down.

However, common garden variety invertors have a habit
of delivering 240V at all costs. i.e. batteries going flat.

It isn't always going to be the case that a crash causing a
tear in a mains powered cable is going to trigger a fault
condition in the invertor. e.g. a single strand copper could
lightly brush an externally connected metal surface.

Admittedly, the actual power delivered to external surface
would likely be minimal however there is potential for some
danger.

In any 240V situation, install a RCD circuit breaker to any
connected equipment. An isolating relay (a fairly big one
is normally required for the actual power supply lines, but
it can be controlled using a standard 10-30A automotovie
relay) that runs from the ignition is a good idea.

Better protection would include a sensor that detects
when the motor is physically running.  Harder to implement
and I don't know of one off the shelf you can buy.

For the paranoid: install a big red button on the back of
your vehicle with a sign that says In Case of Emergency
Press to Disconnect All Power Sources.  this should trigger
a set of relays disconnecting ALL batteries.

Frankly the risks are fairly minimal, all things considered,
but there are situations where it could all go pear-shaped

The real concern I have is that when driving, not in a crash,
some fault will occur enabling full 240V to be distributed to
the shell of the vehicle.  e.g. through a faulty earth link.

This could make it hard to get in or out of the vehicle without
a shocking experience.

Driving? Mobile? Use the 12/24V setting.  Parked, go for 240V.
Long stay, normally recommends gas unless you have a brute
of a solar panel (my preferred option).

There's no one size fits all solution.

The thing to remember, for first responders, etc, is that the
invertor powersupplies, while they can deliver lethal power
they are not powered by a 500 megawatt powerstation and
usually have *some* fault detection circuitry. Anyway, a
short circuit condition will pull too much power from the
invertor and either a) shut it down or b) blow it up.

The second thing is that most cars/trailers/vans aren't wired
by a licensed electrician so the real danger is that some moron
puts a 240V cable in harms way. e.g. behind the clutch pedal(?)
which when cut shorts 240V into the dash wiring causing a
rather rapid fire/explosion.

My opinion? Minimal risk of running 240V whilst driving although
exercise caution because it is a serious amount of voltage/
current. Your setup determines it's level of safety. Risk of fire
is far greater than risk of electrocution. Carry a fire extinguisher
...the right one (please)!!  

Cheers.


On Mon, 19 Dec 2011 11:25:30 +1100, terryc

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Re: 240V in a moving behicle? Really a safety issue?
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I dont see how that is possible, the mains supply is isolated, and
even if the "neutral" was bonded to the car chassis, you can only get
a shock if you touch the active while in contact with the chassis.

Note also that in this case, any damage to the active that brought it
into contact with the chassis, would - just like in a domestic
situation - result in a short circuit that would blow a fuse, shut
down or destroy the inverter thus killing the mains supply.   Of
course, if you were to contact the active while touching the chassis,
then you would cop a full 240v shock



The only way I can see around this situation is to have an ELCB, and
bond the neutral to the chassis BEFORE the ELCB.

You would of course need to ensure that you have an isolated output
inverter with insulation between the input and output of sufficient
dielectric strength to withstand mains voltages, including any spikes
that may occur when switching inductive loads such as motors on/off.

I'm not giving this as absolute advice, Do not go out and do this
without confirming that it is legal and safe way to do it, I don't
know what regulations (if any) there are on these situations but am
putting it up for discussion by someone who knows about this.









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Re: 240V in a moving behicle? Really a safety issue?
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I should have thought if current is flowing then touching the neutral
will if you are grounded still earn you a belt

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Re: 240V in a moving behicle? Really a safety issue?

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How about an "inertia fuse"?

A pellet of copper - say 1cm dia & 1cm high wedged between sprung contacts
with enough tension to grip the pellet during acceleration/braking but not
the abrupt change of direction/speed in a collision.



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