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[jaymac]

Anywhere do  high amp power switches  as most seem to be pretty low or  is it not that critical for an on/off switch?

[malcolmfrary]

Apart from the voltage, there are two current ratings for any switch.  One is what it can switch, the other is what it can carry once switched unless the thing has been arranged to instantly use full power.  A master switch will not normally need to switch anything like the eventual load that it will carry, since the additional load will arrive later. 
What it can switch off has an effect on contact life as well - at the instant of breaking, the voltage (either raw or back EMF if chopping an inductive load) usually creates an arc which eventually, over a lot of operations, creates pitting.  Anybody remember filing contact breaker points?
If in doubt, get the big 'un.  This applies to much in life.

[chas]

What is it that you are switching?

[Bob K]

I use a changeover switch on my boats.  One side goes to the charging socket positive, the other to the boats power, with the common to the battery positive.  This is so I can charge batteries in situ without having to keep unplugging connectors.
When you turn the power on the motor/s are at neutral and current switched is very low.  ESC, rudder servo etc. Real power is only taken from the batteries when you move the throttle up, but the switch is not making or breaking then.
When switching power off the motor/s are at rest so very little power is involved.  A 2A switch can usually handle a motor that can peak at 5A providing you switch with the motor at rest.  Always best to check the switching/carrying amps for the switch you intend using. 

[steamboat66]

rapid electronics have 20 amp changeover toggle switches for £2.52! order code 75-0252. you'll never burn that out.

[jaymac]

Thanks all   just seems weird that they  usually are low amps and  my boats are always around the 30/40 amps  albeit that is running      to me  if there is  that rate in the circuit then I would expect there is that rate going through the switch
Thanks steamboat too many connections for my old brain  even this one 75-0253
has 2 more than need

[malcolmfrary]

If a switch is not operated, it is just two wire ends going nowhere, zero current.  Once the switch has been operated, there is in theory zero volts across it, so no power turned into heat there.  While it is operating or releasing, and not quite fully making contact, all sorts of stuff happens, which is what the different figures show.
A quite light switch will handle a very heavy ESC because the ESC wants very little current at switch on.  A different story when switching a bunch of filament lamps.  They want all the current in the world until they warm up.  And the switch on the ESC is very small because it it only powering the ESCs control circuit.
The downside of heavier switches is providing something strong enough to not bend or break when operating the switch.  High current switches tend to need more force to operate them.

[Brian60]

I think what Malcolm is saying is that in the real world a switch is just a switch, it will do what you want. The makers rate them at say 12v 5amp because if they didn't you will always get some crazy idiot who tries to put a 1000v and 40,000amps through one, then claim its the manufacturers fault for not labelling their product and can we have mega compensation please

[JimG]

If a switch is not operated, it is just two wire ends going nowhere, zero current.  Once the switch has been operated, there is in theory zero volts across it, so no power turned into heat there.  While it is operating or releasing, and not quite fully making contact, all sorts of stuff happens, which is what the different figures show.

In real life a switch has a resistance over the contacts especially after it starts getting dirty with use. This can cause it to get warm with higher currents.

A quite light switch will handle a very heavy ESC because the ESC wants very little current at switch on.  A different story when switching a bunch of filament lamps.  They want all the current in the world until they warm up.  And the switch on the ESC is very small because it it only powering the ESCs control circuit.

With brushless escs there can be a large surge of current to charge up the capacitors on the input. This is more pronounced at higher voltages and can cause a large spark on connecting the battery. If you are switching the power to the esc then you will get an arc on the switch contact. Many high voltage battery connectors have a third contact with a resistor in series to restrict the current on connection. (It connects before the main connection which bypasses it when connected.) I have a plane using a 6S Lipo and you can see the pitting on the end of the connector from the spark.

Jim

[malcolmfrary]

I think what Malcolm is saying is that in the real world a switch is just a switch, it will do what you want. The makers rate them at say 12v 5amp because if they didn't you will always get some crazy idiot who tries to put a 1000v and 40,000amps through one, then claim its the manufacturers fault for not labelling their product and can we have mega compensation please

It will do what you want as long as what you want is within the figures.  You don't often see the lifetime operations guess quoted, but it exists.
As JimG pointed out, real life is not quite the same as theory.  Big capacitors are very good at stabilizing voltage when a sudden change in current is demanded, but by the same token, they do want that same very high current when initially charging, and they take it through the switch.  A pre-charge circuit with a switch with contacts suitably timed is one way round.
Back in the elder days, it was always good for a bit of merriment to leave a fully charged high voltage one lying around, but it did need you to find one that didn't leak its charge away too fast.