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I know nothing about BECs, so was intrigued when Al Nucci asked what type our BEC was.
Subculture piped up with this response and I thought it was worth sharing.
A switched mode supply basically works by switching an inductor coil in
and out very quickly (usually about 400 times a second). They can be
configured to drop or increase voltage, called buck and boost respectively.
A magnetic field is induced in the inductor when it is doing this, and
it is that which makes them electrically 'dirty'.
Best quality units will have a grounded metal shield around them, steel
being best, but aluminium works and is lighter. That deals with the
inductor on the unit. Also a ferrite is usually wound around the output
lead to nix any nasty frequencies induced into the wiring by the conversion.
A simple analogy would be to imagine you're watering the lawn with a
hosepipe. The water pressure is too high, and you can't adjust with the
tap, so what could you do? Well you could add a bypass, and shunt a bit
of the water off down the drain, that's your linear BEC. Or you could
get some one to squeeze the hose on and off with their foot, that's the
switched mode. The latter mode doesn't waste any water, although energy
is expended by the person doing the squeezing- hence switched mode
supplies are never 100% efficient.
Linear converters don't create any dirty fields, but they generate a lot
of heat when the voltage differential is high and the current demands
are great.
For example. Lets say we have a model submarine operating off 12 volts,
and we want our usual 5 volt feed to the radio kit. Let's also assume
the current required is 1A, which is adequate for two or three servos if
they're not stalling, or thirsty models.
To see how much power is wasted in heat, we subtract 5 volts from 12
volts, which is 7 volts, and multiply that with the current, which gives
us 7 watts of power wasted in heat. That's 140% greater than the power
being delivered. Can you say inefficient? Plus you'll need a sizeable
heatsink to get rid of the heat if the regulator is to survive.
If the model was operating on a lower voltage, say 7.2 volts, then
things become much more benign. 7.2-5= 2.2, times that by the current
equals 2.2watts, under a third of the power wasted. Hence why linear
regulators work best in low voltage boats.
An equivalent switch mode supply will only use about half a watt.
Subculture piped up with this response and I thought it was worth sharing.
A switched mode supply basically works by switching an inductor coil in
and out very quickly (usually about 400 times a second). They can be
configured to drop or increase voltage, called buck and boost respectively.
A magnetic field is induced in the inductor when it is doing this, and
it is that which makes them electrically 'dirty'.
Best quality units will have a grounded metal shield around them, steel
being best, but aluminium works and is lighter. That deals with the
inductor on the unit. Also a ferrite is usually wound around the output
lead to nix any nasty frequencies induced into the wiring by the conversion.
A simple analogy would be to imagine you're watering the lawn with a
hosepipe. The water pressure is too high, and you can't adjust with the
tap, so what could you do? Well you could add a bypass, and shunt a bit
of the water off down the drain, that's your linear BEC. Or you could
get some one to squeeze the hose on and off with their foot, that's the
switched mode. The latter mode doesn't waste any water, although energy
is expended by the person doing the squeezing- hence switched mode
supplies are never 100% efficient.
Linear converters don't create any dirty fields, but they generate a lot
of heat when the voltage differential is high and the current demands
are great.
For example. Lets say we have a model submarine operating off 12 volts,
and we want our usual 5 volt feed to the radio kit. Let's also assume
the current required is 1A, which is adequate for two or three servos if
they're not stalling, or thirsty models.
To see how much power is wasted in heat, we subtract 5 volts from 12
volts, which is 7 volts, and multiply that with the current, which gives
us 7 watts of power wasted in heat. That's 140% greater than the power
being delivered. Can you say inefficient? Plus you'll need a sizeable
heatsink to get rid of the heat if the regulator is to survive.
If the model was operating on a lower voltage, say 7.2 volts, then
things become much more benign. 7.2-5= 2.2, times that by the current
equals 2.2watts, under a third of the power wasted. Hence why linear
regulators work best in low voltage boats.
An equivalent switch mode supply will only use about half a watt.
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