|By Peter Giling|
The choice of using 5V adaptors for supply of RocNet was obvious.
There is a massive assortiment of 5V adaptors to choose from, and also for good prices.
But depending on the load drawn from the 5V adapter the following problems could occur:
It prooves that all these negative aspects are referring back to the too-low voltage output from the adaptor itself.
The indicated voltage of 5V is not very seldom as low as 4,2 or 4.3 volt.
Adding that to the small but normally acceptable loss in the RJ12 cables, could lead to the effects as indicated above.
So we need a better supply.
The GCA_Pi06 has been developed to provide a real stable 5V 3A power to a RocNetNode setup.
It contains a switching power regulator with solid output of 5V.
It only needs a 8-20 Vac or 12-24 Vdc input line, minimum 16 VA, for the full load of 3 Amp.
3 Amp might be overdone, but most regulators otherwise are made for 1 Amp, which will be too close to what we at least need.
GCA_PI06 makes a home power line unnecessary under the model railroad layout.
Linear regulators are not suitable in this case.
The Raspberry alone already consumes 600-700 mA at 5V.
A standard 16V transformer will give you easy up to 22V after rectifying.
This means that a linear regulator like LM7805 has to radiate approx (22-5) V x 0,7 Amp is approx 12 Watt into heat!
Even with a massive cooling part it will be pretty hard for this very well known regulator.
This board will be at minimum efficiency with max load and then it is still 77%.
With the same 22V and normal 1-1,5A load the efficiency is approx 85% so the board will have to radiate approx 1,2 W.
In this case we do not need any additional cooling,
The pc-board has as much surface as possible dedicated for that.
The Pi01, Pi02, Pi03 and Pi04 are connected directly to this board by a RJ12/45 cable in which the I2C lines are passed to all connectors.
According to drawing below, also chaining from one PI02 or PI03 to the next is optional.
Prevent making loops.
With the introduction of Rasberry Pi 3, there is new situation.
PI 3(as we call for short) is consuming much more power.
With powering all boards via GCA_PI06 supply, there will be a problem when cable(s) between
PI 3 and GCA_PI06 are too long (> 0,5 m).
The used RJ12 cables can not handle that current.
So two possiblities are to be mentioned to overcome this minor problem.
Fortunately, the boards are designed to install either RJ12 or RJ45 connectors.
RJ45 will make wiring more solid, and also, more than one wire is used for power supply.
In kits, available from GCA, there can be a choice between RJ12 or RJ45 connectors.
Regarding to the use of this power unit together with GCA_PI03:
All 3 pins of JP1 on GCA_PI03 should be connected together.
The easiest way to do that is just bend 3 pins towards each other and solder them together.