Oakley Sound Rack Power Supply Unit (RPSU), RPSU User Manual

Oakley Sound Systems

Rack Power Supply Unit
(RPSU)

PCB Issue 1

User Manual

V1.0.1

Tony Allgood
Oakley Sound Systems
CARLISLE
United Kingdom

1

Introduction

This is the User Manual for issue 1 of the RPSU circuit board from Oakley Sound. The
Oakley RPSU is a power supply unit designed to be used in conjunction with the Oakley rack
projects like the HVM and SE330. However, it may also be used with a Dizzy module as part
of a larger DIY project.

As well as giving details as to what the PSU board does, this document contains instructions
on how to wire up your board to your source of power, any external switches and the optional
power indicator. I will also give you some information about suitable sources for your low
voltage AC power supply.

The Oakley PSU allows for various options in the installation. You can use the unit either in
full wave rectification mode for connection to tapped linelumps or twin transformer
secondaries, or in half wave rectification for single phase AC output wallwarts and linelumps.
If all this sounds very confusing at the moment, do not worry, in this manual I will try to make
it clearer so that you make the right decision about what power source you will need.

If you are building the RPSU as a complete DIY project please also download the latest
Builder's Guide. This can be found on the main RPSU webpage along with our very useful
generic parts and construction guides.

2

Safety Warning

This supply has been designed to work with isolated low voltage AC inputs only. Connection
to any alternating current supply is done at your own risk. Low voltage is classified as being
less than 25V with respect to the ground potential. Voltages above this level can, and often
are, lethal to living creatures.

Oakley Sound Systems will not advise on building or modifying this board to allow for direct
connection to the mains, or other high voltage sources, further to what is provided in this
document. Please do not ask us for additional information pertaining to direct mains
connections or using internally mounted transformers as we will not give it.

For safety and legal reasons we cannot recommend powering this board from any other
supply than low voltage AC output mains adapters.

Oakley Sound Systems are not liable for any damages caused by the misuse of this product. It
is your responsibility to use this product safely. If you have any doubt about installing a safe
power supply, then please do not attempt to do so.

3

The Oakley RPSU module

This power supply board will allow the conversion of a suitable low voltage alternating
current (AC) to be rectified, smoothed and regulated. The module is designed to be fitted to a
suitably large metal panel which functions as a heatsink for the two regulator devices attached
to the RPSU circuit board. The metal panel should have adequate airflow around it and it is
expected that it will be part of the metal enclosure your rack project is built into.

It is possible, if the RPSU is only powering a small amount of electronics, that the unit can be
used with either no heatsinks or just small clip-on types. However, it is up to the builder to
determine whether or not this is possible. If in operation the two power devices get too warm
to touch for more than ten seconds you will need additional heatsinking. If the RPSU is
powering just one HVM it will need heatsinking.

The voltage output of the power supply module is a split rail 15V supply. This means it
generates both +15V and -15V. That is, two power rails, one of a positive voltage, the other a
negative one. These voltages are measured with respect to a common ground which is
normally connected, via your house's wiring, to the earth that you stand on. The voltage
across both rails is 30V, with the common ground sitting exactly in the middle of this at 0V.

The output current capability is the maximum current you can draw out of the power supply.
The current taken from the supply is determined by the amount and type of modules you are
connecting to the power supply. One HVM will draw around 80mA from the +15V supply
and 80mA from the -15V supply.

The Oakley RPSU features current limiting but only what is built into the two power devices.
Although this will probably stop your project from bursting into flames it is not to be relied on
if the fault continues for a long period of time. The RPSU is fitted with fuses and the correct
choice of fuse will probably save your project in the event of a major breakdown.

If you are using a single phase 500mA (or 0.5A) AC wallwart* then the most current you can
take from this power supply module is around 125mA from each rail. This is enough to drive
one HVM. You may think that a 500mA power pack should be able to drive up to 250mA for
each rail. But simple arithmetic does not work when you are dealing with conversion from AC
to DC. The various parts of the power supply require power to work and this reduces the
useful power we can actually draw from the supply. The rule of thumb is that the AC current
drawn is roughly 1.8 times that of the DC current drawn. This means we can take 278mA
from both supplies, that is 139mA for each rail. To allow for some safety margin we drop this
down to 125mA per rail which allows for a 10% overhead. This is plenty enough for one
HVM but not much else.

Various companies make wallwarts* and linelumps** with a greater capacity than 500mA. If
you can get a 1A output one than this will be able to drive up to 250mA per rail. With any
single phase supply you will be using your RPSU in half wave rectification mode. Single phase
mains adapters are the most common and have only two wires coming from them. They are
normally connected to the rack with a barrel type plug.

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