pedalpa.org.uk
power storage, regulation and control

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One easy solution to usuing 12v power in audio systems is to step it up to mains voltage with an inverter, and then use standard mains amplifiers. In some ways this would be greener, as it would be possible to use an unmodified existing amplifier system, if you already had one. But:

efficency - in stepping up and down, power is lost - that's wasted pedalling.

safety - low voltages (below 50v) are a lot safer to work with, particularly in oustide, potentially damp conditions. This also reflected in safety legislation - less that 50v means fewer requirements.

We do not offer mains power for performer's equipment. This isn't a problem as we can normally find a solution in advance - we can provide an amplifier for bass & guitar, and even a [midi] keyboard if necessary. We also reserve the right to allow mains powered equipment near our system, and will refuse to provide power for a mains inverter.

We use a main 'crate' that holds the mixing desk, contains the main lead-acid battery and incorporates the power distribution unit and the main audio amplifier.

our smaller battery - one input, one output and 4mm sockets. This is useful for smaller systems, but can also be used near the bass amp, which if on a long power cable, would suffer badly from volt drop; the battery acts as a large resevoir capacitor (as used in some car audio systems).

Power distribution panel

The upper panel* in the image above is the very simple distribution panel; input sockets for the bikes on the left hand side, and output sockets (switched, in groups) on the right. The central part contains an switch, cicruit breaker and ammeter, all in series with the internal battery. The ammeter does not show the current passing through the system, but the current to/from the battery, giving a very visual indication of whether the battery is being charged or drained.

* - the lower panel is the main stereo amplifier, described elsewhere.

voltage regulation

Most car audio equipment functions with a supply between about 10 and 15v. Large amplifiers can be, to some extent, self-regulating; they switch in at about 10v, increasing the cyclist's load, making it harder to raise the voltage to a possibly damaging level. Lead acid batteries also provide a regulating fucntion, turning any surplus energy into charging current. However, installing some kind of shunt regulator is very much recommended, that switches in an extra load across the supply if it reaches too high a level. Shunt regulators can also sit 'across' the supply rather than having specific inputs and outputs, making the use flexible.

It's also bearing in mind that whilst equipment designed for auto use can withstand such voltage ranges, other equipment may not. If so, it may be worth using local low-power voltage regulation to avoid any potential damage to the equipment, Bear in mind, though, that a lot of equipment may have regulators internally anyway - have a look inside if you're happy to.

In practice it has been found possible to connect generators and loads together in a kind of ring-main system - especially useful when there are bike generators both sides of the stage, and amps at the back.

It is important, when connecting powered audio equipment together, to the audio earth is connected to a consistant point voltage-wise. If powering a mixer from the internal inverter within an amplifier, it is possible that the audio earth is complete disassociated with the 12v supply rails. As soon as 12v powered equipment is connected, this changes, so it is worth defining the audio earth as being the negative side of the 12v supply. This tends to be default, but should always be checked, particularly with step-down power supplies for CD players and the like.