More on overheating PowerRoll device, etc.

Greetings,  The problem with overheating PowerRoll systems is not
just due to the fact that the magnets are crammed in a small space.
The problem is that the all of the magnets are operated at a single
voltage for the entire time they are active.  With pianos that operate
at lower pressure, it is possible to reduce the voltage to a low enough
level that overheating does not occur.  Also with systems that use lock
and cancel for the expression coding, this is less of a problem.

The big problem for the PowerRoll is the Duo-Art which has steady
on/off expression coding and has very high operating vacuum at the
theme primaries.  The theme primaries are at pump pressure and the
whole system has to have enough voltage to overcome this pressure.
When expression or pedal valves operate for an extended period at this
high voltage, overheating occurs.

I modified the one PowerRoll that I did receive by adding additional
voltage regulators.  Only the theme valves operated at high voltage
and since they are on for only a brief period, they did not overheat.
The note valves were connected to a lower voltage regulator which
allowed enough voltage to operate against stack pressure.  The
expression and pedal valves operated off another regulator that was
even lower since they are on pedal regulator vacuum and need the least
voltage.  I never had a problem with overheating with this modification
and sold the device to someone who had also been using it without
trouble.

The Chase/Gerety system uses a "pick and hold" system whereby the
valves are operated initially at high voltage and then held open at
a lower voltage which is not high enough to cause overheating.  They
do not overheat even if valves are held on indefinitely.  Very little
cooling air is needed and they will operate in enclosed spaces.

Best regards,
Spencer Chase
Laytonville, Calif.
http://www.spencerserolls.com/