Track Power
Voltage vs Scale
Recomandations
At no load, a typical open-frame unregulated power supply
will put out more volts than it is rated for. For
example, a 14-volt power supply will put out 15 to 16
volts. But, when it's loaded with the rated current, it
will sag to its rated voltage.
Team Digital note: See Power Supplies for
additional information.
Boosters have voltage regulation built in. That is, they
try to maintain a certain amount of voltage on the track
at all times. When power-supply voltage fluctuates due to
sag or house-voltage variations, track voltage will
remain about the same.
For regulation to work, there must be more input voltage
than the regulator is set for. That is, if you're trying
to regulate at 15 volts, you must have more than 15 volts
going into the regulator for it to maintain 15 volts. How
much more? Just more. But if the house voltage
fluctuates, more today may be less tomorrow. So you need
enough more to accommodate power-supply variations, and
house-voltage fluctuations - say, two volts more.
When you put AC voltage into a booster, the first thing
it goes through is a bridge rectifier to convert it to DC
voltage. When it goes through this rectifier, it gains
about 40% in voltage, then looses a few volts when going
through various electronic components of the booster.
Let's say we're using a 14 VAC power supply for HO scale.
This converts to about 16.6 volts when factoring in
electronic component drop - only about 1.6 volts more
than is needed for the track. But remember, an unloaded
power supply puts out more than its rating. So if we
figure that the power supply will really be putting out
about 15 VAC most of the time, we'll have about 18 volts
to regulate down to 15 volts - enough for good
regulation.
While this excess voltage has to be burned of as heat, it
is necessary for good regulation. More voltage than that
will gain you nothing, and will have to be burned off as
even more heat.
So the key is this: put in the voltage that is ideal for
the device. Any less voltage makes performance suffer.
Any more makes excess heat that has to be dissipated.
The ideal input voltage depends on which scale setting
your booster is set for, not what scale you're actually
running. The booster puts more voltage on the track when
set for HO scale than when set for N scale, so it needs
more voltage in when set for HO scale than when set for N
scale.
• For the N-scale setting, 12 VAC is about ideal
• For the HO-scale setting, 14 VAC is about ideal.
• For the O/G-scale setting, 18 VAC is about ideal.
The ideal voltage is different if using a DC power
supply. When going through the bridge rectifier in the
booster, DC voltage does not increase like AC voltage
does. However, it still loses voltage as it passes though
various electronic components. So, if using a DC power
supply:
• For the N-scale setting, 16 VDC is about ideal
• For the HO-scale setting, 19 VDC is about ideal.
• For the O/G-scale setting, 25 VDC is about ideal
Heat
With all things electronic, heat is the enemy. Now, I
can't say that if a booster runs cooler it's guaranteed
to last a certain length of time, no more than anyone can
say if you don't smoke you'll live to be 100. All
boosters are different, used differently, and will have
different life spans. But, like not smoking, we can say
that if a booster runs cooler, its life expectancy will
probably be longer than if it runs hotter.
Right here, I want to make something very clear. If your
booster, without a fan, is heating up to a point of
shutting down without continuously drawing at least 75%
of its rated power, something is wrong. Either the
booster is defective, or the power supply is putting in
too much voltage. And while you should use a fan on your
booster whether or not it is over heating, putting a fan
on an overheating booster will only mask the real problem
- the problem of making too much heat is still there. If
your power supply is putting in too much voltage, causing
this problem, get rid of that power supply, and get one
that puts out the correct voltage for the scale setting
you are using.
There are two components to heat: making heat, and
retaining heat.
Putting a fan on the heat sink will dissipate heat that
is made, and prevent heat buildup. But it won't stop the
components from making excessive heat to start with - and
making excessive heat can be almost as bad as heat
buildup.
The best tactic for the longest-possible booster life and
best performance is two steps: first use the correct
voltage for the scale you're running (to lessen the
amount of heat made), then put a fan on the heat sink to
dissipate what heat is made.