Please
'Boom' Responsibly As
most of you have noticed, the noise ordinances have
become much tougher lately. Most of this is due to
idiots, yes IDIOTS, who drive through residential areas
with their windows down while their system is playing at
full power. To make things worse, the music they listen
to has all sorts of foul language that's not suitable for
small children, (who may be playing outside). There are
even a few people, who are even beyond idiot status, that
play their systems at full power through residential
areas after 10:00 PM (when many people go to bed). I
don't believe that this type of behavior is good for the
industry. If the fines get too stiff, people will stop
buying large systems. If this happens, more people will
get out of car audio (who wants a mediocre system).
People get interested in things because they're exciting.
A deck and four 6.5" speakers are not going to
interest many of the younger car audio enthusiasts. If
car audio enthusiasts keep annoying more and more people,
the fines will keep getting tougher. All of this will
only reduce interest in the equipment that fuels the
industry. If you want to listen to your system at full
volume, get out on the highway where there's little
chance of bothering anyone. When you get to a red light,
turn it down. If the only thing attractive about you is
your 'system', you have some work to do. Bottom line...
Think about what you're doing. Think about other people.
It's not the end of the world if you have to turn the
volume down for a little while.
Forced Air Cooling
Using fan cooling to force air
through the fins of an amplifier's heat sink,
will significantly increase the reliability of an
amplifier. It is especially important when the
air flow to an amplifier is restricted (like when
it is under a seat). If you only install one fan
on the amplifier, make sure it forces air through
the fins of the heat sink. As I said in another
section, the semiconductors are mounted to the heat sink. Some people cut a hole in the
bottom of their amps to blow air onto the circuit
board. If that's the only fan, it will do very
little good. If you have a fan blowing on the
fins of the heat sink and want to mount another
fan blowing inside the amp. it will serve to keep
the transformer and large filter caps cool (not
necessary unless you're driving your amp hard for
long periods of time). If the amplifier has a
built in fan, make sure that the added fan does
not interfere with the built in fan. For example,
do not try to force air into the exhaust of the
fan cooled amplifier. Also, if an amplifier has a
built in fan, do not make any new openings in the
amplifier's case. Chances are very good that you
will adversely affect the cooling of the
amplifier.
Current Flow and Safety:
The following diagram shows the
relay controlled by a switched 12 volt
source. It shows a fan and a neon tube (it could
be virtually any 12 volt device) being supplied
power from terminal 30 of the relay. The power
source is the battery/charging system. To have a safe system, we have a fuse at the battery. With a Bosch relay,
you can use any fuse up to a 30 amp fuse (the
relay is rated for 30 amps). The required size of
wire segments A, B and C is determined by
the size of the fuse (and the current demand from
the electrical accessories). If the total
required current draw will be only about 10 amps,
you could use a 16g wire and fuse 'A' would need
to be a 10 amp fuse. If the total current draw
was going to be 25-30 amps, you'd need at least a
12g wire and a 30 amp fuse. The rating of fuse
'B' is determined by the current draw of the fan and the wire connecting the fuse to the
fan. If the fan draws no more than 5 amps (very
likely), you could use a 5 amp fuse and a 16g
wire (16g is the minimum size I'd recommend using
because when you use anything smaller, it's
difficult to get good, reliable connections). The
size of fuse 'C' and wire 'E' are determined by
the current draw of the neon. Fuses 'B' and 'C'
should be as close to the relay as possible.
The main points to remember
are...
The wire supplying
power to the relay must be protected by a
fuse and the fuse must be rated to open
before the wire overheats and converts
your vehicle into a raging inferno.
If there's a single
wire carrying the current away from the
relay to a fused distribution point (like
wire 'C'), it must be the same
size (or larger) as the main
supply wire.
The fuses going to the
individual electrical accessories must be
rated to protect the wires
supplying the current to the device(s).
If the wire feeding the
individual accessories is the same as the
main supply wire, the main fuse (near the
power source) will protect all of the
wires.
If you want your cooling fans
to operate only when your amplifiers are on, it
will be necessary for them to be powered only
when the remote output lead has 12 volts on it
(when your head unit is powered up). I would NOT
recommend powering them directly from the remote
power lead. It would probably be damaged by the
current draw of the fans. The diagram below is a
connection diagram that may be used to supply
power to the fan(s). If you have multiple
amplifiers and signal processors, the output from
terminal 30 can also be used to supply power to
the remote terminals of those devices.
Controlling a fan with a
thermistor
If you only want the fans to
come on above a specific temperature, you can use
a thermistor. Since you won't be designing a
circuit for mass production, you want something
that is fairly flexible and can produce the
desired results without a lot of testing. The
diagram below is a circuit which uses an op amp
as a comparator with an output which goes high
when pin 5 goes higher than pin 6. I decided to
use a thermistor with an op-amp to prevent the
self heating that you get when you try to drive a
relay coil with the thermistor. Both methods work
but unless you know which thermistor you need for
a particular relay, you'll have to use trial and
error to find the right part.
In the following demo, you can
change the temperature and voltage on the
potentiometer. To change the voltage on the
potentiometer, click above or below the arrow (on
the right side of the potentiometer). This
controls the reference voltage on the negative
input of the op amp. Setting it lower makes the
fan come on at cooler temperatures. To change the
relative temperature, click on the thermometer.
The value above the thermometer is an
approximation of the thermistor's resistance.
When the conditions are right, the relay will
engage and the fan will run. Click HERE
to make the demo fill this window.
When initially setting up this
circuit you need to adjust the voltage at pin 6
to 1/2 of the voltage on pin 8. This will cause
the fan to switch on at approximately 150F. You
can set it lower if you want the fan to come on
earlier.
If you want to use an FET to
control the fan, the diagram below shows you how
to connect the FET to the op amp. Keep in mind
that you must insulate the tab of the FET. If the
tab of the FET touches to ground, the fan will
run. As an alternate FET, you can use an IRFIZ44.
It's a fully insulated part and won't require an
insulator. If the fan draws more than ~1/2 amp,
the FET might benefit from a small heat sink.
If you need more info on the
circuits above, E-mail me and I'll try to help.
Possible supplier: Mouser electronics http://www.mouser.com
Parts list:
Thermistor: 334-4227-503
Potentiometer: 531-PT10V-100k (not critical)
Op amp: 511-LM358N (critical)
FET: 570-IRF540 or IRFIZ44 or IRFZ44
Bipolar transistor: 625-MPSA06 (or equal)
Resistors: None are critical and can
likely be purchased at Radio Shack.
You should remember:
1.A cooler amplifier will last longer and will be less likely to
fail.
If you find a problem
with this page or feel that some part of it needs
clarification, E-mail
me.
