SO-- you are interested in how a motor
Basically, a motor maul is a mobile
power supply-- that allows the radio operator to run a larger amplifier,
that would otherwise not be possible-- without adding custom-mounted
alternators, regulators, and large battery banks.
First, you must use a class C amplifier-- that has
a copper circuit board, with 'better than average' internal components.
Amplifiers with printed
circuit boards and solder traces, will not work well when volted.
The purpose of “volting” is to push the amplifier to beyond its safe and
capable levels for a short period of time. This will give the operator a
power advantage when keying against another operator, with the same size
The transistor data sheets for the
2sc2879 transistor do not measure output for anywhere near these voltage
levels-- so the data sheets (or voltage/current ratings) do not apply.
I strongly recommend competition-grade
amplifiers. Stick with trusted names in the business. Just to name a
few--- Dave Made, X Force, and Fat Boy. --- I personally recommend going
with external driver amplifiers, and connecting only the last amplifier in
line to the motor maul. Many radio operators have ran 1x4, 2x4, or even
2x8 amplifiers (with an internal driver section) with no problems on a
motor maul..... But-- I don't recommend doing this...., and after you read
this entire explanation, I think you will understandably agree-- when you
connect the motor maul to an amplifier with an internal driver, you are
ALSO volting the driver section-- meaning: you will
be driving the final section harder than the builder intended-- possibly
over driving it.. You don't need to drive an amplifier to its max when it
is volted up.
Over Driving + Over Volting =
plenty of smoke
instructions/explanation --- below....
The 400 amp motor maul will replace
multiple alternators by using FOUR
12 volt batteries. (A minimum of 800 cca
each)-- All of the batteries must be the same brand/model-- along with the
same age/and purchased at the same time. (This will ensure the batteries
have more of a chance to equally hold a charge).. The motor maul's charge
lead is connected to the vehicle's starting battery under the hood-- and
the stock alternator... This is the standard 12 volt charging system, and
this is what keeps the FOUR added batteries charged, that are installed
after the motor maul.. When the motor maul is activated (radio key up)-- a
relay inside the motor maul engages, which disconnects the 12 volt
charging system from the motor maul. (you can run a motor maul in a
computer-controlled vehicle).. Then, the motor maul has another relay-- bu
this time it closes, so the added FOUR batteries transfer from a parallel
circuit to a series circuit – and the voltage is increased to 24 volts.
This series circuit is controlled with a
variable regulator, on a wired remote control. The voltage can be
selectively adjusted anywhere from 12 to 20 volts, from the driver's seat.
Keep in mind-- the lower the voltage, the harder the motor maul will have
to work... The higher the voltage, the harder the amplifier will have to
So, you must find a happy medium that
agrees with both the motor maul AND the amplifier. I have found 17 to 18
volts works best. An external volt meter must be used. Some prefer digital
volt meters, I personally prefer analog volt meters. The one I use was
built for precision measurement. Very similar to a Bird
watt meter, but it measures volts. (automotive-type voltmeters are
not recommended, they are not as accurate as the other types)
Speaking of meters-- I highly recommend
monitoring your amplifiers wattage output, using a dual-line section, dual
display meters, and watt slugs-- parts from the Thruline watt meter, made
by Bird Electronics. This wattmeter IS the industry
standard, from which all other meters are measured. You can connect
extension cables to the dual-line section, and mount the display meters up
front-- near the driver's seat. The meters will just be a glance away.
Monitoring forward and reflected watts could prevent a costly mistake, if
anything goes wrong.
The motor maul is connected through the
coaxial cable, between the radio and the first amplifier in line. How this
works, is that the motor maul samples transmitted RF energy from the
radio, when keyed up. This sample tells the motor maul to switch from
“charge mode” to “key mode” ... You want this “switching” to happen as
quickly as possible-- so you want the motor maul next in line after the
radio, so that the motor maul is switched to “key mode” before the RF
signal reaches the amplifier that is connected to the motor maul. There is
a way to connect an external switch, so you can switch modes manually--
but I personally have not tried this.
Charge Mode: the FOUR batteries after the motor maul,
are charged from the alternator, through the battery under the hood--
using a cable connected from the positive lead from the battery under the
hood, to the positive charge lead on the motor maul.
Key Mode: the FOUR
batteries after the motor maul, are being pulled from-- by the last
amplifier in line, on a 24 volt system (relay switched series circuit)--
stepped down to a selectable voltage between 12-20 volts, using a
variable voltage regulator,
with a wired remote.
Installation notes: Use a
minimum of 4ga cable-- for charge lead, and cables to connect the 4 added
batteries to the motor maul. I personally use 2/0ga welding cable (all
power/ground), and a 250 amp alternator.. I also use TWO 8D
lead-acid batteries.. (TWO 8D's equal SIX group 31 semi-truck
batteries).. Lead-Acid batteries recover faster than AGM (absorbent glass
mat) or “sealed/maintenance-free” batteries. But,
emit fumes-- they are not recommended for install in closed quarters. Give
plenty of room for ventilation, when using Lead-Acid batteries.
IMPORTANT: use exact
length cables from each battery to the posts on the motor maul. If not,
the current will be looking for the shortest and easiest path, and the
signal (while in “key mode”) will be unbalanced. Also make sure the cables
are well-insulated, and will not short out on the outer metal case of the
DO NOT independently
ground the batteries after the motor maul. Or the amplifier that is
connected to the motor maul. Ground them to the correct labeled posts
---or the adjoining cables--- on the motor maul. (observe polarity). You
must ground the negative charge post on the motor maul directly to the
frame (this is the combined ground for the batteries and amplifier
connected after the motor maul -- so a sufficient ground is very
Antenna System -
Do Not run an antenna that has an SWR
reading any higher than a 1.2 for best results .. A drill-through antenna
mount is highly recommended (chassis ground). Use RG-213/U coax as a
minimum, out of the back of the last amplifier in line (400 amp motor
maul). Use an Antenna that is rated for at least twice the peak wattage
output of your last amplifier in line. Open-Coil antennas are recommended.
From my personal experiences- I have found that antennas with bolted-on
coils, or two or more metal types on the same antenna-- do not work well.
thanks "Manic" for authoring and submitting this article!