GMC Electrical FAQ Part III
Q: I want to install an inverter. How do I decide on the wattage?
A: Determine what AC appliances you want to operate simultaneously. Add
their wattage together and buy an inverter with 20% more capacity. For
example, suppose that you want to operate a desk top computer with standard
monitor, a color TV and home stereo at the same time. Assuming a few
numbers for our example: 120W + 120W (computer + Monitor maximum values) +
220W + 80W = 520 watts. So, select an inverter of at least 625 watts. For
most types of invert the 20% additional capacity accounts for many
manufacturer's practice of over-reporting the real capacity of their inverter.
Q: What kind of wire do I use to connect my inverter to the batteries?
A: I recommend marine grade fully tinned wire of the appropriate gauge. The
wire is more flexible than the automotive variety and resists corrosion
better. The improved flexibility will aid during installation. The tinned
wire reduces resistance caused by corrosion. High resistance connections
for high amperage devices like inverters can cause fires. I recommend using
one gauge larger than the chart to minimize voltage drop. Voltage drop
wastes power and causes the inverter to operate outside its ideal design
parameters.
Q: Can I power my Air Conditioner with an inverter?
A: Not economically. Compressor surge power is quite high and requires an
inverter in the 2kW range. The problem is that the battery drain would
require large banks to run the AC for any appreciable amount of time. A
typical 2 golf cart battery bank would be discharged to 50% of full
capacity in just half an hour. If you need to run the roof AC, start your
genset and charge your battery banks at the same time.
Q: How do I wire my coach for an inverter?
A: Decide where you will use inverter supplied power. You can then either
wire separate outlets for the inverter or separate out a branch circuit
from the existing wiring.
Q: Which branch circuit is best to use for inverter wiring?
A: It depends on what you want to use the AC power for. One convenient
circuit is the branch that powers the kitchen wall and dinette (curb side)
wall in the Palm Beach models. To use this circuit for your inverter, you
will need to separate the branch wiring from the existing bundle and
install a sub panel for the inverter circuit. This type of installation
requires a way to switch between the inverter output (11V AC) and the house
mains 110V AC. Inverters with a built-in transfer switch simplify this type
of installation. Otherwise you can install a separate transfer switch.
Q: How do I wire an inverter into a branch circuit?
A: Wiring is best done by a professional. If you are skilled, the following
is a general guide. First trace the outlets that you want to use as a
branch circuit. This can be done by disconnecting the coach from ALL 110V
sources including gensets and inverters. Open the distribution panel and
disconnect all wire bundles except the bare copper grounds. Insert a wire
jumper in the outlet that you want to use as a branch. NOTE: MAKE CERTAIN
THAT THERE IS NO 110V PRESENT IN THE COACH WHEN PERFORMING THIS OPERATION!
Use an Ohm meter to identify the circuit that you have jumpered by testing
wire pairs for continuity at the main distribution box. Label the wires.
Move the jumper to the next outlet and repeat the process. When you have
identified all outlets and wiring that you are interested in using on the
inverter, double check to make certain that no other outlets are wired to
your selected circuits. You can do this by moving jumpers to other outlets
while monitoring the selected branch circuit wire for continuity. Remove
the selected branch circuits and their associated grounds from the main
distribution box. Wire the inverter AC input to one of the breakers that
previously protected the branch circuit. Wire the output from the inverter
to the sub panel as the input. Connect the branch circuit(s) wire that you
chose previously to breakers in the sub panel.
Q: How much capacity do I need to power a microwave?
A: It depends heavily on the individual microwave, but a good rule of thumb
is to double the cooking power to determine AC power requirements. For
example, a Sharp 850 watt microwave uses 1500 watts of input current. You
can size the inverter by reading the AC panel on the microwave. Some 600
watt microwaves consume just under 1000 watts of input current.
Q: I want to run my inverter with a transfer switch as a battery backup for
my computer. Will it work?
A: It may. Automatic transfer switches are fast, but not fast enough for
many computer power supplies. The result may be a power glitch that causes
your computer to reboot. The glitch is very short (a few tens of
milliseconds) but still long enough to affect some computers. Other
computers may not be affected.
Q: How do I eliminate transfer switch glitches that affect my computer?
A: Run your inverter all the time, or install a small UPS (Uninterruptable
Power Source) between the computer and the outlet it's plugged in to.
Q: My TV (or stereo) works fine when running on shore power, but when the
inverter is running I get audio noise/snowy picture. What causes it?
A: Lower cost inverters use square waves or modified sine waves for their
output. The noise that you hear is the high frequency components of these
lesser quality outputs coupling through your TV or stereo. You may be able
to reduce the problem by installing a power line filter from Radio Shack.
These filters are often used to reduce radio interference from HAM radio
operators. They sometimes work for low cost inverters. The best solution
(and much more expensive) is to operate from a better inverter such as a
sine wave inverter.
Q: I have a dash radio that is draining my engine battery.
A: Switch your 12V source for the radio to the house battery.
Q: My radio is turned off but my batteries still discharge. What's going on?
A: It could be several different things. First, the LCD displays on new
automotive radios often create interesting patterns when they are turned
off. To reduce current draw, open the faceplate. This disconnects the LCD.
NOTE: many newer radios include a remote control using infrared light.
These systems may have significant drain due to the remote control. For
best effect install a radio kill switch.
Q: I want lots of light at night, but how do I conserve my battery?
A: Florescent lights are the most energy efficient for a given amount of
light. Halogens are the next most efficient, while incandescent are the
worst. The GMC OEM lights are ordinary incandescent. Use warm bulbs in
florescent fixtures where possible. When brighter more focused task
lighting is required use halogens. Use incandescent where the original
fixtures are the only alternative.
Q: How do I save energy when using the range hood?
A: If you can replace the hood vent fan and motor do so - new motor/fan
combinations move just as much air but use less than 30% of the energy.
Q: I saw an article about slowing the range hood fan by installing a two
position switch. Is this a good idea?
A: Not if you need to conserve energy. The design works by reducing the
operating voltage using a resistor. This wastes energy as heat. As an
alternative, look for a motor controller using Pulse Width Modulation (PWM)
technology. With this approach the fan motor uses only the electricity
needed and wastes very little.
Q: What areas of the OEM coach configuration can be improved most to save
battery power?
A: Most motors (range hood, vent fans), the incandescent lights, and water
pump. Most of these motors can be replaced with new units that consume 30%
of the power while still delivering the same or better than OEM
performance. A similar savings is possible with the water pump. Fantastic
fans replace OEM vents with a larger opening that has less air resistance.
Many times the Fantastic fan cover can be simply opened without running the
fan to get good airflow.
Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (831) 462-5199 / full service marketing
fax: (831) 462-5198
http://www.henry-davis.com/ http://www.henry-davis.com
Q: I want to install an inverter. How do I decide on the wattage?
A: Determine what AC appliances you want to operate simultaneously. Add
their wattage together and buy an inverter with 20% more capacity. For
example, suppose that you want to operate a desk top computer with standard
monitor, a color TV and home stereo at the same time. Assuming a few
numbers for our example: 120W + 120W (computer + Monitor maximum values) +
220W + 80W = 520 watts. So, select an inverter of at least 625 watts. For
most types of invert the 20% additional capacity accounts for many
manufacturer's practice of over-reporting the real capacity of their inverter.
Q: What kind of wire do I use to connect my inverter to the batteries?
A: I recommend marine grade fully tinned wire of the appropriate gauge. The
wire is more flexible than the automotive variety and resists corrosion
better. The improved flexibility will aid during installation. The tinned
wire reduces resistance caused by corrosion. High resistance connections
for high amperage devices like inverters can cause fires. I recommend using
one gauge larger than the chart to minimize voltage drop. Voltage drop
wastes power and causes the inverter to operate outside its ideal design
parameters.
Q: Can I power my Air Conditioner with an inverter?
A: Not economically. Compressor surge power is quite high and requires an
inverter in the 2kW range. The problem is that the battery drain would
require large banks to run the AC for any appreciable amount of time. A
typical 2 golf cart battery bank would be discharged to 50% of full
capacity in just half an hour. If you need to run the roof AC, start your
genset and charge your battery banks at the same time.
Q: How do I wire my coach for an inverter?
A: Decide where you will use inverter supplied power. You can then either
wire separate outlets for the inverter or separate out a branch circuit
from the existing wiring.
Q: Which branch circuit is best to use for inverter wiring?
A: It depends on what you want to use the AC power for. One convenient
circuit is the branch that powers the kitchen wall and dinette (curb side)
wall in the Palm Beach models. To use this circuit for your inverter, you
will need to separate the branch wiring from the existing bundle and
install a sub panel for the inverter circuit. This type of installation
requires a way to switch between the inverter output (11V AC) and the house
mains 110V AC. Inverters with a built-in transfer switch simplify this type
of installation. Otherwise you can install a separate transfer switch.
Q: How do I wire an inverter into a branch circuit?
A: Wiring is best done by a professional. If you are skilled, the following
is a general guide. First trace the outlets that you want to use as a
branch circuit. This can be done by disconnecting the coach from ALL 110V
sources including gensets and inverters. Open the distribution panel and
disconnect all wire bundles except the bare copper grounds. Insert a wire
jumper in the outlet that you want to use as a branch. NOTE: MAKE CERTAIN
THAT THERE IS NO 110V PRESENT IN THE COACH WHEN PERFORMING THIS OPERATION!
Use an Ohm meter to identify the circuit that you have jumpered by testing
wire pairs for continuity at the main distribution box. Label the wires.
Move the jumper to the next outlet and repeat the process. When you have
identified all outlets and wiring that you are interested in using on the
inverter, double check to make certain that no other outlets are wired to
your selected circuits. You can do this by moving jumpers to other outlets
while monitoring the selected branch circuit wire for continuity. Remove
the selected branch circuits and their associated grounds from the main
distribution box. Wire the inverter AC input to one of the breakers that
previously protected the branch circuit. Wire the output from the inverter
to the sub panel as the input. Connect the branch circuit(s) wire that you
chose previously to breakers in the sub panel.
Q: How much capacity do I need to power a microwave?
A: It depends heavily on the individual microwave, but a good rule of thumb
is to double the cooking power to determine AC power requirements. For
example, a Sharp 850 watt microwave uses 1500 watts of input current. You
can size the inverter by reading the AC panel on the microwave. Some 600
watt microwaves consume just under 1000 watts of input current.
Q: I want to run my inverter with a transfer switch as a battery backup for
my computer. Will it work?
A: It may. Automatic transfer switches are fast, but not fast enough for
many computer power supplies. The result may be a power glitch that causes
your computer to reboot. The glitch is very short (a few tens of
milliseconds) but still long enough to affect some computers. Other
computers may not be affected.
Q: How do I eliminate transfer switch glitches that affect my computer?
A: Run your inverter all the time, or install a small UPS (Uninterruptable
Power Source) between the computer and the outlet it's plugged in to.
Q: My TV (or stereo) works fine when running on shore power, but when the
inverter is running I get audio noise/snowy picture. What causes it?
A: Lower cost inverters use square waves or modified sine waves for their
output. The noise that you hear is the high frequency components of these
lesser quality outputs coupling through your TV or stereo. You may be able
to reduce the problem by installing a power line filter from Radio Shack.
These filters are often used to reduce radio interference from HAM radio
operators. They sometimes work for low cost inverters. The best solution
(and much more expensive) is to operate from a better inverter such as a
sine wave inverter.
Q: I have a dash radio that is draining my engine battery.
A: Switch your 12V source for the radio to the house battery.
Q: My radio is turned off but my batteries still discharge. What's going on?
A: It could be several different things. First, the LCD displays on new
automotive radios often create interesting patterns when they are turned
off. To reduce current draw, open the faceplate. This disconnects the LCD.
NOTE: many newer radios include a remote control using infrared light.
These systems may have significant drain due to the remote control. For
best effect install a radio kill switch.
Q: I want lots of light at night, but how do I conserve my battery?
A: Florescent lights are the most energy efficient for a given amount of
light. Halogens are the next most efficient, while incandescent are the
worst. The GMC OEM lights are ordinary incandescent. Use warm bulbs in
florescent fixtures where possible. When brighter more focused task
lighting is required use halogens. Use incandescent where the original
fixtures are the only alternative.
Q: How do I save energy when using the range hood?
A: If you can replace the hood vent fan and motor do so - new motor/fan
combinations move just as much air but use less than 30% of the energy.
Q: I saw an article about slowing the range hood fan by installing a two
position switch. Is this a good idea?
A: Not if you need to conserve energy. The design works by reducing the
operating voltage using a resistor. This wastes energy as heat. As an
alternative, look for a motor controller using Pulse Width Modulation (PWM)
technology. With this approach the fan motor uses only the electricity
needed and wastes very little.
Q: What areas of the OEM coach configuration can be improved most to save
battery power?
A: Most motors (range hood, vent fans), the incandescent lights, and water
pump. Most of these motors can be replaced with new units that consume 30%
of the power while still delivering the same or better than OEM
performance. A similar savings is possible with the water pump. Fantastic
fans replace OEM vents with a larger opening that has less air resistance.
Many times the Fantastic fan cover can be simply opened without running the
fan to get good airflow.
Henry Davis Consulting, Inc / new product consulting
PO Box 1270 / product readiness reviews
Soquel, Ca 95073 / IP reviews
ph: (831) 462-5199 / full service marketing
fax: (831) 462-5198
http://www.henry-davis.com/ http://www.henry-davis.com
