I am posting a collection of answers I have given (sometimes more than
once) to folks here on the list, and in private messages. Hopefully this
FAQ will be added to my web site this weekend.
GMC Electrical FAQ Part I
FAQ version 11/9/99
About this FAQ: This list of frequently asked questions is a compilation of
questions that I have been asked on and off the GMC mail list. The answers
reflect my opinion and in no way represent a legal expert opinion. You
alone are responsible for determining the safety and effectiveness of any
answer given here. Electricity can be dangerous. You could kill yourself.
You could kill others. Your coach electrical system could stop working.
Your coach could burn. Other BAD things could happen. This FAQ is
maintained by Henry Davis.
If you have the necessary skills to make the repairs and modifications
listed here you already know about all the BAD things. If you don't know
all of the BAD things or lack needed skills and techniques, get a
professional to do the job for you. Always use approved materials and
techniques for RV wiring.
Suggestions or comments to hdavis
Converter - Accepts 110V AC and creates 12V DC. Although converters are
available, most people buy a charger which also can function as a converter.
Charger - Accepts 110V AC and produces 13+V DC to charge batteries.
Automotive chargers are available in several technologies. The lowest cost
charger applies a constant current to the battery. If left on too long it
will damage the batteries. The most complex and capable chargers are
multistage chargers. These devices recharge batteries at maximum rates
without damaging them. Many chargers can operate as chargers and converters.
Combiner A combiner is an electrical apparatus used to permit two battery
(banks) to be charged "intelligently." The combiner relies on the fact that
the voltage across a charging battery will rise as the battery charge
increases. When the charging voltage is great enough, the combiner
electrically connects both batteries in parallel to permit them both to
become charged. When the batteries are not being charged the combiner
electrically isolates the two banks. Using a combiner in place of the
isolator that is original equipment in the GMC permits the electrical
isolation (keeps the engine battery from becoming discharged) when you use
the coach 12V electrical AND allows both batteries to be charged when
charging voltage is present. This can simplify the electrical system if you
want to permit charging of the engine battery from the coach charger.
battery isolator - a diode based device that permits both battery banks to
be charged from the alternator (and allows the alternator to provide 12V to
the coach wiring) but blocks current flow from one battery to another. This
stops the two banks from discharging themselves in a short period of time.
The discharge happens because (generally) one battery bank is different
electrically from the other. This leads to the "stronger" of the banks
experiencing current flow out as the batteries try to reach equilibrium
electrically. As one banks discharges into the other it will overshoot a
little bit so that it becomes the weaker of the banks. Then the second bank
tries to charge the first - and overshoots a little bit. The "seesaw"
current flow eventually discharges both battery banks.
Battery bank - in the GMC one 12V battery or 2 6V golf cart batteries in
series to create a 12V bank. The GMC has two banks - the engine (usually
one battery) and the coach bank (a 12V or 2 6V). Some coaches have added a
third bank to extend the time between recharges.
statpower - a company that manufactures a variety of battery related
equipment including charger/converters and inverters.
statpower40, TrueCharge 40, TrueCharge 40+ - A series of multistage battery
charger/converters that convert 110V to 12V (24V if you have that type of
system - GMCs are generally 12V systems). The multistage charger permits
rapid charging of battery banks by employing a high current phase until a
specific battery voltage is reached. The current is then reduced for
another period of time until a different higher voltage is reached. The
process continues reducing current with the goal of supplying the maximum
charge current without boiling the battery electrolyte. The chief advantage
to the multistage chargers is that they can restore a battery to a specific
charge level much more rapidly than an automotive trickle or taper charger.
In addition, these devices only supply a float current when needed, so
batteries aren't overcharged. Charge time for a given battery bank differs
based on the type of batteries used, but a typical golf cart battery
configuration will recharge to the 75% point in about 2.5 hours assuming a
discharge to 25%. This represents the fastest recharge possible and maximum
useful battery capacity with reasonable battery life. The Statpower
products also function as a converter to provide 12V from the 110V shore
power (or genset). The charger can charge batteries while supplying the
coach 12V but it requires more time to charge the batteries when they are
operated in the 25-75% range.
Inverter - a device for converting 12V DC from the batteries (or
alternator) to 110V AC. There are many different types of inverter, each
with different properties. The least expensive inverter supplies a
near-square wave output which is passed through a simple filter to make it
more sine wave-like. These are very inexpensive but relatively inefficient.
The power filtered out to make the output more sine wave-like is turned
into heat and is lost. Some inverters lose 45% of converted energy this way
(so if you are trying to power a 100W AC item at 110V you will actually
expend close to 200 watts of DC - half of which is turned into heat). Small
inverters of this type are useful for powering small items used
occasionally (or if you don't care to conserve power).
The next most expensive inverter is a modified sine wave inverter. This
device is more complex than the simple inverter but is more efficient.
Where the square wave inverter loses much energy to heat losses, the
modified sine wave inverter is more efficient. It also costs a bit more. It
is better for running some type of motors and electronics. most Statpower
inverters are modified sine wave inverters.
The most expensive inverter is a sine wave inverter. It produces AC that
looks just like the power company. It is generally the most efficient of
the inverters. Electronic equipment and motors operate like normal when
using these inverters.
You do not need an inverter unless you dry camp AND want to not run your
genset often.
Transfer Switch - a device used to select between 110V AC input sources
such as the shore power cable, genset, and inverter. Automatic transfer
switches sense when AC is present on the lines and switches to the
preferred source.
Wire size or gauge - wire must be of a size sufficient to carry the current
that will flow through the wire. Wire has a resistance. Resistance means
that the wire will lower the voltage from the source to the item using the
electricity. Longer wires have more resistance and therefore more voltage
losses. The larger the gauge the lower the voltage drop (loss) from source
to the item. This means that you lose less battery capacity while getting
brighter lights, faster turning motors, etc. Some items like motors can
fail when the voltage drops too low because there isn't enough torque to
turn the motor but there is enough heat generated to destroy some parts.
Q: I am considering a multistage charger (TrueCharge 40) but my buzz box
converter still works. Is it worthwhile to install a new converter?
A: The Statpower charger can still be a very good investment depending on
your use of the coach. When you need to replace the existing converter it
is worth considering the TrueCharge. In the meantime, how you use your
coach determines whether or not a multistage charger is needed to make your
coach function well. If you dry camp (camp without electrical hookups)
managing your battery banks is an important part of your camping
experience. If your stays are short enough that you never need to recharge
your house bank you can make do just fine with the old style buzz box.
Recharging is done hooked to shore power. If you need to recharge from the
genset, a multistage charger will significantly reduce the time required to
charge your battery banks.
Q: Where do I get a combiner
A: West Marine carries them. I'm not sure about other suppliers. Part
number West marine for 150A combiner 128293 - price on sale is about $100.
Q: How much do multistage chargers cost?
A: Refurbished 40 amp Statpower units are sometimes available for less than
$200. New 40 amp Statpower units are in the $400 range depending on where
you purchase them.
Q: What is the difference between Statpower and Trucharge?
A: Statpower is a company. They sell their products under several brand
names including ProWatt, Statpower, TrueCharge, and ProSine. In general,
The ProSine inverters are the highest capability (and capacity) of all
inverters sold by Statpower. The TrueCharge charger/converters include the
same battery charging circuitry used in the ProSine inverter/charger
combinations.
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
once) to folks here on the list, and in private messages. Hopefully this
FAQ will be added to my web site this weekend.
GMC Electrical FAQ Part I
FAQ version 11/9/99
About this FAQ: This list of frequently asked questions is a compilation of
questions that I have been asked on and off the GMC mail list. The answers
reflect my opinion and in no way represent a legal expert opinion. You
alone are responsible for determining the safety and effectiveness of any
answer given here. Electricity can be dangerous. You could kill yourself.
You could kill others. Your coach electrical system could stop working.
Your coach could burn. Other BAD things could happen. This FAQ is
maintained by Henry Davis.
If you have the necessary skills to make the repairs and modifications
listed here you already know about all the BAD things. If you don't know
all of the BAD things or lack needed skills and techniques, get a
professional to do the job for you. Always use approved materials and
techniques for RV wiring.
Suggestions or comments to hdavis
Converter - Accepts 110V AC and creates 12V DC. Although converters are
available, most people buy a charger which also can function as a converter.
Charger - Accepts 110V AC and produces 13+V DC to charge batteries.
Automotive chargers are available in several technologies. The lowest cost
charger applies a constant current to the battery. If left on too long it
will damage the batteries. The most complex and capable chargers are
multistage chargers. These devices recharge batteries at maximum rates
without damaging them. Many chargers can operate as chargers and converters.
Combiner A combiner is an electrical apparatus used to permit two battery
(banks) to be charged "intelligently." The combiner relies on the fact that
the voltage across a charging battery will rise as the battery charge
increases. When the charging voltage is great enough, the combiner
electrically connects both batteries in parallel to permit them both to
become charged. When the batteries are not being charged the combiner
electrically isolates the two banks. Using a combiner in place of the
isolator that is original equipment in the GMC permits the electrical
isolation (keeps the engine battery from becoming discharged) when you use
the coach 12V electrical AND allows both batteries to be charged when
charging voltage is present. This can simplify the electrical system if you
want to permit charging of the engine battery from the coach charger.
battery isolator - a diode based device that permits both battery banks to
be charged from the alternator (and allows the alternator to provide 12V to
the coach wiring) but blocks current flow from one battery to another. This
stops the two banks from discharging themselves in a short period of time.
The discharge happens because (generally) one battery bank is different
electrically from the other. This leads to the "stronger" of the banks
experiencing current flow out as the batteries try to reach equilibrium
electrically. As one banks discharges into the other it will overshoot a
little bit so that it becomes the weaker of the banks. Then the second bank
tries to charge the first - and overshoots a little bit. The "seesaw"
current flow eventually discharges both battery banks.
Battery bank - in the GMC one 12V battery or 2 6V golf cart batteries in
series to create a 12V bank. The GMC has two banks - the engine (usually
one battery) and the coach bank (a 12V or 2 6V). Some coaches have added a
third bank to extend the time between recharges.
statpower - a company that manufactures a variety of battery related
equipment including charger/converters and inverters.
statpower40, TrueCharge 40, TrueCharge 40+ - A series of multistage battery
charger/converters that convert 110V to 12V (24V if you have that type of
system - GMCs are generally 12V systems). The multistage charger permits
rapid charging of battery banks by employing a high current phase until a
specific battery voltage is reached. The current is then reduced for
another period of time until a different higher voltage is reached. The
process continues reducing current with the goal of supplying the maximum
charge current without boiling the battery electrolyte. The chief advantage
to the multistage chargers is that they can restore a battery to a specific
charge level much more rapidly than an automotive trickle or taper charger.
In addition, these devices only supply a float current when needed, so
batteries aren't overcharged. Charge time for a given battery bank differs
based on the type of batteries used, but a typical golf cart battery
configuration will recharge to the 75% point in about 2.5 hours assuming a
discharge to 25%. This represents the fastest recharge possible and maximum
useful battery capacity with reasonable battery life. The Statpower
products also function as a converter to provide 12V from the 110V shore
power (or genset). The charger can charge batteries while supplying the
coach 12V but it requires more time to charge the batteries when they are
operated in the 25-75% range.
Inverter - a device for converting 12V DC from the batteries (or
alternator) to 110V AC. There are many different types of inverter, each
with different properties. The least expensive inverter supplies a
near-square wave output which is passed through a simple filter to make it
more sine wave-like. These are very inexpensive but relatively inefficient.
The power filtered out to make the output more sine wave-like is turned
into heat and is lost. Some inverters lose 45% of converted energy this way
(so if you are trying to power a 100W AC item at 110V you will actually
expend close to 200 watts of DC - half of which is turned into heat). Small
inverters of this type are useful for powering small items used
occasionally (or if you don't care to conserve power).
The next most expensive inverter is a modified sine wave inverter. This
device is more complex than the simple inverter but is more efficient.
Where the square wave inverter loses much energy to heat losses, the
modified sine wave inverter is more efficient. It also costs a bit more. It
is better for running some type of motors and electronics. most Statpower
inverters are modified sine wave inverters.
The most expensive inverter is a sine wave inverter. It produces AC that
looks just like the power company. It is generally the most efficient of
the inverters. Electronic equipment and motors operate like normal when
using these inverters.
You do not need an inverter unless you dry camp AND want to not run your
genset often.
Transfer Switch - a device used to select between 110V AC input sources
such as the shore power cable, genset, and inverter. Automatic transfer
switches sense when AC is present on the lines and switches to the
preferred source.
Wire size or gauge - wire must be of a size sufficient to carry the current
that will flow through the wire. Wire has a resistance. Resistance means
that the wire will lower the voltage from the source to the item using the
electricity. Longer wires have more resistance and therefore more voltage
losses. The larger the gauge the lower the voltage drop (loss) from source
to the item. This means that you lose less battery capacity while getting
brighter lights, faster turning motors, etc. Some items like motors can
fail when the voltage drops too low because there isn't enough torque to
turn the motor but there is enough heat generated to destroy some parts.
Q: I am considering a multistage charger (TrueCharge 40) but my buzz box
converter still works. Is it worthwhile to install a new converter?
A: The Statpower charger can still be a very good investment depending on
your use of the coach. When you need to replace the existing converter it
is worth considering the TrueCharge. In the meantime, how you use your
coach determines whether or not a multistage charger is needed to make your
coach function well. If you dry camp (camp without electrical hookups)
managing your battery banks is an important part of your camping
experience. If your stays are short enough that you never need to recharge
your house bank you can make do just fine with the old style buzz box.
Recharging is done hooked to shore power. If you need to recharge from the
genset, a multistage charger will significantly reduce the time required to
charge your battery banks.
Q: Where do I get a combiner
A: West Marine carries them. I'm not sure about other suppliers. Part
number West marine for 150A combiner 128293 - price on sale is about $100.
Q: How much do multistage chargers cost?
A: Refurbished 40 amp Statpower units are sometimes available for less than
$200. New 40 amp Statpower units are in the $400 range depending on where
you purchase them.
Q: What is the difference between Statpower and Trucharge?
A: Statpower is a company. They sell their products under several brand
names including ProWatt, Statpower, TrueCharge, and ProSine. In general,
The ProSine inverters are the highest capability (and capacity) of all
inverters sold by Statpower. The TrueCharge charger/converters include the
same battery charging circuitry used in the ProSine inverter/charger
combinations.
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
