When GM designed and built our coaches there was no thought given to running 120vac household appliances off the batteries as there were no cost effective devices for producing 120vac from 12vdc. They provided a shore power cord and a generator to do so. There also were no cost effective devices available to do multi stage charging of the house 12vdc lead acid batteries while at the same time supplying a steady 12vdc to run the lights and 12vdc stuff in the house part of the coach when plugged in to shore or gen power so they used what was available - a simple 120vac to 12vdc power supply which most now call a buzz box. It would bulk charge the house battery bank but if left in for very long would over charge those batteries.
Over the years many POs replaced the buzz box with a more modern multi-stage battery charger when they became available from people like Iota, Progressive Dynamics, etc. Those would not over charge the house battery bank but could also supply a steady 12vdc to the house when plugged in. When not plugged in, the 12vdc for the house came from the house battery bank. Still later, some POs also added devices that could produce 120vac from 12vdc so they could use household appliance when not plugged in.
GM finished coaches started out with a separate battery to start the Oman generator and the Oman had an on-board battery charger and voltage regulator to do so. Before long in the production cycle they switched to starting the Oman from the house battery bank making the Oman generator and regulator superfluous but they remained in place to the end. Some POs disconnected that regulator.
All through production GM sought to recharge both the chassis and house lead acid batteries via the engine driven alternator. To do so GM used a diode isolator. That worked well but did not allow shore power or generator power to recharge the chassis battery. Some POs replaced the diode isolator with a voltage controlled relay that would do so.
All of these devices have names that sound confusing at first:
Produce 12vdc from 120vac is called a converter/battery charger
Produce 120vac from 12vdc is called an inverter
Allow charging both chassis and house batteries from alternator or shore/gen power is called a combiner
Hope this makes it all a bit easier to understand.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed & hand crafted
in the 1907 former Masonic Temple building
in historic Kerby, OR
http://jerrywork.com
Over the years many POs replaced the buzz box with a more modern multi-stage battery charger when they became available from people like Iota, Progressive Dynamics, etc. Those would not over charge the house battery bank but could also supply a steady 12vdc to the house when plugged in. When not plugged in, the 12vdc for the house came from the house battery bank. Still later, some POs also added devices that could produce 120vac from 12vdc so they could use household appliance when not plugged in.
GM finished coaches started out with a separate battery to start the Oman generator and the Oman had an on-board battery charger and voltage regulator to do so. Before long in the production cycle they switched to starting the Oman from the house battery bank making the Oman generator and regulator superfluous but they remained in place to the end. Some POs disconnected that regulator.
All through production GM sought to recharge both the chassis and house lead acid batteries via the engine driven alternator. To do so GM used a diode isolator. That worked well but did not allow shore power or generator power to recharge the chassis battery. Some POs replaced the diode isolator with a voltage controlled relay that would do so.
All of these devices have names that sound confusing at first:
Produce 12vdc from 120vac is called a converter/battery charger
Produce 120vac from 12vdc is called an inverter
Allow charging both chassis and house batteries from alternator or shore/gen power is called a combiner
Hope this makes it all a bit easier to understand.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed & hand crafted
in the 1907 former Masonic Temple building
in historic Kerby, OR
http://jerrywork.com
