Home » Public Forums » GMCnet » Understanding (Trying to) the 12V/120V System
| Understanding (Trying to) the 12V/120V System [message #71503] |
Fri, 22 January 2010 08:26  |
Oldngray
Messages: 544
Registered: August 2009
Location: Punta Gorda Florida
Karma: 0
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In my coach, none of the outlets are hot unless on Gen/Shore power. Looking at the wiring diagrams in the manual, (I'm not sure I read this stuff correctly) the coach does not provide for conversion from 12V to 120V.
Is this correct?
Richard MacDonald
Punta Gorda, Florida
Sold our TZE April 2015
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| Re: [GMCnet] Understanding (Trying to) the 12V/120V System [message #71514 is a reply to message #71503] |
Fri, 22 January 2010 10:09  |
Rick Denney
Messages: 430
Registered: January 2004
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Richard MacDonald writes...
> In my coach, none of the outlets are hot unless on Gen/Shore power.
> Looking at the wiring diagrams in the manual, (I'm not sure I read
> this stuff correctly) the coach does not provide for conversion from 12V to 120V.
> Is this correct?
Yes, that is correct. Defining some terms will help--don't be offended
if I cover old ground:
Converter: A device that changes 120VAC to 12VDC (nominal).
Inverter: A device that changes 12VDC (nominal) to 120VAC.
Alternator: A device that produces 12VDC (nominal) from an
engine-driven belt, and serves as a battery charger.
Generator: A device with its own gasoline engine that produces 120VAC
and (in some cases) 12VDC (nominal) to charge the battery used to
start its own engine.
Battery Charger: A device that charges the batteries connected to it
by providing a voltage higher than the voltage produced by the
batteries so that current will flow into the battery rather than away
from it. Converters and alternators are examples, and SOME inverters
also have battery chargers built into them. Since all devices in a
motorhome that produce 12VDC (nominal) are used as chargers, they all
produce voltage higher than a charged battery, which is why I have
been writing "nominal" next to "12VDC". The actual voltage will range
from the low 13's to the mid 15's, depending on the device and the
charging cycle.
Multi-Stage Charger: A battery charger that provides three or four
charging stages--a fast charge, a soak charge, a maintenance charge,
and an anti-sulfation cycle.
Isolator: A device that allows a charging device to separately charge
two batteries without allowing current to flow from either battery to
the other, or back to the charging device. Isolators work by using
large diodes, which act as one-way check valves for 12VDC.
Combiner: A device that joins two batteries into the same circuit in
the presence of charging voltage, and disconnects them with not in the
presence of charging voltage. Thus, the batteries are joined for
charging and separated when being discharged, preventing one battery
from discharging another.
Transfer switch: A device that determines which source of 120VAC power
will be used. It will disconnect one source fully, and then connect
the alternative source. May be manual or automatic.
Note that sometimes two or three of the devices above will be
integrated into the same box.
Now, the explanation will be a lot easier.
Most fancy modern motorhomes are equipped with an alternator,
generator, isolator, inverter/charger, and automatic transfer switch.
When shore power is connected, the inverter is idle, but the
multi-stage battery charger within it charges the house batteries.
When the generator is started, the transfer switch will automatically
switch to that source, and since the generator provides 120VAC, the
inverter will still be idle. When neither the generator nor shore
power are connected, the transfer switch will automatically engage the
inverter to produce 120VAC. The use of an isolator means that most
modern motorhomes will not charge the chassis/engine battery from the
charger built into the inverter, but will charge the house batteries
from the alternator.
Motorhomes in the GMC era didn't have all that stuff, because much of
it was not affordable or available at the time. So, GMCs were equipped
from the factory with an alternator, generator (option), isolator, and
a converter (used as a battery charger but without multistage
charging). The use of an isolator means that the GMC will not chrage
the 455's battery from the converter, but will charge the house
battery from the alternator. The transfer switch is "manual" on most
GMC-upfitted coaches, meaning that to switch from shore power to
generator you have to physically move the shore power cable from the
campground outlet to the generator's outlet. The use of a converter
instead of an inverter means that without shore power or the
generator, no 120VAC will be produced and only 12VDC devices will
work. If you must have 120VAC, you have to fire up the generator or
plug into shore power.
There are many possible improvements. One is to install a combiner
across the battery terminals on the isolator so that all batteries
will be charged when any charging source is present, either in the
house or from the alternator. The Yandina C100 combiner is about $70.
Many GMC owners have done this.
Another is to replace the original converter with a converter that
includes a multi-stage battery charger. The price for this is between
$150-200, either for the Progressive Dynamics or for an Iota
converter/charger of an output of about 40-45 amps. This is probably
the most popular first upgrade, often necessitated by the failure of
the original converter.
Still another is to eliminate the generator outlet and replace it with
a built-in automatic transfer switch. I found an Iota 50-amp automatic
transfer switch (your coach may only need a 30-amp model) for $80 on
ebay. Some GMC's had these from their upfitters, and some owners of
coaches not so equipped have installed them.
One can also replace the converter-charger with an inverter-charger
that will perform the converter duties (through the charger) and also
provide 120VAC when there isn't another source. These also often have
built-in transfer switches. To get one large enough to be worth
building into the coach, bring your checkbook. An alternative is to
purchase cheap, small inverters as needed just large enough to power
the device that needs it. Most do not attempt to run their large
120VAC appliances (e.g. roof AC, water heater) from the
batteries--they just draw too much and run the batteries down too
quickly. It takes a LOT of batteries to power the roof air even for a
little while.
Rick "whose coach has a multi-stage converter/charger, combiner, and
automatic transfer switch, in order of importance" Denney
'73 230 Ex-Glacier "Jaws"
Northern Virginia
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'73 Glacier 230 "Jaws"
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| Re: [GMCnet] Understanding (Trying to) the 12V/120V System [message #71515 is a reply to message #71514] |
Fri, 22 January 2010 10:22 |
Oldngray
Messages: 544
Registered: August 2009
Location: Punta Gorda Florida
Karma: 0
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Senior Member |
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Thanks Rick, that was a wonderful explanation.
I have the Yandina Combiner and the Progressive Converter installed.
When I asked about the Inverter I had not performed a proper search, my bad, now I have found quite a bit on the subject and along with your explanation I will be able to understand what I read with a lot more clarity.
Thank you.
Richard MacDonald
Punta Gorda, Florida
Sold our TZE April 2015
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| Re: [GMCnet] Understanding (Trying to) the 12V/120V System [message #71519 is a reply to message #71514] |
Fri, 22 January 2010 11:12 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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Senior Member |
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We need to capture Rick's excellent post. Maybe in Terry's GMC Jargon? <http://www.bdub.net/GMC_Jargon.htm> Or maybe a Wiki. (Didn't we start one of those awhile back?)
| Rick Denney wrote on Fri, 22 January 2010 08:09 |
... Defining some terms will help--don't be offended if I cover old ground:
Converter: A device that changes 120VAC to 12VDC (nominal).
Inverter: A device that changes 12VDC (nominal) to 120VAC.
Alternator: A device that produces 12VDC (nominal) from an
engine-driven belt, and serves as a battery charger.
Generator: A device with its own gasoline engine that produces 120VAC and (in some cases) 12VDC (nominal) to charge the battery used to start its own engine.
Battery Charger: A device that charges the batteries connected to it by providing a voltage higher than the voltage produced by the batteries so that current will flow into the battery rather than away from it. Converters and alternators are examples, and SOME inverters also have battery chargers built into them. Since all devices in a motorhome that produce 12VDC (nominal) are used as chargers, they all produce voltage higher than a charged battery, which is why I have been writing "nominal" next to "12VDC". The actual voltage will range from the low 13's to the mid 15's, depending on the device and the charging cycle.
Multi-Stage Charger: A battery charger that provides three or four charging stages--a fast charge, a soak charge, a maintenance charge, and an anti-sulfation cycle.
Isolator: A device that allows a charging device to separately charge two batteries without allowing current to flow from either battery to the other, or back to the charging device. Isolators work by using large diodes, which act as one-way check valves for 12VDC.
Combiner: A device that joins two batteries into the same circuit in the presence of charging voltage, and disconnects them with not in the presence of charging voltage. Thus, the batteries are joined for charging and separated when being discharged, preventing one battery from discharging another.
Transfer switch: A device that determines which source of 120VAC power will be used. It will disconnect one source fully, and then connect the alternative source. May be manual or automatic.
Note that sometimes two or three of the devices above will be integrated into the same box.
Now, the explanation will be a lot easier.
Most fancy modern motorhomes are equipped with an alternator, generator, isolator, inverter/charger, and automatic transfer switch. When shore power is connected, the inverter is idle, but the multi-stage battery charger within it charges the house batteries. When the generator is started, the transfer switch will automatically switch to that source, and since the generator provides 120VAC, the inverter will still be idle. When neither the generator nor shore power are connected, the transfer switch will automatically engage the inverter to produce 120VAC. The use of an isolator means that most modern motorhomes will not charge the chassis/engine battery from the charger built into the inverter, but will charge the house batteries from the alternator.
Motorhomes in the GMC era didn't have all that stuff, because much of it was not affordable or available at the time. So, GMCs were equipped from the factory with an alternator, generator (option), isolator, and a converter (used as a battery charger but without multistage charging). The use of an isolator means that the GMC will not charge the 455's battery from the converter, but will charge the house battery from the alternator. The transfer switch is "manual" on most GMC-upfitted coaches, meaning that to switch from shore power to generator you have to physically move the shore power cable from the campground outlet to the generator's outlet. The use of a converter instead of an inverter means that without shore power or the generator, no 120VAC will be produced and only 12VDC devices will work. If you must have 120VAC, you have to fire up the generator or plug into shore power.
There are many possible improvements. One is to install a combiner across the battery terminals on the isolator so that all batteries will be charged when any charging source is present, either in the house or from the alternator. The Yandina C100 combiner is about $70. Many GMC owners have done this.
Another is to replace the original converter with a converter that includes a multi-stage battery charger. The price for this is between $150-200, either for the Progressive Dynamics or for an Iota converter/charger of an output of about 40-45 amps. This is probably the most popular first upgrade, often necessitated by the failure of the original converter.
Still another is to eliminate the generator outlet and replace it with a built-in automatic transfer switch. I found an Iota 50-amp automatic transfer switch (your coach may only need a 30-amp model) for $80 on ebay. Some GMC's had these from their upfitters, and some owners of coaches not so equipped have installed them.
One can also replace the converter-charger with an inverter-charger that will perform the converter duties (through the charger) and also provide 120VAC when there isn't another source. These also often have built-in transfer switches. To get one large enough to be worth building into the coach, bring your checkbook. An alternative is to purchase cheap, small inverters as needed just large enough to power the device that needs it. Most do not attempt to run their large 120VAC appliances (e.g. roof AC, water heater) from the batteries--they just draw too much and run the batteries down too quickly. It takes a LOT of batteries to power the roof air even for a little while.
Rick "whose coach has a multi-stage converter/charger, combiner, and automatic transfer switch, in order of importance" Denney
'73 230 Ex-Glacier "Jaws"
Northern Virginia
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Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Understanding (Trying to) the 12V/120V System [message #71544 is a reply to message #71514] |
Fri, 22 January 2010 15:28 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Professor Denny,
I wish you had published this treatise before I went through my "learning
curve!"
Gene,
It would terrific if you put this on your website!
Thanks,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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