battery or converter supply 12v systems

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cujman

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When my TT is plugged into 120vac are the 12v systems (ie lights)running off the battery or the converter.  Thanks

Cujman
 

AStravelers

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The converter supplys the 12V to lights and everything else, also keeping the battery charged while on shore power or generator power.
 

Rene T

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I think actually both. The reason there's a battery if for big power suckers like the slide outs because just the converter would not do it. On mine, there's a sticker next to the slide out switches that says a battery must be installed to operate the slides.
 

Heli_av8tor

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True Al, but the batteries are still connected when on shore or genny power.
The coach 12 system, the batteries, and the converter are all connected to a common point.
 

Gary RV_Wizard

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For practical purposes, the power comes from the converter.  For a more detailed answer, keep on reading.

In most systems, the battery(s) and the converter/charger are connected in parallel, so they both function as power sources. Since the converter is normally the higher voltage source, it provides the bulk of the power. Further, any amps drawn from the battery get almost instantly replaced by the charging function.  This is essentially the same as your car, where the engine alternator and battery are a combined source.
Some old systems (1980's?) contained a relay that actually switched the 12v source between battery and converter. These systems had a separate charging line to the battery.
 

John From Detroit

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Rene has the correct answer more or less

Two answers... Normally in a modern trailer or Motorhome, if you are on shore power the CONVERTER provides all the "12 volt" systems with at least 13.6 volts (Float voltage for the batteries) or even 14.6 (Charge voltage) Depending on two things.. The state of charge of the batteries. and the load on the system (how many lights and stuff you have on)

IF the load exceeds the converter's ability. (Can happen for short terms like running a slide in and out) the batteries make it up.

The will cover anything made this century.. But

answer 2:
With some OLDER systems.. Well the battery is SLOWLY charged by the converter and provides power to "Senistive" loads (Like radios) where as the converter provides the "I don't care if the DC is really DC or not" loads like light bulbs.
 

cujman

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Thanks to all who responded.  It really helped my understanding of how this works.  Seems to me the electrical in RV's is really convoluted

Cujman
 

Gary RV_Wizard

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Not convoluted, but it's a fairly complex system that utilizes power from multiple sources and maintains batteries as well.  Plus, if it's a motorhome, it also manages two different 12v systems (house and chassis) and two charging sources.
 

Frank B

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cujman said:
Thanks to all who responded.  It really helped my understanding of how this works.  Seems to me the electrical in RV's is really convoluted

Cujman


Not really.


As Gary explained, there is really only one 12 volt system in the whole RV. But just as there are many devices attached to the 12 volts, like lights, slide motor, water pump, Etc, there are also two or more inputs to that system. The battery is one, and the converter is another. If you have solar, then there is yet a third. 


Again, as Gary explained, it is the highest voltage source that will provide power to the 12 volt system if there is a demand placed upon it.  As Rene explained, they all work together. Don't expect the solar to provide any power at night, and don't expect the converter to provide any power when the unit is unplugged, and don't expect the battery to provide any power if it is dead.


It basically depends upon which one is the strongest source of power at any given moment.

 

grashley

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This probably repeats what was already said, but maybe it will help.

The RV has a 120V system which is powered from shore power (or generator).  This system powers the 120V items such as a microwave, A/C, 120V outlets for coffee pots, TV, etc., water heater and fridge, and the converter.

The 12V system powers the slides, power tongue jack, almost all lights, vent fans, control circuits for furnace, water heater, fridge, and A/C.  Furnace runs on 12V / propane. The power is supplied from the battery and/or converter and/or solar.

Propane supplies fuel to the stove, oven, furnace, and water heater and fridge in LP mode.
 

AStravelers

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cujman said:
Thanks to all who responded.  It really helped my understanding of how this works.  Seems to me the electrical in RV's is really convoluted

Cujman
Well, the electrical system in an RV is different than a typical house system which is typically all 120V (& 240V) AC power. 

There is definitely a learning curve in understanding the 12V systems in an RV.

Here are a couple of links which will provide understanding on how the RV electrical systems work:
http://www.marxrv.com/12volt/12volt.htm
http://www.marxrv.com/12volt/12volta.htm
 

LarryS

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I am restoring a 1983 Pace Arrow, but the 12v system has me confused:
1.  With shorepower on I read 13.2v at the + bus of the 12v converter panel  - 12v systems work - but read only 12.1v at
house batteries (no charging)
2.  When disconnecting shorepower,  voltage drops to 0 at the 12v bus input, but 12v continue to work!  (strange)
    a.  I expected to see 12.1v at panel when 120v removed from charger
    b.  but with no voltage at panel I would have expected 12v lights to be off.
charger is separate from converter, charger output is "Y"-ed into power lead to batteries and to converter panel bus.
I did see continuity from battery end of wire to converter, but do not see voltage.
Thanks.
 

grashley

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Welcome to the Forum!

Generally, you get more response if you start a new thread rather than adding to a month old thread.  Here, we do not get upset over either approach.

With no external power to the coach, the batteries should read 12.6V when fully charged.  You should have the same reading at the buss.
With shore power, the converter should boost the voltage to 13.3 or higher if the batteries need charged.  The voltage should be the same at the buss and the battery.

On my FW, the power box has two heavy gauge wires at the 12V buss.  One goes to the converter and one goes to the battery.  Essentially, there is one wire from the converter to the battery with the buss connected in between.  I do not understand how you get no power at the buss, yet the things the buss feeds work.  I could see landing gear or slide outs working with this situation, since they generally get power directly from the battery.  But lights or water pump working sounds strange!

Just reread your post.  Usually the converter (converts 120VAC to 12VDC) IS the charger and is wired as you describe.  Do you have a separate battery charger?  Then what does the converter do?
 

LarryS

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I can certainly move this to a new thread if that is proper and it might get more attention .. .. .. .. Thank you for your response.

This is an old rig ('83) with the 110 panel and 12v panel in tbe same box, but the charger is a separate unit, wired in.  I see only 1 wire coming from tbe house batteries and it is "Y-ed" to the charger output.  So logically (to me) I should see either battery voltage or charger output at the 12v bus input.  If there was an open circuit breaker or fuse in the bus/battery line I would expect the 0 voltage w/ no charger input, but I would also expect no 12v equipment to operate.  Thus my bafg
flement
 

LarryS

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It has the original ('83) Converter/Distribution Panel: PD734Q74RLTZB with a newer (2016) add-on charger PD9145A.
 

grashley

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To make things clear to my poor mind - your camper came with a converter built into the power center, but that one has been unhooked, and the new, separate converter wired in to its' place.  The old one is no longer electrically connected to anything.
 

LarryS

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No, if I understand it correctly the original unit was an AC Supply + AC/DC converter, but had a single voltage battery charge function (13.2v) and was know to burn up batteries.  A PD9145A was added into the circutry to add a "floating", safer charge.

What I do not understand is why there is no DC voltage shown on the converter panel input when AC input is removed and how can the 12v RV systems continue to operate?  I only see 1 power wire heading toward the house batteries. 

I must be missing something rudimentary here.
 

John From Detroit

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I suspect the converter (original) may not have been disconnected. When you are plugged in it is powering the house. the 9145 is wired direct to the battery which like this line



9145---battery---fuse or breaker----switched----power panel---Stuff

The switch is open (Disconnect switch)( or the fuse blown or the breaker tripped.
 

LarryS

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Thanks.  Any idea where the older Fleetwoods would typically mount a disconnect switch? And if that switch/fuse were blown why would 12v systems continue to operate on battery power?
 

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