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Old 02-02-2023, 12:39 PM   #1
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shore power with no house batteries

I have a 2017 Forester 3051s on shore power with no house batteries in it during the winter. Is it OK to connect the 12 volt converter cable to the 12 volt out cable that our in the battery box to run my 12 volt system?
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Old 02-02-2023, 01:15 PM   #2
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Yes you can connect all of the positive cables together that were on the battery positive post, same with the negatives. Make sure you insulate the positive cables so that they do not touch the chassis or the negative cables.

Without a battery in the circuit it is not a good thing to attempt to run the slides or leveling jacks. The converter may not be able to provide adequate current to reliably run those systems.
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Old 02-04-2023, 09:16 AM   #3
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Your 12V systems will work without these cables being connected together. The converter and the batteries connect to the same distribution system If one is pulled out of the system the other supplies power.
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Old 02-04-2023, 10:03 AM   #4
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Not exactly

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Your 12V systems will work without these cables being connected together. The converter and the batteries connect to the same distribution system If one is pulled out of the system the other supplies power.
Not exactly. Some accessories (e.g., power awning, power steps) are powered from the battery with inline fuses. They are not connected to the fuse distribution board. They are connected together by virtue of their common connection at the battery positive terminal.

Even though the batteries have been removed, these accessories could be powered from the converter if they were connected to the heavy wire wire coming to the battery from the converter.
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Old 02-04-2023, 10:13 AM   #5
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In addition to the 12 volt loads serviced by the fuses in the main converter panel, this being a motorhome, it should be noted that there is commonly a Battery Control Center typically in the entry stepwell with it’s own set of interlocks and fuses feeding additional accessories. The BCC typically runs slides, jacks, arctic pac, awning, etc. If attempting to operate such devices without the batteries attached, one would need to investigate or ensure that the BCC would get power directly from the converter.

It’s my understanding that the house batteries would, if attached, act as a buffer, dampener, filter, and/or regulator for the 12 volt power to accessories. I would be concerned that regulation and filtering would be lost, and the 12 volt devices might be subject to high or low voltage surges or spikes if powered strictly from the converter output.

Backing up a bit here, why have the batteries been removed? I can think of only a few reasons to remove the house batteries from the motorhome, but normal winter storage is typically not one of them, especially since you have shore power. If the batteries were in place, the question of operating the house without them wouldn’t need to be asked.
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Old 02-04-2023, 12:31 PM   #6
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The installation I have worked on the awning, slides etc are powered thru the 12V without fuses at the distribution panel rather inline of some sort. I have not found any of these clamped directly to the batteries but connected to the 12V system somewhere down stream of the batteries.


So I read the replies and as a test I opened my disconnect and removed the cables form my batteries and holly molly both my slides and awning work while on shore power with that said maybe it may work different on some rigs but none that I have worked on.
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Old 02-04-2023, 12:32 PM   #7
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On a real plus going out and checking I found that my negative connections on both batteries need service. lol
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Old 02-04-2023, 12:42 PM   #8
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maybe it may work different on some rigs but none that I have worked on.
Then you haven't worked on FR GT/FR3 motorhomes. Don't know if this thread referencing a Forester MH is the same as those units.
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Old 02-04-2023, 02:35 PM   #9
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Curious

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The installation I have worked on the awning, slides etc are powered thru the 12V without fuses at the distribution panel rather inline of some sort. I have not found any of these clamped directly to the batteries but connected to the 12V system somewhere down stream of the batteries.

So I read the replies and as a test I opened my disconnect and removed the cables form my batteries and holly molly both my slides and awning work while on shore power with that said maybe it may work different on some rigs but none that I have worked on.
Let us know where they interconnect if you figure it out. I'm curious.

On many fuse distribution panels there are multiple positive tie points. The one directly from the converter (labelled +Vcc on a WFCO 8955), goes through two 30A fuses in parallel to the other two (labelled +POS) and the fuses. The from the cable from the positive battery terminal terminates in one of the +POS tie points. The other one is open on our trailer but could be used for a connection to slides or awnings with inline fuses.
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Old 02-04-2023, 04:11 PM   #10
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Re previous comments about " buffering" and inadequate power to operate slide w/ o batteries installed, converters manufactured in this century are closely regulated and filtered enough that they do not require a battery to be connected. Mfr's usually state such in theit literature/manuals.

As for power to operate a slide, unless the slide motor draws more than rated output of converter no need for a battery. Most converters are in the 55-60 zmp range and slide circuit is fused commonly with a 30 amp fuse, drawing far less if slide me mechanism is properly maintained.

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Old 02-04-2023, 04:16 PM   #11
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Re previous comments about " buffering" and inadequate power to operate slide w/ o batteries installed, converters manufactured in this century are closely regulated and filtered enough that they do not require a battery to be connected. Mfr's usually state such in theit literature/manuals.

As for power to operate a slide, unless the slide motor draws more than rated output of converter no need for a battery. Most converters are in the 55-60 zmp range and slide circuit is fused commonly with a 30 amp fuse, drawing far less if slide me mechanism is properly maintained.

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Thanks for your comments. Thatís good to know.
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Old 02-04-2023, 07:38 PM   #12
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Then you haven't worked on FR GT/FR3 motorhomes. Don't know if this thread referencing a Forester MH is the same as those units.

OK whats your point? Did I say I did work on one of those? whats your problem.
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Old 02-04-2023, 07:50 PM   #13
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I think...

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OK whats your point? Did I say I did work on one of those? whats your problem.
I think Bubbles is referencing your posts #3 and #6. He is suggesting that your experience on one motorhome should not be generalized to all motorhomes, particularly those of other brands.

These vehicles can have appliances (loads) that are not fed from fuses on the distribution (fuse) board.
  1. Sometimes they use inline fuses and are each connected to the positive battery terminal
  2. Sometimes they use inline fuses and are connected to a spare terminal on the distribution board
In the first case, those loads wired directly to the batteries won't get power unless all the wires are gathered together and connected, to the receive power from the heavy cable connecting them to power fed from the distribution board. (Might have to connect all the negative terminal wires too.)
In the second case (yours), you can remove the batteries and plug into shore power without making other connections.
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