so i'm a little confused

[bob h]

Regarding the 12v system and shore power. Does everything run off 12v and shore power charges the battery or does shore power get "converted" and power all the lights, fridge, etc. Barring some broken part or lack of shore power can the trailer run the battery dead while hooked up and cause the fridge to fail for example.

Looking at 22 2327tb. Have not purchased yet.

Thanks in advance.

[Eagle5]

Hi Bob,
I believe we are all a little confused! (ha-ha)
In general, the 12 VDC appliances run off the batteries, and the batteries are recharged (or kept charged) by the Power Center. Typically, the lighting and fans are strictly 12 VDC, and this includes the blower for the propane-fired furnace.
Things like the refrigerator are typically 120 VAC, or automatically switch to propane if not plugged into Shore Power. (Refrigerators also use a very small amount of 12 VDC for lighting and controls.)
Most Shore Power systems are 30 amp @ 120 VAC single-phase, which represents 3,600 watts of power.
Most Power Centers generate 45 amps @ 12 VDC, which represents 540 watts of power.
As long as you are plugged into Shore Power, you should not run-out of power.
Welcome to the forum.
Eagle5

[bob h]

Thank you very much.

[Morich]

Fully agree with Eagle 5 and no change with what he has said but there may be a bit different spin in the way I find folks thinking of batteries.
I don't think of them as items like interior lights working off the batteries, nor off the AC shore power as we are plugged in as the batteries are a "storage" item.
So there are times when we are plugged in and might think of things running off the AC but it might be more correct to think of the storage as we might and extra water tank on a hose off to the side of the main water faucet.

We we are using less water than the faucet is putting out, the water is likely to come from that direction but if we use more water and the faucet can't keep up, then water will come from the faucet as well as the tank!

We have RV desinged in most cases to let the shore power go to a charging or converter system( that may have different names for the same thing!) which WILL supply more DC than we use. That is the normal setup. But if we add some tiems that require more DC than the converter/ charger/ etc. is able to put out, the power will be coming from that converter AND the batteries!

It can avoid some confusion if we don't get into the habit of DC power always coming from one or the other as the batteries are just a storage which is hung on the side of the power flow and can being power comming or going!

Or another way to think of it might fit if you have fed some teenagers??
Is the pantry providing the food or is it you as you are adding it as they are eating it?
Depends on whether you are putting it in faster than them taking it out!! So when we speak of where the DC power comes from, it can be like finding an empty box and asking if it came from the pantry or what you just brought home!

[bob h]

Thank you both. I really appreciate your knowledge and insight.

[creativepart]

There is always one guy that has a different opinion.

In a travel trailer the onboard Converter takes shore power and coverts it to 12vdc. The output is directly connected to the power center that distributes 12v power to all of the 12v loads, i.e. lights, water pump, LP furnace blower, etc.

However, the 12v battery or batteries are also directly connected to the power center to run those loads and to receive a charge by the converter.

You could think that the batteries are running the loads and the converter is replacing the power being used by the loads on the batteries. But is it? Remove the battery and things will still run normally just on the converter. In fact, your battery can be dead or nearly fully discharged and the converter will still power your 12v loads. So, what’s powering your 12v loads? The Converter or your battery?

Note: In RVs without a Converter, that use an Inverter Charger, it is the battery that is always powering 12v loads. The Power Center is not utilized by the 12v charge from the inverter. The charger in an inverter charger is direct connected to the batteries not the load center.

[thompwil]

Generic but somewhat helpful

[Morich]

I agree with most of this drawing and part of what Creative is saying but I feel there is more to this as it does show what I feel can get us into trouble if we think of power as only going out of the converter!



It feels like a nit picking thing but one of the best tools we have is the human mind but it also is like any tool and we need to watch carefully that we keep it tuned and sharp!

So if we look at the drawing snip above, the item doing the charge, whether it is called converter, converter/ charger or only inverter, it is connected to the load center and batteries. I think we are all saying the same on that point.

When any spot is connected together like the battery, converter, and load center, they are considered the same electrically except for minor drops due to wiring resistance. All points in this yellow circle are considered the same electrically speaking. I think we can agree on that?

Where my nit picking is going is that we can fool ourselves if we think power can only go out from the converter output!
If we have a low battery like 10 volts and we go back to the converter output we will see ten volts at the output. If we are not clear on the nitpicking point, we can jump to the idea that the converter is only putting out 10 volts, so it must be bad!

NOT TRUE!
What we are seeing is not the converter output but the battery output!
So we may change out the converter and as we do we turn it on and we now see a good 13.5 volts at that point. Why the change? Did we do right and change the right part or did we just fool ourself?
We may have turned off the AC breaker feeding the converter while we did the converter change and now we have it turned on!

So was the converter really bad or was it as simple as the AC breaker was actually off but not tripped fully so that it showed off.
Just wasted a bunch of time, money and effort changing converters because we did not think of the converter output also being input from the batteries!

Yes, I will agree with the drawing that the output will only be output if we go inside the converter and get to the diodes, etc. but if we are testing at the points most of us will be on, power can be coming out of the converter or coming from the batteries!
I would mod the drawing to show as this?


One of the biggest follies on RV repair is when we take it to a shop, they find no power coming out of a board like on a frig and when they change that board all is fine, so we are told it was a bad board when it was really just a bad connection from corrosion not letting the board work but since the new board has new clean connections, it works!

Stay alert to save grief!

[creativepart]

If the battery has only 10v of output you won’t be able to know that if the RV is on shore power. Because the Converter will be outputting 14+v to charge the battery and to power all 12v loads. The battery voltage would read 14+v.

It is true that both the battery and the converter are powering the RV’s 12v loads at the same time.

Originally Posted by Eagle5

In general, the 12 VDC appliances run off the batteries, and the batteries are recharged (or kept charged) by the Power Center.

The key to the answer of this question is in that circled area in Richard’s post. It shows the Converter directly connected to the power center as well as the battery. If, as suggested previously, the battery powers the loads and the converter just replaces that charge as it’s used then the battery would be directly connected to the power center and the converter would be directed connected to the battery… not the power center.

[thompwil]

The 120vac to 12vdc converter is an output only device. It provides 12vdc to the system and charge to the batteries. The block diagram is quite clear on that. The purpose of block diagrams is to gain understanding of system overviews and flows. It is not a schematic.

[creativepart]

Sorry for the esoteric answer to the OP’s initial question: “Barring some broken part or lack of shore power can the trailer run the battery dead while hooked up”.

The simple answer to that is No.