Powering a 12 volt fridge and battery

[Ed Harris]

I am reading this whole thing and a few things occur to me.

Most of the time when talking about surge or transient voltage I think we are referring to the input or 120VAC side of the converter.
Transients here could cause problems in the converter and as a result at the 12vdc output of the converter as well.

When there are voltage swings in the 12vdc side the battery certainly acts to help filter or absorb these mostly and therefore helps provide protection on the 12vdc side of the converter.

I am guessing when the question was asked about the battery helping to protect the system this is really what was being asked?

It is very common in 12vdc applications to use a large battery to help provide filtering from a noisy power supply and the battery is very effective in that role.

I suspect that when there is a load on the 12vdc side (like when running the fridge) and the battery is being charged too(like from the T.V) that the output side of the converter is isolated anyway from the rest of the converter.
Diodes in the converter output would prevent current from flowing back and causing problems just as they always would when using other forms of battery charging when the converter is powered.

I can compare it directly to running a genset or Solar charging.Each is charging the battery and not bothering the converter.

As for the fuses in the distribution panel,there are different ways they can be connected and for the life of me I understannd some of them like I understand the convention of using the Black wire as the Positive connection.......not at all.

In my new Scamp I discovered that the battery is just connected to the whole trailer thru one of the fused output circuits of the converter.
This makes no sense to me at all and when I asked Scamp to explain it to me,they could not. "It is just how we do it" thats all.

I figured this out when trying to determine which fuses controlled what loads and I could not disconnect one of the circuits even with the fuse out and discovered this is the one the battery is connected to.

This also tells me that the converter in this Scamp can have no actual charging circuit at all but that it just charges depending on the load throughout the entire trailer and the status of the battery.

I am astounded by the lack of science involved here and I have to wonder how many of us have trailers wired this way and don't know?

Anyway there is much to consider here if we want to understand it but the bottem line I think is that these 12vdc systems are just as resilient as the condition of the battery lets them be.

[Byron Kinnaman]

I am reading this whole thing and a few things occur to me.

Most of the time when talking about surge or transient voltage I think we are referring to the input or 120VAC side of the converter.
Transients here could cause problems in the converter and as a result at the 12vdc output of the converter as well.

When there are voltage swings in the 12vdc side the battery certainly acts to help filter or absorb these mostly and therefore helps provide protection on the 12vdc side of the converter.

I am guessing when the question was asked about the battery helping to protect the system this is really what was being asked?

It is very common in 12vdc applications to use a large battery to help provide filtering from a noisy power supply and the battery is very effective in that role.

I suspect that when there is a load on the 12vdc side (like when running the fridge) and the battery is being charged too(like from the T.V) that the output side of the converter is isolated anyway from the rest of the converter.
Diodes in the converter output would prevent current from flowing back and causing problems just as they always would when using other forms of battery charging when the converter is powered.

I can compare it directly to running a genset or Solar charging.Each is charging the battery and not bothering the converter.

As for the fuses in the distribution panel,there are different ways they can be connected and for the life of me I understannd some of them like I understand the convention of using the Black wire as the Positive connection.......not at all.

In my new Scamp I discovered that the battery is just connected to the whole trailer thru one of the fused output circuits of the converter.
This makes no sense to me at all and when I asked Scamp to explain it to me,they could not. "It is just how we do it" thats all.

I figured this out when trying to determine which fuses controlled what loads and I could not disconnect one of the circuits even with the fuse out and discovered this is the one the battery is connected to.

This also tells me that the converter in this Scamp can have no actual charging circuit at all but that it just charges depending on the load throughout the entire trailer and the status of the battery.

I am astounded by the lack of science involved here and I have to wonder how many of us have trailers wired this way and don't know?

Anyway there is much to consider here if we want to understand it but the bottem line I think is that these 12vdc systems are just as resilient as the condition of the battery lets them be.

Unless there's a mechanical relay in the converter to disconnect the output, then the output is connected all the time to the 12 Volt system.

I can only think of one case where you could get transients into the converter output. If remove the house battery from the trailer and have a poor connection to the battery in TV then transients are quite possible. Even with a relay and no other protection it would be possible to damage the output circuits of the converter. Like I said earlier not to worry. My guess is that they all meet SAE specifications. Since I believe this to be the case the rest is academic.

Side note: It's kind of fun to play with high voltage load dumps and watch is cause the smoke to be let out. But, then it's back to the drawing board to fix so it doesn't happen.

[Ed Harris]

Unless there's a mechanical relay in the converter to disconnect the output, then the output is connected all the time to the 12 Volt system.

I suppose you are correct.The relay would just open and thus disconnect when the converter is not powered.

I still wonder exactly what they are thinking by connecting the battery as I described in my Scamp?

I know with earlier converters there are just step down transformers and nothing else providing 12vdc and enough protection to keep things safe.
Although come to think of it in my Trillium 4500 there was a selector switch on the converter(transformer unit) to choose Battery or Shore Power or Off.