Surprising comment regarding motorhome colour.

[AdrianChen]

Understood! - Yes I guess the aly wont necessarily spring back to the original shape especialy if the core is damaged!

On the boats they would have the top damaged skin removed, new core put in (given the original might be crushed) and a new skin laid up. Painful, but not sure how you would get aly repaired.

 

[The Wino]

Is that including the doors?

I think they make them cheaply as they tend to fall off boeings!

 

[Minxy]

A Faraday cage!
Are you serious?

Your phone wont work.

Graydo

Agreed.

According to Carthago they are a Faraday cage, you just have to hold the phone out of the window

Incidentally my mobile phone signal drops significantly when the window blinds are closed , if I close the blinds on the skylights too I get no signal whatsoever.

Same for us in our Carthago with aluminium walls inside and out unless we're in a very strong signal area.

 

[stewartwebr]

Are we all getting a little carried away with regard to electromagnetic radiation, microwaves etc. The faraday cage protection which some manufacturers promote as part of their design concept is for protection of lightning strikes, nothing more.

Morelo:

Overview

Morelo motorhomes feature a Faraday cage construction, particularly in their roof, which uses an aluminum layer to provide protection against electrical fields, especially lightning strikes. This aluminum is integrated into the roof's GRP sandwich construction, channeling electrical charges through the vehicle's exterior, thus protecting occupants and electronics.

 

[mikash]

Depends why you want a Faraday Cage. An aluminium box with windows keeps out most electromagnetic noise, and lightning, but the windows will let in phone signals, including the 5G signals that everyone knows cause Covid . Look at a microwave oven door. That has a metal sheet perforated with small holes, and that's what is needed on the windows to keep out phone signals about 2.4GHz.

It's actually quite difficult to keep out all modern radio and wifi signals. We had a metal shipping container in the corner of a large warehouse, and it needed metal mesh seals on all the doors - the rubber seals leaked in too much. And you couldn't take in your phone, or your Bluetooth smart watch.

The latest low-energy buildings here in Finland have had a fair bit of problems with cell reception due to the new windows which sometimes block signals just as well as they do block heat losses. It's mostly the thin metal films used in the windows that are the problem. We have pretty stringent building energy requirements these days, for new buildings the U value for windows has to be below 1 (normal double pane windows are 2-3) which basically mandates triple glass construction with improved spectrally selective properties (opaque for NIR, transparent for visible light) which are often achieved with some sort of thin metal coating of one or more panes.
My parents for example had to replace a living room window with a special "antenna glass" window that has some sort of passive antenna-pattern-thingy laser etched to a metal film coating so it will collect cell signals and spread them into the room behind it while still retaining good U-value. So now they can actually use phones inside the apartment and not only on the balcony or next to an open window.

As for the van color, I think if you have an AC and the means to run it when needed, then the color becomes more of an energy consumption issue and less of a comfort issue. I recall reading about a 20% difference in AC energy consumption on a sunny day between a black and a white car somewhere, but don't quote me on that..
There are also paints these days that can be relatively dark (high absorption in the visible range) but designed to be very reflective in the IR range and hence significantly cooler than you'd guess based on the color. I'd definitely look into that to make your cool custom paintjob literally cooler

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[TheMobileWanderer]

As for the van color, I think if you have an AC and the means to run it when needed, then the color becomes more of an energy consumption issue and less of a comfort issue. I recall reading about a 20% difference in AC energy consumption on a sunny day between a black and a white car somewhere, but don't quote me on that..
There are also paints these days that can be relatively dark (high absorption in the visible range) but designed to be very reflective in the IR range and hence significantly cooler than you'd guess based on the color. I'd definitely look into that to make your cool custom paintjob literally cooler

That's helpful, thank you. I wouldn't have thought about any difference between visible range and IR range.

 

[TheMobileWanderer]

Most GRP laminates are way too resin rich which makes them brittle and liable to cracking and crazing and heavy of course, the strength of any composite is in the fibre not the resin so there should be just enough to hold the fibres together and anymore than that is just excess weight. GRP is lighter than aluminium but you need a thicker panel to get the strength so it ends up swings and roundabouts really, If you want a lightweight panel you just need some woven carbon fibre in there yes GRP is less likely to show dinks and is easier to repair. TheMobileWanderer if you look at Vario body construction you will see that the sides and the front/rear panels are all stuck together with GRP covering the joins and then blended and filled/painted.

Re colour, any shade will look a lot darker on a motorhome than it does on a car, and yes the black decor panels on the side of our get very hot compared to the white bodywork.

Useful info funflair. Thanks.
On the subject of GRP being heavier, or not, than aluminium, I'm reading about a few different grades of aluminium. 5083 or 6082 seem most suitable and might be more resistant to scratching or rippling than 3xxx or 4xxx grades?
(More research necessary)

 

[Rog NotJane]

Any holes in a Faraday cage can be modeled as wave guides. You get a decaying standing wave so the level of attenuation of a faraday cage is roughly proportional to twice the “size” of the aperture. That means if you put a hole 20cm into your sheet the cutoff frequency is about 20Ghz - easily high enough for mobile signal to pass though.

This also explains why autorouter’s shipping container wasn’t a great shipping container. Even those 1cm gaps round the doors let 1Ghz through. 4G band 20 is 800Mhz.

The big mistake Morelo’s marketing department are making is assuming that a hollow conductor is automatically a Faraday cage. I guess saying our vans are hollow conductors so any electric current passing through them is distributed across the surface and doesn’t interfere with any electric fields inside the van for example your nervous system when the van is struck by lightning… but don’t worry, the aperture size of the various openings in the van will allow cell phone propagation with minimal degradation isn’t quite so snappy as “it’s a Faraday cage, how cool is that”.

The MHF Physics Committee Christmas lectures this year will focus on Faraday cages and hollow conductors if anyone is interested.

I’d also paint the van whatever colour you like. White is a bit boring.

 

[BusyBuilder]

We have a Hymer in a bronze type colour (can't remember the name). Anyway when the sun comes out we can hear it expanding by the knocking sound. When we first heard it I was convinced that someone was knocking on the door. It goes on for quite a while, especially in the morning when the sun comes up.

 

[manners]

We have a Hymer in a bronze type colour (can't remember the name). Anyway when the sun comes out we can hear it expanding by the knocking sound. When we first heard it I was convinced that someone was knocking on the door. It goes on for quite a while, especially in the morning when the sun comes up.

That's normally our alarm in Spain in the winter, if it doesn't go off it's probably worth a lie in

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[TheMobileWanderer]

Any holes in a Faraday cage can be modeled as wave guides. You get a decaying standing wave so the level of attenuation of a faraday cage is roughly proportional to twice the “size” of the aperture. That means if you put a hole 20cm into your sheet the cutoff frequency is about 20Ghz - easily high enough for mobile signal to pass though.

This also explains why autorouter’s shipping container wasn’t a great shipping container. Even those 1cm gaps round the doors let 1Ghz through. 4G band 20 is 800Mhz.

The big mistake Morelo’s marketing department are making is assuming that a hollow conductor is automatically a Faraday cage. I guess saying our vans are hollow conductors so any electric current passing through them is distributed across the surface and doesn’t interfere with any electric fields inside the van for example your nervous system when the van is struck by lightning… but don’t worry, the aperture size of the various openings in the van will allow cell phone propagation with minimal degradation isn’t quite so snappy as “it’s a Faraday cage, how cool is that”.

The MHF Physics Committee Christmas lectures this year will focus on Faraday cages and hollow conductors if anyone is interested.

I’d also paint the van whatever colour you like. White is a bit boring.

I was thinking about a faraday cage only from the perspective of minimising potential effects of lightning strike. However with further reading, it seems, vans with pop-up roofs lose that protection. I wonder whether having several large skylights would, for similar reason, also compromise the faraday structure thus making it a non-starter?

 

[The Wino]

I was thinking about a faraday cage only from the perspective of minimising potential effects of lightning strike. However with further reading, it seems, vans with pop-up roofs lose that protection. I wonder whether having several large skylights would, for similar reason, also compromise the faraday structure thus making it a non-starter?

I think the pop up top is glass fibre so unless it has a metal mesh incorporated won't act as a fariday cage. It would be interesting to know the importance of having that protection as there are many motorhomes of various construction and I have never heard of anyone suffering injuries in a lightning strike. As the vehicle sits on rubber tyres that insulate it from earth I suspect it's less than the chance of many other of lifes hazards not least motorhomes not undergoing crash testing and being full of heavy objects that are often poorly secured. In the context of a self designed motorhome I think the crash resistance is very unlikely to be as good as a motorhome based on a van cab and a much higher risk than lightening

 

[TheMobileWanderer]

I think the pop up top is glass fibre so unless it has a metal mesh incorporated won't act as a fariday cage. It would be interesting to know the importance of having that protection as there are many motorhomes of various construction and I have never heard of anyone suffering injuries in a lightning strike. As the vehicle sits on rubber tyres that insulate it from earth I suspect it's less than the chance of many other of lifes hazards not least motorhomes not undergoing crash testing and being full of heavy objects that are often poorly secured. In the context of a self designed motorhome I think the crash resistance is very unlikely to be as good as a motorhome based on a van cab and a much higher risk than lightening

You may be correct, in terms of the comparison of different risks. I doubt that I could do much about crash testing except to rely on a IVECO daily chassis cab as the base vehicle.

I wonder how many motorhomers have been killed/seriously injured in a crash whilst driving their moho and what proportion of them were at fault. Most that I've seen are driven leisurely and mostly defensively.

On F. cages; it seemed a reasonable aim with minimal additional cost at time of build though I've no idea whether Carthago (where I first saw mention of such a cage), would actually be effective.

 

[matbic]

Your choice of colour is rather dark, it will get hot in the sun. We have a nice dark colour van at the moment it gets very hot - we are changing to a much lighter colour!

How about painting just the roof in white?

 

[TheMobileWanderer]

Your choice of colour is rather dark, it will get hot in the sun. We have a nice dark colour van at the moment it gets very hot - we are changing to a much lighter colour!

How about painting just the roof in white?

Thanks.
For clarity; post #13 is the green I was thinking of. I hadn't thought of doing the roof white. I've contacted axalta because, it seems, different colours have a different IR reflective value and that's not as simple as black = low and white = high. Awaiting response.

Interesting that there's more focus on IR reflection because it affects a/c power consumption and so, may reduce mileage in EVs.

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[The Wino]

Thanks.
For clarity; post #13 is the green I was thinking of. I hadn't thought of doing the roof white. I've contacted axalta because, it seems, different colours have a different IR reflective value and that's not as simple as black = low and white = high. Awaiting response.

Interesting that there's more focus on IR reflection because it affects a/c power consumption and so, may reduce mileage in EVs.

I'd be interested to see the evidence that IR reflection affects EV range presumably less IR absorption would make the battery pack cooler but once warmed up I'd be very surprised to see a significant ( say 5%) difference.
One thing to think about with the roof is the coverage with solar panels and type of panel. If they are spaced off the roof and cover most of it the colour it's painted underneath would make very little difference and it would probably cool the MH like safari roofs on older series landies.

 

[mikash]

I'd be interested to see the evidence that IR reflection affects EV range presumably less IR absorption would make the battery pack cooler but once warmed up I'd be very surprised to see a significant ( say 5%) difference.
One thing to think about with the roof is the coverage with solar panels and type of panel. If they are spaced off the roof and cover most of it the colour it's painted underneath would make very little difference and it would probably cool the MH like safari roofs on older series landies.

I would reckon the range gains are from less AC energy consumption primarily. Certainly not in the 5% ballpark, but 1-2% maybe.

I agree that if you have whole roof covered with solar (and also tend to park awning side south), the significance of paint color diminishes quite a bit.

 

[Rog NotJane]

I was thinking about a faraday cage only from the perspective of minimising potential effects of lightning strike. However with further reading, it seems, vans with pop-up roofs lose that protection. I wonder whether having several large skylights would, for similar reason, also compromise the faraday structure thus making it a non-starter?

Our fully GRP van has a lightning conductor fitted during build. I think that’s the way to go. Also, lightning strikes are vanishingly rare. You are much more likely to crash (I think, I have not checked the actual stats and I don’t know what sort of driver you are). Skylights will not compromise the van being a hollow conductor.

Either way, your van will never be (and Morellos are not despite the price) a faraday cage

 

[TheMobileWanderer]

I'd be interested to see the evidence that IR reflection affects EV range presumably less IR absorption would make the battery pack cooler but once warmed up I'd be very surprised to see a significant ( say 5%) difference.
One thing to think about with the roof is the coverage with solar panels and type of panel. If they are spaced off the roof and cover most of it the colour it's painted underneath would make very little difference and it would probably cool the MH like safari roofs on older series landies.

What I read on their website was that paints which absorb more IR, heat up more, require more use of aircon which drains batteries, hence lower range in an EV. Similar, I expect in higher usage of leisure batteries on moho.

My solar will be off roof on a rack and so should provide shade, which may reduce roof temp.

 

[The Wino]

What I read on their website was that paints which absorb more IR, heat up more, require more use of aircon which drains batteries, hence lower range in an EV. Similar, I expect in higher usage of leisure batteries on moho.

My solar will be off roof on a rack and so should provide shade, which may reduce roof temp.

Depends if you have hab aircon and how much time you spend where the vehicle is too hot compared to too cold! In the UK I suspect over a year there are probably more days when you need heat than cooling so a more IR absorbent paint could increase ev range as any heating requires battery use! The website of a company selling paint that has the advantage or reducing ir absorption will of course emphasise the positives and ignore negatives especially if it's a premium price!

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[TheMobileWanderer]

Our fully GRP van has a lightning conductor fitted during build. I think that’s the way to go. Also, lightning strikes are vanishingly rare. You are much more likely to crash (I think, I have not checked the actual stats and I don’t know what sort of driver you are). Skylights will not compromise the van being a hollow conductor.

Either way, your van will never be (and Morellos are not despite the price) a faraday cage

In case I'm confusing the matter by using the term, Faraday cage, I'll clarify.

Aircraft are designed such that they won't be affected by lightning strike. In a simulation of lightning strike, it was shown that a car isn't affected. That's as much as I was aiming for, not because I'm paranoid but because at time of build, it shouldn't be of much additional cost to achieve similar resistance to lightening as with a car.

Also, I want a smooth outer skin with no rippling, hence consideration of potentially 3mm aluminium.

 

[mikash]

Depends if you have hab aircon and how much time you spend where the vehicle is too hot compared to too cold! In the UK I suspect over a year there are probably more days when you need heat than cooling so a more IR absorbent paint could increase ev range as any heating requires battery use! The website of a company selling paint that has the advantage or reducing ir absorption will of course emphasise the positives and ignore negatives especially if it's a premium price!

Maybe, when there was significant incoming IR radiation available. Like a cool but sunny spring day. At other times, maybe not. High absorption equals high emissivity so if there was not much incoming IR to absorb, the car surface would radiate heat out faster than an IR reflective (low emissivity) surface would, so you'd be heating more, not less.

 

[BusyBuilder]

We don't worry about the van getting too hot as we live north of the wall.....sun ? whats that ? the only difference between winter and summer up here is ....the rain is slightly warmer.

 

[cyberyacht]

We see quite a few non white vans in Europe even in summer, mainly pvcs , the black ones look good but must get hot in the sun.

But they can save the weight of an oven by cooking their food on the panels.

 

[manners]

In case I'm confusing the matter by using the term, Faraday cage, I'll clarify.

Aircraft are designed such that they won't be affected by lightning strike. In a simulation of lightning strike, it was shown that a car isn't affected. That's as much as I was aiming for, not because I'm paranoid but because at time of build, it shouldn't be of much additional cost to achieve similar resistance to lightening as with a car.

Also, I want a smooth outer skin with no rippling, hence consideration of potentially 3mm aluminium.

I'm sure I've seen a video or photo of Carthago testing it with a simulated lightning strike.

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[Rog NotJane]

In case I'm confusing the matter by using the term, Faraday cage, I'll clarify.

Aircraft are designed such that they won't be affected by lightning strike. In a simulation of lightning strike, it was shown that a car isn't affected. That's as much as I was aiming for, not because I'm paranoid but because at time of build, it shouldn't be of much additional cost to achieve similar resistance to lightening as with a car.

You are confusing the term and over complicating the requirements. Aircraft are hollow conductors. That gives them protection against lighting strikes. They have different requirements since they’re flying through storms.

You don’t need, or want, your van (or an aeroplane) to be a faraday cage. You really just need a good path to earth from the highest point on your van to ground. That could be the body of the van or it could just be a good conducting strip.

I suggest you book in for the MHF Physics Committee Christmas lecture. It’s only four hours on the 25th starting at about 1pm.

 

[The Wino]

B

Maybe, when there was significant incoming IR radiation available. Like a cool but sunny spring day. At other times, maybe not. High absorption equals high emissivity so if there was not much incoming IR to absorb, the car surface would radiate heat out faster than an IR reflective (low emissivity) surface would, so you'd be heating more, not less.

Basically an IR reflective paint will act just the same as increasing insulation as I see it. The question is how much difference does the paint make per pound cost compared to increased insulation.

 

[TheMobileWanderer]

B

Basically an IR reflective paint will act just the same as increasing insulation as I see it. The question is how much difference does the paint make per pound cost compared to increased insulation.

Interesting point.
At first, I thought it would be cheaper to add more insulation, if necessary. Then I thought, to do that in an existing moho would be more difficult and more costly than doing it at the build stage. And then I recalled, there's a limit to the depth of walls and roof, in terms of skylight fittings etc. So I would max out on insulation and if heat became an issue later, then I could add an IR-reducing paint if it would have the desired impact and if I hadn't done it at build stage, when it would have been a cheaper job.

 

[Rog NotJane]

I think you’re worrying too much about a detail. Put this much effort into where to place the bog. Getting that wrong will cause you much more grief than the tiny difference in insulation or massively unlikely lightning damage you’re worrying about.

 

[funflair]

In case I'm confusing the matter by using the term, Faraday cage, I'll clarify.

Aircraft are designed such that they won't be affected by lightning strike. In a simulation of lightning strike, it was shown that a car isn't affected. That's as much as I was aiming for, not because I'm paranoid but because at time of build, it shouldn't be of much additional cost to achieve similar resistance to lightening as with a car.

Also, I want a smooth outer skin with no rippling, hence consideration of potentially 3mm aluminium.

With a 3mm aluminium skin you will have no payload left, take a tip or two from established manufacturers

With regards to outside colour it's not just the heating effect to bear in mind, assuming it's aluminium when the external face warms up it expands but the internal is unaffected so the wall becomes stressed and takes a slight bow of up to 5mm or more at the centre and the darker the exterior the more the bow, this needs to be taken into account when you construct the inside as essentially you are now building inside a box than can move.

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