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Old 06-01-2017, 12:47 PM   #31
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Hi,

I believe you are really speaking of non-ionizing radiation. The terms EMR, EM, EMF, or variants include things like sunlight, which I find useful for various purposes.

So, given that you are far more concerned about non-ionizing radiation, I would like to firstly point out that the inverse square law is really to your advantage when considering potential designs.

Generally, the influence of non-ionizing radiation from domestic electrical systems (12 VDC or 120VAC) systems not explicitly designed to create a magnetic field (such as the wiring in your bus that turns on lights and motors and makes things hot) is extremely low.

I highly recommend you to take measurements from existing systems at nominal distances you would encounter in your vehicle.

One thing that truly puzzles me is the often repeated statement that exposure to magnetic fields greater than 2 milligauss is hazardous. I find this hard to believe, considering that the average field strength of the earth's magnetic field is ~400 milligauss at the surface where we sit.

I will conclude by stating that I have found it impossible to convince people otherwise who are themselves convinced that they become ill with exposure to artificial electromagnetic fields. No amount of structured measurements, physical proof or evidence convinces them otherwise.

Simply sitting outside in an open grassy field on a sunny day will expose you to more ionizing, non ionizing, and electromagnetic radiation than you would ever experience inside a metal vehicle like a school bus.
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Old 06-01-2017, 12:58 PM   #32
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Does the bus skin act like shielding? Concerning generators are usually mounted underneath the floor. Some people have even mounted their solar electronics under the floor and it certainly wouldn't be difficult to run the electrical system under the steel floor.

I was also going for the inductive cooktop, as a reported energy saver, until I started reading about possible problems. With that kind of strong EMF inside a metal shell, is there any reflection of those frequencies within the bus or does EMF just stop when it hits metal?
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Old 06-01-2017, 01:27 PM   #33
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so i looked up the asc 12/8 charge controller. They actual show a little diagram that lays out the working.

The design is very simple and very robust but also very inefficient.
It is unable to use a solar panel at its best performance point.
To get the best out of it you will need to use solar panels with a voltage output under load that is close to your battery voltage.
May be good for remote locations where reliability is the main concern but with limited solar panel space a mppt charge controller would be my choice.

a couple of smaller charge controllers have the benefit of less loss in case of partial shading.

Putting your charge controller close to the panels and buffering the output DC wires with an additional LC filter should take most of the emf away from the wires.

Twisting DC wires will help with the magnetic field radiated from he wires. In vehicles where often the chassis is used as the return line the magnetic fields can be very strange and unpredictable.

Later J
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Old 06-01-2017, 01:30 PM   #34
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fascinating, MarkyDee. i'm actually a bit of a science nerd so i'm aware of some of the physics but thank you for putting it all together so nicely. yes, part of my bus conversion objective is to eliminate the use of appliances and such that give me grief. going purely DC and eliminating an inverter and certain types of charge controllers was the biggest issue. i don't expect to eliminate every source of EMF, only reduce what i can and eliminate the big ticket items. the fridge is a big one, of course. also, good on the clarification of twisted pair versus other solutions! that one was really buggin me.

as to grounding: you said specifically to make sure all the conduit is grounded at only one point, ya, i gotcha on that one. if i shield my fridge, say in simple reflective insulation to help insulate that appliance EMF from radiating into the bus space as well as save energy by further insulating a fridge, i would assume that that insulation would need to be grounded in order to avoid similar circumstances as with the conduit correct? sounds like a mess. can i just screw a grounding wire into the insulation and into the metal bus body?
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Old 06-01-2017, 01:42 PM   #35
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looked up the mc wiring.

flexible in steel or aluminum. This is good from a fire and rodent or abbrasion issue but not so for EMI . conduit is the way to go. aluminum does not do anything for DC magnetic fields, it would somewhat for alternating magnetic fields.

interesting stuff that quiet zone..

twisting wires has as disadvantage that you will need a longer length so larger I2R losses ( heat) . twisting the wires will also reduce the cooling area of the wire so again even more heat. just use lager gauge wire.

later J
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Old 06-01-2017, 01:43 PM   #36
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I think the answer is "it depends".

A microwave oven is a specially designed metal box that has a high frequency electromagnetic generator inside of it. The electronic spectrum of microwaves is readily absorbed by hydrogen atoms, thus molecularly heating water and popping your popcorn. Stray microwaves generated could potentially reflect inside the cavity of a larger closed volume, but would be attenuated by the inverse square law.

An induction cooktop doesn't use the same principle. It uses an electrical winding alternating at high frequency to induce foucault currents into a corresponding chunk of ferromagnetic material (translated: a copper coil winding with a kilohertz frequency alternating current pulsing through it, and your cooking pot set on top of it)

Since the ferromagnetic metal is the sink for the magnetic field generated by the coil, the foucault currents disperse into the material and shed the energy as heat, making the pot hot.

If you operate the cooktop without the pot, the coil shuts down because it will overheat (nowhere for the energy to go)

During the transition of putting the pot onto the coil, the inverse square law (again) attenuates the electron field induced by the coil. By the time it could reach the metal skin of the vehicle, it is too weak to make a measurable difference. Obviously, if you pressed the inductive cooker up against the skin of the bus you'd have an exciting time.

None of these induction cooktop scenarios allow your body to "absorb" these fields because you are not ferromagnetic enough to get eddy currents induced into you.

I would possibly be more concerned about the microwave oven if it had leaky faraday shielding, but again the inverse square law would be helpful - face pressed against the oven would be bad, even standing a foot away from it would not be a big deal.







As a thought experiment, imagine standing inside a dark, perfectly sealed metal box or tube. In your hand is a flashlight. When you turn on the flashlight, does the box get increasingly bright and stay illuminated after turning on the light, or does the flashlight simply illuminate normally, and everything becomes dark after turning it off?

Assuming things act as they do in reality, what has happened is the electromagnetic radiation from the flashlight has absorbed into the walls of the metal box, and some into your body as heat, which is where the electromagnetic energy that was previously visible light has jostled the molecules that have intersected their path, increasing the molecules kinetic energy.

Consider now a larger flashlight, or possibly a microwave oven or induction cooktop. The same thing is happening, but with larger amounts of electromagnetic radiation. All result in the transfer of heat energy.

Clearly, certain frequencies of electromagnetic energy interact with matter differently (such as 2ghz microwave frequencies being specially attenuated by hydrogen atoms) but even those simply result in dielectric heating.

At the end of the day, any type of electromagnetic heating, caused by photon emission (your garden variety EMF), dielectric heating (molecular frictional heating), or ionizing radiation (from radioactive decay) will heat and denature molecules.

This denaturation can cook eggs, brown meat, and cause cancer. I think the simple answer is to not cook yourself.

Avoid intense dielectric heating by being smart about operating such devices, don't place your body parts on hot (high kinetic energy) pans, and avoid being made out of ferric materials affected by lorentz forces.


PS
Dielectric heating is the basis for area denial "pain rays" that the us military uses, for example. Same goes for Frey effects. If there was one particular concern I would have with electromagnetic effects exposure, it would be with microwave ovens. But my concern is small - you place yourself in far more potential harm doing things like driving down the highway in a vehicle.


Quote:
Originally Posted by Robin97396 View Post
Does the bus skin act like shielding? Concerning generators are usually mounted underneath the floor. Some people have even mounted their solar electronics under the floor and it certainly wouldn't be difficult to run the electrical system under the steel floor.

I was also going for the inductive cooktop, as a reported energy saver, until I started reading about possible problems. With that kind of strong EMF inside a metal shell, is there any reflection of those frequencies within the bus or does EMF just stop when it hits metal?
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Old 06-01-2017, 01:45 PM   #37
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Since the ASC charge controller is continuously shunting current to ground (shorting out the panels) you are creating a magnetic field spike every time that turns off and on. I am not worried at all about the field, but it does indicate to me that it is a simple and inefficient design. (and a little lazy, given what resources are available now for power control components)

Quote:
Originally Posted by joeblack5 View Post
so i looked up the asc 12/8 charge controller. They actual show a little diagram that lays out the working.

The design is very simple and very robust but also very inefficient.
It is unable to use a solar panel at its best performance point.
To get the best out of it you will need to use solar panels with a voltage output under load that is close to your battery voltage.
May be good for remote locations where reliability is the main concern but with limited solar panel space a mppt charge controller would be my choice.

a couple of smaller charge controllers have the benefit of less loss in case of partial shading.

Putting your charge controller close to the panels and buffering the output DC wires with an additional LC filter should take most of the emf away from the wires.

Twisting DC wires will help with the magnetic field radiated from he wires. In vehicles where often the chassis is used as the return line the magnetic fields can be very strange and unpredictable.

Later J
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Old 06-01-2017, 01:48 PM   #38
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and oh, i forgot,

the EMI as you mentioned emitted from solar controllers is only there because of the wires to the panels and to the batteries. proper filtering and shielding would reduce this quite a bit.
Indeed nobody pays attention to these things and the wires work then as antennae.
A proper set up would not have that much radiation to begin with.
later J
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Old 06-01-2017, 01:52 PM   #39
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I would add to this, that shielding properly should give some fractional improvement in system efficiency. Every stray electron that gets lost and creates an electromagnetic field is one that could have been used to help motivate your battery chemistry to retain it's charge separation.



Quote:
Originally Posted by joeblack5 View Post
and oh, i forgot,

the EMI as you mentioned emitted from solar controllers is only there because of the wires to the panels and to the batteries. proper filtering and shielding would reduce this quite a bit.
Indeed nobody pays attention to these things and the wires work then as antennae.
A proper set up would not have that much radiation to begin with.
later J
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Old 06-01-2017, 03:48 PM   #40
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Flashlight metaphore

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I think the answer is "it depends".
Thanks, that does make sense about the reflectivity of frequencies.

The fact that this does affect the OP says it affects us all to some degree, even though most of us are not sensitive to it.

No hope for appliances, and that's very intermittent use anyway. Marguaritas are not an every day thing anyway. From what you've said mounting electronics under the bus should attenuate the stray energy?
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