# Shielding Passengers from EMF



## bliksem (Aug 3, 2009)

The EMF from the ICE car most likely came from the coil and spark plugs and not from the alternator.


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## meanderingthemaze (Jan 25, 2010)

What are you basing that on, high v. low voltage?

Are you suggesting that the motor does not produce enough EMF to register on a measuring device?


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## bliksem (Aug 3, 2009)

I am suggesting that the alternator in the ICE car, does not produce enough EMF to register on a measuring device.


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## meanderingthemaze (Jan 25, 2010)

It's a detail, but are you guessing? 
Are you concerned at all about the EMF from an EV motor?


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## Tesseract (Sep 27, 2008)

meanderingthemaze said:


> ...
> So the point of this post is to ask about what any of you are doing to shield EMF, or what can be done?


The two major things to consider are whether the controller enclosure a sealed metal box or is it installed in one and that the positive and negative battery cables are strapped together over their entire loop from pack to controller. Additionally, electrostatic shielding (like "coax") of the cables from the controller to the motor can be helpful.

The magnetic flux in the motor itself is contained within a closed path.

The brushes can be a significant source of EMI; a finer mesh metal screen than stock pretty much eliminates that.

For the people that are concerned about such things to the point of not wanting to drive an EV, well, there probably isn't much helping them. Maybe suggest they wear their tin foil hats while driving?




meanderingthemaze said:


> Anyone Toyota engineers on this forum?


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## TigerNut (Dec 18, 2009)

bliksem said:


> I am suggesting that the alternator in the ICE car, does not produce enough EMF to register on a measuring device.


If the brushes in an alternator are near the end of their useful life, then you can usually hear that as a whine in the car stereo output - it will go up and down with engine RPM. If one of the diodes is toast it may also cause a similar effect.


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## meanderingthemaze (Jan 25, 2010)

@tesseract  (was that confusion over the typo, or the question???)



> For the people that are concerned about such things to the point of not wanting to drive an EV, well, there probably isn't much helping them. Maybe suggest they wear their tin foil hats while driving?


Perhaps you are right, but actually I did talk a couple people out of that fear. 

There are other reasons for shielding too, like interference. But I am guessing that it's not a big deal since I don't hear many EV drivers complaining about static in their radio. 

Your answer is a little above my head. Are you saying that the controller is the main thing that needs to be shielded to prevent "leakage" of interference or EMF? Also, since current is running through the battery cables, would those have to be shielded as well?

Also, AC motors wouldn't have the brush issue right?


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## dtbaker (Jan 5, 2008)

my understanding is that EMF strength dissipates rapidly with distance... I doubt the EMF from motor/controller would be measurable inside the cabin? The closer source would be the traction battery cables when they are pulling big amps; which can be minimized if they are not on the INSIDE of the cabin, and if you run the 'to' and 'from' cables next to each other to cancel.


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## Tesseract (Sep 27, 2008)

meanderingthemaze said:


> @tesseract  (was that confusion over the typo, or the question???)


It was more a comment on how extremely unlikely any engineer from an automotive OEM would dare to participate here; in particular, Toyota, given what a stellar job the engineers seem to have done there lately. 




meanderingthemaze said:


> ...
> Your answer is a little above my head. Are you saying that the controller is the main thing that needs to be shielded to prevent "leakage" of interference or EMF? Also, since current is running through the battery cables, would those have to be shielded as well?


I've explained this several times before but.... suffice it to say, there are two kinds of noise - magnetic and electrostatic - and minimizing them requires very different methods. 

Magnetic fields are produced wherever there are changing currents, like on the battery side of the controller. These fields will induce similar currents in any other _closed loops_ of wire. By routing the cables from the battery pack to the controller next to each other (even better is to twist them together) the magnetic fields produced by each conductor cancel out. So, the worst possible thing you can do when wiring up your EV is to run the battery cables on opposite sides of the vehicle (and for some reason that is exactly that people instinctively prefer doing... go figure).

Electrostatic fields are produced whenever there are changing voltages, and since a motor controller chops the voltage to the motor, that makes it an effective generator of electrostatic noise. This type of noise induces voltages in any _open stubs_ of wire, but only if the wire is in specific fractions of a wavelength (in particular, odd increments of 1/4 wavelength). Without getting too bogged down in the details, let's just say that the cables between the controller and the motor in a typical EV are way too short to be effective antennas (electrostatic fields are how radio waves propagate, btw) so you don't really need to worry about them.

The controller can be a significant emitter of both types of noise by virtue of the extremely rapid changes in both current and voltage that take place inside of it, in particular from the pulses of current drawn from the input capacitor by the switches, and the recovery current from the freewheeling diodes. Minimizing the loop area and length of these interconnections is critical for good performance as well as minimizing noise. 



meanderingthemaze said:


> Also, AC motors wouldn't have the brush issue right?


Correct, but as I've already mentioned, that is a relatively easy noise source to suppress.


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## meanderingthemaze (Jan 25, 2010)

tesseract, thanks so much and sorry for making you explain that again. This is part of the reason I think we need a resource that has this information more or less spelled out in a user friendly way, so that people like you don't have to repeat the same information over and over again. 



> It was more a comment on how extremely unlikely any engineer from an automotive OEM would dare to participate here; in particular, Toyota, given what a stellar job the engineers seem to have done there lately.


Fair enough 



> The controller can be a significant emitter of both types of noise by virtue of the extremely rapid changes in both current and voltage that take place inside of it, in particular from the pulses of current drawn from the input capacitor by the switches, and the recovery current from the freewheeling diodes. Minimizing the loop area and length of these interconnections is critical for good performance as well as minimizing noise.


So a reputable controller like Curtis should be engineered well and take this into consideration?


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## Qer (May 7, 2008)

meanderingthemaze said:


> So a reputable controller like Curtis should be engineered well and take this into consideration?


Ehm... Curtis makes analogue controllers that originally were designed to handle low voltage and modest performance in fork lifts but scaled it up to higher voltage to be able to run an EV at decent speed. I doubt they considered the finer details more than "Hey, it doesn't blow up, let's ship it!"...

See this link for more gruesome details:

http://www.zeva.com.au/tech/curtis/

However, despite this it still seems to manage to be pretty reliable. It is, however, not engineered well. Or rather, it would probably be considered engineered well in the ancient times it originates from (when a spiral track in a plastic disc were considered state of the art for distributing music and digital wrist watches were high tech), but today it's pretty much a living relic.


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## EVfun (Mar 14, 2010)

I think you should put 2 turns of negative traction pack cable under the passenger seat and 2 turns of positive traction pack cable in the backrest of passenger seat. It's unlikely any passenger will be exposed to EMF as the high voltage wiring inside the vehicle should scare them away


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## meanderingthemaze (Jan 25, 2010)

EVfun said:


> I think you should put 2 turns of negative traction pack cable under the passenger seat and 2 turns of positive traction pack cable in the backrest of passenger seat. It's unlikely any passenger will be exposed to EMF as the high voltage wiring inside the vehicle should scare them away


lol.......


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## meanderingthemaze (Jan 25, 2010)

Qer said:


> Ehm... Curtis makes analogue controllers that originally were designed to handle low voltage and modest performance in fork lifts but scaled it up to higher voltage to be able to run an EV at decent speed. I doubt they considered the finer details more than "Hey, it doesn't blow up, let's ship it!"...
> 
> See this link for more gruesome details:
> 
> ...


OK, well, would you recommend any other AC controllers that would substitute?
Here's the proposed conversion:
1969 Datsun L521 Pickup
HPEVS' AC-50 Drive System w/ Curtis 1238-75
108V Pack Voltage (18x6V Lead-Acid)
Est. final weight: 3000-3500lbs (depending on the batteries used, ie: size and AH)


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## EVfun (Mar 14, 2010)

I think their AC motor controller are a couple of decades newer in design. There are not that many of them are in running EVs yet. The only reason there are just a few in on-road EVs is that they just recently became available. I wouldn't lump them in with the 1221 and 1231 series controller designs. 

It is worth noting that the slower switching of the Curtis also tends to lower the EMF they produce (but works the FETs harder.) I wouldn't really worry much about the EMF because exposure time is low, we are out of our cars a lot more hours than in them.


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## piotrsko (Dec 9, 2007)

tessaract always does a nice job of explaining stuff.

realize you should be within a modified FARADAY cage and most of your EMF radiating junk will be outside this cage (think lightning strikes on cars).

most of the guys complaining about radios were AM listeners, which has it's own set of problems.

If you use a cell phone you have potentially more exposure.

might need to use aluminum foil gloves also to go with the hats


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## Qer (May 7, 2008)

EVfun said:


> I think their AC motor controller are a couple of decades newer in design.


Ah, yep. It wasn't obvious from the thread it was exclusively AC and since most EVers use DC I thought we were talking Curtis 1231C or similar.

I wonder if it's even possible to do an all analogue AC controller suitable for EV's. It sure wouldn't be very practical though.


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## Duncan (Dec 8, 2008)

Hi Meandering

At the risk of offending you by making this too simple

We are exposed to high frequency electromagnetic waves all of the time
There are called "light"

The "ability to do harm" changes with the frequency

Gamma rays are nasty!

Below a certain wavelength they are "ionizing radiation"
This means that they have the ability to rip an electron loose from a molecule
This can lead to damage

Above that wavelength they have too little energy to do this 

Anything from your motor or controller is way, way, longer wavelength

And contains much much less energy than light

You can get damage from lower energy wavelengths by heating - think of a microwave or a large radar
The damage is caused by heat buildup

It is difficult to make enough energy go that way - no way its happening accidentally 

Think about your magnetic field - compare it to a fridge magnet - are the keys in your pocket pulling mysteriously?

No?

Then there is no problem

Exception
Some early cars were rumored to cause interference with the electronics in early pacemakers
So if you wear a pacemaker you may want to contact the manufacturer

I bet he will tell you that a modern device is shielded or cell phones would be making heart patients drop like flies

Overall - Don't worry about
It is not a problem

Anybody who is worried probably wears a tinfoil hat and prays to Martians
-


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## meanderingthemaze (Jan 25, 2010)

> At the risk of offending you by making this too simple


Don't worry, I like kindergarten explanations



> We are exposed to high frequency electromagnetic waves all of the time
> There are called "light"


L-i-g-h-t, I think I've heard of that.



> Anybody who is worried probably wears a tinfoil hat and prays to Martians


I am totally busted, you got me. Off to the corn fields to reunite with the mothership.

Really though, people tend to fear the unknown, plain and simple. It's usually a good survival device, but sometimes in an unintuitive world, things can get distorted. 

I think this perception is a problem, because as I stated in the first post, there are a lot of people who have this fear, or at least concern. It "sounds" plausible if you don't know much about it.

I am not only interested in building a car for myself, but in getting others to do it to. Think of how many backyard mechanics are out there wasting their time working on ICE's (no offense) when they could be working on a conversion. This is very much about the environment for me. If you choose to drive a car daily, it should be electric. In order to convince people that it is a better way to go, you have to overcome these roadblocks in people's heads.

Anyway, somehow we got off the technical topic, so I'll leave it there.

Thanks for the extra ammunition.

Best,


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## sunworksco (Sep 8, 2008)

3M manufactures several different types of EMF shielding materials.
I have even seen a clothe blanket.The image below is an EMF material for building walls,placed under the sheetrock board.
http://www.caplinq.com/blog/linqstat-is-cost-effective-way-to-shield-entire-house-from-rfiemi_167/

Regards,
John


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## meanderingthemaze (Jan 25, 2010)

Thanks John,

I wish they would explain how it works.


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## Tesseract (Sep 27, 2008)

meanderingthemaze said:


> Thanks John,
> 
> I wish they would explain how it works.


By being electrically conductive!

Go look up "Faraday cage"... that will explain a lot.


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## EVfun (Mar 14, 2010)

From the link:
"LINQSTAT Volume-Conductive Film is a carbon-filled polyolefin. To the layman, this means that it is a plastic that is filled with carbon powder."

Carbon is conductive. They made plastic sheeting conductive like tinfoil. We joke about tinfoil hats, but it really does provide EMF shielding (if your wrap your whole head ).

P.S. - looks like we are reading down the list at almost the same time this morning Tesseract


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## sunworksco (Sep 8, 2008)

I have seen another 3M blanket that had small shards of copper,aluminum and other conductive materials.
Regards,
John


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## meanderingthemaze (Jan 25, 2010)

So the conductive materials absorb the radiation because it offers a path to follow? Grounding it out in a manner of speaking? Perhaps it's beyond the scope of a forum explanation, it's been a long time since physics and I'm feeling not much smarter than a 5th grader these days.


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## PTCruisin (Nov 19, 2009)

meanderingthemaze said:


> So the conductive materials absorb the radiation because it offers a path to follow? Grounding it out in a manner of speaking? Perhaps it's beyond the scope of a forum explanation, it's been a long time since physics and I'm feeling not much smarter than a 5th grader these days.


A conductor is much like a mirror with regards to EM radiation. The radiated electric and magnetic fields set up time-varying currents in a conductor, causing the conductor to re-radiate (reflect) the fields back out into free space. The conductor does not have to be solid. If the conducting material encloses a volume then no radiation will reach the enclosed volume. 

Carbon is actually a semiconductor (think resistor) and it is used in radar absorbing material (RAM) for the purpose of reducing the strength of the fields through absorption. RAM is used on stealth aircraft to reduce the radar cross-section by absorbing much of the radiation before is has an opportunity to set up currents on the conducting skin of the aircraft. The density and distribution of the carbon within the RAM is critical to the success of the stealthiness. Too much carbon will behave more like a conductor and too little carbon will allow reflections from the aircraft skin.

I think the only danger with EM radiation and EVs is UV exposure (sunburn).


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## meanderingthemaze (Jan 25, 2010)

OK, that's a good explanation. Thanks


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