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Old 04-19-2010, 01:50 PM
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meanderingthemaze meanderingthemaze is offline
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Default Shielding Passengers from EMF

I've been out campaigning for votes for my project (see signature) and talking to a lot of people about EVs and why they should be driving one. I thought I had heard just about all the anti-EV concerns, but then I met a few people who kept going on about the EMF radiation that you would be subjected to riding in an EV.

Well, I'm a pretty easy going person so I listened, and frankly I didn't have an answer because I had never really thought of that as being a health hazard. But who knows right?

Anyway, I found out that Plug-in America took the same tool the EPA uses to measure EMF and they put it in a Toyota RAV4 EV's passenger cabin. The needle barely moved when they ran the car. Then they put the same tool in an ICE car, and the needle was bouncing around all over the place. So, what they concluded was that Toyota had shielded their motor compartment well enough to block the EMF from going into the passenger compartment. But the ICE cars do not shield their alternators, so that explains the high EMF in the ICE passenger compartments.

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

Anyone Toyota engineers on this forum?

Thanks
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Old 04-19-2010, 02:23 PM
bliksem bliksem is offline
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Default Re: Shielding Passengers from EMF

The EMF from the ICE car most likely came from the coil and spark plugs and not from the alternator.
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Old 04-19-2010, 02:55 PM
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Default Re: Shielding Passengers from EMF

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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Old 04-19-2010, 03:22 PM
bliksem bliksem is offline
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Default Re: Shielding Passengers from EMF

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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Old 04-19-2010, 04:16 PM
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Default Re: Shielding Passengers from EMF

It's a detail, but are you guessing?
Are you concerned at all about the EMF from an EV motor?
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Old 04-19-2010, 04:24 PM
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Default Re: Shielding Passengers from EMF

Quote:
Originally Posted by meanderingthemaze View Post
...
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?


Quote:
Originally Posted by meanderingthemaze View Post
Anyone Toyota engineers on this forum?
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Last edited by Tesseract; 04-20-2010 at 03:00 AM. Reason: typo
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Old 04-19-2010, 04:33 PM
TigerNut TigerNut is offline
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Default Re: Shielding Passengers from EMF

Quote:
Originally Posted by bliksem View Post
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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Old 04-19-2010, 05:36 PM
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Default Re: Shielding Passengers from EMF

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

Quote:
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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Old 04-19-2010, 08:26 PM
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Default Re: Shielding Passengers from EMF

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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Old 04-20-2010, 04:04 AM
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Default Re: Shielding Passengers from EMF

Quote:
Originally Posted by meanderingthemaze View Post
@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.


Quote:
Originally Posted by meanderingthemaze View Post
...
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.

Quote:
Originally Posted by meanderingthemaze View Post
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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