Magnets and ECU

[Sully008]

Does anyone know if having a large magnet near the ECU will cause any adverse effects? I have a pair of speakers that I'm going to install and the magnet will be fairly close to the ECU.

[SergntMac]

Good question...The EEC is inside a tin enclosure, so I can't really say how it may be affected. However, it is a PC board populated with micro-chips, just like any video card.

[Sully008]

Hmm... I guess I have 3 options in order of ease:

1. Put it in there and hope nothing happens. I had these in my XR without issues and it was near that ECU (EEC-IV).

2. Find a anti-magnetic shield and cover the driver.

3. Move the ECU.

[Breadfan]

Generally speaking you will have more issues with magnetic interference from a magnetic-based storage medium. Hard drives, tape drives, cassettes, etc, they use electromagnets to arrange items into bits - a magnetic field can scramble these causing data corruption.

Magnets also affect cathode ray tubes and can cause picture pull and discoloration if an unshielded speaker is placed near a color TV or monitor.

You will have less of an issue with printed circuits and IC's. But, large magnetic fields can do tricky things so I can't discount the possibility something could go wrong.

How close are we talking about here? My ECU is up under the dash/firewall area not too far from the pedal assembly. I can't see door speakers being close enough to cause a problem, and can't think of any area nearby you'd want to mount a large enough speaker to cause a problem.

Considering where hte ECU just let us know where you are mounting hte speakers and their size - I bet you'll be fine.

To be safe you can put some EM sheilding around the ECU an extra layer to be safe.

How expensive is good EM shielding? Well that all depends on if your local grocer is having a half-price sale on aluminum foil.

Yup, put some foil around the ECU and even ground it if you're worried (don't cover any vent holes though!) and it will provide extra sheilding for the ECU.

[Sully008]

Breadfan,

Thanks for your informative reply. The reason I'm asking is these speakers are designed to be mounted under the dash. The driver will be located near the firewall, close to the ECU. So... I'll go rummage through the kitchen drawer for some tin foil...

[MarauderMark]

How expensive is good EM shielding? Well that all depends on if your local grocer is having a half-price sale on aluminum foil.

Yup, put some foil around the ECU and even ground it if you're worried (don't cover any vent holes though!) and it will provide extra sheilding for the ECU.

Hmmm , i never knew that ..

[SergntMac]

the tin case I mentioned is fairly good at protecting the EEC, but I have no idea what to expect from a larger magnetic field.

[TheDonk]

I hate to bust the bubble here but, grounded foil may help protect the
electronics from RFI ( radio frequency interference ) but it won't shield
it from magnetic fields.
Mike

[TripleTransAm]

The thing to remember is that magnetic fields themselves shouldn't cause any problems. How many of us have had amplifier or receiver problems on home stereo systems by placing the speakers too close to the units? As mentioned, magnetic fields will cause problems with recordable media that uses magnetic coatings (ie. tapes, floppy disks, etc.).

The real problem with electronics is electromagnetic interference, and that's due to wild unexpected currents being induced in the circuitry of whatever piece of equipment we're worried about here. And the only way to induce currents in any circuitry is through a changing magnetic field. Since the item in question is a magnet with a fixed magnetic field, it's not going to induce any current in anything. I believe you have a greater chance of picking up interference from the alternator or ignition circuitry than anything else you can have operating in and/or on a motor vehicle (remember those old radios in cars with minimal shielding? whhhiiiiinnnnnnneeee.....)



The theory behind it all:

Take a length of wire and run it through an ammeter (measures current), making sure there is a complete circuit path.

Place a magnet beside this wire. Check the ammeter... no current seen.

Flip the magnet poles... check the ammeter: still no current but if you were quick you might have spotted a momentary blip of current!

Flip the magnet poles repeatedly and you will see an alternating current (ie. electrons flowing forward then backwards then forward again then... etc.etc.).

This is the concept behind an alternator, except that in the alternator, the magnet poles are in a fixed position and the wire is moved through the magnetic field, not vice versa.


The reverse phenomenon applies as well: by sending a current through the wire sitting in a magnetic field, the resulting magnetic field from the current can generate a repulsion (much like seeing sexy photos of RF Overlord) or attraction... this is the concept behind a speaker. So the larger the current "blip", the stronger the resulting magnetic field 'blast' from the wire. Now, how many times has a speaker cable managed to erase a tape? Or induced interference in cheap electronics?

Finally one thing to consider: these PCMs are designed to withstand a great deal of harsh climates, from temperature to humidity to vibration to interference. Heck, the casing itself is nothing more than an RF shield... open up a PCM and you'll see there's nothing preventing the manufacturer from having used a cheapo plastic case, yet the guts are encased in a thick metallic shell. I'm betting the alternating current going to a speaker in a car stereo system isn't going to overcome this protection and induce any stray interference in the PCM's circuit paths or components.


Cool image to imagine:
when working on the hybrid electric project for a Ford competition in 1992 (Ford Escort wagon converted to hybrid electric operation: rear wheel drive using electric motors, fed by a small small small methanol-operated generator up front), we had two very well insulated power feed cables running in parallel too close to each other, the length of the vehicle (to our 'accelerator' electronics, which were sitting up front at the time from the rear-mounted batteries). Whenever we slammed on the "gas" pedal, the cables would literally fling themselves away from each other, a result of the sudden magnetic impulse due to the 'sudden-on' rush of current on the cables. Then nothing... you only saw this 'jerk' happen during a change in current, worse when going from 0 to max current in one shot. Needless to say, our 'home-made' electronics caught all sorts of garbage from the induced magnetic impulses. Once the current flow was steady, no further violent interaction.

[Breadfan]

http://en.wikipedia.org/wiki/Electromagnetic_shielding

You are correct about RF, but EM can be shielded too and foil can do that as well.

The question is, and I'm a bit cloudy here, will the magnet act the same as EM, or do they cause different reactions to electricity...ya know?

[Breadfan]

The thing to remember ...

Great post! Interesting read!

[TripleTransAm]

Thanks... after just re-reading that huge mess, let me summarize:

A speaker magnet's field is static (unchanging). The only thing that might generate a magnetic field is the coils inside the speaker magnets. Will these speaker coils have enough current to generate an appreciable magnetic field? Hard to tell without trying, but doubtful. Will this field be strong enough to disrupt a PCM? Very doubtful.

I've never experienced any sort of PCM malfunction while driving under very high tension power utility lines. While the distances are of different magnitudes, I still doubt a speaker coil would spit out enough electromagnetic crap to disrupt anything electronic. If that was the case, I'd most likely be shielding the speaker itself before anything else... just imagine what it would be doing to the lesser-shielded equipment like radio, amplifier, climate control, power door lock modules, light modules, etc!

[Mad4Macs]

Geez! I had to put on my tin-foil hat just to read this thread! I only hope I got it on before the rest of my brain short circuited

[Marauderjack]

Sully,

Why not just take a magnet and stick it to the EEC box and check it out before you install the speaker??

I don't think you will have a problem but it pays to test it first!!

Marauderjack

[metroplex]

The solid state circuitry used on the PCM is most likely shielded or designed to withstand a certain EMI limit. Ford and other OEMs are very critical of EMI requirements. They spend thousands if not millions of dollars on EMI testing before a vehicle platform hits the showroom floor.

It may not be nuclear hardened (to withstand EMP) but it will work fine for 99.9% of our daily routine/application.

A large magnet should not have any effect on the PCM since the PCM does not use magnetic storage.