She doesn't seem to realize that most of her grandkids are fairly liberal. I generally don't bring up politics with her, but I can never resist a joke. For reference, this is the link I posted on my sister's wall that inspired Grandma's response..
Tuesday, January 26, 2010
Eric, how's your car run without an ECU. I do own that Mercedes still...not a computer chip in the thing, except for the stereo.
|We've heard of electromagnetic pulses cutting steel in milliseconds, but apparently they can also be used to stop moving cars just as fast. The cannon demonstrated in the video here is still a prot...|
I don't understand your question. How does my car run without an ECU? It doesn't. My car needs an ecu. How COULD it? Possibly by ditching the FI system for carburation. There was a carburated civic in the early 80's I think. |
I suppose that was a profoundly poor way of asking "is it old enough to keep running on its own without an engine computer once started", and I've got the answer for that.
Would it be possible to add shielding around the vulnerable elements in your car to keep it from being effected by this?
You could shield your ECU to protect against an EMP, though idk how you'd test it and it'd always be a factor of how close you are to the source. However, he refers to this working by inducing a current in the wires to destroy the microprocessors. Maybe one of the EE guys can give a better idea of how to protect against that. Maybe diodes on each wire going in and out of your ECU? You'd probably need whatever protective measure you take on just about every component in your car, as there are usually a few other processors around the car, in the gauge cluster, ABS, radio, etc. |
If it was a priority, I'd go with an older car (60s, 70s) that doesn't rely on the electronics. If you just want to be prepped against nuclear or EMP bombs, an 80's or 90's car that keeps all the important electronics in the ECU would be sufficient, since you could easily keep a spare ECU in a shielded box. I've actually got a spare ECU, I'd just need to figure out what kind of shielding my box would need. |
You would also need to heavily shield everything connected electrically to the ECU.
Really? The frame of the car is connected electrically. |
Maybe it's not tight enough? If the wavelength of whatever is smaller than a gap it could squeeze through, I think?
What's not tight enough? |
You would essentially develop a separate grounding system that was shielded.
The big point is you can't just put a shield around the ECU and be good to go.
EMP is very very broad band, and high power. You basically can't have any gaps in a Faraday cage trying to protect against EMP.
So you're saying you can't have a connector going into a faraday cage? Even if your connector incorporated diodes, fuses, or breakers to prevent the excess current introduced by the EMP from traveling into the cage/ecu ? |
breakers/fuses/diodes are too slow for huge current spikes in general. Think of a lightning strike. This is something that would need to be taken into account in the design of the ECU. There are ways to make devices survive EMP, Andy knows more about them than I do.
If you have anything on the outside of the Faraday cage it will act essentially as an antenna, and then re-radiate what it received on the outside on the inside of the Faraday cage (to some extent). If you attach the ground to the Faraday cage while an EMP was going on you'd end up having the ground have a strong e-field potential across it and that would result in a strong potential difference across two grounds that were at different points in the cage. You might be able to have a single ground connection to the Faraday cage, but I dunno.
Even if the ECU survived, if you didn't protect everything other parts would be damaged. Your O2 sensor no longer works, you can't actuate the fuel injectors because they're damaged, what happens to the ignition system? Would spark plugs/plug wires/distributor be damaged in any way by this, a lot of that stuff is designed for high voltage, but require a pretty low current, so the plug wires might be damaged. Seems to me the only way to make it through an EMP for certain is a diesel that has mechanical everything. Then don't worry about shielding.
I wasn't anticipating grounding the faraday cage, I was expecting you'd want to insulate it from ground. Is that not the case? I was looking at it as insulation to block out the EMP, is that impossible? Are you actually trying to conduct it away instead?
Of the sensors I've dealt with, the O2 seems to be the most robust, though I don't actually know how it detects the presence of oxygen, I don't think there is any circuitry involved. My impression was that an EMP would induce enough current to destroy small integrated circuits. Fortunately in either case, the O2 sensor is one of the most optional sensors on a modern car. Currently, my car is running without one. However I'd be concerned with the more essential sensors that are used to less destructive environments such as the Throttle Position Sensor (TPS) or the Mass Air Flow Sensor (Some reason abbreviated MAP on my car), though I don't believe those contain any ICs either. I think I've heard of the fuel injectors being susceptible, but as they're nothing more than a solenoid, that also seems suspicious. As for the ignition system, my car still has a mechanical distributor, which would probably be fine, though a lot of new cars are going to electronic distributors (i forget what they call them) which would probably be toast. I think the amount of current required to damage the spark plug wires or spark plugs would probably be enough to physically melt the smaller wires in the car. At the range where the intensity is that great, I don't think there is anything you can do.
Damn, I'd love to take apart a car that had been EMPed, or within the EMP radius of a nuke. Anyone know how to calculate the emf intensity at x range from a y sized nuclear blast?
This website has some inconclusive info:
I'm thinking my current ideal approach would be to have spares of the necessary components in a shielded box. So far I'm thinking the definites include:
Low Amperage Fuses
IAT (Intake Air Temperature)
For your reference, in addition to the sensors on my car I listed above, all of you probably have 2 O2 sensors, a Knock Sensor, an Airbag Computer, an ABS computer, Some sort of chip in the gauge cluster, and possibly an EGT (Exhaust Gas Temperature Sensor) |
Keeping spares in a shielded container is an awesome idea. You'll be the only person around with transportation when SHTF.
"Overall it appears that your best bet for ensuring you have an operating vehicle after a high-altitude EMP burst is to have an older diesel car or truck. Make sure it’s sitting on good rubber tires and not parked next to a metal building."
Shame I'm trying to get rid of that Benz, almost.
Yeah but it helps if your old car works, also. |
A resistor could be destroyed by an EMP, it doesn't have to be an IC. Think of a resistor like a fairly high current fuse. If you really want to be with a vehicle after shtf you want mechanical systems, or have a replacement part for every essential electrical components (including wires).
The way you block EMP is to have a conductive surface (read Faraday cage) surrounding anything electrical that you want to protect.
Since the chassis in a vehicle is connected to the ground, you would need to disconnect everything from the chassis ground, and run a shielded (read wrapped in Faraday cage) ground wire going to that point. If you leave ground connections to the chassis you will still suffer the consequences of the EMP. If you just shielded the electrical components (ECU, MAP, etc), and left the wires unshielded you would still have the same problem as if you didn't bother doing anything.
How much current do you really expect the EMP to induce if you're frying resistors but not fuses? I think you're imagining an EMP of much greater intensity than I am, and I think we need to establish some kind of a reference field in order to draw any sort of conclusions. In either case, I'm talking about having spare parts, I've given up on the idea of shielding components within the car, I'm just trying to figure out what parts I'd need as spares and what to keep them in to determine the feasibility of that as an alternative. I'm relatively confident I could replace every essential electrical component in my car in under an hour (assuming I had spares, which save for 4 sensors, I do), assuming wires, transformers, relays, bulbs, electric motors, and fuses are all good.
I'm a bit confused about your description of the car electrical system. The car chassis is the ground, but it is not grounded. The rubber tires do a pretty good job of electrically insulating the car from the ground, which is why they aren't very susceptible to lightning strikes.
I found a site with some interesting info, though unfortunately it only gives the voltage intensity for SREMP (Source-Region ElectroMagnetic Pulse) but not HEMP, which is what I'm concerned with since SREMP looks impossible to protect against, and would be confined to the destructive range of a Nuclear blast. They also mention the military standards for shielding against EMP, which suggests that it is at least feasible to do it for protection at a certain, unknown range. Hopefully that info is readily available. |
I think you would fry fuses, just not quick enough to save an IC. Certainly the fuses will blow before the resistors do, but I think the resistors will still be destroyed, if not with in the Faraday cage. According to wikipedia http://en.wikipedia.org/wiki/Electromagnetic_pulse#Starfish_Prime a 20-30 kV/meter field would be expected. Assuming 30 kV/meter and a 1 cm long resistor the voltage across that resistor will be 300 V. Assuming these are .25 W resistors (average for the ones hobbiests use, not what you'll find on a PCB the ones on a PCB have a lower power rating, but are smaller in size) it would have to be a 360 kohm resistor to not blow. In other words fuses are toast, transformers are toast, relays are toast resistors are toast, some wiring is toast.
This article: http://www.fas.org/nuke/intro/nuke/emp.htm says closer to 100 kV/m. (From playing with the starfish test I figure there will be 100 kV/m @ 100 km or so)
A quick rule of thumb is the E field strength falls off with the square of the distance, so from the field strength spec from military shielding, and figure out how far from a nuclear device it would have to be to be safe.
"Ground" is generally a reference point with in a circuit unless it's labeled "earth ground." In a car the car chassis is a ground (not an earth ground). A car is not that far away from a Faraday cage, with modifications to it the car could be an effective Faraday cage, but you would need to remove anything connected to the chassis ground in order for that to work.
I've never heard (and couldn't find) statistics on the probability of getting struck by lightning in a car vs not in a car. I know cars are safer to be in when they're struck by lightning than anything else, not so much because of the tires but because of the cars body/chassis conducting the current around you rather than through you. ("Rubber tires provide zero safety from lightning. After all, lightning has traveled for miles through the sky: four or five inches of rubber is no insulation whatsoever" http://www.lightningsafety.com/nlsi_pls/vehicle_strike.html)
any one know what the field strength in a typical microwave oven? Then you could say if it survives 1s of microwaving you're good to go @ x distance
What determines x distance? |
The E field put out by the microwave is going to have strength E_mw if we suppose a nuke puts out field strength E_nuke and we know that the field strength falls off at the rate 1/(d^2). E_mw = E_nuke /(d^2), so d = sqrt( E_nuke / E_mw )