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  #1 (permalink)  
Old 11-15-2009, 03:31 PM
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Mutiplex Wiring Systems

Has anyone used one of these systems yet. Looks like it would save a lot of time and material.

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Old 11-15-2009, 04:58 PM
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For that kind of money it better wire itself.

Vince
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Old 11-15-2009, 07:32 PM
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I've seen the article in two different magazines now, and frankly I'm struggling with how it really saves any wiring. Assuming you use one power cell at each end of the car, the only wiring you save is the wires that go between the firewall and the trunk. On most cars, that's four wires for brake/turn signals/taillights plus one for the gas tank sender. Maybe one more for a trunk release. You still have to run several large-gauge power wires to the back, so where's the savings?

Also, think about your interior wiring. The articles claim that this concept simplifies wiring through the firewall. Really? Since the master cell can't do any power switching, that means that all the interior lights and power functions (power seats, power locks, stereo, etc) need to come from one of the two power cells. How is that better than the normal way where there are simply one switched and one unswitched bus that power these accessories, dome lights, etc?

Now, on top of that, if you have a bad circuit with conventional wiring, you lose that function, but only that function. If one of the power cells (or the data link to it) goes bad, you lose EVERYTHING controlled by that cell.

Finally, you can make a repair to conventional wiring on the road. How long does it take to get a replacement power cell?

Sorry, this seems like the answer to the question no one asked.
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Old 11-15-2009, 08:08 PM
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This thing is old technology borrowed from the petro chemical industry. We were installing things like this 15 years ago they were called "cable concentrators". They fell out of favor for the very reasons mentioned above. Save your money and do a traditional wiring job, you will be glad you did.

Vince
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Old 11-16-2009, 06:28 AM
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Quote:
Originally Posted by 302 Z28
This thing is old technology borrowed from the petro chemical industry. We were installing things like this 15 years ago they were called "cable concentrators". They fell out of favor for the very reasons mentioned above. Save your money and do a traditional wiring job, you will be glad you did.

Vince
Actually, the 1987 Cadillac Allante used a multiplex system such as this for the lights. In that case, the system had smarts that could detect a burned out bulb (such as a brake light, for example) and temporarily use a different bulb (say a taillight) for that function. It's interesting to note that GM dropped the system in the later cars. It's also interesting to note that Mercedes took a big hit in quality and customer satisfaction over the last few years because they loaded their cars with WAAAAY too much electronics. Brake by wire???
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Old 11-16-2009, 10:15 PM
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It's a PLC

Hey Ya'll, I read about this product in HR Mag. Although I can't vouch for this particular product, the concept is not new and its not out of favor either. PLC's are everywhere in industry. Manufacturing, material handling, packaging,any automated application you can imagine. This is a small version of a PLC. The reduction of wiring is only surpassed by the number of relays eliminated to control any given function. I think it is great to see it moving into automotive applications, its about time, its been used in industry for many years now. The program logic that you can write is nearly endless. The contact wear and tear on switches(inputs) is eliminated(less than a milliamp). You can use one switch input to control multiple functions(outputs). Switch inputs can be looked at in the program in either state(N.O./N.C.). Digital as well as Analog inputs can be programmed to control a given output device. It may be not everyones cup of tea, for for the tech savy folks it can be sweet. Just some simple examples, one brake light switch input(digital)could be used to turn on the brake lights and turn off the cruise control with only one set of contacts and no relay. A tach input(analog) could be used to control revs, a trans brake, nitrous solenoids, turbo or blower boost, water or methanol injection, etc. depending on which switch you pushed or what your programmed turn on levels are. Not to mention the remote key fob controls or the keypad control that can be mounted to the dash or console in a recharge pad that will control any function in the car. You could actually build a car with NO switches on the dash and control all functions with the keypad, then shut off the car, remove the keypad from the charger cradle and put it in you pocket, rendering the car totally disabled. This is good technology. The KISS folks won't like it. I'm not gonna run out and buy one today, but it may have its place in a future rod build for me. And I haven't even touched on the magnitude of control possible with this baby. Lets see, at full throttle position I want to disengage my cruise control, my A/C compressor, kick in my nitrous, close my waste gate, turn off my tailights, turn off lic plate light, open my electric cutouts, turn on my methanol/water injection and turn the stereo off so I can hear the engine, engage the rev limit and set the rpm I want the sequence to happen all done with one input and NO relays. The possibilities are only limited by your imagination. olnolan
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Old 11-17-2009, 07:04 AM
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The benefits of PLC control are undeniable for sure, but comparing this thing to a modern PLC just may be a bit of a stretch. My job before I retired from DuPont was an Electrical Designer and I got very familiar with PLC in my daily work. We used several different brands, Allen-Bradley SLC500's for small jobs and the Allen-Bradley PLC5 for larger jobs. We also used the very inexpensive Cutler Hammer PLC occasionally. While everything stated above is true the limiting factor in most PLC's is the I/O. In order to handle high amperage loads ( in this case automotive in the neighborhood of 20-40 amps) you either have to have a high amperage I/O card in the rack, or in the case of a safety standard that requires relay redundancy, a relay. I know it sounds counter productive to have a PLC operate relays, but industry still requires a certain amount of fail safe, especially in critical operations. I will not argue the use of relays in PLC application as there is not enough time or space to respond to it here. DuPont had an Electrical Engineering standard that is almost one hundred pages dealing with this very issue. Some engineers I worked with compared it to trying to understand the Book Of Revelations.

Where this Multiplex thing may come in handy is the analog and digital I/O. If it can be configured to use 4-20ma I/O(1-5vdc) , RTD (resistance) I/O, T/C (thermo couple) I/O it will survive IMHO. It has a tall hill to climb to become cost effective to replace current wiring systems and instrumentation measurement however.

Vince

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Old 11-17-2009, 08:27 AM
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I'm an aerospace engineer and we've been using mux wiring systems on space launch vehicles for decades. On a 100 ft tall booster, the savings in wiring is a BIG factor. On a car, not so much. Here's another example. How do you configure the dash illumination, high beam indicator, and interior lights? In a conventional system, the dome lights (for example) are powered by a simple fused feed to the bulb(s), with the ground side provided by the pin switches in the door jambs (or the headlight switch). With a mux system, the pin switches feed the master cell, and separate power wires need to be run from one of the power cells to the lights. If you use the forward power cell, that's a new wire that needs to penetrate the firewall. If you use the rear power cell, that's another wire that needs to run from the trunk forward. This doesn't save any copper or any connections, in my opinion.

Next, consider the high beam indicator. In a conventional system, a simple wire from the dimmer switch runs to the indicator light on the dash. In a mux system, this wire needs to come from the forward power cell, again requiring a new penetration through the firewall and more copper than the conventional design.

Finally, consider the dash illumination. On a conventional GM pull-style headlight switch, there is an internal connection that powers the rheostat in the switch. This, in turn feeds the dash illumination bulbs. Since there is no power provided the headlight switch in the mux system, you need to feed the dash illumination from one of the power cells. More copper and yet another new firewall penetration. Oh, and since the rheostat is wired internally to the headlight switch, you now need to modify the switch if you want to dim the dash lights (or you need to use a different rheostat).

Let's also consider gauge senders. Unless you plan to use a boatload of D-to-A and A-to-D converters, the wiring from the senders to each gauge must still be discrete point-to-point wiring that bypasses the mux system. These wires still need to penetrate the firewall, so once again, there is no savings.

If the car has EFI, well, ALL of those wires must bypass the mux system as well.

I stand by my original post. At best, the mux wiring provides no savings in either copper or number of connections. At worst it increases complexity and failure modes. Yes, there are a lot of other things you CAN do with the system if you use the programming capabilities of the mux system. Is it really worth all this complexity just to have your dome light slowly diim as opposed to just turning off when you close the door?
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Old 11-17-2009, 05:05 PM
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Sorry I asked

I really did not mean to stir this up since different people have strong feeling about this. On the other hand there seems to be a lot of information about the system out there.
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Old 11-17-2009, 05:20 PM
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Quote:
Originally Posted by JamesCowan
I really did not mean to stir this up since different people have strong feeling about this. On the other hand there seems to be a lot of information about the system out there.
Hey James, no one is stirred up, we are just having a civil informed discussion about this system. There are some highly educated people on this forum who are more than glad to contribute to the discussion.

Glad your here
Vince
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Old 11-17-2009, 05:58 PM
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Quote:
Originally Posted by 302 Z28
Hey James, no one is stirred up,
X2.

I just wanted to point out that the articles I've read (and the one in Auto Restorer by Larry Lyles was the worst) cleverly pick only the wiring examples that show the mux system in the best possible light (Yeah, I know, Duh!). They do not address the issues I've brought up.
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Old 11-18-2009, 06:57 PM
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Yes. Thats what I was meaning to say.
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