Electrical Question

[instantkevin]

mixing two different types of metal in an electrical circuit (i.e. aluminum and cooper) can be a bad thing. this is how heat is generated for electric circuits (i.e. electric space heaters). I know for a fact that if you run an electrical current through 2 different types of metals (normally wrapped around each other, for effieciency) you will genereate heat.

but if you are using the aluminum just for cosmetics (i.e. a dashboard), why would you be tryin to run a circuit though it? if you need to ground somethig out, ground it to something else.

assuming you are not intentionally running current through it, if you car is like most modern cars and has the battery and engine block grounded to the chassis of the car, then it would be an electrical hazard (if your aluminum is exposed and can be easily touched).

on modern cars, for this reason, there is no exposed part of the chassis in the passenger compartment (or any metal connected to it). you would have to isolate the metal from the chassis (rubber grommets, carpet, plastic screws, etc).

I'm no pro, I'm just telling you what I know.

[Earlsfat]

Originally Posted by instantkevin

if you are using the aluminum just for cosmetics (i.e. a dashboard), why would you be tryin to run a circuit though it? if you need to ground somethig out, ground it to something else.

Well, it's just going to be trim pieces, there will be no current anywhere near it, unless i try to do a back-lit chevy symbol... but still I'm not trying to run a circuit through it.

Originally Posted by instantkevin

assuming you are not intentionally running current through it, if you car is like most modern cars and has the battery and engine block grounded to the chassis of the car, then it would be an electrical hazard (if your aluminum is exposed and can be easily touched).

Well, the entire outside of the dash (leaning towards steel) will be covered in in adhesive, 1/16" foam, and then by vinyl. Then there will be trim aluminum pieces screwed into that. THEN, it will be bolted to the firewall, etc which is connected to the frame... I think that is what the other guy was talking about.

Originally Posted by instantkevin

on modern cars, for this reason, there is no exposed part of the chassis in the passenger compartment (or any metal connected to it). you would have to isolate the metal from the chassis (rubber grommets, carpet, plastic screws, etc). .

Well since maros are unibody, is the body part of the chassis for electrical purposes? Like if I put a bolt into the trans tunnel for my new console that I'm making out of steel, is the battery being grounded to the frame going to mess me up?

Hmmmm... I MAY just coat the inside with that plasticoat stuff you use on screwdrivers, etc. It's only like 3.99 a bottle, and 2 or 3 will handle that. But if I have a screw going through the trim aluminum piece, into the steel dash main piece which is bolted to the firewall, etc..... Problem???

Originally Posted by instantkevin

I'm no pro, I'm just telling you what I know.

I appreciate it all the same.

Thanks.

[Morley]

Originally Posted by wrightz28

Jim, last I checked, aluminum is not a conductor

This is going to come as quite a surprise to the aircraft industry.
There is no metal that won't conduct electricity, some just do it better than others and Aluminum is one of the better conductors out there.

[Morley]

Jim/Earl,

If you are going to make a dash/gauge panel out of aluminum you MUST allow it to touch ground. Otherwise you are going to wind up with possible RFI problems. Having electricity running through the gauges mounted in a metal panel that isn't grounded will induce a voltage charge in the panel and if it isn't grounded it won't be able to dissipate that charge.
It won't matter if the chassis is steel and the panel is aluminum as long as you have the parts electically bonded well and don't let them get wet.
I am an A&P mechanic by trade and so I work with dissimilar metals and their effects every day. The myth that aluminum and copper create heat when electricity is passed through them is just that, a myth. As long as the 2 metals are properly bonded to each other and kept dry there won't be a problem. Think of it this way, a plane is made up of mostly aluminum and the plane has removable panels on its skin (for inspections, disassembly, etc) and those panels are held on with steel screws and have been since we started making planes from aluminum and there haven't been any "heat" problems from that.

[wrightz28]

Originally Posted by Morley

This is going to come as quite a surprise to the aircraft industry.
There is no metal that won't conduct electricity, some just do it better than others and Aluminum is one of the better conductors out there.

Okay maybe this is the madness behind my reason, hear me out as I'll be free to admit I'm learning much every day about electric.

Aluminum, in most cases is used due to it's recycleable ability, and is easy to form but yet somewhat durable in a thin guage. Guage being the key word, if you had 2 strips of aluminum, both 1 foot long, one being a thin gauge and one being thick, which would pass the most current? Then thicker one right? Same apples to orange in wiring, a thicker gauge wire is used to handle more amperage right? So if aluminum is used most the time in a thin guage, it would be a poor(er) conductor.

And yeah,Kevin, that heat thing is pretty bunk. What could happen, is say the wiring is used in garage in the midwest. You have copper feed wire capped to a "cheap" light fixture using a different type metal (aluminum for sake of arguement). On the cap, no tape is used. So on one of those nice cool damp mornings, some condensation builds, then you would have a reaction between the 2 metals (wires). Same applied for plumbing, your not supposed to use a steel pipe clamp on a copper pipe. Some Fords have heater core problems from this very reason causing electrolisis (s/P?) of the coolant.

[Earlsfat]

Originally Posted by Morley

Jim/Earl,

If you are going to make a dash/gauge panel out of aluminum you MUST allow it to touch ground. Otherwise you are going to wind up with possible RFI problems. Having electricity running through the gauges mounted in a metal panel that isn't grounded will induce a voltage charge in the panel and if it isn't grounded it won't be able to dissipate that charge.
It won't matter if the chassis is steel and the panel is aluminum as long as you have the parts electically bonded well and don't let them get wet.

Ok. Let me get this straight... I am making an entire dash (and center console) out of steel (22 gauge?). It will be covered in naugahyde and have aluminum trim bolted to the steel panel probably with aluminum screws. ALL the wiring will be properly insulated and grounded to a solid ground... someplace. As far as the gauges, radio, power lock and window switches and other electrical components go, some will be resting/mounted on naugahyde and some (mostly the gauges) will be mounted into aluminum trim panels.

QUESTION: Am I going to have a problem?

(Morley, it sounds like you're saying the guy that made the original statement I was referring to was dead wrong?)

[Morley]

Originally Posted by Earlsfat

Ok. Let me get this straight... I am making an entire dash (and center console) out of steel (22 gauge?). It will be covered in naugahyde and have aluminum trim bolted to the steel panel probably with aluminum screws. ALL the wiring will be properly insulated and grounded to a solid ground... someplace. As far as the gauges, radio, power lock and window switches and other electrical components go, some will be resting/mounted on naugahyde and some (mostly the gauges) will be mounted into aluminum trim panels.

QUESTION: Am I going to have a problem?

(Morley, it sounds like you're saying the guy that made the original statement I was referring to was dead wrong?)

As long as the metal parts are electrically bonded to each other, then to ground, you'll be fine. Even the screws will suffice for an elecrtical bond between the aluminum trim and steel substructure you are planning on building.
Yes, the other response you got was wrong, there wouldn't be enough juice flowing through the framework to do anything to you. What it can do is cause RFI problems, like that nice alternator whine you get in the radio if wires aren't grounded properly and/or an isolation loop used in the power wire. But with fuel injection is becomes more than an annoying whine, it can fry the ECM (worst case) or cause erroneous sensor readings, shortened/lengthened injector pulse widths.all kinds of havoc.

[hotrod_chevyz]

Originally Posted by wrightz28

Jim, last I checked, aluminum is not a conductor

It is. Both thermal and electrical. In fact it has the capability to be a superconductor.

[Earlsfat]

THANK YOU FELLAS.

I'll post up my progress when I get around to actually doing something, right now I just can't decide on a layout.

[instantkevin]

I know for a fact that heat can be generated by electrical current being ran thru to dissimilar metals. otherwise, toaster, electrical heaters, or heated gloves wouldnt work. have a look:

http://home.howstuffworks.com/toaster1.htm
(these metals have been mixed into one piece, but same concept)

http://en.wikipedia.org/wiki/Thermoelectric_effect
(this talks mostly about converting heat to electricity, but note that it also works "vice versa").

essentially your problem is whether or not you plan on grounding anything to the aluminum (gauges, accessories). if you do, I wasnt 100% sure if there would be heat created (at the junction of where the two different metals meet). this is what i was making you aware of in my first post.

if you dont plan on grounding anything to the aluminum there shouldnt be a problem. If the metal never came into contact with the chassis or any other circuit, it would never cause a problem. (I dont see why you would want to ground anything to aluminum trim pieces anyway).

If I bolted a big chunk of metal to the metal of my floor board, there would be no reason to ground an accessory to that piece of metal instead of the actual floorboard/chassis.

you can have different types of metal (in a car or plane), but why intentionally run circuits through them, when you can just ground to what already exist.

all grounded objects (in a car) are attached to the same piece of metal. (i.e engine is grounded to chassis, stereo is grounded to chassis, everything grounded to chassis). why try to ground thru something else????

it doesnt make sense to me.

[Morley]

Originally Posted by instantkevin

why try to ground thru something else????

it doesnt make sense to me.

He isn't grounding through the dash and or pieces. He just needs to make sure those pieces are grounded. If you have something like an electrical gauge cluster in a metal box and each gauge runs to ground BUT the metal box isn't grounded it will pick up induced electrical current from the electricity passing through the gauges mounted in it. This induced voltage is where the RFI would come from.

About your toaster

Nichrome wire has a fairly high electrical resistance compared to something like copper wire, so even a short length of it has enough resistance to get quite hot.

Note the "high electrical resistance". Neither copper, steel or aluminum fall into this catagory, they are all very good conductors of electricity. They make household wiring from aluminum and a lot of aircraft wiring is aluminum. That wiring then goes to copper contacts either in switches, printed circuit boards, breaker panels, outlets...the list goes on.
The only real worry of aluminum and other metals coming in contact with each other is dissimilar metal corrosion. Which, if the metals are kept dry, won't be a problem.

[Morley]

If you are looking for ideas on what to make your dash out of, have a look here http://www.fibreglast.com/ They have colored carbon fiber/kevlar cloths and everything else you'd need for the dash build up.

[instantkevin]

Originally Posted by Morley

He isn't grounding through the dash and or pieces. ...This induced voltage is where the RFI would come from.

ok. that's logical. It sounded like you were recommending using the aluminum for a ground connection. which, im my mind, would allow for problems in an unusual circumstance (like a 9-volt battery being dropped on it, and shorting the gauges out or poppin a fuse... or possible electrical shock when a laptop is rested on the metal). which isnt life-threatening, but just bad circumstance.

So, in other words, ground the metal to prevent radio interference, but use a typical ground for any accessories . thats understandable and makes sense. thanks for clearing that up.