Automotive applications, protecting from the elements

[Joel Rainville]

I've built little side marker circuits for my car. It simply consists of 10 ~2V LEDs with each its own current limiting resistor, and a main 2W 68R resistor in series with the whole thing so I can tap into the existing 12-14.4V volt directly.

[Edit : I really only needed 1K resistors for each LED to let ~12ma through each one, but I didn't have enough of those, so I used what I had plenty of, which was 300R resistors for each LED, and a big 2W 68R in series with the whole circuit so that I would still get ~12ma without the need to buy 1K resistors. Not that they cost much, I just didn't feel like taking the Mazda for a trip ]

As you can tell from the picture, I've flooded the whole circuit with a thick coat of epoxy glue. The underside where the copper traces are was sprayed with 3 coats of automotive clear lacquer.

In your opinion, should this be enough to keep the circuit working at least a couple of years? The 1986 Mazda 323 it's getting attached to probably won't last that long anyway... :lol: The whole thing is gonna be held up by 10 small LED holders mounted through holes drilled in the car's front fenders. The holders have little legs that'll spread open inside the car panel when the LEDs are inserted. I plan on superglueing a few of the LEDs inside the holders once I am happy with it.

I'm also hoping the epoxy will save the solder joints from breaking after being submitted to the constant vibrations... But will the epoxy itself hold up to it?

Any ideas on how I could make this even more weather/roadproof?

 

[Dean Huster]

It's been said that the three nastiest environments for electronics are in aerospace, undersea and automotive applications. For us, automotive applications are the most common, of course, and you have to contend with engine and exhaust heat, weather temperature extremes, automotive chemicals (water, oil, gasoline, tranny fluid, battery acid, power steering fluid, windshield washer fluid, rear end lubricants, brake fluid, etc.), extreme vibration and G-forces and road chemicals such as deicing salt and oceanside salt-laden air.

Any time I make wiring connections in an auto, I use uninsulated crimp connectors, crimp the connections and then solder the connections and cover them with heat shrinkable tubing, usually two layers. Automotive crimp connectors suck as they are mashed-together crimps and not the gas-tight crimps of the electronics industry. So the solder insures a good connection and a heck of a lot of mechanical stability against vibration and shock (mechanical).

If you look at the factory wiring for most autos at the lights, there's usually nothing more than a rubber boot around things. They rarely go to the trouble to encapsulate or conformal coat things. On the other hand, they're figuring a life expectancy of just a few years for the entire auto, so they don't worry about lights that last 100 years.

Dean

 

[Joel Rainville]

Hey Dean,

Thanks for your reply. It's installed now, and your comments confirm my findings while messing with my car's wiring. It looks pretty sloppy in general, there are loads of unused connectors exposed to the air, water, etc... So I expect my little epoxy-coated circuit to outlive the rest of the car. Maybe someone at the scrapyard will salvage my side markers in a few years and reuse them on another car! :lol: Who knows :lol:

 

[Russlk]

I don't know about red lights on the front 1/2 of the car. Is that legal?

 

[Joel Rainville]

I guess not. Although they are only used as turn indicators?... they are always off otherwise. I'll check and if I have to I'll replace them with amber ones. :?

Edit : Well, apparently I'm fine, in Canada at least, but we seem to follow guidelines published for the whole continent?... There are basic requirements that a car must meet with regards to headlights, flashers, tailigths, reflectors, fog lights, etc. Superfluous lighting of any color is fine as long as it doesn't exceed a luminous output limit. My little side markers would fall into the same category as those cheesy license plate neons if I understood the rules correctly.

A cop who'd want to give me a ticket would either have to measure the light output or based on visual inspection declare it as a potential danger to other drivers and vehicles. My little LEDs are far from producing enough light to blind other drivers, even at night... Looks like I'm clear. 8)

 

[hjl4]

Joel,

Speaking by experience, You can have retro reflective surfaces that are RED anywhere on your vehicle.

But if it considered a light, the front half of the vehicle can eminate white, green, yellow or amber only. That is the law in all of NOrth America according to Department of Transportation(D.O.T.)
On the rear half of the vehicle, RED only and white acceptable for license plate only, And rear backup lights when in reverse.
Also amber turn signals on rear is acceptable.
Technically, a cheesy purple light rear license plate trim, is illegal. D.O.T. regs.
But, then again,Its all at the discrepancy of the COP.
In other words , at least here in Mb, if you piss off the COP, he'll probably write you up.

BTW Looks good.

 

[Joel Rainville]

Yeah, I think you're right. That law stuff is hard to read :lol: I'll make them amber. Thanks for your input 8)

 

[Nigel Goodwin]

Yes, it's similar in the UK, a lot of it is down to the discrepancy of the police officer - basically if he can be bothered to fine you?.

It's become popular in the UK for idiots to drive round at night with their front fog lights ON, even when it's not foggy. This IS an offence, and if stopped you can be fined - I've got two friends who have been pulled up for this, the first one got a warning (nice cop 8) ), the second got a £60 fine!. I'd been warning the second one ever since the first one got stopped, but he wouldn't listen! - and neither would his brother, funnily enough one £60 fine cured both of them :lol:

Just remember something!, from a good few years ago!.

A guy I knew (who was a bit of a boy racer) had a Ford Capri, with four big spotlights on the front - he also hadn't paid his car tax (Road Fund Licence), which on a UK car is displayed in the windscreen. One night he's driving along this nice straight road, and a car coming the other way didn't dip their headlights - so he bangs all four spotlights ON. Next second blue flashing lights and a siren appear on the approaching car :cry:

Anyway, as he's no car tax he was certainly going to be prosecuted, so he quickly pulls up, jumps out of the car, and runs across to the Police car before they can get out. He yanks the door open, and shout's "what the *%£$** do you think you're doing, not dipping your headlights, do you know how to *&%$"£"**ing drive?" - the two Police officers apologised for their error, and drove off - without getting out of the car and checking his!.

Lucky bluff or what?.

 

[bloody-orc]

now that was wery lucky! (And funny as hell) :lol: :lol: :lol: :lol: :lol:

 

[Oznog]

The epoxy does greatly reduce the dissipation of the resistors. Unfortunately I can't say by how much, I'd expect by at least half.

Potting is a difficult decision because it creates new problems under some circumstances. Epoxy is stiff and expands at a different rate than the PCB when the temp changes. That can actually damage the board. Components also expand from their own heat (especially when potted) and in stiff material like epoxy this may create compressive forces.

 

[Joel Rainville]

Good points Oznog. I was worried about heat dissipation from the 2W resistor, since it seemed to heat quite a lot after a while, but that was when it was constantly powered on my breadboard. But since it's used only as a flashing turn signal on the car, it should be fine.

On the other hand, winter's freezing temperatures will probably destroy the potting and possibly the whole circuit in a few seasons. The epoxy I used is rated at -45C. Montreal winters get very close to that figure when the wind factor is added to the ambient temperature...