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main relay vs ignition switch while driving

well, mine have never lasted 20 years that's for sure. i'm 6 for 6 on

88-91 civics having this problem. i first encountered it when a vehicle was only 10 years old, and its previous owner had evidently had problems with it for some time prior to selling.

regarding solder, this is a soft alloy that operates at a highly elevated temperature relative to its melting point. expose it to thermal cycling [the relay runs hot you'll notice] and you have a problem just waiting to happen. the solution is to either use a different switching arrangement that doesn't generate as much heat [cycle] /or/ to use a different jointing method like spot welding or crimping. but the relay manufacturer should know all this. i still say this relay is a cheap and cheesy design. the circuit board is low quality and the relay internals are designed primarily to prevent intervention, not for serviceability [either kind]. i say mitsuba knew exactly what they were doing with this relay right from the start [relays are old technology and their problems are well known] and that they elected to go for what they knew would result in life limitation.

life limitation is nothing new. i once had a car clock that failed. on disassembly, i discovered a soft solder rivet had separated breaking the electrical supply. the interesting thing was, the rivet was held in tension by a spring! solder [lead] tends to creep over time, especially when kept warm. life limitation? you bet! there was no other practical explanation for the rivet/spring combo. a fuse would have protected against overload and the spring had no mechanical function. anyway, i soldered a wire in place instead and the clock worked again, just like a repaired relay.

Reply to
jim beam
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Something like that. The crux of the problem is that the solder is used to support the relays instead of the relays being cemented to the board and solder used to stabilize the connection. Beginners are taught not to use solder for strength or for carrying current, but I guess relay module mfrs aren't bound by the same code. They use solder for both simultaneously.

Mike

Reply to
Michael Pardee

Disclaimer - only my guess: Lead alloys seem to make better contact when carrying current, as seen in car batteries with broken internal connections. I realize battery terminals do the opposite because of powerful corrosive influences. Anyway, I suspect the current creates a hot spot that effectively welds a small spot in the connection and adjusts itself in size so that the connection stays slightly below the melting point. When the current stops and the spot cools it is prone to cracking, and something must change when the whole thing cools off even more.

As I said, just a guess.

Mike

Reply to
Michael Pardee

Yeah, the solder will fail in 8-10 years. But it's the electrical components that will last.

Spot welding or crimping would be expensive and not already in their machine assembly line. One solution might be to replace the relays with transistors, heat-sinks and some breathing holes.

I don't know why a spring is put into a [digital?] clock without a purpose. You sure the spring isn't a spring resistor?

Reply to
Burt

transistors always drop voltage - not necessarily what you want. and

30A rated devices aren't cheap.

it was an electric dial clock. no, the spring wasn't a resistor - it would have been rated at ~10+W for a milliamp application. a "real" resistor would have done the job better if that was what was required. besides, it was hooked onto the chassis at one end, and onto the tab retained by the lead rivet at the other - no reason to use a lead rivet when it could have been brass, copper, etc.

Reply to
jim beam

jim beam wrote in news:qJKdnUFO4qA7gZvYnZ2dnUVZ snipped-for-privacy@speakeasy.net:

They also are much more vulnerable to failure than a simple electromechanical relay. Lots of destructive spikes in an auto electrical system.

Maybe a bimetal thermal protection device? If too much current is drawn,the strip bends and breaks the electrical connection.

Reply to
Jim Yanik

news:qJKdnUFO4qA7gZvYnZ2dnUVZ snipped-for-privacy@speakeasy.net:

It's the current you want not the voltage. Transistors are proven.

Common, solid state devices have high marks for reliability than mechanical relays. A relay will have moving part that can produce arcing. Also, any spikes can be quashed by a shunt diode.

Reply to
Burt

news:qJKdnUFO4qA7gZvYnZ2dnUVZ snipped-for-privacy@speakeasy.net:

it's watts you want to look out for. watts = volts x amps. if the voltage drops across a p-n junction, and it does, about 0.6V, at 30A, that's 18W you're wasting [and heat you have to dissipate]. relays, for all their other faults, don't have that kind of problem.

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agreed, but they're not always the best solution. using silicon transistors on a 12V system is going to step down your voltage 5% each time it encounters a junction. that makes relays look attractive from an efficiency viewpoint.

Reply to
jim beam

In applications where zero voltage drop is important there are already ways to do this by selecting the appropriate transistor. A small voltage drop of (.2V or .6V) isn't enough to slow down the fuel pump.

The relays used in the main relays can cost more and will generate heat. So much heat that you can't put your fingers on it for more than a second. Eventually, it'll run so hot that the contacts will weld together.

Reply to
Burt

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