When there is a problem with the ignition switch
the car can stop even after the engine has ignited.
(I 've experienced that already!)
Can the same thing happen when the main relay has gone
I am afraid my Honda Accord has a bad main relay.
After (if!) the engine starts, is it dangerous to drive it?
Can the car stop suddenly even while running, or a bad
main relay basically affects only the ignition process?
Generally,ordinary body vibrations keep the main relay working once the
motor has started running.(and that the car's interior is usually cooler
once you have it running)
A bad relay affects the fuel pressure available;that's why the failure
moded is often "starts then immediately quits,then only cranks,no
startup,until the car sits for several minutes".
The motor uses up the stored fuel pressure,then starves and quits because
the fuel pump is not running,because the relay is not powering it.
The fuel injectors need a pressurized fuel supply rail.
come on matt, there's limits to that. vibrations at what frequency?
what g's? how much do you want to spend? besides, it's not vibration
that causes the solder to crack - it's thermal cycling.
bottom line, the relay /does/ suck, but then again, a sub $60 fix on a
what is typically a >10yr old car is not that bad a deal. how much do
you need to spend to get a domestic past the 10yr mark?
Don't be silly... I was responding to the assertion that the vibrations help to
keep the relay working right. That's just silly - if a relay is RELYING on
vibrations from the running car to work properly, it's either faulty, or a
really poor design to begin with.
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.
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.
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.
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.
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
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.
Actually,IIRC,the vibration stuff was Tegger's guess.
I believe it's that once the car starts and is running,the car interior
(and relay)is cool enough that the solder joints/relay parts have
contracted and make OK contact.I note that often after a 15 minute wait,a
balky starting motor runs,and only fails after another heat soak.
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