MACS Monthly Newsletter - 2017 - JAN2

AES Wave

motor with the other to the larger gage 12volt supply from the battery via a fusible link
wire capable of handling 50 or more amps. The
whole idea with relays has always been to control a high current circuit with a low current
circuit. How much low current flows through
a relay's coil can be a factor with either the relay's ability to operate the contacts or the life
of the driver circuit inside the module that is
controlling the relay. If, for example, you were
to decide that instead of investing the money in
purchasing a relay tester (i.e. a U-Activate relay
tester or Lisle Relay Test Jumper Kit from AES
Wave) that you would just use the common relay swap tactic. (Figure 3) That's fine if the relay

looking OE relay that has a winding with 320
ohms. Doing the simple math of Ohm's Law
(volts / resistance = amps) you'll see that the
module's built in driver circuit will now have to
handle 160 mA with that "known good" relay
instead of 37 mA that it was designed for. This
means you could now have two problems; the
one the vehicle came in with and the new one
you created by damaging a module!

Counter EMFs: "You knew the job was dangerous
when you took it F.R.E.D."
Inductance is a function of electronics that involves magnetic fields in coil windings referred
to as inductors. Inductance can be good or bad.
The good part (relay operation, solenoids, ignition coils, etc.) does the job we want
it to while the bad part involves voltage spikes that can be guilty of everything from burning up switch
and relay contacts to creating electrical interference (EMI) or ultimately
even zapping a "F.R.E.D." (Frustrating Ridiculous Electronic Device)
into oblivion. Inductance is, simply
put, the reaction caused by invisible
lines of magnetic flux (electromagFigure 3: A relay is a relay? Not hardly. Look at the various designs and schematic / pin call netic fields) as they collapse across
outs printed on each of these relays. Some are diode suppressed and some are resistor sup- a coil as that coil turns off. The vepressed. Some relays normally open, some normally closed, etc. Just because it fits the socket
is no sign you should use it! Testing a relay? With the electrical load turned on or a sub- hicle's battery or alternator made the
stitute load in place, measure for excessive voltage drop (over 0.1 volts) between pins 30 and electrical current to create the electro87a. Also, with circuit dead, measure between pins 85 and 86 with an ohmmeter. Compare to
specs or known good relay of same p/n. Relay testers such as the unit that allows you to easily magnetic field to begin with but the
get at the relay's terminals (top center) are helpful as are the relay activators (top right) that coil winding condensed them into
allow for an inductive amp clamp to measure the circuit's current draw. Also, keep in mind
that when you remove a relay for testing, always check for proper female terminal retention a small space. The phenomenon of
in the relay center / B.E.C.
the magnetic field collapsing upon
the windings of the coil is called selfyou are trying to substitute with a known good
inductance.
It is the first stage of creating a
one has a 'twin' in the relay center. If it doesn't,
then you might be tempted to plug one in from very large jump in voltage (step up transformer
your 'collection' of known good parts. Bad a.k.a. ignition coil) required to fire a spark plug.
idea unless you use a relay with a similar coil EVERYONE reading has felt the high voltage of
winding resistance. Too low of resistance and secondary ignition. HUGE ouch - very painful.
the driver circuit inside the controlling module Many if not most reading this have also felt the
can be damaged. Many modules are current primary ignition voltage on a bare hand. Slight
protected with fault detection (DTCs) but quite ouch - somewhat painful. Self-inductive volta few are not. That means you might pop in age spikes are used in every auto electronics
a Bosch style 5 pin relay with an internal coil application from the aforementioned primary
resistance of 75 ohms in place of the identical ignition coil winding to the 60 plus volts in dieJanuary 2017

MACS Service Reports

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2017