"Then we remembered that the relays were mounted to a fiberglass bulkhead
and the case needed to be grounded so we attached a ground from the relay
mounting base to ground bar.
Tried the gear.....now it worked...BUT it instantly fried the ground
wire on the relay small terimal......"
This means I have no idea how this circuit was wired, but it was not as
Lancair specified. The usual intermittent relay as provided by Lancair has
2 large terminals to transfer high amperage juice (motor power), an "S" terminal
and an "I" terminal. "S" stands for Switched and was to be supplied with
+12 VDC to the coil from the control circuit (thru selector switch and pressure
switch - and squat switch on the up side if desired). The ground side of
the relay coil is provided by the case. "I" stands for indicate and
supplies +12 VDC to an Indicator light from the contactor itself when 12
volts is present across the large terminals.
There should not have been a "ground" wire on either of the small
terminals. If you grounded the "I" terminal, then you have demonstrated
one oversight that Lancair made in their wiring diagram. When the contact
was made, current flowed thru the contactor and the "I" terminal straight to
ground. That ground wire was not rated for 50 or so amps, the level
of the circuit breaker protected circuit that runs the motor (using #8 wire, not
18, 20 or 22 - just big enough to light an indicator bulb).
If you understood this, you will see why some of us recommend
that small diodes be used to disallow any feedback to the other relay "I"
post (both diodes arrow head pointed to the indicator lamp) to allow itself
burn up rather than start a wire fire should the indicator wire be shorted (as
you found out). I actually have also added an inline fuse back at the
relays for additional safety.
Note that if the pump breaker is pulled and the up or down relay is
selected, the indicator light will not come on since there is no power present
at the contactor. This is the problem that can cause an intermittent relay
to destroy itself through over heating because aircraft electric work was being
done with the master switch on and the pump breaker pulled, but not the relay
breaker and the "pump selected" indicator light is not on..
Some recommend no change, but instead of pulling the pump breaker, pull the
relay breaker so no power relay can be selected, thus no power to the
pump. Of course, some have also wired other miscellaneous thigamajigs
(technical term of art) to that same breaker and so they don't want to pull it
to just disable the pump. These folks are likely to ruin their
intermittent use relays at some point. This results in the suggestion that
the relays be inline fused or go thru a breaker after
the pump breaker so that pulling the pump breaker removes all electricity from
all pump related circuits.
A continuous duty relay coil draws little power so that the contactor is
relatively weakly pulled in and held for long times without over heating (i.e.
master relay). An intermittent duty relay has a coil that draws more
power, snappily closes the more heavily sprung contactor and holds
it for short periods of time. This sort of coil will heat up if
held too long. The firm make and break of such a relay is to reduce arcing
and contact burning.
But, perhaps your original relays were like the continuous duty master
relay, a special case relay. This is where one of the large terminals is
marked "BAT" and is directly connected to the + terminal of the battery.
This relay is internally wired so that the BAT side is also connected to one
side of the coil. Thus, the single small terminal need only be grounded to
activate it. Of course, I couldn't explain why your wire burned if
such a relay was used.
Lancair was advised of these conditions many, many years ago.
Their only change was to add the diodes to the Legacy pump wiring diagram.
The rest is history as no two wiring diagram are alike if they exist at
all.