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Old July 19th 19, 02:36 AM posted to,
Jeff Liebermann Jeff Liebermann is offline
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First recorded activity by DIYBanter: Jul 2007
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Default How the heck does a typical home transfer switch work?

On Thu, 18 Jul 2019 18:45:43 -0000 (UTC), "Arlen G. Holder"

Generac sent me the owners manual for my 09067-9 generator, which contains
exploded diagrams, for example, here's the exploded diagram of the 09067-9
Generator Control Panel:
And the wiring diagram for the 09067-9 generator itself:

The wiring diagram of the generator shows the (missing) controller,
with all the connections to the automatic transfer switch. Pg12 of
the manual, lower schematic, shows wires 23 and 194 going to the
transfer switch. Since the other end of these wires goes only to the
solenoid (relay) coil, I would presume that these should have 0V
across them when the transfer switch is on utility power, and 12VDC(?)
when it on generator power. Put an LED and resistor across both
solenoid coil terminals so you can see what's happening without
fumbling with a volts guesser.

Unfortunately, there's no schematic for the controller logic board
which runs the show. Near the controller logic board is SW1, which is
the "start/stop" switch. That should NOT activate the relay on the
transfer switch. This is the generator test switch which I previously
indicated was on all such autostart generators.

SW2 is labeled "Set Exercise Switch" which is something like a "test"
switch but also is not intended to test the transfer switch. There
should be something in the manual on how to use this switch. Here's a
video that might offer a clue on what I think is a similar generator:
"How To Set Exercise Time on Generac Air Cooled Generator Pre Nexus
Controller APSwrap"
There's quite a bit on how a proper test switch should operate:

This is a typical generator test which demonstrates proper operation:
"Home Generator Transfer Test"

Also on the schematic is the fuse F1 (15A), which appears to protect
the controller 12VDC battery line. Check this fuse if you have a good
12VDC battery, but no controller function. If this 15A fuse is
actually blown, you potentially have a high current short somewhere in
the generator on the 12VDC line. Be careful tracking this one down.

And here's the exploded view for the 79848A transfer switch:
And the wiring diagram for the 79848A transfer switch:

Remember, you have but one life to give for your backup power system.

Jeff Liebermann
150 Felker St #D
Santa Cruz CA 95060
Skype: JeffLiebermann AE6KS 831-336-2558