Crossposts deleted

I'm all for building stuff that does what you want it to. But when you
start talking 7 kw of power plus the potential to have life endangering
consequences I start to drag out my "safety first" speech.

Officious speech mode on
There must be a POSITIVE interlock to avoid backfeeding to the grid.
This interlock should satisfy BOTH the power company and the electrical
inspector. Period. No discussion. Positive in this case means you, your
neighbor, an electican, or your power company guy can all work it
correctly without fear of screwing up. It should also be physically
positive in the sense that it won't bend short of using a vice grip or
prybar. Your description says something about some vague "mechanical
device" to accomplish this. I don't buy it.
Officious speech mode off

Other than that, why are you going though all the hassle of relays, 9
volt batteries, etc when all you need to do is switch a couple of circuits?

I also think you will have some issues with trying to power the whole
house with the 7 kw generator. I see a few neighbors trying to run their
houses with 5 kw (granted these are a bit smaller), modern houses take a
LOT of power, if several things come on at once, you kill the generator.
But with proper power management, you should have enough power to run
a small window AC unit as well as the rest of the required items like
refrigerator, freezer, well, and a few lights.

Most folks just use the 60 amp (??) Square D transfer switch to have 4
circuits that can be cut over to the generator. $100 or so, UL listed,
NEC compliant, looks like a sub panel, takes an afternoon to install.
The even simpler route is to have the critical items (eg furnace)on
plugs, just move the plug from grid to generator as required.

Cheers.

Ignoramus25850 wrote:
I have been playing with using relays of various kinds, as well as
contactors. I already built 2 phase converters, and a remote switch,
for instance. I have a few 90A and 75A contactors and solid state
relays and mag starter buttons and whatnot.

Here's what I have been thinking about. I have a 7 kW Onan DJE
generator that I have for emergencies. I want it to power my entire
house in emergencies (I know that I cannot run AC and some other
devices while under generator power).

It is expensive and painful to install a transfer switch. I want to
make something easier and cheaper to power the house in case of
emergencies, while at the same time preventing backfeeding.

I can, instead of a transfer switch, build a system that includes a
contactor, a mag starter, and a relay that only closes the main
generator contactor when the main circuit breaker is in the OFF
position.

It would work something like this. There will be a mechanical device
and a switch such that the switch could be closed only when the main
breaker is off. When the main breaker is on, the switch could not be
closed.

There will be a DC circuit, powered by a 9V battery, that would be a
signal input to a solid state crydom relay. The power contacts of the
relay would be in series with the power from generator. When the relay
is closed (only when the mains breaker is open), and a START button is
pressed on the start/stop switch (like ones used for mag starters),
the main contactor would close. The STOP button interrupts input to
the contactor, causing it to open. Turning the little switch near the
main breaker off would also interrupt the circuit, opening the
contactor.

This seems to be a very fool proof system. I can build it in 30
minutes, except that I would need more time to fabricate a mechanical
switch opener/closer.

I would like to ask that those who can visualize what I am describing,
to comment on this plan. Thanks

i