Our 50amp transfer unit only switches power from grid to generator after
30 seconds from when it sees power from the gen.

http://www.green-trust.org/wiki/inde...ransfer_Switch

Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

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

Ignoramus25850 wrote:

On Tue, 06 Sep 2005 11:24:10 -0400, Steve Spence wrote:
Our 50amp transfer unit only switches power from grid to generator after
30 seconds from when it sees power from the gen.

http://www.green-trust.org/wiki/inde...ransfer_Switch

What I am describing is a manual switch. ...

Yes. And?

You will definitely need to check w/ your local utility. They may have
requirements that any transfer switch you put in place be a listed
device.

I'm happy with my automatic switch.

Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

Ignoramus25850 wrote:
On Tue, 06 Sep 2005 11:24:10 -0400, Steve Spence wrote:

Our 50amp transfer unit only switches power from grid to generator after
30 seconds from when it sees power from the gen.

http://www.green-trust.org/wiki/inde...ransfer_Switch


What I am describing is a manual switch. The user would have to
perform the following steps manually:

1) Turn off the main breaker.
2) Turn on the mechanical switch for DC input circuit to the relay,
which becomes possible only if the main breaker is off.
3) Turn on the generator (could be done at any other time in this
sequence)
4) Press the START button on the start/stop switch.

At any time, if the interlocked mechanical switch is turned off, the
contactor would open and electrical power would no longer be supplied
to the house from the generator. The interlocked switch must be in the
off position for the main breaker to be turned on.

i


Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

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

"Ignoramus25850" wrote in message
...
On Tue, 06 Sep 2005 11:24:10 -0400, Steve Spence
wrote:
Our 50amp transfer unit only switches power from grid to generator after
30 seconds from when it sees power from the gen.


http://www.green-trust.org/wiki/inde...ransfer_Switch

What I am describing is a manual switch. The user would have to
perform the following steps manually:

1) Turn off the main breaker.
2) Turn on the mechanical switch for DC input circuit to the relay,
which becomes possible only if the main breaker is off.
3) Turn on the generator (could be done at any other time in this
sequence)
4) Press the START button on the start/stop switch.

At any time, if the interlocked mechanical switch is turned off, the
contactor would open and electrical power would no longer be supplied
to the house from the generator. The interlocked switch must be in the
off position for the main breaker to be turned on.

I caught your concept of a "manual transfer device".

Where I live there MUST be mechanical interlocks. That means if either
breaker is forced into the other position BOTH breakers change state at the
same time. I am talking about internal switching from one device to
another. Steps 1&2 would have to happen with one operation.

The utilities used to have a requirement for "visible blade disconnection" I
got into a situation where no one made a 4000 amp visible blade disconnect.
So they changed the spec to mechanical interlock.
I will bet that your contactors are not 'service rated'. Do you know the
fault current your generator is capable of? How about the serving utility?
10000 amps is pretty common I have seen places where special circuit
breakers were needed because the fault current was over 10k.

Call the local jurisdictional authorities and talk to them. I do not know of
a utility that would allow what you describe. I am familiar with the
utilities in 4 western states.



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