Our cabin recently was subjected to multiple days of no electricity during
to a bad storm taking out trees and power lines
I would like to set up a generator to run the following
1) well water pump 3/4 hp (120v)
2) refrigerator (120v)
3) freezer (120v)
4) hot water heater (240v)
5) stove (240v)
I would like to set it up so that is one appliance is drawing power,
everything else waits.
It would also be nice to set up the chain in the order listed above
It should also be noted that:
a) the stove is optional since there is a great fire pit where food can be
cooked and hot water heated in large enough quantities for hand and
dishwashing and sponge baths.
b) the hot water heater is big enough to hold enough water from one
heating cycle for all daily hand and dishwashing needs + couple of showers.
Which means that unless there are more than 2 people using the cabin, it
would only need to run once - possibly in the morning to start the day
c) the freezer only needs to run once every 2 days
d) the refrigerator only needs to run once a day if access is controlled,
otherwise twice a day will keep it cold enough
e) the well water pump only needs to run if water pressure has dropped
low enough to trigger it.
I already have an electric start generator to run everything at the same
But I would prefer not to load it to the gills at the same time,
So I'm looking at
1) a box that will make sure that when the generator is going, it will
sequentially feed the 5 devices and then shut off by itself when there is no
2) If the generator is going, then IF a higher priority device wants
power it can bump of a lower priority one. After which the bumped device
Any help and suggestions are appreciated
I think you're making a simple problem into a very complicated one.
The "box" you're seeking would need current/sensing, relays
on the various loads and a microprocessor to enforce your
rules. I know of no commercially available product,
but if it was availbable, I suspect no one would pay the price
for it for the above application.
You say the generator you have could run everything on the
list, but you don't want to fully load it. So, take the stove
which is a huge load out of the equation, since you say it's
optional. Now you can run everything else at far less than
the generator capacity. Or you can just work the breakers
manually on the loads like the rest of the world does.
Or are you a troll?
On 7/13/2011 3:54 PM, firstname.lastname@example.org wrote:
It's pretty simple. If he already has a generator that can handle the
entire load, but doesn't want to "load it to the gills at the same
time", just turn something off. The generator is only going to work as
hard as it has to, to keep up with the load. This is why the generator
specs tell how much fuel consumption @ full load, half load, etc.
Yeah, and the easy way to do this is to not cook after a shower. The
OP already has direct control of the biggest item which is the stove.
The rest seems pretty automatic already. He has indirect control of
the water pump, and indirect control over the fridge and freezer
(don't open the door).
The OP can just turn off any of these at the panel.
You can install relays to do this automatically, but it would cost
Is there any particular reason why it needs to be so complicated and
automagic? If the generator you have can handle all of the load and if
the loads have the duty cycle you described the generator will almost
never need to run at full load (and if it does so what?). If it does and
the generator labors why can't you simply turn off the range or water
heater for a while?
I imagine the water is the biggest load. Maybe at least 5 kw.
The stove depending on the elements will be less..
Each device would have to have a relay of required rating. Put the
heater priority first.
This could be a timer, 2 hours before sunrise, 2 hours before dinner.
You would need a computer or processor to do the rest.
Shutting the fridges off during defrost is hazardous, especially
Stupid units don't have adjustable setponts, user specified with
control panel, but a smart controller may loose programming with power
off. A lot of problems.. During power outage, manual may be the way to
Some years back we were having a problem with oil flow when both the
oil-fired water heater and oil-fired boiler were on at the same time.
We put a relay on the water heater circuit so that if the furnace was
on, the water heater would not run. I suppose that with five
appliances you could hook up a series of five relays in a way to give
a sequence of priorities. There's probably a micro-chip device that
can be programmed to do the same thing, although I've never heard of
It's pretty straight forward to put a lockout relay on two devices hat
already are controlled by low voltage circuits. What he wants is a
couple orders more complicated.
If ou really have a generator capable of running everything then you
have a pretty large generator. Stoves and electric hw heaters draw a
lot. So you don't really need to worry about it.
Microprocessor controllers are available for everything from elevators
to traffic signals to industrial washing machines...
Rigging one up to do what the OP wants would cost a lot of money,
require that every load is controlled via a relay panel and would have
to have sensors which could interface the generator to the controller
so it can know when to shed load to wind down when it is about to
As another reply said here, this is orders of magnitude more complex
than a few relays being interlocked via auxiliary control contacts...
My suggestion is to use some self control instead of sequencing,
prioritizing, and adding a lot of controls and relays. Don't use a lot of
hot water until the cooking is done. Let the freezer and fridge draw the
few amps they need as called for.
Price this setup first, Then look at how often it is really needed. They
with the money you'd spend on the control panel, buy a bottle of really good
bourbon, a couple of steaks, and relax with them. I bought another bottle
of Maker's Mark 46. That and a couple of rib-eyes makes more sense that the
once in dozen years power/generator problem.
Heating anything with resistive electric heat is an offense against
the laws of natures God. Since you didn't mention space heating I'll
assume that it is not electric. That raises the question of what it
is fueled by. If you want to put your home on an electricity diet
then put in an propane fueled hot water heater, a propane fueled
stove. You then have a propane adapter fitted to your generator so
that you no longer have to handle gasoline unless you run out of
propane. That would leave only the well pump, refrigerator, and
freezer to be powered by the generator. You will have reduced the
load on the generator considerably and made the generator much easier
If you really want to implement a priority sequential operating scheme
then you will need four relays with normally closed auxiliary
contacts. The control voltage for all of the relays comes through
each auxiliary contact in turn. As long as the the relays upstream of
the load in question are open then their auxiliary contact will be
closed and control current will be available to the relays down line
from each relays auxiliary contact. If the water pumps relay is
pulled in then the remaining loads will not have control current and
they will remain off. Once the water pressure reaches cut out then
that relay would relax thus closing it's auxiliary contact and
permitting the refrigerator to run. When both the water pump and the
refrigerator have reached their set points the control power would
reach the freezer's relay allowing the freezer to run until it is cold
enough and control current would then be passed along to the hot water
heater. When the hot water heater reaches it's upper limit then it's
relay would relax thus closing it's auxiliary contact and permitting
the stove to get power. If any higher priority load comes on it opens
the control power circuit to the lower priority loads and they drop
out until control power is again available because the relays for the
higher priority load is now open thus closing it's auxiliary contact
and passing control current along the chain to the lower priority
load. This scheme has the virtue of electrical simplicity but it does
mean that you will have to be careful in what load you are using so as
not to start a higher priority load when what you really want to run
at that moment is a lower priority load. Manually opening and closing
switch rated breakers is a much cheaper and somewhat more flexible way
to accomplish this but if you have to have automatic load selection
then that is the simplest means I know to accomplish that.
On Thu, 14 Jul 2011 13:00:02 -0700 (PDT), Tom Horne
I think you left out some CTs. I would have to see it on paper to be
able to follow your suggestion. If you get bored, I would like to see
a rough sketch of what you come up with. This doesn't seem to be as
"simple" as you suggest, but I could be wrong.
I hear there may be a few NASA engineers in need of work shortly.
If you have the budget I'm sure you can find someone to design the
system, write the software,find the parts, assemble the parts, and
It could be done with a computer controlling it or it could be done
electomechanically with a set of relays. Either way you will need to
build it. There is a small control processor that a lot of people
like to play around with if you want to take that path I believe you
can get some kits for it. Either solution will require you to get
some rather large contactors or some pretty big thyristors for most of
your loads. I think you will find it rather frustratng to have your
stove repeatedly turned off as you are trying to cook because other
things needed to come on. I would expect you to have a few hundred
hours as well as several hundred dollars into this before you are
That sound like it's worth it to you? Cause I think the opinion in
the group is that it's not worth it. But perhaps you view this as a
challenge and want to do it for the experience?
Everyone I know with a large generator just moderates their behavior
to manage the load. The minor difference in wear to your generator
from it occasionally working at a higher load is not going to be
You never clarified what specific generator you have?
# It could be done with a computer controlling it or it could be done
# electomechanically with a set of relays. Either way you will need to
# build it.
Not a problem
Have experience putting together computer controlled devices
# There is a small control processor that a lot of people
l# ike to play around with if you want to take that path I believe you
# can get some kits for it. Either solution will require you to get
# some rather large contactors or some pretty big thyristors for most of
# your loads.
Thank you for point out major parts needed
# I think you will find it rather frustratng to have your
# stove repeatedly turned off as you are trying to cook because other
# things needed to come on.
As pointed out in the original post, the stove is really a minor issue for 2
1) Minimal use in the summer to keep cabin cool
2) Fire pit set up to cook, and even bake most about anything
Stove to be set up for use as an (low-priority) alternate.
# I would expect you to have a few hundred
# hours as well as several hundred dollars into this before you are
# That sound like it's worth it to you? Cause I think the opinion in
# the group is that it's not worth it. But perhaps you view this as a
# challenge and want to do it for the experience?
Some of my "hare-brained" schemes turned into money-makers over the last 40+
Paid for all the others that were economic or technical duds.
Also trying to avoid re-inventing the wheel is such a produc is already on
# Everyone I know with a large generator just moderates their behavior
# to manage the load. The minor difference in wear to your generator
# from it occasionally working at a higher load is not going to be
# You never clarified what specific generator you have?
14Kw Generac, that I got in lieu of cash payment.
The cabin, which was built as all electric, will serve as a test bed.
And although the idea of converting to propane is a good one, it's only
going to happen as fridge, stove fail and need to be replaced.
Ultimately would like to move it to city house and then run it off the
natural gas line, as a SHTF backup
The thing about natural gas is that it rarely stops flowing when the power
goes out, and can be backed up with propane if needed.
But I don't want a generator that is running 24/7
I would like to have one that is set up to start when demand occurs, service
the demand, reset all the systems that need re-setting (load up water
pressure, heat up hot water tank, chill down freezer/fridge) and then shut
down and wait for next demand point.
One comment from an OP raised the issue that I do NOT need a linear decision
tree for usage.
In effect if the stove is in use, the only other critical system is water
So it would be interesting to have hot water tank go on ONLY after water
pump stops but not when pump or fridge/freezer is running.
And I definitely was thinking of running a processor to control the logic
and servicing the systems
Could even be run off the 12V battery for starting the generator.
Could even have a trigger to start the generator if the battery falls below
a certain level of charge.
I think the problem can be solved
What I would like to figure out is:
1) What are the possible solutions
2) What do I need to implement possible solutions
3) What are the final costs involved in such implementation
Ultimately I think my "solution" could be an "intelligent" transfer switch,
that not only separates the circuitry from the (utility) supply line, but
also allows for more efficient use of a smaller generator that does NOT
require a lot of manual control to operate.
You do realize that fuel consumption is greatly influenced by
the load don't you? For example, I doubt that you will save by
running two 2Kw loads for two hours, as opposed to running
one 4Kw load for one hour. In fact, I would not be surprised
to find you'd use MORE fuel. And certainly the generator is
going to have twice the number of hours and revolutions on it
because it's spinning at exactly the same speed for twice as
long. This sounds like assuming you would save on gas
by making two trips of 100 miles at 30mph instead of one
trip at 60mph.
Usually switching in and out loads is done to reduce
the size/cost of the generator needed. But you've said the
generator you have is capable of handling the entire load.
Given the loads, this generator must be larger than the typical
backup home generator. What is it's capacity?
On 7/15/2011 8:29 AM, email@example.com wrote:
Which "typical" do you mean? With the phenomena of McMansions and
everyone needing to drive trucks for personal transportation other
things have scaled up. It isn't at all unusual to have 50 kw gensets
installed for homes to make sure the hot tub and other essentials can be
operated in emergency conditions.
Funny how so many responders can't address the question and instead respond
in other ways...
Just goes to show the rule that 90% of the universe is "chaff" and it most
of life is about separating the wheat from the chaff...
In this case it's more of a question of making sure you understand
what you are getting into. It wasn't clear that you did. It's still
not completely clear. You do wish to build this?
If so narrow it down a bit. There are a lot of answers to your
general question of doing this. How do you wish to proceed? What
mix of digital verses electromechanical infrastructure do you want to
build for this? Do you wish to completely roll your own or is money
no object and assembling this from commercially available stuff an
option. The $10k another poster joked about is not totally outlandish
if you wish to buy a complete or near complete solution.
It's not a task that is beyond some of the members of this group but
even laying out a solution would probably require more time than
anyone is going to provide for free. Best you should expect from here
is some general suggestions on where to start looking. But there are
a number of direction you could head and we'd need to get an idea of
which way you want to go first.
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