Generator Controller

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GAK

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Hello Friends,

I live in a small development of five houses with a shared well. The well only produces about five gallons a minute so we have it fill a 12,000 gallon cistern and then jet pumps to pressurize.

Now we are talking about adding a standby generator to keep things moving when power is out.

Installing a generac and transfer switch would be no problem at all, and I have installed a few. However I would like to have the generator controlled by the demand for water so it isn’t running continuously with no call for water and no load so it isn’t just sitting there running wasting propane.

To do this I can run a switch loop through a pressure switch to control the jet pump, and use a float for control of the well pump. Also I would like to maybe set up a minimum run time so as not to short cycle the generator if a couple people are showering or something.

Another option could be to have the generator run for like 15 minutes every hour then off for 45 minutes on for 15 off for 45 etc.

Is any of this possible with the generac transfer switch or some other brand? Does anybody have a better idea how to do this?
 
As operating rules-
Pressure, flow, or level switches start the generator. Probably should have a minimum on time for those so a short request event doesn't start the generator (maybe 5 seconds? 20 seconds?), that's a "delay-on-operate" relay (aka "plain old time delay relay").

Ensure a minimum run time for the generator. The ATS should be programmable to do that.
 
Something else to consider, starting a generator for a 5 minute pressure boost is probably not the best solution. I would look into a battery backup, like Generacs PwrCell.

Then you could manually charge the batteries should you ever need to.
 
How long are your typical power outages? What's the propane consumption per hour of generator running? How many gallons can the pressure tanks with the jet pumps supply before low pressure switch engages? I would hate to see the generator start every time someone flushes a toilet or runs a sink. Might be best to just let the generator operate normally and keep running during the outage.
 
I just did one last week, where they needed to keep the well house running, but they didn’t want to pay for a unit big enough to power all four houses/cabins.

We ended up just doing the well house and 1 cabin, I thing I put an 18kW into that one, just one transfer switch, dominoes sable to keep the price down a little for them.

And now at least one cabin will have power.
 
Seven-Delta-FortyOne said:
Something else to consider, starting a generator for a 5 minute pressure boost is probably not the best solution. I would look into a battery backup, like Generacs PwrCell.

Then you could manually charge the batteries should you ever need to.
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I think you are correct about short cycling the generator just for a pressure boost not being practical. If there was a way to program the generator to run from say 6AM to 9AM then 5PM to 8PM may work better.

The PwrCell battery I’m sure would work great, but at a cost of 15 to 20 grand I think I would rather just buy the propane.
 
Todd0x1 said:
How long are your typical power outages? What's the propane consumption per hour of generator running? How many gallons can the pressure tanks with the jet pumps supply before low pressure switch engages? I would hate to see the generator start every time someone flushes a toilet or runs a sink. Might be best to just let the generator operate normally and keep running during the outage.
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We do not typically have power outages. We are part of a very reliable electric cooperative. We had a bad storm in 2013 that had us out for several days. The only other outage we had was a couple years ago when we were part of a rolling blackout that lasted about an hour.
We are thinking more about an extended outage that would be human caused like terrorism, ransomware, cyberattacks, or something like that.

I was looking at the Generac 7.5KW, and it say about 1 gallon per hour at half load and 1.5 gallon per hour at full load.

Pressure switch are set to kick on at 50 pounds off at 70 pounds and enough capacity in pressure tanks for about a 40 gallon cycle.
 
Probably a control circuit like what is used by air screw compressors. When pressure is called for, the generator will run, after the pressure switch is satisfied, the generator will continue to run for a predetermined time, at least 15 or 20 minutes. If pressure is called for again in that amount of time, the timer is reset. Also, a time delay for the pumps would be needed to give the generator time to come up to speed before loading, especially with a small generator. During off peak hours, the generator will be off.
 
hillbilly1 said:
Probably a control circuit like what is used by air screw compressors. When pressure is called for, the generator will run, after the pressure switch is satisfied, the generator will continue to run for a predetermined time, at least 15 or 20 minutes. If pressure is called for again in that amount of time, the timer is reset. Also, a time delay for the pumps would be needed to give the generator time to come up to speed before loading, especially with a small generator. During off peak hours, the generator will be off.
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That’s exactly the theory of operation I was thinking. Just don’t know what extra parts would be needed to accomplish it.
 
Not too difficult if you’re fluent in controls. You would need a relay powered from each pressure switch to give you the necessary contact inputs for the timer, the pumps are probably driven directly off the pressure switches, so contactors will be needed for each pump to delay the start sequence. Closure of any pressure switch (booster and main pump) would reset the timer, the timer would drive the generator start. (Another timer would delay the pump contactors, only one would be needed just to energize the contactors once the generator is up to speed)
 
12000 gallon cistern at 5 gpm it will take 40 hours to fill the cistern.

The controls are going to be very elaborate to cycle the gen for the well pump and the jet pumps

I think your idea to cycle the gen on a timer is the best option. Shut the gen off at 11:pm bring it on at 6:am

During the day run for 20 min and off for 40 min.

What size gen are we talking about to run the three pumps?
 
Eddie702 said:
12000 gallon cistern at 5 gpm it will take 40 hours to fill the cistern.

The controls are going to be very elaborate to cycle the gen for the well pump and the jet pumps

I think your idea to cycle the gen on a timer is the best option. Shut the gen off at 11:pm bring it on at 6:am

During the day run for 20 min and off for 40 min.

What size gen are we talking about to run the three pumps?
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I think you are right. If we figure 100 gallons per person per day we would use 1500 gallon per day. Should be able to make enough water for household use in 5 hours, and in an out of power situation I think everyone can sacrifice a little comfort and cut back on usage, so it should be way less.

We have three 5 horse jet pumps that can be staged in, but in reality one pump is all that ever runs. One pump pulls 12.5 amps.

I’m not sure what size pump is in the well, but I’m sure it’s not more than a horse or two. I put my meter on it a couple years ago and it didn’t pull much, I can’t remember exactly how much though.

I was looking at a 7.5 KW generator but I’m not sure how that size would handle starting the two motors. I could load shed the well pump until the jet pump is satisfied. Or maybe jump up to a 10KW gen.

As far as setting up a run timer, is that something that can typically be programmed in the generator itself or would a separate timer that intercepts the generator start wire be needed?
 
hillbilly1 said:
Not too difficult if you’re fluent in controls. You would need a relay powered from each pressure switch to give you the necessary contact inputs for the timer, the pumps are probably driven directly off the pressure switches, so contactors will be needed for each pump to delay the start sequence. Closure of any pressure switch (booster and main pump) would reset the timer, the timer would drive the generator start. (Another timer would delay the pump contactors, only one would be needed just to energize the contactors once the generator is up to speed)
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The pumps are run through contractors with a 240 volt coil. One side of the coil runs through the pressure switch, the other side is run through a float in the cistern to keep the pump from running dry.
 
zbang said:
Kinda like what I put in #2? Could use a delay-on-release relay for the off signal.
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Yes, now that the op has given more info, it may be even easier to do. If the op is using a residential Generac generator though, the transferswitch will be pretty basic with no adjustable time delays, on those the generator controls the switch, not the other way around. Really the switch would be out of the picture anyway, since a power outage would transfer, and stay in the transfered position until utility returns. The trick is getting the Generac generator to start and stop, because it doesn’t have a manual start/stop input other than the factory Auto/Off/On switch. The op would need a generator that has a two wire start input where the transferswitch controls the generator.
 
Eddie702 said:
If the gen has an auto-off-on switch could not the timer control be wired into the auto side and disconnect the auto portion of the switch?
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Tried that on a Generac commercial generator, the switch was part of a printed circuit board. Generac wanted $1500 to change the controller to a two wire manual start. Changed out the whole generator to a Kohler that would work as a life safety unit. Generac’s controller was way too slow. It would take over 60 seconds for the generator to start and transfer. Not usable for emergency lighting. Can’t remember if the residential units were the same.
 
Thanks everyone for the replies and advice.
With what has been said so far it seems that controlling the generator with pressure and level switches would be a poor design choice. Programming it to only run for certain predetermined times would be a better way to go.

So now the question is

What is the best way to have a generator not run continuously during a power outage? Other than operating it manually of course.
 
GAK said:
Thanks everyone for the replies and advice.
With what has been said so far it seems that controlling the generator with pressure and level switches would be a poor design choice. Programming it to only run for certain predetermined times would be a better way to go.

So now the question is

What is the best way to have a generator not run continuously during a power outage? Other than operating it manually of course.
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Running it on pressure and float switches is not much more complicated, it’s the generator itself that makes it complicated. If you get a standard two wire start generator, (not Generac) it is relatively easy
 
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