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pod 11-06-2012 07:14 PM

multiple sump pumps on generator issues
I live on the water and my basement is below sea level for much of the tidal shift (protected by a seawall) but seepage occurs at high tide. A single sump pump is adequate to keep me dry usually. Occasionally there will be a hurricane or storm surge which increases the percolation flow through the soil and outstrips one pump. I drop a second pump in the pit and that works. In extreme situations (Hurricane Sandy's surge) I needed four pumps working at the same time. No problem if the power is on. If winds have taken down the power I need a generator BUT it would take an enormous generator to handle the possible surge currents of four hefty sump pumps (typical operating current 7-10 amps @ 120v but start up currents 4-5 times greater (or maybe more)). How can I solve this problem. I don't want to buy a huge generator to use once every 5 years; I don't mind buying a couple of 4K generators or a single 8K-10K (est cost $1000) but except for the surge start current these puppies will be running constantly as the water rises and shut off sequentially as the tide recedes. Except for the surge I could run 4 pumps on a moderately sized generator.

Thus I am thinking of a way to "soft start" the pumps so they don't trip the generator breakers. They will come in sequentially, i.e. the second one will be started when the first is running continuously, the third will be started when the two original pumps are not enough, etc.

Any clever ideas about how to permit four pumps on a single generator without requiring a huge generator? Thanks.

AllanJ 11-06-2012 07:22 PM

Have the pump floats adjusted so the pumps start at different water levels.

Let's say that the first pump to start is pump #1. If the water level keeps rising because water is coming in too fast for pump #1 the pump #2 starts. Etc.

You might need to enlarge the pit. There must be so many seconds before the water level rises enough to start the next pump, to prevent overloading the generator.

pod 11-06-2012 07:33 PM

multiple sumps pumps on generator
Thank you Alan.
I can control when they come on because only the first pump is on a float. The subsequent ones are actually dewatering pumps (always on once plugged in). So I see what you are saying. Since I can control when they come on, the generator would only have to deal with one surge at a time. In that case the third or fourth ones would be the only challenge to a moderately sized generator. The running power draw of a pump is, say, 1200watts (10 x 120) So with two going I would be drawing 2400 watts and the start of the third may trip the generator breaker. Also most generators are intended to run at 50% power in steady state. It may take four to six hours for the surge to back off. Can you think of a way to permit the third and fourth pumps to start on a moderately sized generator (say 6500 watts since these seem to cost about $1000).

AllanJ 11-06-2012 07:34 PM


mpoulton 11-06-2012 07:34 PM

Different float valve settings should fix the starting current problem. Also, due to the reactive power behavior of induction motors, it is actually easier to start a motor on a circuit that already has other motors running on it - the other motors back-feed power to help start the new motor. But you might consider using just two pumps - a normal one for normal conditions, and a second very large pump for emergencies. They make submersible pumps in all sizes, from tiny to car-sized.

AllanJ 11-06-2012 07:36 PM


pod 11-06-2012 07:41 PM

The pumps are sized differently. The first true sump pump is 2200GPH; the other ones are larger dewatering pumps which do about 4000 GHPH (and draw more current to do that). I know that all four were required to keep me just dry. So at that point I was pumping out seepage of about 15,000 GPH. Also there is a problem with too big a pump since it can pump down the pit and run dry until the pit refills----it is a strange situation where there are thousands of gallons of water under the floor but I can only take off so much at a time. I tried a trash pump but it pumped dry quickly and had to be shut down and restarted over and over---not practical. That is how I settled on the sequential moderate sized pumps.

pod 11-06-2012 07:51 PM

I am not very knowledgeable about motors but is ther some way to "soft start" a pump (have it come up to power gradually). I remember from college that there are "Varians" or some such=variable voltage transformers where you could dial up the output from zero to 120 volts. Could one of those be fitted to the motor for starting and then switched out of the circuit when the pump is up to speed or do pump motors have to have full voltage to start?

mpoulton 11-06-2012 11:56 PM


Originally Posted by pod (Post 1046263)
I am not very knowledgeable about motors but is ther some way to "soft start" a pump (have it come up to power gradually). I remember from college that there are "Varians" or some such=variable voltage transformers where you could dial up the output from zero to 120 volts. Could one of those be fitted to the motor for starting and then switched out of the circuit when the pump is up to speed or do pump motors have to have full voltage to start?

You can't do it with a single-phase pump, but you certainly can with a three phase motor. This could be a great solution for this application. A 3-5HP three phase pump with a VFD (variable frequency drive) can take a single-phase input from your regular generator and provide completely variable pump speed.

zappa 11-07-2012 04:40 AM

This sounds like a good application for a generator that can run on natural gas or propane.

pod 11-07-2012 07:28 AM

There is a pump for sale on craigs list here in R.I. (Pacer SE3LLD5.0C-280 GPM (3") 5-HP Electric Water Pump (230/460V 3-Phase) which appears to have the capacity (280 x 60 =16,800 GPH) and would likely fit in the sump pit. I don't understand how the VFD controls the speed or how much a VFD costs. Could you explain in layman's terms. This is attractive to me in that a single pump could be dialed up to pump at variable rates to adjust to the infiltration rate of the water (do I understand this correctly?). How would the generator sizing be determined. I'll try to determine what the full load power requirement of the pump is but I presume you need a generator of greater than 5 HP to drive a 5 HP pump because of losses, etc. I'll read on it since it sounds very useful. Remember I am electronically unsophisticated but willing to try and learn.
Zappa: I do intend to get a propane or NG generator so that I don't have to schlep gasoline around. Thwe Propane is probably the least expensive way of the two.
Thanks for the suggestions.

pod 11-07-2012 07:51 AM

Actually I did some reading on the pump. It is really an electric dewatering pump for high volume applicatons, it does not sit in the pit and get wet. It is a trash pump design connected with a stout 3" input hose that has a strainer that sits in the pit. It is self priming. If I could set this up in the basement and have a variable ouput control (this vfd device) that would be ideal. Can it be done for a reasonable cost?

mpoulton 11-07-2012 11:26 AM

It probably can be done at a reasonable cost, depending on your definition of reasonable. However, there is no way to do it without really understanding how it works and getting pretty technical. VFDs are not intended for use by consumers - they are industrial equipment, intended to be installed and used by trained technicians. They require programming. But you can figure it out.

Something like this one should work:

If you get a 3-phase generator instead of single phase, your options would be much greater because most VFDs are intended for 3-phase input. Regardless, your generator needs to be able to supply a bit more power than what the pump requires. Perhaps 25% more. There is no startup surge when running a motor on a VFD, because it slowly accelerates up to speed. For the VFD above, at 5HP output it requires up to 36.3A input at 230V (8350W) so a 10kW generator would definitely be safe. You could run it on a smaller generator, but you may not be able to turn it up to full power without tripping the generator's circuit breaker.

windowguy 11-07-2012 11:41 AM

your ingenuity to make this happen the most efficient way is commendable..

but perhaps relying on so much technology might just let you down. Since you seem to have a very clear grasp on just how much water comes in the basement, and at what times (tidal ebb and flow) and you've seen a worst case scenario with Sandy.... Is it possible for you to just bite the bullet and be there manually to cycle each of the 4 on and off in rotation to not trip the breaker on your one pump? If it is just a high tide issue are you talking 2 to 3 hours?

I hate to sound so simplistic, i'm only suggesting it because it seems like you have a very good grasp of how much and when you want the pumps to go on and off.. just be there to make it happen.

And FWIW i'm spending a lot of time trying to figure out how to "keep an eye" on my sumps that perhaps will run for TWO WEEKS after the storm with no power.. So i feel your pain.

pod 11-07-2012 04:53 PM

Thanks very much for sharing ideas with me. This forum is good.

m poulton.....excellent knowledge base and I appreciate your willingness to share. I dream of a world where I can turn a dial and adjust the pump output to suit my requirements up to about the 15,000GPH limit. I am somewhat intimidated by the VFD but I have read about it and grasp the concept at least. I should mention that the basement in question has no vital infrastructure (furnace, water heater, electric service panel, etc.). I put all those up stairs when I renovated the house. I also built a hatch in my floor between the basement and first floor, 4' x 4' with a chain fall pivot in the ceiling above the hatch. What is in the basement are my tools, hobbyist type tools, table saws, planers, band saws, radials, chop saws, hand tools in chests and the usual stuff that accumulates in a basement or garage. I could move everything to the first floor if the big one threatened. I didn' do that for Sandy (having the tools on 4' x 6" blocks was my intermediate measure and I got away with it. With electrical power intact from the utility I was able, just able, to hold the tide at bay since I ran out of pumps and places to put them.

If I was without power I would likely have taken 2-3 feet of water once the tide breeched the seawall (which it just barely did). I could live with that for a few hours if the basement was emptied of tools or if I hung them from the ceiling joists. The basement is unfinished with a concrete floor and concrete/cinderblock walls.

All of which is prefatory to the question raised by windowguy (thanks) about whether I am overthinking this issue, or over designing it. If I am not home none of the systems will protect me from a big flood challenge. If I am home with power, no problem. If I am home and lose power, that is the specific scenario I am trying to cover. The 3 phase, 10 KW propane or NG generator plus the VFD plus the megapump solution going to set me back at least $3K (if I shop wisely for used equipment) and probably $5-6K if I go new and have an electrician do the wiring and guidance on the assembly of the system. Hiring a helper to help me hoist everything valuable up to the first floor through the hatch when the big one looms is a couple hundred max. The big ones are uncommon. Sandy didn't match the '38 hurricane level, or the one in ?1990 but it was a challenge. Even those prior ones wouldn't have reached my first floor although the '38 storm may have literally filled the basement which has about a 7 foot overhead from the floor to joists.

So, I need to ponder the issue further. I think you have helped me arrive at the most excellent system solution (M. Poulton et. al.) and now I have to decide whether it is worth building it or whether I should just empty the basement of valuables when the superstorms threaten. There are many factors to consider. The utility was embarassed by Irene's widespread power outages and has spent the year since trimming trees near power lines. Perhaps that is why Sandy didn't interrupt power. But for the potential loss of power I am good.

Thanks very much to all who responded to my question. In just a few days I have a good grasp of the best engineering solution and the cost. Now I need to fish or cut bait after an appropriate period of pondering. I am very grateful for the cooperation and generous contributions of time and thought. Tonight there is a snowy northeaster but it is child's play (50 mph winds and temps just at freezing) compared to the superstorms. I am snug and dry.

Experiences like this consolidate my wonder at the internet: Instant colleagues who are smarter than I am and willing to talk. Thanks again.

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