My basement has been wonderfully dry since the installation, 2 years ago, of a "french drain". However, the whole system relies on a working sump pump, and my generator is manual start, not automatic, and there's no automatic in my future.

For a variety of reasons, I've rejected the small 12v backup systems, mostly because the second pump won't fit in my sump, but also because the pump I have is really efficient and fast and has had no trouble keeping up even in the crazy rains of this past September from the hurricane and tropical storm. It's a 1/3 HP pump, 120V.

So, I'm thinking about an inverter, and I'm not 100% sure I need a pure sine wave unit or not. Some places claim it's a "must have" and others have "modified sine wave" systems that seem to be designed for sump pump backup.

I do know that I want automatic cutover to battery power, so an Unintteruptible power supply system seems to be the optimal solution.

Anyway, I've googled until I'm dizzy, so I was wondering if anyone here had a setup with inverter backup for a 120v sump pump.

Short answer to your question, no, I do not have an inverter back-up for my sump pump.

My neighbor had a battery back-up for his sump pump; it automatically cut in when the power went out. He was never satisfied with it because of the short life of the 12 volt deep discharge battery he had; at best in a real rainstorm (when needed most) he got 1 to 1 and a half hours life. I don't know the power draw of his pump. Our power outages typically run longer than that. On one occasion I had to run a long extension cord from my house to his to keep his pump running. He ended up with an automatic stand-by generator.

So, in addition to resolving the inverter issue, if you haven't already done so, calculate the power drain and how long the battery will last. Can you make it home or can someone else start the generator in time before the battery dies? You are probably already on top of this issue, but just though it would be worth mentioning.

I have run my sump pump on two different portable generators and the new auto stand by generator. Don't know their sine wave properties, but the pump ran fine. My impression is that motors are less sensitive to sine wave concerns than other electronics, but that is far out of my expertise.

Good luck.

The right answer is to consult with the manufacturer of the equipment you want to use.

With that said, it's *very* unlikely that your sump pump could be damaged by any modern generator's modified sine wave inverter power. Supposedly inductive loads like sump pumps work more efficiently on a true sine wave, but that shouldn't matter unless you're right on the edge of your sump pump's capacity. If you are, you should replace it anyway.

As bws48 and chaosmagnet have stated this is not a straight forward question. Its determinate on a variety of factors, from the construction of the motor, duration of the inverter and how much you wish to invest.

Typically, an inverter is a interim power source between loss of power event until the generator is energized. Not certain of how the inverter will be used.

As stated by chaos the modified or clipped sine wave from the inverter will not impact a small motor. The size of the unit is determined by the operation of the pump. Ideally, a pump should run for no less than 5 minutes to prevent short cycling.

Also, you need to consider the depth of the sump. For example, if the sump pit takes 5 minutes to fill and approximately 5 minutes to empty and you require 30+ minutes to return home from work - the inverter will require a capacity to operate 3 maybe 4 cylces of the pump.

Now comes the fun part. What is the construction of the motor? Induction, split case, capacitor, etc.? Each will determine the inrush current required to start the pump moving. From the sound of what you are describing - probably a generic motor requiring about 1000-1100(W) starting and 500-550(W) running. Please note this will not be used in the calculation below, it is just an estimate.

As inverters are rated in VA the load must also be expressed in VA. However, the maximum load applied to an inverter is no more than 75% of its stated capacity (eg. 1000VA cannot exceed 750VA continuous load). To calculate for a given motor:

VA MOTOR RUNNING
[HP * Efficiency (standard motor) * 0.8](kVA) * 1000(VA/kVA) or
HP * 0.746 * 0.8 * 1000 = VA
1/3(hp) * 0.746 * 0.8 * 1000 = 198.93(VA) or 200(VA)

VA MOTOR TOTAL RUN TIME (simplified version of the algorithm)
200(VA) * 20(minutes or 4 cycles) = 4000(VA)

VA MAX LOAD FACTOR ON INVERTER
4000(VA) / 0.75 (max load factor) = 5333(VA)

VA SAFETY FACTOR (aka Cover My Butt)
5333(VA) * 1.5 (safety factor) = 8000(VA)

Hope this helps.

Yeah, that's the math I was needing. It's a 1/3 hp motor, it works very well - it drains the sump in under 60 seconds, and in the tropical storm, it was running about every 5 minutes, so I was planning on a fairly large battery system (I have access to a large number of 71 amp-hour AGM batteries, more than enough for what I need). The key need is to be able to keep the pump going for a 24 period of intermittent on-off, about 10 minutes run time per hour under the heaviest flow conditions we can reasonably expect it to manage. Now all I have to do is pick something that won't set me back $700 for the inverter. Thanks.

Evening Martin,

Apologies, I thought you speaking of both the inverter/ups as one unit.

The battery capacity would be the 8000 VA.

The inverter by itself is a little more involved. You need to know the VA of the motor plus the charge rate/capacity of the cells being used (assuming sealed lead acid).

Can develop a better load profile over the next few days if you need something prior to ordering.

Keeping the sump pump operating during a major storm was the prime motivator for purchasing a standby generator recently. If not for a generous neighbor sharing his portable our (finished) basement would very probably have flooded over two days with no power.

I would have probably just gotten a portable to run the fridge and freezer if not for the need to handle this scenario automatically.

Go to any home center and buy a water back up unit.Mine worked great over a 3 day power outage.No short life batteries,don't have to be home to start anything up.

They run off a water line,using the venturi (sp?) principal to move more water out then used to drive it.

We have a well, not municipal water supply.
No electric=no water.

Battery charging is not an issue. I have a constant voltage charger that's optimized for AGM batteries, and as I mentioned, I have all of the battery power I could ever want. All in, I can easily sustain a constant 4 amp load, continually, for over 12 hours.

So, I have an AGM battery bank, that's charged off the mains with a automatic maintenance charger.

I have a sump pump, its a Zoeller 98-0001 115-Volt 1/2 Horse Power Model M98 Flow-Mate Automatic Cast Iron Single Phase Submersible Sump/Effluent Pump.

It requires 9.4 amps while running,it has a permanent slip capacitor motor. I can not find the VA rating of the motor, I'll assume 1200 or so, given I don't know the reactance.

Based on my math I'd best use a 1,500 watt inverter.

This product seems to meet all of the requirements:

http://www.theinverterstore.com/the-inverter-store-product.php?model=pwric1500w-top-rgb