VFD for Single Phase Motors

$380 bucks. What would you save with a VFD on a downhole pump?

http://www.grainger.com/Grainger/wwg/productIndex.shtml?from=Search&newSrch=yes&operator=keywordSearch&search_type=keyword&action=Go%21&QueryString=VFD&submit.x=11&submit.y=14

Try about $4000 or so in fuel.

the wife's uncle live off grid. He runs his household on a 3000 wat inverter. BUT the well pump demands more than the inverter can deliver so they have to start a 10kW diesel genset to pump water.

Last year the fuel bill was just over $8000. If the inverter could start the well pump I have a small genset that can charge the battery bank and burn less than half as much fuel. However, they need that big 10kW genset if they want water from the well. So most of the time the big genset runs very inefficienctly, resulting in a huge fuel bill. Yeah; I know this is a poor design. I didn't do it and only now am I asked to fix the cock up done by others.

Hello elnav:
just curious, does the pump run continuously when water is needed, or is the water stored in a tank, and the pump run intermittently. I realize there are issues with water tanks in cold climates, perhaps an elevated water tank or a tank supplying water pressure utilizing a smaller intermittent pump, could be used to cut the energy bill. My thinking is that the large generator could be used efficiently for short periods transferring water and recharging the batteries then shut off.

PS. I'm assuming you're thinking of using the VFD to reduce starting load so you could run the pump on the smaller generator, I think it would work, I'm just curious how close you are to starting the pump with a smaller generator. I'm sure you've already thought about getting the generator as close as possible to the pump or over sizing the wire, I have also played with putting large capacitors across the line .Just some dumb ideas, but I'm guessing the smaller generator would easily run the pump once it was started.

The short answer is - yeah sorta!

The full answer is much more complicated. The uncle is 3rd generation logger. Not exactly technical, but a good man felling 100 foot trees or getting a D12 unstuck from gumbo. The family homestead is so far from the power utility lines they wanted $50,000 to run a line to the farm. Gary who was more familiar with diesels and heavy equipment said - nuts! I'll just use a welder for a generator. You know the kind; engine driven 120/240 AC output as well as 200 or so amps DC for heavy welding and run by an engine. He had several of them around anyways. Back in those days fuel wasn't a big cost item and it was bought in bulk for the heavy equipment in any case.

Gary isn't into being green or into saving energy. He's a logger! Consequently an energy efficient installation wasn't on his mind. He just wanted modern conveniences in his home.

But now the logging industry has almost died, and little new work coming, its a different picture. Back then fuel was less than 50 cents a gallon now its $5.60 a gallon. Last year the fuel bil for the genset was $8000.

Water is almost on demand but only when the generator is running. - 30F below makes any sort of above ground storage tank impractical and we have six continuous months of frost around here.

I have already been through the duty cycle bit and storage tank scenario. We would have to contrive some sort of heating from the wood furnace to keep water from freezing six months of the year. The problem is the start surge. With a 300 foot deep pump the water column weight makes for a huge start surge. There is no drain-back. So the pump has to push a 300 foot column of water when starting. There were a lot of mistakes made in setting this system up. Now that the logging business is not so lucrative there isn't a lot of money to throw away for starting over and doing it right. I have to try and fix what is already there, - - if possible - - -

The 3000 watt Outback inverter can surge to about 7kW; but even that isn't enough to start the well pump. It needs the full output of the 10kW of the diesel generator and it takes more than 3 seconds to come up to speed and get off the start windings.

Two thoughts just occurred to me, first I don't envy you your problem , second how deep do you have to go in the ground to stay above freezing temperatures, I'm still thinking a secondary storage tank buried say 8 feet deep could work. All you would need is a backflow preventer and a small pump (or for that matter air pressure, if you recall the old RV systems) that could easily be run off your inverter once the tank was filled from the well pump, to have continuously available water without running the generator or least continuously running the generator.

Yes a buried cistern tank would work. Frost depth is around five - six feet hereabouts. But getting a decent 500 - 1000 gallon tank suitable for potable water isn't cheap. Will have to look around for something like that. But it would cost more than a $349 VFD driver.

Gary sold off most of his equipment except for one skidder and one feller-buncher. And of course the grader for snow plowing the drive out to a public road. That means he now has to rent a machine to dig holes for tanks. So that means more expenses.

I will keep that idea in mind. Gary is gone for the summer logging over on Vancouver island but should be back in late fall.

Maybe we can get something done before too much snow falls.

reading farther down now I understand. I was going to say that the net energy to move the water is the same VFD versus no VFD. Its the start up that kills you. Then the VFD will have near zero inrush and as it ramps up until the pump speed gets high enough to overcome the head pressure you'll get no water out. and the energy will be wasted.

I was thinking you might look at a PLC direct for a $200 system that will automate the well operation to really save on batteries. a 5 watt solar panel would keep the PLC running.

Wasting a bit of energy while the pump spins up is going to be less expensive than continuing to feed a 10kW genset that normally only delivers less than 3000 watts. Not to mention which the increased maintenance and service cost as a result of wet stacking is also an expense item. Typically genset engines need oil changes every 100 hours or so.

If I can deliver 4000 - 5000 watts of charging power for every hour the generator is running and manage the pump surge with an inverter, that represents more of a saving in fuel than running a 10kW genrator at inefficient loading plus the need for more frequent oil and filter changes. Using a smaller genrator loaded to its optimum bsfc point makes for more economical use over a year.

Better check again - the Telemecanique VFD's on the Grainger site all appear to have single phase input but 3 phase output - don't think I've seen a VFD with a singler phase output.

I have a friend in Alaska that installed a small DC pump with a battery and solar panel. He has a generator but it takes very little to charge the pump battery. He has an elevated tank for storage and delivery to the small house pump.

Mike

I was wrong, after further investigation VFDs and single phase motors with high starting loads do not get along, or at least according to the manufacture I called this morning. I am waiting for a response to confirm this from a second manufacture but it seems to make sense, I based my previous opinion on fractional horsepower fan motors. Single phase VFD's have become available to the HVAC industry as of late, for use on condenser fan motors, and evaporater fan motors. Fan motors for the most part start completely unloaded, unlike compressor or pump motors that can start under heavily loaded conditions. Should a second manufacture give me a different opinion or option I will keep you informed.

Combining the conversation of this morning and rethinking, a VFD potentially could be used to control pump rpm, however the pump would have to start at rated voltage and frequency, and then be backed off which would be useless in your application.

As to the tank storage, I hoped there was construction equipment lying around, unfortunately that is not the case. As you know cheap down and dirty is my motto, I'm not quite sure what the expense of the larger diameter PVC pipe is compared to buying a specialized tank but with a little jury rigging moderately long links of large diameter PVC can store quite a bit of water. I was thinking of 12 inch diameters, however PVC is available up to 24 inches.

Franklin, the pump manufacturer also tells me the same thing. Unless the motor is a 3 phase unit, there is no point in connecting a VFD. The installed pump is single phase as that is the only power available.

Had not thought of pipes for water storage. So how do you cap the ends? I do not recall ever having seen end caps lying around for 12" or larger pipes. Normally they terminate in something else like a pump house or resevoir or into a Tee fiting to join with another pipe run.

http://www.us.piping.georgefischer.com/index.cfm?uuid=15DC034BD60EB5F068CCE7848137E240&o_lang_id=2