Switching from AC Well Pump to DC

Dook

My home is on the side of a hill. At the bottom of my property I have a 3/4 hp AC well pump that I believe is 100' down the well. It has to pump water all the way up to a storage tank that is 108' above the ground, so that's 208' total lift.

I've been running the well pump off a generator for the past five years but the generator now has a problem, it puts out inconsistant volts, and I don't want to have to keep replacing generators every five years so I was thinking about switching the well pump from an AC one to a DC submersible with maybe another DC pump at the surface to help boost the water up to the tank.

To run electricity to the well would be about $4,000 so that's not something I want to do. Also I have bought a couple of inverters, one 1500 watt and another 5000 watt, to try and run the AC pump but neither one can handle it's start up amps.

If I do switch over to a DC powered well pump I have two 170 watt solar panels that I can use to recharge the batteries. How many batteries would it take? I think two would be plenty.

Any suggestions?

BB.

Re: Switching from AC Well Pump to DC

On suggestion would be to use a Grundfos SQF series pump. They take (not sure what PE means):

30-300 VDC, PE.
1 x 90-240 VAC –10%/+6%, 50/60 Hz, PE.

They are soft start, so you can run them from battery bank, AC genset, or even just solar panels...

If you are just pumping to a cistern/pond/tank--Then just a Solar Array of sufficient size to meet the voltage/current/Gallons Per Day for your water needs. No batteries, no Generator needed. When the sun is up (and the tank switch is on), it will pump as much water as it can (based on sun/solar array). And, you can still use a backup genset when needed.

Otherwise, you can install a 3 phase pump with a VFD (variable frequency drive) to give you soft start and RPM control (limit power, better match pump performance to well/piping limitations). The VFD can also work with a single phase pump with an external capacitor (well head capacitor) too.

VFD controllers are usually not to expensive and can be fairly friendly with off grid inverters/battery based systems. However--if you can avoid the whole battery thing (i.e., no pumping at night/during bad weather)--I would. Adding batteries/AC inverter can make the power system upwards of 4x more expensive (less efficient, battery charger, batteries, and battery replacement every 5-8 years or so--and more often if the batteries get damaged by pulling them to zero state of charge, etc.).

Does any of this sound interesting?

-Bill

CDN_VT

Re: Switching from AC Well Pump to DC

Dook

What Generator size & type have let you down.
Post as much info of distance / power / size , So ALL may help.
An old 2000 watt screaming honda can out-start a inverter type for a motor start. That I have played with.
The Numbers of spec's can run wild , since the datum(base line) moves as one wishes .

VT

Dook

Re: Switching from AC Well Pump to DC

CDN_VT wrote: »

Dook

What Generator size & type have let you down.
Post as much info of distance / power / size , So ALL may help.
An old 2000 watt screaming honda can out-start a inverter type for a motor start. That I have played with.
The Numbers of spec's can run wild , since the datum(base line) moves as one wishes .

VT

The generator I bought was cheap, Champion 3,500 watt/4,000 surge. It only cost me $300 five years ago but I really expected it to last me longer than it did. The generator bogged down whenever I would turn on the pump but it would always wind back up and it never died.

The water tank on my hillside is 108' in height above the well but about 410 feet in distance from it.

Dook

Re: Switching from AC Well Pump to DC

BB. wrote: »

On suggestion would be to use a Grundfos SQF series pump. They take (not sure what PE means):



They are soft start, so you can run them from battery bank, AC genset, or even just solar panels...

If you are just pumping to a cistern/pond/tank--Then just a Solar Array of sufficient size to meet the voltage/current/Gallons Per Day for your water needs. No batteries, no Generator needed. When the sun is up (and the tank switch is on), it will pump as much water as it can (based on sun/solar array). And, you can still use a backup genset when needed.

Otherwise, you can install a 3 phase pump with a VFD (variable frequency drive) to give you soft start and RPM control (limit power, better match pump performance to well/piping limitations). The VFD can also work with a single phase pump with an external capacitor (well head capacitor) too.

VFD controllers are usually not to expensive and can be fairly friendly with off grid inverters/battery based systems. However--if you can avoid the whole battery thing (i.e., no pumping at night/during bad weather)--I would. Adding batteries/AC inverter can make the power system upwards of 4x more expensive (less efficient, battery charger, batteries, and battery replacement every 5-8 years or so--and more often if the batteries get damaged by pulling them to zero state of charge, etc.).

Does any of this sound interesting?

-Bill

The Grundfos SQ-3 pump sounds like what I need but I checked online and they're $1,700. I can't believe it runs on either AC or DC. Plus I need to find out how much GPM it puts out per the amount of power it gets.

It would be nice if I could run it straight off my two Sharp 170 watt (72 volts combined) solar panels and set up a timer that would turn it on each day at noon to run for about half an hour.

BB.

Re: Switching from AC Well Pump to DC

A 6 SQF 3 would appear to pump 295 foot head at 3.5 gpm with 340 watts of power (data sheet here--PDF).

Yea--those pumps are not cheap. The idea would be to pump most of the day (slow pumping). Keep the pump and solar power loads "small".

-Bill

stephendv

Re: Switching from AC Well Pump to DC

The Grundfos models are slightly different:
- SQF is an AC or DC pump with built in MPPT that can run directly off solar panels
- SQ is an AC only pump with soft start

There's another option which is any 3 phase AC pump and a variable frequency drive (VFD) that effectively converts your single phase 110V into either 110V 3phase or 220V 3phase and makes the pump a soft starter. There are lots of posts about this here, just do a search for VFD.

BB.

Re: Switching from AC Well Pump to DC

Thank you Stephen. I have fixed the SQF in my other posts.

-Bill

Dook

Re: Switching from AC Well Pump to DC

Looks like I'm going to purchase the Grundfos 6 SQF-3 pump, my neighbor said he would help me pull the AC well pump and put the Grundfos one in. I've never changed a well pump before so I have a few questions:

-This Grundfos pump runs off of AC or DC so does it require two different sets of wiring, a three wire set for the AC side of this pump and also two thicker DC cables for the DC side?

-How does the top of the pump connect to the PVC pipe, is it just PVC glue and band clamps or is there a screw in connector?

-If there is a screw in connector do I use teflon tape or some type of glue for the threads?

Dook

Re: Switching from AC Well Pump to DC

Also, is there a DC timer that I can install and set it to operate for a half hour each day. It would have to accept power from two Sharp 170 watt solar panels, they put out 72 volts DC combined.

KeithWHare

Re: Switching from AC Well Pump to DC

Dook wrote: »

Looks like I'm going to purchase the Grundfos 6 SQF-3 pump, my neighbor said he would help me pull the AC well pump and put the Grundfos one in. I've never changed a well pump before so I have a few questions:

What you have to do to pull and replace the pump depends a lot on the existing pump. If it is hanging on galvanized pipe, it will be a lot harder than if it is hanging on rolled PVC. Also, the pipe is likely to be full of water and so will be heavier.

If your well is in an area that freezes, there is likely to be a pitless adapter.

-This Grundfos pump runs off of AC or DC so does it require two different sets of wiring, a three wire set for the AC side of this pump and also two thicker DC cables for the DC side?

The Grundfos SQF pumps take three wires, a ground and two others. According to the manual, it doesn't make a difference how you hook it up. To minimize voltage drop, I used #10 wire on the 6 SQF-2 I installed. All of the electronics are in the pump.

You will need butt connectors and heat shrink tubing to seal the connections.

-How does the top of the pump connect to the PVC pipe, is it just PVC glue and band clamps or is there a screw in connector?

-If there is a screw in connector do I use teflon tape or some type of glue for the threads?

The top of the 6 SQF-2 I installed had a 1.25" inner diameter (ID) threaded with a reducer to 1.0" ID. We used both Teflon tape and thread seal. If you do a web search on installing pumps, you can find discussions of the merits of tape, thread seal, or both. The next trick is tightening connections tight enough but not too tight.

The SQF pumps have a check valve at the top of the pump. A well driller I talked to said that he'd had problems with Grundfos check valves on the SQ pumps so he recommended an external check valve immediately above the pump. I thought a bit of redundancy was better than having to pull the pump so we followed his recommendation.

If you are using rolled PVC or schedule 80 threaded PVC, you should also use well spacers about every 20 feet. This keeps the torque of the pump from twisting the pipe and wire into the inside of the well.

I had a variety of discussions with a variety of people about the merits of a safety rope. If you use one, make sure it will not contaminate the water. We ended up using 1" galvanized pipe, which is heavy enough that any sufficiently strong safety rope would have been way too large and so did not use one.

Also, is there a DC timer that I can install and set it to operate for a half hour each day. It would have to accept power from two Sharp 170 watt solar panels, they put out 72 volts DC combined.

Probably not. A electric clock type timer will not work well running directly off of PV panels. Something about losing time at night when the sun is turned off.

Keith

Dook

Re: Switching from AC Well Pump to DC

Wow. Thanks for the information.

How has your 6 SQF-2 performed?

How high do you pump water?

Does your pump put out the GPM that the chart say's it should?

KeithWHare

Re: Switching from AC Well Pump to DC

Dook wrote: »

Wow. Thanks for the information.

For more details and pictures on the installation I helped with, take a look at the tread http://forum.solar-electric.com/showthread.php?16236-Well-amp-Pump-at-a-clinic-in-Haiti

How has your 6 SQF-2 performed?

How high do you pump water?

Does your pump put out the GPM that the chart say's it should?

So far, the 6 SQF-2 has performed as expected. Since it is in Haiti and I normally am not, I haven't watched it as much as I would like.

The well is 275' deep and produces about 12 gallons per minute. The pump is about 250'. The static level is about 180'. The top of the holding tank on the roof is about 20' above ground. So static level to roof tank is about 200 vertical feet, plus about 100' horizontal. Pump was pumping about 6 gallons per minute using about 480 watts, which is pretty close to the charted values for a 6 SQF-2.

We installed a water meter so that we have a clue how much water is actually being used. (A DLJ75 3/4" Water Meter from shop.watermeters.com) Since we didn't have to worry about freezing, we did all of the connections above ground and built a housing around them.

Keith

Dook

Re: Switching from AC Well Pump to DC

Well I changed out my AC pump to the Grundfos 6 SQF-3 and it works great on just two 170 watt solar panels.

A few things I learned:

-Make sure the safety rope is not tangled before you begin and tie it to something before lowering the pump into the well, darn thing started to soak up water and got heavy then fell into the well so now I have to hope the ABS glue and two band clamps are strong enough to keep the pump from falling off the end of the tube.

-As you begin to lower the well pump into a deep well it will only go so far because well pumps FLOAT! I didn't know that. The pump and it's supply tube have air in them so they will only go so far down. You have to turn it on to begin filling the tube with water to make the pump heavy enough for it to go all the way down. My pump is at 275' down and we got it about half way before we figured out we had to turn it on to get it to go farther.

Now, since I only have solar power down at my well I would like to get a DC powered pressure switch that will turn on the well pump when the water in the tank on the hill gets too low. Does anyone know of one that works off of DC?

inetdog

Re: Switching from AC Well Pump to DC

Dook wrote: »

Well I changed out my AC pump to the Grundfos 6 SQF-3 and it works great on just two 170 watt solar panels.

A few things I learned:

-Make sure the safety rope is not tangled before you begin and tie it to something before lowering the pump into the well, darn thing started to soak up water and got heavy then fell into the well so now I have to hope the ABS glue and two band clamps are strong enough to keep the pump from falling off the end of the tube.

-As you begin to lower the well pump into a deep well it will only go so far because well pumps FLOAT! I didn't know that. The pump and it's supply tube have air in them so they will only go so far down. You have to turn it on to begin filling the tube with water to make the pump heavy enough for it to go all the way down. My pump is at 275' down and we got it about half way before we figured out we had to turn it on to get it to go farther.

Now, since I only have solar power down at my well I would like to get a DC powered pressure switch that will turn on the well pump when the water in the tank on the hill gets too low. Does anyone know of one that works off of DC?

An instructive story, and I am glad that you were able to get it all working!

There is nothing inherently different about a pressure switch designed for use with DC and one designed for use with AC as long as it is not directly interrupting the power to the pump. The problem with switching DC is that it is harder to actually open the connection under load without a destructive arc burning or welding the contacts. You best bet is to use a relay connected to the pressure switch to control the pump. You will be able to find DC rated relays for the voltage and current you need far easier than finding a pressure switch, whose contacts are relatively delicate and are rarely used to directly control even an AC pump motor.

Do you really need a pressure switch (that is, is the tank on the hill under pressure?) If it is open to the atmosphere rather than being pressurized, you would get more reliable behavior from a level sensor at the tank.

If you are trying to avoid running wires from the tank back to the pump, you have a difficult problem in accurately measuring the difference in pressure between an empty and full tank at the top of the hill.

One way of doing this would be to use a float valve at the tank and put a small pressure chamber on the pump side of the float valve. That would create enough of a pressure difference to be easily sensed at the pump. But you would have to take other precautions to prevent the pump from "short cycling", a condition in which it turns on, pressurizes the small tank and then immediately turns off. That kind of use can rapidly destroy a pump, and a small leak in the line from pump to tank could cause that to happen while the float valve stays closed. The float valve should also be one which does not open again until the water has dropped some distance below the level at which it closed.

Dook

Re: Switching from AC Well Pump to DC

inetdog wrote: »

An instructive story, and I am glad that you were able to get it all working!

There is nothing inherently different about a pressure switch designed for use with DC and one designed for use with AC as long as it is not directly interrupting the power to the pump. The problem with switching DC is that it is harder to actually open the connection under load without a destructive arc burning or welding the contacts. You best bet is to use a relay connected to the pressure switch to control the pump. You will be able to find DC rated relays for the voltage and current you need far easier than finding a pressure switch, whose contacts are relatively delicate and are rarely used to directly control even an AC pump motor.

Do you really need a pressure switch (that is, is the tank on the hill under pressure?) If it is open to the atmosphere rather than being pressurized, you would get more reliable behavior from a level sensor at the tank.

If you are trying to avoid running wires from the tank back to the pump, you have a difficult problem in accurately measuring the difference in pressure between an empty and full tank at the top of the hill.

One way of doing this would be to use a float valve at the tank and put a small pressure chamber on the pump side of the float valve. That would create enough of a pressure difference to be easily sensed at the pump. But you would have to take other precautions to prevent the pump from "short cycling", a condition in which it turns on, pressurizes the small tank and then immediately turns off. That kind of use can rapidly destroy a pump, and a small leak in the line from pump to tank could cause that to happen while the float valve stays closed. The float valve should also be one which does not open again until the water has dropped some distance below the level at which it closed.

Yeah, there's no pressure switch that will work for me. My water tank is about six feet tall so I would need a pressure switch that would turn the well pump on and then turn off at only 3 lbs higher pressure.

I can't put a float in the tank because it's 410 feet away from my well house and 107 feet above it on the hill. Also I don't have electricity at the tank either.

Texas Wellman

Re: Switching from AC Well Pump to DC

Glad you got it going. The bad news is that it may never come out. The rope can get between the casing and pump and bind it up like chinese handcuffs. I hope this isn't the case for you.

Not sure what to say on the float switch deal. You have an extra 107 ft of head on top of the pump? Quite a distance. Since 107 ft of head = ~43 psi I suppose you could set it up to turn on anytime the pressure gets below 43 psi and then you would have to figure out how to turn it off since the extra 6 ft of head would only equal 2 psi. Not aware of any 42 on /44 off switches!!

tmarch

Re: Switching from AC Well Pump to DC

With the correct connection you can put a electric float at the tank and run some 18 gauge wire to the controller to shut the pump off when the tank is full.
I use underground sprinkler wire for this.

Dook wrote: »

Yeah, there's no pressure switch that will work for me. My water tank is about six feet tall so I would need a pressure switch that would turn the well pump on and then turn off at only 3 lbs higher pressure.

I can't put a float in the tank because it's 410 feet away from my well house and 107 feet above it on the hill. Also I don't have electricity at the tank either.