Am I screwed?

tjernigan · October 2021

I'm trying to get my well pump on solar. I spent about 800 dollars and got the controller, battery, inverter ect. However, I didn't realize my well pump is 230vac. Is the only way to get the system on my solar to buy an 800 dollar 230 volt inverter?

BB. · October 2021

Yes. (sorry--just trying to be funny and follow your post title).

Longer answer... You need to understand the actual current (power, VA, Watts) draw of the existing well pump. Most typical in-well pumps have very high starting surge... Can be 5x (+/-) the running current.

There are several ways to proceed from here--But they are all going to take time, work, and money to address.

Unless you have a very small well pump (less than 1 HP), it is going to take a relatively large Battery bank (to supply surge current) and AC inverter to start it.

Also you need to look at how many hours per day you are pumping... If you are pumping for the home, maybe 1 hour of pumping per day. If you are also irrigating your yard, garden, and such--Many hours per day (larger battery bank, larger solar array).

To proceed--There are VFDs (variable frequency drives--Basically 2 or 3 phase variable frequency AC inverters) that can give you a "soft start" (starts at low frequency and then spins the motor up to speed over a few seconds). However, you need to have an already compatible pump (possibly a 3 wire pump with capacitor at well head, or a three phase pump already installed--Unlikely for most North American homes that have 120/240 VAC split phase 60 Hz power).

The next option would be a "solar friendly" in-well water pump. These are typically very efficient 3 phase motors (Permanent Magnet type) with an integrated VFD (to give soft start and adjust RPM based on flow/pressure needs). These sort of pumps run in the $2,000 range--Plus interface hardware and pulling the old pump and installing the new pump.

Some brands/models of pumps can run on solar panels directly, battery bank, gensets or relatively small AC inverters right out of the box (just install a transfer switch from AC inverter to AC mains to AC Genset to Solar panels)... Of course, if the pump only runs when the sun is up on "solar only"--Then pumping to a cistern during day, and small transfer pump for night works well.

If you have room for a cistern--Then "slow pumping" can work well... Your slow pump runs many hours per day to fill the cistern (at low wattage) and the cistern+surface pressure pump supplies the house needs.

Other options include--Say you are looking for emergency water power (utility power fails)... One cheaper/easier method would be to get a good size genset plus fuel storage (propane, diesel, gasoline, natural gas) and pump to a cistern... Then use a small water pump to pressurize the home (you can even use RV/Boat water pumps)--Run the genset a couple times a week to fill the cistern--And the small pressure pump to supply the home (very easy with solar+battery bank).

I am certainly no well pumping expert here--If you can tell us more about your needs (existing well, well pump, depth, GPM/GPD water needs, your water+power needs, nearest major city--figure out hours of sun per day, etc.), we can certainly help you figure out where you go next.

-Bill

tjernigan · October 2021

Thanks so much for the reply and yea I kinda figured I was in a pinch. so I do have a 3 wire pump and capacitor. It is a 3/4 HP pump so I believe the max draw amp listed was 8. Since The only option to get this to work off of solar is investing in over a thousand dollar inverter, I'm thinking my new best option is like you suggested, buying a 500 dollar generator and just running the generator until the pressure tank is full then cut it off. This past weekend, I emptied the tank and turned on the pump and it only took about 1-2 minutes for the pump to kick off so with just the fuel in the tank, that generator could run that pump probably for a week or two as long as I am being conservative about my usage.
I do plan on expanding my solar to encompass my whole house at which time I will invest in a larger split phase inverter. However at the moment this was an attempt to use a small array only for the well pump.

BB. · October 2021

These are not cheap, but (if it works for you--I am not an expert in this stuff), there are VFDs for 3 wire 230 VAC pumps (technially single phase with remote starting capacitor):

https://franklinwater.com/products/drives-protection/residentiallight-commercial/subdrive-utility/#Features

If it does work for you, a much smaller AC inverter and battery bank could be used (much less surge/starting current).

However, the above unit is something in the $1,000 Range.

There should be other VFD units out there... But you will have to do some more research.

-Bill

MichaelK · October 2021

tjernigan said:

Thanks so much for the reply and yea I kinda figured I was in a pinch. so I do have a 3 wire pump and capacitor. It is a 3/4 HP pump so I believe the max draw amp listed was 8. Since The only option to get this to work off of solar is investing in over a thousand dollar inverter

Sorry, but most likely an inverter only costing 1000$ won't cut it. There's a pump chart posted by another poster, mike95490 I think.

I can't cut and paste it here, but a 3/4hp pump at 230VAC needs 8.4A to run, but needs 31.4A to start. This starting surge is known as the "inrush", and you have to take that into account. For my own pump, that I am running on solar, the running amperage is 9.5A, but the starting amperage is 38A. I run my pump with a Schneider XW+6848 inverter, that is supposed to handle a starting surge of 52A. It seems to effortlessly.

In your case, Schneider's Conext 4024 has a rating of 41A, so that might be able to run your pump. I have one in my workshop, though I have not tried to start anything as large as a well-pump with it. It does run all my power tools just fine. So, take a look at Schneider's Conext 4024 to run your pump. A Trojan L-16 battery bank and 2000+ W of solar panels should power it just fine.

BB. · October 2021

@Michealk--Thank you for reminding me. This is the chart @Mike95490 posts (I don't think it has changed):

-Bill

https://forum.solar-electric.com/discussion/comment/377852#Comment_377852

Image: https://us.v-cdn.net/6024911/uploads/editor/e1/mfu6dfpt42i4.jpg

mike95490 · October 2021

deep well pumps are a tough load to start because of their high starting surge.

i've been running one for 11 years off my inverter, 1/2 hp actually consumes 1,000A per the inverter meters

allow 10x for the starting surge for 2 seconds

BB. · October 2021

Mike, consumes "1,000A"...??? 1,000 Amp surge at 12 VDC battery bank? 1,000 Watts running?

-Bill

mike95490 · October 2021

BB. said:

Mike, consumes "1,000A"...??? 1,000 Amp surge at 12 VDC battery bank? 1,000 Watts running?
-Bill

When you add in the PF weirdness, motor losses and all the inefficiencies for the motor, the inverter internal power meter display reads 1,000w AC, dead even, when the pump motor runs. Both my XW-6048 ( 2011 ) and my new XW-6848 ( 2021) give the same reading, for a 1/2 hp, 240VAC pump. ( my 24/7 base loads are about 200W, which is subtracted when i test. )
All the book learning says 750w for 1hp.
At my "system voltage" of 65VDC, that's 15.4A DC from the battery

wellbuilt · October 2021

I’ve been pumping water into a holding tank for 4 years .
I have a 200 gallon tank in my utility room and a 275g tote out side , so 400+ gallons that lasts me a few weeks .
I use a park model RV pump (120$ ) to pressurize the house it works good
my cabin has 3 full baths , kit sink and Dish washer , Landry .

I can shower and do dishes .

You can just pump with the generator to fill the tank every few weeks .
My totes (3) cost 100 bucks from a bakery.

My well is 735’ deep I never really figured out how to get a regular pump to work so I ended up going with a SQF solar pump .
It was expensive but it seamed like the easiest way to get water out of the ground.

I was going to power it with solar panels but I may just add the solar panels to my system and fill my water tank when the sun is out .

My well has a slow refill rate so I can’t really can’t pump mor then 30 mins at a time .

tjernigan · October 2021

Ok so I did a little more research on looking at my well pump. I have a franklin electric 2801074915 control box. It is 230v with two leads and a ground. The max AMP is 8.0 with a normal amp of 6.8. So it draws just under 2k watt starting. Is it possible to get a 2k watt 120 inverter, run two 120 lines from the hot terminal, and the ground to the control box? From what I can see, I don't actually need the inverter to put out 230, I just need to get two 120 lines from the inverter to the control box. Now I am not an electrician so I apologize if I am completely getting this wrong but 2x8amps from the pump is well supported by the hardline terminals on the inverter and the terminal shouldn't have any problem providing 120v via two cables on one terminal right?

BB. · October 2021

According to this link:

https://store.waterpumpsupply.com/frqdcobox34h.html

The pump should be a 3/4 HP @ 230 VAC single phase motor.

Assuming you are in North America (Texas?), your standard home power is 120/240 VAC @ 60 Hz split phase power...

Your power is L1/L2/Neutral from a pole (or under ground) transformer. L1 to L2 is 240 VAC. L1 to Neutral is 120 VAC, and L2 to neutral is 120 VAC. The transformer is a "center tap" neutral and L1 vs L2 are 180 Degrees out of phase from each other:

101 Single-phase Power Systems

A 120 VAC inverter will not work here... More or less, it is the L1/Neutral for 120 VAC. And this will not drive your pump. This is a "two wire" (two power wires) pump. The green wire is a safety ground and does not normally carry any current to run the pump.

The three wires to your pump are L1/L2/Safety ground. If you connected 120 VAC (for example, L1 from inverter to L1+L2 of pump and Neutral to ground)--The pump will not run. L1 to L1+L2 is basically putting zero volts on the motor power leads. If I understand your suggested configuration correctly.

If you had a 120 VAC inverter that was large enough--You would need a "step up" or "boost" transformer (120 to 240 VAC)--But that adds cost and a large transformer has its own issues (an AC inverter needs to "start" the transformer and too small of inverter with a large transformer will fail).

More or less, for reliable operation, the maximum "useful" AC inverter would be around 1,200 to 1,800 Watts maximum.

To run a larger than 1,800 Watt rated AC inverter, highly suggest a 24 or 48 volt battery bank... This allows you to use much smaller copper cabling for your DC battery bus wiring.

Using Mike's chart.. .A 3/4 HP 120 VAC motor will start/run at 40.5/8.4 amps... A typical good quality AC inverter will supply 2x rated output for a few seconds surge power.

40.5 amps * 120 VAC = 4,860 VA (sort of Watts)
4,860 VA / 2 = 2,430 Watt (VA) rated AC inverter suggested (rated at 120/240 VAC split phase or 240 VAC only)

Some inverters have better starting surge (low frequency inverters), and other have less (typically high frequency inverters).

Low frequency inverters have a larger/heavier transformer... High Freq have smaller transformers and are lighter weight.

-Bill

tjernigan · October 2021

So I absolutely take your word for it that this will not work and now this is just me trying to understand electricity. I guess if i'm understanding circuits right, the 120 from the inverter won't flow because there is no complete circuit without the neutral. And the ground going to ground does not complete that circuit.

BB. · October 2021

You got it... Sort of like having a single 1.5 volt battery and a 3 volt light bulb. Can't do it.

With 2x 1.5 volt batteries in series--You can get 1.5 volts (across each battery), or 3.0 volts across both batteries in series.
Why do we insert two AAA batteries in a battery pair in opposite orientation Why are the and

Why do we insert two AAA batteries in a battery pair in opposite orientation Why are the and

-Bill

Am I screwed?

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