Running a 115vac well pump, battery voltage is being pulled down tell inverter shuts off

suprasolar · July 2017

Ok so I think I need to give more info on what I have going on here because everyone is saying this is a bad way to go about doing things.

What I have is a 30 acre piece of land that currently has no trees on it and I will be building a cabin starting next year. For the time being I have a large 400 gallon tank sitting on a hill with drip lines coming out the bottom of it going to about 50 trees I have planted. This piece of land is about 2 hours from where I currently live and work, so I go up to it about once a week. I have this system setup with a timer that is currently running a 24 vdc piece of crap pump that is also down in the well and pumps about a gallon a min. it is set to come on for 2 hours ever 6 hours and draws about 4 amps. well in the future this will not work to feed water to the cabin and it currently doesn't have to abiltiy to fill the tank all the way because there is 1gpm or more leaving the tank once it gets partialy full and is increasing pressure going out to drippers on trees. If I fire up the 110 volt pump which is putting out 20 to 25 gpm then I can it for 20 mins and have the tank totally full for it to drip for 6 hours. Once these tree have established themselves then there will be no need for this. In the future this will be supporting the cabins need water with a pressure tank and will hard ever need to run. I size it this big for future needs.

For everyone that keeps tell me about 1 Hp equaling this or that. I know how to use a meter and have a good fluke meter so I know what my current draws and voltages are. I also believe It is the batteries a this point because appearantly these batteries can trick you and there soc can't be read by checking the voltage. so yes I will be doing some load testing.

Horsefly · July 2017

Your place and your plan sounds great.

I guess I am fully willing to accept that you are reading the meter right. That said, there simply is not a 115V 1HP pump that only draws 8A. So I would say you are more likely to have a 1/2 hp pump. Try looking around on the web for how much current a 1HP, 115V single phase pump draws. I think you'll see my point.

Estragon · July 2017

1hp= about 750w output.

8a@115v=920w input. The motor maybe not fully loaded (eg. with lower than rated head) so input could be 8a? Wouldn't that be like getting better mileage in my car with a tailwind?

suprasolar · July 2017

Horsefly said:

Your place and your plan sounds great.

I guess I am fully willing to accept that you are reading the meter right. That said, there simply is not a 115V 1HP pump that only draws 8A. So I would say you are more likely to have a 1/2 hp pump. Try looking around on the web for how much current a 1HP, 115V single phase pump draws. I think you'll see my point.

not sure where your info is coming from Horsefly

https://www.google.com/search?q=hp+to+watts&ie=utf-8&oe=utf-8

thank you estragon

besides doesn't have and thing to do with this, when I was looking at pumps I was comparing watts needed vs. gpm I could get at my pumps depth

here is the pump info again
https://www.amazon.com/Hallmark-Industries-MA0414X-7-Submersible-Stainless/dp/B00NTT2JO4/ref=sr_1_3?ie=UTF8&qid=1499728755&sr=8-3&keywords=hallmark+deep+well+pump

I'd say I'm doing pretty good at 8 amps when max current draw is 10.5

Horsefly · July 2017

The conversion that you point to says that a 1HP of power is the same as 746W. It has nothing to do with how much electrical power has to be provided to a 1HP motor. You are assuming an induction motor is 100% efficient, and it is far from it.

The kind of data I've seen (which matches my experience with our well pump) is more like is discussed here: http://www.engineeringtoolbox.com/elctrical-motor-full-load-current-d_1499.html

Or even just a simple Google search of "How many amps is a 1 hp motor?" : https://www.google.com/search?q=1+hp+pump+amps&rlz=1CAHPZS_enUS724US724&oq=1+hp+pump+amps&aqs=chrome..69i57j0l5.9814j0j4&sourceid=chrome&ie=UTF-8#q=How+many+amps+is+a+1+hp+motor?

I'm not trying to argue with you. Like others, I was trying to help. If your problem was in the batteries (or not) it makes sense to do a review of what your real loads / needs are before you throw more batteries at it. If you are getting near 100% efficiency out of a deep well pump, you should be happy. On top of that, you should consider selling it to a research organization so they can figure out how it does it.

animatt · July 2017

I have a 1hp truper submersible pump. I have not checked it recently but for a long time(various checks over time) it's power consumption was very close to 750-800 watts.

Marc Kurth · July 2017

bsolar said:

you measure them really with a carbon pile load tester .. batteries can be funny .. but the bottom line in your case is you shouldnt try to run a 1000+w load on batteries .. hate to scold you, but what we're doing is 'solar' power .. not battery power .. if you want a 'battery' system visit the local battery supply shop and invest in about 10 grand worth of batteries, make a huge bank, and get the shop charger from hell to keep them charged, what do you want with 'solar'? ... if you do want to have a solar system re-think your approach ...for example if you could fill a large tank during the day with your pump you could feed it to your house ect with a 12v rv pump that pulls about 30 watts ...

I will respectfully disagree......completely.

Seriously, you are categorically saying that what many of us do on a daily basis is wrong. I do this for a living, but tell me more about why you feel this way and I just might learn something.

Marc Kurth
Bastrop, TX

Marc Kurth · July 2017

All else being equal, battery voltage sag is heavily dependent upon on battery design (manufacturer) temperature and load.Some lead-acid batteries can take very heavy loads without causing inverter dropout, others cannot.

I deal with In higher end AGM's and in general, an 80 amp load on our 100 ah battery will hold 12.2v at full charge. At 70% charge it will still deliver 12.0v. Please note that I am talking about a huge load relative to battery bank size.

With good batteries, a 90 amp load on a standard sized 24v battery bank with (4) 220ah 6v batteries, will deliver 12.0v when it is at 50% DOD.

Not all batteries are created equal.

Marc

mike95490 · July 2017

Horsefly said:

I just was re-reading the original post. If this is really a 1hp pump, I think the OP's numbers are wrong. The rule of thumb is that for 120V single-phase, it's about 14-16A per HP. He says the current is 8A, but that can't be for a 1HP pump. If we assume an optimistic 14A and ignore the power factor, that's 120V * 14A = 1680W. If we assume an 85% efficiency for his inverter, the draw while the pump is running should be 1680 / 0.85 / 24 = 82A which is quite a bit. He's doing this for 10 minutes, which is a fairly long time for that big of a load. I guess I'm not surprised it pulls down the battery voltage like he says, independent of how good his batteries are.

My 1/2 HP well pump only runs for 2-3 minutes each time it fills the pressure tank, and when it is running (with virtually no other loads) my inverter indicates about 1,000W.

That's all very close to the same numbers I forecast too, except I run my pump for about 4 hours to fill elevated tanks.

mike95490 · July 2017

Pump info. Until you get into really exotic motors, all brands consume the same.

Image: https://us.v-cdn.net/6024911/uploads/editor/s6/m4x9r39skdbr.jpg

Image: https://us.v-cdn.net/6024911/uploads/editor/fy/e9wy6xy1vr99.jpg

suprasolar · July 2017

I don't know how HP became the issue, horsepower is just a bulls*** number to put on something for uneducated people. Take cars for instance manufactures have been misleading consumers for years. The fact of the matter is the 55 amp continuous load at 24vdc. The start surge is not a issue either, IT START, IT RUNS, IT just doesn't last as expected unless the panels are pumping in power

jonr · July 2017

Agreed, but sometimes important for others. Part of the discrepancy is that the Hallmark pump has no service factor (ie, 1.0 vs ~1.5 for reputable brands). I also suspect that they are playing games with the HP rating. Like basing it on the electrical consumption (750 watts per their specs), not output.

But conventional well pump power draw does vary with head, gpm and efficiency - don't try to predict it too accurately. An aside: as non-intuitive as it might seem, lowest power draw (edit: centrifugal pump) is at the max pressure (0 gpm).

Also note that when it comes to AC, watts is not equal to amps times volts (as read by a typical multi-meter).

Running heavy loads while the sun shines is a good strategy - even if the batteries can handle it.

BB. · July 2017

And there are different types of well pumps... Centrifugical pumps, you can reduce their power requirement by placing a valve on the output--Restricting water flow reduces pump torque.

Positive displacement pumps must not have any (artificial) restrictions on the output. As the pressure goes up, gallons per minute (flow), remains roughly the same, but pump torque goes up. And more power is needed to drive the pump.

As Jonr and others have noted--AC Amps * AC volts does not equal Watts... It equals "VA" (volts * amps). VA is useful for sizing wiring and AC inverter output, etc. However, it does not map well to Watts used... Typically VA * PF = Watts where PF (Power Factor) is typically around 0.60 to 0.80 for induction motors.

Measuring DC current on the inverter's input and DC voltage does give you a much better idea of actual pump "power" needs. Using "made up numbers":

80 DC amps * 12 VDC * 0.85 AC inverter eff = ~816 AC Watts to the motor
816 Watts * 1/0.65 Power Factor = 960 VA to motor
960 VA / 120 VAC = 8.0 AC amps to the motor

AS Mike has posted--Induction Motors are not terribly efficient. And note that his ~9.8 AAC current is at 230 VAC rating--Not 115 VAC.

Note that for AC Induction Motors, the PF numbers tend to "get worse" (1.0 is "perfect", 0.50 is very bad) when the motor is running at less than full rated output power.

-Bill

jonr · July 2017

Only thing I would add is that the "perfect" PF achieved with capacitors added to a motor can be dangerous. Could become over-corrected and lead to resonance.

BB. · July 2017

Generally, PF is "corrected" to a maximum of ~0.95 with capacitors. Any closer to 1.0 and the motors+caps run the risk of generating high voltage on the AC line (for example, when the power is lost or turned of and the motor+loads coast to a stop).

-Bill

Running a 115vac well pump, battery voltage is being pulled down tell inverter shuts off

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