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rachelsdad
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# Posted: 29 Feb 2024 08:31
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I'm looking at a Shurflo 4028, a 115 Volt pump for the camp and here are the specs:
https://www.pentair.com/content/dam/extranet/web/nam/shurflo/data-sheets/pds-4008-171 -X65.pdf
For whatever reason I cannot wrap my arms around the draw this will put on my battery bank.
1 AMP at 115 would equal 115 watts per hour of use correct? Or am I waaaay off? The chart is confusing to me.
I was up from 3 a.m. researching
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Nate R
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# Posted: 29 Feb 2024 08:56
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Yes, 1 amp at 115V for 1 hour would be 115 watts used.
So 115w out of your battery bank.... if it's a conventional 12V battery, you'd have used 9.6 AH (running at 115w for an hour. 115/12 = 9.58)
Of course you lose some power converting it from DC in the battery to AC in an inverter.
-Nate
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rachelsdad
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# Posted: 29 Feb 2024 09:07 - Edited by: rachelsdad
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Thanks Nate,
I have 4kw of Lithium but for whatever reason my head was spinning on the AC math! Hopefully I am reading that chart correctly.
I find it hard to believe we would use it for more than two hours per day, and that is an over estimate.
I've been messing with an upgrade in my head to my water supply for a few years but I've been terribly busy at work. I took my first vacation last year in seven years and my next one will be a week at camp...off grid island in the ADK's and I'll knock off all the stuff I've been meaning to do.
Thanks again.
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gcrank1
Member
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# Posted: 29 Feb 2024 09:24
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I always round up the calculated amp (or watts) draw.
it is easier for me to think in amps for my 12v system since Im an old mechanic.....
But conversationally when talking 120vac stuff run off my 12vdc input inverter just take the device amps rating at 120vac and multiply by 10 to get the amps draw off the 12 battery.
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Fanman
Member
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# Posted: 29 Feb 2024 16:57
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Quoting: rachelsdad 1 AMP at 115 would equal 115 watts per hour of use correct? Or am I waaaay off?
It doesn't work that way. Yes, 1A at 115V would be 115 watts, NOT 115 watts per hour. Watts is a unit of power, which is energy used over time; there is no such thing as "watts per hour". 115 watts over one hour would be 155 watt-hours of energy used.
Now, about your batteries: 4kW doesn't tell you what the energy capacity of your batteries is; it tells you how fast you can withdraw that energy (a rate of 4000 watts). Capacity would be given in kilowatt-hours (or amp-hours). Amp-hours times battery voltage gives watt-hours.
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Brettny
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# Posted: 1 Mar 2024 08:33
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Amazon sells prety cheap submersible well pumps or even jet pumps. Since the pump is 120v I would look into one of them. I bet there really not much more money but can pump 4x the water. So the bigger draw for a shorter period should also mean minimal power difference.
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paulz
Member
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# Posted: 1 Mar 2024 10:27
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Quoting: Fanman 115 watts over one hour would be 155 watt-hours of energy used.
Another electrical dummy here. What is the calculation for this?
Quoting: Fanman Now, about your batteries: 4kW doesn't tell you what the energy capacity of your batteries is; it tells you how fast you can withdraw that energy (a rate of 4000 watts).
And, how fast would that be, one hour?
Thanks.
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ICC
Member
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# Posted: 1 Mar 2024 11:39 - Edited by: ICC
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Quoting: paulz Quoting: Fanman 115 watts over one hour would be 155 watt-hours of energy used. Another electrical dummy here. What is the calculation for this?
I believe the number 155 is a typo.
115 watts drawn for a one hour interval would be 115 watt-hours of energy used.
115 watts x 1 hour = 115 watt-hours
~~~~~~~~~~~~~~~~~~
Quoting: paulz Quoting: Fanman Now, about your batteries: 4kW doesn't tell you what the energy capacity of your batteries is; it tells you how fast you can withdraw that energy (a rate of 4000 watts). And, how fast would that be, one hour?
The statement that the battery is 4kW is not very useful. It could mean that the maximum power draw can be 4kW (4000 watts). That would be much like having an inverter that is rated as a 4000 watt inverter. The 4000 watts is the maximum draw and has nothing to do with how long the 4000 watts can be used.
To be absolutely correct we also do need to check if the watts rating is for a continuous load or a peak load, but that is another story.
The capacity of a battery is measured in watt-hours or amp-hours @ a certain voltage as Fanman noted.
So to the original question...
1 amp draw at 115 volts = 115 watts
If the pump was used for one hour,
1 hour x 115 watts = 115 watt-hours of energy used.
Then the efficiency of the inverter must be accounted for. Fifteen percent loss, or less depending on the inverter.
Finally one could also look at the energy efficiency of the lithium battery. There is some loss when charging and discharging. By that, I mean there is a loss of energy when charging a battery. Any warming of the battery is a loss. Same with discharging, there is a loss.
If that is hard to comprehend, maybe it will help to understand if we consider that when charging or discharging we are converting energy from chemically stored to electrical energy, and the reverse. There is always a cost, a loss, when converting energy.
I believe that there can be a 2 to 5% chemical conversion loss of energy when charging and a similar amount when discharging. The amount of loss is going to vary with the rate of charge/discharge.
Most of the time I believe this chemical conversion loss is not considered and with a good solar charging system and lithium batteries can be safely ignored.
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Atlincabin
Member
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# Posted: 1 Mar 2024 20:05
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And, hard to imagine that you would use that shurflo for two hours a day unless you are watering a lawn or have a huge family that takes a lot of showers. That said, better to err on the side of too much power use than too little when figuring your battery needs.
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Grizzlyman
Member
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# Posted: 2 Mar 2024 10:06
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Quoting: paulz What is the calculation for this?
Calculation is amp = watt/volts
The measurement you want for capacity/discharge is amp-hours…. Meaning how many amps your battery can supply per hour.
As NateR said the pump is 1 amp/hour @115v. That means on a 12v battery it’s 9.5 amp/hour at 12v.
I second Brett’s comments about jet pump vs shur-Flo. Shur flo is meant to be more of a water delivery pump for creating pressure in a line where no pressure tank exists- like in an rv. Shut-Flo will create running water where no pressure exists.
Jet pumps are meant to deliver large amounts of water to a holding tank or to pressurize a tank and come with a pressure trigger, so that if the tank loses pressure it will refill automatically.
I use both personally and the shur-Flo delivers that water from the tank to the tap.
I bought a jet pump for $180 last year that will fill a 60 gallon tank in minutes…. And that’s on top of a 50’ bluff. The 3/4 hp draws something like 12
Amps@115 which would peak 120 amps on a 12v.
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gcrank1
Member
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# Posted: 2 Mar 2024 11:08 - Edited by: gcrank1
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Fwiw
When a spec says something is x amps (or when it is spec'ed as watts that means amps x volts, as said) that means it uses that x amp(s) in 1 hour.
IE: a device that uses 4 amps uses that 4 in 1 hour
OR: that 4 amps x 12v equals 48 watts, again, used in 1 hour.
Thus you can calc that if you run the 4 amp device for 2 hours it used 8 amps.
None of that accounts for the 'losses' that always occur in use, that is why I tend to 'round up' (a method that has served me well for practical use).
Also
Folks tend to under estimate their elec power use and over estimate their power production, especially with solar.
Another common solar mistake is over estimating how many real charging hours are in a day.
And
With my lfp 100ah batteries I typically use about 80ah's before swapping out (maybe this year I'll put the solar back together).
That 4amp draw would run for 20 hours.
If I was using lead acid I would try to only use 30ah's, or no more that 50ah's (to keep from killing them prematurely). The same 4amp draw would only run for 7.5 to 12.5 hours.
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ICC
Member
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# Posted: 2 Mar 2024 13:24
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Quoting: gcrank1 When a spec says something is x amps (or when it is spec'ed as watts that means amps x volts, as said) that means it uses that x amp(s) in 1 hour. IE: a device that uses 4 amps uses that 4 in 1 hour OR: that 4 amps x 12v equals 48 watts, again, used in 1 hour. Thus you can calc that if you run the 4 amp device for 2 hours it used 8 amps.
That is not completely accurate.
Amps are a measurement of current and for our purposes is the amount of current that is flowing at a particular moment in time. Amps has no relatuonship to the duration. Well, to be technically more correct there is a time factor when just talking about amps. The ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time with 6.241 × 1018 electrons, or one coulomb per second. So time is a factor but we don't want to get into coulombs and all that stuff that is not necessary to understand electricity in our motor vehicles, cabins and homes)
So, for our purposes, if a device is rated at 4.0 amps that is the amps being drawn at any instant the device is operating. Some devices such as motors and transformers will have a surge of current (amps) when they are first turned on. Then they should settle down and draw pretty much the rated amps that are listed on the rating label.
Amperes or amps is a measurement of the volume of electricity.
Labels may also list the watts used by the device. In that case, the watts are derived by multiplying the amps x volts. To use the above example a 4 amp current on a 12 volt circuit will be; 4 amps x 12 volts = 48 watts. Period. There is no time factor either.
Watts is the combined measurement of the voltage and the amperes which is the amount of power.
Amps x volts = watts.
When we combine the Amps with a measurement of time we have amp-hours (Ah), a measurement of charge or capacity. Amp-hours = Current over time. Batteries will have an amp-hour rating, such as 150 Ah. That means it should supply 150 amps for 1 hour and then be depleted. Of 15 amps for 10 hours.
150 amps x 1 hour = 150 Ah
15 amps x 10 hours = 150 Ah
When we combine the watts with a measurement of time we have watt-hours (Wh), a measurement of energy. Watt-hours = Power over time. If we operate a 48 watt device for 1 hour we use 48 watts x 1 hour = 48 Wh (watt-hours0 of energy. Run that device for 2 hours and we use, 48 watts x 2 hours = 96 Wh of energy.
Amp-hours and watt-hours are related. Watt-hours include the voltage of the system.
Amp-hours x volts = watt-hours.
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gcrank1
Member
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# Posted: 2 Mar 2024 14:26 - Edited by: gcrank1
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That is why I, as an old mechanic, like to think in amps for a simple offgrid system. If there are watts involved I turn them into amps by dividing by the voltage.
Then it is easier for me to envision the depletion of my battery's available amp-hours.
Ie: the 4 amp draw x how many hours use out of my amp hours actually useable from the bat.
It gets more complicated when an inverter is used. If you invert the 12 into 120vac the amps at the device are basically 1/10 of what it would be on 12v. That is great for the size and length wires that need to be used (fusing too) but turning 120vac from the 12v battery depletes the bat by 10x what the 120vac running amps are. (not accounting for losses).
I think a fair number of folks think when they invert to 120vac that the hypothetical example 4amps in 12v become the .4 @120 thus reducing the depletion load from the battery to the .4; ie, they miscalculate the load/time at the source battery.
At least that is what keeps coming up in conversation when I talk to people with cabins or rv's.
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Fanman
Member
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# Posted: 2 Mar 2024 21:28
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Quoting: ICC I believe the number 155 is a typo. 115 watts drawn for a one hour interval would be 115 watt-hours of energy used. 115 watts x 1 hour = 115 watt-hours
Correct. 155 was a typo on my part, sorry if it confused anybody.
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rachelsdad
Member
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# Posted: 5 Mar 2024 05:15
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Head still spinning after reading all of the excellent responses.
Just to clarify....my system is inverted to AC. 4 x 1kwh Volt batteries, 9 panels and I figure the majority of the use would be during daylight as it is a late spring, summer, early fall use for the family...me a bit more during the colder darker shoulder seasons. All my lights are 4w (40 watt equivalent), LED and at most I would have four on overnight....big overestimation.
As for the reason I'm heading in this direction...I have a 300 gallon IBC tote I fill with a generator powered pump from the lake.
It seems like this will not put any major strain on the system....just wanted to be sure.
Thanks!
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Brettny
Member
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# Posted: 6 Mar 2024 09:45
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Your system looks bigh enough to almost run a small fridge. A small water pump is nothing.
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rachelsdad
Member
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# Posted: 7 Mar 2024 03:15
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Thanks Brett!
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