Water pumps use electricity to pump water and I’m going to teach you how much power it takes to do just that here in lesson #8 of this electrical system sizing chapter of the EXPLORIST.life Mobile, Marine, and off-Grid Electrical Academy.
Now the methods of estimating power usage I’m going to teach you in this video will work for many different types of water pumps and sizes of freshwater tanks, so if you keep an open mind and think critically, you’ll be able to apply this information to your own specific project.
How much Power does a Water Pump Use?
The formula for daily power consumption is: Watts x Minutes / 60 = Watt Hours
This shurflo pump is pretty much the most popular one for most RVs and Van conversions, so we will use this as our example. It lists its power consumption as 7.5 amps at 12V.
To convert from amps and volts to watts, we would just multiply amps x volts and that gives us 90W.
Now, this water pump only uses power when it’s actively flowing water, so we just need to figure out how long per day we are running the pump.
For example, it may take you 5 minutes to do your dishes after dinner, but I know when I’m trying to conserve water from my freshwater tank. I may be standing at the sink for 5 minutes, but I only have the water running for like 30% of the time. Only when i’m actively rinsing, but not scrubbing.
So… you can really get into the nitty gritty details there OR you can just say that the water pump is running for 5 minutes after each meal; so 15 minutes total, and base the calculation on that and you’ll just not use as much power in real life as you are calculating. If you want to figure out the exact number, you can always measure with a stopwatch if you like.
90 Watts x 15 Minutes / 60 = 22.5 Watt Hours
In the context of an off-grid battery bank, if this power were being drawn from a 12V battery, 22.5 watt hours divided by 12V results in 1.875 amp hours, which is only 1.875% of a 100Ah 12V battery for those 15 minutes of water pump use.
Can you calculate energy consumption from gallons used?
Basically, yes. It is possible to calculate energy pulled from a battery bank if you know how many gallons of water you are using.
That same 7.5A pump from earlier can flow 3 gallons per minute (11.3 LPM). If we have a 30 gallon fresh water tank, and our faucet doesn’t have any kind of flow restrictor on it, this means that the pump would drain the tank from full to empty in 10 minutes of run time.
90 Watts x 10 Minutes / 60 minutes in an hour = 15 Watt Hours
If you had that same setup but had a 1gpm flow restrictor in your faucet, that would slow the flow of the pump and it would take 30 minutes to drain the tank.
90 Watts x 30 Minutes / 60 minutes in an hour = 45 Watt Hours
Conclusion:
So, there you have it. Several different methods to determine how much power a water pump uses in a mobile, marine, or off-grid electrical system.
We will refer to this lesson later in this academy when we discuss full power audits, so be sure to bookmark it for future reference and come back to it if you need a refresher.
In the next lesson, I’m going to teach you how to determine the power required for a Maxxair vent fan.
