Question on 12v water pump and proper awg wire related to distance from battery

Heisenberg
Heisenberg Registered Users Posts: 23 ✭✭
in Off Grid Solar & Battery Systems #1
I have a 12v water pump that is rated for 7.0 maximum amps

http://www.pplmotorhomes.com/parts/rv-pumps-water/shurflo-pumps.htm

Assuming I have this powered by my 12v solar battery bank, how would I determine the proper wire gauge to use based on the distance between pump and battery bank?

I do not have the exact "future" location of the pump figured out yet, but I am roughly guessing it will be close to 20 ft of wire run from pump to batteries.

Thanks:D
· Share on Twitter

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Question on 12v water pump and proper awg wire related to distance from battery

    First, the wire has to be large enough to carry the current. That's not much of a problem for 7 Amps.
    Second, it has to be large enough to keep the Voltage from dropping too low. This is figured with a Voltage drop calculator.

    Now, interestingly, if the negative is carried by the vehicle chassis it's one big conductor so the V-drop should technically be calculated on "half distance" rather than a "round trip". So whereas normally across 20 feet we'd pick 10 AWG to keep the V-drop below 3% but under such a situation 14 AWG might be used instead.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Question on 12v water pump and proper awg wire related to distance from battery

    Even the "simplest" of questions always leads you into pages and pages of vendor information that never answer the "basic questions".

    For example, what is a "12 volt" pump rated voltage? Finally, in the installation document, a debugging tip:
    Proper voltage with the pump operating (±10%)

    So, we know the operating range is 10.8 to 13.2 volts (pretty narrow range at the high end--But nobody seems to have any complaints, in general).

    Given the operating voltage of a 12 volt battery under significant load can be as low as 11.5 volts--Then the voltage drop for the wiring should be no more than 11.5-10.8=0.7volt drop. And the minimum fuse size is 10 amp recommended--So we can use 10 amps for our drop calculations (error on the conservative side).

    Using a generic voltage drop calculator and 20' of wire run (this calculator assumes wire run is 2x entered one way distance), 0.7 volt drop, we get:

    10 AWG @ 20 feet gives 0.5 volt drop.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • YehoshuaAgapao
    YehoshuaAgapao Solar Expert Posts: 280 ✭✭
    #4
    Re: Question on 12v water pump and proper awg wire related to distance from battery
    BB. wrote: »
    Using a generic voltage drop calculator and 20' of wire run (this calculator assumes wire run is 2x entered one way distance), 0.7 volt drop, we get:

    10 AWG @ 20 feet gives 0.5 volt drop.

    -Bill

    ElectricianCalculators.com has hardcore calculators. And you can enter any voltage you want (PV strings). It has 5 calculators in it. The one you want (because it has almost everything) is the "Table 310.16 and voltage drop calculator". "Voltage Drop Calculator" is a simpler screen that has only 1 tab and doesn't worry about code book wire ampacity. "Raceway and trough fill" is good for determining conduit sizes.
    · Share on Twitter

Categories