One of the ongoing difficulties encountered by off-grid users is how to determine the amount of power used or required.
For AC power measurements a relatively cheap device is something called “kill-a-watt’ which you can purchase from Amazon for around $20. Unfortunately a similar meter for DC measurements is somewhat more expensive at $200 and upwards to $600.
In addition power measurements is something involving calculations which seem to scare off many people who think it’s too complex. It is not, and can be handled by a basic 4 function calculator
The low priced multi meters seldom go beyond 10 amps and many DC systems have current levels above that. Any good solar panel of 130 watts and greater feeding a 12V panel will deliver in excess of 10 amps.
What is needed for DC is a “meter shunt” If you lack the money you can make your own using heavy copper. Professionally made shunts use a special alloy but pure copper wire will work although it has a 5% variance as temperature changes.
For technical details google shunts and various DIY sites will show you how. Don’t take my word for it; google it and see for yourself. The expensive DC power meters that count accumulated use have a micro-processor but you can usae a watch to manually do the same job.
Commercially made shunts cost $20 – $50 each so when I needed quantity 10 to measure individual battery currents in one installation I fabricated shunts using copper bar stock. The important aspect was that all of them read simultaneously so the variance due to temp changes was not as critical.
Its important to know how much power (watts) you need in order to select the solar panels or wind generator for your system. Going by the rating plate doesn’t really help because the rating plate only indicates maximum power draw not actual running watts. If a motor is involved with the appliance there is starting amps and running amps. Resistive devices like a lamp bulb or heater ther is cold inrush and hot running amps.
It has been my experience that newcomers to off-grid quite often get this aspect wrong. Either they overspend and buy way more capacity than they need or they under estimate and run out of power when they need it the most.
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