RV Solar

Re: RV Solar

Niel is correct about Digital Gauges being more accurate than Analog... First, it is just easier to read to 3+ decimal places on a digital scale than to try that on a precision analog meter (I probably still have a few meters from the days where there was a mirror stripe behind the needle to make sure that you don't read parallax). Also, temperature compensation, earth's magnetic field, and shock/vibration all lead to more accurate and rugged digital meters. Also, digital meters typically have higher input resistance which makes more more accurate readings too in some instances (also less self-discharge than analog meters on a battery system).

Another reason that, if you are interested in accuracy of your battery's condition, you should pick one of the meters that Niel suggested is that it is very difficult to find out how much capacity of battery you have used (or charged) by just watching current and voltage. There is also battery temperature, chemistry, resting conditions and such that all affect the voltage readings of the battery.

The meters that Niel linked to also include totalizers--basically, monitor current over time (possibly current*voltage over time--that I am not sure about)... Basically, this is how you would know that you have used 50% of your 100 amp*hour battery's energy as these meters will simply read 50 amphours of current consumed. And, the meter will also track how much you have charged your battery too--makes it much easier to really know what you are doing to your batteries.

Lastly, shunts... Basically, if you have a current meter without a shunt, you have to route a heavy gauge cable to the meter and back to the bus to read the current. With a shunt, you place it with a short piece of cable between the battery and the bus bar and route very small gauge wire (properly protected with fuses and/or resistors) back to your monitoring point. You will have a better installation with a shunt because you will have shorter runs, need less copper, fewer losses, and a much safer installation due to less chance of shorts (ask me how I know that running wire from the battery to the amp meter and back to the battery on our old 4WD truck).

You can build your own system, but unless you find/make an analog DC current totalizer (like the kWatt*hour meter on the side of your house), you will be missing one of the most important pieces of instrumentation for monitoring your battery use over time. Also, because batteries are not idea systems, the people like Xantrex put routines in their totalizer gauges that reset to zero/full after a period of time on charge (time and voltage)--and some of them allow you to program in the bank capacity so that they can display percent capacity--handy for those users (like wives) that may not care about the details.

-Bill