Adding a volt meter with a switch, basic question

Say your meter was this one:

http://www.amazon.com/niceeshop-Digital-Display-Voltage-Voltmeter/dp/B00825NB24

TYPE : LED;
Power range : DC 4.2 V - 30 V ;
Current consumption : 12mA ;
Accuracy : 0.1V;

Say you have a 200 AH battery bank and it has a 0.05% self discharge rate (average to low average for a flooded cell lead acid battery):

• 200 AH * 0.0005 self discharge = 0.1 amps self discharge
• 12 mA = 0.012 amps for meter power (may be less current as input voltage rises)

The meter (according to specifications) would draw almost 1/10th the self discharge of a 200 AH flooded cell battery--So, I would not put a switch on it unless you wanted to (perhaps turn it off in winter if lock the cabin up). If the battery is small (i.e., 20 AH), then you probably want a switch to prevent discharging the battery just to run the meter display.

Yes, you should put a fuse near the + battery/solar bus (1/2 - 1 amp or so, depending on wire gauge) just to protect against a short circuit in the wiring.

On the solar panel--You might want to try the first meter you got... The charge controller will pulse on/off the array (i.e., jump around between 14.x volts battery charging and ~21 volts Voc)--See if this meter gives you "useful" readings in the afternoon as the battery transition into absorb and float. Its readings may jump around a bunch at that point.

-Bill

For a 12 mAmp load current (mostly used to light the LEDs), it will be close enough (I the one I linked too--The volt meter is not adjustable and a few people complained that it was not very accurate).

You can treat this just like a standard cable voltage drop problem...

http://www.calculator.net/voltage-drop-calculator.html

100 feet (one way run) of 22 AWG wiring and 0.012 amps:

Voltage drop: 0.039
Voltage drop percentage: 0.33%
Voltage at the end: 11.961

Hardly affect the digit to the right of the decimal point.

Of course, if you want a more accurate reading--Then use a LCD meter or one that draws its operating power different from the measurement leads.

-Bill

If you have a PWM type solar charge controller (and not a MPPT type)--The Vpanel input, Vbatt output, and charge controller will be about the same (within a 1/10th of volt or so) of each other if:

• All is working well (battery in the range of 10.5 to 14.8 volts or so)
• There is light on the solar array.
• Charge controller thinks the battery bank needs charging (PWM controller "turns on" in bulk mode 100% of the time).

Voltage:

• 11 volts on the battery bank is pretty low--Generally, we suggest that you avoid going below ~11.5 volts under load
• 12 volts on the battery bank with no load is ~50% state of charge
• 13 volts is the battery is not being discharged (~12.7 to 13.6 volts is float charging)
• 14 volts is the battery starting to get a good charge on it
• 14.5 to 14.8 volts is what the charge controller will hold at the battery for ~2-4 hours or so to fully charge the battery bank. Vpanel should slowly rise from 14.5 to ~21 volts as the charging current is reduced.
• Vpanel should be pretty close to zero volts at night.
• Load Control should be ~Vbatt voltage unless Load Control turns off (battery near dead, over current from LC terminals, etc.).

At this point, I would worry that you are not getting enough charging current to your battery bank--The battery bank is probably not getting fully charged... And at 11 volts either you have heavy loads (for the size of the battery bank) or are significantly discharging below 50% state of charge.

If flooded cell batteries, I would get a good hydrometer. Also, assuming the charge controller and everything else is working OK, I would turn off your loads and/or get an extra battery charger on the battery bank and get it fully charged (check specific gravity of all cells, etc.).

-Bill