Voltmeter Install

OK, so I wanted to add a voltmeter. I go to my favorite bookmark and buy one - this one

*Then* I decided to really start studying. Sorta backwards, I know. It's the C in OCD.

Anyway, I get it, wire it to a 12v. sealed lead acid battery I have on my bench along with a very old RS multimeter. Multimeter reads 12.6v. New voltmeter reads 13.2v. Yikes! A 0.6v. difference! Referring to that chart above, that's huge. Now what?

Slowing down a bit, it became apparent that I needed some kind of reference voltage and/or a way to reasonably accurately measure and, ideally, calibrate the voltmeter to the reference. I didn't want to spend a lot of money on something like a TriMetric

Digging around the interwebs, I found this meter. It gets good reviews, has two decimal point readout and, most importantly, has a potentiometer so I can calibrate it to a reference voltage. When I got it and wired it to my reference battery it read 13.1v.! Watts up with that?! I borrowed a friend's multimeter which measured the reference @ 13.05v. Back to shopping. This time I ordered this multimeter. Can't afford a Fluke Multimeter.

While waiting for the new multimeter, I have finished the mounting plate (shown above) with a mini rocker switch so I can turn the meter off if I want to - it is pretty bright. I also made up a length of wires I will use wire to 12v. source on WFCO panel. With everything wired to reference battery, I find that I can use the potentiometer to adjust the output of the voltmeter to compensate for any voltage drop I may see from the hookup. The idea here is to get as accurate a 12v. system reading as I can.

Although, I'm pretty confident I will be able to dial the meter to closely match the chart I showed above, it's probably more important to note the battery voltage when fully charge using whatever you use to measure and to try not to let the voltage drop below -1.0 volt. That seems to be safe and probably about what the standard pod indicator lights read @ half full.

I hope that helps and please feel free to correct or comment!

-fred

Short answer: To monitor health of 12v. battery system and charging system.

Longer answer...

Lead acid batteries like the one's commonly used on our pods actually have a very narrow (voltage) range of health often referred to as State of Charge.

A resting battery (not hooked up to shore power) would be considered at a State of Charge of 100% with a voltage of 12.7v or above. Often 13.2v is a 100% resting charge of many batteries. A battery showing 10.5v or below is considered at a State of Charge of 0%. It's dead, kaputt, out of juice and may not come back to life (unless you have a decalcifying charger like a Battery Minder).

It is a widely accepted practice to *not* drain lead acid batteries beyond a 50% SOC or 12.06v. I've attached a chart which I am using to refer to. The voltmeter and chart help me determine when I need to recharge the batteries and it will show that the converter/charger is pumping volts into the batteries.

And....it simply gives me a sense of power! 

That's a bit of an oversimplification, but I hope it helps.

-fred

 

I thought of another reason you won't want to keep the voltmeter on all the time - the blue glow at night will fill the pod.  We cover the display on the tv/dvd player for that reason.