dc volt gauge

[ronsmith]

I need to find out what type dc volt meter-gauge would be best to hook up on my solar panel battery. Analouge or digital? Which one uses least amt. power?

[drdongle]

A moving coil ( analog) meter is the simplest and requires no power beyond that of the power source being monitored, Digitals can offer more accuracy, and are often observable in the dark ( LED units, and back lite LCD's) but usually require a separate power source ( some can be powered by the monitored source) and draw more current than an Analog meter because of the internal electronics, and display.

[ronsmith]

thanks, I'll go with an analouge meter.

[ghurd]

I think too much faith is placed on voltage alone.

A half dead battery can read 'full' by voltage while charging,

because they read surface charge.

For small systems, a meter just to check every so often...

I use either (customer's choice) connected to a momentary contact switch.

Push the button, see what it says.

I like the 6 LED 'Alternator Testers'. Cheap and simple.

Kind of a close enough is good enough idea.

Only seen them for 12V.  $3 at H.F., about $6 at Radio Shack, other places too.

They all look about the same...

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=22-112

Dr. D is correct saying most digital meters can NOT be powered by the sorce they are testing. 'Majic Smoke' will be released.

G-

[Norm]

  I'll agree wholeheartly on the voltage bit....

a simple example using some rechargable batteries....those alkaline batteries in a digital camera they were getting old...I checked

them after charging about 1.6 for each that would be a total of 6.4, the camera operates on

at least something like 4.8 ....okay 6.4 should be plenty but yet it would just start to work then go off...checked voltage...still about 1.6

each ...but yet the other Nmhd rechargables with

only 1.3 each would work the camera just fine...

so I imagine the alkaline rechargable ones just

didn't have enough amps...as soon as they were

hooked to a load the voltage dropped to zilch...

took a while for me to figure that one out....

                  ( :>) Norm.

[jimjjnn]

The only way that I know to check for correct voltage of a battery is always with a load. Then you will see pretty much the correct value.

[John II]

I'd highly recommend you build or purchase an analog expanded scale voltage gauge. The advantage of an expanded voltage scale is that they do a full swing of the meter in the 11 volt to 16 volt range for a 12v setup or 22v to 32v for a 24v setup etc. But they can be made for any voltage. They are much easier to read and more precise for it's intended usage.

Several Alternative Energy dealers sell them. I have a couple of new ones, but I purchased them several years ago, and couldn't tell you where I got them from now.

Here's some resources I'm sure there are alot more on the web :

http://www.backwoodssolar.com/Catalogpages2/meters2.htm

http://www.fieldlines.com/story/2004/9/14/23945/6905

http://www.homepower.com/files/voltmeters.pdf

http://www.homepower.com/files/bat-o-meter.pdf

http://www.solorb.com/elect/solarcirc/xsvmeter/

http://www3.telus.net/chemelec/Projects/Volt-Meter/V-Meter.htm

Not expanded scale but still interesting meters:

http://www.shoreline-electronics.com/PanelMeter.html

John II

[ghurd]

Here is a 24V $4 analog, color coded even...

http://www.goldmine-elec-products.com/prodinfo.asp?number=G13794&variation=&aitem=3&mite
m=6

G-

[RP]

It seems like you could make any volt meter expanded scale by connecting a zener diode in series with it.  For example a 10v zener diode won't conduct until you cross that voltage so you'd hook it in series with a meter designed for 4 volts full scale (if it existed) and now it would only read from 10-14 volts.

I'd guess you could also use a string of silicon diodes (0.6volts drop each) to do the same thing.

[jimjjnn]

It used to be common to use diodes singly or in strings with a selector switch on power supply regulators (ex: LM317) to vary voltages. Each diode would raise the ground connection .6 of a volt above ground reference.

[commanda]

This does work but tends to be non-linear at the turn-on point of the zener due to the dynamic resistance of the p-n junction. A zener diode rated at 10 volts, won't actually drop 10 volts until a certain amount of current is flowing. If you do this, I suggest you use the lowest wattage rating zener you can.

If you want to do it properly, the circuit is in my diary. One op-amp, 2 pots, a zener, and a couple of resistors.

Amanda