Dual LED voltage gauge for dual battery car
 

http://i188.photobucket.com/albums/z.../100_0738a.jpg

In March 2012 I built the EPES for my Civic: Externally Powered Electrical System. Basically, an alternator delete with a dual deep cycle battery system that's capable of 3+ hours drive time with headlights running and full recharge capability via AC plug in. For longer drives, alternator can be reconnected via a switch. For details, see thread http://ecomodder.com/forum/showthrea...ery-20008.html for details on the EPES project.

Having dual 12-volt deep cycle batteries begs for a nice dual voltage gauge display. So I finally built it. The real driving force behind that need was that my particular ScanGauge has a very jumpy voltage display; the apparent voltage goes up and down seemingly without rhyme or reason. So it's not a good tool for monitoring batteries, a critical task in my application. This gauge solved that issue. Readings respond instantly to known changes, such as lights being switched on or off. Otherwise the display stays perfectly stable.

I found this panel gauge available on Amazon for $10.98 plus shipping:
http://ecx.images-amazon.com/images/...500_AA300_.jpg
Here's the link to the item: Amazon.com: Mini Blue LED Digital Volt Meter 4.5~30v for 9v 12v 24v: Electronics (also available in red)

The good:
Low cost.
Easy to understand wiring: One red wire, one white on each gauge.
Relatively small: 48mm x 29mm x 21mm deep.
Very accurate: the two gauges read identically when connected to the same source and match my nearly new, ~$60 multitester.
The leads are detachable via a plastic connector.

Not quite so good:
No brightness control. They are the brightest thing on my dash, can be read in full sunlight.

I built two of these into one project box, which I then velcro'd to my dash. One hot lead goes to my lead acid battery, the other to the lithium. I joined the ground leads inside the case and ran that lead to a switch, and then to ground. I soldered the ends of the gauge leads to my 6' long, 22 gauge wire leads. The other connections at ends of those leads are crimp connectors. I folded over the 22 ga wire so the red crimp connectors would have a double thickness of wire to grab onto.

Panel gauge out of its wrapper:
http://i188.photobucket.com/albums/z...n/100_0731.jpg

The back side with removable connector:
http://i188.photobucket.com/albums/z...n/100_0732.jpg

Partially assembled, with project box dimensions visible:
http://i188.photobucket.com/albums/z...n/100_0733.jpg

Squeeze tabs visible here.
They do not depress enough to allow insertion into mounting hole.
This is due to gauge innards fully occupying the available cavity.
http://i188.photobucket.com/albums/z...n/100_0736.jpg

Shows squeeze tab ground and cut away to allow mounting.
http://i188.photobucket.com/albums/z...n/100_0737.jpg

My "Dremel" (actually a Black & Decker) did all the plastic cutting, except a few small cuts done with a box cutter.
http://i188.photobucket.com/albums/z...n/100_0738.jpg

I still plan to post a photo of how it looks on the dash. Any day now!!

Dealextreme.com also sources volt meters like this for about $5 a pop, in a variety of colours and types, just takes awhile to get around the earth.

https://dx.com/p/mini-3-digit-blue-d...147222?item=33

...a single meter with a momentary button to "switch" between the two voltage inputs would've been simpler and smaller.

True. Would require sourcing a SPDT (?) momentary contact switch, probably not that hard to find if you know where to look.

With my setup, there's never any doubt as to which battery's data is showing. And, this setup lets me see both without taking my hands off the wheel. That's also worth something.

Have you solved the "brightness" problem yet? Sometimes, there's a provision in SOME meters to dim the display brightness by pulse-width modulating the DC-voltage to the display segments...maybe your displays have this capability...or...something similar?

Nothing visible on the front of the meter. Likely someone with more electrical knowledge than me could re-engineer the components to adjust brightness. Even if there are a couple contacts on the back to control brightness - which I did not see - building the circuit and switching for it is more than I want to take on now. I'm happy with it as it is.

Here it is, installed.
Originally built with two blue gauges, I changed it to red today. The LEDs are brilliant red but show up as bright orange here.

http://i188.photobucket.com/albums/z...ersredLEDs.jpg

Lithium voltage in upper display, deep cycle lead acid in the lower. Both batteries had recently been charged up so they showed the "surface charge". They settle down to 12.8V and 12.5V respectively after a bit of use or after sitting unused several hours.

Just use a piece of window tint to dim the displays. :thumbup:

I'm surprised you had problems with the SG voltage monitoring gauge. I've always found it to be quite solid when I was running an alternator delete on the Paseo. Yeah, the voltage bobs around a bit, but it seems logical to me: higher voltage with engines off, lower with engine on, fan on higher settings, etc.