Things that Work! SunAmp's Bar Graph Voltmeter Richard Perez A battery's voltage is an essential information for system users. Accurate voltmeters are not only expensive, but for nontechies, they are also confusing. What do all the numbers mean to me? SunAmp has made a very rugged and accurate bar graph meter, called the BCM, that measures a battery's voltage. This meter is very simple to install and understand. The meter uses a vertical string of color-coded Light Emitting Diodes (LEDs). It provides, at a glance, the user with accurate information about his battery's voltage. SunAmp's Bar Graph Voltmeter Both the shipping container and documentation are much more than is required. This unit could fly to the Moon in a paper bag and be installed by the average ten-year old. The bar graph voltmeter is totally solid state, tightly sealed, and tiny. It measures 2 inches wide by 4 inches tall and is about 3/4 of an inch thick. It is encapsulated in epoxy potting compound. The SunAmp BCM uses a color-coded vertical string of thirteen LEDs. BCMs are made for 12, 24, or 48 Volt battery systems. Here's the voltage scale for the 12 Volt model I tested. At the bottom of the scale is a red LED that flashes when the battery voltage is less than 11.6 VDC. This bottom LED indicates that the battery is just about totally discharged. The next two red LEDs up the scale light at 11.65 and 11.7 VDC respectively, indicating that the battery is getting close to empty. Next there comes two amber LEDs that indicate at 11.89 and 12.02 VDC. The next six green LEDs indicate at 12.14, 12.26, 12.38, 12.51, 12.63, and 12.75 VDC. This string of green LEDs roughly indicates a lead-acid battery's state of charge over most of its normal operating range. An green LED lights at 13.70 VDC indicating that the battery is fully charged and undergoing float charge. A flashing red LED at the top of the scale indicates a battery voltage of 14.80 VDC. The BCM uses the "moving dot" or single LED illuminated mode, rather than all LEDs below the indicated voltage are lit or "string mode". This provides the same accuracy and resolution while saving power because only one LED is lit at a time. Installing the Bar Graph Voltmeter The BCM is very simple to install. It comes with a five foot long cable containing two wires, one red and one black. Each wire has a battery ring connector attached. The red wire goes to the positive pole of the battery and the black goes to the negative. The BCM survives backwards (reverse polarity) hook-up, so even if you get the wires reversed no damage will occur to the meter. There is a double-stick Velcro fastener on the meter's back. You can stick it anywhere. Installation of this meter is so easy as to be trivial. The Test System I installed the BCM in our test system on 26 September 1990 and it has operated continually (24 hours per day) since then. The BCM is wired directly to a 12 Volt, 100 Ampere-hour battery (ten series connected Alcad nickel-cadmium cells). The battery is sourced by two photovoltaic modules (one ARCO 47 W. and one Solarex 55 W.) through a photovoltaic regulator (a CC20 made by Heliotrope General). The inverter installed in this system is a 1,300 Watt PowerStar UPG model. This system is in daily use here on Agate Flat. It powers five OSRAM EL series compact fluorescent lights, a Sangean AM/FM/Shortwave radio, all our small nicad rechargers (and there is a fleet of 'em), and a satellite TV system. I installed this system to test equipment without modifying the main system that powers all Home Power's computer stuff. This small PV/nicad system powers a substantial amount of our lighting and informational needs. Its flexible nature allows us to install and test equipment in a working system without having to shut everything in our world off. BCM Performance I have been checking the readings on SunAmp's BCM against a Fluke 87 Digital Multimeter for the last six months. The Fluke 87 DMM has a DC accuracy of 0.1%. The BCM indicates within the 0.5% accuracy claimed by it maker. I like the simplicity and utility of this meter. Its color coding makes it easy to understand. The flashing LEDs at the bottom and top of the scale really get my attention. It is so easy to install and read that even the most non-technical person will be able to use it effectively. I like this meter's rugged, sealed construction. It's even waterproof! This meter will certainly outlast other less accurate types costing more. Power consumption of this meter is around 0.1 Watts, making it efficient enough to be left on line all the time. Compared to other metering schemes that use LED displays, the power consumption of the BCM is very low. Conclusion SunAmp has made an easy to install, easy to understand, and highly accurate LED bar graph voltmeter for batteries. The BCM comes with a five year warranty. Its manufacturer's suggested retail price is $59.00 and it is worth it. Other bar graph voltmeters meters are available, but none have this combination of accuracy, utility, and ruggedness. Access Author and Tester: Richard Perez, C/O Home Power, POB 130, Hornbrook, CA 96044 ù 916-475-3179. Manufacturer: SunAmp Power Company, 1902 North Country Club Drive, Mesa, AZ 85201 ù 602-833-1550.