Things That Work! The Vanner Voltmaster Dan Lepinski 1454 Words 12 Volts vs 24 Volts Ever try to purchase a 24 Volt stereo? How about 24 Volt ham or CB radio gear? They're out there, but they're nearly impossible to find and are much more expensive than their 12 Volt cousins. So why use 24 Volts for the battery voltage instead of 12 Volts in a home power system? Simple! When you double the battery voltage in your system, the current flowing through the wires is reduced by half for any given wattage (power). The lower the current, the less loss you have in the wires and connections. In systems that use more than 4,000 Watt-hours daily, a 24 Volt system is highly recommended. To run your 12 Volt appliances from a 24 Volt system you "could" connect them across one half of the battery bank. You would get the 12 Volts you need. You'd also be discharging only half of the battery in the process and be setting yourself up for some serious battery troubles by unevenly cycling the batteries. Unevenly cycling batteries can cause considerable damage, especially in lead-acid battery systems. The Voltmaster The Voltmaster, manufactured by Vanner, Inc., is designed to allow the use of 12 Volt devices in a 24 Volt environment, but without any of the problems just mentioned. By keeping a careful electronic watch on your batteries, the Voltmaster transfers current from the stronger half to the weaker half whenever one battery discharges more than the other. It keeps the charge level equal in the two halves, regardless of the 12 Volt loads utilized. Packing & Documentation The Voltmaster packing was excellent. The carton-within-a- carton protection scheme plus the environmentally nasty styrofoam nuggets form an substantial shield against the roughest of handling almost any shipper could dish out. The instructions are printed on a giant vinyl sticker conveniently and permanently attached to the unit. The large print is easy to read and leaves little room for error. Additional information such as alternate circuit configurations, recommended wiring sizes, and technical information are available directly from Vanner. Installation With only three connections, the Voltmaster is very simple to install and operate. There are no meters, adjustments, switches, or anything else to confuse the non-techie. Vanner thoughtfully provides a wire table with recommended wire sizes for each of their models. By looking up the model in use, and the distance from the battery, the minimum wire size recommended by Vanner can be easily determined. Vanner establishes a maximum of 0.1 Volt loss in the wire as their criteria for suggesting wire size. The connections to the Voltmaster are made through nickel plated 1/4 inch studs mounted securely on the case. While these are well suited to handle the maximum 50 Amp load rating of the largest Voltmaster, they fall a bit short of dealing with the lugs needed for wire sizes larger than number 4 AWG. The studs are long, however, and allow for the use of large washers whenever the larger lugs are required. The Voltmaster in Use We tested the Vanner model 60-50A, the top of the Vanner line. It can shuffle 25 Amps (continuous duty) from one 12 Volt battery to another in a 24 Volt string. Thus you can run continuous 50 Amp 12 Volt loads. You can run 12 Volt loads even bigger than this off of half your 24 V pack, as long as the loads are intermittent so the Vanner has a chance to catch up. The Voltmaster is absolutely silent. No fans. No humming. No noise. Period. The only way to tell that the Voltmaster is operating is with an accurate voltmeter measuring the voltage across each half of your battery. While Vanner does offer the EM70 monitor as an option, it is only capable of activating user-supplied external devices such as lights or an audible alarm. A simple battery voltage imbalance warning device and low voltage alarm for use in renewable energy homes would be a welcome addition. A Slight Gremlin The Voltmaster does create some radio interference. This is not a malfunction. It is simply caused by the way the circuits operate. In today's modern power equipment, digital (on/off) switching is used to achieve the very high efficiencies we all enjoy. I found that the interference was worst around 20 kHz on my ham radio. The strength of the interference varied from just perceptible to moderate, at comes completely masking weaker signals. Efficiency The Voltmaster idle current (energy consumed when no work is being done) is a scant 17 milliAmps (0.4 watt) or about 10 watt-hours per day. Under sustained heavy loads that used between 30 and 50 Amps, the unit was just perceptibly warm, indicating that the Voltmaster's efficiency is high. I took measurements with two Fluke multimeters. During periods of heavy charging when the current into the battery exceeded 80 Amps, the Voltmaster consumed only about 60 watts. In one test, I charged half of my 24 Volt, 160 Ampere-hour NiCd pack with a 60 Ampere 12 Volt NiCd TODD charger. In this configuration the Vanner was forced to transfer half of the current to the remaining 12 Volts of the pack. The Vanner did the job with 91.3% efficiency. In a dozen other tests the Voltmaster's measured efficiency never fell below 90%. Reliability The 60-50A has been in use in our home for more than 6 months. From the date of installation it has never skipped a beat. The unit has been run beyond its specifications on several occasions without a failure. Mr. Chuck Bennett, VP of Sales and Marketing at Vanner, told me the unit can be operated without the center tap connected to the batteries, using only the Voltmaster to provide half of the input voltage. He also said that the Voltmaster is so reliable that the output from the 12 Volt center tap can be shorted to either the +24 Volt or ground points without damage. While I don't recommend that this be duplicated, I tried it. The results? It's still working! Under short circuit conditions, the Voltmaster limited its output current to slightly over 64 Amps, or about 30 percent higher than the 50 Amps specified for this model. The Voltmaster comes with a 1 year parts and labor warranty. [CAPTION: The voltmaster allows use of 12 Volt loads (or charging sources) on half a 24 Volt pack. Sever Major Benefits 1) 24 Volt charge from 12 Volt source. This can mean a great deal to the owner of 24 Volt home power battery system. Normally, to increase the size of the PV array in a 24 Volt system, you must purchase PV panels in pairs. With the Voltmaster, this is no longer true. By connecting a single PV panel between the +12 Volt and +24 Volt studs on the Voltmaster, it will automatically distribute the charging current between the two halves of your battery. The only extra item needed in this arrangement would be diode in series with your panel to prevent any current from flowing back through the panel at night. Later, when you can afford the next panel, you can restore a normal wiring and charging arrangement by merely connecting the two new panels into the proper series and parallel configuration with your existing PV array. 2) Weak half a battery. If half of the battery bank turns out to be weaker its voltage will droop more under discharge. The Voltmaster transfers current from the stronger half to the weaker half, keeping them at a more nearly equal charge level. Your weaker battery will have life easier, and its condition will deteriorate more slowly. Price There are three models of Vanner Voltmasters. The ten Ampere 60-10 runs $216.55 retail. The 60-20A can supply twenty ampere continuous DC loads, and retails at $304. The 60-50A (the one I tested) costs $457 retail. Conclusion If you're in the process of designing a 24 Volt home power system, or if you're using a 12 Volt system right now and are contemplating the move up to 24 Volts, including a Vanner Voltmaster in your design plans could be a very intelligent addition to your system. Not only will it let you continue to use your 12 Volt equipment with the new system (and treat your batteries right), but it can actually make expanding your PV array easier on the budget by providing a simple means to add one panel to your system at a time. Access: Author: Dan Lepinski, 791 Lakeshore Dr., Klamath Falls, OR 97601 ù 503-885-5698 Manufacturer: Vanner, Inc., 4282 Reynolds Dr., Hilliard, OH 43026 ù 614-771-2718