Things that Work! Cruising Equipment's Amp-Hour +2 tested by Richard Perez Cruising Equipment introduced their first battery Ampere-hour meter two years ago. It rapidly became everyone's first choice for system instrumentation. Well, the fine fellows at Cruising haven't been idle. They have invented a new model Ampere-hour meter with radically better features, more intelligence, and it measures two systems at once! Battery Ampere-hour Meters A battery Ampere-hour meter keeps a net count on current flow into and out of the battery. It is a meter that tells us how much electric energy has been consumed from our battery. One chronic problem with all Ampere-hour meters is battery efficiency. No battery is 100% efficient. Some of the energy used to recharge the battery is lost as hydrogen and oxygen (via electrolysis) and some is lost to heat. A battery Ampere-hour meter must factor battery efficiency into its measurements. The early model Cruising Equip. Ampere-hour meter used a control to set a specific battery efficiency. This meant that the user had to know the efficiency of his battery, and set it correctly on the Ampere-hour meter. Well, most of us don't know our battery's efficiency. Diddling the control through a hole in the meter's case turned out to be vague. What setting the early model Amp-hour amounted to was several months of dedicated trail and error adjustments. Both Steve Willey, of Backwoods Solar, and I fool around with electronics extensively. It took both of us months to accurately adjust the potentiometer on the early model Amp-hour meters. After the meter was properly adjusted to the battery's efficiency, then all went well. Until the battery aged and its efficiency changed. Then the whole adjustment rodeo went on again. The good news is that the new Cruising Equipment Ampere-hour meter is smart enough to learn the battery's efficiency for itself. It also updates this efficiency info regularly so the meter is aware of changes in the battery's efficiency. Shipping and Documentation The meter arrived in fine shape nestled in its plastic bubble wrap. The early docs were marked "draft copy not for public distribution" and were obviously not ready for prime time. Cruising Equip. is still working on producing the documentation for this Amp-Hour+2 meter. The meter itself measures 4.5 inches wide, by 3 inches tall, by 1.75 inches deep, and comes with two shunts for current measurement. The unit is well encased in heavy plastic. Wiring access is via a multi- conductor cable poking out of the unit's back. The Amp-hour+2 Meter's Functions The Amp-hour+2 does more than measure bi-directional battery Ampere-hours. It is also a battery voltmeter and battery ammeter. The Amp-hour+2 can perform all of its measurements on two separate battery packs. Voltage resolution is to 0.01 VDC, with a range of 8 to 16 VDC in 12 Volt models, and 16 to 32 VDC for 24 Volt models. Current resolution is 0.1 Amperes with a range of ±255.0 Amperes. Ampere-hour measurement resolution is 1 Ampere-hour with a range of ± 2000 Ampere-hours The Amp-hour+2 uses an LCD (Liquid Crystal Display) with 0.4 inch tall numerals for information display. This display is well back lit by two green LEDs for night time viewing. There are two switches on the front panel. One selects the function of either net battery Ampere- hours, battery voltage, or battery amperage. The second switch selects the one of two separate battery packs. This is a smart meter. This meter uses a microprocessor chip that talks to electronic memory (both RAM and ROM). The Amp-hour+2 has far more inside than a collection of op-amps. It has the intelligence to actually determine the efficiency of a battery and use this data to deliver far more accurate Ampere-hour measurement. Meter determined battery pack efficiency is displayed for both battery pack channels. Remember the Amp-hour+2 does all its measurements (even efficiency) for one or two battery packs. Installing the Amp-hour+2 I installed the meter in our system on Agate Flat. The first thing I noticed was a different shunt than the one used by the earlier model Amp-hour meter. The Amp-hour+2 uses a 500 Ampere, 50 milliVolt shunt with a resistance of 0.00001½. The previous meter used a 100 Ampere, 100 mV. shunt with 0.0001½ resistance. The new Amp- hour+2 uses a shunt that has ten times less resistance than the previous model. The very low resistance of the new shunt is important because it is wired in series with between the battery and all loadsŠlike the inverter. Our inverter can consume over 400 Amperes when starting large 120 vac appliances. I installed the Amp-hour+2 meter's shunt in series between the negative pole of the battery pack, and all loads and power sources. The meter five wires to install it in the system. For a schematic of how this is done see the illustration on page 10 of this issue. Wiring the second battery into the meter is done with three additional wires which go to the second battery bank's positive pole, and the two terminals of the second shunt . I could resist a peak inside the Amp-hour+2 meter. When the case came apart, I was confronted by two levels of densely populated printed circuit (PC) boards. A large surface-mount, microprocessor hangs out in a leadless chip carrier. Both PC boards are double sided and jammed with top quality electronic components. In terms of the level and amount of technology, Cruising Equipment customers are getting a good deal for their bucks. Programming the Amp-hour+2 Meter The meter needed to be told several bits of information about our system. The Amp-hour+2 needs to know our battery pack's capacity in Ampere-hours. It needs to know at what voltage and current we wish to consider the battery pack to be fully recharged. The Amp-hour+2 uses this information make more accurate measurements of the battery packs' state of charge. Programming is accomplished by inserting a tool into the side of the case and pushing a button. Accuracy of the Amp-hour+2 I ran the Amp-hour+2 against two Fluke 87 Digital Multimeters. As far as I can tell after six weeks of testing, the Amp-hour+2 is at least as accurate as the Fluke 87s. The preliminary documentation I got with the meter contained no accuracy specifications. Bottom line is I couldn't catch the Amp-hour+2 making any errors in relation to the measurements made by the Flukes. Using the Amp-hour+2 This meter provides a whole new level of information about our battery packs. I had always wondered what the efficiency of our old lead-acid batteries were. Well, according to the Amp-hour+2 our old L-16s have an efficiency of 71%. This is low and tells you why I am replacing all our lead-acid cells as fast as I can install recycled nicads. Measurement of battery efficiency is a breakthrough, and credit goes to the Cruising Equip. Crew for a job well done. It is extremely handy to be able to measure battery voltage and net battery amperage using the same display. It much more functional to have all these high tech electronics monitoring more than one battery bank. There is a hell of a lot of information and intelligence in this small box. And there is a whole bunch of other features that I haven't even covered so far. For example, high and low battery alarms, and a Pulse Width Modulator regulator option. Cost The Amp-hour+2 is not cheap. The Amp-hour+2 model, which does two battery packs and comes with two shunts, lists for $399. A model called the Amp-hour+ has all the same functions as the two battery model, but only measures a single battery bank. The Amp-hour+ lists for $329. and comes with one 500 Ampere, 50 milliVolt shunt. Conclusion An Ampere-hour meter is the most useful instrument to have in a battery based system. Cruising Equipment's Amp-hour+2 meter is the smartest, most accurate, and most versatile Ampere-hour meter I have ever used. It is the only Ampere-hour meter to actually determine a battery pack's efficiency, use this data in its calculations, and display this data to the user. Cruising Equipment's new Amp-hour+2 meter is hot stuff. Access Author: Richard Perez, c/o Home Power, POB 130, Hornbrook, CA 96044 „ 916-465-3179. Maker: Cruising Equipment Co., 6315 Seaview Ave. N.W., Seattle, WA 98107 „ 206-782-8100.