Battery Monitors: The E-Meter Vs. the Sophisticated SALT
In the February 15, 1997 issue, we reviewed battery monitors and stated that Cruising Equipment’s E-Meter was the only one of the four models tested that could tell you how much energy remained in the battery. It didn’t take long for the folks at Sea Air Land Technologies, manufacturers of the SALT system, to cry “Foul!” Measuring and reporting on energy remaining, they pointed out, is one of the primary functions of their system. We decided to take another, closer look at the two monitors. And, while we were at it, we added two more products not previously tested.
What We Tested
The E-Meter is a single battery (or single battery bank) unit that uses a resistive shunt as a current sensor, while the SALT monitors up to four banks of batteries (or an equal number of current-consuming devices) that relies on Hall effect current sensors.
To these we added the Heart Interface Link 2000—essentially a pair of E-Meters in one package—with a pair of shunts so that it can handle two banks of batteries; and a different model of the SALT System, which uses resistive shunts in place of the Hall effect loops.
What They Do
The battery monitors we tested will all read your rate of discharge and feed it to a microprocessor that is programmed to multiply it by the time elapsed, subtract that result—in ampere-hours—from what’s available in a full battery, apply some preset (or user-set) information, and display how much battery life is remaining. This display can be either in operating hours left (as on the E-Meter and the Link 2000) or in ampere-hours (as with the two SALT models).
The remaining life of a battery, regardless of how one chooses to report it, is dependent on a number of factors: the size in ampere-hours of the battery or battery bank involved, its age, the ambient temperature, the rate of discharge, and the number of and length of discharge cycles. When running your alternator or generator (solar, wind, etc.) at the same time, the microprocessor will add that current input to your system and give you an accurate reading of the net rate of charge or discharge at the time. The various models differ in the number of inputs that they can monitor.
How They Do It
Sensors. Basically there are two ways that these devices sense current flow. One is by measuring the voltage drop across a resistive shunt with very low resistance in the line from the battery. These shunts are generally made of manganin—an alloy of copper, manganese, and nickel, which maintain a stable resistance over temperature extremes. Resistive shunts are wired in series with the circuit measured.
The other device is the Hall effect sensor. When a wire, such as a battery cable, is passed through one of these magnetized loops, the monitor measures the strength of the magnetic field of the current flowing through the wire. Hall effect sensors have an advantage in that they don’t have to be connected in series with the circuit they measure. On the other hand, they can drift over time and temperature and must be conditioned periodically. They also require a small amount of power.
Sea Air Land Technologies swears by the Hall effect sensors—they call them SALT Loops—although they also make a model that employs resistive shunts. Cruising Equipment, which makes the E-Meter and the Link 2000, swears at them.
According to SALT, shunts offer installation problems that can cause overheating. They feel that the risk of overheating is present even when all wiring is done correctly. The folks at Cruising Equipment feel that Hall effect sensors are temperature sensitive and unreliable for low current applications.
Readouts. Another major point of difference between SALT and Cruising Equipment lies in the area of just what information should be displayed.
A battery monitor should act much as a fuel gauge for your battery, giving you the same kind of information that your fuel gauge does. It’s a lot easier dealing with fuel, however. After all, a gallon of fuel, for all practical purposes, remains a gallon of fuel regardless of the air temperature and the rate at which you burn it. Any variations, such as expansion and contraction with changing temperatures, are very small and can safely be ignored. The same goes for the size of your tank: Effectively, if your 100-gallon tank is half full, you can be sure that you have 50 gallons of fuel left.
A battery or battery bank, like a fuel tank, stores energy, expressed in ampere-hours (Ah) instead of gallons. Unfortunately, though, a 100-Ah battery won’t deliver 100 Ah unless you’re drawing current at an extremely low rate. The actual effective capacity of a battery is strongly dependent upon the rate at which you deplete it. It can also vary with temperature and the age of the battery. The difficulty in making battery state-of-charge measurements can be likened to a fuel tank made of rubber that expands and contracts while your boat is underway.
SALT has chosen to stick with ampere-hours when it comes to expressing remaining battery capacity. They feel that it’s a measure that most boat owners can relate to. Cruising Equipment, on the other hand, uses an algorithm called Peukert’s equation—a mathematical relationship between rate of use and percent of battery capacity remaining—to enable them to express reserve battery capacity as operating time remaining.
Both products also display volts, rate of current draw, and ampere-hours drawn.
How We Tested
Our basic performance tests were simple enough. We fully charged a new gel cell battery and then applied varying loads with all the monitors connected. We compared voltage and current readings with those we obtained from a laboratory meter.
We also tried to reproduce conditions that would demonstrate alleged shortcomings. These tests included high-temperature operation, extended operation at a low current draw, and operation at extremely high currents. Finally, we examined the human factors involved—clarity of instructions, ease of installation, and ease of use.
What We Found
Our tests showed that, under normal (and even under somewhat abnormal) operating conditions, all four monitors performed as advertised. There were, however, some definite differences among them.
SALT System Monitor with SALT Loops
This SALT unit consists of a display, a microprocessor module, and from one to four SALT Loop sensors. Up to four battery banks, or a mix of battery banks, charging devices, and current-consuming appliances can be monitored. Controllers for various types of chargers are also available.
The three-button display panel is 4-1/8" x 3-1/8" and requires a 2-1/2" x 3-1/2" hole. The microprocessor module is 5-1/2 x 4-1/2 x 1-7/8". The two-line, black-on-green backlit display has two rows of 3/16" characters and will display up to 32 characters.
This capability lets you label the various functions you’re monitoring, such as “house,” “alternator,” “charger,” or simply “Channel 3.”
All components of the SALT system appear to be solidly made and reasonably resistant to moisture. The controls on the face of the monitor are membrane-type, pressure-sensitive buttons with tactile feedback.
This is a very sophisticated system and careful reading of the manual is required—probably an unavoidable consequence of the system’s extreme versatility. Some additional components are needed, such as terminal blocks, fuses, fuse holders, wire and terminals. All the steps are laid out and installation is not difficult.
Wiring the SALT System for a single channel is simple enough and requires only five wires. The number of wires needed goes up as you add channels and functions, and the manual’s diagram—which illustrates a full-house, four-channel installation—can be intimidating.
Initial set-up can require patience. SALT has chosen to keep its controls down to a minimum, so that there are only three buttons to push. Pressing combinations of buttons sequentially produces menus and allows you to calibrate the unit, set alarms and pre-set it for the capacity of your batteries. All the output information is shown on the same screen; the display scrolls through the five pieces of information provided for each activated channel.
The Salt displays voltage, amps, capacity remaining (either as Ah or percentage of charge remaining), kW hours, and battery efficiency. It will monitor charging circuits, alternators, solar panels, or wind generators, and control charging and shut off.
The operator can stop the scrolling whenever desired, and “freeze” the display. Scrolling through the many menus and settings by pushing the correct choice of three arrow keys is tedious and, if you are not careful, confusing. Persistence will yield many accurate functions to keep your boat’s electrical system working well.
The system will also do diagnostics. An optional module and software permits hookup to an MS DOS computer. This program, called SALT Link, displays system information numerically or graphically and controls communications between the monitor and the computer or to a remote computer through a modem. It enables you to monitor 21 events and reset your system remotely. There are also logging capabilities for record keeping.
Under normal conditions, the SALT System worked impeccably. The only errors we could find were at extremely low current drains in which the ampere reading was high by a few tenths of an amp. Following suggestions from a competitor of Sea Air Land Technologies, we continued this low drain for an extended period, but we couldn’t obtain the large cumulative effect that was predicted. SALT informs us that the algorithm used in the SALT microprocessor updates each time the battery is charged fully, eliminating the possibility of cumulative errors; our tests support this claim. When we used a hair dryer to raise the SALT Loop to 150°F, we found that we did, in fact, introduce an error of 0.3 amps (10.3 amps instead of 10.0).
When we allowed the SALT Loop to cool down, the error persisted—until we recharged the battery, which restored the unit’s original accuracy. SALT points out that running with an ambient of 150°F will have much more deleterious effect on the batteries than on the SALT Loop; it’s an argument that seems reasonable to us. We found no errors when we heated the meter to a temperature of 125°F (that’s about the most it’s apt to see in real life).
The SALT System with one Salt Loop lists for $425; additional loops cost $75 each. It carries a 12-month warranty.
Bottom Line: The SALT Systems Monitor Plus operated well and would be a good choice if you want to moni- tor multiple devices. Installation is easy, as is operation. Properly labeled data scrolls smoothly across the display screen. You should be careful not to place the SALT loops where they will be overheated.
SALT Monitor with Shunt
From a user’s standpoint, this system is identical to the SALT System just described, except for the sensors, which are resistive shunts instead of Hall effect loops. It worked well under all our test conditions.
Sea Air Land Technologies will provide different capacity shunts for different circuit requirements. The SALT Systems Monitor with one resistive shunt lists for $425; additional shunts cost $50 each.
Like the model with SALT Loops, the resistive shunt model carries a 12-month warranty.
Bottom Line: Although installation of any resistive shunt system involves either adding a length of wire for each shunt or cutting existing wiring and attaching proper terminations, the use of resistive shunts avoids concerns about ambient temperature. On the other hand, the shunt must be able to handle the maximum current load without overheating.
This system is not our first choice for a single circuit, but it becomes more attractive as more circuits are added for monitoring.
Cruising Equipment E-Meter
The E-Meter, also sold as the Link 10 by Heart Interface, consists of a single case containing the display, controls, a microprocessor module and a resistive shunt. It’s intended to monitor one battery (or battery bank).
The round instrument case has a 2.5" diameter bezel and is 2.9" deep, requiring a 2" mounting hole. It mounts through a bulkhead or panel. There’s a single-line red LED display of 3/8" numbers against a black background—very visible. There’s also a four-segment “bar graph” display labeled “E” to “F,” re-emphasizing the fuel gauge analogy. Functions are not directly identified on the screen display, as on the SALT monitors; four status indicators light up to let you know what you’re reading. The controls consist of two membrane-type push-buttons.
The two buttons control an astounding number of functions, from control of scrolling (auto/manual) to locking out the controls to prevent unwanted fingers from screwing up your settings. Most importantly, the buttons are used to make initial settings: battery type, battery capacity, and the value that must be used in Peukert’s equation to permit an accurate indication of time remaining.
The manual is simpler to deal with than SALT’s, largely because of the smaller number of functions that come with the single-channel E-Meter.
Installation is easy. There are five wires to the meter. To attach the shunt (it should be mounted close to the battery), you remove the negative cable from the battery and attach it to one end of the shunt; then take a short battery cable and connect the other end of the shunt to the battery.
To check on concerns expressed about shunt overheating, we connected the shunt provided with the E-meter to a DC welder, and ran 200 amps through it for about 10 minutes with no signs of overheating.
The E Meter displays volts, amps, amp-hours consumed, and time remaining as standard functions. You can have the meter scan between these functions at four-second intervals without constantly pushing the buttons. There are 17 additional functions that allow you to set various parameters to your own needs. By setting up these special functions you can read average current drain at 16- or 32-minute intervals if you have equipment cycling, or set alarms, or read the deepest discharge or the average discharge. You can even set the alarm at your own discharge floor for your battery. In all, there are 50 possible functions. Most boat owners will not want that many. The real strengths of this product are its easy installation, ease of use, and readability in a compact package.
The E-meter lists for $249 and is warranted for 18-months
Bottom Line: The E-Meter is our top choice for owners with only one battery bank. It’s easy to install, easy to use and is relatively inexpensive.
Heart Interface Link 2000
The Link 2000 is, essentially, two E-meters in a single case. It has a double shunt suitable for monitoring two banks of batteries. Unlike the Amp Hour+2 meter which we tested in an earlier report, the Link 2000 includes Peukert’s correction for effective operating time under varying loads.
Like the E-Meter, the Link 2000 stows all its workings in a single package, which includes display and controls. The case has a 5-3/4" x 3-3/4" face, which requires a panel cutout of 4-3/4" x 2-3/4," with about 1-1/2" depth required behind the meter.
The various functions are activated by pressing one of the nine buttons on the membrane face of the display (they have tactile feedback); an indicator light shows which function is currently being displayed.
Careful, step-by-step installation instructions and a clear wiring diagram are supplied—we felt that the Heart Link 2000 came with the clearest instructions of the four models tested. Nine color-coded wires must be wired to a terminal strip, and wires then have to be run from the terminal strip (user-supplied) to the various items of equipment to be monitored. Set-up is straightforward. We found that more buttons reduces the confusion of combinations of buttons, or nested menus.
As with the E-Meter, you can use the default settings for everything except battery capacity (if you have flooded lead-acid cells). A more thorough set-up includes such things as the Peukert coefficient for your particular battery and the time period for which your current consumption should be averaged. This period is used for calculating time remaining—it can make a difference when you don't have a constant load.
Standard function displays include voltage, amperage, amp-hours, and time remaining. And, there are 16 special functions, which, among other things, allow you to toggle automatically between hours and kilowatt hours, use one channel as an amp- hour meter for one or more energy sources, or set your own preferences for charge level and more.
The Link 2000’s list price is $550, and it carries a warranty of 30 months to the original purchaser only.
Bottom Line: For an owner who has two battery banks that require monitoring, or other devices to supplement normal charging, the Link 2000 is a good choice. It’s likely to have all the functions anyone would ever want (the Link 2000R even includes a smart voltage regulator).
We looked at the questions each manufacturer has raised about the other’s products; we don’t feel that, in actual practice, any of the systems should present real problems.
For most owners concerned only with the state of charge of their house battery bank, the E-Meter is clearly the top choice. For the other extreme, a cruising sailor who has solar panels and possibly a wind generator to supplement his engine’s alternator, either of the SALT Systems is the clear choice. We prefer the use of resistive shunts to the Hall effect loops, as long as the shunts are sized properly for the application.
If you have two circuits to monitor, either the Link 2000 or the SALT System with shunts will do the job well, at roughly the same price. Both have advantages, and both have drawbacks. Or, as we noted last February, you can simply hook up two E-Meters.
The Link 2000 has an easier to read display and less confusing controls, but is limited to two circuits. The SALT System minimizes panel space, but requires room for a small box somewhere behind the panel. The Link reads out time-remaining; the SALT reads out ampere-hours remaining; our staff has mixed feelings about which they prefer. Either unit can be misleading if your electrical load changes dramatically after you take a reading. Both require a little thought and a bit of understanding on the skipper’s part.
Contacts— E-Meter, Cruising Equipment Co., 6315 Seaview Ave. NW, Seattle, WA 98107; 206/782-8100; Link 2000, Heart Interface, 21440 68th Ave. S, Kent, WA 98032; 206/872-7225; SALT, Sea Air Land Technologies, 505 107th St., Marathon, FL 33050; 305/289-1150.