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EnerGenius® IQ Dual Microprocessor Rectifier / Battery Charger

Primary Product ID

Powers DC loads and delivers reliable, high-performance battery charging

  • Dual microprocessor control
  • Battery check system
  • Black box data recorder
  • C-UL, CE, IBC, and optional ABS certifications
  • Modbus communications option

Applications: Electric utility, oil & gas, process automation, engine starting, communications

EnerGenius® IQ is a utility-grade DC power supply/charger offering industry-first on-board battery checking and data logging systems. By integrating monitoring and logging capabilities into the charger EnerGenius IQ cuts the cost of these features by 75% to 90% over previous solutions.

EnerGenius IQ is ideally suited for global application with a wide range of input voltages and certifications including: C-UL listing, CE marking, IBC seismic, ABS type approval and optional OSHPD certifications.

The optional CommsGenius™ multi-function communications processor provides advanced networking capabilities including Modbus remote communications, digital load sharing, and charger / comms setup using a USB-connected PC.

Patent Pending

iso ul_listed ce IBC innova1 cse TAcircle small

Frequently Asked Questions
What is EnerGenius IQ?

EnerGenius IQ is a highly reliable, utility-grade battery charger/rectifier with microprocessor control and well-filtered output. It simultaneously supplies smooth DC to critical loads, recharges the connected system battery and automatically maintains flooded lead-acid, VRLA, or nickel-cadmium batteries in peak condition.

When was it released?

Revenue shipment started in 2006.

How is EnerGenius IQ similar to other utility/industrial charger/rectifiers?

Like other utility/industrial chargers, EnerGenius IQ is designed to power critical equipment and recharge and maintain associated stationary batteries. Applications include utility substations, electrical switchgear, DC control systems, engine starting, and related infrastructure equipment.

How is EnerGenius IQ different from other utility/industrial battery chargers?

The award-winning EnerGenius IQ offers significantly lower total cost of ownership than any competing product:

More than a charger:

  • IQ offers unique features that boost DC system reliability
  • Integrated Battery Check system automatically tests performance of the connected system battery.
  • On-board “Black Box” data logger captures relevant digital & analog charger and DC system data for later download and analysis.

Class-leading quality, reliability and safety:

  • 5-year standard warranty, backed up by > 500,000 hour observed MTBF
  • Dual microprocessor control provides internal fault tolerance superior to either conventional analog or single microprocessor-controlled chargers.

Unmatched standards compliance:

  • Safety agency listings include C-UL listing for all 60 Hz units and C-UL listing + CE mark for all 50/60 Hz units
  • IBC seismic certification for all wall mounted units. OSHPD pre-approval optional.
  • EMC immunity to IEC 61000-6-2, ANSI C37.90 and ANSI C62.41.

Lower operating cost:
2% to 10% higher operating efficiency than competing units. For a charger delivering continuous 1200W output the annual savings of 7.5% efficiency would be 1,139 KWH/year. Cost savings over 20-year life of the unit for electricity priced at $0.10/KWh would be $2,278, or nearly the purchase price of the charger.

“Future-proof” architecture:

  • Easily field-upgradeable firmware extends the charger’s useful life by enabling new features to be retrofitted to the charger by employing a simple software update procedure. Other, old technology chargers need to be replaced to upgrade function and features. The ability to add new features during the long life of the EnerGenius IQ protects users’ capital investments.
  • PC interface adds an easy-to-use GUI for charger and communications setup and for analysis of Black Box data logger data. The PC interface makes these features easier and more intuitive to use.
What awards has the charger won?

The 2007 Innova Award, presented by Battery Power Protects and Technology
The 2009 Consulting/Specifying Engineer Product of the Year Gold award

In 2009 Consulting-Specifying Engineer (CSE) named the SENS NRG and IQ chargers as 2009 Products of the Year in the “emergency, on-site, and standby power” category. CSE’s panel of industry experts evaluated a wide range of product entries and selected SENS chargers as Product of the Year finalists. CSE’s subscribers voted to determine the Product of the Year winners. SENS IQ and NRG chargers took top honors. CSE’s subscribers consist primarily of consulting-specifying engineers, a highly trained and informed set of professionals who specify a wide range of systems for industrial projects. Recognition from these engineers is significant, because of their highly relevant knowledge in SENS’ product categories.

The 2007 Innova Award recognized the EnerGenius IQ as the product with “the technology that has the most promise of impacting/improving the power industry.” Battery Power Products and Technology awards its Innova Awards based on voting by professionals in the power industry. The EnerGenius IQ won the award against other Best Technology entries from Intersil Corp and Argonne National Laboratory.

What applications is the EnerGenius IQ designed for?

Any DC-powered mission-critical application, such as utility substation, power switchgear, engine starting and DC-powered control systems. It excels at recharging VRLA, flooded lead-acid or nickel-cadmium types of batteries.

What industry approvals and certifications does EnerGenius IQ carry?

All EnerGenius IQ chargers are C-UL listed. 50/60 Hz models are C-UL listed and CE marked. As of 2012 IQ is the only product in its class to be have received third-party certification to the seismic requirements IBC 2000, 2003, 2006, 2009 and 2012. The IQ is certified to an SDS level of 2.50G, qualifying it for critical applications in all parts of the United States. In addition, California OSHPD pre-certification is available on wall mounting IQ’s (Cal-OSPHD number OSP-0131-10).

How reliable is the EnerGenius IQ?

Extremely reliable. Field-demonstrated MTBF is in excess of 500,000 hours gives us the confidence to offer a full five-year warranty.

What did SENS do to make the IQ reliable?

High reliability is tough to accomplish. SENS addressed all of the disciplines necessary to succeed. These disciplines include:

  • Understanding customer needs & incorporating knowledge from prior products
  • Robust product architecture
  • Engineering reliable hardware
  • Engineering reliable software
  • Manufacturing execution
  • Design for service and support
What lessons from customers did SENS learn?

In mission-critical systems the only things matters is uptime. Nobody really cares about the specific components of the DC system hardware – the battery charger, the battery, or any other DC system hardware. SENS’ view is that because customer downtime is by far the highest cost associated with a battery system, Job #1 is to reduce the probability of a DC system failure. That’s why we made the effort to put in features like Battery Check, the Black Box data logger and dual microprocessors.

What is “robust product architecture”?

Architecture is the high-level plan for the product that describes how the various hardware and software systems interact, and how this will evolve over time. One of many examples where SENS is ahead of its time is our dual microprocessor architecture. Recall news of “unintended acceleration” in drive-by-wire cars. The battery charging equivalent of “unintended acceleration” is runaway charging voltage, the consequences of which can include fire or explosion.

EnerGenius IQ includes two “brains” (microprocessors), each of which operates a different switch analogous to your car’s ignition switch to enable the charger. Both switches must be “ON” for the charger to operate. If one processor is for some reason unable to shut down the charger in case of runaway voltage the other one will do the job. Dual microprocessors are like having a second driver in the car ready to hit the brake if the primary driver loses control.

How does SENS engineer reliable hardware?

We combined the field-proven power train of our bulletproof ECU charger with a new (in 2006) modular software system. The SENS design team is trained at some of the top engineering schools in the US, and includes expertise in SCR and switchmode power conversion, electromagnetic compatibility, analog and digital microcircuits, embedded software development, mechanical design and product safety engineering. After extensive computer-based design our team builds prototypes, performs rigorous FMEA (failure mode effects analysis), tests, and tests again.

What about software engineering?

SENS uses a best-practice engineering approach called “regression analysis” to validate software quality. At SENS, regression analysis includes extensive software testing of all charger functions against a documented procedure at every release. The rate of software errors, or “bugs”, is logged and charted over time. New software is withheld from release until it clearly demonstrates high quality release-level stability.

How is the assembly quality of SENS chargers different from others?

SENS is the charger industry’s Lean manufacturing expert. SENS’ Lean manufacturing lines perform multiple quality inspections of every product during its assembly. For more details see http://sens-usa.com/upload/lean_production.pdf.

In our industry, SENS is unique in employing a technique called, “touch for quality”. Touch for quality means that all fasteners inside the charger have a high visibility mark applied by assemblers and test technicians at each successive workstation. The act of applying this mark causes each successive operator to look carefully at the fastener. In the course of looking at the fastener it’s easy to see a multitude of problems, including missing or incorrect hardware or uncompressed locking device. Touch for quality has virtually eliminated one of the most frustrating problems customers face in the field: loose hardware.

How is SENS design for service and support different?

One of the hardest things to acquire during a service call is information about the battery system, such as site environmental conditions, alarm history, history of charger adjustments and internal charger data at time of failure.

Now, SENS’ unique Black Box data logger makes charger and DC system data acquisition and analysis possible. The charger writes regular records to the Black Box that that can quickly reveal most of the necessary information needed to isolate and correct problems. Unauthorized charger adjustments, for example, often cause battery under- or overcharging. By showing the history of charger adjustments, SENS’ Black Box can identify when and if unauthorized charger adjustment was the cause of battery problems.

In addition, once the Black Box data is transferred into SENS Insight analysis program on a PC the charger data can be quickly compressed and emailed to SENS or a service partner for analysis.

Do you have any live examples of how the Black Box helped resolve a service issue?

Yes. One an intermittent charger problem and the other a site configuration problem:

An IQ customer reported that the ammeter of his 50A charger very occasionally read 70 amps, which is far beyond the maximum current limit adjustment. Intermittent problems like this are often difficult to reproduce, leading to frustrating and costly delays for both user and service technician. Black Box data emailed from the customer, however, revealed the source as a wiring harness workmanship problem, rather than electronic component or design failure. This has led to corrective action in the wiring harness.

A different IQ customer that located his battery and charger in very different ambient temperatures was able to demonstrate to himself from the Black Box temperature and voltage logs that he could improve charging and accuracy and battery life by adding the remote battery temperature compensation option.

In addition to UL listing and CE marking what else does SENS do to enhance user safety?

Chargers with higher AIC breakers include arc flash protection

What is “arc flash” protection, and why does it matter in a battery charger?

Per recommendation by our circuit breaker manufacturer, SENS has installed plasma diverters in some models to insure that any hot gas ejected during overcurrent operation is directed to a safe place inside a closed portion of the charger housing. This insures that even under extreme breaker trip conditions a nearby operator would be protected from any breaker trip residue. This is conservative design practice that we have not seen emulated on competing products.[1]

[1] One NRTL listed competing product employs 48-volt DC rated breakers in the 130 volt DC output circuit. This is unsafe engineering practice and is contrary to UL requirements for use of circuit protective devices.

How does Battery Check compare with standalone battery monitors?

In comparison to standalone battery monitors, the IQ Battery Check system is fully integrated into the charger. It is intuitively easy to use, and requires no separate hardware, wiring or software. And its cost is extremely low. In contrast to standalone battery monitors employing discrete hardware, Battery Check makes use of the charger’s power supply, microprocessor, and high accuracy digital to analog (DAC) and analog to digital (ADC) converters.

Intended as a general early warning of possible battery problems, Battery Check gives a simple PASS/FAIL indication of battery status. Its purpose is to summon a trained battery technician to the site where he would localize the problem and take appropriate corrective action.

Some standalone battery monitors are able to provide detailed, trended cell-level diagnostics that reduce troubleshooting time. While valuable on large UPS systems that sometimes include hundreds of cells, these systems require costly hardware, complex cabling to each battery jar and specially trained technicians to operate. Total cost of these investments can easily exceed $10,000 to $50,000. Even after installation, the complexity of some standalone monitors causes some users to give up using them.

How does Battery Check work?

Initiated either manually or on a user-adjustable automatic schedule, Battery Check gives a Pass/Fail assessment of the battery’s ability to carry the connected system load. It does this by reducing charger output and allowing the battery to support the load. A healthy battery supports the load. During the check the charger stays active as a DC power “backstop” to prevent dropping of the critical load in case of a missing or failed battery.

At the conclusion of a successful Battery Check the Black Box logs the successful result. When the charger detects a Battery Check failure three things happen: The check is terminated and the charger returns to its charge mode prior to the check; a latching visual, audible and remote alarm is issued and “battery check fail” is logged into the Black Box. The audible alarm can be cleared with a key press, but the visual and remote indications persist until a successful check (of a new battery) or until following a procedure specified in the user manual.

Is Battery Check adjustable?

Yes. All parameters are adjustable, including whether it is enabled, whether to run automatically, duration of test, frequency of automatic test and test voltage setpoint.

On what type of DC load does Battery Check give the most accurate results?

Battery Check gives highest accuracy results in a DC system with a relatively large constant load, in general, greater than 10% of the charger’s rated output current.

How does Battery Check work with light loads?

Battery Check is most useful with heavier loads because it depends on the connected load to stress test the battery. There are two issues that limit its effectiveness on very light loads:

Very light continuous loads on large batteries place such small stress on the battery that even weak batteries can sometimes pass

In switchgear and engine start applications the periodic loads are much larger than steady-state current draw. In these applications Battery Check does not today give an accurate picture of the battery’s ability to support the large intermittent loads

If a weak battery can pass the test what’s the use of Battery Check?

Battery Check actually emulates the regular site assessment practice that many electric utilities employ, but automates the work. For example, after arrival at a substation maintenance crews frequently shut down the charger before commencing other PM work. Just prior to leaving the site the crew verifies that the station battery has performed to expectation and then restarts the charger to verify that the charger delivers acceptable recharge current.

IQ Battery Check is better than the manual process described above because:

  • With Battery Check the AC breaker never is turned off, so there is no risk of dropping the load, even with a dead battery
  • The routine can be scheduled to run automatically, reducing the time that maintenance staff spend at the site
  • Test results such as voltage during the test are automatically logged in the Black Box data logger. These results can be reviewed and analyzed if necessary
  • When a charger is equipped with available Modbus data communications, the battery check can be manually initiated and monitored remotely
If Battery Check doesn’t always give perfect results why use it?

Many system failures are caused by simple human factors such as forgetting to close a battery breaker. Battery Check can catch some human factors problems before they create a crisis.

Battery Check’s emulation of present generation maintenance techniques presents an opportunity for cost savings through more efficient deployment of maintenance staff.

When demonstrating DC system integrity Battery Check is the less risky alternative to turning off the charger ‘s AC breaker because it protects from several potential ways battery energy could fail to reach the critical load:

  • The battery has failed
  • A battery jumper was not replaced after maintenance
  • The battery circuit breaker is defective or has failed
  • There is a failure in wiring or wire terminations
What is the “Black Box” data logger?

The charger writes a wide variety of digital and analog values to its storage device once per hour. The values can later be viewed using SENS’ Insight software on a PC in chart and table format.

What analog values does the “Black Box” record?

DC voltage, charger output current, temperature, AC input voltage and a variety of internal voltages, temperatures and other data points that can be used for troubleshooting. The charger writes the minimum, maximum, and average values for most variables every hour.

What digital values does the “Black Box” record?

All alarm conditions are captured, even if they occur momentarily.

What else values does the “Black Box” capture?

All user adjustments are recorded. Each adjustment causes the Black Box to write both new and old values. In case of battery problem this is a great help in determining whether an unauthorized adjustment led to under or over charging.

  • Reboots
  • Automatic battery check events
Why did SENS include “Black Box” data logger?
  • To reduce troubleshooting time and uncertainty, particularly when we are remote from the installation
  • To record events leading up to, and associated with, system failures
  • To help users take corrective action based on facts
  • To help SENS deliver better customer service
What other chargers offer a Black Box data logger?

None that we know of.

How are the log files read and interpreted?

SENS supplies a PC-based program called SENS Insight to import, manage and interpret the charger’s log data on a PC.

Where do I get SENS Insight? How much does it cost? How do I use it?

You can download it from our Download Center. You will need to register on the site, but downloading the software is free of charge. Instructions for use of the software are included in the download.

Beside your standard format what other formats can I use to analyze charger data?

Standard embedded charts and tables are are available.

With regard to chargers, what do “parallel operation”, “load share” and “forced load share” mean?

Parallel operation: Two chargers are connected in parallel to the same battery

Load share: The degree to which current is shared between two chargers connected to a common DC bus. In theory, two chargers delivering exactly the same output voltage through DC leads of exactly the same resistance will share the load equally.

Forced load share: A scheme intended to cause chargers to share output current despite normal manufacturing tolerance and unavoidable variation in resistance of charger output cabling

How does digital load sharing, differ from older “forced load share” charger schemes?

The IQ’s digital load share system is different from the several conventional forced load share schemes in three main ways:

  • Connecting the IQ load share cable automatically propagates every charger adjustment parameter from one unit to the other. This essentially “clones” the chargers.
  • Two IQ chargers connected in parallel act as one. Selecting a different charging mode of one charger causes the other to also change mode at the same time.
  • The optional battery remote temperature compensation probe delivers the same temperature data to each charger to insure commonality of operation

In addition, operation of the IQ digital load share scheme is completely independent from of the AC source, meaning that two chargers powered by different grids or from different input voltages will reliably load share.

How does the IQ digital load sharing system work?

Digital load share is activated by connecting a load share cable between the optional CommsGeniusTM card installed in one IQ charger to the control card of the other charger. Once both chargers are started, settings from the charger in which the CommsGenius is installed are written to the other charger. This makes the charger adjustments identical in all respects.

Why are adjustments in one charger disabled with load sharing enabled?

Settings are propagated only from the charger hosting the CommsGenius to the other charger. To insure that the second charger retains all values supplied to it by the lead charger the second charger’s keypad is disabled. After the load share cable is disconnected the second charger’s keypad is automatically re-enabled.

How does the load-sharing system work?

The IQ load share system is a digital implementation of the analog Joint Integrated Avionics Working Group (JIAWG) 88-M7A protocol. This provides a low bandwidth output current control loop dedicated to current balancing. It provides good current sharing without compromising output load regulation performance.

In contrast to the “droop” load share system this implementation does not rely on output conductor voltage drop. The drops need not be matched, and the system performance is good even if the conductor resistance is extremely low. The load share system adjusts voltage set point continuously so that both chargers maintain current balance within 10% of each other when delivering a high percentage of their output.

How reliable is the current share system?

It is highly reliable for several reasons. Voltage adjustment range is limited to +2% if a current share line fault occurs, meaning there is very limited range for maladjustment in case of a fault. Load balancing does not depend on matching of input voltage, phase, or frequency, and does not depend on matching SCR trigger delays. The current share system has low bandwidth for high noise and ripple rejection, meaning there is a low probability of misoperation due to external influence. If a charger goes off-line, there is no impact on the other charger. If the load share system were to fail both chargers would revert to non forced load sharing operation.

Can chargers with different current ratings be used in load share configuration?

Yes. Any IQ chargers with the same rated output voltage can be paralleled. Load currents will share according to percent of rated charger output.

Why don’t the chargers share current precisely at light loads?

This is deliberate for reasons of stable system operation. In the JIAWG 88-M7A protocol the “leader” and “follower” chargers are designated automatically. If we try to match output currents too closely, electrical noise and other disturbances could cause the automatic selection of the “leader” charger to change from unit to unit erratically, resulting in output voltage disturbances. To prevent this “hunting” behavior we deliberately included a fixed offset in the system. At light loads this offset shows up as somewhat unbalanced current. The following values are typical of this offset at light loads:

Leader: 134.3 volts DC, 1.6 amps

Follower: 134.6 volts DC, 0.7 amps

How many chargers may be connected together in parallel?

When using forced load sharing the limit is two chargers. When using random load share, without the forced load share system, there is no upper limit on the number of chargers.

Should the forced load share option be used between two chargers connected to two different batteries?

No. Forced load share should only be used when two chargers operate in parallel on the SAME battery.

Why does remote temperature compensation require the CommsGenius card?

Safety: The IQ’s control card is at battery potential. The CommsGenius, however, is isolated from battery potential. Connecting the remote temp sense probe to the isolated CommsGenius thus eliminates the risk of voltage on the probe itself.

Performance in a redundant charger system: In a redundant charger system where both chargers are connected to a common battery both chargers must use the same voltage reference. This is accomplished by deploying the common sensor value to both chargers via the CommsGenius.

How do you recommend attaching the remote probe to the battery?

SENS recommends fixing the remote probe directly to the battery, instead of sensing ambient air near the battery. This is particularly important when battery blanket or other temperature controlling elements are used with the battery.

On battery systems where one polarity is connected to earth ground we recommend connecting the remote probe direct to the grounded terminal. On floating, or ungrounded, battery systems we recommend fixing the temperature probe to the battery itself.

Both methods are explained in detail in the installation instructions accompanying the remote probe.

Why does SENS use dual microprocessors in the IQ?

Three reasons:

  • It’s important for charger reliability to separate the I/O intensive functions of the user interface, Black Box system and communications from the simple control and regulation of the charger. Separating basic control and regulation from I/O intensive functions makes it easier to add new features to the charger.
  • Each processor operates a different set of alarms or communications cards, giving redundancy of alarms. The “control” processor drives the summary relay, while the “monitor” processor drives the individual relays and communications card.
  • To enable full redundancy in the overvoltage shutdown system. Please see the overvoltage shutdown section below for details.
What other utility/industrial charger uses dual microprocessors?

None that we know of.

How do you reliably prevent the charger’s voltage from running away?

We don’t think an IQ would ever lose voltage control. But if either of the two potential causes for overvoltage runaway were to occur here’s how we address each case:

In case of a shorted rectifier bridge component this would short circuit the transformer secondary winding, causing the AC input breaker to trip, stopping all input to, and output from the charger.

If there were to be a control system failure: Each of the two microprocessors runs different firmware and actuates a different transistor to enable the power train. Both processors must command their respective transistors to be ON in order to enable SCR drive. Either processor has the authority and actuator mechanism to turn off the charger. Should a failure occur in a processor, its firmware or actuator transistor the redundant function of the other processor remains capable of shutting down the charger.

Why is overvoltage shutdown redundancy so important?

Runaway charging voltage is like unintended acceleration in a car. An out-of-control charger will overcharge the battery, increasing the possibility of fire or explosion.

What is “selective” overvoltage shutdown and why does it matter?

Where there are multiple sources of DC on a single bus it is important to shut down only the source of the overvoltage problem. We do not want to turn off the “victim” devices. They need to stay operational after the problem source is shut down to insure continuity of power to the critical load.

The IQ’s overvoltage shutdown system determines whether it is the cause or the victim of an overvoltage event. If it is the victim, the charger remains on but delivers no output during the overvoltage event.

How do you prevent nuisance overvolt shutdowns?

False overvolt shutdowns are unacceptable. SENS addressed the multiple possibilities this could happen as follows:

  • IQ is EMC hardened against all reasonable electromagnetic immunity threats as specified by ANSI and IEC.
  • The selective overvolt shutdown system discussed above prevents the problem of other chargers or other power supplies shutting down a good IQ.
  • The IQ shutdown logic requires the charger to be in an unambiguous overvolt condition for several seconds before the shutdown occurs. This prevents momentary transient events from turning off the charger.
Can the charger’s firmware be upgraded in the field?

Yes, and without the need for a PC or other specialized equipment.

What’s the benefit of field-upgradeable firmware?

Upgradeability enables new features and functions developed over time to be retrofitted to the installed base, protecting customer investment in the IQ regardless of date of purchase. If a firmware upgrade is required to activate the new feature it’s easy to do. Upgradeable firmware allows customers desiring these new features to retrofit their existing charger, bringing it up with new production units. This “future-proofs”” your charger investment.

How is the firmware upgraded?

SENS supplies a small card containing the new firmware that fits into a port on the charger’s control card. The upgrade process for both of the control card’s dual processors takes less than five minutes.

Our firm is very risk-averse. How can we be sure the upgrade will work correctly?

SENS performs extensive regression testing on all firmware release candidates prior to shipment. We track defect rates and release only after there is objective evidence that the new release candidate is stable.

All SENS firmware includes CRC (cyclic redundancy check) and other error-checking algorithms to ensure data integrity. The field software loading process has been extensively tested and, is 100% tested in every charger prior to shipment.

How often has SENS made major firmware releases?

Roughly once per year. See the Firmware Update History page.

What competing firms offer easy-to-install upgrades on a regular basis?

None that we know of.

What alarms are included as standard?

AC fail, charger fail, low DC voltage, high DC voltage, battery on discharge, battery discharged, ground fault alarm and battery check failure. Indication of normal operation or alarm conditions are displayed as multicolored LEDs on a charger mimic panel and in text form in a 2 x 20 LCD. All chargers include a summary Form C contact as standard for alarm indication. Other options for remote indication of alarms are multiple Form C contacts or network communications.

How does the SENS “charger fail” alarm work?

Does it measure low current or low voltage?
The IQ’s “charge fail” alarm is more sophisticated than simple low current or low voltage indicators that cause false alarms. If either of the following conditions is met the “charge fail” alarm will activate:

Low voltage AND no current AND AC power on. This condition indicates that the control system’s command for output is going unanswered.

Excessive voltage AND high current output. These conditions indicate that the control system’s command to stop producing output is going unanswered. This condition activates the overvoltage shutdown system.

What is the purpose of the low current alarm?

The low current alarm can be useful to users wanting to know if their load is still consuming power from the charger/DC system. At this time remote indication is possible only over the Modbus communications interface.

The Modbus option can address either one or two chargers of the same voltage rating. When should two chargers in a system each be equipped with a Modbus card?

If each charger is connected to a different battery each charger should be equipped with its own Modbus card. If the two chargers are connected in parallel with a common battery use only one Modbus card.