About That Blocking Diode...
          In our industry, we may occasionally see a specification for a battery charger that has a requirement for a "blocking diode".  Sometimes the specification is more vague, with wording like "The charger shall not discharge the battery during an ac power failure."  This is often interpreted as requiring a blocking diode.
     Some History
          The blocking diode requirement has been around for a long time.  After World War II, when electronically controlled chargers first started to appear, the favored design was the magnetic amplifier.  The MagAmp, as it is still called, is rugged and reliable.  It also has a hidden "feature:" it cannot produce zero output current, although modern designs can come close.  A common technique to overcome this difficulty was to add "loading" resistors on the output terminals.  The resistors were sized to absorb the minimum current output at the desired operating voltage.
          When a MagAmp is used as a battery charger, the loading resistor can add extra load to the battery during an emergency (e.g. ac power failure).  To maximize the battery backup time, manufacturers inserted blocking diodes between the loading resistor and the output terminals of the charger, a simple and effective solution. Eventually, the diode requirement became a de facto law, even for chargers based on other control technologies.
     The Downside
          You knew there would be one...right?  It is easy to see that a blocking diode consumes both dollars and Watts.  It has to be rated to carry the full output current of the charger forever.  In doing so, it wastes energy.  In a 50Adc charger, a blocking diode can continually consume 60 Watts or more, about 1% of the total power output.  In addition to the cost of the diode, there needs to be a heat sink, mounting considerations, and of course, additional space in the charger enclosure.
          A common perception today is that the blocking diode is necessary to prevent discharging the battery in the event of a charger failure.  However, the blocking diode isolates the battery only from the filter capacitors and the rectifier components (SCRs and diodes).  Even the so-called polarity diode is "unprotected" by the blocking diode.  Actually, protection against charger failure is built into the dc output protection (fuse and/or circuit breaker), since a capacitor or SCR failure is catastrophic and produces a short circuit.  As we know, the original purpose was to isolate the loading resistor.
     The Upside
          SCR type chargers don't need blocking diodes, because they don't need loading resistors.  The load on the battery during an ac power failure consists only of the current necessary to operate alarm circuits and, in the AT series, the main control circuit.  And this current would be present even if a blocking diode were included.
          Yes, the SCR/SCRF Series battery charger does have a blocking diode.  This product line was designed "back in the day", when many more specifications called for a blocking diode.  The AT10.1 and AT30 Series charger do not have one.  We think our customers appreciate the lower price and higher efficiency.  Long-term reliability is higher, also, since there is one less highly stressed component.

Altitude And Temperature De-Rating (JD5006-00)
          A standard industrial battery charger / rectifier may be operated at any ambient temperatures (up to 158 °F / 75 °C) or higher with proper de-rating.  Any standard rating may also be operated at any elevation (up to 10,000 feet / 3,000 meters) with proper de-rating.  No battery charger/rectifier should be operated beyond these limits.  For further details with a de-rating graph, please refer to our Altitude And Temperature De-Rating Application Note (JD5006-00).

CASM PC Board Adjustment (JD0036-00)
          The adjustment of the SCR/SCRF Series Combined Alarm Status Monitor (CASM) is a subject of frequent request.  We often are asked to provide user set points for batteries and loads.  Adjustments of the CASM PC Board are documented in service instruction (JD0036-00).

Float & Equalize Settings
          Common customer calls come in concerning the proper Float and Equalize settings on the charger for their specific battery.  Each type of battery has different float and equalize settings.  Consult your battery manufacturer's documentation for specific values and settings for your battery type.  The following table contains suggested values for commonly used batteries.

* Sealed Lead-Acid battery types should not be used in ambient temperatures above 95°F/35°C, and should not normally be equalized.  Please consult your battery manufacturer's documentation for specific equalizing recommendations.

Ground Detection Issues (JD5032-00)
          The most common requests for information from our customers are for ground detection options.  Often when a ground detection alarm activates, the user believes the fault is the alarm setting or limited to the inside of the battery charger.  For your convenienceIf an alarm is activated, the problem is best determined by measuring the voltage difference between the battery (-) to chassis ground and the battery (+) to chassis ground.  The measurements should be the same if no other ground detection has been added to the dc bus.  This will often determine severity of the fault.
          The best way to troubleshoot the location is to disconnect sections of the dc system and continue to measure as above.  Switching power supply loads have large capacitors connected from the dc input and chassis ground, and may have enough leakage current to cause ground faults.  Another common problem is that the user has a grounded load and the Ground Detection Option is activated all the time.  This may become undesirable.  Most Ground Detection Options can be disabled by reading the user's manual.  Battery chargers that charge only a portion of a bank cannot use ground detection.  This is a rare occurrence, and most often comes in the form of two (2) 130 Vdc battery chargers being used to charge a 260 Vdc bank.
          For your convenience, we have codified a handy trouble-shooting guide called Ground Detection In The Real World (JD5032-00).  Hopefully, this will be a great resource our users of our battery charger products in lieu of an actual technical service call.

High/Low Alarm Set Points
          Customer calls also come in concerning the set points for high and low alarms.  Set points require application review.  The dc load is commonly a factor for the High alarm setting.  The Low set point is determined by knowing how much time a site has available to respond to correct a problem if it occurs.

HLVA PC Board Adjustment (JD5019-00)
          The printed circuit board (GK0045-XX) used in the High-Low DC Voltage Alarm is used in many SCR/SCRF Series battery charger options.  Adjustment is tricky because the circuit has a delay between the time adjustment is reached on the actual board and the time lamps and relays activate.  It is easy to over-adjust the alarm.
          During adjustment of the High alarm, connect a meter to R10 on the pc board and output (-).  The voltage will start to ramp down from 10 Volts to zero when the proper adjustment has been reached.  Adjust the Low alarm the same way, only move the meter to R22 on the board.  See also service instruction (JD5019-00).

NEMA / IP Enclosure Types
          Enclosures used for HindlePower industrial battery chargers meet NEMA Standard 250-1085, and are available for types 1, 4 and 12.  An optional drip shield assembly is also available as an add-on to a standard NEMA-1 type enclosure, making the combined assembly compliant to NEMA-2 (*) type standards.  To determine a general equivalency between NEMA types and the European IEC 529 "IP" enclosure standard, use the table below.  Remember that there is no exact correlation between NEMA and the IEC IP system, and you must ensure that any enclosure for IEC standards meets the requirements outlined in the second "The IEC IP System" table below.

• NEMA-1 type enclosures meet or exceed IEC IP23

• NEMA-12 type enclosures meet or exceed IEC IP32

     The IEC IP System
          The degree of protection afforded by an enclosure is designated by a four-character code, "IP" followed by a two-digit number.  The meanings of the numbers are defined below.  For example, IP21 protects against the ingress of moderately sized solid objects (approximately ½in / 12.5mm) and dripping water.

SCR/SCRF Series Load Sharing (JA5054-00 / JD0019-00)
          The SCR/SCRF Series Forced Load Share option (EJ0133-00) requires careful initial setup, and needs periodic adjustment.  Carefully read our service instruction (JD0019-00), and use a quality Digital VoltMeter (DVM) for setting up the chargers to load share.  A common problem arises when too little load is connected to the charger set.  Keeping load current the same is difficult when the current is very small.  The SCR/SCRF Series load sharing option is not recommended for such an application.  The AT10.1/AT30 Series Forced Load Sharing option (EJ5126-##) can accommodate such low load applications.  Please see user instructions (JA5054-00).  We always recommend using our more advanced microprocessor-controlled batter chargers (AT10.1 / AT30) in 12, 24, 48, and 130Vdc applications.

UMC Digital DC Meter Irregularity
          Some users of the Universal Maintenance Charger (UMC) in its early configuration experienced some irregularity in the displays of the unit's low-profile digital dc meters.  Corrective action was taken in the form of a design review.  The power supply for the digital meters was reconfigured and began shipping with all newly-manufactured UMCs as of 12/23/2004.  If you are experiencing any irregularities with your UMC digital dc meters, a meter power supply upgrade kit is available for free.  This kit contains a revised meter power supply, and installation instructions.  Please have the Serial No. for your UMC handy, and contact our technical service specialist Rich Fauerbach for availability.