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1. Selecting The Right Rectifier/Charger
J. Allen Byrne
Engineering, Training & Tech. Support Manager
Interstate PowerCare
A Division of Interstate Batteries
allen.byrne@ibsa.com
2. Overview What is a rectifier/charger?
Various types.
What is the intended use?
Where is it going to be used?
What technology?
Considerations.
3. What is a Rectifier/Charger? Rectifies ac to dc.
Charges a battery.
Manages a battery.
Powers a load.
Manages the load.
4. What is a Rectifier/Charger? Rectifier.
Rectifies AC to DC
Considerations.
Input voltage and Frequency,
Technology.
Power Factor.
Efficiency
5. What is a Rectifier/Charger Charger.
Conditions the dc so that it is suitable for charging a battery and powering the load.
Considerations.
Voltage range.
Regulation.
Noise
Efficiency.
Control.
6. Considerations. Technology
What is available?
7. Rectifier/Charger Types Silicon Controlled Rectifiers
Use SCR’s for rectification,
along with conventional
transformers to regulate
the charger output
Typical use
Switchgear
Industrial
Motive Power
8. Rectifier/Charger Types SCR
Advantages.
Easier to interface with a microprocessor.
SCR’s provide more precise control of output voltage.
Less sensitive to line frequency changes.
Disadvantages.
Generate somewhat “un-smoothed” dc voltage which may lead
to higher ripple voltage and current.
Bulky and heavy.
Poor power factor resulting on higher KVA power input.
9. Rectifier/Charger Types Controlled Ferroresonant.
Uses a ferroresonant
transformer to regulate the
charger output. A ferroresonant
transformer is a three-winding
transformer, having one winding
in parallel with a capacitor.
Silicone diodes perform rectification.
Typically Used.
Telecom
UPS
Utility
10. Rectifier/Charger Types Controlled Ferroresonant.
Advantages.
The output is relatively independent of the input.
The electronic controls are simple which make for reliability.
Disadvantages.
Lack the sophisticated control circuitry may not adequately manage
batteries
Can work well with flooded batteries, but may overcharge and
damage VRLA batteries.
Sensitive to slight changes in line frequency.
Have low efficiencies since the ferroresonant transformers dissipate more
heat than conventional transformers.
Large and bulky, quite heavy.
Make an audible humming noise while charging
Typically Used.
Telecom
UPS
Slowly being phased out
11. Types of Rectifier/Chargers Switch Mode - Fan Cooled.
An electronic rectifier that incorporates
a switching regulator.
Typical use.
Telecom.
UPS
Utility
Generally, this is now the rectifier of choice
12. Types of Rectifier/Chargers Switch Mode - Convection Cooled
Typical Use.
Telecom
Dirty locations
Low temperature locations
13. Types of Rectifier/Chargers Switch Mode - Main Advantages.
Hot swappable.
Should have safety features for:
Auto disconnect before removal.
Post-mate enable.
Current walk in of load.
Light weight.
One person change-out.
Ship overnight.
Fairly efficient over wide output range.
14. Types of Rectifier/Chargers Switch Mode – Fan Cooled
Main Disadvantage.
Fan life. Look for:
Easily replaceable fans.
Fan on demand.
Fan speed control.
Continuous (reduced output) without fan.
Redundant fans on higher power rectifiers
15. Single Cell Charger Useful thing to have.
Ensure that it is isolated from
utility ac line.
No external metal parts.
When using on live battery,
avoid sparks.
Reverse polarity protection.
16. Rectifier/Charger Types Considerations.
The industrial battery charging market is dominated by SCR
and Ferroresonant chargers.
They have been in existence for many years.
Switchmode dominate in the telecom and UPS arena.
New switchmode technologies are slowly making an entry
into the industrial charger marketplace.
The reason is due to the higher efficiency, smaller size and
lower weight that the switchmode technology offers over
ferroresonant and SCR
17. Rectifier/Charger Type Comparison
18. Considerations. Input voltage.
What is available?
120V - 208V - 240V single phase?
208V – 480V three phase?
Usually the higher the input the lower the power loss.
-12 to + 10% normally specified.
What is expected deviation from nominal voltage?
Power loss at -12% can be 15% higher than
at nominal line.
Input frequency range?
Limit inrush current.
19. Considerations. Output voltage.
What is Required?
24V - 48V - 120V – other.
What is the load?
What is the voltage window of the load?
Is the voltage window sufficient for battery?
What is battery float voltage?
Is equalize required?
Ensure current walk-in to load.
20. Counter EMF Cell Example:
A 120Vdc system where the load
is limited to 130Vdc, but the
batteries can be charged at
140Vdc. During normal operation
the load voltage is reduced to
10Vdc less than the charging
voltage.
As the batteries discharge, the
CEMF device connects the load
and the batteries together,
directly with no voltage drop.
21. Correct Charging Voltage Specific Gravity + 0.845 = Open Circuit Voltage (OCV)
Example: 1.300 SG + 0.845 = 2.145 OCV.
Charging voltage must be higher than OCV.
Depends upon grid alloy type and temperature.
Usually in the range of 0.10 and 0.20 V at 77°F
For lead-calcium, typically 0.12 V.
Example: 2.145 OCV + 0.12 V = 2.265 V.
22. Manufacturers’ Recommended Battery Float Charging Voltages -
23. Considerations Temperature compensation.
Adjusts output voltage to compensate for
ambient temperature variations.
Benefits every type of battery.
This is important with VRLA batteries in order
to reduce chance of thermal runaway.
Typically 2.8- 3.0 mV per degree C.
It is important to set at nominlal temperature.
24. Typical Temperature / Voltage compensation for a VRLA battery
25. Considerations Efficiency.
Efficiency = Output ÷ Input
What is efficiency over output loading?
If charger is to be used in parallel/redundant
configuration, efficiency at 50% load or less
is important.
Power loss at -12% can be 15% higher than
at nominal line.
The higher the input voltage the lower the power loss.
Go for high efficiency.
26. Efficiency and Energy Savings Battery Charger Energy Conservation Program
27. Efficiency. Equipment is less efficient in Canada!
28. Considerations Power Factor.
PF = Cosine of phase angle that current leads or lags voltage.
What is the PF over output loading?
If charger is to be used in parallel/redundant
configuration, PF at 50% load or less
is important.
PF should be as close to unity as possible.
Active PF correction is good.
Go for PF as close as possible to unity.
29. Considerations Emissions testing:
Input & output conducted emissions.
Radiated emissions.
Immunity testing:
RF field
RF conducted
ESD
Surge
Voltage dips & interruptions
30. Considerations Certifications.
NRTL Testing. UL, CSA, etc.
NEBS. Network Equipment Building Standards.
Other Certifications.
CE, IEC, Seismic, Nuclear, FCC, FAA, NEMA, etc.
31. Some Certifications UL-1564. Standard for industrial battery chargers.
UL 1012. Standard for battery chargers.
CSA-C22.2 Canadian standard for battery chargers
(CSA-NRTL/C to UL 1012 & UL 1564 Standards)
Note. CSA is also a participant in OSHA’s “Cooperative Arrangement between the U.S. Occupational Safety and Health Administration (OSHA) and the Standards Council of Canada (SCC)”.
UL 60950. Safety.
Telcordia. GR-63-Core
ANSI/IEEE C62.4
FCC. Part 15 for conducted noise.
NEMA PE 5-1996. Specs for utility type battery chargers.
32. Considerations Some important features
33. Considerations Some more important features
34. Questions? Thank you for listening
35. J. Allen Byrne
Office. 301 696 9669
Mobile. 240 344 5445
e-mail. allen.byrne@ibsa.com