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TRANSCRIPT
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KOEHLER JAN 2011Greenbuilding Jan 2011
Green
Building
Power
Forum
2011
SystemEffectsofPolarityinDCDistributedSystems
Bill Koehler
Sr Engineering ManagerROAL Electronics USA, Inc
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Outline1. Techniques used for polarity protection and correction
2. Advantages and disadvantages of polarity protection and correction3. Examples4. System and peripheral effects5. Conclusions
Polarityprotectiontechniques
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Facts & Definitions
] FACT: DC SYSTEMS REQUIRE POLARITY PROVISIONS
] Polarity protection A means to protect the equipmentfrom failure if the user connects the equipment in theincorrect polarity
] Polarity correction A means to permit the equipment tooperate in either polarity with no signs to the user orequipment
] CLASS 2 POWER A DC Circuit that must be 100W or less,
limited to a maximum of 5A and Less than 60VDC Example 12V Circuits are limited to 5A = 60W Example 24V Circuits are limited to 4.17A = 100W
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Polarity Protection
] Polarity protection is often utilized in DC Peripherals
] Simple, low cost, primarily to protect the peripheral,not the System
] If connected incorrectly, the user can easily becomeconfused due to the unexpected result
] May effect other parts of the system
] Peripheral may not turn on and give no fault
indication
] The result is a perception that the system is flawedand possibly defective
] Wastes time during installation
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Reversediode
Load
+
Polarity Protection Techniques
] Advantages: + No losses under normal operation
+ Simple
+ Inexpensive
] Disadvantages: -Disrupts the system if connected
backwards or opens a fuse and takesdown the circuit
-Need added heatsink for continuousoperation or something that breaks thecircuit
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Seriesdiode
Load
+
Polarity Protection Techniques
] Advantages:
] + Simple
] + Inexpensive (More expensive thenreverse diode)
] Disadvantages:
] - Heatsink may be required
] - Increased losses under normalcondition (~2W for a 100W load or2%)
] - If connected reverse it is notalways obvious that the equipment isconnected incorrectly
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Mechanical
Polarity Protection Techniques
] Advantages:
] + Simple
] + No losses
] Disadvantages:
] - Can be complicated and add cost
] - Typically easy to defeat
] - Custom connector may add considerable cost
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Polarity Correction
] Why hasnt polarity conversion been used in thepast? Cost penalty
Reduced efficiency Historically didnt add any benefit in traditional systems
] Until Now . In DC Distributed Systems
End user has the ability to connect many peripherals to asystem
In Class 2 DC systems, we have the ability to reconnect ormove peripherals without an electrician, it is critical tohave a system that is foolproof to the consumer level
People are not knowledgeable about polarity With polarity conversion we can avoid the perception that
a system is flawed when the peripheral is connected ineither polarity
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Diodebridge
Load+
Polarity Correction Techniques
] Advantages:
] + Simple
] + Relatively inexpensive
] Disadvantages:
] - Losses can be considerable (upto 4W or 4% efficiency loss for a100W system)
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Relaycircuit+
Load
Polarity Correction Techniques
] Advantages:
] + Low losses (coil only)
] + Relatively inexpensive
] Disadvantages:
] Reliability (Mechanical Device)] Load sees negative voltage spike
during relay switching
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Transistorcircuit+
Load
Make it Simple and the Technology will be Embraced!!DONT Inconvenience the Installer or Consumer with new Technology
Advantages
] Low losses possible with propercomponent selection (0.2W or 0.2%losses are possible) on a 100W circuit
] May eliminate the need for connectorsfor power at the peripheral end
Disadvantages
] Added cost (
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Rds(on)adjustedfordevicetypessuitabletosupplyvoltage
Aseriesdiodewouldhavelossesof4%,2%and1.5%forsupply
voltagesof12V,24Vand48V
TransistorcircuitPolarity Correction Techniques
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Atpowerlevels50W,thetransistorbridgecircuitisabettertradeoffofcost/
performance
Summary
Comparison of losses and cost based on a 100W peripheral
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Occupancy Sensors
Smoke/fire alarms
Access points
Security cameras
LED Lighting
Projectors
Hard Wired
Hard Wired
Hard Wired
Hard Wired
Devices applicable to polarity conversion
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Any Device on the Emerge Grid
Devices applicable to polarity conversion
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Summary
] Every peripheral to be connected to a DC system should employ eitherpolarity protection or correction to avoid damage to the equipment
] Polarity protection is the best solution for many low power simple DCsystems
] Polarity correction should be employed in systems that have a high degreeof end user interface and a potential for connection in either polarity
] Integrated Polarity Correction is the best solution for High VolumeApplications.
Attracts innovation from Semiconductor developers
] For many DC distributed systems a polarity correction feature would bedesired to eliminate confusion of the end user
] The small added cost and efficiency loss is minor compared to theperception of system FAILURE!
] The result is ease of installation with NO POSSIBILITY of user error
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