NEPTUNE Power Low Voltage Circuit Fall 2003 Quarterly Meeting Tim McGinnis Sept 11-12, 2003

LV Circuit 5V/12V DC-DC Converter External Load Control Internal Load Control External Load Isolation Current Monitoring Ground Fault Monitoring

48V:5/12V Converter Controller needs: 5V, +/-12V –May have own dedicated supply Relay inputs require: +12V Current sensors require: +/- 12V Need to confirm voltage and capacity req’ts Plan for MARS is to build converter PCB with COTS/MIL level converter module Plan for NEPTUNE ???

External Load Control Requirements –4 science connectors 22.5 A (9000 W) 25 A (1200 W) –Need to switch both legs for fault isolation

External Load Control Mechanical relay –provides complete galvanic isolation –has near-zero on-state resistance –cannot interrupt DC current without excessive arcing

External Load Control Solid state relay –can interrrupt DC current –non-zero off-state leakage – if cable cut, small fault current will result –non-zero on-state resistance – results in device heating

External Load Control Mechanical/Solid State Hybrid –SSR to make/break current –S2 to shunt current around SSR to minimize I 2 R heating –S3 & S4 to provide galvanic “deadface” isolation in case of faulted instrument

External Load Control Heating problem may also be solvable by paralleling devices 1000V relay has R DS(on) of 0.4Ω With single device I = 25A, P D = (25) 2 * 0.4 = 250W With 4 paralleled devices I = 25/4 A, P D = (6.25) 2 * 0.4 = 15.6W

External Load Control Device Rating (V)R DS(on) (Ω) 25A (W) 2 devices in parallel (W) 4 devices in parallel (W) 8 devices in parallel (W)

Paralleling devices allows the shunt switch to be eliminated Requires good current sharing –Need to select parts with similar R DS(on) –IR can provide matched dies in a module ($$) –Need good PCB design R DS(on) goes up with temperature so there is some inherent current balancing External Load Control

PCB Layout for paralleling 2 & 4 MOSFETs with low resistance connection between drains and sources

External Load Control Junction-to-Case-to-Sink is < 1°C/W At 15W, < 15°C temp rise If we can keep the device case < 100°C (ambient fluid ~40°C), the temperature rise will be minimal Need to model the local fluid warming, convection, etc.

How much heat dissipation is allowed? 3W? 15W?

External Load Control How much heat dissipation is possible from TO-247? Multiple, parallel solid state relays? Parallel mechanical and solid state relays?

Internal Load Control Provide 48V power switching to internal loads –Controller –Optical transport equipment –Data Communications Network equipment –Time Distribution equipment –Other ?

Internal Load Control Do not need isolation – so do not need deadface relays Maximum current through any device –Controller = 20W, 0.4A, P D = 1mW –Optical transport = –L2 Network Switch = –L3 Network Switch = Can be accomplished with single MOSFET devices

External Load Isolation Good practice to provide galvanic isolation between controller and external loads Need to buffer the low level controller outputs to the levels required for the solid state and mechanical relays MOSFETS require voltage input (5V, 100nA) Mechanical relays require current (12V, ~200mA)

External Load Isolation IR makes a photo voltaic isolator with 2500V isolation and output designed for MOSFET driving

External Load Isolation IR makes a photo voltaic isolator with 4000V isolation and output designed for switching up to 60V at 2A

Current Monitoring F.W. Bell Magneto-Resistive 3500V isolation Supply: +/- 12 or 15Vdc (40 mA) Output: +/- 2.5Vdc 5,15,25,50 A models Linearity 0.25% Total Accuracy 1% $32 each 35mm x 23mm x 7mm Measured current on PCB trace

Current Monitoring Engineered Components Company Hall Effect 500V withstand 10A and 100A models (can add wraps) Vcc: 4.5 – 10.5 Vdc (7 mA) Output: 0.2V to (Vcc-0.2V) Linearity 1% $30 each 23mm x 24mm x 9mm Measured current in flying lead

Over Current Protection Controller would have maximum current setting –Default value (?) –User value from Observatory Control System Controller monitors current and opens switch if value exceeded Needs to happen rapidly to protect bus Both 400V and 48V supplies have high current capacity and could potentially collapse the system if overcurrent What is short circuit surge current from converters? Could it damage anything? Do we need another “fuse”?

Ground Fault Monitoring Difficult to protect individual user circuits if they all connect to 400V or 48V bus If fault is detected, need to cycle power off to all loads (~1 sec?) to find faulted circuit Users need to know about this potential load disconnection – may need to provide their own batteries

Ground Fault Monitoring Martha’s Vineyard –can detect 50kΩ fault (500μA at 24V) at each connector due to separate converters –sends fault current to user who has the option to remain connected or not LEO-15 –can detect 100μA fault on bus –finds faulted connector by turning loads off sequentially –Requires < 1μF between conductors and sea

Ground Fault Monitoring

Balanced short circuits are not detected

Ground Fault Monitoring Balanced short circuits are not detected

Ground Fault Circuit 1 400V and 48V circuits would have constant 1mA to ground (~0.5W) 0Ω(2mA) ground fault would result in ~5V across 2.5k resistor 400/48MΩ(1μA) ground fault would result in 2.5mV across 2.5k resistor Should be reasonable range for acquisition & detection Also provides high impedance grounding of the 2 power buses Doesn’t require any switching