Power Supply Segmentation

by Web FishJul 11, 2013 @ 10:31am

For the last couple of months we've been trying to make our mind on power system segmentation. On one hand having separate circuits for the navionics package and the main propulsion seems like a no-brainer - less interference from the powerful brushed motors and speed controllers, separate management of consumption leaving the central microprocessor powered even during deep drain of the propulsion battery bank, being able to store and run at different voltages, etc. On the other hand, the main propulsion bank offers 160+ Watt-hour of capacity which comes at a cost - total SLA battery weight (without the water-tight enclosures) is 8.5 lb. Adding extra capacity as SLA cells adds more weight, adding extra solar panels adds either more weight (glass crystalline) or cost (thin film plastic) to the project. In addition, we have built excellent redundancy with the 4 SLA cells and 4 solar panels which will now need to be replicated on the navionics side (at lower power level / capacity). On top of that the Iridium sat-com modem can draw upwards of 2A on its 12V bus for nearly 60 seconds, so we still need plenty of juice on the navionics segment for normal operation.

For now we will be powering the main electronics from the 4.4V SLA bank through a separate voltage regulator and see if we can work out a good capacity meter to be able to throttle down / cut-off propulsion at a predictable residual level and potentially further adjust comm-link session frequency to save power. This will allow the vessel to drift in case extended periods of low solar harvest rates (weather, panel damage) without completely loosing telemetry and control. Testing will tell if this is the right way of handling it - we still have space on the deck frame for 2x5W auxiliary panels on each side. But we can definitely live without the extra 4 lb of weight...

The Solar Panels

by Web FishApr 25, 2013 @ 04:49pm


The solar panels provide the main (and for now - only) source of power for the vessel. Electric power generated by the panels is used for driving propulsion pods, rudders, as well as all navionics (processor / controllers / comm). The harvested power is split between current consumption and battery bank charging. Battery banks kick in when solar power is below pre-defined threshold. 

  • Current selection: HighFlex Solar HF35W
  • Status: Finalized

  • Criteria: Weight, power output, efficiency (watt/sq.ft.), mounting, cost 
  • Finalists: Solbian SL40Q, HQRP 30W Flex panels, SunFlex 50W panels 
  • Main decision factors: Weight, availability, cost

 (click image for larger view) 

Spec highlights:

  • 27" x 13" x 1/8" panel size
  • < 2 lb panel weight
  • 4.7 V no-load output voltage
  • 4.5 V output voltage under nominal load
  • up to 7 A @ 4.4 V short current

 

Caveats:

  • Low output voltage requires adjustments to the rest of the power package;
  • These panels are MAGNIFICENT! At less than 4 ponds per side, we are harvesting up to 60-65 Watt power at high noon. Very, very exciting!