Project: Regulating the 12v Output of the Nomad 7 Solar Panel

This article is in a series about using the Nomad 7 Solar Panel for amateur radio use on backpacking trips.  Our prior article was, "Project: Fabricating a Anderson PowerPole to 3.4mm dc connector for the Kenwood TH-F6A".

Something went wrong during field testing of recharging our Kenwood TH-F6A HT radio using the Nomad 7 Solar Panel.  Sadly, our TH-F6A stopped charging (lights went out) and would then no longer turn on.  This issue occurred within only a few minutes of charging in full sunlight.

There are a couple of possibilities for the failure:  
  1. The TH-F6A blew one or more of its three fuses due to the relatively high voltage (15Vdc) of the Nomad 7 Solar Panel in full sun.  The TH-F6A is rated at 10Vdc to 16Vdc though the radio's internal voltage regulator converts voltages greater than 10Vdc to heat.  It is possible the 15Vdc caused overheating and blew one or more of the fuses.  
  2. A fuse was blown when the 3.4mm connector was plugged into the radio with power applied to the connector (not supposed to do this per the manual).
  3. Other failure mode?  If you have an idea, please post a comment to this article.
We will post an update once the radio has been diagnosed and repaired by Kenwood.

In the meantime, we decided that adding a voltage regulator to bring the voltage to about 11 volts would be a prudent move.  We found an inexpensive ($1.75), lightweight, and low-power, adjustable DC-to-DC switching voltage regulator for sale on eBay that fit the need.   This regulator can be set to produce a stable 11Vdc with an input voltage between 5Vdc and 32Vdc.  The seller claims the MOSFET (LM2577 operating at 50KHz) switching voltage regulation design is 94% efficient.  This means more solar power directed to the battery and less lost to heat.

DC-DC Auto Boost Buck Adjustable Voltage Regulator with Anderson PowerPole connectors soldered to both the input and output.
DC-DC Auto Boost Buck Adjustable Voltage Regulator
Here is the specification sheet that came with the module:

Technical Parameters

  • Model Specification:DSN6000AUD Automatic Buck module
  • Module Properties:Non- isolated boost (BOOST)
  • Rectification:Non- Synchronous Rectification
  • Input Range:3.8V ~ 32V
  • Output Range:1.25V ~ 35V
  • Input Current:3A ( max ) , no-load 18mA (5V input , 8V output , no-load is less than 18mA. Higher the voltage , the greater the load current . )
  • Conversion efficiency:< 94% ( greater the pressure , the lower the efficiency )
  • Switching frequency:400KHz
  • Output Ripple:50mV ( the higher the voltage , the greater the current , the greater the ripple )
  • Load Regulation:± 0.5%
  • Voltage Regulation:± 0.5%
  • Operating Temperature:-40 ℃ ~ +85 ℃
  • Dimensions:48mm * 25mm * 14mm ( L * W * H )
To keep it flexible we went ahead and soldered on a pair of Anderson PowerPoles at the input and also the output.  Everything still fit nicely within the carrying pouch of the Nomad 7 Solar Panel.  We also modified our operating procedure so that we will only plug and unplug the 3.4mm connection to the TH-F6A when no power is applied.

There is a small brass set screw on the voltage regulator module.  Turning this set screw allows for very precise selection of output voltage.  We used our multimeter to monitor the voltage during adjustment.  Once set, we used a large piece of heatshrink tubing to encapsulate the module and electrical tape to seal the ends.  This will keep the module waterproof which is important on backpacking trips.

Testing

1) Measure the voltage output of the voltage regulator.  Our voltage regulator produced about 11Vdc which was exactly where we wanted it for use with the TH-F6A.

2) Charge the TH-F6A battery.  We used our second Kenwood TH-F6A for testing.  The battery was a little low so we plugged everything together and it charged perfectly.

3) Confirm that TH-F6A still functions after charging.  After charging the battery, we disconnected the radio from power.  We then turned on the radio and everything worked perfectly.


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