QRP Ops Battery Power... FYI

 

My trusty dusty 9 year old FT-817 operating from the

Glacier feed creek bed of Kautz Creek in Mt.
Rainier Nat. Park.  Note the milk carton speaker

reflector- the sides fold in for storage.  A 3S 2600

ma/hr LiPo battery props the front of the radio up.

I now use an Elecraft KX3 for my QRP operations to the field.  Previous to owning my KX3 I was a Yaesu FT-817 user for 9 years.  I sometimes take my old Heathkit HW-9 QRP transceiver to the field  for the thrill of making Qs with 1984 technology.

Previous to my current QRP Ops power sources... I used Sealed Lead Acid batteries of different sizes.  I used 1.2 a/h for my KX1 and a 7 a/h burglar alarm panel battery for my 817. This battery weighed in at just under seven pounds.  Now I use Lithium Polymer hobby batteries for just as many watts at ~20% of the weight.  

Turnigy 4S / 4000 ma/hr LiPo battery.

I purchased this at hobbyking.com, USA store.

On extended backpacking outings of up to 4 nights in the woods I will take my 4000 ma/hr 4S LiPo battery which weighs in at 14 oz.  The maximum charged battery voltage is 16.7 volts which is a bit high for the FT-817 or the KX3.  I tried a couple of three amp diodes in series to drop the voltage down not to exceed the 817's 16 volt max input voltage.  This worked well but I could feel the heat from the 1.4 volts dropped across the diodes which means that I was wasting Watts.  Web surfing for an adjustable efficient voltage lowering solution took me to http://www.dimensionengineering.com/products/de-swadj3 to purchase their swadj3 voltage regulator which is made to replace a LM-317 linear (heat wasting) regulator to drop the 817's voltage to 11 volts- which is considered to be the optimum operating voltage for the little radio to produce 5 watts output.  Using a piece of PCB, heat shrink tubing, and Manhattan construction I built a Regulator Module with Power Pole input/output connections and a LED to remind me to shut it off with I QRT.

FT-817 users might find  http://www.ka7oei.com/ft817_pwr_opt.html interesting regarding optimum input voltages for optimum power output. 

I tested the Dimension Engineering swadj3 efficiency in a quasi-lab set up.  Watts in vs Watts out calculated to ~93% efficiency.  And I can not detect any regulator noise  in the HF bands that I operate on.

While out on single day portable QRP ops... I use a 3S LiPo 2600 ma/h battery which weighs about 7 oz.  This battery charges up at 12.4 volts and I've depleted it down to 11.4 volts on a single outing.  This battery works well with the FT-817 at full 5 watts output... as well with the KX-3 at reduced power of 5 watts.

I carefully charge my LiPo batteries with a Turnigy Accucel 6 amp smart charger.  This device will charge SLA, NiCad, LiPo, LiFe batteries.  It gets its power from an external 13.8 V supply.  A large wall wart will work with this charger if the charge current is programmed to be low. 

I purchased my batteries and charger at www.hobbyking.com.  I've read that some folks have issues with hobbykings batteries or their service.  I am perfectly satisfied with them so far.

View more Photos of my QRP field ops battery equipment HERE:  www.flickr.com/photos/kr7w-sota/sets/72157632536012941/show/   The photo captions give more info.  599kr7w@gmail.com

I hope this info is useful to someone.  Regards...

30
73
Rich Kr7w