Powering the Yaesu FT-857D for SOTA

This post is an update on powering the Yaesu FT-857D for a SOTA activation.

Before reading on.  When deciding on the power requirements for your radio, you must undertake your own research to determine which battery type and capacity is suitable for your station and operating conditions.  I have no affiliation with battery makers or suppliers and do not endorse any of the products or items pictured or discussed below.

In June 2013 I posted details on using a 4S 5 Ah LiPo battery as the primary power source for the FT-857D.  In that post I highlighted the requirement to use a DC-DC regulator to regulate the supply voltage to the radio.  Why?  A 4S LiPo when charged correctly, using a balanced charger, has a full-charge state at 16.8 volts or 4.2 volts per cell, which exceeds the 857D manufacturers recommended DC input supply.   😦   The manufacturer recommends a supply voltage at 13.8 volts +/- 15%.  🙂

While the combination of 4S LiPo and DC-DC regulator works very well, having another component to carry in the back pack further complicates the SOTA station set up.  Lets say I forgot to pack the regulator, or if the regulator failed in the field, the likely outcome is a non-activation.  Imagine walking two hours to a summit only to find you left a critical part in the car or at home!   The first principle for SOTA operations is safety the second should be keep the station set up simple (KISS).

What next, trial a Lithium Iron Phosphate (LiFePO4) battery, with a nominal cell voltage at 3.2 volts.   September 2013 I purchased a 13.2 volt 4S 4.2 Ah LiFePO4 battery from a well-known Australian (AU) supplier HobbyKing.  The maximum voltage for a LiFePO4 cell is 3.6 volts and the minimum is to 2.8 volts.  The ideal working range is 3.0 to 3.3 volts per cell.

The 4S LiFePO4 maximum charged state is 4 * 3.6 or 14.4 volts and the minimum safe discharged state will be 4 * 2.8 volts or 11.2 volts.  The nominal operating voltage is 4 * 3.2 or 12.8 volts.   The 857D recommended supply voltage is 13.8 +/- 15% ( 11.7 to 15.8 volts), therefore you can connect the 857D direct to a 4S LiFePO4 battery via a suitable fused link.  🙂

Components: LiFePO4 battery, alarm unit, Watts Up meter and fuse lead

Components: LiFePO4 battery, alarm unit, Watts Up meter and fused lead.  All connectors are Anderson 35 Amp PowerPoles.

One question?  The recommended minimum operating voltage for the 857D is 11.7 volts yet the safe minimum battery voltage is 11.2 volts.  No doubt the radio will under perform at 11.2 volts, how do you deal with the minimum range?  Fortunately you can buy a nifty small monitor/alarm device that plugs into the battery’s balanced charger plug. See picture below.   The device cycles through each cell, displaying the cell voltage then the total of all cells.  The unit has an audible alarm (very loud) which is triggered when any one single cell is equal to the alarm setting.   The alarm settings range is from 2.6 volts to 3.8 volts per cell in 0.1 volt increments.  To deal with the radio minimum supply voltage, I set the alarm to 2.9 volts which is 11.6 volts for the 4S LiFePO4.  Make sure the alarm is not set to trigger below the safe minimum at 2.8 volts per cell, otherwise you may damage a very expensive battery.  2.9 volts per cell is a good compromise.

A couple of notes on RC battery monitoring/alarm units.

  • Before you buy, check the manufacturers specifications, some alarm units draw the unit supply from one or two cells.  In the case of the 4S battery, operation of the alarm unit may unbalance the battery thereby reducing its longevity.
  • In direct sunlight you cannot read the digital display, therefore the alarm function is critical when you are busy recording chaser details in the log.  A typical SOTA pile up may run for 30 to 45 minutes.

How do I monitoring the Ah rating of the battery and the combined cell voltage?  I use a Watts Up meter in combination with the alarm unit to monitor the Ah and voltage state.

Watts Up meter very easy to read

Watts Up meter very easy to read

Alarm unit in daylight, difficult to read

RC battery alarm unit in daylight, you would agree it’s difficult to read

Alarm unit displaying cell 'No2'

alarm unit displaying Cell ‘No2’

Cell 2 voltage

Cell 2 voltage

Combined voltage of all 4 cells

combined voltage of all 4 cells

Operating the 857D at 40 watts

In recent months I have chased SOTA DX in Europe and the UK from VK1 SOTA summits.  When chasing DX, I set the 857D output power between 5 and 40 watts.  Using a 4.2 Ah 4S LiFePO4 the radio will maintain 40 watts output for 1.5 hours of regular calling and exchange of signal reports.   The SOTA signal report/exchange format is short and quick helping to reduce the TX time and time spent on a summit.  Happy with the performance of the 4S LiFePO4, I purchased a second unit to extend my time on air.    At QRP levels, 5 watts, the 4.2 Ah battery will last 4 to 5 hours of constant use, making it suitable for a day of multiple activations.

Charging a LiFePO4

I use a balanced charger with the charger settings set to ‘LiFe’, charge current 1.5 amps (conservative) and charge configuration set to ‘Balanced’.  The charger will stop charging when the battery reaches a predetermined state.  I normally place the battery in a protective bag while charging, I have left the battery out of the bag to show the balanced lead connected to the charger.  The DC supply to the charger is six 7Ah 12 volt SLA batteries.  The SLA batteries are charged during the day by a 20 watt solar panel and regulator.

Battery charger set to LiFe and balanced charging

battery charger set to LiFe and a balanced charge cycle

display of individual battery cell voltages through the balanced charge cycle

display of individual cell voltages through the balanced charge cycle

Charger in action: display summary of the battery the charge cycle

charger in action: summary of the charge cycle

Final note.  From time to time I like to operate a FT-817ND on SOTA peaks, I use the same 4S LiFePO4 to supply power to the 817.   I have fitted Anderson 30 Amp Powerpole connectors on all of radio power leads and battery supply leads.  This approach maintains the (KISS) principal, making a battery change quick easy.  Also helps when I make a last-minute decision to swap radios between the 857D and 817ND.    You can use whatever connectors suit your operation.

If you have further questions, please contact me using the ‘contact me’ form.

Reference / Links
13.2 volt 4S 8.4 Ah LiFePO4 battery

First post: 21 February 2014
Last Update: 14 August 2016

16 thoughts on “Powering the Yaesu FT-857D for SOTA

  1. Pingback: SOTA – 4S 8.4 Ah LiFePO4 Battery | Get out of the Radio Shack and Live Life

  2. Hi Andrew,

    Thanks for this article, which I found a couple of months ago, and which has been my main source of information (and inspiration!) to put together my own power supply for a FT-857 for SOTA – looking forward to my first SOTA HF activation soon.

    The only thing I couldn’t find easily was the compact fused lead you show in the first picture, although I did manage to find one a bit clunkier and heavier (trying to source various pieces of equipment in Germany can sometimes be a nightmare!).

    Cheers, Rob DM1CM

    • Hi Rob,
      Thanks for the feedback, I try to keep the blog current and relevant to amateur radio operators interested in portable and QRP operations. My focus is sharing my SOTA experiences, however the practical aspects of SOTA can be applied equally to any portable or field operation. With regard to the in-line fuse block, I have replied to you off-line. 🙂
      Cheers, Andrew VK1AD

  3. I have a Yaesu 857D but I’m totally inept with its operation. Can you advise me where I can get “starter info” – I only want to set it up to receive on different channels for starters. The manual is over my head.
    Bob Robertson

    • Hi Bob, I recommend contacting your local amateur radio club and seek advice on setting up the radio. Do you have an amateur radio operating licence?

  4. Hi Andrew, I have been considering switching over to a 4S LiFePO4 battery pack for a while and found your article to be very informative. TU for this well researched and practical article. 72, Paul AA4XX

    • yes it’s Interesting which way to go with powering your FT 857. I had my old friend Peter VK3PF staying for the weekend the conditions have been bad on Hf for some time. I suggested to Peter that we use my FT857, which I had been using for some time to get a better result at giving the chasers a chance. We used the 857 all day yesterday and varied the output power from 30-60watts depending on the degree of difficulty for the chasers hearing us. We activated 6 summits for the day using 20-30C charged to 16.7 volts, the first battery just dropped below 12 volts as we started the 5th summit so the 20-30C hard case have been very good. I use a full wave 4 way bridge rectifier for my voltage control mounted on a small heat sink.
      Admittedly the performance of the 857 as opposed to the 817 compensates for the extra weight.

  5. Hi, Andrew I know it’s an old post but I’m researching using these batteries now. I understand the Turnigy battery charger needs a specifically rated power supply, did you source this from HobbyKing as well or use something else. I have read on another blog about some power supplies from HB being poor quality. Many Thanks Grant VK3VIM

    • Hi Grant, The charger (TURNIGY Accucell-8150) manual specifies the input voltage may range from 10 to 18 volts at a max current of 7 amps. I operate the balanced charger with a 12 to 14 volt input source (40Ah SLA which is charged by a 20w solar panel + regulator during the day) with sufficient input current to charge the LifePO4 at 1.5 amps. I purchased the balanced charger in June 2013, a solid performer without fault. The LiFePO4 batteries are charged prior to and after each activation. Based on the number of SOTA activations since June 2013, I would have charged one or both LiFePO4s approximately 280 times.

      I hope the above info helps explain my set up and the reliability of the charger. I have a copy of the user manual in PDF, I’m happy to email a copy.
      Andrew VK1NAM

      • Thanks for the reply Andrew, that clears up what type of power supply is required for the charger. I thought it may have been something special required from HobbyKing. I’d appreciate a copy of the manual (mycallsign) at vk3vim.net, I can do a bit of further reading. Thanks for your help.

  6. Hi Andrew and really congratulations for your article!
    I’m interested on adopting a similar solution for my Ft-857.

    At the moment at Hobbyking european wharehouse (I live in Italy) I could buy a ZIPPY Flightmax 8400mAh 4S2P LiFePo4 battery. I think it should ok, and give me a double operative time with the radio (compared to your battery), right?

    However, I’d like to know more in detail how you connected the battery to the radio: which type of connectors are these? And how do you plug battery into the Yaesu connector?

    Thank you and bye!


    • Hi Stefano
      Thanks for the feedback.
      I use Anderson 35 amp PowerPole connectors on all radio power leads and batteries. The Yaesu connector remains in place, I just add a pair of Anderson connectors to the radio power lead. I will send photos to you tomorrow.
      Andrew VK1NAM

      • Thank you Andrew.
        Strangely, PowerPole connectors aren’t so much diffused here in Italy… But it’s not a problem, I will use some different connections.
        However I’m waiting for your photos!
        Thanks again!
        73′ de IU3EPW

  7. Pingback: Power for the SOTA Station – 5 June 2013 | VK1NAM Summits on the Air (SOTA)

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