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. 🙂
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.
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.
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