Category: Contests

After four months, I finally received the battery I ordered on October 7, 2021. I am currently running it through it paces and recording everything that I find.

I have connected the battery to my FT-991A at my QTH, and am treating it like an off-grid power source. So far, everything looks great, and it seems like it will work pretty closely to the way I predicted.

One of my next steps it to also build a “box” to put the battery into, and make it more versatile.

Updates will be coming, shortly.

In the previous post, I gave the reasons “why” I wanted to go with LiFePO. In this post, I will try to give the details on the calculations that I’ve done, before reaching the decision to buy what I bought.

I ordered a 12V 54Ah Deep Cycle LiFePO4 Battery, a Folding Fast-Charge 12V Solar Panel, and a USB Phone Charger, Voltmeter, & Terminal Adapter Wiring Kit from Dakota Lithium on May 24th. As of May 29th, I have not had all of the items shipped to me, so what follows has not been tested in the real world. These are just my calculations.

Of course, before I start, I will say that I do understand that there are a lot of different factors that will effect these calculations, some of which I may have not even considered. Things like available sunlight, transmit power, transmit frequency (how often… not MHz), other devices connected, are all variable factors that I am aware of.

• The Battery. 12.8 volts / 54Ah / 691.2Wh
  • Size – 9.01” x 5.43” x 8.38”
  • Weight – 17.6 pounds
  • Discharge – 50 A max continuous, 100 A max pulse 10 second pulse
  • Charge – 25 A max

I will just do the calculations for the battery and the radio, without the solar panel connected. The solar panel can be connected while the battery is being used, so I will just be using it as a way to keep the battery “up” for as long as possible. Without any load on the battery, the solar panel will charge the battery in about 19 1/2 hours. Not a lot of input, but enough to help make it through the night, I think. I may end up upgrading the solar part of this in the future, but we’ll see how it works out this way, for now.

• The Radio. Yaesu FT-991A
  • Supply Voltage – 13.8 volts (+ or – 15%) – Calculations will be based on 12.8 volts, which is the battery voltage.
  • RX Power Consumption – 2.2 A
  • TX Power Consumption – 23 A (HF/50 at 100 watts)

Based on a 100 watt output (which is the full power of the radio), here is what I came up with:

Standby only battery run time = 24.54 Hours

Transmit only battery run time = 2.34 Hours – This is obviously an unreasonable number, since there is absolutely no way to transmit at 100 watts for that long. Even if I were to run FT8 or FT4 at a full 100 watts, the duty cycle would be 50%, meaning that I would be transmitting half the time and listening the other half. That would bring it to 4.68 Hours.

When operating portable and on Field Day, I normally use SSB (voice or phone). The duty cycle for SSB is actually much lower than 50%, since the radio is only transmitting while you’re talking. The calculations for this are a little trickier. Simply pressing the push-to-talk (PTT) button, without any talking, the radio consumes about 5 amps. Any time you talk, the radio will draw between 15 to 22 amps at 100 watts. For the sake of my calculations, I based the amperage draw at 20 amps at 100 watts.

Since I am a “search & pounce” type of operator, normally, I also based my transmit time to 20% (the other 80% of the time, I would be listening). I might be wrong on this, but if my “transmit only battery run time”, above, is correct (at 2.34 hours) then only transmitting 20% of the time would work out to about 5 times longer, or 11.7 Hours.

Of course, the other factors that are even harder to calculate (for me, anyway). The 80% of the time that I would be listening. The amount of power that the solar panel will put back into the battery. Any other devices that I connect to the battery (I’m going to try to stay away from doing that, this year). The voltage curve stays pretty flat until about 80% on the battery, too. Does that mean that all of my calculations are off by that much?

Another big thing that I have not figured in, at all is that I can just turn down the power on my radio. If I go to 75 watts, will the battery last 25% longer? If I run at 50 watts, will it last 50% longer? If that’s the case (which I actually doubt), I should be able to run 17.54 hours at 50 watts, even without the solar panel.

Since one of the main reasons for wanting this battery was for Field Day, since it is a 24 hour event, I wanted to have a battery that would last that long, by itself. I could have went with the 100 Ah battery, but for the price difference, I decided that the 54 Ah battery supplemented with solar would work just fine.

After I test all of this out in the real world, I will post an update.

For quite a while, now, I had been thinking about getting a LiFePO battery for the van. There’s a few different reasons that I’ve wanted to, but the main reason is radio noise. The battery will have almost no interference, compared to the gas powered generator that I had been using. The one thing that really pushed my decision, recently, was when Jason and I went up to the fly-in car show at the airport on May 1, 2021. Jason set up his hambulance and I set up my big ear antenna and generator.

Because of the way the show was set up, I was not able to get the separation between the antenna and generator that I would normally get at a portable operation or Field Day. The generator was set up just in front of the vehicle, toward the driver’s side, and the antenna was set up just behind the passenger’s door. Normally, I set them up as far away from each other as possible (at least 100′ away from each other) to avoid as much noise from the generator getting into the antenna. Normally it works pretty good, but I still get noise (whether grounded or not).

What happened at the airport event was that I was able to operate on 40 meters, but 20 meters was mostly unusable. Since the timing of the event was during the day, it would have been great to be able to get on 20 meters. There were multiple QSO parties happening (7th Area, DE, IN, and New England), so I’m sure there was plenty of signals out there. I just couldn’t hear them on 20 meters (except for a few high powered stations).

On May 24th, I decided, with Field Day coming up, I wanted to get a different power setup, so I finally pulled out the CC and bought a few items from Dakota Lithium. As I write this on May 29th, I have not received everything that I ordered, but I just wanted to go through some of the calculations that I did, before deciding on what I wanted, and making the purchases.

First of all, I will point out that I have never been one for “running a frequency”. I am more of a “search and pounce” operator when it comes to any sort of contest or QSO party. The reason that I am throwing this out there is that depending on how much you transmit, you will use more or less power. I have done all sorts of calculations, and will include those in the next post. Secondly, I will add that they are just my calculations, and I have not yet put any of it to the test, in the real world. I will do an update after I’m able to spend some time testing things out.

I will definitely be getting more things to complete the project, but here is what I purchased, so far, from Dakota Lithium. I ordered a 12V 54Ah Deep Cycle LiFePO4 Battery, a Folding Fast-Charge 12V Solar Panel, and a USB Phone Charger, Voltmeter, & Terminal Adapter Wiring Kit.

In the next post, I will try to detail my calculations.