Battery for QRO operations

[IU4QPM]

Hi everyone, since the first day I got my amateur radio license I have always been attracted to portable activity.
I have always used QRP devices with a maximum of 10W so I was able to play with relatively small batteries (maximum 8Ah).
Yesterday my wife gave me an FT891 which can be set up to 100W with a maximum absorption of 22A in SSB.
I will use it at maximum 50W or 60W so as not to have to carry a nuclear power plant with me
Do you think this battery would be good for a setup like this? How long could this last?
Alternatively, I would also have a 98Ah car Pb (ex service battery) available. Transport would not be a problem.
Thanks a lot to everyone.
73
Matteo

Screenshot 2023-09-22 231812.png (163.27 KiB) Viewed 9117 times

[kc0myw]

Congrats on the new radio, that's pretty nice of your wife to get it for you!

I have no experience with the battery you linked to, but it looks like a 30Ah LiFePO4 battery, which would likely run that FT-891 for quite some time!

You could try it, but I would NOT recommend using a standard car battery as they are designed for short bursts of high current and not an ongoing low/medium current draw like our radios use. I have in 1 or 2 cases used the battery in my vehicle to power my radio during a POTA activation (I think 1 time I got to the park, put up my antenna, and then realized my battery was still at home on the charger) and the voltage on the car battery dropped quite rapidly with radio type use. I have, however, used a Deep Cycle marine battery with great success but they are big and heavy.

I would suggest trying the FT-891 with your current 8Ah battery and see how it works for you. I have a 9Ah LifePo4 battery that I use for many of my POTA activations and it is what I would use with an FT-891 if I get one. I've been looking at them, but just don't want to part with the dollars, hihi. My main POTA radio currently is an FT-450D and running it at 50W my 9Ah battery gets me through most activations lasting less than 2 hours on SSB and CW.

I really suggest getting a meter like this one or similar and then you can see the total Ah you use during an operating session. Then you can more easily figure how big of battery you need for a certain length of time.

[IU4QPM]

Congrats on the new radio, that's pretty nice of your wife to get it for you!

I have no experience with the battery you linked to, but it looks like a 30Ah LiFePO4 battery, which would likely run that FT-891 for quite some time!

You could try it, but I would NOT recommend using a standard car battery as they are designed for short bursts of high current and not an ongoing low/medium current draw like our radios use. I have in 1 or 2 cases used the battery in my vehicle to power my radio during a POTA activation (I think 1 time I got to the park, put up my antenna, and then realized my battery was still at home on the charger) and the voltage on the car battery dropped quite rapidly with radio type use. I have, however, used a Deep Cycle marine battery with great success but they are big and heavy.

I would suggest trying the FT-891 with your current 8Ah battery and see how it works for you. I have a 9Ah LifePo4 battery that I use for many of my POTA activations and it is what I would use with an FT-891 if I get one. I've been looking at them, but just don't want to part with the dollars, hihi. My main POTA radio currently is an FT-450D and running it at 50W my 9Ah battery gets me through most activations lasting less than 2 hours on SSB and CW.

I really suggest getting a meter like this one or similar and then you can see the total Ah you use during an operating session. Then you can more easily figure how big of battery you need for a certain length of time.

Thank you very much for the reply.
Wattmeter just bought on Amazon.
About the Deep Cycle marine batteries it's a great idea! Tomorrow i'll search on Internet which battery is good to me.
Meanwhikle i use my 8Ah like your advise.

73
IU4QPM

[Brian - K3ES]

Hi Matteo,

The LiFePO4 batteries that I use have a built-in battery management system (BMS) to protect the battery. In addition to a low voltage cut-off (battery charge expended), they have a high current cut-off. If you draw more than the rated current, the BMS will shut down the battery. After protective shutdown, the battery must be connected to a charger before it will function again. Check the specs on your battery to be sure it will support the current draw from the FT-891 at the power level you plan to use. In general, higher capacity batteries support higher current draw, but check the manufacturer's specs to avoid problems in the field.

Best 73 de Brian - K3ES

[kc0myw]

Nice point and reminder Brian!

I hadn't considered that when typing up my previous comment and generally don't give it much thought because of the equipment I have so it's great that you mentioned it.

Just as a matter of reference, the battery that I have that I was referring to in my previous post has a max continuous rating of 12A and max peak/pulse spec of 24A for 2 seconds. I don't monitor my power usage all the time, but in the times when I have used my power analyzer I don't recall seeing the peak amps over 8 or 9 when operating my FT-450D at 50W.

[SkipRD]

I use that brand (50 Ah version), two of them in parallel, in my shack. I use a different brand (same chemistry), two 20 Ah in parallel in a Harbor Freight box for portable operation. That portable box works great for me for picnic-table style POTA operations.

With my IC-7300 at QRO levels and my style of operating (a mix of CW and SSB with a high transmit percentage), I average a draw of about 5 Ah per hour of operation, so theoretically 30 Ah is fine for 6 hours of operation. I haven't tested it with my FT-891 (installed in my truck), but I expect the Yaesu would be slightly higher (it's not a very efficient radio). The FT-891 specs say it draws 2A on standby, up to 23A on transmit. Getting the meter as recommended above would be a good idea.

The batteries in my portable box say they're good for 20A max continuous, so with 2 in parallel I'm good even at highest xmit levels. 12A max for the Eco-Worthy seems low to me; my 50 Ah Eco-Worthy batteries in my shack say they're good for up to 40A continuous. In any event, at QRO levels with your FT-891, you might be close to 12A.

Have fun going portable. It's great fun!
73 Skip K4EAK