The other day i took delivery of this battery its 12ah , i decided to go a tad bigger than what others have used , my thinking was i would mainly be using fm or ssb rather than cw at 5w output . But i think i may of over estimated ! fully charged on sat morning at 13,8v and after 2 activatons at times running at 25w i measured when got home and its now 13.22v ! not a huge drop at all , i know the lipo and lifeo4 batteries normally drop to around 12v mark and stay around there for quite some time . This not even got close to the 12v at all !
Another idea was to build a lightweight 18650 pack of either 5 / 6Ah and see how i get on running my mobile fm Radio . Plus if i need to top up after an activation i can plug the charger in from the 12Ah battery or on my 30A fused supply direct from the car battery and charge up on way to next activation .
Whats the problem? if you don’t mind carrying the weight then you have the choice to turn up the power. I made a 9Ah pack of A123 25650cells to use with my FT857… that I use occasionally for SOTA… I’d like a 12Ahr pack!
One point that’s important is that the normal mobile radios for 2M/440 etc have a more limited operational input voltage range… for instance the FT857 starts to have weird Audio at 11V input…
Richard , its lighter than a SLAB for sure but not the lightest pack when you consider what else in on your back and i add extra weight carrying a few extra bits for the pooch . Would you like the link to where i bought it from but i warn you its not cheap but no where near the price of the tracer batteries , and it has a built in bms so no ballance charging is needed . I am using a Anytone AT778UV which is a very compact 2m&70cm radio with max output of 25w which is plenty . Its just a thought when im got a much longer walk , i think the battery is around 1.6kg
that would run a 25w rig for quite a while. what does it weigh?
My 4.2 AH Lifepo4 recently survived 4.5 activations, about 60 contacts mixed SSB and CW via an IC703 running 10w output on HF. The fifth activation was when the voltage finally dropped below 12v (at which point the 703 then drops to 5w but does not close down). so I made the final few contacts using a 3S LIPO which was my backup. the battery voltage at 12v total is 3.0 per cell and the recommended lower limit for long battery life is 2.8v per cell. I could have continued but decided against it.
I reckon a 12 AH would probably do 12 activations at that rate. Of course if you are using FM you know it is a power hungry mode, 100% power while you transmit. SSB and CW are much kinder to your battery, ie more efficient.
My earlier activations were made with a 2.1 AH gel cell which was ample to make 30 contacts using the 703 at 10w. it draws about 250mA on rx. Look at your rig to work out what your usage on rx and tx will be, estimating your total transmit time etc.
I have commented before so sorry if this is repetitive, but I believe many operators have learned how hungry FM rigs are on battery and tend to extrapolate from that when deciding on power sources for SOTA. however it is usually an overestimate and many operators are pleasantly surprised when they find out that the battery required is a lot less than they expected.
Having found that the kx3 I recently obtained requires only 220 ma on receive, less with the dial lights off, I think I can obtain even greater life from my 4.2 AH battery.
The 12ah is around 1.6kg , and i might use it to power my yaesu ft 891 as that’s capible of 100w but 50w is my licence limit . My 1st activation on Saturday once set up only lasted around 35 minuites , over 10 contacts with 4 s2s and action was pretty fast so soon was off back to the car, 2nd one was around an hour and similar amount of contacts .
I already have 4 18650 3ah cells was thinking to join in pairs to make 3ah upto 6ah and join the pairs in series to get tge required voltage .
All good, one point to note is that the LIPO and LIFEPO4 batteries have a dangerous level of current available on their terminals. Powering a radio at 20 amps is a doddle for even the 4.2AH batteries. Look at the rating on them, my 4.2AH says 20C. That means it can source 4.2 times 20 amps, ie. over 80amps. It could start a small car. Your 20AH battery could probably start my tractor’s diesel engine. This means take great care to fuse the leads to protect the battery and avoid fire and explosions. It is great for DC motors in model planes and cars where they want to accelerate or take off quickly, unnecessary for radios but their AH rating is marvellous for SOTA.
73 Andrew VK1DA/VK2UH
Yes i understand about the high power this battery tecnoligy uses , used to race RC cars and used brushless high spec motors . That is why i chose lifepo4 a bit safer. This is also why some of theese electrical e cigarettes have exploded as bigger ones used 2 x 18650 . Im sure the cels i got are 30c . Was going to use a bms ratger thsm ballance charging . Controls the discharge rate without the fear of going too low or charging too much .
To paraphase Mark Twain, there a lies, damned lies and Chinese battery specifications.
My experience of (now older) 18650 LiIon cells is they are unable to supply massive discharge currents. This is noticeable pulling 2A+ on an 817 where the terminal voltage drops on load. Mine were 2200mAhr brand new but from a batch that failed sampling quality tests. They work fine but I wouldn’t want to pull much more current than that from them.
And, of course, no battery is too big especially if you can convince someone else to carry it.
I know if you went to a 4 cell battery it would be 14.8 v normal voltage and 16.8v max voltage which is far too much . But if went 3 cell 11.1v normal and 12.6v on max charge . Either too high or too low … typical
"… i know the lipo and lifeo4 batteries normally drop to around 12v mark and stay around there for quite some time .
Please take care, there are notable differences between “LiPo” (without Fe, different chemestry) and LiFePo4. The reference value for 1 cell common “LiPo” is about 3.7 V and the range 3.0 … 4.2 V. In most load cases the actual voltage shows the discharge state quite good.There is a nearby constant descent over 80 or 90 % discharging time.
When I was testing my LiFePo4 6.6 Ah with a drain of 6 A the Voltage starts with 13.7 V and was falling to 12.6 V after a verry short time. Then the Voltage was falling slowly to 12.5 V at 50 % discharge and from there to 12.3 V at 80 % discharge. So the Voltage depends more from the load than from the discharge status.
(edit 2/4/19 0:54: some numbers were missing and now amended)
And, running my FT817 with 5 W SSB, a speech processor and heavy calling and speaking the 6.6 Ah were good for at least 6 h operation. So your 12 Ah may be good for at least 2.5 h heavy operation with 25 W.
Trx build for “12 V” mostly have a nominal supply voltage of 13.8 V +/- (10 or )15 %.
Starting with 4 cells LiPo full charged and with a small load current (trx on stand by or receiving) means you have about 16 … 16.8 V, more then +15%. With 3 cells you reach -15% (11.7 V) fast and faster with a higher load current when transmitting. Using LiFePo4 is much better. With 4 cells full charged you have not more than 14.4 V (+ 4.4 %). Discharged to 10 % remaining energy the voltage may be about 12 V at a load value equal to the capacity value.
The Specifications of the FT817 are looking a little bit funny but good for use with 3 cells LiPo. The supply Voltage is given with ‘13.8 V +/- 15 %’ (11.73 … 15.87 V).
In the next line I read “Operating : 8.0-16 V”!
The 817 will work down to quite low voltages. However, there is a minimum supply voltage to get 5W which I think is around 10.5V. As the voltage increases, the output stays at 5W and the case gets hotter! So the 817 is ideal for use with a 3S LiPO cell pack.
