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Author Topic: FT-891 QRP  (Read 663 times)

AE0Q

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    • AE0Q Amateur Radio
Re: FT-891 QRP
« Reply #15 on: March 31, 2021, 10:17:33 AM »

Generally speaking, in portable operations, you are receiving about 70% of the time. This gives you and average current draw of 2.0 amps per hour. A 20 AH battery should be fine for a day of portable operation. Add a portable 20 watt solar array and you could operate well into the night.

With the popularity of POTA (Parks On The Air) and WWFF park activations, many portable stations are actually transmitting MORE than receiving.  To activate a park you have to CQ all the time if not working someone so (1) park hunters can find you, and (2) so you can keep your frequency in the SSB bands (not a problem on CW).

Most park activators only stay at a park up to a few hours (many close at sunset), so a 20 AH battery is still usually good for a day of activating a park or two even with a 100w output radio.

In the interest of overkill I got a 40 AH LiFePO4 battery, but even on the longest park outing with 2 of us operating we have never used more than 25 AH of its capacity.

Glenn AE0Q
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NSGA Edzell 1974-77  CTM2  GM5BKC : NSGA Rota 1972-74   ZB2WZ, SV0WY
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KB1GMX

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Re: FT-891 QRP
« Reply #16 on: March 31, 2021, 01:54:49 PM »

AE0Q,  Have you actually done that?  Not trying to troll or be snarky..

I've tried that it doesn't work.  Why?

First the battery is 20Ah to exhaustion.  However the radio like
many quit full power TX at about 11V some maybe 10.7V.
Also as the battery voltage goes down at least a few radios
on TX draw more current.

So on average that 20Ah battery is maybe good for 4.7 hours if the
TX time is short and represents about 10% of the time transmitting.
That .6 hours (36 minutes) of TX in 6 hours.  You may get more but
can you count on that, maybe at best.

For that I'd use a 33Ah battery for 6 hours and also cut back TX
power for those stronger stations.

20ah battery is about 140watt hours.  Average 100W radio
eats 240watts during TX.  During RX its anywhere from
25 to 36watts (depends on volume and specific radio).
Listen only is maybe 10 hours likely less.

However even a 20W solar panel (nets about 1.45A charging
current using MPPT controller) can easily add two or more
hours to the 20AH battery life.  Larger panel of 40W or more
will put you well over the top and able to charge the battery
while receiving.

Small case:
 The FT817 .45A on RX average, 2A on TX average.
 An 8Ah gell cell will run it do exhaustion as the FT817
is one of the few that will run below 11VV.  Note for lead
exhausted is terminal volts is when the battery falls
under load to below 1.9V per cell or 11.4V.
That combo can run most of a day (about 16 hours
RX only).  Add a 10W panel (about .57A) and you
charge during receive (when sun shines) and only
transmit time counts, so easy to do a day.

Lithium tech does not change the math as you need
enough voltage to keep the radio happy even if battery
is only 40% discharged.  Its advantage is far lighter
by as much as a half to 1/3rd for the same total
watt-hours.  The best case is for LiFepo4 and
more amp hours the better. Price is not cheap.

Did the math, went and did field days and noted results.

Allison
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AE0Q

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    • AE0Q Amateur Radio
Re: FT-891 QRP
« Reply #17 on: April 02, 2021, 02:50:55 PM »

AE0Q,  Have you actually done that?  Not trying to troll or be snarky..
I've tried that it doesn't work.

I'm not sure what your question is.  I haven't used a 20 AH battery, I have a 40AH LiFePO4 battery and use an inline voltage and current monitor, the little digital ones everyone sells.  I know how much power my 100w radio uses when on the air all day.  My wife and I made 7000 QSOs from parks in 2020, using a TT Eagle at full power out and the 40AH battery, and never used more than 25AH in a single long day of operating.

I said "a day of activating a park or two", and earlier in that sentence my definition of activating a park is a few hours.  WWFF/POTA activations mean lots of CQing, definitely not 10% transmitting time, much more like 50% or greater. 

Given that a LiFePO4 battery holds voltage above 12.0V for about 85% of it's rated capacity, a 20 AH battery would be OK for an average day of activating a park or two with a 100w radio.

If your point is that a 20AH battery won't be enough for park activating, you need to read the comments by many dozens of POTA activators that use those batteries with the really popular FT-891 100w radio (and other radios, of course).

I think this is now in the wrong forum...
« Last Edit: April 02, 2021, 03:04:02 PM by AE0Q »
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KB1GMX

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Re: FT-891 QRP
« Reply #18 on: April 04, 2021, 09:59:16 AM »

AE0Q,

My question was aimed at the guy suggesting a 20Ah battery
was enough.  I crossed you and another reading the whole
mess.  The intent is unlike you (you know your radio and
its needs)  many have no idea the power needs of their radio
(IC7300 wants more) and what voltage it must have to keep
working reasonably.

I can believe 40Ah makes it but 20 would require running the
power down to keep going.  I've seen more than a few either
forced to cut power or worse quit early.   Also other batteries
(lead!) without battery booster will fail sooner as even 33AH
if you get 60% of the Ah before the terminal voltage starts
to fade you only got 20Ah of it. A booster has aa poer cost so
you may only get 80% ignoring that's near maximum DOD
for lead. Again understanding the battery and what the
radio will tolerate are critical.

So you used you case ( one I understand well) of 25Ah for a active
session and with 40ah that's really good.  With 20Ah it would be a
short fall  or require cranking down the power.  Heavier radio
(power consumption wise) that would be much harder to do.

So happens I have a TT Eagle, a solid radio and fairly battery
friendly compared to some in the 100W class.  RX power c
onsumption is lower than many.  The exact number for mine
is 1.45A at normal speaker volume and 18A(+-) TX.   The
TX current at low power is also better than most 10W out
(carrier SSB) is about 6A (with compression on),   Compared
to my TT M430 Triton at .28A RX and 18A TX, the TS440S/AT
at 2.9A RX and 20A TX and doesn't go below 5A even at 5W.
That and the TS440 stretches my arm, its heavy.   Oddly  my
Atlas 210x, RX is well under .3A (200mA, bulbs replaced with
LEDS) and TX can peak to 18A but at reduced power its
around 10A and like many older radios without speech
processing the average power is lower.  Weights about the
same as the Eagle but only 5 bands.

Just running the TT EAGLE RX only for 10 hours hits 15Ah,
I monitor a lot so I know the required power.   I've sucked a
33A AGM dry with daytime ops in a contest where the full
100W SSB was needed.   Add 40W or more of solar and
its adequate.  Next step up for FD was 66Ah and 110W
solar, no issues for the weekend.  The extra battery was
cushion against no or limited sun and the over night
stretch.

Lithium does not last significantly longer, its only lighter
 (much less, maybe half)  for the same AH.   Depending
on the chemistry you may get more of the AH you carried
than lead without resorting to battery booster.   I'm also
a user of Lithium tech especially when weight is important.
 A 13Ah mil battery (195WH) I have is less than 49 ounces
(1.39Kg) and the average 8Ah gell cell is easily twice that.

The whole thing is what you can carry, how big, how heavy,
how far, and operate for how long.   Also how disappointed
will one be if the battery quits before your ready to.

I do run the home station completely off solar/battery
(150ah battery and 400W solar) so I have a better idea
of what is required to make it run say a whole contest
weekend. I monitor it all with a few West Mountain Radio
PWRCheck units for charge status and load status.


Allison
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