Batteries for FT-817

Equipment Radios & Power
21

In reply to MM0FMF:

my own FT817 reports it is
not producing 5W

Very interesting. The other day I started experimenting with mine (both - the two gave virtually identical results) to try and determine the truth or fallacy of the “817 runs on 9.6V” contention. Didn’t get very far, but did get the following initial results on 2m:

12.0V - 3.7W out - current taken 1.65A
13.8V - 4.2W out - current taken 1.95A
16.0V - 4.4W out - current taken 2.00A

Haven’t worked out what it means yet and a lot more experiment to do, but it does lead me to believe that although the receive side may be designed to work on 9V the transmit side certainly isn’t!

Interesting stuff. Well I think so!

Me too! just wish I had more time to play.

73 de Paul G4MD

22

In reply to MM0FMF:

As I intend to do ‘some’ 70cms operations this year and will be carrying
a 20W PA and 70cms antenna in addition to everything else

Just a quick point Andy - I am considering jettisoning my 70cms linear in favour of a larger antenna. I have found to produce 25W output the linear is taking 9A peak and the 3.3AH SLABs that I use are regularly getting 100% depleted. It wasn’t a problem when there were only a couple of contacts to be had, but with activity now on the up, it has become an issue. Maybe time to check the efficiency of your linear.

73, Gerald

23

In reply to G4MD:

We live in interesting times. If John G3WGV hadn’t said what he said I would have blindly continued with the aim of getting somewhere around 13.8V for my 817 in much the same way that Theophilus Painter believed the human being had 48 chromosomes. We actually have 46 (44 + 2 sex determining) and the 817 produces more watts that you’d think from less than 13.8V. For 30 years nobody disputed Painter’s figures. Nor did they independently verify them.

I put the 817 into a dummy load through an so-so power meter (sadly I don’t work for the people with the nice RF labs anymore). Using FM and 145.5MHz, I used a variable PSU and recorded the following for a fairly old 817 mk1 (old style PA).

PSU FP POW Bar Power/Current
9.6 9.3 flash No 3.9 / 1.1
10.0 9.6 flash Yes 4.0 / 1.4
10.5 10.0 flash Yes 4.1 / 1.8
11.0 10.6 flash Yes 4.2 / 2.1
11.5 11.0 flash Yes 4.3 / 2.1
12.0 11.5 out Yes 4.3 / 2.1
12.5 12.1 out Yes 4.3 / 2.1
13.0 12.6 out Yes 4.3 / 2.1
14.0 13.6 out Yes 4.3 / 2.1

PSU = psu voltage
FP = FT817 displayed voltage
POW = FT817 power indicator flashing or out
BAR = FT817 power bargraph, at full scale no/yes
Power = rf power in watts
current = psu current in amps

Which makes interesting reading indeed. That’s about a 10% change in output power as the voltage drops below 11.5V. I would hazard a guess the linearity will be suffering as the volts drop but I don’t think that at the powers involved it will be a big problem. Also it shows that the flashing power level does not mean what you think it means!

Now as I don’t have access to the nice RF lab with a programmable PSU and IEEE488 instruments where I could have automated the tests so I didn’t repeat that test on all the bands. Although a quick scan shows max output, 5.1W occurs on 50MHz and the output on 1.8MHz and 3.5MHz is just about 4W. I’m not sure if that is revealing a frequency sensitive error in the power meter or if the 817’s output drops with lowering frequency. The second option intuitively feels wrong.

Looking at a Panasonic discharge chart it suggests that a 3 cell pack (nominal 11.1V) would be about 13V fully chared, about 10.65V at 50% discharged, and about 9.8V at 75% discharged. So the regulator is only needed to allow you to really squeeze the last 25% out of the packs and maintain something near max output. Or to use a pack with an initial voltage above the max rated supply voltage. Without a buck-boost regulator derating a Li pack by 25% allows you to compare it with a SLA.

Charging can be complex but the radio control people seem to have all the bits you need including chargers and balancing circuits. To protect the cells from over discharge, the best packs have a shutdown circuits included.

Confused? Hopefully not. Still the solution that’s most obvious to me is to swipe Barry’s pack when he’s not looking! :slight_smile:

Andy
MM0FMF

24

In reply to MM0FMF:
Quote: “Still the solution that’s most obvious to me is to swipe Barry’s pack when he’s not looking”

I’ve been searching for years for somebody to carry my pack ---- oh, I see what you mean!!!

Reference looking after Li-Ion packs (MM1BJP posting) - I have treated mine to good healthy neglect and I find that even if I forget to charge the pack there is enough oomph in it even when left for weeks. After an activation of any duration it, obviously, needs recharging but when I have done the activation on the internal 817 pack I generally just throw the Li-Ion into the bag and use it without problems.

What I do find interesting is Andy’s Power - v- Voltage measurements and the meaning of the flashing icon; having done an activation recently with the internal pack and three bars (not flashing) I am going to have a quick measure of mine to see what comparitive results I get as I had assumed I did the activation on 2.5 watts.

Meanwhile, don’t hold your breath for an activation from me this weekend - it is batten down hatch time again up here!

73

Barry GM4TOE

25

In reply to MM0FMF:

It’s interesting to note that the current consumption is fairly constant over the voltage input range above 11V. Given that the output power also hardly varies over a 4 volt range, the increase in power consumption is

  1. Heating up the FT817, helping to shorten its life
  2. Wasting ampere hours that you’ve had to carry up the hill!

The manual says the FT817 takes 2A on transmit and that ties in well with the above figures. If we make the reasonable assumption that the 4 volts between 9.8V and 13.8V are merely creating more heat (since there is no increase in output power, it has to be going somewhere else) then that’s 8W or 0.67Ah of wasted power at a nominal 12V. In the context of 2.5Ah batteries, that’s rather a lot!

I originally used 2.4Ah SLA batteries with my Mk 1 FT817. When I got the 2.5Ah LiPo battery I found that there was virtually no difference in how long the battery lasted but the FT817 sure ran a lot cooler. So did I while I was climbing up the hill.

The FT817 is not designed for efficient operation at 13.8V. At 13.8V input it is producing far too much heat for the small case to properly dissipate, especially during FM (100% duty cycle) operation. Anything above 13.8V is most definitely courting disaster.

73, John

26

Some more sums, using Andy’s figures this time:

At 9.6V input, the FT817 takes 1.1A (10.6W) and produces 3.9W output, so its overall efficiency is 37%.

At 14.0V input, the FT817 takes 2.1A (29.4W) and produces 4.3W output, so its overall efficiency is just 15%.

Looking at it another way, at 14V the FT817 is taking 18.8W more input power to produce just 0.4W more output, compared to the 9.6V figures. For every hour of transmission you are wasting 1.5Ah of battery power, just to get 0.4W more transmit power.

It really makes no sense to run more than about 11V into an FT817!

73, John.

27

In reply to G3WGV:

It’s an eye-opener John. 25 years of 13.8V experience is hard to get out of the blood. Especially the experience with VHF linear amps and how they become very horrible very quickly as the supply voltage drops!

I’ve got a business trip to the Far East looming on the near horizon so I suspect that I’ll be investing in some LiPo packs and chargers very soon especially as the 2.8Ahr SLA I have has now done 80-odd activations and certainly didn’t seem to be holding its charge so well on the last 2 summits.

Andy
MM0FMF

28

The original post on a substitute LI-Ion pack was to “http://www.datamind.co.uk/Templates/frmTemplateP3.asp?CatalogID=1973&Zoom=Yes&SubFolderId=106” I think.

The price will make your eyes water!!!

73

Barry GM4TOE

29

In reply to GM4TOE:

The price will make your eyes water!!!

Indeed. Try here for the sort of LiPo batteries I use at a much more palatable price.

This site specialises in LiPo batteries and chargers, mainly for the radio controlled model world. There is a huge amount of information about LiPo batteries and how to look after them. Any of the “3S” (that’s three cell) batteries will do the trick for an FT817. I use the FLIGHTPOWER EVO25-2500 3S.

One thing that “they” often don’t tell you is that all Lithium rechargeable batteries have a shelf life, regardless of how much, if at all, you use them. Typically batteries start to show a reduction in capacity at about four years old. So you want to make sure that you are buying fresh batteries, not ones that have been on a suppliers shelf for a few years!

73, John

30

“http://www.datamind.co.uk/Templates/frmTemplateP3.asp?CatalogID=1973&Zoom=Yes&SubFolderId=106”

Doesn’t work for me:

There is an error in the Url you are trying to get.

Stewart

31

In reply to G0LGS:

Remove the trailing "
http://www.datamind.co.uk/Templates/frmTemplateP3.asp?CatalogID=1973&Zoom=Yes&SubFolderId=106

73, John.

32

In reply to G3WGV:
They look good to me.

What charger do you use ?

Keith.

33

In reply to G8HXE:

I have an Apache Li-Poly Smart Charger 2500 which doesn’t seem to be available any more. the nearest equivalent seems to be the Bantam e-STATION LP4 from FlightTech, which will charge up to 4S and 2500mA from a nominal 12V DC input.

73, John.

34

In reply to MM0FMF:

For comparison my results for FT817ND with internal battery using Elecraft DL1 (about 10 % accuracy). CW signal and power set to 2.5/5.0 W nominal. Battery display shows 9.8 V in receive.

80 m 2.0 W/3.8 W
40 m 2.4 W/4.8 W
30 m 2.4 W/4.6 W
20 m 2.3 W/4.7 W
17 m 2.3 W/4.6 W
15 m 2.4 W/4.4 W
2 m 2.5 W/3.0 W

Actually I bought the DL1 to test ATS3B, so here are the results for that too. 8xAA alcaline battery (now 11.8 V) and 9 V battery were used. The total TX+RX current consumption is for the 9 V battery.

80 m 3.2 W/2.0 W/360 mA
40 m 3.1 W/2.0 W/430 mA
30 m 3.8 W/2.5 W/480 mA
20 m 3.9 W/2.5 W/530 mA
17 m 3.7 W/2.3 W/470 mA
15 m 3.5 W/2.2 W/470 mA

I think I will not bother to optimize the power more now.

73, Jaakko OH7BF/F5VGL

35

In reply to MM0FMF:

Hi Andy

I’ve now expanded my measurements on my '817’s and come up with very different results to yourself. Mine are newish - around 12 months - so presumably have the “new PA” (deduced from your reference to an “old” one…)and would seem to operate in a fundamentally different way.

Tables don’t come out very well on the reflector, so I’ve not included all the results here but if anyone is sad enough to want them in full I will e-mail them as an excel spreadsheet on request. Summary of findings as follows:

Test conditions - 145MHz FM

Firstly flashing power indicator. Whether it flashes is related to voltage applied as measured by the internal voltmeter - if it indicates less than 11.4 volts, it flashes, whether on Rx or Tx.

Second, when internal batteries are installed, when the external applied voltage is below the terminal voltage of the battery (10.4 in my experiments) some current is drawn from the internal battery, as the external voltage reduces more power is sourced internally, at 9V no significant power is taken from the external source.

Third, in a test with no internal battery installed, power output increased approximately linearly with increasing externally applied voltage, as did transmit current, up to an applied voltage of approx. 13, above which power out and current remain more or less constant. For my radio this ranged from 2.0W at 9V to 4.0W at 13.5V. Efficiency was farly constant at 16-17 % throughout the range.

Finally, Rx current stays essentially constant whatever the applied voltage.

What does it mean? You decide! I shall continue dragging my slabs up the hills…

73 de Paul G4MD

36

In reply to G4MD:

Interesting measurements Paul. I wonder whether the PA stage was revised when the rig became the FT-817ND, so altering the voltage - power out relationship. Like you I will carry on with the SLABs as a cheap and easily recharged source of power. Perhaps when they are expended there will be something better available at a more reasonable cost than at present.

73, Gerald

37

In reply to G4OIG:

Hi Gerald

I’ve just plotted my power out vs applied voltage readings and guess where the transition from linear increase to constant output occurs - 13.8V. I’m now happy that for my radios at least the SLABs are a good option.

73 de Paul G4MD

38

Curiouser and curiouser…

Had a few spare moments this evening so thought I’d investigate the variation in power out on the various bands. Turns out that at 24MHz and below, my '817s give around 4.8W at 9V, virtually constant up to 15V; at 28MHz and above, we’re back to the 2W at 9V increasing with increasing voltage up to 13.5V or so. So if you only run HF, maybe the 11V Li-Po battery isn’t so bad after all…

But I’m still sticking with my SLABs!

73 de Paul G4MD

39

Some interesting results. Perhaps the design of the PA did change the voltage characteristics between the Mk-1 and Mk-2, though I understood the changes to be more about preventing spurious (and damaging) oscillations at low voltage when the internal batteries were in use. There is no question, I would hope, that as you increase the supply voltage the losses (in W) increase and therefore case heating becomes a progressively greater problem.

Let’s look in a bit more detail at the discharge characteristics of an LiPo battery. The nominal cell voltage is 3.7V, so a three cell pack is nominally 11.1V. Fully charged (no load) each cell is 4.2V (12.6V for the battery) and fully discharged (on load) 3V per cell (9V).

Now let’s do the same for a lead acid battery. Nominal cell voltage is 2V, so a 6 cell SLAB is nominally 12V. Fully charged (no load) each cell is 2.3V (13.8V for the battery) and fully discharged (on load) 1.75V per cell (10.5V).

Both types of battery have extremely low internal resistance, though that of a LiPo battery is somewhat lower. At the current levels we deal with, internal resistance is not really a factor. Both batteries have a fairly linear discharge level vs voltage profile but the LiPo battery discharges over a wider voltage range, which is potentially a disadvantage.

So much for numbers. What about practice?

I used to use SLABs on my FT817 and I still do, on the odd occasion that I NEED 13.8V because I am also using my 50W linear amp. I found that with a 2.8Ah SLAB the voltage would settle down to around 12.5V quite quickly and stay close to that figure until the battery was close to exhaustion.

With LiPo batteries, I find that the voltage settles quickly down to around 12V and discharges very slowly down to 11.8V before dropping off very quickly as the point of exhaustion is reached.

So practically we are only talking of a difference of between 0.5V and 0.7V across the useful discharge range of the two battery types. If we refer back to the various figures given above, we can see that makes very little difference to the power output of an FT817.

But what a difference there is between the two technologies for equivalent capacity batteries in terms of the weight you have to carry and the space taken up in your rucksack!

40

In reply to G3WGV:

I had one chuckle from this very useful post: I know what you mean by a LiPo battery, of course, but just as Li is the chemical symbol for lithium, so is Po the chemical symbol for polonium - not an element I would want to carry about casually!

73

Brian G8ADD