Bzzt! Wrong. Note the word “trickle” in my original post. It trickle charges as opposed bulk charging which is what happens when you select CHG from the menu.
I have one of the windcamp 3S LIPOs installed in my 817. When using an external supply, the switch on the custom battery cover is turned off, which does appear to isolate the internal battery. In practice the LIPO has been so good I rarely use an external battery.
817 works better towards 11v…
and so, I prefer LIPO 3S
I ran the external MX amp on 16.8V and it delivered 75 to 80W so I’ll stick with that and add a diode or two for the radio itself.
I do not use the internal battery. Yes I have a bridge rectifier on a heatsink but a tad bulky .
I’m going to order a 5ah 3s lipo and see how get on . Technically on 6w fm with sql open I should get 2 hours on transmit. But obviously not full tx neither Rx all the time .
Worth a try but not advisable to drop below 9.6v .
3v per cell is a lipo fully discharged zone 10v would be advisable .
Matt
Today my anderson connectors arrived so I made a plugin voltage reducer. I used 4 diodes to get it down. If the voltage of the battery drops to 15.5V or so, I can remove the diodes. Now I can use the amplifier on 4S giving me up to 80W of power while on SOTA.
Hello Umberto,
why are u saying, that the FT817 is working better towards 11v?
Saluti
Julian
The 817 will give full power from around 10.5v upwards. At 13.8v you still only get the same output power but the radio runs very much hotter. So around 11v gives full output without getting too hot.
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Tested the same right now.
Under 9.5V I also get the full output power.
So everything easy. I saw huge discussion about 3S LiPo, 4S LiPo with reduce circuits like diodes in series (lol) or 4S LiFePo4. But in the end with my technical knowledge I must say why the hell not everyone uses 3S LiIon or 3S liPo.
I tested everything out except the 4S liPo with 16.8v because it is stupid in my opinion. At the end I came to the conclusion to use 3x 18650.
They are cheap, used in a lot of devices and I had some at home from other projects (also my headlamp uses one 18650).
Activated 4 peaks, with round about 100 QSO’s and like 4 hour operation time. Charged the batteries back home and it drained only 2000 mAh from 3500 mAh. So pretty good results.
73
Julian
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I’m planning tu use an LM338 too, using a typical application citcuit as per data sheet.
Data sheet says it requires a differential Vin -Vout of at least 3V, so I think I can regulate it to obtain , say, 11 V to get full power. So it’ok until Vin drops to about 14 V …but what happens when battery discharges and Vin drops ? Do you have to switch regulator off?
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This gives somewhere to warm one’s hands.
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I took a risk and use 4S LiPo for my 817. Battery has almost 17V when fully charged and nothing bad happens.
You have to be careful because maybe another 817 will not be so understanding…
vy 73 de Mariusz
If you look at the rather eye-watering circuit diagram you will see that the input voltage, whether from the battery pack or the external supply, only goes as far as the voltage regulators. The outputs to the rig are 5V, 6V and 9V. Running from a 13.8+ supply leads to extra heat. This may not seem to be a problem, and for SOTA it probably isn’t a problem, but in other circumstances it can end up as a serious problem. When I had my first FT817 I used to have long ragchews on 2m FM, and long sessions on digital SSTV. One night the rig stopped working. When I took the lid off I found that one printed circuit track had got so hot that it lifted from the board and then broke. I got back on the air by soldering a wire across the break but after that was much more careful about how hot I let the rig get!
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And the three driver FETS and the FINAL board. They’re all fed from the unregulated supply.
If people want to exceed the manufacturer specs then that’s fine and their business. No doubt they probably juggle hand-grenades for giggles too. Maybe you’ll only fry the drivers and PA. But if you take out the lower voltage regulators, you could destroy all the digital circuitry which is basically writing off the whole set.
Sure there are a few people who have run their radio on far too high a voltage and not had a problem. They remind me of when we see programs about smoking and lung cancer and the number cigarettes kill. Then someone always rolls out the case of some old guy in his 90s who’s smoked for 75 years and doesn’t have lung cancer or even a cough. He’s an outlier, a statistical freak. Much like the few 817s running off nearly 17V.
I just checked the abs max Vds for the 2sk2596 pre-driver and 2sk2973 drivers is 17V
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3S LiPo is what I have been using for both my FT817 and KX2 for years. Simple, reliable and free as recycled from a Dyson battery pack. I recently managed 4 activations in Spain before the voltage dropped so much that the radio cut out (I had forgotten to pack my iMax B6AC)! Then I simply switched to a spare 3S LiPo.
Just realised I also use the 3S LiPo pack to power my VHF handie if the integral battery is flat!
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If 3S 18650 with 3500 mAh for the FT817 ( I’m making like 200+ QSO SSB 5W) isn’t enough, I use 21700 with 5000mAh or I take 2x 3S 18650 with me. That should last a complete weekend 
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I think you are right, my eyes are as old as the rest of me, but I got a good magnifier out and felt at times that I was going around in circles! It was easier when my station was all valves and no semiconductors… 
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ISTR the 13.8V line to the drivers/PA is not switched. So they’re powered all the time.