817ND on 15V?

When you actually take everything into consideration, the 3S Li-Fe-Po4 battery is the optimum choice for the FT-81X radios. A 4S Li-Po is 16.8v. Use at your own risk.

Note, full battery voltage is applied to the final, the rest of the radio is regulated down. The optimum point is 11v.

Vy73 – Mike – KD5KC-- El Paso, TX.


Interesting discussion.
Note that many of the electrolytic capacitors in the FT-817 are only rated at 16V. Running on a fully charged 4S LiPo battery will be placing strain on the electrolytics and causing additional heat dissipation in the voltage regulators.
I have been using a switch-mode DC-DC converter to drop the volts to about 11 V. I have not noticed any RFI issues from the switch-mode converter.
Peter VK3PF


My personal favourite was the 2500 maH 3S flat battery pack as it fits directly inside the FT-817/8 batttery compartment and used to give me enough for two, half hour, SSB HF activations and still be around half charged when I finished. You just need to make up the correct lead for the 817/8 and it’s a very tidy solution.

But Aleksander has received 4S LIPO batteries hence the various suggestions in this list about how to make those work.

73 Ed.


The reason I got a 4S are QRO activations or field days. I use the Chinese MX50 amp in combo with 817nd and on 16V it can deliver up to 60W and maybe more. Its components are apparently rated up to 24V for 100W.

Just yesterday I installed the 2.5Ah battery into the radio itself. It serves for SOTA activations that are more demanding physically, therefore I don’t want to haul the 10Ah battery and the amplifier with me.

And if I am doing QRO I don’t want to waste my 2.5Ah battery, it’s a backup.

Hey there.

I’ve been really lucky in that respect. I truly value a good battery that will fit inside the FT-817. It keeps operations super simple. For a while I had 4 batteries that fit, 3S at 3600 mAh each. Over the past several years all but one has died off. And they were promptly discontinued of course!

More recently I discovered some that once again fit into the FT-817 easily, and are 3S at 3000 mAh. I bought 4 of them. And of course, now they have been discontinued also. What can you do?

Vy73 – Mike – KD5KC – El Paso, Texas…

I posted about this before in this thread :

Two diodes are over the NC contact of the relay.
When the voltage is high (and when you have some power to spare …) , the relay is activated and keeps the diodes in circuit, also the LED is ON. After a while, when the input voltage drops to approx. 15V, the relay is released and shorts the diodes, so the circuit draws almost no power for the rest of the time.

It is automatic, but of course I must not forget to insert the little box, hi.
No harm will be done if I feed my KX3 with 16.8 V, it will just say “OVER 16V” in the display, and refuse to operate (Yes , I tested that !).
Not sure what the FT817/818 would do …

Here a better picture of the reducer, it weighs just 40 g.

73, Luc ON7DQ


I don’t know about the 817, but a PSU failure putting exessive voltage into an 857 of mine destroyed several components, putting it out of action. The 857 has similar circuitry to the 817 so I would avoid testing it!

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This makes sense. I have run my ft-857 as high as 16.1 volts from a LiPO battery and it got quite warm. Warmer than I remember it getting when running at a more normal 14 volts from my LiFePO battery.


I have the 3AH Windcamp battery for my 817. Replaces the old NiCad battery and allows you to run the full 5 watts. Other Ham Radio Equipment for sale | eBay

Made this today with a Zener diode 1N6277A. the diode side is crimped only so I don’t have to worry about solder melting. The operating temp of the diode is -55C to +175C. It drops the voltage by .6 volts, enough to bring my one LiPO battery down from 16.2v to 15.5 or so when fully charged. During testing it got warm but no where near 175C.


4S LiPO fully charged is 16.8V

Yes, but it doesn’t stay at that voltage very long sitting there. Mine comes down to 16.2 after about a day.

A power diode rated for up to 2 amps would be sufficient. No need for a zener, the reverse breakdown will never be an issue.

Two diodes would provide better protection. Protect your $600 radio by adding another $1 diode. Makes sense, I reckon.



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This seems like an appropriate place to ask this. Is there any issue with having the stock internal battery fitted inside, while connecting the 817 to an external LiPO?

Not really.

The stock battery will be trickle charged when you connect up an external supply. This means some of your energy from your precious external battery is used to top up the internal battery. If your external battery is exhausted then you can disconnect it and use the internal one.

However, the standard NiMH batteries provided, the original 817 and 817D versions, are woefully gutless. IMHO they are just extra weight to carry about for activators. I used to have one installed as a backup but you can normally make something out of a few 18650 cells that weighs less and lasts much, much longer. So I haven’t had an internal battery for about 8 years or so. Just a wee extra LiPo “just in case”.

Just to be clear, the external battery will not charge the internal battery unless you have selected “CHG” from the menu (row 11, key A.)

Lamentably true. However you can install high capacity NiMH cells in the provided battery box, I use 2500 mAH cells. However the battery box is intended for disposable dry cells so it will not permit the NiMH cells to be charged in the rig. This can be bypassed by cutting and insulating the ends of the green wire to the battery box, so that the cells can be charged in situ.

@2E0FGX: You may try to wire the diode bridge in the way all 4 diodes will be utilized - see the “version 2” below. In your “version 1” only two diodes conduct (and produce heat). The voltage with V2 will be a little bit higher (aprox +0.3V) but you will get a bit more current even at lower voltages. 73 Igor

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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