You need to be careful when using an 817 with a 11.1V nom Li-Po battery. These batteries can be damaged if their voltage drops below a certain level. Opinions vary but it’s just over 3V minimum per cell (9V for a three cell pack). More is better.
Further to this, experimental results for voltage inputs on my FT817ND were as follows:
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As supply voltage is lowered rig dropped out on receive at 7.2V and would not restart with start button.
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As supply voltage is raised rig was re-startable at 8.0V.
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Rig produced the same 5W RF power output for input voltages between 7.9V and 13.8Vdc.
So…
4) In order to protect 11.1V Li-Po batteries in future, a diode dropper chain was fitted.
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Fitted three 1N5404, 3 Amp diodes all in series with FT817ND positive supply line.
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Minimum voltage for FT817ND in RX mode upstream of diode chain: 9.4V (FT817ND sees 7.2V and therefore cuts out). Now the Li-Po cannot get dragged below 9.4V (ie 3.13V/ cell).
Above photo: 3 x 1N5404 series diode chain in series with FT817ND power input from 11.1V Li-Po
Nothing to do with the above but incidentally:
Li-Po VOC versus Amp-hours
3.7 V/cell = empty
3.8 V/cell = 20%
3.9 V/cell = 40%
4.0 V/cell = 60%
4.1 V/cell = 80%
4.2 V/cell = FULL
Hope this helps to protect your Li-Po’s.
73, John