Max input voltage on DC Power Connector....

[n4rg]

Manuel, et al,

Looking at the schematic and referencing the spec for the L78L05 part. The L78L05 has a max input voltage of 30VDC (when output voltage is between 3.3-9VDC). However, U9 (LT6231) has a max input voltage of 12.6VDC. I am having problems reconciling the max input of 16VDC.

The reason that I am asking is I have battery packs (4x of 18650 Li-Ion at 3500mAH) which gives me (peak charge) of 16.8VDC.

L78L05 data sheet: https://www.st.com/resource/en/datasheet/l78l.pdf
LT6231 data sheet: https://www.analog.com/media/en/technic ... 3012fc.pdf

Thanks,

Herb

[pe1nnz]

Hi Herb,

Going above the 13.8V voltage put more stress on the PA class-E MOSFET and the voltage regulator. The LT6231 opamp is generally not directly connected to the input voltage and do not suffer from this stress.

Even with 30V on the input the power dissipation in the 78L05 regulator is about 1.5W for a 60mA (trusdx) current draw, temperature will raise but I doubt it will reach the maximum 125 degrees celcius, so this might this be OK, if not thermal protection kicks in.

Another story is the PA MOSFET. The class-E filter network is designed for good efficiency at 13.8V. Changing the supply voltage, means the that impedance is changing and might no longer match with the filter network and antenna resulting in heath effects and more power draw that might go above the 1-2W power dissipation limit to destroy things. More power means also higher voltages that can destruct the MOSFET or capacitors or the RX isolation stage. So as long you can keep efficiency and power reasonable (>70%, <5W) then things are OK with an increasing supply voltage.

Hope this helps, but the recommendation is to not go above 13.8V.

[SP9TKW]

Herb,

Check technical data for your 18650s. Usually 4.2V is stated as maximum charging voltage and nominal (working) voltage is 3.7-3.8V

Charging your batteries to maximum reduces their lifespan considerably.

I have homebrew 4S1P unit with BMS and I never charge it more than 14.5V. It serves me well for last three years during SOTA & POTA activations.

It is worth noting that even if you charge your battery to the maximum it reduces voltage to nominal value very quickly. In practive I found that it is enough for 1-2QSO SSB.

GL 73 Marek

[n4rg]

Manuel and Marek,

OK, thanks. So just to be clear the 13.8VDC is a limit due to efficiency, NOT with max voltage of parts within the (tr)uSDX radio. I understand the efficiency and such. Things will get "warmer" but won't damage a device by exceeding max input voltage.

I agree on the 18650 quickly discharging below the max charging voltage, however my charger is commercially bought so I cannot change the max charging voltage.

Thank you Gentlemen!

Herb

[dl6sez]

Hello OMs,

best to cycle standard LiIon batteries is 85% to 20% (or up to 30%) for a maximum of lifetime in cycles and capacity.

My 2 Cents
73 de Chris

[Sparksnov]

just put few diode i series dc cable drop the voltage



quote=n4rg post_id=7056 time=1692880787 user_id=1641]
Manuel, et al,

Looking at the schematic and referencing the spec for the L78L05 part. The L78L05 has a max input voltage of 30VDC (when output voltage is between 3.3-9VDC). However, U9 (LT6231) has a max input voltage of 12.6VDC. I am having problems reconciling the max input of 16VDC.

The reason that I am asking is I have battery packs (4x of 18650 Li-Ion at 3500mAH) which gives me (peak charge) of 16.8VDC.

L78L05 data sheet: https://www.st.com/resource/en/datasheet/l78l.pdf
LT6231 data sheet: https://www.analog.com/media/en/technic ... 3012fc.pdf

Thanks,

Herb
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