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Support of 30V input voltage #5

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MagnusPer opened this issue Apr 16, 2021 · 3 comments
Open

Support of 30V input voltage #5

MagnusPer opened this issue Apr 16, 2021 · 3 comments
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hardware Feature / bug in hardware

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@MagnusPer
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MagnusPer commented Apr 16, 2021

Many mowers today uses 7-cells Lithium batteries with a charger voltage of 29.3V. To support those battery types I suggest a hardware configuration by a jumper on the next version of PCB to support more than todays max 25.2V.

Short term until hardware support - describe needed modification on hardware to manually perform.

@Selective031 Selective031 added the enhancement New feature or request label Apr 16, 2021
@Selective031
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After our discussion I looked into it, and should not be a problem to include in a future revision. It´s only a couple of resistors to replace.

@MagnusPer
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MagnusPer commented Apr 16, 2021

I created this issue more to inform other persons that having the same need. However either in this issue or in the Readme section describe the needed changes.

@Selective031
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This has been added to the README:

Do NOT connect a 7 cell battery! When fully charged it will output 29.4 Volt (7 * 4.2 = 29.4 Volt)
If you really need to provide a 7 cell battery, you need to replace a couple of resistors, they are in the package of SMD 0603. Without replacing them you might risk to blow up a couple of pins on the STM32 MCU.

The resistor that needs to be replaced:
-R3 30K
-R4 7.5K
-R6 30K
-R5 7.5K

With the above resistors, an input voltage of 25.2 would give us 5.0.4 volt, which we can handle.
But if using 30 Volt you will get about 6V which will burn the pins. You need to replace two of them (R3 or R4 and R5 or R6), so you don´t go above 5 Volt.
Use this link for calculating the divider. Also when you replaced them, you need to update the software to calculate the correct voltage.
https://ohmslawcalculator.com/voltage-divider-calculator
Do this at your own risk.

@Selective031 Selective031 added hardware Feature / bug in hardware and removed enhancement New feature or request labels Apr 25, 2021
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