12v input TVS diodes

[Jean-Marc Douroux]

Hello,
Pay attention to the voltage of the TVS diode protecting the 12V input (D201 in the diagram above). A 15V diode is too tight and risks shorting knowing that alternators can charge from 14.2 to 14.6V and that some LiFeYPO4 batteries could be charged at more than 15V according to their manufacturer's specification for increase their lifespan, which is confirmed by the endurance tests of these batteries. There is no risk in raising the threshold voltage of the TVS between 17 and 20V.

[BellaX]

Hello,
Pay attention to the voltage of the TVS diode protecting the 12V input (D201 in the diagram above). A 15V diode is too tight and risks shorting knowing that alternators can charge from 14.2 to 14.6V and that some LiFeYPO4 batteries could be charged at more than 15V according to their manufacturer's specification for increase their lifespan, which is confirmed by the endurance tests of these batteries. There is no risk in raising the threshold voltage of the TVS between 17 and 20V.

Depends. The switcher used has a max. operating voltage of 18 V and absolute max. voltage of 20 V. So you have
to find the right TVS breakdown voltage between max. charging voltage and max. input of your pmic.

The TVS diode breakdown voltage is 16.7 V minimum. I have connected my lab power supply to give you numbers.
The current rises at 17.7 V. At 18.5 V the current is 50 mA. Beyond this voltage the current rises dramatically and the 
polyfuse will break down.

But you are right, if someone is using a non-standard battery he has to check the voltage range of all devices.

Best regards
Chris

[Sailoog]

Hello,
Pay attention to the voltage of the TVS diode protecting the 12V input (D201 in the diagram above). A 15V diode is too tight and risks shorting knowing that alternators can charge from 14.2 to 14.6V and that some LiFeYPO4 batteries could be charged at more than 15V according to their manufacturer's specification for increase their lifespan, which is confirmed by the endurance tests of these batteries. There is no risk in raising the threshold voltage of the TVS between 17 and 20V.

Thank you Jean-Marc. Good point. I will try to do some testing this weekend and suggest testers push the prototypes to the maximum voltage they can generate.

[Adrian]

Depends. The switcher used has a max. operating voltage of 18 V and absolute max. voltage of 20 V. So you have
to find the right TVS breakdown voltage between max. charging voltage and max. input of your pmic.

The TVS diode breakdown voltage is 16.7 V minimum. I have connected my lab power supply to give you numbers.
The current rises at 17.7 V. At 18.5 V the current is 50 mA. Beyond this voltage the current rises dramatically and the 
polyfuse will break down.

But you are right, if someone is using a non-standard battery he has to check the voltage range of all devices.

Best regards
Chris

Valid point about the TVS.

The Pololu module can take up to 50V according to their specs:
https://www.pololu.com/product/3782/specs
The LDO we use for the MAIANA LEDs is also good up to 45V.

So we could go with a higher voltage TVS as is. Though as you mention, this will limit the range of switchers we can consider when replacing the DC/DC module.

That being said, the MAIANA UART adapter uses a SMBJ14CA which has the same breakdown and clamping voltages as the SMBJ14A on the MacArthur HAT.

[Sailoog]

Test done. Look at the picture, the system has been running for over an hour at 18V. Everything works as usual but the power module gets very hot (using the scientific method of holding your finger for 3 seconds before burning it).

The power supply on the left was powering an RPi4 running OpenPlotter with 2 opencpn instances, the signal k server, a GPS, an IMU, and an 8-inch monitor.

System drops at 20V but everything survives undamaged even above 25V.

On this scenario it would be really recommended using an small heat-sink for the power module but the question here is: is there an alternator, charger, MPPT... capable of charging 12V systems at that voltage? The most I can find are LiFePO4 chargers at a maximum of 15.6V.

   

[kagouraki]

Test done. Look at the picture, the system has been running for over an hour at 18V. Everything works as usual but the power module gets very hot (using the scientific method of holding your finger for 3 seconds before burning it).

The power supply on the left was powering an RPi4 running OpenPlotter with 2 opencpn instances, the signal k server, a GPS, an IMU, and an 8-inch monitor.

System drops at 20V but everything survives undamaged even above 25V.

On this scenario it would be really recommended using an small heat-sink for the power module but the question here is: is there an alternator, charger, MPPT... capable of charging 12V systems at that voltage? The most I can find are LiFePO4 chargers at a maximum of 15.6V.

Actually no. The charging voltage for lead acid batteries is 14.4-14.8 V. If you have voltages higher than this, having noise in your setup is the less of you concern at the moment...