USB-C to Barrel Jack Voltage issues

[dpatel522]

Hello, I have an odd situation that I'm having trouble understanding (most likely due to ignorance on the subject).
I purchased a USB-C to 20V 5A 5.5x2.5 barrel jack cable with the goal of running it to a buck converter to drop down to 12v 8.3A. Essentially wanting to be able to use the 100W USB-C ports on my power supplies to output more than 3A at 12v.

The issue is, this worked when plugged into a Jackery Explorer 100+ LiFePO4 battery bank, but doesn't work on any other USB-c 100W source (EcoFlow Delta 2, Anker 140W bank, plugged in 100W laptop charger, etc). In all other scenarios, the measured voltage after the converter seems to be quickly jumping around between a little over 8v and a little under 11v as measured by a Fluke meter.

The buck converter is a 8v-40v input to 13.8v 10A output.

I've tried the same thing with a 18v-60v input to 12v 20A output and i can get 12v out on any source. The problem is by the time I power my devices, the voltage drop is significant enough to be dipping below 11v at the device which causes it intermittently stop working.

I'm not sure why the Jackery source works and all others cause the output to wig out. All sources were checked to see if they can provide 20v 5A out.

Any help is appreciated.

Dipak

[Timeline]

Are you talking about this one? https://www.adafruit.com/product/5452

Note that this cable is designed for supplies/chargers that support the PD charging protocol when plugged into a PD Type C adapter and the cable then negotiates the 20V PD output. My guess is only the Jackery Explorer supports PD charging while the others do not. You would have to find out from those other manufacturers if the products you are trying the cable on supports PD charging at 20V.

[dpatel522]

You are correct, that is the cable I'm using. I've verified that the cable isn't the problem as it output 20v correctly by itself. The issue arises when I plug in the buck converter. If I use the 20v to 12v one, it works fine. However, if i use the 20v to 13.8v it starts to freak out. I've tried swapping out the 13.8v one with one of a different brand it I get the same result.

[Timeline]

Ah I see. When it freaks out are you seeing the 20V input side being effected (making the whole thing not work right) or does the 20V input look normal while the output is troublesome? Also does this happen at any current draw level or are you trying to pull the nearly 8A current?

[dpatel522]

I put one of these (https://www.adafruit.com/product/4232) between the battery and USB-C cable. When using the 12v converter, it shows 12v coming out. When I use the 13.8v buck converter, that meter blinks out with no power to it anymore and the voltage at the tail end (as measured with a Fluke meter, jumps around and freaks out).