Power Distribution Board Burned After Soldering a New Capacitor - Page 1
Forum section: electronics / projects

author: ipek.grgc
author_rank: Contributor
timestamp: January 16, 2022, 03:30:22 pm
content: Hi Everyone,I have a Matek FCHUB-6S PDB. It has 3 to 6s battery input voltage, supports up to 27 volts. I have been using it as a power regulator for a while since its the only thing I have that has a 5v and a 10v regulated output. It was powered via another PDB: Holybro PM07 power module. This one supports up to 12s batteries.Matek's main power cables was soldered to one of the ESC pads of the PM07. Everything was working fine untill I made 2 changes. At first, I changed the power connectors of my battery packs' and PM07's to XT90s antispark plugs. Tested and the system worked fine +20 times. No sparks at all. And then I decided to add an electrolytic capacitor to Matek's main power input for extra protection against voltage spikes.After that, antispark plugs started to spark! Even the contact points of XT90s' got darker in 4 plug ins and outs. I was trying to figure out why they started to spark. At the 6th plug in, I saw a huge bright spark came out from Mateks new capacitors legs and smelled that something has burned out. I immideately unplugged the battery from PM07.I thought electroliytic cap was the one that burned but it wasnt. I seperated the capacitor from matek for investigation. The smell was coming from the board, the cap was fine. I checked for any shorts on the Matek with a multimeter. It doesnt make a beeping sound but it shows a value: 57 ohms. Regarding to its manual if it shows a values over 50 ohms it should also beep. I am confused about that. So I guess there is no shorts but something on it doomed. Couldn't find what that is though. I am attaching its before and after pictures. The before picture is the one with the blue rubycon cap on, also its in a case. The after pictures are the bare board pictures without the cap and close-ups.Can a capacitor cause something like this? It should have protected the circuit, instead did it fry it? Or did the resistor in the antispark plug burned and its spark caused Matek to burn? I am open to any ideas about what might have happened or done wrong. I will try to find a power supply and a better multimeter to conduct better tests on it.By the way, all other equipment is healthy. And the cap was 470uF 35V with 0.073 impedance.Thank you,Ipek

author: CaptDon
author_rank: Super Contributor
timestamp: January 16, 2022, 06:06:21 pm
content: What in the world is an anti-spark plug???Thinking you hooked up the supply voltage backwards.It's fried now.

author: ipek.grgc
author_rank: Contributor
timestamp: January 17, 2022, 12:33:22 pm
content: Quote from: CaptDon on January 16, 2022, 06:06:21 pmThank you for your reply. I have checked everything in the power system, no reverse polarity connection in there. Still trying to figure out what happened.I shouldn't have said antispark plug, connector might be a better terminology. Antispark connector is commonly used in electric vehicles (e-bike, scooter etc.) and rc vehicles such as drones. I attached the one I have below.

author: ConKbot
author_rank: Super Contributor
timestamp: January 17, 2022, 07:03:58 pm
content: Quote from: CaptDon on January 16, 2022, 06:06:21 pmFor those not in the know with hobby RC stuff, you can get connectors with integrated resistors and a pre-charge contact so the input caps on ESCs are charged during the process of mating the connector. This prevents contact arcing, which can be severe and destructive on 20-50V batteries, with hundreds or thousands of uF to charge, and a battery that is good for hundreds of amps in a surge and is relatively low inductance.The connectors are already marginal enough for the currents being shoved though them, saved by limited duration. A rise in resistance would just ruin them. Normal connectors would just use a long-wipe design that can get pitted, and the slide to clean metal on metal contact in the fully seated position. But the simple cylindrical design of the common connectors doesn't support this.

author: ipek.grgc
author_rank: Contributor
timestamp: January 18, 2022, 11:53:02 am
content: I bought a DC power supply and a new Matek PDB. Now the setup works fine, no weird sparks anywhere. I am afraid to solder a new capacitor on the Matek FCHUB-6s PDB again, so I will use it as it is. I think cap wasn't the problem, but I can not risk my boards again.Used the DC power supply to do some test on the burned Matek PDB. Desoldered the electrolytic cap before these tests, as I mentioned. Gave it 11 Volts via DC power supply, emulating a 3S lipo battery. It sparked again, and the spark was coming from below the PDB. It looks like the PCB is damaged under the power pads, I am not sure if this happened because of the spark or the damage caused the spark. A burnt smell is coming from the same spot. Other than that the 5v and 10v regulators on the PDB look fine and their smd leds are on. I am attaching the pictures of the suspicious spot. Both the new and the burned Matek PDBs'.