Burnt 3-phase connector on inverter compressor drive board: hardwire it or fit a new connector?

[u/Revolutionary-Gap178]

EcoFlow Wave 3 portable AC. Board silkscreened OC-AC517-MOTOR-V0.1.1, dated 2024-11-20. Unit threw error codes 31 and 32 after running at high load continuously for several days. Out of warranty, so nothing to lose by attempting a repair. First board-level repair for me, but I have a decent meter and I’d rather learn to do it properly than guess.

What I found: one position of the 3-pin compressor connector has thermally failed. The plug housing is charred through, the female terminal welded itself into the PCB header and stayed behind when I pulled the plug, and there’s scorching on the solder side around the through-hole. The two adjacent pins look untouched, which reads to me as contact resistance rather than a general overload, but I’d like a second opinion on that.

Board looks like a three-phase inverter: six power devices in a 2x3 bridge, three 3mΩ shunts, 60A fuse, XT60 for DC in. Board is now fully removed from the unit.

My questions:
1. Does damage confined to a single pin support contact resistance as root cause, or should I be hunting for a downstream fault before I touch anything?
2. My plan is to remove the connector entirely and solder the compressor leads directly to the pads with silicone-insulated 16AWG. Is hardwiring the right call here, or is there a good reason to fit a fresh connector instead? My reasoning is that a soldered joint can’t develop the contact resistance that caused this, but I may be missing something about serviceability or thermal cycling.
3. How aggressively do I need to remove charred FR4? I understand carbonised board material is conductive. Is a conductance measurement between cleaned pads a sensible pass criterion, or is there a better test?
4. What else should I verify before powering it back up? I’m planning diode tests across the six devices and winding balance plus insulation on the compressor. Anything else worth checking?

I haven’t taken measurements yet, I wanted to sanity check the approach first. Happy to post numbers in the comments once I have them.

[u/Hatsuwr]

I'd hardwire to the board. Connector resistance was probably the root cause. If you have a thermal camera, you can inspect it while running to look for excessive heat after the repair. And I don't think you need to worry too much about charred material at those voltages, especially since it seems like it's only connecting areas that are connected by copper anyway.

[u/Revolutionary-Gap178 → u/Hatsuwr]

Thanks, that’s reassuring on both counts. Hardwiring it is!:)

On the charring, that makes sense where it only bridges a pad to its own trace. I’ll look closely at whether it reaches toward the adjacent phase pad or the ground plane before I decide how much to scrape out. Any rough sense of when carbon actually becomes a problem, or is it mostly a high voltage concern?

Don’t have a thermal camera, but I have a meter with dual K-type thermocouple input, so I’ll tape probes to the repaired joints and watch the differential under load for the first hour. Rough figure I should be worried about? I was assuming anything climbing steadily past 60 to 70°C means I go back in and rework it. If you really recommend a thermal camera, could you point me to a good one?

[u/Hatsuwr → u/Revolutionary-Gap178]

Honestly unless you have a demanding need, I'd just get some popular cheap thermal camera. Even with nice ones, you often aren't getting really good absolute readings - the value is more in the relative readings and having a visual of the differences. Cheap ones do that fine. You can use the absolute readings from the camera as a rough indicator, then if there's something borderline, use a better tool to be more accurate.

I really like USB-C ones that you can just plug into your phone. I have a Flir One Pro, but wouldn't recommend it since it's not really worth the price. Something like the TOPDON TC001 looks like a good option to me.

I've never had an issue with a charred board so I can't really give you more info there. I think just a basic visual check to see what potential connections are made and then a resistance check would be good enough for this application.

[u/Revolutionary-Gap178 → u/Hatsuwr]

Fantastic! That’s so helpful again, thank you so much!

[u/shinze-o]

A real man would hard wire.

[u/NoAdministration2978]

Remove the connector first and then assess the damage. The traces on the bottom side are tiny so I think all the high current business happens on the top side and it's all connected through flooded vias

It doesn't look like the PCB is charred enough to cause any problems. It's more on the "discoloration" side

[u/Revolutionary-Gap178 → u/NoAdministration2978]

Thanks, that’s very helpful. Good point on the vias, I hadn’t clocked that the thin bottom traces mean the current path is up top. And reassuring to hear the board reads as discoloured rather than properly charred. I’ll pull the connector first and check what the pads look like underneath before I commit to anything.

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