BYD Seal 05: Relay Box Overheating Concern After Switching from Safe Mode

[SENTAVR]

I bought a BYD Seal 05 2 days ago. It showed a 17% charge at the dealership. I drove it home and the charge reached 70%. I checked the settings and saw that the car was in Safe Mode at 70%. When I opened the hood, I noticed that the box containing the relays was very hot. I think this is related to the Safe Mode. I switched it from Safe Mode to AI Mode and drove, and this time I noticed that the relays were lukewarm. Is this normal, or should they not be heating up to this extent?

 

[Stuart Wright]

BYD Seal 05 is a PHEV (it's called the BYD Seal 05 DM-i).
The SOC rising from 17% to ~70% while driving is normal for the DM-i system. The engine can run a generator and push significant charge into the traction battery on the move, especially if the car was in a charge-friendly strategy.
The box you refer to likely houses the high-voltage junction box, contactors, and the DC/DC converter. During engine-driven charging the system can move a lot of current into the pack, so that box can get very warm from electrical losses and heat soak after shutdown.
Safe mode and AI mode change how aggressively the hybrid system uses and replenishes the battery. In a conservative mode the car may push more generator charge into the pack to keep it near a target SoC, which increases current through the junction box and makes the casing feel hotter. In AI Mode the car may cycle SoC more and charge less aggressively in that moment, so the hardware feels only lukewarm.
For the Seal 05 DM-i, a noticeable rise in SoC while driving and a hot HV junction box after engine-assisted charging can be normal.
Your observation that it was hotter in Safe Mode and only lukewarm in AI Mode fits expected behaviour.

 

[SENTAVR]

BYD Seal 05 is a PHEV (it's called the BYD Seal 05 DM-i).
The SOC rising from 17% to ~70% while driving is normal for the DM-i system. The engine can run a generator and push significant charge into the traction battery on the move, especially if the car was in a charge-friendly strategy.
The box you refer to likely houses the high-voltage junction box, contactors, and the DC/DC converter. During engine-driven charging the system can move a lot of current into the pack, so that box can get very warm from electrical losses and heat soak after shutdown.
Safe mode and AI mode change how aggressively the hybrid system uses and replenishes the battery. In a conservative mode the car may push more generator charge into the pack to keep it near a target SoC, which increases current through the junction box and makes the casing feel hotter. In AI Mode the car may cycle SoC more and charge less aggressively in that moment, so the hardware feels only lukewarm.
For the Seal 05 DM-i, a noticeable rise in SoC while driving and a hot HV junction box after engine-assisted charging can be normal.
Your observation that it was hotter in Safe Mode and only lukewarm in AI Mode fits expected behaviour.

Thank you for the detailed explanation.