FWIW my 2019 was also built 6/2019, has MSD P/N 24294004.
Mine also blew in L mode. I wasn’t doing anything special though just cruising around 70mph and maybe 15 to 20kw of power draw.Almost forgot, I almost always drive in regen mode (“L”) and I was in the process of approaching a red light, so regen was engaged and I did see an error message that mentioned regen braking.
Working extensively in electronics, typically a fuse “should” never blow unless there is a failure downstream causing an excessive current draw.I don't get what is going on here. It seems like GM has gone through at least three iterations of this part: 24294004, 24291219 and 24281696. From what I can tell the part is just a huge 500 volt 400 amp Omron type fuse in a plastic shell with a lever. How hard is it to get this right? Beginning to worry about about engineering mistakes as to location or type of fuse used. I realize that it is a very small percentage of blown fuses but come on now. Do they degrade slowly or blow all at once? The kW the Bolt draws or makes in regen is within this fuse's parameters. Catastrophic failure for something this essential that is not a moving part (like a serpentine belt) gets me worried.
Exactly my point. This fuse should handle 200 kW. GM needs to test every fuse they install up to 95% current and s**t can the ones that fail. Maybe the fuse gets confused because electrons flow both ways and gives up.Working extensively in electronics, typically a fuse “should” never blow unless there is a failure downstream causing an excessive current draw.
Great info and research, but once again exactly what I said in my first post.. "Begining to worry about engineering mistakes regarding the location or type of fuse used." We don't know how hot it gets under the rear seat and there is no obvious heat sink. The fuse appears to be rigidly mounted in its case with no way to gently expand. Do we know for a fact that the control system can even detect a small voltage drop due to micro cracking? We do not.Just an observation before we begin to pontificate on what GM should or should not do or why fuses never blow at less than their rated current.
Have you noticed the dates when these MSD discussions start in this forum? This is not a comprehensive list:
These suggest to me the common theme: Summer-Northern Hemisphere. Warm environment and increased driving.
- July 3, 2018
- Aug 6, 2018
- Aug 12, 2019
- Sep 3, 2018
- Aug 26, 2018
- Jun 5, 2020
- Aug 2, 2018
The hypothesis that the MSD is failing due to thermal stressing and micro-cracking gets a bit more support. Why?
View attachment 29675
- Summer driving adds to thermal stress. MSD fuses rated at 20C are suddenly facing 40C+ from hot asphalt and longer drives.
- Cyclic stress of a mechanical fuse element does not necessarily result in the fuse 'blowing'. It just builds up enough resistance to cause a voltage drop detected by the control system. It could be a 40V drop (0.1 Ohm @ 400 Amp current). There is a manufacturer's engineering paper showing that up-down-up current cycle causes heating and cooling stresses that eventually cause a sudden increase in resistance. A second paper supports the same conclusion.
Note that the curves do not rise to infinite resistance. They jump to ~1000 micro-ohm (0.001 Ohm) and then rise from there. The rise is precipitous and sudden; it's just metal crystallizing after a certain number of cycles. Add some current and the Bolt EV controller will shut down due to voltage drop.
- Current cycling happens very frequently in an EV. It's not just when to turn the car on. It's every acceleration, deceleration, DCFC charge, and regen. (Everything goes through the MSD, and current goes in both directions). There may be 5-10 cycles per minute of driving--the number of cycles can build up quickly and a susceptible MSD may fail.
- It's generally hard to test for fatigue without a destructive test.
If so, this may be a weak point for the Bolt EV MSD design in general. Engineers may have designed the MSD based on GM hybrid experience with the Volt that may have fewer, lower stress cycles than the fully electric Bolt EV. If you design based on fuse manufacturer's specs, the MSD should 'blow' on a time-current graph like this:
View attachment 29676
At 1x rated current (400A) the MSD should never blow! But there is no thermal cycling information from the fuse supplier.
There are ways forward however...
- There appears to be an awareness of the problem. Eaton launched a new line of EV fuses in May. Their sales sheet includes design factors to test under driving profiles and simulate pulse current profiles. Those tests are new and show that EV fuses are subject to very different stresses than distribution fuses. Perhaps these new EV fuses are being included as new GM part numbers.
- There is always the Tesla or Toyota approach of using a Pyroswitch to break the HV circuit. A Pyroswitch does not rely on heating to 'melt' and break the circuit. A separate monitor circuit check for current, or crashes, and triggers a pyrotechnic device that cuts the fuse link. It costs more, does more, but will not suffer thermal stress cycling. Maybe the next generation?
That’s what I thought, but given all the info above, I doubt my keys falling into the wireless charger opening caused this. But now I wonder if on a hot day it is better to NOT use regen, avoiding additional cycling.There is an DC-DC converter that reduces the power from 380v+ to 12v
I was told by my dealer two to three days for the part to arrive.Keep us posted. I really want to know if the MSD you ordered has the fuse inside it or not.
If the fuses are not totally blowing and getting micro-cracks which cause resistance but still flow current then GM/LG are negligent for not writing software that show a service needed light and pops codes but allows the car a limp home (or a least to the side of the road) mode at reduced speed. I once had my cruise control shut off at 70 on a busy highway in L and it was no laughing matter where seconds can make a difference. I can't imagine what a joy it must be to go dead stick in a similar or worse situation.
We should have a pretty good idea. The fuse is located on top of, and actually connects/straddles, modules 5 and 6. It is directly under the rear seat cushion.We don't know how hot it gets under the rear seat and there is no obvious heat sink.