jray3
Posts: 1623
Joined: Tue Dec 06, 2011 1:05 am
Location: Tacoma area, WA
Contact: Website

Re: MCU 20A 450VDC fuse investigation

Wed Jun 05, 2019 11:20 pm

Okay, this is enough evidence of mechanical failure for me to put a pre-emptive fuse replacement on the maintenance schedule. My original lasted 80k miles, but a friend's only made it 45k. What lower mileages have the OBC fuses blown at? I'm thinking of a 40k interval (so am already halfway there on my 1 year-old fuse). If someone researches a replacement (especially with a spring clip mount), please post it.
2012 i-SE "MR BEAN" 102,600 miles
2000 Mazda Miata EV, 78 kW, 17 kWh
1983 Grumman Kurbwatt EV,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

PV1
Site Moderator
Posts: 2990
Joined: Fri Apr 27, 2012 4:22 pm
Location: Pittsburgh, PA
Contact: Website

Re: MCU 20A 450VDC fuse investigation

Thu Jun 06, 2019 7:02 pm

kiev wrote:If the fuse blows during operation of the OBC, then it is very likely that the two snubber capacitors in the HV output section will also be destroyed. This scenario has been reported dozens of times in the past 2 years in the OBC Troubleshooting and Repair thread.

So looking at this another way-- could the fuse have a limited lifetime due to age, wear and tear, etc?

This theory makes a lot of sense. By my calculations, the fuse has approximately 9 amps flowing through it for up to 5 hours at a time during a level 2 charge. While it may not warm to any significant degree, it is a heat load that can fatigue the fuse. Also, the car is usually driven after being charged, so now a warm fuse is getting jostled by driving. Plus, as the fuse ages and develops weak spots, this causes more heat buildup, further degrading the fuse until it eventually breaks, usually under the thermal strain of charging. The DC-DC converter can pull 3 amps at most, usually less than an amp during normal operation, so even a fuse on the verge of blowing could keep power flowing without too much trouble while driving, which means we see most failures during a charge.

When this fuse goes, the full charging current is interrupted, which could likely be causing a voltage spike on the charger side and blowing the capacitors by over-voltage.

kiev wrote:...driving on our typically smooth and pothole-free highways...

So jealous :lol:
(https://scontent.fakc1-1.fna.fbcdn.net/ ... e=5D8F852F)
:idea: :idea: :idea: :!: :!:

Dropbox maintenance in progress. If any of my links aren't working after November 17, please PM me and let me know which one isn't working.

Thanks.

Aerowhatt
Gold Member
Posts: 442
Joined: Wed Jan 28, 2015 1:52 pm

Re: MCU 20A 450VDC fuse investigation

Sat Jun 08, 2019 9:09 am

jray3 wrote:Okay, this is enough evidence of mechanical failure for me to put a pre-emptive fuse replacement on the maintenance schedule. My original lasted 80k miles, but a friend's only made it 45k.,


Do you have information on how both cars were charged most of the time L1 or L2. Any significant charging habit difference between them. If it is this fuse causing a cascade failure (likely). It seems like higher amperage would stress it more, if it is heat stress that is the main culprit.

Aerowhatt
(July) 2014 cool silver ES, acquired new 4/2015 (40.9ah at ~34K miles)
(Aug) 2014 Labrador Black Pearl ES, acquired new 3/2016 (39.7ah at ~20k miles)

Don
Site Moderator
Posts: 2856
Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: MCU 20A 450VDC fuse investigation

Sat Jun 08, 2019 12:22 pm

jray3 wrote:If someone researches a replacement (especially with a spring clip mount), please post it.

The fuses look very much like standard 1.5 inch household cartridge fuses . I have a pair of 20 amp AC fuses mounted in ceramic snap in holders that I'm using in the circuit for charging my Volt - They are connected to a pigtail which plugs into the 40 amp circuit for my wife's seldom used ceramic kiln

Anyway, it doesn't seem like it would be very hard to buy a fuse holder, remove the snap in holder pieces from each end and solder those pieces to the 'legs' you cut off your old fuse - Then you'd have a snap in fuse which could move a tiny bit as it heated and cooled and that would take the physical stress off the internal components of the fuse . . . . might make it less prone to failure

How hard is it to change that fuse? Pop the top off the OBC and it's right there, easy to get at, or do you need to remove the charger from the car?

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1979 Honda CBX six into six

kiev
Posts: 926
Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

Re: MCU 20A 450VDC fuse investigation

Sat Jun 08, 2019 2:15 pm

It's in the MCU under the small access cover plate. (hence the thread title...haha)

It is very easy to access, and i may just make a temporary jumper with a piece of 26 or 24 AWG.

Added a picture of an open MCU to show the fuse in the first post.
kiev = kenny's innovative electric vehicle

Return to “General Technical Discussions”