jray3
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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" 105,400 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
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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: :!: :!:

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Thanks.

Aerowhatt
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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
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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
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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

JoeS
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Re: MCU 20A 450VDC fuse investigation

Sat Nov 02, 2019 8:15 pm

@kiev, were you able to find a source (other than Mitsu) for that MCU fuse? In looking at your datasheet, it looks like the PEC part number is 27430011. I've had no luck with my searches and I like jray3's suggestion of a Littelfuse KLK020, except I'm unclear as to how to hold it in place for the screw-mounting tabs (are mounting clips available?). Perhaps time for me to get proactive and do some preventive maintenance on my two i-MiEVs.

Coincidentally, one of my Xantrex 3.3kW grid-tie inverters died this week after working flawlessly for 13 years. It had a blown Littelfuse KLK020 - replacing it revived the display circuitry but the inverter is still dead... yet another project (sigh).
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

kiev
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Re: MCU 20A 450VDC fuse investigation

Sun Nov 03, 2019 7:42 am

i found these at Mouser, HEV030.ZXISO. The ISO format is the one used in the MCU and it is 10.3mm diameter, not 7.2mm. (PEC103 vs PEC72)

The 20A and 40A were out of stock with 12 week delivery and min order of 240 pieces, so i bought the in-stock 30A. My thoughts were that any short circuit of the wires between the OBC and MCU that will take out a 20A fuse, will also take out a 30 or even a 40.

i haven't found the drawing to show the dimensions and specs of the fusible element yet for comparison with the PEC fuse. i wanted to buy some of each rating for testing but the min order is outside of my budget.

https://www.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/advanced-power-system-fuses/littelfuse_lowcurrenthevfuse_datasheet.pdf
kiev = kenny's innovative electric vehicle

DBMandrake
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Location: Scotland

Re: MCU 20A 450VDC fuse investigation

Sun Nov 03, 2019 12:08 pm

Interesting thread, however to play devils advocate for a moment, I am quite sceptical that the fuse could be the initial point of failure.

It seems much more likely that the dielectric of the capacitor is breaking down, either due to the capacitors being marginally speced, degrading with age, or a slightly out of the ordinary voltage spike, and that the short circuit current of the failed capacitors would be enough to blow the fuse.

Convince me otherwise. :)

Another thing that makes me sceptical is that I can't believe the designers wouldn't have performed live tests with a deliberately under rated fuse to observe the behaviour of the unit when the fuse blows, especially if there is anything that could cause a voltage spike when the fuse blew.

Of the reported failures how many are capacitors only, how many are fuse only, and how many are capacitors and fuse ?
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

jray3
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Re: MCU 20A 450VDC fuse investigation

Sun Nov 03, 2019 6:29 pm

Both of the charger replacements I’ve done had both failed capacitors and fuse. The 40k failure had been charged primarily at L1, and the 80 kilomile failure was almost exclusively charged on L2 and CHAdeMO. Both cars did have L1 charging interrupted by yanking the power plug a few times.
2012 i-SE "MR BEAN" 105,400 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

DBMandrake
Posts: 189
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: MCU 20A 450VDC fuse investigation

Mon Nov 04, 2019 2:45 am

From memory these two capacitors are in parallel ? If so, another good question would be in all cases where the capacitors have failed have both of them failed together or have there been any cases where only one failed ?
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

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