kiev
Posts: 1227
Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

Under the Cover--an Inside Look at a 2018 On-Board Charger (OBC2)

Fri Sep 20, 2019 6:40 pm

i just got kiev back today with the new style On-Board Chargger, calling it OBC2. It has a date code of 2018.05.17 and is quite different from the 2012 version.

Overview
Image

Top Board
Image

AC Input (no more doghouse)
Image

Boost Transformer
Image

HV Output
Image

Current Sense Resistor and Fat Blue Caps (snubbers?)
Image

These will be much easier to repair-- no Waffle Plate™, all the high power diodes and transistors can be seen along the bottom board edges.
kiev = kenny's innovative electric vehicle

coulomb
Posts: 222
Joined: Sun Jun 10, 2018 8:32 pm
Location: Brisbane, Australia

Re: Under the Cover--an Inside Look at a 2018 On-Board Charger (OBC2)

Sat Sep 21, 2019 6:18 am

kiev wrote:i just got kiev back today with the new style On-Board Chargger

So naturally, the first thing you did was to rip the covers off :D

These will be much easier to repair-- no Waffle Plate™, all the high power diodes and transistors can be seen along the bottom board edges.

This is indeed great news. Still made by Nichicon; I wonder what prompted the change of design.

Thanks for the photos.

JoeS
Site Moderator
Posts: 3909
Joined: Thu Dec 15, 2011 5:47 am
Location: Silicon Valley, California

Re: Under the Cover--an Inside Look at a 2018 On-Board Charger (OBC2)

Sat Sep 21, 2019 7:49 am

kiev, thank you very much for the photos of the new OBC/dc-dc innards. Any comments whether this new design has improved the component thermal management? I was always disturbed that the case of this module becomes hot despite the the liquid cooling system.
coulomb wrote:This is indeed great news. Still made by Nichicon; I wonder what prompted the change of design.
What's interesting is that they went to all the trouble to make this new design fully interchangeable with our 'older' 2012 configuration. As evidenced by the number of failures on this forum, Nichicon/Mitsubishi must be experiencing an unusually-high failure rate, prompting them to redesign this unit rather than continue producing the original configuration - this is very good news, IMO. Nice of Mitsu to (rather belatedly) step up to the bar and extend the warranty.
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

Don
Site Moderator
Posts: 2986
Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: Under the Cover--an Inside Look at a 2018 On-Board Charger (OBC2)

Sat Sep 21, 2019 4:42 pm

My concern is . . . . if your original doesn't fail in the first 10 years, you're out of luck. If it fails later, I'll bet this new one is $4K if you have to BUY one from Mitsu . . . . and that would likely mean trashing your 11 or 12 year old car, regardless of the low miles you might have on it

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE Premium, Raspberry Metallic
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon
2006 Itasca Navion Sprinter Motor Home

kiev
Posts: 1227
Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

Re: Under the Cover--an Inside Look at a 2018 On-Board Charger (OBC2)

Sat Sep 21, 2019 6:56 pm

i think if you were to proactively replace the 20A MCU fuse as a maintenance item, then your old OBC would work just fine for a good long time.

i'm still doing research on the failure modes. i'm struggling to understand how the MCU fuse could experience an over-current condition and blow, without taking out the little 20A fuses on the input of the DCDC or the output of the OBC.

Also i don't understand how shorting by the snubbers caps would cause the MCU fuse to experience an over-current. If the snubber caps were to fail shorted, then the rectifier diodes in the waffle plate would likely fail and repairs would not be possible. Yet several have been repaired by replacing just the caps and fuse.

But i can see how an interruption of the OBC output current outside of the OBC, such as a mechanical break in the MCU fuse, could create an inductive over-voltage condition on the output side of the boost transformers that could cause the snubber caps to split.


Another weak link might be the AC input relay contacts; but i see that they have the same relay in the new box, so there will likely be a few failures on the AC side such as we have seen on the old box.
kiev = kenny's innovative electric vehicle

DBMandrake
Posts: 286
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Under the Cover--an Inside Look at a 2018 On-Board Charger (OBC2)

Sun Mar 01, 2020 11:51 am

kiev wrote:i think if you were to proactively replace the 20A MCU fuse as a maintenance item, then your old OBC would work just fine for a good long time.

i'm still doing research on the failure modes. i'm struggling to understand how the MCU fuse could experience an over-current condition and blow, without taking out the little 20A fuses on the input of the DCDC or the output of the OBC.

Also i don't understand how shorting by the snubbers caps would cause the MCU fuse to experience an over-current. If the snubber caps were to fail shorted, then the rectifier diodes in the waffle plate would likely fail and repairs would not be possible. Yet several have been repaired by replacing just the caps and fuse.

It makes perfect sense to me actually.

If you place a short across the 360v output of the on board charger (at the 1000pF caps) the charger electronics will have current limiting at or below around 10 amps and probably complete fold over protection so that it would shut down completely in the case of a short. This will protect the electronics of the charger proper, (including rectifiers) and also prevent the small fuse on the OBC PCB from blowing as the current will never exceed it's 20 amp rating unless the current limiting system failed. (And the fuse in the DC/DC converter is irrelevant as it isn't a fault current path in the shorted cap scenario)

However the only thing limiting the current drawn from the traction battery by the shorted cap is the 20 amp MCU fuse - nothing else is in the current path except the 250A fuse in the traction battery enclosure, and that's not going to blow first. :D
But i can see how an interruption of the OBC output current outside of the OBC, such as a mechanical break in the MCU fuse, could create an inductive over-voltage condition on the output side of the boost transformers that could cause the snubber caps to split.

While your theory of the fuse blowing first and causing an inductive spike is interesting and certainly feasible, occams razor doesn't require it IMHO.

I think it's as simple as a poor quality capacitor failing spontaneously well within its supposed limits, or perhaps being under-speced for it's role in the circuit or a bit of both.

Consider the following scenario - one of the caps goes shorted for whatever reason during charging. The OBC is already putting out ~10 amps in constant current mode. A short is not going to cause it to put out any more current because it is already electronically limiting to 10 amps. If it has fold over protection, and I can't see why it wouldn't, it will shut down if it continues to put out 10 amps but the output voltgage drops abnormally low. This protects the semiconductors from over dissipation and is easy to do - I've built linear regulators with fold over shutdown in constant current limit mode, and it makes them nearly indestructable done right.

Once the OBC shuts down the the risk of the OBC's own fuse blowing is gone, however the traction battery will continue to supply hundreds of amps until either the cap vaporises or the fuse or both.

If the cause of the failure is a defective capacitor spontaneously going short circuit and then blowing the fuse, I would expect to only ever see one capacitor of the parallel pair failed.

On the other hand if your theory about inductive spike due to a blowing fuse is right I'd expect to see both capacitors blown at least in some cases. Have there been any reported cases yet where both caps fail ? Certainly in mine one split completely into three pieces (blew the bonding legs off both sides of the ceramic chip) but the second capacitor was unharmed.

That to me suggests the capacitor failing was the root cause of the failure, and that replacing them with better rated (higher voltage, high current rating) types like I did is prudent.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

Return to “General Technical Discussions”