Care and Feeding of the OBC/dc-dc

[JoeS]

Hi guys, I moved the last two posts in here as we are trying to keep the OBC troubleshooting thread specifically focused on repairs to that unit. Thanks.

 

[manic]

Just bought a 2012, and new to these Mievs. The thread on DC DC failures is a daunting read for a new comer. I had to skim past a lot of it.

I suspect most owners as yet unaffected by this issue will be looking for preventative/cautious AC charging methods.

From what I have gleaned from investigations we have three primary theories

1) Heat related failure from insufficient cooling.
2) 12V battery fault/weakness triggering unexpected switching that leads to an over current scenario
3) Cutting AC power off at the power point instead of through EVSE or leaving to fully charge.

My main concern is point 3. No one would design an AC charger that is not tolerant to power cut offs at the source. Surely?

From the poll thread , the majority of owners who reported failures explicitly stated that they did not use timer switches and always went for full charge or EVSE controlled disconnect.

And there are other threads that reveal that many users have used timer switches over the years, so one would expect those users to have been first up with these issues if AC cut off is the cause.

So, to me, AC cut off presents itself as the most unlikely cause. Unless someone has actually identified a weakness in the protection circuit?


I have a Minicab Miev which does not have the timer remote feature. I want to prolong battery life by only 100% charging when needed. And I want to schedule the charge to occur when the ambient temperature is closer to ideal.

A smart switch on the power outlet would allow me do this.

This OBC investigation leaves me stuck between two options.

1) Charge manually when returning home at hotter times of the day , with car left to charge to 100% more often.

2) Use smart timer switch to charge automatically when ambient temperature is at a sweet spot and limit SOC to amount required , usually <=80%


Option one reduces the AC cut off risk but increases stress on the battery pack and increases thermal stress on the OBC

Option two is kind to the battery and OBC whilst charging but the AC cut off theory still has me spooked!

Which one would you choose?

 

[kiev]

Howdy and welcome to the forum,

There seems to be two areas of failure in the OBC, one is to components on the AC input side of the device, and the other to components on the High Voltage DC output side.

To protect the AC side in this situation, i would set a timer and go press the trigger to stop the EVSE when it rings.

Replace the MCU HV fuse before it fails is good insurance against the second failure mode.

Make sure that you have a good strong 12V aux battery, false economy to try to wring the very last bit of use out of a weak, old or worn out aux.

 

[manic]

Ok more reading, and I found your post on the
MCU fuse theory.

My mind is blown - the fuse should protect a circuit yet here we have one, supposedly, that nukes the OBC when it blows! That's nuts.

Has this been confirmed? If you were to cut the MCU fuse whilst the vehicle is charging , the blue caps would be vaporised?

Kiev, have you replaced your fuse as precaution and if so , which fuse are you using?

As for charge automation I will command a smart switch to start charging X minutes before I am due to drive. And stop charging using the pilot switch when I set off. Not the most flexible solution but better to be safe whilst these investigations are still inconclusive. Perhaps on from that I will look at tapping into the pilot signal for remote disconnect.

 

[kiev]

i bought a 30A 450V Littlefuse, 0HEV030.ZXISO, from Mouser, but i think digikey and other electronics vendors could also supply them. i have a 20 AWG jumper that i made and am considering to replace the fuse with that after the OBC warranty expires.

Take a look at the 2013 Ion not charging thread (Active Topics) for some fairly recent repairs and discussion.
http://myimiev.com/forum/viewtopic.php?f=23&t=4377

If the MCU fuse opens while charging then it is interrupting up to about 10 Amps of current flowing in a couple of large inductors in the OBC. This produces a large voltage spike as the magnetic field collapses, and the current is looking for a path and it will make a path; if you cannot afford a path, one will be created for you.

 

[manic]

Ok so to be clear, you are in warranty but you have still chosen to replace the OEM fuse with a higher amp little fuse? What do you mean by a jumper?

I'm still on OEM fuse after 8 years so maybe another OEM is the go .

In terms of spec difference is it simply 30amp vs 20amp, or are the littlefuses more robust in some other way?

 

[kiev]

The OEM fuse is made by Pacific Engineering and is only available from a Mitsubishi dealer part$ department at a slightly higher price. Mitsubishi part #9499A656.

The Littelfuse is equivalent device, and is available from electrical parts vendors for slightly less. i would have bought a 50A, but could only get 20, 30 and 40 to use in analysis and investigation of causes for OBC failures.

The spec rating of 30A vs 20A is the only difference. It can carry higher current before fusing.

The jumper is a short piece of wire with crimped lugs that replaces the fuse altogether; The ZXISO style fuse has terminal lugs attached to the fuse body at the spacing of the screws.

If you still have OBC warranty, or if you just want to reduce the risk of an old fuse wearing out and breaking due to mechanical fatique, then replace the old Mits fuse with a new Mits fuse is cheap insurance.

 

[pbui19]

...

3) Cutting AC power off at the power point instead of through EVSE or leaving to fully charge.

My main concern is point 3. No one would design an AC charger that is not tolerant to power cut offs at the source. Surely?

From the poll thread , the majority of owners who reported failures explicitly stated that they did not use timer switches and always went for full charge or EVSE controlled disconnect.

And there are other threads that reveal that many users have used timer switches over the years, so one would expect those users to have been first up with these issues if AC cut off is the cause.

So, to me, AC cut off presents itself as the most unlikely cause. Unless someone has actually identified a weakness in the protection circuit?
......

2) Use smart timer switch to charge automatically when ambient temperature is at a sweet spot and limit SOC to amount required , usually <=80%
....

Option two is kind to the battery and OBC whilst charging but the AC cut off theory still has me spooked!

Which one would you choose?

you could modify/hack your timer and your J1772 trigger, so that your timer control the trigger, and thus turning the charger on/off gracefully as intended.