MCU 20A 450VDC fuse investigation

[kiev]

Basically anything that abnormally interrupts a charging session has the potential to cause OBC damage, for example:

1. Fatigued MCU Fuse
2. Weak or Leaky Snubber Capacitors
3. AC input power: interrupt, voltage fluctuation, etc
4. 12V Aux battery: weak, old or worn out, dropping voltage to ECUs, dropping relay contacts, etc
5. ? placeholder, Did i leave anything out?

[JoeS]

Kenny, thank you for running those simulations. Interesting to me is how design tools have evolved over the years.

Yes, count me in for a group buy (two plus one spare), although I'll probably hold off installing until after my warranty runs out as I'd like a new-design OBC from Mitsu.

Re: clipped-in fuses vs. screwed-down pigtails means four contact surfaces instead of two. Since the ECU is a sealed compartment I would expect no corrosion-inducing moisture that might affect the clip/fuse contact surface, so perhaps it shouldn't matter. Hey, could put a bag of desiccant in there to make sure.

Re: Chargeus Interruptus can't think of any more reasons off the top of my head. In my case I had been running mechanical timers on the input to my i-MiEV EVSEs for about five years so my fuses must be about ready to pop.

Is there a known sequence inside the car that gracefully shuts down the OBC when the J1772 handle button is pushed?

[coulomb]

i found these at Mouser, HEV030.ZXISO.

[ Edit: Disregard this post. It was based on the incorrect assumption that the OEM fuse was 7.2 mm diameter. It's 10.3 mm diameter, so no bending of tabs is needed. ]

I'm thinking the 15 A part with the "bolt down (axial)" termination style would work out slightly better (there is also a 30 A bolt-down (axial) part if you are worried about it blowing too quickly). So that's the 0HEV015.ZXBD part (link is to Mouser USA with price in US$).

My reasoning is that you have to bend the tabs to make the fuse fit with the bolts at 45 mm apart, and the axial mounting versions have slightly longer tabs. You'd be bending like this:



I made that diagram from the drawing for the ISO (non axial) termination versions, but the principle would be the same. I suspect it's still going to be a bit of a fiddle to get the bolts in, depending on the bolt head size. It might even be worth using M4 bolts (I assume that's what they are) with smaller heads.

[coulomb]

Is there a known sequence inside the car that gracefully shuts down the OBC when the J1772 handle button is pushed?

I was wrong when I initially thought the LEAF ignored the J1772 plug's push-button. It does indeed immediately and electronically (i.e. safely) ramp the charge current down to zero when the button is pressed. It's just that there is absolutely no indication that anything has changed; the blue LEDs stay the same, there is no beep or anything else to suggest that the current has stopped. As soon as you let go of the button, the current ramps back up to normal.

I actually find this handy when changing current on my adjustable current limit EVSE. If you want to terminate the charge, you therefore have to press the button then remove the J1772 plug.

[kiev]

i had to put a leading zero on that part number to get mouser's search to find the part, 0HEV0rr.ZXISO where rr is the amp rating, e.g. 15,20,30 etc.

[edit] the OEM datasheet is on post#3 on page 1 of this thread.

[nuggetgalore]

G'day.
thanks for investigating the fuse quandaries.
But I am still con-fused (pun) how to go from here. Should I aim to get the same amperage or as suggested by some to go to 30 A? I a m less concerned with the body type, I can make it fit.
It all then depends on what I can get in a reasonable time and how few I can buy ( PEC may only sell boxes of 200) I don't know?

[coulomb]

Should I aim to get the same amperage or as suggested by some to go to 30 A? I a m less concerned with the body type, I can make it fit.

We've been ignoring the possibility of some sort of fault that ends up pushing say 25 A through the wires to the fuse. It's unlikely, but it could happen, and if it does, it could start a fire. The main job of the fuse is to protect the wire.

The wire on one side looks like it's barely 2.5 mm², if so safe to about 22 A. So I'm going to say that from a safety perspective, we really should go to the trouble of finding a 20 A rated fuse.

I note that the Eaton fuse I found is rated at 20 A (they don't make these PV fuses with a rating higher than 20 A). But they are out of stock at present (other suppliers might have that part number in stock). The manufacturer says it's specifically designed as a photovoltaic fuse, which also has me slightly worried. I don't know much about fuse selection, other than the need to have a DC rating. It's also about 50% more expensive, possibly because it's rated for 1000 VDC.

Is there a cross sectional area marking on the thinner of the two wires, or an AWG designation?

[kiev]

That was an issue i found-- the minimum order quantity from PEC.

i needed something quick to get back on the road so i ordered what was available from Mouser, which was the 30A since they were out of stock in the 20A version and it had a 12-week lead time.

Fuses are intended to protect wire, in this case the OBC-to-MCU wire, from an overcurrent event which could melt it and start a fire, and my guess was that any abnormal situation which could develop enough energy to blow a 20A fuse would likely also blow a 30A.

But in this case there are also 20A fuses soldered to the OBC and the DC/DC converter boards inside the OBC box to protect this wire. They are a smaller form factor, but in all the OBC failures nobody has reported blowing either one or burning the wire. They are not an easy bolt-in replacement such as the MCU fuse, but there are a total of 3 fuses for that one wire.

i can't think of any reason to have an MCU fuse except in the case of a car wreck while driving in which the rear end gets crushed forward to pinch and cut the wire and cause a short. If that happens you would want a fuse there.

[DBMandrake]

That was an issue i found-- the minimum order quantity from PEC.

i needed something quick to get back on the road so i ordered what was available from Mouser, which was the 30A since they were out of stock in the 20A version and it had a 12-week lead time.

With all this talk of finding alternative fuses I'd like to point out that the original Mitsubishi fuse is still readily available from 3rd parties and at a reasonable price, so there's not really any need to look for half baked alternatives that aren't a good match. I ordered mine from here:

https://www.amayama.com/en/part/mitsubishi/9499a656

On examination after receiving it the fuse is the genuine Mitsubishi branded part.

The seller is in Japan and it took a little bit under 2 weeks to arrive in the UK including customs delays. Minimum order is one fuse, although I ordered two just to have a spare on hand if the first one went splat due to overlooking any damaged components so I wouldn't have an additional delay waiting for a second fuse. (As it was, the repair was successful the first time, so I still have one spare new fuse on hand, along with spare capacitors )

My only gripe is that the package incurred customs fees and a resultant customs delay as ordering two fuses pushed the total value over the threshold where customs charges apply in the UK. (Tip to anyone ordering in the UK - if you're not in a hurry to complete the repair order one fuse and avoid the customs fees hassle...)

[misterbleepy]

My only gripe is that the package incurred customs fees and a resultant customs delay as ordering two fuses pushed the total value over the threshold where customs charges apply in the UK. (Tip to anyone ordering in the UK - if you're not in a hurry to complete the repair order one fuse and avoid the customs fees hassle...)

That happened to me too - but luckily still way way cheaper than a new OBC