Replacing fuse in DC/DC Junction box and battery junction box?

My Nissan Leaf Forum

Help Support My Nissan Leaf Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

QueenBee

Well-known member
Joined
Aug 8, 2010
Messages
1,565
Location
Portland
A local 2011 LEAF had the AC compressor short to ground which blew the fuse in the DC/DC junction box and the battery junction box. They aren't getting it repaired by the dealer as it'll cost as much/more as the car is worth. So looking through the service manual sounds like a fun enough project. What I'm curious about is if anyone has attempted to repair these two fuses? It's not dealership serviceable but it'd be a little disappointing if these really weren't replaceable by someone with a bit of electronics skill.
 
QueenBee said:
A local 2011 LEAF had the AC compressor short to ground which blew the fuse in the DC/DC junction box and the battery junction box. They aren't getting it repaired by the dealer as it'll cost as much/more as the car is worth. So looking through the service manual sounds like a fun enough project. What I'm curious about is if anyone has attempted to repair these two fuses? It's not dealership serviceable but it'd be a little disappointing if these really weren't replaceable by someone with a bit of electronics skill.
I have looked in the '13 manual and can as of yet not find the type of fuses that are required. I agree these fuses should be accessible without the removal of the battery pack. I would guess they would be bolt on 60A HRC (24KW/400V for the feeder but may be sub fed by independent fuses for HVAC). Because of the possibility of the high ampere inrush current with a bolted fault it is a good idea that they would be difficult to access but should be replaceable with proper troubleshooting by qualified personnel ( without the removal of the pack)...IMHO.
 
QueenBee said:
What I'm curious about is if anyone has attempted to repair these two fuses? I
I have not, however here is a link to a picture of the fuses in the DC/DC junction box.
http://www.marklines.com/img/report/en/rep1119_014_l.jpg
I see there is a 4th fuse in the picture in addition to the 3 that are clearly tied
to high voltage.
 
cliff said:
QueenBee said:
What I'm curious about is if anyone has attempted to repair these two fuses? I
I have not, however here is a link to a picture of the fuses in the DC/DC junction box.
http://www.marklines.com/img/report/en/rep1119_014_l.jpg
I see there is a 4th fuse in the picture in addition to the 3 that are clearly tied
to high voltage.

Wow, I had not seen this site before!

Here's the junction box in the battery. Don't see fuses. http://www.marklines.com/img/report/rep1049_031.jpg

http://www.marklines.com/en/report/rep1049_201202

So I bought the LEAF!

Found the AC compressor cheap, and the DC/DC junction box for $450. Sure seems like it should be easy replace those fuses though. I wonder why they aren't dealer serviceable? Maybe concerns about maintaining its weatherproofing?

I can't find anyone with the battery junction box but worst case is its $650 new, assuming it's stocked. If I had a way to charge and test modules it would be fun to buy an entire pack and resell the modules. Though at that point I might as well buy a rear ended totaled LEAF.
 
QueenBee said:
A local 2011 LEAF had the AC compressor short to ground which blew the fuse in the DC/DC junction box and the battery junction box.

Thinking about this, a short to ground should not have done anything. One of
the main safety features of the Leaf is that neither side of the battery is connected
to ground(somewhat like power in a hospital). So the positive must of shorted to
the negative, but only the positive had a fuse to protect the wire, so what
happened to the negative? With the fuse in the battery box going, this would
suggest to me that the negative could have taken more current than it should
before the fuse went. Is this a design error not having a fuse on the negative
side? But once the positive fuse went, then why did the other fuse go?

The 3 fuses in the DC/DC junction box are all 30 amp fuses, to the heater,
charger, and compressor. the 4th fuse is a 15 amp for the converter.
 
cliff said:
QueenBee said:
A local 2011 LEAF had the AC compressor short to ground which blew the fuse in the DC/DC junction box and the battery junction box.

Thinking about this, a short to ground should not have done anything. One of
the main safety features of the Leaf is that neither side of the battery is connected
to ground(somewhat like power in a hospital). So the positive must of shorted to
the negative, but only the positive had a fuse to protect the wire, so what
happened to the negative? With the fuse in the battery box going, this would
suggest to me that the negative could have taken more current than it should
before the fuse went. Is this a design error not having a fuse on the negative
side? But once the positive fuse went, then why did the other fuse go?

The 3 fuses in the DC/DC junction box are all 30 amp fuses, to the heater,
charger, and compressor. the 4th fuse is a 15 amp for the converter.

Ah good point, the tech specifically said ground but yeah he must have really meant the negative. A short to ground would have actually been easier to fix as it would have detected this happening and shut the car down, then it would just be the compressor being replaced.

I'm not very familiar with fuses but it's common enough with breakers/GFCI that a fault can successfully trip more than one so it seems plausible that this could happen with fusses?

It's my understanding that the isolated ground like in a hospital isn't helping much with regards to safety but is just trying to keep the ground reference used in hospital equipment cleaner by connecting the equipment directly to the panel and then bonding all of the metal junction boxes, conduit, etc. back to the panel separately vs using all of these being connected. So back at the main service panel neutral, EGC and isolated grounds would all be bonded.
 
If the compressor circuit failed one leg to ground and then the other leg to ground, the other fuses could see short circuits and blow (depending upon where the grounds were in relation to the fuses and main contactor). The DC ground detection system would try to open the main contactor to isolate the battery as soon as it detected the first ground, but fuses would blow if the grounds became short circuits quickly. Have you checked the main contactor and insulation to ground of all high-voltage wiring? Good luck with your repairs.

Gerry
 
GerryAZ said:
If the compressor circuit failed one leg to ground and then the other leg to ground, the other fuses could see short circuits and blow (depending upon where the grounds were in relation to the fuses and main contactor). The DC ground detection system would try to open the main contactor to isolate the battery as soon as it detected the first ground, but fuses would blow if the grounds became short circuits quickly. Have you checked the main contactor and insulation to ground of all high-voltage wiring? Good luck with your repairs.

Gerry
Ah, true, seems possible that both legs could fail to ground. I'll know more when I talk to our local LEAF tech when he's back tomorrow. More good news: He's optimistic that they he'll be able to get approval to install used parts and I made it clear that I would not expect any warranties of the parts and any additional diagnostic/rework time as a result of the use used parts/defective parts/etc. would be on me. He said the time to replace the compressor and DC/DC junction box is 8 hours and 4 hours to replace the junction box in the battery. So add $200 for a used compressor and the labor bill will be about what I was expecting it was going to cost just to have them replace the compressor!

Our local LEAF tech is pretty good and has been working on them since the beginning so I'm pretty confident in his diagnostic. The original owner had actually first had the dealership that is closest to us diagnosis it but then decided to have it towed over to him.

I'm thinking I'll just buy a DC/DC junction box then have him give me the old one so I can look at repairing it and then reselling. That way the timing if he's doing all the work doesn't get in the way. Found a local junk yard which has it and the compressor.

Then late last night I heard back from hybridautocenter.com I assumed that anyone who was tearing apart packs would have the a bunch of the battery junction boxes. They do and they are cheap! Need to ensure I get the correct revision which I'm having trouble reading the parts diagram but should be easy to get sorted out today when I get a copy of the repair quote.
 
Looks like you got it all settled before I wandered in, QueenBee. I would do the same thing, swap the dc/dc junction box and then teardown the dead one.

It's not clear to me, but I suspect the only the fuses in the dc/dc junction box are blown. In the 2011-2012 cars, the main pack fuse is in the orange disconnect that is in the backseat footwell. Does the car otherwise start and drive without AC?

The 2013+ cars have a different "HV junction" setup, and thus the 2013 service manual wouldn't be much help, Electric Eddy. At any rate, Nissan does module swaps and wouldn't have a normal tech replace fuses in the dc/dc. For example, we've seen the same with 2011-2012 chargers and diode issues: they always just replace the entire charger.
 
JeremyW said:
Looks like you got it all settled before I wandered in, QueenBee. I would do the same thing, swap the dc/dc junction box and then teardown the dead one.

It's not clear to me, but I suspect the only the fuses in the dc/dc junction box are blown. In the 2011-2012 cars, the main pack fuse is in the orange disconnect that is in the backseat footwell. Does the car otherwise start and drive without AC?

The 2013+ cars have a different "HV junction" setup, and thus the 2013 service manual wouldn't be much help, Electric Eddy. At any rate, Nissan does module swaps and wouldn't have a normal tech replace fuses in the dc/dc. For example, we've seen the same with 2011-2012 chargers and diode issues: they always just replace the entire charger.

I've been trying not to bug the tech on his days off so haven't started pestering him with questions. I believe I'll get a copy of the quote this evening when I get the title but this is what he said was wrong so I've been looking around based on that information.

The high voltage side of the A/C compressor shorted to ground and blew the fuse in both the junction box internal to the battery and the fuse inside the DC/DC converter.

The car isn't driveable right now. It will be interesting to figure out exactly what is wrong with the battery junction box. Maybe it has fuses as well as the fuses in the service plug?
 
Can you sick leaf spy pro on it and see what codes pop up? I wonder if it's failing isolation tests thus failing to go into ready... I also think if the dc/dc cannot function you also won't go into ready so it just might be that, if the dc/dc fuse is blown.
 
The dc/dc junction box is not difficult to open, but doing so will require cutting through the sealant used to make it weather tight. This is what my 2012 looked like once opened up. It looks like the fuses are under the cover at the bottom right, which would require disconnecting some of the internal wiring connectors to access.

22927161999_c69ec49888_b.jpg


I haven't found any fuses inside the the battery including the battery junction box, aside from maybe one in the battery heater if equiped. Replacing the battery junction box will require removing the battery, so I wouldn't go there unless you have to. If there is a failure indicated in the battery (such as P3373 or P30F4 Total Volt Over Discharge / Sensor) hopefully its just the fuse in the service plug. Assuming the fuse is in the plug itself it could be swapped out without dropping the battery. Note there are several different styles of plug, you'd need to get the right one to match your battery.

Rob
 
So my LEAF tech thinks there was a catostophic failure in the junction box in the battery but I'll know more when I get it back. Found the compressor and DC/DC junction box at a local junkyard which I dropped off to him and they passed his multimeter tests. Just found the battery junction box on eBay randomly sorting through Nissan LEAF parts that was listed with the BMS so will shortly have all the parts!

FWIW it appears the 2011/2012 battery junction box with battery heater could be used in a battery without a battery heater as it appears to be just an extra connector that could be left unplugged or the wiring disconnected but my tech was leary so I'm glad I found one with out it.
 
If there was a dead short across the battery terminals, besides potentially welding the main contactors, there's a chance the pre-charge resistor was damaged if someone just cleared the dtc's and tried to start the car again. Normally, the DTC's should have prevented inadvertent restart until a tech could take a look..

Basicly, theres a large capacitance in the inverter input and if the contactors were allowed to just connect the battery to this large capacitance, there would be a huge inrush that could actually damage the caps and cause a voltage spike. So, in every production EV, there's a pre-charge circuit that puts a fairly large resistance between the battery positive terminal and the dc components until the voltage rises to near normal levels, then the main positive contactor is switched in.

Hoping that it's just the DC/DC junction box and the AC compressor that will fix it up. Dropping the pack and opening it up can't be inexpensive. At least you have that part if it in fact failed.
 
JeremyW said:
If there was a dead short across the battery terminals, besides potentially welding the main contactors, there's a chance the pre-charge resistor was damaged if someone just cleared the dtc's and tried to start the car again. Normally, the DTC's should have prevented inadvertent restart until a tech could take a look..

Basicly, theres a large capacitance in the inverter input and if the contactors were allowed to just connect the battery to this large capacitance, there would be a huge inrush that could actually damage the caps and cause a voltage spike. So, in every production EV, there's a pre-charge circuit that puts a fairly large resistance between the battery positive terminal and the dc components until the voltage rises to near normal levels, then the main positive contactor is switched in.

Hoping that it's just the DC/DC junction box and the AC compressor that will fix it up. Dropping the pack and opening it up can't be inexpensive. At least you have that part if it in fact failed.

Oddly it's not as bad as you'd think. 8 hours of shop time to replace the compressor and DC/DC junction box and only 4 hours to replace the battery junction box, it's the parts that are the bad part, dealership wanted $922 for the junction box and new junction box cover (apparently it changed on the new part number). I'm not sure exactly what testing the battery junction box failed but he's a top LEAF tech so I fully trust that his diagnosis is correct.

Was just adding up my costs. I'll be into this $3,500 after all the parts and labor including sales tax. Then I can probably repair the DC/DC junction box if it's just the fuses and resell it. Though it needs a detailing and some seat covers.

The other good news is I've convinced my spouse that we can finally sell the ICE and be a fully solar powered two EV family!
 
I had a similar problem with one of my 2012 LEAF SL. The car could not move and heat. The dealer said that my AC Compressor blow my junction box. I think this faillure should be cover under warranty because the car is less than 5 years/60000 miles.

What do you think? Warranty or not?

Thanks!
 
LeafQC said:
I had a similar problem with one of my 2012 LEAF SL. The car could not move and heat. The dealer said that my AC Compressor blow my junction box. I think this faillure should be cover under warranty because the car is less than 5 years/60000 miles.

What do you think? Warranty or not?

Thanks!
Definitely would be covered by the warranty. The car my original post was about was something like the 216th LEAF made and the warranty had just passed 5 years a few weeks prior.
 
To follow up. I bought the DC/DC junction box/converter and the AC compressor from a local junk yard for $550. Then I bought a battery junction box from ebay for $80. It turned out to be different than the item pictured and had the connections for the battery heater. My LEAF technician at the dealership was hesitant but after poking around at it he was OK with using that one. Then I paid $1400 at the dealership for the labor to replace all three components. Was quoted 8 hours for the AC compressor + DC/DC junction box and 4 hours to drop the battery, open it up, and replace the junction box.

Now that I've got the battery junction box back it was obvious what was wrong. The resistor was cracked and was open instead of the 30 ohms it should have been.

So it's all running again!
 
Wow only 30 ohms, even with lowest battery voltage, that is potentially thousands of
watts! So the system has to really make sure things are not turned on during pre-charge.
Interesting that the resistor survived long enough for the fuse to blow.
 
Back
Top