Ok. What happened here?!

[steilkurve]

Hey folks.

Happened to be looking under the bed where my MultiPlus II and 500 AH of BB batteries are when the AC started on the batteries.

I saw a spark coming from the 400 amp fuse holder. System continued to work fine and the fuse is intact but the holder and part of the positive connecting into the holder is melted. What could have caused this?

I've ran AC on batteries multiple times since this system was installed 2 years ago... And in this case, I even had 15 amp of shore power coming in.

Any ideas what may have caused this?

See photos and thanks for your pointers here!

[uncle_bob]

Originally Posted by steilkurve

Hey folks.

Happened to be looking under the bed where my MultiPlus II and 500 AH of BB batteries are when the AC started on the batteries.

I saw a spark coming from the 400 amp fuse holder. System continued to work fine and the fuse is intact but the holder and part of the positive connecting into the holder is melted. What could have caused this?

I've ran AC on batteries multiple times since this system was installed 2 years ago... And in this case, I even had 15 amp of shore power coming in.

Any ideas what may have caused this?

See photos and thanks for your pointers here!

Hi

The most likely reason is that one of the nuts holding down either the fuse or the cable is loose. If so, the resistance goes up and you get heat. Heat melts things. The arc ( = sparks) also does the parts no good at all.

Short term fix would be to carefully tighten the nuts. The "careful part" involves being very sure your tool does not hit anything that is grounded with battery power applied. One way to do this is to disconnect the batteries and solar.

Long term, the fuse holder looks like it's past end of life. Time to replace it.

Bob

[steilkurve]

Originally Posted by uncle_bob

Hi

The most likely reason is that one of the nuts holding down either the fuse or the cable is loose. If so, the resistance goes up and you get heat. Heat melts things. The arc ( = sparks) also does the parts no good at all.

Short term fix would be to carefully tighten the nuts. The "careful part" involves being very sure your tool does not hit anything that is grounded with battery power applied. One way to do this is to disconnect the batteries and solar.

Long term, the fuse holder looks like it's past end of life. Time to replace it.

Bob

Thanks. This makes sense. I actually had bought two fuse holders back when I did the install. I'll swap them. Do you think I need to replace the cable? Would that kind of resistance/heat damage it, beyond just the heat shrink around the crimp?

[bbdo]

Originally Posted by steilkurve

Hey folks.

Happened to be looking under the bed where my MultiPlus II and 500 AH of BB batteries are when the AC started on the batteries.

I saw a spark coming from the 400 amp fuse holder. System continued to work fine and the fuse is intact but the holder and part of the positive connecting into the holder is melted. What could have caused this?

I've ran AC on batteries multiple times since this system was installed 2 years ago... And in this case, I even had 15 amp of shore power coming in.

Any ideas what may have caused this?

See photos and thanks for your pointers here!

what kind of cable are you using? i made the mistake of using 1/0 copper coated aluminum (CCA) which had a similar outcome at high amperages. Ended up melting the disconnect switch.. and then replacing all cables with proper 2/0 rated welding cable, not the CCA junk. Based on the picture, this looks kinda similar..

[steilkurve]

Originally Posted by bbdo

what kind of cable are you using? i made the mistake of using 1/0 copper coated aluminum (CCA) which had a similar outcome at high amperages. Ended up melting the disconnect switch.. and then replacing all cables with proper 2/0 rated welding cable, not the CCA junk. Based on the picture, this looks kinda similar..

I'm using 4/0 welding cabling. Paid a bundle for it and it's been fine for 2 years. Would have melted earlier.

Think something coming loose is more lilely as per Uncle Bob. I'm no longer at my trailer but looking at my photos again, I actually wonder if the cable is not coming out of the crimp...

[ITSNO60]

Were the fuse holder nuts torqued to spec when installed? It's been my experience that once you have a melt down, or a partial melt down the only permanent fix it replacement of all components that were affected. Just cleaning up overheated parts and re-using doesn't always result in a long time fix.

I also believe in using name brand parts.

[waninae39]

use copper or cooper with zinc atop lugs of the correct size and capacity and use a hydrlic crimper
use anti-oxidant grease on all power connections
use the proper torque
also lock nuts are very useful

[G8trwood]

Curious if you saw a spark from a lose connection or a fuse trying to blow (if the system kept working )
Class T fuse and cable clamps to stop wire vibration at the terminal? Definitely overheated. How tight was the connection at disassembly?

[uncle_bob]

Originally Posted by steilkurve

I'm using 4/0 welding cabling. Paid a bundle for it and it's been fine for 2 years. Would have melted earlier.

Think something coming loose is more lilely as per Uncle Bob. I'm no longer at my trailer but looking at my photos again, I actually wonder if the cable is not coming out of the crimp...

Hi

Looking at the "spray pattern" around the fuse holder, it appears that the source of the sparks / debris is in the vicinity of the fuse holder itself. Also, a loose crimp joint gives you a whole bunch of black / melted / charred plastic at the joint.

Still, all of this is only a random guess. Until somebody tears into the actual system, there's really very little to go on.

Bob

[richard5933]

I'd be swapping that fuse holder out for a Blue Sea class T setup. Something like this:

https://www.bluesea.com/products/550..._-_225_to_400A

The class T fuses are recommended for use with lithium setups because when they blow they blow completely. Other types of fuses can actually reconnect as the blown fuse melts back together after the initial blow (paraphrasing here). Class T fuses have the highest amp interrupt rating.

The Blue Sea fuse holders are heads and shoulders above the stuff you can generally get from places like Amazon. Looks like you have a Blue Sea fuse holder there, but it is not a class T.

Likely the cause of this problem was a loose connection somewhere, as mentioned earlier. It can be on the fuse holder, but it could also be inside the end of that battery cable. It's probably a good idea to give it a thorough inspection to be sure that it's mechanically tight inside - the wrapping looks great but there is no way to know what's inside it.

How was that lug crimped onto the cable? Hammer-smacked crimp tool or hydraulic crimper?

[Mollysdad]

Originally Posted by steilkurve

I actually wonder if the cable is not coming out of the crimp...

I saw that too. Is it possible the heat started there? Did you make the cables?
In any case, I'd replace the burned one.
When I redid the batteries, I bought this one for Amazon.


At the time it seemed like overkill but I do feel like the strands are as close to a solid block as possible.

[ITSNO60]

For folks who don't have the inclination to invest in hydraulic crimp tools and make their own cables you can't beat https://www.batterycablesusa.com/

They did all mine, and shipped them in 3 days for under $4 shipping! (Makes you wonder why so many places charge such exorbitant amounts for shipping)

[DaveG]

Originally Posted by steilkurve

Thanks. This makes sense. I actually had bought two fuse holders back when I did the install. I'll swap them. Do you think I need to replace the cable? Would that kind of resistance/heat damage it, beyond just the heat shrink around the crimp?

If the cable at the connector is discolored you need to replace at least the connector and cable back to where copper looks normal.

[GammaDog]

The folks above offered great advice.

I sometimes play “what else might it be”? I’ll offer two ideas…

1. Is there a rating on the fuse holder itself? Is it possible that the 400a fuse is in a holder with a lower rating?

2. Are the holes in the lugs sized properly for the posts? An oversized hole would produce less contact surface which would potentially lead to overheating.

[steilkurve]

Originally Posted by richard5933

I'd be swapping that fuse holder out for a Blue Sea class T setup. Something like this:

https://www.bluesea.com/products/550..._-_225_to_400A

The class T fuses are recommended for use with lithium setups because when they blow they blow completely. Other types of fuses can actually reconnect as the blown fuse melts back together after the initial blow (paraphrasing here). Class T fuses have the highest amp interrupt rating.

The Blue Sea fuse holders are heads and shoulders above the stuff you can generally get from places like Amazon. Looks like you have a Blue Sea fuse holder there, but it is not a class T.

Likely the cause of this problem was a loose connection somewhere, as mentioned earlier. It can be on the fuse holder, but it could also be inside the end of that battery cable. It's probably a good idea to give it a thorough inspection to be sure that it's mechanically tight inside - the wrapping looks great but there is no way to know what's inside it.

How was that lug crimped onto the cable? Hammer-smacked crimp tool or hydraulic crimper?

Thanks.

I followed plans from explorist.life when I built this system. It recommended an ANL fuse. Still, I wanted to do a T fuse but in the middle of the pandemic, getting one from a reputable manufacturer was weeks.

On my crimping, I did use a hydraulic crimper.

[steilkurve]

Originally Posted by Mollysdad

I saw that too. Is it possible the heat started there? Did you make the cables?
In any case, I'd replace the burned one.
When I redid the batteries, I bought this one for Amazon.


At the time it seemed like overkill but I do feel like the strands are as close to a solid block as possible.

Well, it wasn’t the crimp (which was originally done by a crimper like the one you posted). It was still super tight when I disassembled the faulty components today.

[steilkurve]

Originally Posted by GammaDog

The folks above offered great advice.

I sometimes play “what else might it be”? I’ll offer two ideas…

1. Is there a rating on the fuse holder itself? Is it possible that the 400a fuse is in a holder with a lower rating?

2. Are the holes in the lugs sized properly for the posts? An oversized hole would produce less contact surface which would potentially lead to overheating.

Fuse holder is good up to 750 amps.

And lugs are 5/16 and 3/8 to match the posts of the fuse holder on one side the battery disconnect switch on the other.

[steilkurve]

Closing the loop. First off, thanks for all the replies. Helped me find the culprit I think.

Disassembled everything today. What I found:

-All nuts were still tight, except the one where the bulk of the melting happened. That one was loose.

-This nut was torqued to spec on install. That said, I believe the way I routed the cable (in a U shape and going through a role) to reach the Victron Lynx made it tug on the terminal connection during travel. The fact the cable is so short/rigid and didn't have any flex didn't help either I'm sure.

-The fuse itself looked intact. The bulk of the damage was really around the loose nut and the cable terminal.

So, I had a spare fused holder and replaced the burnt one with it. Also swapped the cable completely and used more flexible Temco welding cable that will, I hope, provide more flexibility during travel. For good measure, I'll fasten the cable to the plywood, just before the fuse holder.

Question. I used the serrated nuts that come with the Blue Sea fuse holder and they stayed tight on all the other posts but should I swap them? Hate nylon nuts so I won't go there, but are serrated better than a good old nut and lock washer. That's what I have everywhere else in my install.

[ITSNO60]

Originally Posted by steilkurve

Closing the loop. First off, thanks for all the replies. Helped me find the culprit I think.

Disassembled everything today. What I found:

-All nuts were still tight, except the one where the bulk of the melting happened. That one was loose.

-This nut was torqued to spec on install. That said, I believe the way I routed the cable (in a U shape and going through a role) to reach the Victron Lynx made it tug on the terminal connection during travel. The fact the cable is so short/rigid and didn't have any flex didn't help either I'm sure.

-The fuse itself looked intact. The bulk of the damage was really around the loose nut and the cable terminal.

So, I had a spare fused holder and replaced the burnt one with it. Also swapped the cable completely and used more flexible Temco welding cable that will, I hope, provide more flexibility during travel. For good measure, I'll fasten the cable to the plywood, just before the fuse holder.

Question. I used the serrated nuts that come with the Blue Sea fuse holder and they stayed tight on all the other posts but should I swap them? Hate nylon nuts so I won't go there, but are serrated better than a good old nut and lock washer. That's what I have everywhere else in my install.

I would definitely use a serrated flange nut, it has more surface contact area than a nut and washer. If you are worried about it working loose you can run a second nut up and jam the 2 together, if the post is long enough.

[waninae39]

The nylon nuts are a much better holder than serrated or lock washers.

you can apply some non-permeant Loctite