Popping 50a buss at battery terminal, instead of popping breakers

[J-LU]

Hello everyone and anyone that may be able to help me on this one.

I blew two 50a buss at battery terminal instead of tripping the breakers inside. Is this normal or do I need to replace the breakers? I would think the breaker would trip before it hit the 50a buss at the battery?

Seee what happened was....

I have used the Dyson fan (pictured in the past but this time it was in heat mode). I'm not sure that it draws that much of a current in space heater mode than basic fan mode. If this is normal and I am being an idiot, please advise as this would not be my first go around as such!

Also, I am wondering if I am in the correct setting for lithium batteries. I have included this photo as well.

Any help would be much appreciated, I have gotten so much knowledge from the folks on this page in the past. So thank you in advance.

V/r
jlu

[richard5933]

Are you running this through an inverter? If so, it sounds like you're asking it to draw too much from the batteries to supply the needed power.

The circuit breakers are likely on the 120v side and the heater/fan isn't drawing enough to trip them.

[jeffmc306]

J-LU, no worries, we all come here for answers and to learn.

Is the fuse you’re blowing located on the battery post? If so, I think 50A is the wrong size which would explain why it keeps blowing.

I requested the electrical schematics from Airstream for our 2019 27’ Globetrotter but they don’t change much from year to year. In the schematic, it shows a 110A AT style fuse. I am pretty sure ours was 100A before I replaced the AGM batteries for a Battle Born GC3.

I’ll attach a photo of the location of the fuse from ours and the section of the schematic. That is the fuse for the feed to the inverter.

Good luck!
Jeff

[Wazbro]

That Dyson fan/heater probably draws 1500 watts on high, that's 12.5 amps at 120 volts protected by 15 or 20 amp breaker, with inefficiency that would be over 130 amps at 12 volts. So normal to blow a 50 amp fuse if your inverter is drawing power through them.

[J-LU]

Yes, to everyone! You guys answered all my concerns. I do think the 50a buss might need to be the 110a but it also explains as to why it blew and not the breakers. You guys rock, I do apologize that this is fundamental electronics but sometimes I just need things explained like this.

I truly appreciate the help on this. I will get a hold of battle born to see if I need to update to the proper buss fuse.

Thank you again for the education!

V/r
jlu

[ITSNO60]

Before changing the fuse size the wire needs to be verified that it is large enough to handle the current of the new fuse without overheating.

[richard5933]

Originally Posted by ITSNO60

Before changing the fuse size the wire needs to be verified that it is large enough to handle the current of the new fuse without overheating.

THIS^^^

Do not just upgrade the fuses without upgrading all the wiring involved.

Fuses are generally intended to protect the wiring, not just the device at the end of the wiring. If you put in a larger fuse without putting in larger wiring your wiring essentially becomes the fuse, and if you draw more current across it than the wiring can safely handle a meltdown begins, often ending in a fire.

Here's a great chart to help you calculate the correct wiring size for the load and length of the conductors:

https://www.bluesea.com/resources/1437

Looks like you'd likely need a 2/0 wire on the inverter circuit here.

Another important thing to remember when trying to operate a heavy load like an electric heater is your battery bank size. If you're trying to run a 1500-watt heater you'll want to have a sizable battery bank.

A common install has just two 100Ah lithium batteries, and with this load going you'd only last about 1-1/2 hours till fully depleted. Less if you have any other loads. Not something I'd recommend doing often either - my opinion is that running systems to the full capacity should be done only infrequently, as doing this all the time can shorten the life of the batteries and other components.

[Nishad]

... Brian and Richard are spot on.

[jeffmc306]

J-LU, of course you need to verify the wiring size before replacing any fuse with a larger one.

That’s why I asked the question if your fuse was attached to the battery post like in the photo I showed with the fuse circled. IF your wiring is the same as in the diagram, it’s a 4 ga. wire and the fuse was a 110A from the factory.

IF NOT, and it’s been modified by an installer or someone else, VERIFY the size before installing a larger fuse.

It would help if you shared a photo and what else was done. You mention Battle Born so I’m assuming (the dealer?) installed BB lithium instead of AGM or flooded acid batteries. As long as they did not modify the factory wiring and the fuse is connected to the 4 ga. Inverter wire, it’s my opinion the wrong size fuse was installed at some point.

If you’re not comfortable with DC electrical work please seek professional assistance.
-Jeff

[richard5933]

Originally Posted by jeffmc306

...it’s a 4 ga. wire and the fuse was a 110A from the factory...
-Jeff

You've got a 110A fuse on a 4 ga. wire? According to the charts I've seen that's marginal at best and likely under sized if it's more than a couple of feet long.

[waninae39]

fuses are designed to save the wiring , ie no fires, melting , too hot etc.

NEVER change the fuse size WITHOUT increasing the wire capacity. This is applies to trailer, house, office, industrial building. This is the law in many places also

IMHO, its best to have a biggest size cable you can fit/afford. these will also have the lowest loses

[uncle_bob]

Hi

Backing up a bit:

The gizmos that say "Buss" on them are Buss brand fuses. There are multiple brands of fuses out there. The 50A fuse you show is a 12V part. The other pictures are of the 12V distribution panel. It's a good guess that the 50A fuse is the "main" fuse for that panel. It is only a guess though ....

If indeed that is correct, it's going to blow when more than 50A is pulled into the *combination* of all the conventional 12V loads. It is not associated with the inverter. The inverter pulls way more current. Its fuse and cabling is in a different location.

If the fan is running on 120V and you are "off grid" then the inverter is involved. If you overload the inverter, it is likely to cut out. That may or may not blow the inline fuse.

This still leaves the question of the blown 50A device. Best guess: to much plugged into various 12V outlets around the trailer.

Bob

[jeffmc306]

Originally Posted by richard5933

You've got a 110A fuse on a 4 ga. wire? According to the charts I've seen that's marginal at best and likely under sized if it's more than a couple of feet long.

Guys - please take a moment and read the factory wiring diagram. This is what JC provided (not me). Just trying to show what it was coming from the factory.

Yes, I upgraded my wiring gauge when replacing it with a Victron MultiPlus II and Battle Born setup. Definitely recommended.

[richard5933]

Originally Posted by jeffmc306

Guys - please take a moment and read the factory wiring diagram. This is what JC provided (not me). Just trying to show what it was coming from the factory.



Yes, I upgraded my wiring gauge when replacing it with a Victron MultiPlus II and Battle Born setup. Definitely recommended.

I've thought for a while that Airstream tends to undersize their wiring. This looks like a good example. It must work for the most part or we'd hear of problems more often, but it's certainly not ideal.

[Sjugar]

Not sure if this contributes, but… we blew that same fuse when using the inverter and accidentally turned on the vacuum. Ours was 100A.

2019 27’ FC FBT - no electrical upgrades.

[J-LU]

Great discussion, I'm really thankful for all the great and thoughtful information.

I have attached the photos of my batteries and the location of the 50a fuse.

[jeffmc306]

J-LU, something doesn’t look right in the photos.

First, there’s a 100A fuse on the left of that dual-fuse holder. The wire connected to that 100A fuse is too small of a gauge for that much current.

The largest gauge wire is connected directly to the battery post so it’s not protected by any fuse. In my original factory install, the inverter’s 4 ga. Wire was connected to a 100A fuse on a single fuse holder.

Did the dealer install the Battle Born batteries for you? It’s difficult to troubleshoot through the photos without being able to trace where the wires go. Mine didn’t look like yours with the dual fuse holder.

My suggestion is to seek out a person with Airstream knowledge (another dealer or JC) or someone from a local Airstream club who can help.

Maybe another Airstream owner who also had a Lithium install done by a dealer can offer help.

[Joey Joe]

Originally Posted by jeffmc306

J-LU, something doesn’t look right in the photos.



First, there’s a 100A fuse on the left of that dual-fuse holder. The wire connected to that 100A fuse is too small of a gauge for that much current.



The largest gauge wire is connected directly to the battery post so it’s not protected by any fuse. In my original factory install, the inverter’s 4 ga. Wire was connected to a 100A fuse on a single fuse holder.



Did the dealer install the Battle Born batteries for you? It’s difficult to troubleshoot through the photos without being able to trace where the wires go. Mine didn’t look like yours with the dual fuse holder.



My suggestion is to seek out a person with Airstream knowledge (another dealer or JC) or someone from a local Airstream club who can help.



Maybe another Airstream owner who also had a Lithium install done by a dealer can offer help.

I have to agree. It looks like the wire at the far left of the original photo is the one that should have the 50a fuse. It looks to me that this setup is wired wrong.

The two largest red wires are the supplies into your trailer. The smaller of the two is for your DC panel and the larger of the two is your inverter. Both of those wires should be attached at the fuse block - smaller one to the 50a fuse and the larger one to the 100a fuse. From what I can tell here, you’ve got the 50a fuse between the two batteries, and nothing connected to the 100a fuse.

If you’re not confident with electrical wiring, have a professional look at this.

[Joey Joe]

Reference photo from my 22 Classic.

[JeffKim]

FWIW, our 2023 GT 25' came with a 100A MRBF fused to the inverter which is 4 AWG (marginal as pointed out). I would guess this was the same in the 2022 27'.

Not relevant, but when I installed our lithium batteries inside, I pulled the 4 AWG out of the battery box and cut out 5' or so then reused 100A fuse and holder on the Lynx distributor. It gave me a little comfort removing some wire.