The Bubba Electric system is being dismantled

[HueyPilotVN]

I have been considering the option of doing a transfer of the Bubba system to the new Tiffin.

The decision was made for me today. The configuration of the current system has proved to be unsafe.

The battery bank is to large to safely power a 3,000 watt invertor, or the Romex AC cables are not heavy enough.

I have a 600 watt class T fuse between the disconnect switch and the Invertor. My AC power went out today while driving home to Lake Havasu City in 110 degree heat with the AC on. It stopped cooling. I then realized that I also had no 120 volt AC.

When I got home and looked in the back compartment, I was shocked and felt like I had dodged a bullet.

Somehow the Invertor pulled so much current that it not only melted a 600 watt class T fuse, but it also started a fire that thankfully went out.

The monster cables were not involved except where the fuse melted the ends connected to the fuse.

The panels, controllers and batteries were not involved at all. The Invertor has burn marks and the AC input and output cables are melted.

As I write this it occurs to me that the Romax cables might have been to small for the surge.

My thoughts are to use the panels, batteries and charge controllers to simply augment and replace the house battery bank in the new Tiffin. I was not going to even try to interface with the 50 amp system.

Here are some before and after pictures of what happened today.

 

[ferfer]

Oh Bill, I do not know what nor how to express my thoughts. Just glad you dodged this bullet!

Jennifer

 

[HueyPilotVN]

Two fires within 8 months would have been very hard to explain.

 

[DonTom]

The battery bank is to large to safely power a 3,000 watt invertor, or the Romex AC cables are not heavy enough.

My guess is that you have a shorted power transistor or capacitor in the inverter, right at the input, which drew a ton of current and melted the wires. I will bet the inverter has a serious issue. Perhaps did overheat, but I think the wires most likely melted because of a short on the input of the inverter.

-Don- Reno, NV

 

[HueyPilotVN]

I think what saved this from being another disaster was Lou Schnider's suggestion to insert a regular AC circuit breaker in both the input line to the Invertor and the output line to the main AC panel.

Looking at the Romex it looks like they melted and shorted out. The breakers probably stopped the welding rod type fire of the class T fuse. The romex was the same 12 gauge as the rest of the RV.

Anyway, The experiment is over. No more Bubba Electric Company of any new version.

 

[DonTom]

I was looking at the thick red wire. I didn't notice it looks like there was a serious short on the AC output.

For where to use and not use Romex, I found this. But I have a hard time buying the wires melted together. I still expect a short causing them to melt.

-Don- Reno, NV

 

[HueyPilotVN]

The first step will be to remove the Romex from the two circuit breakers and reestablish the original wire to the main panel from the transfer switch and remove the Invertor and battery bank from the circuit.

I will dismantle the batteries.controllers and solar panels to transfer and create a simple solar rechargeable 12 volt supply for the coach system in the new rig. The only interface will be to power the existing invertor in the factory system for the refer and such.

The should simply create a solar rechargable 12 volt coach battery bank with longer run time and no high current AC power draw.

 

[DonTom]

The first step will be to remove the Romex from the two circuit breakers and reestablish the original wire to the main panel from the transfer switch and remove the Invertor and battery bank from the circuit.

When you find the exact cause or location of the short, please post it here.

-Don- Reno, NV

 

[HueyPilotVN]

I believe at this point that the short either happened in the Invertor or the Romex cable and I will give a follow up answer.

The fuse only melted and caught fire because of the dead short in a 30 amp AC circuit.

It also shows that even a one hundred dollar Class T fuse does not blow and disconnect fast enough to avoid a fire.

 

[DonTom]

I see we both have the same 300AH Ampertime battery. Just that I only have one per RV. Looks like you have four for 1,200 AH.

-Don- Reno, NV

 

[HueyPilotVN]

Five, but one of them is the coach battery and located up front.

The reason for four in the rear was to see if I could run Air conditioning off batteries and have 24/7 120 volt power.

Not really a smart use of money. Much less expensive to use a generator.

I will not do it again or recommend it.

It was kind of a survivalist experiment.

 

[DonTom]

Not really a smart use of money. Much less expensive to use a generator.

As I have said many times, not everything is about money. There are times and places where you are not allowed to run the genny.

I use my inverter a lot more than the genny, in both of my motorhomes. Except for the times I need to charge my electric motorcycle when it's too far from a charge station or even a 120 VAC outlet.

-Don- Reno, NV

 

[Lou Schneider]

Wow, Bill. Talk about dodging a bullet! Looking at the pictures, it seems like the major heat source was the inside the Class T fuse holder. The fuse should have blown before the fuse holder got hot enough to catch it's enclosure on fire. If it was this one from Amazon it's only rated for 400 amps which means a 600 amp fuse was 50% too large for it. Amazon.com

Each 300 a/h battery is limited to a maximum of 200 amps by it's BMS so a bank of 4 in parallel can supply up to 800 amps. This may have contributed to the damage but IMO the primary cause of the fire was the fuse exceeding the rating of the fuse holder which let too much current flow instead of blowing when something shorted.

 

[DonTom]

I am now wondering if my first guess was correct. Perhaps the AC wires caught fire because of the fire that started below at the DC input. IOW, a short on the input of the inverter. If the Romex AC cables are not burnt further up where I cannot see in the photo, then perhaps the short was only on the DC side.

If the current was that high on the AC inverter output, I would expect the inverter to shut down well before that much damage.

So I am still betting on a short on the input of the inverter and had nothing to do with the Romex cables--at least until I see more evidence.

BTW, I just did a web search, and here is a 600-amp rated Class T fuse holder.

-Don- Reno, NV

 

[Rene T]

Bill, just a word of caution, you better be thinking about replacing all of your smoke detectors SOON!!!!!

 

[Mark_K5LXP]

I'm with Don, the fuseholder is the likely culprit. It got hot enough to ignite the plastic box and that's what burned the romex above it. Even a few milliohms of resistance at hundreds of amps is a lot of watts. Confine that to a small area and there's no limit to the temperature it can rise to. In my travels, this doesn't happen suddenly, a compromised connection gets progressively worse from thermal cycles and vibration over time. That's why periodic voltage drop tests are important, and re-torquing terminals. It only takes one.

Mark B.
Albuquerque, NM

 

[Primerump]

I believe at this point that the short either happened in the Invertor or the Romex cable and I will give a follow up answer.

The fuse only melted and caught fire because of the dead short in a 30 amp AC circuit.

It also shows that even a one hundred dollar Class T fuse does not blow and disconnect fast enough to avoid a fire.

lucky it was not worse.. but glad you escaped yet another fire..

so I will ask you why 600 amp fuse ? what gauge wire is that to the fuse and battery ?


I will agree with Mark here and suggest terminal and cable resistance is the culprit, coupled with high currents and too high of a fuse rating.

the other issue I see is the inverter quality.. does that unit have temperature shutdown ? pulling an overload like that should have triggered a failsafe shutdown in the inverter. perhaps it doesn't have one ?

This highlights what I have said all along about high currents and 12V.. it's not good practice to put anything larger than 1500 Watts on 12 Volts. If you want to do 3000 Watt or higher inverters then 24 or 48V is needed. best practices suggest limit current to 100 amps or so, just because your system is 12 Volts doesn't mean your solar has to be too. think about it... do you really have any high power consumption at 12 V ? no, the only reason to have the inverter is for 120/240 Volts so the battery voltage can be sized accordingly.

 

[DonTom]

does that unit have temperature shutdown ? pulling an overload like that should have triggered a failsafe shutdown in the inverter. perhaps it doesn't have one ?

AFAIK, all the larger inverters have several different types of shutdowns, even the cheaper Chinese MSW inverters. No way will a dead short on the AC output cause that type of damage on the 12-volt side of the inverter.

AFAIK, high temperature, low DC voltage, high DC voltage, AC overload, and incorrect range of AC voltage will all shut down the larger inverters. And an audio alarm, at least on all the larger inverters I have owned.

IMO, it has to be a dead short on the DC side in the inverter or a DC short to ground somewhere, if not the inverter.

-Don- Reno, NV

 

[RayIN]

Five, but one of them is the coach battery and located up front.

The reason for four in the rear was to see if I could run Air conditioning off batteries and have 24/7 120 volt power.

Not really a smart use of money. Much less expensive to use a generator.

I will not do it again or recommend it.

It was kind of a survivalist experiment.

Hey, you're good. I wonder how much stuff Thomas Edison burned up before something worked reliably.

 

[Sunnyfalls]

For a 3000 Watt Inverter 12VDC input side,you should have a 300A Class T fuse in a Class T fuse block rated well above that which also has Ignition Protection to prevent a fire. For a 3000 Watt Inverter 120VAC output side, you should also have a 20A circuit breaker. I agree with Don, you most likely had a short on the 12VDC input side...and your 12VDC fuse block was inadequate. And yes, a propane modified generator is a far more economical and safer approach for powering air conditioning than creating a high energy battery bomb just looking for an excuse to go off. At least you get to live and learn.

Gayle & Bob
Los Gatos Casita

https://www.borstengineeringconstruction.com/Our_Los_Gatos_Casita_Spring_2023_Trip.pdf