The Bubba Electric system is being dismantled

[Sunnyfalls]

Something else came to mind... Are you using LiFiPO4 batteries with BMSs? If so, if you exceeded your 600A fuse long enough for it blow, this might indicate that some of your BMSs may no longer be working properly and providing over-current protection?

A 3000 Watt Inverter fed from low resistance LiFiPO4 batteries using low resistance 4/0 cable can generate a 2700A capacitor inrush current. This horrendous inrush current only lasts for less than a microsecond. So it will not blow a fuse. But it could damage the LiFiPO4 BMSs and the Inverter...especially if this is allowed to frequently occur. We use an Inverter capacitor precharge system with our 3000 Watt Inverter fed from our 100AH LiFiPO4 battery using 4/0 cables to avoid this issue. This white paper provides a pretty good explanation of this capacitor inrush current subject:

https://lithionicsbattery.com/wp-co...nverter-DC-Capacitance-and-Inrush-Current.pdf

And without the BMSs to protect the LIFIPO4 batteries from generating continuous high current above their maximum current rating when faced with a short in the 12VDC side of the Inverter input, you might get what you described...or much worse.

Gayle & Bob
Los Gatos Casita

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

 

[Lou Schneider]

Something else came to mind... Are you using LiFiPO4 batteries with BMSs? If so, if you exceeded your 600A fuse long enough for it blow, this might indicate that some of your BMSs may no longer be working properly and providing over-current protection?

Even though the 4 batteries can theoretically supply 800 amps before tripping their overcurrent shutdowns, I don't think the 600 amp fuse blew. Instead there was a sustained draw of more than the 400 amp rating of the fuse holder.

I count 6 connections and a disconnect switch between the last battery and the inverter.

12 volts divided by 600 amps = 0.02 ohms total circuit resistance. Ignoring the switch and wire resistance, to blow a 600 amp fuse at 12 volts each connection would have to average 0.003 ohms (3/1000 ohm) or less, which is a pretty good connection.

It's not hard to imagine the total circuit resistance limiting the short circuit current to less than the fuse's 600 amp rating but more than the 400 amp capacity of the fuse holder, causing it to severely overheat long enough to catch it's plastic enclosure on fire. It's quite likely the correct 400 amp fuse would have quickly blown under the same conditions without overheating the fuse holder.

I also pre-charge the input capacitors on my high power inverter. My pre-charge system is an ice pick circuit tracer with a small 12 volt light bulb in the handle. Harbor Freight has a nice one for $4. Put the tracer in series between the inverter and the battery post before you make the last connection and the light bulb will limit the current as it glows brightly and then dims as the capacitors gain a charge. They are charged when the light bulb goes out, usually after a few seconds and you can safely make that final connection.

 

[HueyPilotVN]

I went back over all the orders from Amazon, (where I usually by this stuff), and I now think that the class t fuse was a 400 amp fuse.

I recently had to upgrade the disconnect switch to a 600 amp one because the lower rated one actually fused a contact and I could not turn it off. That may be why I thought it was a 600 amp.

Any way my experiment is over. I will only transfer the panels, controllers, and batteries to just provide a longer run time for the 12 volt chassis battery bank. No more creating a 120 volt AC supply other than the limited factory invertor for just things like the refer. No more air conditioning from the battery bank.

The new coach is way to cool to burn down.

The new coach also has three air conditioners, so it would take a lot of power just to even try to supply them.

Finally a question for Lou. Is there such a device as a current limiter that would support a long run time from a big battery bank without the worry of a over current surge other than a Class T fuse for the new bank?

 

[Lou Schneider]

I went back over all the orders from Amazon, (where I usually by this stuff), and I now think that the class t fuse was a 400 amp fuse.

I recently had to upgrade the disconnect switch to a 600 amp one because the lower rated one actually fused a contact and I could not turn it off. That may be why I thought it was a 600 amp.

Any way my experiment is over. I will only transfer the panels, controllers, and batteries to just provide a longer run time for the 12 volt chassis battery bank. No more creating a 120 volt AC supply other than the limited factory invertor for just things like the refer. No more air conditioning from the battery bank.

The new coach is way to cool to burn down.

Those large batteries are still dangerous, don't forget to put a catastrophe fuse in line with them or they could pump up to 800 amps into the 12 volt wiring. The factory converter's current rating can be used as an estimate of the most the stock motorhome loads will draw or if your solar system puts out more current use it as the controlling factor. Then size the fuse no more than 2x that.

 

[HueyPilotVN]

Currently there are four of the 300 AH in the back bank for 1200 AH. If I also use the front one it will be 1500 AH .
I currently have 1,600 watts to move and potentially room for 2,000 or maybe 2,400 watts of solar on the roof.

 

[Mark_K5LXP]

I haven't kept up with the specific equipment configuration but going with a 24 or 48V setup would offer the same power at more sane current levels. 48V off grid is a common setup which could let you keep your battery A/C.

Mark B.
Albuquerque, NM

 

[Sunnyfalls]

Even though the 4 batteries can theoretically supply 800 amps before tripping their overcurrent shutdowns, I don't think the 600 amp fuse blew. Instead there was a sustained draw of more than the 400 amp rating of the fuse holder.

I count 6 connections and a disconnect switch between the last battery and the inverter.

12 volts divided by 600 amps = 0.02 ohms total circuit resistance. Ignoring the switch and wire resistance, to blow a 600 amp fuse at 12 volts each connection would have to average 0.003 ohms (3/1000 ohm) or less, which is a pretty good connection.

It's not hard to imagine the total circuit resistance limiting the short circuit current to less than the fuse's 600 amp rating but more than the 400 amp capacity of the fuse holder, causing it to severely overheat long enough to catch it's plastic enclosure on fire. It's quite likely the correct 400 amp fuse would have quickly blown under the same conditions without overheating the fuse holder.

I also pre-charge the input capacitors on my high power inverter. My pre-charge system is an ice pick circuit tracer with a small 12 volt light bulb in the handle. Harbor Freight has a nice one for $4. Put the tracer in series between the inverter and the battery post before you make the last connection and the light bulb will limit the current as it glows brightly and then dims as the capacitors gain a charge. They are charged when the light bulb goes out, usually after a few seconds and you can safely make that final connection.

Yes, this makes perfect sense. And none of the batteries self-ignited from exceeding their rating which is further substantiation that the fuse holder was simply inadequate for protecting this mission.

For our 13.6VDC 100AH LiFiPO4 battery and our 3000 Watt Inverter, capacitor pre-charging is accomplished using a 1 Ohm 200 Watt Power Resistor and a Blue Sea Systems 3-Way Switch which is rated for 300A continuous and is rated for 900A intermediate (30 seconds). This 3-way switch, was placed in a non-obtrusive, hidden but easily accessible location on driver side of our customized sleeping area cabinet in the pillow area. This 3-way switch has three positions. Position 1 connects the battery to the pre-charge circuit and then the Inverter. Position 2 completely disconnects the battery from the Inverter. Position 3 connects the battery only and directly to the Inverter. This 3-way switch is FIRST selected to Position 1 to ONLY ALLOW 13.6A (i.e., 13.6VDC divided by 1 Ohm) of current or 185 Watts (i.e., 13.6A times 13.6VDC) of power to flow from the battery through the power resistor to fully pre-charge the Inverter capacitors in about 0.9 seconds (i.e., 5 capacitor time constants times 1 Ohm times 0.18 Farads). Then this 3-way switch is selected to Position 3 to enable the battery to provide its maximum discharge current to the Inverter hence forth. The pre-charge circuit is protected with a 15A ATC fuse and is physically connected between the 3-way switch Position 1 and Position 3 terminals. The battery positive 4/0 AWG cable from the auto resetting circuit breaker is connected to the 3-way switch Output terminal and the Inverter positive 4/0 AWG cable is connected to the 3-way switch Position 3 terminal. All of our Inverter 120VAC power loads are also FIRST removed BEFORE accomplishing this capacitor pre-charge procedure and BEFORE turning ON or turning OFF our Inverter by using our dedicated Inverter/Shore Power Selection Switch and setting it to the OFF Position.

Gayle & Bob
Los Gatos Casita

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

 

[Sunnyfalls]

I haven't kept up with the specific equipment configuration but going with a 24 or 48V setup would offer the same power at more sane current levels. 48V off grid is a common setup which could let you keep your battery A/C.

Mark B.
Albuquerque, NM

Yes, a 48VDC system would be a far better approach for dealing with this level of power. We use a 48VDC system for our remote homestead to integrate generator and hydro power:

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

Gayle & Bob
Los Gatos Casita

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

 

[Sunnyfalls]

Those large batteries are still dangerous, don't forget to put a catastrophe fuse in line with them or they could pump up to 800 amps into the 12 volt wiring. The factory converter's current rating can be used as an estimate of the most the stock motorhome loads will draw or if your solar system puts out more current use it as the controlling factor. Then size the fuse no more than 2x that.

I fully share your concern. I can fully understand the attraction and appeal of wanting to create a high power system that supports operating everything in a RV if one has a large enough RV that can accommodate the reguired battery and solar panel footprint needed for such a mission. But it is a dangerous mission for sure that is fraught with many issues that can bite you badly if you don't accomplish a proper design and installation. LiFePO4 batteries are relatively safe compared to their predecessors. But you will still have a huge amount of energy that can always get rapidly unleashed if there is some manufacturing defect in any of the cells. I feel using a generator is a much more appropriate, much more economical and a far safer approach when all things are considered.

Gayle & Bob
Los Gatos Casita

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

 

[Sunnyfalls]

Finally a question for Lou. Is there such a device as a current limiter that would support a long run time from a big battery bank without the worry of a over current surge other than a Class T fuse for the new bank?

I am sure Lou will chime in...

We use both a Class T fuse and an Auto Resetting Circuit Breaker in series. We use the Auto Resetting Circuit Breaker because the location is not easily accessed. And we use the Class T fuse for redundancy and to ensure that if there is a catastrophic short, the Auto Resetting Circuit Breaker won't just keep resetting, get hot and potentially cause a fire. This has been known to happen...especially when they are used between a battery and a Charger/DC Distribution Panel which will then violate their polarity requirement (either when charging the battery or when using battery power) which prevents them from extinguishing DC arcing. And most importantly, both are high quality, can easily handle the maximum possible current and have Ignition Protection.

Gayle & Bob
Los Gatos Casita

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

 

[HueyPilotVN]

I talked with Lou last night about using a DC to DC charger to limit the exposure of high current draw on the battery bank.

The problem is that like a diode it only flows current in one direction so it would not reverse flow to recharge the battery bank.

I already have one in the box as it was my intent to connect it between the engine alternator to the coach battery. It can be used as a battery boost if needed but requires pushing a button to reverse input to charge..

I realized that the DC to DC was not needed because the coach battery was being constantly charged by the 24/7 AC from the Bubba System.

Lou's practical solution was to cut the size of the battery bank to a safer size.

 

[Sunnyfalls]

Sounds like a prudent solution. Yep, DC to DC Chargers are one way devices like DC Auto Resetting Circuit Breakers. Happy and safe camping!

Gayle & Bob
Los Gatos Casita https://www.borstengineeringconstruction.com/Our_Los_Gatos_Casita_Spring_2023_Trip.pdf

 

[Larry N.]

48V off grid is a common setup which could let you keep your battery A/C.

-48V DC is what telcos use (or did when I worked there) in humongous battery banks for several hours (perhaps 8 or more) of running an entire central office. Of course the bus bars are humongous, too. And the inverters weren't tiny, either.

 

[HueyPilotVN]

I just finished restoring the connection from the transfer switch to the main electrical panel.

I had inserted a loop of Romex between the romex wire from the transfer case and the panel by using two 30 amp circuit breakers. One between the TC and the input to the invertor and the other in the output to the main panel.

I removed the loop and wired new heaver yellow romex between the two circuit breakers.

The input one between the transfer case and the invertor was tripped.

There are pictures below.

It is now functionally the same as factory.

The romex was black and the outer sheath was melted but the plastic coating held and the conductors never were exposed or touched to create the short. The fire caused the melting. Anyway it was not a romex wiring problem.

Does not really matter because it is not going to be reconnected for the Bubba system.

 

[TonyL]

Bill, I know I might be the only idiot wondering but who cares.
Why is it called the Bubba system?

 

[HueyPilotVN]

I considered it a kind of "Backyard Engineering Project" and thought I would come up with a funny and not so serious name.

The use of the name "Bubba" brings to my mind the Good Ole Boy reference.

I thought about a name incorporating the phrase "Rube Goldberg", that refers to something that contains many complex and often unneeded steps to accomplish a goal that could be arrived at in fewer simple steps.

In other words it was a kind of joke name, not meant to put anybody down but rather to contrast the names Bubba with Edison.

 

[TonyL]

Thanks for explaining.

 

[Rene T]

Bill, you need to update your signature.

 

[HueyPilotVN]

Next week, when i actually get it.

 

[Rene T]

Next week, when i actually get it.

Oh , I thought this fire was in the new Tiffin. Then I went back and looked and see that you planned on picking it up around the 12th.