Advice on wiring camp trailer batteries - where/how to fuse, etc, etc...

[skipdup]

Hi. I'm upgrading the batteries on my camp trailer (Schutt VX-2, open trailer with RTT) with two diy 300Ah.

So far, will be using Victron... shunt, DC-DC charger (20-30A), and MPPT 75/12 (through an existing Zamp port on the box). Don't have solar panels yet, but will add some in the future.

Hoping I can get some advice/counsel on:
- where, how, and with what, to best fuse/protect batteries?
- best way to pass through into the neighbor compartment?
- should I adda main battery disconnect?
- best way to recharge asap with Honda 2000i gen? (I have one Victron 30A, if that matters)
- recommend a small inverter? (don't need, but think I might as well have?)
- anything else I should think about?

I plan to size wire and fuses once I decide exactly what I'm doing.

Thanks!
Skip

 

[HRTKD]

Class T fuse to protect the batteries. Mount it right on the wall next to the batteries. Ideally, we want to see each battery with its own fuse. But what usually happens is one fuse covering both batteries.

Drill a hole between compartments and use a rubber grommet to protect the wires from the metal edge.

Battery disconnect is always a good idea.

Battery -> Class T Fuse -> Battery Disconnect

If one Victron 30 amp charger isn't enough, add another. It's OK to put them in parallel.

You have a Victron system, so the Victron VE.Direct Inverter is a natural addition. A Multiplus would allow you to ditch the AC->DC converter and still charge from shore power.

 

[skipdup]

@HRTKD Thank you!! Great info!!

From what I've been reading, and based on your suggestion... T-Class is better/safer than MRBF, right?

I hadn't considered a multi-plus. That might be perfect. Thinking the 12/1200/50. Maybe even adding the 30a charger, if my genny will drive it too.

Thanks again!

 

[HRTKD]

Class T fuses have an higher AIC than MRBF. The downside of Class T is that they're expensive. But they are excellent at protecting your system. They blow quickly. My 175 amp Class T fuse blew and my 80 amp MEGA fuse didn't when I overloaded that circuit. Not all fuses are rated the same, nor do they work the same.

The Honda 2000i is rated for 1600 watts continuous. It could power a larger Multiplus, which means more charging to your battery. Two charging devices is OK. Just don't overload the generator or it will shutdown.

Adding an inverter and solar charge controller to that compartment will require some ventilation. It's going to get hot in there.

 

[scrubjaysnest]

I went with MRBF mounted on the buss bar for each battery.

 

[BoonieBasher]

I went with MRBF mounted on the buss bar for each battery.

Like these?

Blue Sea Systems 5191 MRBF Terminal Fuse Block 30-300A

MRBF Terminal Fuse Block: 30-300A, Max Amperage: 300A, Max Voltage: 58V DC, Accepts 5/16" ring terminals, Mounts on 3/8” terminal studs.

www.currentconnected.com

My concern is that the terminal block is for 3/8" terminal post and my batteries are 5/16". No luck finding 5/16 on the battery side.
EDIT: Should have read closer - "on the busbar for each battery" - great idea to get me to the 3/8" stud.

and these?

Cooper Bussmann MRBF Terminal Fuse 30A - 250A

MRBF Terminal Fuse: meets the ABYC requirements for DC main circuit protection, ignition protected, IP66 rated, 58V DC max voltage

www.currentconnected.com

My camper will have 2 100ah batteries.

Thought I'd top it off with this (Before or after the (+) busbar?

MEGA Fuse Holder + 2 Fuse Bundle

Choose between LittelFuse or Victron Fuses in the MEGA Fuse Holder Bundle for reliable electrical connections and peace of mind.

www.currentconnected.com

Following since I'm in a similar situation.

 

[skipdup]

OK. To sanity check...

Two 125a class-t fuses, as close to battery terminal as possible. Blue Sea?
#4 wire from battery terminal, to fuse, to master switch.
#2 from switch to junction block, and then to inverter (Victron MultiPlus 12/1200/50).

Keep #4 wires equal lengths.

 

[HRTKD]

I can't provide an answer on wire gauge unless you tell me these three things:
Voltage (12 volt, you already said that)
Amperage
Distance

You can get the answers yourself by plugging the above three data points into a wire gauge calculator.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

 

[RV8R]

OK. To sanity check...

Two 125a class-t fuses, as close to battery terminal as possible. Blue Sea?
#4 wire from battery terminal, to fuse, to master switch.
#2 from switch to junction block, and then to inverter (Victron MultiPlus 12/1200/50).

Keep #4 wires equal lengths.

Hi @skipdup

I generally like what @HRTKD has posted for you here & would like to add the following;

1) Assuming 12vdc & DIY batteries the Blue Sea MRBF have an AIC of 10,000amps @ 14volts. Class T is higher, but my question is what AIC can your batteries create ??

MRBF Terminal Fuse - 150A - Blue Sea Systems

Space-saving ignition protected fuse for 30 to 300 Amp loads. Must use with Terminal Fuse Block.

www.bluesea.com

2) I believe the Blue Sea 9001e switch is a wonderful way to connect 2 batteries;

e-Series Selector Battery Switch - Blue Sea Systems

350 Amps continuous rating for inboard gasoline or diesel engines.

www.bluesea.com

3) Wire size / Fuse size / Yadda Yadda Yadda; best to draw up an electrical schematic & post it on here. I like to use “The Wire Barn Calculator” as it allows me to play with critical “Voltage Drop” in critical circuits. On critical voltage drop circuits, the size of wire will be dictated by desired voltage drop as opposed to amps. I design for both amps & voltage drop.

Wire Size Calculator

4) I like the idea of a Victron MultiPlus as you get an inverter & charger . I have a 3000VA MultiPlus @ my Cabin & charge up my AGMs with it & a Honda 2200 when the sun doesn’t cut it with the solar panels. Be aware of inverters & standby energy drain. You can read about my Victron 3000 Multi Here;

Thread 'Tiny Cabin - What To Do'
https://diysolarforum.com/threads/tiny-cabin-what-to-do.85978/



5) Inverter Capacitors; I have AGMs, but your DIY LFP batteries (I assume) have BMS. You are looking at a 1200VA inverter ? With that small of an inverter ( I have no experience ), the Inverter Capacitors energize I am guessing is not an issue, but maybe a Forum Member with experience with such equipment will chime in here. Regardless if Inverter Capacitor Energizing is a “new to you” concept, bone up on it or ask here.

6) Victron BMV 712 Smart Shunt; IMO these are excellent “Battery Monitors” or in your case “Battery Bank Monitor”. I don’t know what you have for BMS on your DIY batteries, but the BMV 712 is very helpful.

 

[RV8R]

On another note;






If you are “redoing” manufacturer’s install, this fuse block up so high & tight radius bends right @ the crimp is a bit bothersome for me.

If that fuse block can be easily lowered then the radius could have a looser “sweep” & not forced up against (I assume) lid of that box.

If that is too fussy for you ,,, don’t mind me I DIY airplanes as a hobby & radius & strain relief can be a little picky .

 

[RV8R]

Some AIC threads;

Post in thread 'Ask Me Anything About LFP Batteries and More! – Industry insider at top EV firm'
https://diysolarforum.com/threads/ask-me-anything-about-lfp-batteries-and-more-–-industry-insider-at-top-ev-firm.86542/post-1135940


Post in thread 'DIY Solar Plans - Is this a safe setup?'
https://diysolarforum.com/threads/diy-solar-plans-is-this-a-safe-setup.75208/post-1309546


Post in thread 'DIY Solar Plans - Is this a safe setup?'
https://diysolarforum.com/threads/diy-solar-plans-is-this-a-safe-setup.75208/post-958715

Post in thread 'House burned down'
https://diysolarforum.com/threads/house-burned-down.83098/post-1091772

The last one was a DIY large 48vdc battery bank & IIRC had a “Mega” fuse that caused the fire.

I assume you are 12vdc diy batteries in parallel. Best to try to sort out the AIC is an issue created between the batteries ,,, this is why each battery needs a fuse / protection of AIC levels.


Post in thread 'Current Connected says to use MRBF on 48v batteries ... is that REALLY right?'
https://diysolarforum.com/threads/c...eries-is-that-really-right.99882/post-1356088

Post in thread 'Class T vs ANL fuse'
https://diysolarforum.com/threads/class-t-vs-anl-fuse.13913/post-155368



Best to figure out what your battery AIC could be.

 

[skipdup]

@RV8R- Thanks!! Really great info!

Yes, I'm looking at lowering that fuse block. Good catch. Half debating one of those amazon switch panels with bluetooth - because I absolutely love, love I say, climbing down the ladder after realizing I left a light on. I just don't know how comfortable I am with their reliability...

1. I need to educate myself on AIC. I have no real understanding. Batteries are Eve MB30 306Ah with JK BMS (B2A8S20P). I have max out current set to 100a. I didn't see an AIC spec on the Eve spec sheet Amy sent. I'll try and read up on this. MRBF seems so much easier and might save me some space above the batteries.

My power needs are pretty small. It's a small trailer with RTT. 12v fridge, LED lights, some Starlink, and water pump makes up 90% of my usage. I just added a zero breeze a/c (I'm in Texas), so that's why I'm going so big on batteries.

2. I already have 2 BS on-off switches. I'm probably going to return for the one you listed. More flexibility for if/when I remove one battery during non-summer temps.
3. Thanks for link.
4. I don't need an inverter. Just adding in case I need/want in the future. Plus, the AIO and large charger is a bonus.
5. Got it. I think I know how to "charge" them.
6. Already have and will use BMV 712.

Thanks again!!

 

[HRTKD]

The super nice thing about the MRBF fuse holders is that it can be connected directly to a battery terminal/post. The downside is that you can connect it directly to a battery terminal/post. I usually try to make sure that the battery terminals (really in my case, the cell terminal because I DIY) have as little stress on them as possible. The MRBF fuse holder elevates where the cable attaches, which means more leverage, unless you provide sufficient strain relief. In a static environment, not a big deal. In a mobile environment (aka the Rolling Earthquake) it matters.

 

[RV8R]

The super nice thing about the MRBF fuse holders is that it can be connected directly to a battery terminal/post. The downside is that you can connect it directly to a battery terminal/post. I usually try to make sure that the battery terminals (really in my case, the cell terminal because I DIY) have as little stress on them as possible. The MRBF fuse holder elevates where the cable attaches, which means more leverage, unless you provide sufficient strain relief. In a static environment, not a big deal. In a mobile environment (aka the Rolling Earthquake) it matters.

If MRBF are used the “Double Bus / Double Fuse” can sometimes be very useful;

 

[skipdup]

OK. So, I think I understand that AIC is calculated taking the internal resistance and using Ohms law to find the current.

Eve says:
"Initial Internal Resistance" is .18 milli-ohms.
"Nominal Voltage" 3.2V. Or, do I use 3.65?
I assume Voltage for calculation is times 4, so either 12.8 or 14.6?

So, at 12.8V and .0018Ohms, current is 7,111A.
At 14.6 and .0018Ohms, current is 8,111A.

Am I on the right track? Or missing it completely?

 

[HRTKD]

See this thread:

Thread 'Calculating the LiFePO4 battery short circuit current'

Apr 9, 2023

I'm trying to understand how to calculate a LiFePO4 battery short circuit current.

I have a 12V 100Ah LiFePO4 battery and the manual states an internal Impedance of 40mΩ.

So how to calculate the short circuit current of the battery?


Thanks.

• Pi Curio
• Replies: 35
• Forum: General Battery Discussion

• 

 

[Drizzt321]

Even if you're on the right track, there's someone doing some pretty neat real-world experiments with dead short fuse behavior.

Thread 'Dead short fuse trip experiment using an MRBF fuse'

Mar 16, 2024

Introduction
Marine Rated Battery Fuses (MRBFs) are sometimes used to replace Class T fuses due to supply chain issues, ease of installation, space constraints, and cost. However, the breaking capacity of MRBF fuses is significanly lower than that of Class T fuses as shown in Figure 1.


Figure 1. Ampere Interrupting Capacity vs DC Voltage Rating

Problem
How will an MRBF fuse behave when subjected to a dead short outside of the fuse specifications?

Background
If the fuse does not quench the arc, then hot plasma could theoretically turn the fuse...

• Johan
• Replies: 121
• Forum: Danger Zone! (Advanced User Experiments Only)

• 
• 
• 

His initial MRBF has it blow and quench the arc, but some molten metal bursts free from the plastic housing of the MRBF. Class-T fuses (and there are some others as well) have sand inside and a ceramic shell so that when they blow any molten metal generally gets caught in the sand and the sand collapses around the blown fuse bits so that it quenches the arc.

MRBF, ANL, MEGA, none of those have that sort of anti-combustion feature. And if for some reason it's blowing because of a battery cell going bad and venting, a venting cell can release hydrogen which if a fuse blowing releases a spark or molten piece of metal, even if it quenches the arc, it could still potentially trigger a fire. Especially if the hydrogen is vented into an enclosed space like a battery box.


I've got a small travel trailer myself, and did my own battery system, including a increased battery capacity recently https://diysolarforum.com/threads/new-small-trailer-battery-setup.100880/

If you need really large wiring and don't have a crimper or want to invest in a crimper for them, I can recommend https://www.batterycablesusa.com/battery-cables-ul to get custom length cables made. Just remember, the larger wiring sizes means they are a lot less flexible, especially at short lengths, so bend radius is going to be very constrained. And that the lug is going to be part of the distance and they very much do not bend. Potentially you can go with 2 somewhat smaller wires (welding wire is great! hyper flexible), so that can be an option and a crimper isn't all that much on Amazon. I'd recommend NOT Amazon for your lugs. McMaster-Carr or https://www.batterycablesusa.com/battery-cable-ring-terminal-lugs or other similar quality vendor.

If you don't need an inverter-charger at all, there are a variety of chargers, including IP67/IP68 rated ones in the Victron world. You could get something like https://www.victronenergy.com/chargers/blue-smart-ip65-charger or https://www.victronenergy.com/chargers/blue-smart-ip67-charger-waterproof. Potentially https://www.victronenergy.com/chargers/phoenix-smart-ip43-charger, but you'll definitely start needing to consider venting, especially the higher in current you go.

Or just get something you stash away, and pull out when you pull out your generator or have shore power. I've used my BlueSmart (https://www.victronenergy.com/chargers/blue-smart-ip65-charger) 15a hooked up to my normal wiring/bus bar to feed in the power, and had it plugged into my internal AC (shore power) outlet. So that's an option, have it hooked up inside to the DC wiring, make sure it's plenty of size for whatever current you selected, and then just plug into your trailer shore power hookup and it'll automatically turn on and start charging.

 

[HRTKD]

His initial MRBF has it blow and quench the arc, but some molten metal bursts free from the plastic housing of the MRBF. Class-T fuses (and there are some others as well) have sand inside and a ceramic shell so that when they blow any molten metal generally gets caught in the sand and the sand collapses around the blown fuse bits so that it quenches the arc.

When I blew my 175 amp Class T fuse it was a non event. The lights went out but nothing else happened. No noise, no shrapnel, no sparks. My system is 48v 280Ah, so not quite as large as the one Johan used for his testing.

Class T fuses are expensive, but I'm a believer.

 

[Drizzt321]

When I blew my 175 amp Class T fuse it was a non event. The lights went out but nothing else happened. No noise, no shrapnel, no sparks. My system is 48v 280Ah, so not quite as large as the one Johan used for his testing.

Class T fuses are expensive, but I'm a believer.

I recall somewhere on the forums someone was building a pack and had a Class-T and was distractedly getting ready to bolt down the other side into the circuit and accidentally shorted things out. Was a spark because of it jumping the air, but otherwise a dead circuit in microseconds and a huge shot of adrenaline and needing to take a break.

 

[skipdup]

Ugh. OK! I'll stop trying to be cheap!
Two 125a Blue Sea Class-t with holders should cover me, right? Or is there a better option?
I feel like I should buy 1 or 2 spare fuses in case (i.e. when) I do something stupid in the field.

I'm going to pause on inverter/multiplus, since I have no immediate need for a/c power. I will use my existing Victron 30A charger, and probably add a 2nd for a total of 60a charging. I can always use those somewhere else if I add the multiplus later.

I really, really appreciate everyone's help!!

 

[HRTKD]

I recall somewhere on the forums someone was building a pack and had a Class-T and was distractedly getting ready to bolt down the other side into the circuit and accidentally shorted things out. Was a spark because of it jumping the air, but otherwise a dead circuit in microseconds and a huge shot of adrenaline and needing to take a break.

Everything was already bolted down when I blew mine. I turned on the battery disconnect. Inverter capacitors sucked the ever living amps out of my battery.

 

[HRTKD]

Ugh. OK! I'll stop trying to be cheap!
Two 125a Blue Sea Class-t with holders should cover me, right? Or is there a better option?
I feel like I should buy 1 or 2 spare fuses in case (i.e. when) I do something stupid in the field.

The beatings will continue until you relent!

Two holders/fuses is the right way to go. I may have said it earlier in the thread, but a lot of people use one, bringing the two batteries together at the fuse holder.

Always buy spare fuses. I started with 175 amp, blew that (my fault) and switched to 225 amp. When I switched I bought extra 225 amps fuses and also a couple of larger fuses (and fuse holder) in case the 225 amp fuse wasn't enough.

The 175 amp Class T fuse accounted for everything my RV could run, except for the inverter's capacitors.

 

[Drizzt321]

Everything was already bolted down when I blew mine. I turned on the battery disconnect. Inverter capacitors sucked the ever living amps out of my battery.

Heh, yeah. I'm really glad I got informed out pre-charge circuit for the future when I have a big inverter.

The beatings will continue until you relent!

Two holders/fuses is the right way to go. I may have said it earlier in the thread, but a lot of people use one, bringing the two batteries together at the fuse holder.

Always buy spare fuses. I started with 175 amp, blew that (my fault) and switched to 225 amp. When I switched I bought extra 225 amps fuses and also a couple of larger fuses (and fuse holder) in case the 225 amp fuse wasn't enough.

The 175 amp Class T fuse accounted for everything my RV could run, except for the inverter's capacitors.

Hahaha.

Ugh. OK! I'll stop trying to be cheap!
Two 125a Blue Sea Class-t with holders should cover me, right? Or is there a better option?
I feel like I should buy 1 or 2 spare fuses in case (i.e. when) I do something stupid in the field.

I'm going to pause on inverter/multiplus, since I have no immediate need for a/c power. I will use my existing Victron 30A charger, and probably add a 2nd for a total of 60a charging. I can always use those somewhere else if I add the multiplus later.

I really, really appreciate everyone's help!!

Generally the reason why you want one fuse per parallel battery is if a battery fails shorted, which can and has happened, you want to protect the other battery(ies) in parallel so they don't give power trying to 'charge' up the failed battery.

Doesn't necessarily need to be Blue Sea, but I'd avoid rando Amazon/Aliexpress fuse holders.

And yes, having a spare fuse would be a good idea. I've never needed mine. But I have it just in case.

 

[skipdup]

Order placed. I'll update once I make some progress. Thanks again!!

 

[RV8R]

Order placed. I'll update once I make some progress. Thanks again!!

Lots of great info on your thread here @skipdup

You are 12vdc LFP, so the Class T Fuse is mucho protection ,,, can’t go wrong with that.

I use the MRBF on my 12vdc AGMs & consider that pretty safe.

So, now that you are slowing down on the purchases , get a design done & post a schematic here & you will obtain even more; opinions / ideas / knowledge with your 12vdc system.

I’m going to try to find my favourite “fuse” video & post it here for ya (check out the NH00 fuse );