Fusing system

[gblcia]

Hi,

I dont understand short protection of whole 12V system completely, need help here please. I got some info from here and there but really not understanding relationships and whole picture and not able to decide.

My questions is about requirement for battery fuse:

1, I got 1 lithium 280Ah max. discharge 200A/peak 400A from Fogstar. It says has short protection, how this works? there is no manual for battery and fogstar didnt answer
Once you short battery - what immediate current would go out, would these be stopped at 400A and disconnect or surge and disconnect? I suppose there would be big surge as i read several times you need to use fuse with high interrupt capacity, but i am only guessing here(Can someone confirm this?)

here is bat.link:

Lithium Leisure Battery - Fogstar Drift 12v 280Ah

280Ah Fogstar Drift Lithium Leisure Battery | Grade A LiFePO4 cells, High Discharge BMS, Bluetooth, Heating | Lowest Prices in the UK. 10 Year Warranty.

www.fogstar.co.uk

2, Okay i suppose than i need fuse for reason above. What kind of fuse would that be? right i ve read T class/ANL and MRBF, where T class has 20k IC, MRBF 10k and ANL 6k or smth.
Notes i saw Mega and MIDI fuses ratings are about 2k IC only, but i saw MIDI fuses from BlueSeaSystems has 5k IC.

So how can i determine correct fit for the battery?
From my understanding we do this only to avoid ARC//meltdown/potential fire when there is short and we get assurance fuse really blows. But what are the numbers are i need to aiming for? I dont mind and dont wanna compromise safety at all, so if i wouldnt know i might be thinking going for smth bulletproof and choose T class with high rating, but they are more expensive compare to MRBF, so what IC rating would be need and how can i find out?

3, I want to use BlueSeaSafetyHub 150A it uses MIDI and ATO blade fuses for power distribution. Now lets say i got short on one of MIDI DC fuse circuit. What would happend here? Would there be high current going throught battery fuse to midi fuse and blow them in what sequence? do you need to consider here how fast each fuse acts - what would be good scenario - to blow midi first rather than battery fuse, therefore i suppose its needed that midi fuses act faster than MRBF or Tclass fuses and i then suppose MRBF/T class are slow acting fuses or is it wrong way round that T class/MRBF will be faster blown and will safe all from damage(i think this one is correct).

4, And lastly how the wire/circuit busbars cope with extreme amps - say i got this safetyhub 150 or any wire?

Now enought about fuses.

I got other question related to earthing in RV(my case is caravan)
How i simply understand earthing is prevention electric shock in case of fault on appliances with metalic cover, where life wire would get to the metalic case of appliances by fault.
I noticed on some pages and friend of mine told me that battery negative must be connected to chassis. Also what i understand that you should take grounding cable from appliances(or inverter) and connect to chassis or you can led all grounding cable to busbar and connect to chassis. Now i dont understand what is logic behind connection to chassis - i though that it is about taking current from fault place to negative of the battery, but why do you need to use chassis for it and cannot use negative cable?

I suppose grounding cable must match cable size of positive cable in circuit.

Please help me to correct and throw some light on what i just stated, i just cannot see smth and understand.

Couple of things - do solar panels need ground? i saw between solar panels(i got series 3*100W) and SCC someone has fuse there, i wonder why -where is danger of running higher current from solar array? only thing case i can think of is parralel connection of panels, but in series i dont get it.

Also how static electricity can cause problems in vehicle and how serious this can be and what needs to be done if so - only way i can think about this is that outside caravan shell should be grounded to chasis to prevent electricity getting anywhere inside, but if someone can say more about this i would be happy and ready to listen.

Sorry i am beginner who wants to understand whats happening and act sensible and therefore i just using very basic common language, me not technician.

 

[gblcia]

One more thing about grounding have Victron Sun Inverter - desc. in manual is:

The AC output is isolated from the DC input and the chassis. Local regulations may require a true neutral, In this case one of the AC output wire must be connected to chassis, and the chassis must be connected to a reliable ground. Please note that a true neutral is needed to ensure correct operation of an earth leakage circtuit breaker.

What does this actually mean...try to think but cannot makes sense out of this...

 

[Pappion]

LiFePO4 Battery BMS has multiple layers of over current shut down. Accuracy vs speed = Limit vs Noise Immunity trade offs. All depends on the Power FETs turning off. FET failure mode is a short, ie can't turn off. More likely to fail due to high current surge.
Use a Class T or better fuse rated for 20K Amps Interruption. Lesser fuses can sustain a DC arc after being blown.
Your branch circuit wiring likely has too much resistance to hit 20K amps at 12v (0.0006 ohms)

 

[Pappion]

A ground is not needed for a GFCI breaker to work. A loss of current, a 5ma unbalance, between hot and neutral will trip it. The assumption is that current is going thru you to ground. Less likely, but valid, to another hot or neutral.
You are also talking about Bonding Neutral to Ground. Wow big deep subject and many discussion on this forum. I will try to keep it simple and useful, but not accurate for every situation. Typically its bonded at the source or house power panel. Multiple sources in an RV is confusing. An Inverter is a source and when running will bond thru an internal relay (unless its cheap). You should be using a Transfer switch to choose one source and isolate from the others, some inverters/converters have this built in. Having two bonds is a big no no, you don't want current running thru the ground wire, it's there for safety. I have heard stories of RV power pedestals shutting down due to ground wire currents.

 

[Pappion]

Solar panels do not need a ground. To late to require it. Many SCC use cheaper robust NMOS power fets on the negative wire, potentially leaving high negative voltage on the wire. The positive wire passes thru (Positive Ground) to battery+. Others use PMOS fets and are Negative Ground.
Solar Panel Inline MC4 fuses should be used if the are more than 2 parallel stings or panels. Fuses should have high enough DCV rating.

 

[gblcia]

willl get T class, but now if i get 200A -> say my battery has peak discharge 400A, contiouns 200A. Say there is care of using inverter and some other shit at once, so i get over 200A...What T will do? about to have all on 4/0 cable -> read that its 230A continous, so what fuse to use here - 200A but dont wanna blow it just by having some surge....!"??!?!?

 

[gblcia]

about grounding inverter, i dont still understand what you wrote, i am too much caveman sounds too much like alien lingo here 4 me

 

[gblcia]

Solar panels do not need a ground. To late to require it. Many SCC use cheaper robust NMOS power fets on the negative wire, potentially leaving high negative voltage on the wire. The positive wire passes thru (Positive Ground) to battery+. Others use PMOS fets and are Negative Ground.
Solar Panel Inline MC4 fuses should be used if the are more than 2 parallel stings or panels. Fuses should have high enough DCV rating.

A ground is not needed for a GFCI breaker to work. A loss of current, a 5ma unbalance, between hot and neutral will trip it. The assumption is that current is going thru you to ground. Less likely, but valid, to another hot or neutral.
You are also talking about Bonding Neutral to Ground. Wow big deep subject and many discussion on this forum. I will try to keep it simple and useful, but not accurate for every situation. Typically its bonded at the source or house power panel. Multiple sources in an RV is confusing. An Inverter is a source and when running will bond thru an internal relay (unless its cheap). You should be using a Transfer switch to choose one source and isolate from the others, some inverters/converters have this built in. Having two bonds is a big no no, you don't want current running thru the ground wire, it's there for safety. I have heard stories of RV power pedestals shutting down due to ground wire currents.

willl get T class, but now if i get 200A -> say my battery has peak discharge 400A, contiouns 200A. Say there is care of using inverter and some other shit at once, so i get over 200A...What T will do? about to have all on 4/0 cable -> read that its 230A continous, so what fuse to use here - 200A but dont wanna blow it just by having some surge....!"??!?!?

 

[gblcia]

A ground is not needed for a GFCI breaker to work. A loss of current, a 5ma unbalance, between hot and neutral will trip it. The assumption is that current is going thru you to ground. Less likely, but valid, to another hot or neutral.
You are also talking about Bonding Neutral to Ground. Wow big deep subject and many discussion on this forum. I will try to keep it simple and useful, but not accurate for every situation. Typically its bonded at the source or house power panel. Multiple sources in an RV is confusing. An Inverter is a source and when running will bond thru an internal relay (unless its cheap). You should be using a Transfer switch to choose one source and isolate from the others, some inverters/converters have this built in. Having two bonds is a big no no, you don't want current running thru the ground wire, it's there for safety. I have heard stories of RV power pedestals shutting down due to ground wire currents.

about grounding inverter, i dont still understand what you wrote, i am too much caveman sounds too much like alien lingo here 4 me

 

[Pappion]

willl get T class, but now if i get 200A -> say my battery has peak discharge 400A, contiouns 200A. Say there is care of using inverter and some other shit at once, so i get over 200A...What T will do? about to have all on 4/0 cable -> read that its 230A continous, so what fuse to use here - 200A but dont wanna blow it just by having some surge....!"??!?!?

Be careful with sizing, you don't want Nuisance Blows at Class T prices. Fuse should be for catastrophic failure and prevent fires from red hot wires.
Conventional wisdom is fuse should be 1.33x Max Current for large and 1.5x for smaller current fuses. They should also be sized to protect the wire. Class T 400A will protect 4/0 single wire, downgrade to 300A for bundled wire, downgrade to 250A for engine compartment. The theme here is how easily can the wire shed the heat. Fuses can take time to blow at or near it's rating.
Blue Sea fuse and wire charts