Cable sizes and fuses 12V van conversion

[Patotofarmer]

Hi,

I'm currently selecting the components for my electrical solar powered system in my Peugeot Boxer van conversion.
And I need some help with the cable and fuse selection, because different calculators give me vastly different results.

These are the parts I already selected and bought (solar panels will be figured out later):

• 4 x LiTime 12V 100Ah LiFePO4 battery
• 250A battery switch
• Renogy 500A shunt
• Blue sea MRBF fuse block (5196)
• Giandel 2000W 230V inverter
• Renogy 50A DC-DC charger with MPPT
• Generic blade fuse holder

Since the inverter is 2000W I calculated that it could pull up to 167A. With a 25% safety that is 200A.
Do I need to use 70mm² wire and a 200A fuse for the connection from the fuse block to the inverter?

I guesstimated a total draw of max 250A with the other 12V loads (lights, fridge, heater, ...). Is that realistic?
Does that mean I need to put a 250A fuse and use 3/0 wire to connect the batteries together and from the batteries to the fuse block, since that's the smallest wire size I can use a 250A fuse with according to this chart?

http://assets.bluesea.com/files/resources/newsletter/images/Choose_the_Fuse_Amperage.jpg

Can I get away with smaller cable sizes because they are all very short runs (30-50cm/ 1-2ft max) or is the wire size really dictated by the fuses I need to use to keep my cables from melting?

Also will a 250A Busbar do to connect my negatives?

Cheers!

 

[12VoltInstalls]

Do not copy my mess, but note the terminal bars / busbars
That is how you should connect your batteries to each other using equal-length cables.

Does that mean I need to put a 250A fuse and use 3/0 wire to connect the batteries together and from the batteries to the fuse block, since that's the smallest wire size I can use a 250A fuse with according to this chart?

Use a Class T fuse at each battery pos(+), and connect from there to the busbars.
Then you can use 150A cabling from batteries to terminal block: easier to manipulate, and less expensive.

SCC outputs (you didn’t mention?) should connect to busbars, DC2DC charger connects to the busbars, 12V blusea fusebox connects to the busbars…and the 2000W inverter feeds from the busbars.
All with appropriate sized wiring and fuses rated at or less than the wire ratings.

“I” would use 2/0 to your inverter- wire will never get hot- and a 175A or 200A ANL fuse on the pos(+) to the inverter.
(my 2kW inverter has a 200A ANL because my table saw can sometimes blow a 160A ANL).
I need to install my upgrade 3000W 12V QZRELB inverter- that will use 250A ANL’s if the loads blow the 200A fuses; I’ll change to a pair of 1AWG on each (+) and (-) input with 150A fuses if necessary.

Once you’re at 2500W+ 12V systems are in the gray zone imho, but it can work.

Anyways I say all that to drive home the point that the busbars add messiness, but they also add ease of servicing and simplify fusing and connection of everything. Not installed in my pic are four 250A marine on/off battery switches between battery(+) and busbars that simplify changing or testing batteries safely.

Can I get away with smaller cable sizes because they are all very short runs (30-50cm/ 1-2ft max) or is the wire size really dictated by the fuses I need to use to keep my cables from melting?

Yes, but no. Note the bluesea chart has cable run length parameters.
Just use the right gage cables. It won’t be as expensive to do the battery cables because you are joining them at a busbar, so you can cable the batteries for the 100A output capacity (and fuse accordingly) and not 200- or 300A.

Do I need to use 70mm² wire and a 200A fuse for the connection from the fuse block to the inverter

A bluesea ATC fuse box iirc is rated 100A.
In my case, my 12V loads cumulative would be ~17A max. I used an 8AWG feed for (-) and (+) and fused that at 30A. It’s never blown. I fused the 14ga to a waterpump at 15A, and everything else is 16ga, so they are fused at 10A.
The MRBF is a bit expensive and unnecessary and has limited usefulness, imho. Never mind that it doesn’t protect more than a single cable.

is the wire size really dictated by the fuses I need to use to keep my cables from melting

The wire size is dictated by the expected load, and for your kind of situation I usually oversize, but fuse as if it were the standard gage wire.
Use the cable size for the load requirement, use the right fuse to protect the wire, and use excellent crimps on the terminals.

 

[Patotofarmer]

Use a Class T fuse at each battery pos(+), and connect from there to the busbars.
Then you can use 150A cabling from batteries to terminal block: easier to manipulate, and less expensive.

Would that mean I need a + Busbar with 4 connections for the batteries on top of the 3 for the DC-DC charger, inverter and blade fuse box (so a total of 7)?
Or is it ok to put multiple cables on one connection?

The MRBF is a bit expensive and unnecessary and has limited usefulness, imho. Never mind that it doesn’t protect more than a single cable.

In Belgium it seems MRBF fuses (including the holders) are quite a bit cheaper than Class T fuses. Why do you prefer class T fuses from the batteries to the Busbar?

 

[Supervstech]

Do not copy my mess, but note the terminal bars / busbarsView attachment 261959
That is how you should connect your batteries to each other using equal-length cables.

Use a Class T fuse at each battery pos(+), and connect from there to the busbars.
Then you can use 150A cabling from batteries to terminal block: easier to manipulate, and less expensive.

SCC outputs (you didn’t mention?) should connect to busbars, DC2DC charger connects to the busbars, 12V blusea fusebox connects to the busbars…and the 2000W inverter feeds from the busbars.
All with appropriate sized wiring and fuses rated at or less than the wire ratings.

“I” would use 2/0 to your inverter- wire will never get hot- and a 175A or 200A ANL fuse on the pos(+) to the inverter.
(my 2kW inverter has a 200A ANL because my table saw can sometimes blow a 160A ANL).
I need to install my upgrade 3000W 12V QZRELB inverter- that will use 250A ANL’s if the loads blow the 200A fuses; I’ll change to a pair of 1AWG on each (+) and (-) input with 150A fuses if necessary.

Once you’re at 2500W+ 12V systems are in the gray zone imho, but it can work.

Anyways I say all that to drive home the point that the busbars add messiness, but they also add ease of servicing and simplify fusing and connection of everything. Not installed in my pic are four 250A marine on/off battery switches between battery(+) and busbars that simplify changing or testing batteries safely.

Yes, but no. Note the bluesea chart has cable run length parameters.
Just use the right gage cables. It won’t be as expensive to do the battery cables because you are joining them at a busbar, so you can cable the batteries for the 100A output capacity (and fuse accordingly) and not 200- or 300A.

A bluesea ATC fuse box iirc is rated 100A.
In my case, my 12V loads cumulative would be ~17A max. I used an 8AWG feed for (-) and (+) and fused that at 30A. It’s never blown. I fused the 14ga to a waterpump at 15A, and everything else is 16ga, so they are fused at 10A.
The MRBF is a bit expensive and unnecessary and has limited usefulness, imho. Never mind that it doesn’t protect more than a single cable.

The wire size is dictated by the expected load, and for your kind of situation I usually oversize, but fuse as if it were the standard gage wire.
Use the cable size for the load requirement, use the right fuse to protect the wire, and use excellent crimps on the terminals.

But avoid those busbars.
They are brass and will waste watts, and heat up under loads.

 

[mikefitz]

to use 70mm² wire and a 200A fuse for the connection from the fuse block to the inverter?

50mm2 or 70mm2 cable, fuse at 250 amps.

connect the batteries together and from the batteries to the fuse

Same cable as used for the inverter, 50mm2 multi strand automotive/ marine grade cable is rated for 340 amps.

4 x LiTime 12V 100Ah LiFePO4 battery

To protect each battery fit a Bluesea MRBF fuse in Blue sea holder directly or as close as possible to each battery positive , suggest a 150 amp fuse. These are 'last resort' protection if a battery fault occurs. If you need isolation switch, connect all the batteries, after the individual fuse, to a paralleling bussbar, then isolator, then distribution buss bar.
From the output of the secondary bussbar feed inverter, Mppt, DCfuse block via a suitable fuse, inverter 250A, DC fuse block, 50A, Mppt, 70A. Example,



Example.

Use suitable rated buss bars for the battery parallel connections, look for copper , not brass, and studs they accept 8mm terminations, example,

Blue Sea Systems 2127 MaxiBus 250A BusBar - 4x 5/16

Blue Sea Systems 2127 250A busbar with 4 studs for installations up to 48V DC. Stainless hardware with optional cover available.

www.12voltplanet.co.uk

 

[12VoltInstalls]

avoid those busbars.
They are brass and will waste watts, and heat up under loads

I understand that you are technically correct and I believe it’s best case to go copper.

Nevertheless, with lots of respect for you, I’ve been using those successfully for over three years now; I know they’re not pure copper and not ‘ideal.’ on my 12V, 5kWh batts, 2kW inverter system I have felt them warming a couple of times (using table saw) but they never have gotten hot, nowhere near too hot to touch, maybe 100*F-ish

Whatever losses I may have are not noticeable in practical usage. Even with only 2000W of panels. Several years ago I ohmed the cables/circuits and laboriously (for me anyways) calculated the loss over the circuits through those busbars (and my crimps).
The percentage of loss was decimal.

It works.

 

[12VoltInstalls]

MRBF fuses (including the holders) are quite a bit cheaper than Class T fuses. Why do you prefer class T fuses from the batteries to the Busbar?

Because they are there as an insurance policy. My batteries are BMS-limited to 100A continuous discharge (200A for 10 seconds?) so in theory they won’t exceed that. BUT if something unexpected happens with the BMS’s, LiFePo batteries could discharge 10,000 amps immediately.
Class T are rated to 20kA. Sure, they are more expensive, but the cost a small fraction of what replacing everything I own would cost.
It’s an insurance policy you can’t buy from an insurance company: insurance pays out for losses, fuses usually avoid losses.

 

[Pappion]

In Europe it may be easier to find LET and LMT fuses , which have better AIC ratings than Class-T.
British standard fuses
Good luck finding fuse holders for them. Size varies by amperage.

 

[Patotofarmer]

In Europe it may be easier to find LET and LMT fuses , which have better AIC ratings than Class-T.

I've also come across NH fuses.
They're widely available here, it's easy to find fuse holders and a lot cheaper than class T fuses.
Would that be a valid alternative?

3NA3836 | Siemens 160A NH Fuse, NH00, 500V ac | RS

benl.rs-online.com

 

[12VoltInstalls]

I've also come across NH fuses.
They're widely available here, it's easy to find fuse holders and a lot cheaper than class T fuses.
Would that be a valid alternative?

3NA3836 | Siemens 160A NH Fuse, NH00, 500V ac | RS

benl.rs-online.com

I cannot answer your question.

However, I will say that if a Class T (or if LET or LMT fuses that I’m also unfamiliar with) meet the spec for DC interrupt without sustaining an arc then it doesn’t really matter if another fuse (NH) is less costly to purchase. Its cost is irrelevant because it will never blow in normal use- never. It is only there to be a measure of fire protection.
Why? Because all your devices / services will be properly fused for these item’s amp load and wire sizes required in consideration of the maximum current load they can present. For example, if you ‘overdrive’ the inverter, your inverter fuse (a lesser expensive type like I mentioned) will blow: in your situation the sum output amps divided amongst the batteries will be less than Class T fuse rating of each battery: in normal use the Class T’s will never blow. So it’s a one-time cost.

However! If your batteries have some unforeseen BMS failure (cheap batteries, like 95% of this type battery we buy) or a mouse chew, or an accidental chafing of a cable, causes a catastrophic failure; the possibility of a 12,000A sudden discharge will be successfully stopped from delivering a current that will make your cables a giant ignitor. Of course ‘we’ can’t predict or stop something catastrophic inside of the batteries, but that is unlikely if we control for adverse events outside of the batteries.

That is my opinion on why to use Class T on the pos(+) terminal of LiFePo batteries.
The cost of Class T’s is a minuscule percentage of the cost of replacing a vehicle or housing or boat or camp.

 

[Dooug]

MRBFs AIC capacity is:
10000A @ 14V DC
5000A @ 32V DC
2000A @ 58V DC

Id run them on a 12v system with 100 AH batteries. Might reconsider on the larger 12v batteries, but if you running on big one then you only need one fuse, class t makes sense. for 4 100ah batteries id just use 4 mrbfs.

 

[mikefitz]

Would that be a valid alternative?

Yes, the fuse is fine, 25kA, 250v DC, the problem may be incorporating the fuse holder in the set up.

 

[12VoltInstalls]

4 100ah batteries id just use 4 mrbfs.

Your choice. I just prefer the security of worst-case protection.

 

[Patotofarmer]

One more maybe stupid question.
But can I connect 2 wires to one single pole on the busbar?
Since I have 4 batteries, I need to connect 5 cables to the battery busbar. So can I get away with a 4pole busbar where I connect 2 cables to 1 pole or do I need to get a 6 pole one (5 pole busbars don't seem to be a thing)?
EDIT: I came across these Daiertek busbars on aliexpress. They claim to be copper and seem decent quality. Does anyone have any experience with these?

300a 4 Terminal Studs Busbar | Positive Negative Bus 300a | Bus Bar Distribution Block - Fuses - Aliexpress

Smarter Shopping, Better Living! Aliexpress.com

nl.aliexpress.com

 

[mikefitz]

connect 2 wires to one single pole on the busbar?

Yes, it's no problem for electrical conductivity. Use for the battery and inverter cables.

 

[robbob2112]

Use the aR rated NH fuses, they have a time current curve similar to the class T fuses. The NH fuses come from 00 through 03 sizes. The nh03 is a lot larger than the nh00 of the same amperage. The larger fuse bodies have higher AIC.

 

[J.H.]

5 pole busbars don't seem to be a thing)?

Marinco 600;amp 5/post with excellent cover.. I have several for busbars. Amazon ..about 100 bucks…could not ask for more

 

[12VoltInstalls]

But can I connect 2 wires to one single pole on the busbar?
Since I have 4 batteries

Yes
I have batt A neg on the bottom and batt A pos on top. That way they are “the same” resistance.
The inverter sits right on the busbar, an SCC can go on top of that. (SCC is likely far less amps)
I am picky