Lithium and fuses

[wazza]

I wish I was an electrical engineer
I’m confused with the electrical system that I’m designing on the boat. YouTube is good but not specific enough for my little brain
Going over to lithium from AGM for the house.
4 x 100ah batteries in parallel. 12v & 400amps.

I’m going fuse the 40ah DC-DC charger, 60a before & 50a after. But after that is where my head blows with too many choices/suggestions.

Should I fuse every battery, if so how much.
160a against short circuit or 50a against an overload?
Should I then fuse after the whole battery bank before the busbars? If so what size? 10 times the amperage?!
Do I need to fuse an inverter from the battery.?
Where else should I fuse…

It’s the fusing that is con fusing(dad joke) and the electrical terminology.

Any help would be greatly appreciated.

//Warren

 

[lustyd]

Just remember that for the most part you’re fusing the wire not the device. Your dc dc charger power is irrelevant, what cable are you using?
One exception to this is the big fuse for the battery.

Also worth mentioning that a single 400Ah lithium is better than 4 x 100Ah. If putting 4 in series check with the manufacturer that that is supported as it’s often not.

 

[Alex_Blackwood]

Just remember that for the most part you’re fusing the wire not the device. Your dc dc charger power is irrelevant, what cable are you using?
One exception to this is the big fuse for the battery.

Also worth mentioning that a single 400Ah lithium is better than 4 x 100Ah. If putting 4 in series check with the manufacturer that that is supported as it’s often not.

Series, where did that come from. I think that he should consult a professional instead of relying on some of the dubious and confusing advice he is likely to get on here. Not saying there isn't good advice. But!

 

[wazza]

Just remember that for the most part you’re fusing the wire not the device. Your dc dc charger power is irrelevant, what cable are you using?
One exception to this is the big fuse for the battery.

Also worth mentioning that a single 400Ah lithium is better than 4 x 100Ah. If putting 4 in series check with the manufacturer that that is supported as it’s often not.

Wire size was the recommended 16mm2 then for the longer run after the DC/DC 25mm2.
I’m putting them in parallel not series.

 

[lustyd]

Series, where did that come from. I think that he should consult a professional instead of relying on some of the dubious a confusing advice he is likely to get on here. Not saying there isn't good advice. But!

Sorry parallel, it’s early!

 

[PaulRainbow]

Wire size was the recommended 16mm2 then for the longer run after the DC/DC 25mm2.
I’m putting them in parallel not series.

Distance from the DC-DC charger to each battery ?

If you fit 4x100Ah batteries you'll need 4 x fuses and 4 x isolator switches. Why not fit just one battery ?

400Ah of Lithium is a lot, what boat do you have and what electrical equipment do you have ?

What charging sources do you have ?

 

[geem]

I wish I was an electrical engineer
I’m confused with the electrical system that I’m designing on the boat. YouTube is good but not specific enough for my little brain
Going over to lithium from AGM for the house.
4 x 100ah batteries in parallel. 12v & 400amps.

I’m going fuse the 40ah DC-DC charger, 60a before & 50a after. But after that is where my head blows with too many choices/suggestions.

Should I fuse every battery, if so how much.
160a against short circuit or 50a against an overload?
Should I then fuse after the whole battery bank before the busbars? If so what size? 10 times the amperage?!
Do I need to fuse an inverter from the battery.?
Where else should I fuse…

It’s the fusing that is con fusing(dad joke) and the electrical terminology.

Any help would be greatly appreciated.

//Warren

Fuse each battery with a NH fuse as close to the battery as possible. You could use a fuse with a lower AIC than NH fuses since your batteries are only 100Ah, but that up to you. 160A fuses would work. Also add an isolator for each battery after the fuse. I used a breaker for the inverter rather than a fuse. This will also allow you to isolate the inverter.

 

[lustyd]

since your batteries are only 100Ah,

The capacity of the battery is entirely unrelated to fuse sizing. Whether 100 or 400 the current delivery capability might be identical and will probably be more related to BMS than cells.

400Ah of Lithium is a lot

Depends on the boat. We have 300Ah in a single battery and I’m considering doubling that as well be spending a lot of time on board disconnected. Starlink uses a lot of juice unfortunately so power usage is higher than it used to be.

 

[PaulRainbow]

Depends on the boat. We have 300Ah in a single battery and I’m considering doubling that as well be spending a lot of time on board disconnected. Starlink uses a lot of juice unfortunately so power usage is higher than it used to be.

Which is why i said "400Ah of Lithium is a lot, what boat do you have and what electrical equipment do you have ?"

 

[wazza]

Distance from the DC-DC charger to each battery ?

If you fit 4x100Ah batteries you'll need 4 x fuses and 4 x isolator switches. Why not fit just one battery ?

400Ah of Lithium is a lot, what boat do you have and what electrical equipment do you have ?

What charging sources do you have ?

Distance around 3m no more.

At the moment the 12v system “normal” for a 34 foot sailing boat plus a freezer. More when I head off grid. Have a 3000w inverter for charging electric outboard.

Charging source alternator solar and 240 just now.

 

[wazza]

Fuse each battery with a NH fuse as close to the battery as possible. You could use a fuse with a lower AIC than NH fuses since your batteries are only 100Ah, but that up to you. 160A fuses would work. Also add an isolator for each battery after the fuse. I used a breaker for the inverter rather than a fuse. This will also allow you to isolate the inverter.

I was going to use MRBF, is that not good enough?
I thought of a fuse breaker instead of an isolator for the inverter, but didn’t know what size. If I use just a breaker is no fusing necessary.?

 

[lustyd]

In that case I’d consider 2x300Ah rather than 4x100 if the budget allows. Be warned that a 50A charger will take 10-12 hours to charge it though

 

[wazza]

In addition to the help I receive on here I will most likely consult a professional to go over my installation. Better to be safe than sorry. But I want a ground to work on.

 

[lustyd]

Hopefully you’re aware, Paul is a pro so if you listen to any of us, listen to him!

 

[PaulRainbow]

Distance around 3m no more.

DC-DC charger wiring only needs to be 10mm, with 60A fuses close to each battery. The Lithium end needs an NH fuse.

At the moment the 12v system “normal” for a 34 foot sailing boat plus a freezer. More when I head off grid.

No such thing as "normal" on a boat. Without knowing what you have, or will have, it's not possible to comment on batter sizes.

Have a 3000w inverter for charging electric outboard.

Very inefficient method for charging an outboard battery. Most outboards can be charged with a "special" 12V charger.

Charging source alternator solar and 240 just now.

How much solar ?

 

[wazza]

In that case I’d consider 2x300Ah rather than 4x100 if the budget allows. Be warned that a 50A charger will take 10-12 hours to charge it though

Too late. I have the batteries now.
To charge to full yes but I’m assuming I’ll have a trickle charge through the solar panels.

 

[wazza]

DC-DC charger wiring only needs to be 10mm, with 60A fuses close to each battery. The Lithium end needs an NH fuse.

No such thing as "normal" on a boat. Without knowing what you have, or will have, it's not possible to comment on batter sizes.

Very inefficient method for charging an outboard battery. Most outboards can be charged with a "special" 12V charger.

How much solar ?

Thank you.

The battery sizes are what they are. 4 x 100ah.

I should look into a special 12v charger for the outboard. I didn’t think there was one. That said it would have drained my AGMs.

At the moment, not enough. 400w.

 

[wazza]

Hopefully you’re aware, Paul is a pro so if you listen to any of us, listen to him!

Didn’t know, do now, thank you very much.

 

[wazza]

If you fit 4x100Ah batteries you'll need 4 x fuses and 4 x isolator switches. Why not fit just one battery ?

Love me love I’m thick but I was under the assumption of 4 x 100ah batteries run in parallel were the same as a single 400ah battery.

 

[Sea Change]

MRBF for individual batteries are good. You may be able to mount them directly on the battery terminals, or do what I did and fit one if these:
Blue Sea Systems 5196 MRBF Surface Mount 3-Way Fuse Block - Common Power Input

The AIC rating on the MRBF isn't really high enough for lithium so I have also got a class T master fuse.

It's not the cheapest way to go about things but it's what I was happy with.