Fuses and circuit breakers for LiFePO4

[Sailing Paul]

I have thought of a way to simplify the shore charging. I will use a cheap AC countdown timer plug. Calculate the time required to take SOC up to 80%, then round down the time to the nearest hour. That way I will not forget to turn off at the right time and I can leave it on when I leave the boat.

Then next time on the boat, charge up to 100% before we leave.

A suitable timer: https://www.brennenstuhl.co.uk/en-GB...-2013-white-gb

[ggray]

Originally Posted by tanglewood

The various standards (ABYC and ISO draft) require both a fuse/breaker and a manual disconnect switch. This is above and beyond any BMS.

Where does the manual switch need to be?

I am installing two 300 Ahr LFP batteries in parallel. Fuse on each positive post, cables then to a power post, and then to a switch.

Does code require switches to isolate each battery as well? Presumably only for emergencies.

[CaptainRivet]

Originally Posted by ggray

Where does the manual switch need to be?

I am installing two 300 Ahr LFP batteries in parallel. Fuse on each positive post, cables then to a power post, and then to a switch.

Does code require switches to isolate each battery as well? Presumably only for emergencies.

To isolate the batteries one by one for maintenance, adjustments, emergencies, tests.
For parallel batteries you need class-T superfast acting. These are your battery protection fuses.

Install fuse-switch-powerpost
From powerpost i assume a main battery cable goes then to main busbar, the cable need also a cable fuse.

[CharlieJ]

ggray #62:
Neither ABYC nor ISO lithium battery standards require switches in the paralleled battery’s individual conductors from the battery B+ terminal and the bank B+ collection point.

The ISO does state:

Multiple disconnect switches are recommended to prevent a dead ship in the event of a LVC/HVC occurrence

[more]

Originally Posted by CaptainRivet

To isolate the batteries one by one for maintenance, adjustments, emergencies, tests.
For parallel batteries you need class-T superfast acting. These are your battery protection fuses.

Install fuse-switch-powerpost
From powerpost i assume a main battery cable goes then to main busbar, the cable need also a cable fuse.

start battery -(or+) to main switch of start battery to engine block- + to start motor of engine.

main baterry + to main fuse from fuse to busbar-from busbar to switch fuse on board

- pol to main switch from main switch to - busbar

on older boat i see oposit. color cable different from contry of manufacture.
t-fuse dont exist in EU and t-fuse dont have eu certificate. also why pay 100$ for fuse when some or better fuse can pay 5-6$
European electronic fuses come in glass and ceramic and in the following sizes: 5x20mm, 5x25mm, 5x30mm, 6.3x32mm, 250V and 500V
Diazed bottle fuses available in 5 sizes: ND-E 16 (D1), DII-E 27, DIII-E 33, DIV-R 1.25, DV-R2
Neozed bottle fuses available in 3 sizes: D01, D02, D03
Knife blade fuses, stud mount: NH000, NHC00, NH00, NH0, NH1, NH2, NH3, NH4
European fuse speeds: gL, gG, gI, gF, gR, aR, aM
Cylindrical fuse sizes: 8X32mm, 10X38mm, 14X51mm, 22X58mm

[ggray]

Thank you Captain Rivet, and CharlieJ.


Thanks More; when you say "from busbar to switch fuse on board" do you mean the switch/fuse on the panel? And what is pol?

It's late and perhaps I'm not thinking clearly.

Originally Posted by more

<snip>

main baterry + to main fuse from fuse to busbar-from busbar to switch fuse on board

- pol to main switch from main switch to - busbar

[mcarthur]

Originally Posted by hjohnson

When I’m away from the boat for an extended period, I use the Cerbo to override the BMS’s voltage target and let my system bus drift down to 13.3V, which is about 60% charge. Then, the day before I head out I remote in again and turn the override off, letting the BMS bring itself back up to 100%. Even if my shore power gets disconnected, I have about a week to get to the boat before I hit LVD.

What Cerbo setting do you use? I have the BMS connected and it's the controller, but I like your idea for remote use.

Originally Posted by hjohnson

... Not only do I know my system voltage from an app and widget on my iPhone, I know the current SoC, how much liquid is in my tanks (fuel, potable water, blackwater) and bilge, as well as the temperature/humidity in the cabin. I’ve also got it rigged to tell me if and how often my bilge pump has operated.

Even more interested - how have you got the bilge pump indicator AND operation count coming through? I'm trying to get mine onto the N2K bus, but counting the operations has me stymied (if you're using nodered and signalk on the cerbo, I'm really, really keen to learn how!)...

[cram]

Originally Posted by Sailing Paul

Hi, I am planning to add a LiFePO4 battery to my boat to run domestic and Nav systems. There are no heavy loads such as inverters, thrusters or windlass. Max draw will be the fridge and autopilot. I was thinking of using a 200A MRBF fuse at the battery, then a 40-50A circuit breaker. I am planning on using 6mm cable to connect to the domestic circuit, good for 50A.

The BMS is rated at 200A, but I would like to have a backup, hence the MRBF fuse.


Will this be sufficient? What do other people do with fuses on LiFePO4?

No.

Your fuse protects the wiring, not the battery. Thus you can't have a 200a fuse with 6mm wire. Your main battery run would be considered a critical load, thus planned for 3% voltage drop or less. Depending on the run length, 6mm would probably be rated for a 30A load, fused at 40 to 60A, depending on fuse type. You most likely need thicker wire to your main DC bus bar.

Why can't you use the existing wiring and fuses?

[cram]

Originally Posted by Sailing Paul

I have thought of a way to simplify the shore charging. I will use a cheap AC countdown timer plug. Calculate the time required to take SOC up to 80%, then round down the time to the nearest hour. That way I will not forget to turn off at the right time and I can leave it on when I leave the boat.

Then next time on the boat, charge up to 100% before we leave.

A suitable timer: https://www.brennenstuhl.co.uk/en-GB...-2013-white-gb

But then if you leave the boat and the batteries are drawn down, say by a bilge pump, they won't be recharged. Just charge them to 100% and let them float at 13.6V.

If you want to under charge your batteries and don't mind your bms not equalizing the cells, set your charger to 14 V bulk and 13.6 float, triggered to recharge at 13.4V. You typically need to maintain 14.4 v for 30 mins to Equalize the cells, which won't happen with your timer either. Chargers need tod be hard wired, not plugged into a socket.

[cram]

Originally Posted by more

ussualy all european boat producer use nh 50ka fuse., you dont need nothing also betwen battery you dont need fuse by law.i dont reed certification books,becouse this is not my job .but if boat producer dont use fuse betven batery i also dont use. iaam not sure for big disconector but for off grid use i like use MCCB Moulded Case Circuit Breaker Battery with termal protection.also this is ussualy 25ka

I had a European boat. It was full of class T fuses protecting key systems and wiring, including the house battery and inverter.

https://www.svb24.com/en/t-fuses.html

For an off grid house if there's a fire, you walk away. You don't have that option on a boat which is why the design specifications for boats are more stringent.

[hjohnson]

Originally Posted by mcarthur

What Cerbo setting do you use? I have the BMS connected and it's the controller, but I like your idea for remote use.

In the menus on the Cerbo, there’s a section for DVCC override. I set the override voltage to 13.5v or so. The day before I leave, I log in and turn off the override. I can’t look at it now (boat is temporarily in the US, And my LTE router won’t roam). It’s a bit of a pain to turn on because the override defaults to 56V or so, and you have to dial it down by pressing up/down arrows. But it works.

Even more interested - how have you got the bilge pump indicator AND operation count coming through? I'm trying to get mine onto the N2K bus, but counting the operations has me stymied (if you're using nodered and signalk on the cerbo, I'm really, really keen to learn how!)...

So for the bilge sump measurement, we have a Tank140 for our other tanks, and had a spare channel on it. Picked up a cheap 4ma-20ma submersible pressure sensor and tossed it into the bottom of the bilge sump. It directly measures the water pressure, which the Cerbo translates into a volume. When we were washing the bilge out last, we let the water fill up to the max we’re comfortable with, called that 80L, and calibrated it that way.

For the bilge counter, a digital input on the cerbo is connected to the circuit that turns in the bilge indicator light on the bilge switch and the Cerbo just counts the actuations. I’m probably going to swap to doing things in node red, as the built in hysteresis on our automatic pump isn’t enough to deal with the length of hose and the small size of the sump.