Lithium battery upgrade charging question

[PaulRainbow]

So are you saying 150A is better? I have updated the planned layout to include isolator switches and fuses

View attachment 203657

What size cables ?
What engine ?
Any big domestic loads, like an inverter ?
Windlass ?
Bow thruster ?

 

[kevsbox]

What size cables ?
What engine ?
Any big domestic loads, like an inverter ?
Windlass ?
Bow thruster ?

Engine is a Beta 20 with a 40a alternator.

She has no big loads like those in your question but I will be adding an invertor in the spring to the lithium setup so we can charge my wife's breathing machine battery when mains is not available.

I believe the cable from the alternator to the current switch and the switch to starter battery is 240AM 35mm, I will not be onboard until Sat so could confirm then
The current cable from the existing house batteries to the switches is smaller, at present this powers lights (interior and exterior), instruments, VHF, phone chargers but as I said an inverter will be fitted in the spring.

In regard to the alternator to stater battery, fro what I read on the internet is that I should use a 50a to 60a fuse. Am I missing something here?


Kev

 

[PaulRainbow]

Engine is a Beta 20 with a 40a alternator.

She has no big loads like those in your question but I will be adding an invertor in the spring to the lithium setup so we can charge my wife's breathing machine battery when mains is not available.

I believe the cable from the alternator to the current switch and the switch to starter battery is 240AM 35mm, I will not be onboard until Sat so could confirm then
The current cable from the existing house batteries to the switches is smaller, at present this powers lights (interior and exterior), instruments, VHF, phone chargers but as I said an inverter will be fitted in the spring.

I would use 35mm cable from the batteries to the isolator switches, and from the engine isolator to the engine. both batteries with 200A fuses (NH or T class for the LFP). 35mm cable is rated at 240A, the 280Ah battery can safely deliver up to 280A, so with this setup you can fit up to a 2000W inverter, if you wanted to, connect the inverter straight to the isolator switch, with it's own fuse. From the domestic isolator you will want to use thinner cable, so fit an additional fuse close to the isolator, rated for that cable.

You will likely find you can start the engine from the LFP in an emergency, consider fitting a parallel switch for this.

In regard to the alternator to stater battery, fro what I read on the internet is that I should use a 50a to 60a fuse. Am I missing something here?


Kev

It's not common to fuse the alternator, all you need is a short length of 10mm cable from the alternator B+ to the battery cable terminal of the starter solenoid, just don't turn the isolator off with the engine running.

For the DC-DC charger use 10mm cable as long as the runs are less than 2m and fit 60A fuses, midi fuses are good here. Don't connect directly to the batteries, connect to the load terminals of the isolator switches.

 

[kevsbox]

I would use 35mm cable from the batteries to the isolator switches, and from the engine isolator to the engine. both batteries with 200A fuses (NH or T class for the LFP). 35mm cable is rated at 240A, the 280Ah battery can safely deliver up to 280A, so with this setup you can fit up to a 2000W inverter, if you wanted to, connect the inverter straight to the isolator switch, with it's own fuse. From the domestic isolator you will want to use thinner cable, so fit an additional fuse close to the isolator, rated for that cable.

You will likely find you can start the engine from the LFP in an emergency, consider fitting a parallel switch for this.

It's not common to fuse the alternator, all you need is a short length of 10mm cable from the alternator B+ to the battery cable terminal of the starter solenoid, just don't turn the isolator off with the engine running.

For the DC-DC charger use 10mm cable as long as the runs are less than 2m and fit 60A fuses, midi fuses are good here. Don't connect directly to the batteries, connect to the load terminals of the isolator switches.

Great info, many thanks

 

[billcole]

Thanks for the links, I am learning as I go along here.
For the fuses -
For the Lithium battery on the positive cable within 6" of battery using a MRBF fuse 150a.
For starter battery same location but 100a.
Does that sound correct?

Fogstar (and others too) do a fuseholder that fits right on top of the battery at the +ve terminal, which is a neat way of complying with the <6" requirement. Note that lithium batteries can supply truly huge currents, so you need a to use a fuse that is rated to interrupt thousands of amps in that location (class t or NH as Paul says above), lesser fuses might just turn into a molten, conductive puddle or something !