Lithium battery upgrade charging question

[kevsbox]

Hi All

I now have all the kit to start this conversion just one think I want to check before I go for it next weekend
This is the cable from the alternator


Which goes to the 1-2-both box here



The red cable on the left of this images goes to the starter battery so is it safe to connect these directly together so the alternator and starter battery are connect and then I use the Dc-Dc charger to charge the Lithium from the Starter?

 

[PaulRainbow]

You can't use a 1-2-both switch, the 2 batteries need to be kept separate. One switch for the engine battery, one for the domestics. The alternator charges the engine battery, the DC-DC charger charges the LFP.

Your original designs don't show any isolators or fuses.

 

[kevsbox]

You can't use a 1-2-both switch, the 2 batteries need to be kept separate. One switch for the engine battery, one for the domestics. The alternator charges the engine battery, the DC-DC charger charges the LFP.

Your original designs don't show any isolators or fuses.

True, isolators or fuses are not shown but not forgotten. I have been looking at this isolator - https://foxschandlery.com/products/e-c-smith-hella-battery-master-switch-isolator-3314


Has anyone got any thoughts on these of suggestions on something better?

 

[PaulRainbow]

True, isolators or fuses are not shown but not forgotten. I have been looking at this isolator - https://foxschandlery.com/products/e-c-smith-hella-battery-master-switch-isolator-3314
View attachment 203596

Has anyone got any thoughts on these of suggestions on something better?

Not especially good, only rated at 100A, go for something better, such as a BEP701 for example:

BEP 701 Battery Switch 275A ON/OFF (8-90010)

or

BEP Contour Panel Mounted Manual Battery Master Switch

What fuses do you have in mind ?

 

[Sea Change]

In place of a 1-2-off-both switch, I've used a pair of keyed isolators, with one key shared between them.

 

[kevsbox]

Not especially good, only rated at 100A, go for something better, such as a BEP701 for example:

BEP 701 Battery Switch 275A ON/OFF (8-90010)

or

BEP Contour Panel Mounted Manual Battery Master Switch

What fuses do you have in mind ?

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?

 

[lustyd]

In place of a 1-2-off-both switch, I've used a pair of keyed isolators, with one key shared between them.

How do you “both”? Usually the keys stay in when on, on the ones I’ve used.

 

[Sea Change]

How do you “both”? Usually the keys stay in when on, on the ones I’ve used.

That's the whole point, you can't. You have to turn off one bank, remove the key, and then turn on the other bank.
That's how I powered a selection of circuits from either the lead acid or lithium banks, without the two ever being in parallel.

 

[PaulRainbow]

That's the whole point, you can't. You have to turn off one bank, remove the key, and then turn on the other bank.
That's how I powered a selection of circuits from either the lead acid or lithium banks, without the two ever being in parallel.

That's no good for the OP, he wants one switch for the engine battery/engine and another for the domestic battery/loads.

 

[kevsbox]

That's no good for the OP, he wants one switch for the engine battery/engine and another for the domestic battery/loads.

I will be using 2 BEP 701 switches now

 

[lustyd]

That's the whole point, you can't.

fair enough, we kept the emergency parallel in place just in case, and have used it to start the engine a couple of times (long story, my fault).

 

[kevsbox]

Thanks for all the feedback, isolation switches on order so just fuses now,
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, any thoughts please?

 

[lustyd]

Thanks for all the feedback, isolation switches on order so just fuses now,
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, any thoughts please?

What cable is going to each?

 

[PaulRainbow]

Thanks for all the feedback, isolation switches on order so just fuses now,
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, any thoughts please?

The LFP fuse needs to be T class or NH

 

[Sea Change]

Thanks for all the feedback, isolation switches on order so just fuses now,
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, any thoughts please?

Maybe I'm not fully understanding, but is that 100A fuse between the battery and starter motor? If so it's almost certainly far too small. Apologies if I've got the wrong end of the stick.

 

[PaulRainbow]

Maybe I'm not fully understanding, but is that 100A fuse between the battery and starter motor? If so it's almost certainly far too small. Apologies if I've got the wrong end of the stick.

Seems backwards.

I'd fit the same fuses for each system.

 

[PaulRainbow]

That's the whole point, you can't. You have to turn off one bank, remove the key, and then turn on the other bank.
That's how I powered a selection of circuits from either the lead acid or lithium banks, without the two ever being in parallel.

How does that work with a starter battery and a domestic battery ?

 

[PaulRainbow]

What cable is going to each?

Good point.

 

[kevsbox]

Seems backwards.

I'd fit the same fuses for each system.

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

 

[Sea Change]

How does that work with a starter battery and a domestic battery ?

I set this up so that I could run the boat off the lead acid, or the lithium, but not risk putting them in parallel.
When motoring, I'd run everything off the lead acid. When sailing, run it off lithium.
For context, I had no DC-DC charger when it set it up.
It wasn't intended to allow an alternative method of starting the engine. That's what the jump leads are for .
Nor was it intended to charge the lithium. That's what the solar panels are for.

It was primarily to ensure a backup power option in case of a BMS shutoff.

Apologies again if this is of no relevance to anybody else. I'll freely admit that the way I've set my boat up in a rather unusual way, which works for me and wouldn't necessarily be ideal for everybody.