Cable cross-section

[marioxp]

I will replace the 65A alternator with a 100A alternator. Therefore, I also need to replace the cables to the battery. I haven't measured it yet, but I assume that the length is 6-7 m. What cable cross-section do I need now?

According to the tables, if I require a 3% voltage drop, the cable cross-section should be 35-50mm, if I accept a 10% voltage drop, it turns out that I need a 16mm cable cross-section. This 35mm or even 25mm cable cross-section seems too much to me. Now it seems to me that the cable is 8-10mm in cross-section.

[Yngmar]

The table is right. 10% voltage drop is far too much. Your alternator cannot regulate above 15V. 10% of that is 1.5V, so you'd get a maximum of 13.5V arriving at the batteries, which isn't enough to properly charge most batteries. Go thick or don't bother upgrading.

[tiger79]

Unless you have a HUGE battery bank, or are running an inverter with the alternator, you'll rarely see a current anywhere near 100A.  Ideally, your alternator should be battery-sensed, so it'll compensate for voltage loss in the cable.  I'd suggest you maybe look at fitting 25 mm2 cable.

[SYJetzt]

In my opinion upgrading a alternator doesn't make sense, except you have a huge NEW battery bank or a lithium bank.
The cause of poor charging systems with insufficient performance is usually old, worn-out lead-acid batteries.
As tiger79 mentioned, you will never see current of 100A with such batteries.
If you're planning to upgrade your alternator, you have to care not only for the cross section of your cables, but also for your diode-splitter as well.
I would also recommend bigger crosssections for the cable. Keep in mind, that the electric losses rely not only on current, but on voltage too. The generated power of your alternator is power= voltage x current. If you have a voltage drop of 5%, you have a power drop of 5% too.

[marioxp]

It really annoys me that charging existing batteries takes years. The charging current drops very quickly and after a short time the batteries are charged with a small current.

The big reason why I bought a stronger alternator is the intention to upgrade to LiFePO4 (280Ah) in the next year.

I know how much of a problem the voltage drop is and that's why I have a MOSFET splitter.

Those of you who have a D2-30 engine have a 100A alternator, can you tell me what cross-section of the cable Bavaria installed in these boats?

[tiger79]

Those of you who have a D2-30 engine have a 100A alternator, can you tell me what cross-section of the cable Bavaria installed in these boats?

The D1/D2 engines have a 115A alternator.  Cable size specified by Bavaria would depend on the cable length and installed battery capacity.

[symphony2]

It depends on where the batteries are located in relation to the engine. However from memory my 33 had at least 70mm cables.

As you know your higher output alternator is unlikely to charge your LA batteries any quicker as the limit is the charge acceptance rate not the potential output of the alternator. This will of course change if you switch to lithium BUT you will have to control the output of your alternator either with a regulator or a B2B charger at a level far below the 115A as the alternator cannot run for any length of time at the sort of rate lithium can accept. Lithium works best with regulated input from solar rather than an engine alternator. With the size bank you are considering the charge from the alternator would be regulated to a maximum of 60A.