Do I need an alternator protection device when switching to Lithium?

[lmxr]

Originally Posted by Simi 60

We have been out here cruising full time for 5 years without seeing a marina

Last time this happened , looking back with hindsight, it was probably 3 months before we noticed.

Non electronic engines and well thought out systems do not necessarily need an alternator to keep the boat going.
Nice to have for night passages, but that's about it, or at least that has been our experience for the past 5 years of full time cruising.

Alternator is disconnected and off the motor in a box.
Engine still starts and runs fine, all systems work as normal.

Disconnected it is indeed not going to cause any problems .

My concern mostly stemmed from some modern engines that require the alternator mechanically. Take for example the Volvo Penta D2 series. There, the alternator is used as a belt tensioner for the belt that drives the water pump. If the alternator bearings fail (e.g. due to severe overheating as a result of blown diodes) then this greatly reduces the usefulness of the engine.

[Paradox111]

Yes, no, maybe?

https://www.zwerfcat.nl/en/lithium-hybrid.html

[SailRN]

Lithium batteries typically have a Battery Management System (BMS) which do disconnect the batteries.


See

https://www.youtube.com/watch?v=jgoIocPgOug

And a good read: https://marinehowto.com/lifepo4-batteries-on-boats/


An excerpt:


The alternator for the Volvo MD2030 with 300 Amps lfp 14.6 max lasted a few hours. I believe BMS was switching on to off I to keep the lfp voltage to safe measure? Boat service replace alternator and it happens the second time? I now read your story on lfp and it explain to me why.”
Unfortunately the reader above learned the hard way. Ask yourself what happens when your alternator is in bulk charge, supplying all the current it can, and the internal BMS decides to “open circuit” or disconnect the battery from the boat? I’ll help out a bit here.
A) The alternator diodes, unless avalanche style, (rare in many existing marine alternators) but all Balmar alternators now use them, can be blown and the alternator can be rendered non-operable. Two years ago I did exactly this. Using the alternator test bench here at CMI the alternator was running at full bore charging an LFP battery. The “system” I set up had a .3A dummy load on, light bulb, to simulate a depth sounder. With the alternator running at full bore I disconnected the battery, just as an internal sealed BMS would do to protect the LFP cells. Poof went the alternator diodes and the light bulb! Worse yet the voltage transient I recorded on the “load bus” (think your navigation electronics) using a Fluke 289 was 87.2V. Ouch. Even if your alternator uses avalanche diodes, like Balmar’s do, the voltage at which they begin to protect the alternator is far too high for the vessels load bus equipment so you still need a way to protect against a load dump.

[CatNewBee]

Originally Posted by SailRN

Lithium batteries typically have a Battery Management System (BMS) which do disconnect the batteries.


See

And a good read: https://marinehowto.com/lifepo4-batteries-on-boats/


An excerpt:


The alternator for the Volvo MD2030 with 300 Amps lfp 14.6 max lasted a few hours. I believe BMS was switching on to off I to keep the lfp voltage to safe measure? Boat service replace alternator and it happens the second time? I now read your story on lfp and it explain to me why.”
Unfortunately the reader above learned the hard way. Ask yourself what happens when your alternator is in bulk charge, supplying all the current it can, and the internal BMS decides to “open circuit” or disconnect the battery from the boat? I’ll help out a bit here.
A) The alternator diodes, unless avalanche style, (rare in many existing marine alternators) but all Balmar alternators now use them, can be blown and the alternator can be rendered non-operable. Two years ago I did exactly this. Using the alternator test bench here at CMI the alternator was running at full bore charging an LFP battery. The “system” I set up had a .3A dummy load on, light bulb, to simulate a depth sounder. With the alternator running at full bore I disconnected the battery, just as an internal sealed BMS would do to protect the LFP cells. Poof went the alternator diodes and the light bulb! Worse yet the voltage transient I recorded on the “load bus” (think your navigation electronics) using a Fluke 289 was 87.2V. Ouch. Even if your alternator uses avalanche diodes, like Balmar’s do, the voltage at which they begin to protect the alternator is far too high for the vessels load bus equipment so you still need a way to protect against a load dump.

Think "START BATTERY"... [emoji12]