The BMS 12/200 manual states in its point 3.4. Installation: 2. Determine the rating of Alternator/Starter Bat+ port fuse. The fuse doubles as a shunt, thus the Smart BMS will limit the input current according to the rating of this fuse. For fuse and corresponding current limit please see the table below. 3. Choosing the right fuse will prevent overheating of the alternator and/or DC cabling. My alternator is a Volvo Pento without temperature regulator 115 Amp F category with a max 155 degrees Celsius, the BMS has a 100 Amp fuse installed on the port. The alternator, according to its manual, (should not run continuously above 110 degrees. However, by max charging (1400-1600 rpm =normal engine cruising speed on my sailboat) it reaches 150 degrees and around 110 degrees by idle / low rpm wherefor I have been in the need to stop the engine in order to prevent damaging the alternator
The Victron authorized technician who installed the complete VINCTRON system states that my alternator would burn for instance an 80 Amp fuse and not protect the alternator and not influence the alternator output/heating because it cannot read signals from the BMS.
Is it in fact possible to protect the alternator from overheating by using a smaller alternator port fuse as literally stated in the manual?
I think to understand, that your LFP battery is overheating the alternator by pulling to much current. In order to decrease the amouth of current, and to lower the temperature of the alternator, the smart BMS should be set according the used fuse. But even then the alternator keeps getting hot.
I’m not a Victron expert in this issue, but would it be an idea to use a DC-DC converter in between the LFP battery and the alternator? For example the Victron Orion XS (max 50A), or the Victron Buck Boost (max. 100A). Those DC-DC converters can be manually set to a pinched charge current, in order to prevent the alternator being damaged.
Yes, use a smaller fuse and the BMS will reduce the current. As a rule of thumb, the alternator maximum continuous current should be no more than 2/3rds of its rated current, so for 115Amp alternator no more than 75A, howeverthis does dependon cooling and engine bay temperatureso a lower currentmay be required. Swap the fuse to limit this.
Thank you. Yes, I am aware of this normal alternative but wanted to explore the other simple and cheap alternative first. Now that it apparently exists.
Thank you for confirming. Do you know this from personal experience and have actually monitored temperature and/or current from alternator, or do you have another than Victron manual source confirming this function?
If I can share another Victron source then the Victron installer should/will revisit the installation and change the fuse to 80 or 60 Amp at no cost.
No personal experience as I have a different Victron BMS but supporting this group has given a wide insight into how it works for other people. How difficult is changing a fuse just to make sure.
Yes, if I could that easy! Even the certified Victron dealer need to order it from USA to Panama where I am. It is a mega and not normal size ALN fuse. In any case, the regional Victron dealer now also confirmed that it should work as the manual says. So, I will order and wait for an 80 Amp fuse now. Thanks.