Brand new Smart BMS 12/200: Alternator overheating when 300A bowtruster used?

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Dosheimer asked Aug 24, '21

Brand new Smart BMS 12/200: Alternator overheating when 300A bowtruster used?

Good Morning altogether!

I have installed the brand new Smart BMS 12/200 on my boat and have a hypothetical concern in combination with a bowtruster usage:

My 100Ah AGM starter battery is connected to a 115A alternator and a Vetus 5012 bowtruster (300A fused). Also the alternator is connected to the Smart BMS 12/200 which is connected to a 330Ah Smart Lithium.

I am using the 100A alternator input fuse on the Smart BMS to have around 90A for charging from the alternator which is around 80% of the alternator rated capacity which sounds well to reduce the motor hours on anchor to charge the lithium in cloudy days and also in order to charge fast when using the motor anyway. So I guess a quite standard cruising sailor setup.

Question: In case I will use the bowtruster at a stage where the lithium battery is charging, should I be concerned about overheating the alternator? Or does the Smart BMS identify somehow this extreme event resulting in a high recharge demand of the starter battery from the alternator and therfore disabling the charging of the lithium for a while? Or do I need to always manually disable the charging of the BMS before using the bowtruster?

Thanks upfront for your comments!

BMS

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Answer 1 · 2021-09-13T23:40:55Z

devodave answered · Sep 13, 2021 at 11:40 PM

The question you raise is more about the regulator and alternator you have. A '115Amp alternator' may well be the original internally regulated (dumb) alternator that came with the motor. For LiFePo4, installing a larger capacity alternator with external (smart) regulator and then derating the field current to keep the alternator in a comfortable working range is a good thing.

Your start battery is supplying the bowthruster, but how is the start battery parralleled with the Lithiums when charging is taking place? Possibly an automatic relay such as an ACR or VSR?Happily your bowthruster will only be used for short periods, and the battery should be providing this surge capacity.

Than answer to your question is that when you activate your bowthruster, the load on the battery may be such that the voltage drops. The regulator may then increase field current to try to return the battery voltage to what it wants. This may make the alternator work harder, but it will only be for the period of time your bowthruster is running.

Unless you are trying to cross the Pacific sideways, I suspect you'll be fine.

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Answer 2 · 2021-09-16T21:35:35Z

Dosheimer answered · Sep 16, 2021 at 09:35 PM

Hi Devodave, thanks for your response.
["...Your start battery is supplying the bowthruster, but how is the start battery parralleled with the Lithiums when charging is taking place?"]
For this I am using the new Smart BMV 12/200 which parallels the starter (AGM) battery with the 330Ah Smart Lithium when the voltage of the starter battery is > 13V.

That´s my today´s setting since a week:
schematic_overview_energy-distribution.pdf

P.S.: Everything between 60° south and 60° north is the sailing area.

schematic-overview-energy-distribution.pdf (490.9 KiB)

schematic-overview-energy-distribution.pdf (490.8 KiB)

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Answer 3 · 2021-09-17T10:31:05Z

mvader (Victron Energy) answered · Sep 17, 2021 at 10:31 AM

Hi, I recommend to watch our alternator movie on Youtube. An alternator rated for 115A is usually not able to deliver 90A while idling. As while idling, the cooling of the alternator is very poor.

But I don't know any more details by heart, nor have the time to look into it for you I'm afraid. But do hope this helps!

https://www.youtube.com/watch?v=jgoIocPgOug&t=45s

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