BSM and DC motor start up load question

[sailordave2929]

Thank you for having me in the group. First time posters so go easy. On our sailboat we currently have lead acid batteries, but I'm upgrading to lithiums. I'll quickly give some of my requirements. We use about 80 to 100 AH per day at 12 volts and our largest load is the windlass at 1000 watts at 12 volts. Our current solar is inadequate at 140 watts and this winter we'll be upping that to 300 watts with the potential to go to 500 watts if needed.
My question for a new setup is more with the BMS and that startup load for the windlass motor. The amp draw is going to be around 80 amps continuous once it's up and running, but on start up that could be 2 to 3 times that amount and will that trip say a 200 amp BMS or what size BMS would you guys recommend? There might also be the case of needing to start the engine with the main house banks which i believe is about a 150 AMPs. My other option is to wire the windlass to the lead acid starting battery that i'll have in the system which will be tied into the alternator. The total capacity of the new battery bank will be around 400 AH at 12 volts. Thank you.

 

[snoobler]

Many BMS list a peak current higher than "rated", but it's never a bad idea to size the BMS for the surge loads.

More panels in parallel is advantageous to panels in series when panel shading is a factor. Panel shading can be devastating to its output, and a single small shaded area on one panel will affect the output of all panels in series with that panel.

 

[Factory400]

BMS ratings are about as reliable as a 1980 AMC Pacer.

Many of the low-cost BMS units have written specs that appear to be totally out of sync with the physical implementation. I am a power electronics engineer so much of this stuff is easy to see.

When I design something that is rated at say 100A, I have designed it for 200A or 300A so the end user can run it at its rating all 24/7/365 in the highest ambient temperature and it still works. That is how most industrial systems are made - with reliability as an up front priority.

In the consumer BMS world - (even though I am a newcomer) it seems that the ratings are comically overstated. For a sailboat application, I would certainly want high-reliability even in the worst of conditions.

With that said - I would consider drastically de-rating the BMS if you are going with the common low-cost models. In my RV system, for example, I am going with two parallel battery systems where each one can provide 100% of the power. If/when one fails - I still have 100% of my needs until I get the broken parts repaired. Each one of the battery systems (and BMS) are continuously rated for at least double the absolute peak they will ever see in real life. Average power will be less than a quarter of the continuous rating.