I’m installing two Victron 12.8V/300Ah NG LiFePO₄ batteries in parallel, Lynx Smart BMS NG (haven’t decided on 500 or 1000 version), and Lynx Distributor in a 2012 Catalina 355.
I have a 5kw bow thruster (kind of overkill for a 35’ boat, but it came with the boat). I was originally going to move the thruster and the windlass to the start battery (and get a bigger battery), but upon further investigation there was no way I going to fish such large cables under the sole.
So I considered connecting the thruster directly to the batteries, but was advised against this as the batteries would not be protected from a huge consumer. Understable concern.
Then I went back to connecting the thruster to the end of the distributor. I have some reliable sources who question whether or not the 1000 amp version of the BMS can handle the roughly 2,000-3,000 amp inrush current. I don’t feel like risking $1,000 to find out.
I’m sorry, I can’t answer your question about inrush current on the Lynx BMS and I despise 12V systems. So, I’m useless to you
If you have the room in a hatch near the windlass and bow thruster, then consider installing a good 12V (ugh) AGM or SuperCycle battery to handle those very intermittent loads, and then charge that battery from your LFP or starter batteries with a low-current DC-DC charger. You can use smaller cables to/from the DC-DC charger due to the lower current and it might make installation easier. Just an idea.
yeah, dedicated thruster battery is probably where I’ll end up. And I believe I have a spot for it - and the thruster cables run right along the hull past this location.
Thanks for the reply. I posted the question mainly to maybe save the next victim some time and trouble.
The specs on your thruster sound wildly out of whack. I don’t even know how a 5kw thruster could even fit in that small of a boat (and why would you ever put that much weight in the bow?).
Your thruster shouldn’t be pulling more power than the peak draw on our windlass on a 30,000 lb boat with a 45kg anchor and hundreds of feet of chain, and we’re using the 500, not the 1000 BMS with no issue whatsoever. Our run is more than 38 feet, but the cable is 0/0
Our first gen 500 BMS was installed and spec’d by an ABYC certified marine electrician, and he said it was overkill.
Are you sure your thruster really pulls that much power? We know people with Nordhavn’s with huge thrusters that don’t pull even a fraction of that. 3000w at 12v is 250A, so even if it’s 5000, you’re still in the ballpark of the 500 with room to spare. I mean, how did they even get that many amps out of the lead or AGM batteries that came before your Li?
Your biggest issue is the cable size, not sure you’re going to get the length without running something as big as your arm unless the run is short.
The 12V 185TT5.0 Bowthruster, which is 6.7 HP (5.0 kW), is recommended for boats 40 to 55 ft, but it sounds like this is what they put in your boat. The manual for this entire series of thusters is here:
Pages 13 and 17 have information relevant to wiring and fusing, and the fuse they call for is 400A, so as I suspected, the 1000 is going to be over double your duty requirements.
