To Which Battery Should the Bow Thruster and Anchor Windlass Be Connected ?

[mglonnro]

I came across this post from 2011 while googling. Now in 2022, I find only opinions _against_ connecting thrusters to the house bank, especially if it's lithium. Not very many of these opinions, but here's a sort of authoritative example:

The second lesson concerns a typical marine topic: bow and/or stern thrusters and their batteries. The conclusion is simple: don’t put thrusters on the house battery, especially don’t do so when using bms protected lithium for the house battery.

The main reasons for that:

• Combining thrusters on one battery with Multis and other electronics is not a good idea: spikes from thrusters cause issues and/or damage to the connected electronics.
• Another reason why combining thrusters with house loads is not a good idea: using the thruster can empty the battery of the whole boat, instead of only its own battery.
• Having thrusters on a lithium battery with a BMS that will disconnect them in case of any issue is not a good idea either: just imagine a sudden cut out in the middle of a manoeuvre without pre-warning. Note that we do not give warranty on our batteries if there is no BMS with full disconnect installed, which basically rules out Victron lithium batteries for such purpose.

https://www.victronenergy.com/blog/2...thium-and-soc/

[Irunbird]

Hi all- as the last post mentions above, he found this while "googling" certain terms and added to an old thread. I have similar concerns related to tying sensitive navigation electronics to the bow thruster battery (an 8D AGM Odyssey in my case). All of this after changing out my old (and very dead) AGM house bank with 3 Victron 24v LiFePO batteries (1200ah in all at 12v). Much has changed since this thread began, and a lot is just not known, but I do know for a fact that my entire DC circuit on the boat goes directly to that big AGM in the foreward part of the boat that also serves the bow thruster and windlass. Given the complexity of this system, and that much of it has not been fully explained by way of a complete schematic, I occasionally find something like this that raises eyebrows like the old mantra that you should NEVER connect electronics to a battery that experiences big voltage swings like that on the thruster. I am not really at liberty to say who installed this (no matter how tempting it may be), but they are well respected and ABYC certified- still, these issues remain and I have been told that some Island Packets are wired similarly and do just fine. So- is this just a relative contraindication? The work around being that you use the thruster very sparingly (which we do anyway) and maybe turn off all nav instruments at the panel before docking and using the thruster?

[GreenWave]

I have a separate dual battery AGM bank (12V) set-up in bow of boat for my bow thruster. It uses an isolator so current can only flow to the battery from the charging circuit. My windlass is on the house (though may switch it to use that thruster bank). I am in middle of switching house bank to Lithium and will use a DC/DC charger to maintain the thruster bank per their needs.

[noelex 77]

Originally Posted by Irunbird

The work around being that you use the thruster very sparingly (which we do anyway) and maybe turn off all nav instruments at the panel before docking and using the thruster?

This should not be necessary. The setup you describe with the house battery powering the windlass/bow thruster is not unusual. It usually works fine.

I would check the voltage drop in your instrument wiring. If the problem persists you can power sensitive electronics with a 12v DC to DC power supply. Even better, add a small 12v battery after the power supply and then you will have a redundant system to power your important navigation electronics should the house battery fail. These extra steps should not be necessary, but they will fix your problem for little cost and you will gain some useful extra features.