Replacing an Magnum ME-SBC with Victron Orion to charge starter battery

[Tenedos]

I am trying to change how the starter battery is charged on our boat. The boat came with a setup that I am still trying to fully understand. Here is what I know:

We have a Balmar alternator that is charging 6 Lifeline AGM batteries. It took me a while to figure out that the Balmar is not charging the starter battery directly. For some reason that I found strange, anchor windlass is also connected to the starter battery, not house battery. I finally figured the starter battery is charged via a Magnum ME-SBC Smart Battery Combiner, which connects house and starter batteries based on voltage.

But this has a bunch of issues. I always run the engine while using the windlass but I figured that the 30A fuse that is installed between ME-SBC and starter battery (per instructions from Magnum) blows up. I replaced that fuse a few times but it doesn't last. I traced it to using the windlass, whenever I use the windlass the fuse blows up. I think the windlass tries to draw a lot of amps, it causes a spike of current going through ME-MBC and blows the fuse. Needless to stay, this is problematic. If we don't use shore power, starter battery is essentially uncharged!

I am thinking of replacing ME-SBC with an Victron Orion DC Charger with 30 amps. Victron documentation states that this is for charging the house battery from the starter battery, and I am planning to do the reverse. I don't see why it would be an issue though.

In the future, I am also thinking of replacing the house battery to Battle Born LifePo4s but that is a separate project for a different time.

Is there any good reason why I should not do this? Anything that I need to be aware of? As always, any advice is appreciated.

[AllenRbrts]

I use an Orion dc to dc charger to charge a starter battery. Works fine. I use what is essentially the ignition wire to enable the charger so it only charges when the engine is on. I have this configuration because the alternator is charging a lithium bank.

[Tenedos]

Thanks Allen. Why do you need an ignition wire? From what understand it is possible to configure Orion to start charging when a certain voltage is reached. Wouldn’t it work if you configure it to start charging at something like 13.1V?

[AllenRbrts]

I think you are correct. I had the ignition wire handy and it worked well as an enable signal.

[stormalong]

Consider moving your windlass load to the house bank. Start batteries are intended to provide a lot of power for a couple of seconds. Your 6 AGMs can supply the windlass load easily and that is where your alternator output goes. Assuming 100 amp windlass load divided by six is about 16 amps per battery even without the alternator output. With the engine running your batteries won't have any load on them but in an emergency you can run the windlass without the engine.

Then you can leave your combined as is.

[MoodyS]

As Stormalong says your windlass is powered by the wrong battery, move it to the house bank where it is directly supported by the alternator and everything else can stay as is. This will also be true if you switch to LifePO but you will need an external regulator with alternator temperature sensor to provide the correct output to the battery and importantly protect the alternator.