question

Per,

first off I'm wondering what sort of engines you have and what chemistry and type/size your domestic bank is as this will have an impact on any recommendation!

Boat systems can be pretty complex and Victron product range doesn't really cover dc alternators hence there's only limited system schematics.

In my opinion, the only thing missing from the victron range is a smart alternator regulator that links into the DVCC function of the system but thats or for another day.

Most marine engines come with alternators that are intended for charging the starting bank back up after cranking and not much more. What's more, is it becomes difficult to use more than one alternator on a battery bank, you need to use a device such as Balmars center fielder to use it most efficiently or sterling power offer a product the pro split r twin 130 model, this has a smart element to it which sends the bias of power to the start batteries and up to 4 other banks. This might well suit your needs to combine charging power. and increase efficiency a bit.

The next option is to change the alternators themselves. install a centerfielder and use cyrix to do the linking, likely the most expensive route, and I'm not sure it's worth it.

I think I would likely, keep it simple. If the existing alternators arent big enough, you could fit a second alternator with an external regulator to one of your main engines, size to be determined by the battery bank size and engine size/PTO limitations you could then leave your existing alternators doing a nice low-stress job, and therefore they will last. Use your additional alternator to provide your DC charging power to your domestics since your inverter could draw circa 250 amps without too much trouble I suspect your battery bank is in the region of 400 ah minimum. so a fairly big alternator can be used. Use some emergency parallels to protect against equipment/battery failure.

Depending on how you use the boat and what sort of boat it is, you might be better to fit a DC generator/or much more solar/ especially if you spend a lot of time at anchor. The trouble with running the main engine to charge the batteries is the low load polishes the bores and reduces engine efficiency increases emissions and shortens engine life.

With regard to trickle charging from solar, there's no real easy way to do it apart from installing small panels dedicated to those starter banks. - I presume you leave the boat on shore power. - I wouldn't worry about it.

The 4 amp multi plus output isn't smart, if you have a dedicated charger already for the starting bank, use that.

Normal alternator charging for lead acids is guided by their internal resistance, as they get towards full the resistance increases and therefore alternator output decreases. - Lithiums don't have very much resistance and therefore the alternator can overheat trying to endlessly supply the power, also they are damaged by over and under voltage, so there needs to be smarter battery protection in place for them which lead-acid doesn't require so much.

If you want to include battery protection the BMV has a relay that can be used to switch a battery protect on/off. I like to use this to switch off the none essential circuits like the fridge and main lighting circuits leaving things like bilge pumps and emergency lighting on. - It does tend to prompt people to charge the batteries before they discharge and do damage.

I don't recommend using battery protects on starter circuits.

Thank you for your reply.

Right now the boat has two Chrysler 318 engines, but I am in the process of planning a re-power. Both the re-power and the electrical upgrade will hopefully go hand in hand.

I think your observations make sense and are in line with what I have found.

Adding a small genset has a lot of benefits anyway, and yes it is in the plan, but later.

Adding a dedicated alternator on one engine is straight-forward.

Victron has the DC-DC chargers switched on by ignition, but without an alternator controller or at least a hefty alternator that seems to be an open loop solution.

Thanks,

per

318’s are pretty rare this side of the pond, only ever seen one!

If you are going down the generator route - and one presumes your repowering in diesel, perhaps simply using an Argo fet and an upgraded or externally regulated alternator on just one engine might see you through when running the main engines for now.

External regs are available from balmar Or sterling power do some cheap ish ones. Most alternators can be modified to fit that you pick up of the auto parts shelf, by a decent alternator shop. (You need an external field wire)

So you would end up with one alt charging one start bank and a second (maybe bigger) alt charging a start bank and domestics.

For when you need it or when your anchored you’ll have your inverter power and topped up by a generator (can be started automatically using either a bmv, multi or CCGX)