I’m wrestling with options and beginning to grasp the flaws in my newly manufactured boat’s 500 AH AGM house bank that I want to replace. At anchor my house load is requiring frequent charging. I attribute this to the 150 internally regulated alternator not keeping up with my short engine run times between anchoring and my load being a bit high due to the current draw. Currently I don’t have any significant monitoring equipment besides voltage readings on my house bank. So, SOC or SOD is a rough guess calculated by wattage ratings of the various loads I run. I love the idea of a switch to an 800 AH Victron house bank. My current set up is a Victron Multiplus 3000/120 (configured at the factory to only use the inverter), a Victron Centaur 100 amp charger as primary charger while on shore power or using the 11.5 KW generator, a dedicated, internally regulated, 150 amp Bosch alternator. Three other dedicated alternators maintain the starter AGMs - two engines and the genset, along with a Centaur 30 amp charger for the starter AGMs shore/generator power charging. No solar.
A couple of ideas I wanted to float. Assume that price was no object for purity’s sake. I am thinking of increasing my alternators size to improve my c rate while not using the generator and get an externally regulated one to tie into an external BMS (Lynx or Smart CL). I will also enable the Multiplus’s charging capability. If I was on a short stop between anchoring id run the genset too or a longer run just the alternator so while underway im getting a better charge rate depending of SOC and distance to next anchorage. Or would it be better (cheaper, less complicated) to just run the generator until the house bank was charged utilizing the 120-amp Multiplus, The 100-amp Centaur and the 150-amp alternator? The tradeoff is mostly the load dump protection and increased loss in keeping the current alternator or going all out with a new one that can better work with the Lifepo4 batteries and their increased draw. Am I missing anything? My biggest issue with this is the noise of running a generator at a peaceful anchorage. It ruins the experience.
Not sure what the 11.5kw genny runs but your not using a lot of the power for charging. If you were just using 240 volt from the multi and price was no issue, swap out the multi for a quattro and 48 volt batteries so your genny can charge fast at 8 times the rate your multi does. swap your dedicated alternator to a 240 volt one and use both inputs on the quattro using an Ekrano GX you can switch the genny off when you start the enging and use the 48 volt battery bms to give you accurate SOC and choose to start the genny only in day time or night if batteries about to expire.
I had 690Ah of AGM from 175A alternator, often the AGMs dictated lower charge currents. Now with 600A lithium I can run the alternator at 120A right till 98% SOC controlled by a Wakespeed WS500. Therefore just changing batteries and adding external control increases the alternator utilisation.
What to do about the alternator depends more on what your engine can support mechanically and power wise.
Thanks to you both. I thought about going to a 24 vdc setup for the house but found far too many things depended on the house’s 12 volts. I still don’t understand the boat builders rational for not using the Multiplus for charging or why one of the engines has two alternators (house and starter). It’s not very cost effective. But to get a better understanding I am thinking I’ll get a Cerbo GX and a display and get a better understanding of the AGMs house load with the Multiplus set to charge and then upgrade.
One of the challenges with boats is the wide range of shore power. Depending on where you are it might be 120 volt or 120/240 split phase or 230 volts. The Mulit is syncs voltage and frequency to shore power. Accommodating 230, 240, 120 volt shore power would involve isolation transformers with multiple taps. Plus 50 vs 60 Hz can be an issue with some AC motors.
By isolating the battery charging from the Multi’s inverter core means the AC loads always receive a consistent voltage and frequency. Probably what the boat builder had in mind.
It’s also generally easier to isolate house bank from other banks and charge them separately. This is especially true if banks use different battery chemistries.
DC-DC converters can generally solve the problem with higher house bank voltages. If 12 volt current is extremely high but of short duration (thrust motors, etc.) a smaller battery bank can sometimes be used for these loads and charged with a smallish DC-DC charger off the house bank.
If running the main engine is less intrusive than running a generator, then focusing on a bigger alternator might be worthwhile.
Of course, if you have the option of solar panels, then that should be considered as well.
You can also parallel more battery chargers if that helps but requires shore power or running the generator. But more charging power means shorter charging cycles.
You definitely need to get a handle on your actual consumption (DC as well as AC). Armed with that, a solution might be more obvious. You’ll need at least a shunt on the battery to monitor SOC. Hooking this to a GX device and then on to VRM will provide some pretty decent logging for evaluating load vs time.