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I get that information if I drill down in the app, but the app is so poorly designed that you have to hop on foot and pat your head to get it. You can only look at one battery at a time and the process of switching batteries is clunky and slow. There is no control of the battery at all and no means of getting notification of problems with the batteries.

I am going to try a couple other apps that supposedly will work with the batteries and provide a different level of information that is easier to get. What I looking for is a battery/app combination that gives me the information on the batteries as a group and lets me know that something is wrong.

Tom
I should mention that I don’t need to dig for the information, it all comes right up when I open the app.
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I have 8-100Ah Renogy smart batteries. I could have bluetooth added, but not interested. 8 batteries communicate with each other over ethernet cable. The readout gauge (by ethernet) gives the average of the 8 for SOC/volts. They self balance themselves and each other. I expect the battery BMS will isolate any battery from the others if there is an internal fault.
 
I'm also looking into this. Right now, I have 2 banks with 2 batts each. Both legs are protected with a 250A fuse. If one battery in a bank dropped out for some reason, the other battery (now working as a single) still couldn't put out more than 250A without tripping the fuse.

If working on the premise that the fuse is to protect the wire then, when fusing two batteries in parallel, an MBRF fuse on positive terminal #1 only protects the 9 inches of cable linking it with positive terminal #2. Having a MBRF on terminal #2 only "protects" the 7 inches of cable before the 250A line fuse (Max 7 inches as allowed by ABYC). What am I missing? There is no "load" to fuse against other than somehow a dead short if the cable insulation was breached. Maybe the possibility that an axe gets loose in rough seas?

If the idea is to fuse it at less than the BMS shutoff, to what purpose? Fused individually with a 200A MBRF, the fuse should blow before a 250A BMS cutoff. One could identify this by checking the Bluetooth and seeing either a fault (BMS shutdown) or no in/out current for that battery (MBRF fuse blown). Then the difference is that my BMS will reset in 10 seconds or, if the MBRF has blown, I have to find a fuse, shut down that battery bank, climb into the ER, disconnect the cable from the battery terminal, etc. etc. The MBRF better address a much bigger problem than I can see.

Side note #1. In all my preparation of a schematic of what I have and what changes will be required for going LFP, I realized that I did not make a notation of the wire gauge for the various legs. Fuses I made notes of, but it turns out that wire gauge info throughout the electrical system would be nice.

Side note #2. Here's a question about fusing and wire guage. Say each bank is properly fused on the positive leg based on the cable size. If each positive is fused at 250A, doesn't that mean that the common ground could see sustained 500A? I think my common ground is the same AWG as the positives. Is it possible that the ground wire needs to be sized to handle twice the positive for two bank? Or three times if three banks? I don't think I've ever seen anything about this.
Mark
I might have missed it , but you stated you have 2 batteries in each bank. What are the amps for a single battery? We are becoming complacent that the BMS will always work properly , but if it fails I want that battery off line. As you stated, ABYC requires fusing with in 7 inches of battery and I'm wondering if they won't consider an internal BMS as a fuse? I'm guessing not.
Cheers J.T.
 
Mark
I might have missed it , but you stated you have 2 batteries in each bank. What are the amps for a single battery? We are becoming complacent that the BMS will always work properly , but if it fails I want that battery off line. As you stated, ABYC requires fusing with in 7 inches of battery and I'm wondering if they won't consider an internal BMS as a fuse? I'm guessing not.
Cheers J.T.
why not, there are some batteries with built in fuses.
ETA. With the many different BMS types in batteries I do wonder how ABYC is going to generalize their recommendations. The fuse per battery may be it.
 
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I don't remember if ABYC says a class T fuse "should" be inline with LFP batteries. Sometimes the wording is hard to parse out, but as MarineHowTo notes, in excess of ABYC isn't an issue and is sometimes best practice.

As to fusing the individual batteries with "inter-bank" terminal fuses, I still don't get it. If a battery in a bank has an overcurrent issue (that the BMS doesn't recognize so that the BMS doesn't shut down), what has the blown fuse protected? The fuse would have to be smaller than the line fuse protecting the entire bank. A blown fuse could stop current flowing into an adjacent battery, but when would the adjacent battery have a draw in excess of the bank fuse? Where and what is the inter-bank overcurrent cause?

JT: Right now my two lead-acid banks each have 2 6v 260Ah batteries with each cable out protected by a 250A ANL fuse. My plan is to have two LFP banks each having 2 12V 280Ah batteries with each line out protected by a 250A class T fuse (per ABYC "should" recommendation). The class T fuse has a slightly faster blow time, but it can still pass more than 700 amps for one second (as does the ANL fuse). That allows me to start my engine with either bank, although like with my lead-acid, I intend to only separate them for maintenance or jollies.

CharlieO points out one of the shortcomings of many of the Bluetooth apps. It is for one battery. That's fine if you have one battery. I have to identify which one of my four batteries I want to look at. That obviously effects the ability to simultaneously monitor four batteries in two banks. I expect that monitoring will only be required initially and I won't end up one of those distracted people constantly staring at my phone. I intend to keep my overall battery bank shunt which gives me SOC, present amperage usage, amp hour remaining, etc. I'll have to find my owner's manual and reset the shunt now that I have 1,120Ah (14,336Wh) available.
 
I don't remember if ABYC says a class T fuse "should" be inline with LFP batteries. Sometimes the wording is hard to parse out, but as MarineHowTo notes, in excess of ABYC isn't an issue and is sometimes best practice.

As to fusing the individual batteries with "inter-bank" terminal fuses, I still don't get it. If a battery in a bank has an overcurrent issue (that the BMS doesn't recognize so that the BMS doesn't shut down), what has the blown fuse protected? The fuse would have to be smaller than the line fuse protecting the entire bank. A blown fuse could stop current flowing into an adjacent battery, but when would the adjacent battery have a draw in excess of the bank fuse? Where and what is the inter-bank overcurrent cause?

JT: Right now my two lead-acid banks each have 2 6v 260Ah batteries with each cable out protected by a 250A ANL fuse. My plan is to have two LFP banks each having 2 12V 280Ah batteries with each line out protected by a 250A class T fuse (per ABYC "should" recommendation). The class T fuse has a slightly faster blow time, but it can still pass more than 700 amps for one second (as does the ANL fuse). That allows me to start my engine with either bank, although like with my lead-acid, I intend to only separate them for maintenance or jollies.

CharlieO points out one of the shortcomings of many of the Bluetooth apps. It is for one battery. That's fine if you have one battery. I have to identify which one of my four batteries I want to look at. That obviously effects the ability to simultaneously monitor four batteries in two banks. I expect that monitoring will only be required initially and I won't end up one of those distracted people constantly staring at my phone. I intend to keep my overall battery bank shunt which gives me SOC, present amperage usage, amp hour remaining, etc. I'll have to find my owner's manual and reset the shunt now that I have 1,120Ah (14,336Wh) available.
Hi Mark
That's a lot of amps !!! I'm guessing that you plan on having your anl fuse with in 7 inches of your + post you would be in compliance with ABYC. My thought was in my set up (4 100 amp in parallel ) if the BMS puked, I want it fused as closely to the battery terminal as possible. Sure don't want anything magical happening in the battery bank/engine room. I have not heard want actually happens with lifepo4 batteries if the BMS fails? Is it a run away voltage/amps that melts down my buss bar and anything connected to it? Still learning and have lots of ??
Cheers J.T.
 
JT

I'm planning on replacing my ANL fuses with Class T fuses when switching to lithium. The difference is mainly the Amperage Interrupt Capacity (AIC). The way I understand it is that some fuse types melt a fusible link, but there may be a problem if the amperage is so high that it still arcs across where the link was. In other words, it pops off for 100 amps but it will still arc if the current is 1,000 amps. The ANL can have that issue and some don't even provide the AIC data. The other issue is that at higher currents the ANL "ignition protection" might not work. The plastic casing pops open, sparking out molten metal. May or may not be an issue, but best to not take the chance.

The Class T fuse has several features that increases its AIC. The fusible link is a piece that falls away, leaving a larger gap. Plus, the area is filled with silica dust. The dust fills the gap and if there is any arching the dust melts to the electrodes, basically becoming a glass insulator. The casing is metal, so no melted plastic or shooting sparks. It has an AIC rating of 20,000 amps. That's a lot, but some of the dead short current tests for 100Ah LFP batteries have been several thousand amps. My dead short current for 2x280Ah LFP in parallel might be under the 6,000 amp range (for an ANL fuse), but since I don't know I'll spend a few bucks and get the better fuse.

The ABYC 7" rule can be extended to several feet if the cable is in a conduit. Most of my larger cables are already in conduits, but that tells me that even the 7" length could be in a conduit. No harm in going above and beyond ABYC. I have some fireproof flexible around and might as well use it up.

What happens when a BMS fails? That depends on the type of failure. If it is an overtemperature failure, the battery goes off line until the temperature sensor cools off. I don't know how long that might take. From the testing I've seen online, the sensor itself is almost instantaneous, but I don't know how long it would actually take a overheated cell to cool off. An overcurrent reset in my spec sheet said 30 seconds, but when top balancing my batteries (and goofing up) it seemed much faster. An undercurrent shutdown could be a different story, depending on how the battery is charged. Some shore chargers will not charge a battery if it is under a certain voltage. There are supposedly special chargers that somehow (maybe have a lower threshold?) can revive a seemingly dead LFP battery. I don't think it will matter with my setup because of having LFP in parallel. In general, a BMS shut down means that the battery will be trying to get back on line momentarily.

A BMS failure doesn't do anything. Lead-acid batteries don't even have them. Runaway current that melts things down means that the rest of your electrical system wasn't properly constructed/fused. It is more likely that a toilet will spontaneously catch on fire.

It is a lot of amps. I don't need that much. What I needed was redundancy so that:

1. I didn't have to worry about alternator issues if a battery shut down momentarily
2. I didn't have to buy some workaround gadget
3. I could "drop into" my existing electrical (except upgraded fuses)
4. I could charge at a higher rate
5. I had enough LFP batteries that my starter current was only a small amount of their rated current

Having the ability to anchor out for several days without a generator is just a bonus.
 
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why not, there are some batteries with built in fuses.
ETA. With the many different BMS types in batteries I do wonder how ABYC is going to generalize their recommendations. The fuse per battery may be it.
It has to do with individual or combined bank AIC. its pretty straightforward and cut and dry
 
JT

I'm planning on replacing my ANL fuses with Class T fuses when switching to lithium. The difference is mainly the Amperage Interrupt Capacity (AIC). The way I understand it is that some fuse types melt a fusible link, but there may be a problem if the amperage is so high that it still arcs across where the link was. In other words, it pops off for 100 amps but it will still arc if the current is 1,000 amps. The ANL can have that issue and some don't even provide the AIC data. The other issue is that at higher currents the ANL "ignition protection" might not work. The plastic casing pops open, sparking out molten metal. May or may not be an issue, but best to not take the chance.

The Class T fuse has several features that increases its AIC. The fusible link is a piece that falls away, leaving a larger gap. Plus, the area is filled with silica dust. The dust fills the gap and if there is any arching the dust melts to the electrodes, basically becoming a glass insulator. The casing is metal, so no melted plastic or shooting sparks. It has an AIC rating of 20,000 amps. That's a lot, but some of the dead short current tests for 100Ah LFP batteries have been several thousand amps. My dead short current for 2x280Ah LFP in parallel might be under the 6,000 amp range (for an ANL fuse), but since I don't know I'll spend a few bucks and get the better fuse.

The ABYC 7" rule can be extended to several feet if the cable is in a conduit. Most of my larger cables are already in conduits, but that tells me that even the 7" length could be in a conduit. No harm in going above and beyond ABYC. I have some fireproof flexible around and might as well use it up.

What happens when a BMS fails? That depends on the type of failure. If it is an overtemperature failure, the battery goes off line until the temperature sensor cools off. I don't know how long that might take. From the testing I've seen online, the sensor itself is almost instantaneous, but I don't know how long it would actually take a overheated cell to cool off. An overcurrent reset in my spec sheet said 30 seconds, but when top balancing my batteries (and goofing up) it seemed much faster. An undercurrent shutdown could be a different story, depending on how the battery is charged. Some shore chargers will not charge a battery if it is under a certain voltage. There are supposedly special chargers that somehow (maybe have a lower threshold?) can revive a seemingly dead LFP battery. I don't think it will matter with my setup because of having LFP in parallel. In general, a BMS shut down means that the battery will be trying to get back on line momentarily.

A BMS failure doesn't do anything. Lead-acid batteries don't even have them. Runaway current that melts things down means that the rest of your electrical system wasn't properly constructed/fused. It is more likely that a toilet will spontaneously catch on fire.

It is a lot of amps. I don't need that much. What I needed was redundancy so that:

1. I didn't have to worry about alternator issues if a battery shut down momentarily
2. I didn't have to buy some workaround gadget
3. I could "drop into" my existing electrical (except upgraded fuses)
4. I could charge at a higher rate
5. I had enough LFP batteries that my starter current was only a small amount of their rated current

Having the ability to anchor out for several days without a generator is just a bonus.
Mark , great info. Here in Wa. st we're only allowed 3 days on the mooring buoy or park dock so I'm in the process of figuring out how long I can go with out firing anything up, and no that wasn't me who accidently connected the fuel system to the head!!! And I told everyone not to smoke, but that's another story. You're right on about ABYC requirements being a minimum, and going above and beyond when possible.
Cheers J.T.
 
It has to do with individual or combined bank AIC. its pretty straightforward and cut and dry
I like the cutaway done by Will Prowse and others that show the different internals. Sorry, I cannot see what is straightforward. AIC (Ampere Interruption Rating) or new term AIR or "Ampere Interruption Rating" of what, the external fuse or the BMS.
 
Fuse.

You need your fusing to have an AIC (Ampere Interruption Capacity) greater than the SSCR (Short Circuit Current Rating) of the battery bank it is connected to. (I’ve never heard the acronym AIR but suspect it is being used to stand for AIC Rating). Class T is the highest common or practical level we as mere boat owners have access to. It is rated at 20,000 amps (at blah blah voltage and yadda yadda temp,etc). I’m using them most everywhere, like on a two battery parallel bank of Odyssey AGM’s for my thrusters and start bank. These are min 5000 A of SSCR each, which is 10,000 A for the parallel pair. This is in itself a frightful amount of current if crowbarred, but still nothing compared to lithium (LiFePO4 in our context). If you drop a bar across the terminals of a 460AH lithium battery you got a SITUATION on your hands.😱 An ANL or MRBF fuse is not up to the task and runs a real risk of an arc flash which has now rendered the whole concept of fusing moot. Remember this is DC, not AC, and is a force to be reckoned with.

I believe the ”straightforward” comment is accurate. Class T fuse, within 7” of battery (or longer as per specified exceptions) if you’re talking lithium. And maybe even for AGM; you need to check manufacturer spec for SSCR. And don’t forget, this has nothing to do with the fuse *size*. The job of the fuse is to protect the wiring , so if you have 4/0 cable connected you need a different fuse size than if you have 1/0 cable connected.

PS If you are further interested in such things, search YouTube for DC arc flash. You’ll find some visually spectacular examples of what *can happen*….not necessarily *will happen*. But we’re boaters right? And well familiar with how often “that shouldn’t happen” becomes “holy crap how did that happen”….and how quickly.
 
I like the cutaway done by Will Prowse and others that show the different internals. Sorry, I cannot see what is straightforward. AIC (Ampere Interruption Rating) or new term AIR or "Ampere Interruption Rating" of what, the external fuse or the BMS.
Batteries all have a max output ratings of the bms
Dakota for example is short circuit 5040 @ 2-500 ms and overcurrent 1400 @70-130ms

So in this instance if I did three in parallel with a t fuse it would take care of it on the last outward one. If I added another one I could split the bank with two fuses, or more likely use an mbrf on each battery to a bus bar so I could use smaller battery cable as well, then to the system from there.

Both BMS, and fuses have applicable ratings that are published, or you may have to email and ask like I did for Dakota.
 
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On a new note. Fabbed up the proof of concept for 600 watts on an r23/25/27. Fits like a glove. Now to design the 1200w version that extends over the rear bimini
 
A few thoughts. First, if you go Victron, in my opinion it's crucial you find a dealer with food tech support and make all your purchases through that dealer. Victron support network is heavily dependent on dealers - pricing is similar throughout. Tech expertise varies widely. The buyer has little option but to work with the dealer they purchased through.

Second, largest Victron battery I could find is 200ah at 24v. Two in series would be 200ah at 48v (10kwh storage). Still a ton of storage.

Third, there are many native 48v batteries in the market now. Why go series (2 x 24v)?

Finally, instead of running dual Quattro's, have you considered some of the inverter/chargers that have more integrated capabilities including native split phase with onboard circuit protection and even MPPT if you add solar down the road?

This type of setup is bleeding edge for boats but well into adoption phase for residential setup (inverters are mostly UL listed these days due to permitting requirements). DIYSolar forum (Will Prowse monitors) has some extremely technical wonks if you have any questions.

Please keep updating your progress and decisions. In my opinion, definitely a place for 48v.

Peter
Hey Thanks Peter!

I've been working with Ocean Planet Energy and been pretty happy with their engagement / support thusfar. I know that Nigel Calder worked with them as they are one of the dealers that are installing the Integral system.

I will be doing two sets of 2x24V 200Ah in parallel for 400Ah @ 48V.

I ended up really wanting to go "all Victron" for the integration / known brand quality. Access to the 48V lithium batteries had a delay and 24V was the same price. I would have ended up with the same number of batteries regardless so it seemed like a wash to me.

I did look at some other inverter options but really wanted to stick with Victron - for their support / overall integration / brand rep.

48V at least for this kind of application does seem largely tried-and-true given its prevalence in residential solar. A lot of the Van folks are also going down this route.

I just finalized the order today so I should be getting stuff shipped / starting on this project soon. Will be sure to update on how things go.
 
Hey Thanks Peter!

I've been working with Ocean Planet Energy and been pretty happy with their engagement / support thusfar. I know that Nigel Calder worked with them as they are one of the dealers that are installing the Integral system.

I will be doing two sets of 2x24V 200Ah in parallel for 400Ah @ 48V.

I ended up really wanting to go "all Victron" for the integration / known brand quality. Access to the 48V lithium batteries had a delay and 24V was the same price. I would have ended up with the same number of batteries regardless so it seemed like a wash to me.

I did look at some other inverter options but really wanted to stick with Victron - for their support / overall integration / brand rep.

48V at least for this kind of application does seem largely tried-and-true given its prevalence in residential solar. A lot of the Van folks are also going down this route.

I just finalized the order today so I should be getting stuff shipped / starting on this project soon. Will be sure to update on how things go.

Thanks for the update. Please keep them coming as you certainly have one of the largest battery storage systems (20kwh) I know of (if not the largest). Also running a 165A/48V alternator is certainly considered bleeding edge in a boat - at least for the time being.

By far my biggest complaint about Victron is my perception that a full Victron system is a large number of components that must be separately cabled together. Also the Cerbo monitoring components do not have nearly enough interface ports so workarounds to expand ports are required. Granted a component approach means flexibility and customization for specific requirements, but comes at a price of cost (both purchase and install) and complexity. Sounds like you did a ton of research and put your money where your mouth is in selecting Victron. Can you offer a bit deeper insight into your decision making? I'm not questioning it in the least, but I'm in the bleachers with my thinking - you're an active player on the field so I'd like to understand.

I'd be interested in your boat for context. Size, usage, etc.

Thanks

Peter
 
I will be doing two sets of 2x24V 200Ah in parallel for 400Ah @ 48V.
Unless the system has some kind of series balance capability you will likely need external balancer between your series pairs. If you can change it..I would strongly recommend going only with 48 volt batts in parallel. You may have this covered already though?
 
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Good question. Occured to me too but since Ocean Planet has a good reputation, I figured they must have accounted for this.

That said, you (@Bmarler ) have an excellent track record here on TF. I'd be curious in your opinion on where Victron fits in the bell curve of LFP innovation these days. I'm curious but not overly knowledgeable. Just seems like they are being surpassed by competitors such as EG4, Schneider, and a few others. Sort of how BattleBorn is now an asterisk in the LFP battery world.

The bigger LFP market is off grid and battery backup. It's all 48V yet Victron doesn't have a 48V battery offering. Heck, even server rack batteries are becoming a bit dated compared to large wall units. Not a big deal as Victron is better known for their controls which is why @dpmcgarry chose them. Nothing wrong with tried-and-true but just curious on winds of change in market. Seems very dynamic in features and capabilities right now.

Thoughts?

Peter
 
Peter,
I feel the same as you. Lfp technology is moving extremely fast. Companies like Victron are not as nimble as other smaller companies that are willing to risk more and stay on the leading edge of adding features and better user integration. 48 volt seems to be where we might be landing for the time being, and suppliers for this are everywhere. Just google search 48 volt power wall and see how many options are out there. The off grid and rv folks are doing the beta testing for us, and we should take advantage of that.
I wouldn’t be installing Victron right now unless I was going 24 volt. And I wouldn’t be planning a 24 volt install when the 48 volt power wall systems have so much more to offer.
I have a few more years to wait before I do an upgrade to my dc system, and right now I’m leaning 48 volt.
Lfp is almost considered a lifetime install, so an end user must choose a point in time snapshot of the devices required to complete the system, because as soon as you buy the required devices new features will be available. In 4 years, I wonder how many of the suppliers of the current crop will still be in the conversation, and how many new ones will be around.
You can go on and on debating all the risks and rewards of the options of the different technologies available, but for most people, simple is best. Having a good understanding of how your system operates is more important than being cutting edge. I feel comfortable with this stuff, but my neighbor down the dock can barely manage his 12 volt flooded batteries.
Then there’s the subject of abyc compliance. Will they be providing guidance on 48 volt systems? Will insurance companies ok them? 48 volt is significantly more lethal than 12 or 24 volt.
I feel like I got off into the weeds a bit…
 
48v also is not really all that great unless you can run a big alternator. those things charge like hell with some RPMs behind them.

the big advantage in general is just wire size and in certain cases charge speed from alternators. other than that its not a huge benefit.
 
48v also is not really all that great unless you can run a big alternator. those things charge like hell with some RPMs behind them.

the big advantage in general is just wire size and in certain cases charge speed from alternators. other than that its not a huge benefit.

In the last three years or so, technology for inverter/charger and batteries have taken a quantum leap, 48V leads the way. Sure there is some 12v and 24v spillover, but the all-in-one inverter/chargers with integral MPPT are really interesting. Surge capacity is very high so starting inductive loads is tolerable. Balancing is seamless. Integral circuit protection and onboard capacitor discharge plus integral cell monitoring are a nice upgrade from even recent iterations.

And then there is cabling size. For most 12v configurations, 3kw DC draw is approaching the practical limit unless batteries are very close (6kw at 24v). With modern inverter charger with 48v 10kwh battery (or more) direct connected, can support 60A 120v AC current draw (plus split phase 240VAC if desired). Not all boats need this flexibility and power, but the capability is there. And it's developing and advancing in the 48v arena with only trickle down to 24v.

Good discussion

Peter
 
While 48 volts might sound great from a internet discussion prospective, it's use is highly limited on a boat.

The available devices set the voltage. Things like lights, pumps, etc...

I see a lot more advantage making your boat all 120 volt, and maybe picking a alternative voltage for the DC side of a inverter system.
 
There is no doubt that a 48 V. system works well in a terrestrial market, but we are boaters. The guys with their feet on the ground don't really have any 12 V. (or 24 V. ) loads as everything is done at 120 V. (or 230 V.) ac. Who at home has a 12 V. dc light?

I think the other problem with 48 V. dc is that this voltage is enough to require that wiring connections (like 120 V. ac) have to occur in a box. I'm not sure on this but I think the NEC limits low voltage DC in a wet environment to 30 Volts. My boat is not wet but I doubt if I could successfully argue that point.
Any NEC experts on here, chime in please! What does ABYC say?

Anybody got any flush mounted 48 V. ceiling led lighting fixture where the connection occurs in a box? I would need about 50 of them. How about the 48 V bulb, do they exist?
What about your bilge pumps, VHF and search light, are you switching those kind of things to 48 V. dc?
If so, how?

Yes, you could power all of these low voltage things using multiple voltage converters but will you have enough 48 V. to 12 V. capacity?

As I would think it's a given that we need 120/240 V. ( 230 V.) ac on board to power the galley, the water heater, the laundry & all of the other 120 V. loads, we will also need only one dc voltage to do the rest of the work. Unless things change I don't see that being 48 V. Maybe I'm wrong!

I see ksanders beat me to the point.
 
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Point is not to convert 12v/24v systems to 48v. Point is to create a dedicated AC generation system that stores and distributes energy efficiently and predictably.

I don't view 48v as another DC voltage on a boat. I view it as a a standalone AC power generation system - same role as a diesel generator except inverter power is better suited to internment, low-draw usage common in boats (and homes for that matter). Right now, features and functions available in 48v are much better than 12v/24v options. Over the last 20 years or so inverter power has gone from convenience to necessity. Why not have a system purpose built? 48v inverter/chargers are better, cheaper, safer, and better integrated than 12v/24 counterparts.

At 36-feet, my boat is unlikely to ever be a candidate for 48v. But I certainly see the use case is near for many boats only slightly larger. Air conditioning and cooking (induction/instant pot/etc) have crept from generator support to inverter support.

Peter
 
If I have a 50 amp dc to dc charger from a start battery to the LP batteries, is it additive to whatever the inverter is charging when on gen or shore power? So if my Victron inverter charger is charging at 120 amp and my pro mariner 50 amp charger going to the start battery is powered, do I get 170 amps going into the LP bank once the start battery is full?

Also. on the 48v subject, I always assumed you just convert back to 12v for anything on the boat. Seems like lots of converters available pretty reasonable. Convert to 12v from the 48v and tie once at the electrical panel. Would think it saves in cable sizing. Is it not that simple?
 
Point is not to convert 12v/24v systems to 48v. Point is to create a dedicated AC generation system that stores and distributes energy efficiently and predictably.

I don't view 48v as another DC voltage on a boat. I view it as a a standalone AC power generation system - same role as a diesel generator except inverter power is better suited to internment, low-draw usage common in boats (and homes for that matter). Right now, features and functions available in 48v are much better than 12v/24v options. Over the last 20 years or so inverter power has gone from convenience to necessity. Why not have a system purpose built? 48v inverter/chargers are better, cheaper, safer, and better integrated than 12v/24 counterparts.

At 36-feet, my boat is unlikely to ever be a candidate for 48v. But I certainly see the use case is near for many boats only slightly larger. Air conditioning and cooking (induction/instant pot/etc) have crept from generator support to inverter support.

Peter
Exactly.
That’s what I thought the conversation was about. Using 48 volt for house120/240 loads. We’ve been increasing the number of ac powered devices on boats for many years. A 48 volt 20 kwh bank will go a long way to eliminating generator usage. Especially with a good solar array to charge it.
We already have two or more battery banks on board now, it doesn’t seem like a big deal to have different voltages in one bank dedicated for house loads.
In fact, how many discussions have there been about fluctuating 12 volt knocking out electronics? Having a voltage stabilized power supply driven off the house bank solves that issue.
It’s not for everyone, but a larger boat with more ac loads can benefit.
 
Exactly.
That’s what I thought the conversation was about. Using 48 volt for house120/240 loads. We’ve been increasing the number of ac powered devices on boats for many years. A 48 volt 20 kwh bank will go a long way to eliminating generator usage. Especially with a good solar array to charge it.
We already have two or more battery banks on board now, it doesn’t seem like a big deal to have different voltages in one bank dedicated for house loads.
In fact, how many discussions have there been about fluctuating 12 volt knocking out electronics? Having a voltage stabilized power supply driven off the house bank solves that issue.
It’s not for everyone, but a larger boat with more ac loads can benefit.
If you already have a 12V bank and a 120VAC powered 12VDC battery charger, you already have the 48V to 12V charging in place. Just run the 120VAC powered 12VDC charger off the 48V inverter 120VAC output, which will probably always be on anyway. In this manner, the existing 12V bank acts as your voltage stabilizer. The old 12V bank will likely last decades like this because it will almost always be in float and you don't need to spend any money on the 12V side of your house bank, you just need to add solar, a 48V bank, and a 48V inverter. It's actually cheaper to do solar at 48V too, so there's that.

The downside of this setup is that there's no efficient way to charge the 48V LFP bank with engine alternator(s), but I think a lot of people are realizing that doing that is hardly worth the effort and expense since they can always still run the whole boat on the 12V bank that they left intact and consider the 48V stuff as all part of the solar package and just think of it as "bonus power" that's there when the sun shines. If you really had to charge the 48V bank from the 12V alternator(s), you would simply turn on the old 12VDC inverter and use it to power the 48V inverter with 120VAC so that it then charges the 48V bank. You would probably need to throttle the 48V charge amperage down quite a bit if it's a big inverter; the 5000 watt model I plan to use delivers up to 70 amps of 48V DC charging which would require close to 300 amps of 12V DC at the inverter input. With my puny 3208TA alternators, I'd likely need throttle the 48V charging to 5 or 10 amps.

If you have the option of adding a big 48V alternator, you could always do that and keep the 12V bank charged via the 48V inverter as described in the first paragraph. Assuming the goal is to add a ton of solar to a 12V boat though, I cannot think of a too many scenarios where this would make sense.
 

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