Can you use a victron DC solar controller as a DC to DC charger?

[S/Y BLUE]

Hey everyone, just strted educating myself on marine DC/AC systems. Life long professional sailor, but never bothered to learn about electricity.
I have read threads about similar topic but nothing really specific to my question. I have a 47ft sailing catamaran and plan to upgrade my DC voltage to 48V lithium from 12V lead. I have twin engines each with 80 amp alternators, and I plan to keep separate DC banks. 48 volt bank powering inverter charger, and all heavy power AC power appliances. With 12 volt bank powering my existing boat systems, all 12V DC. Pumps, autopilot etc. Anyway, one alternator with victron 12V DC to 12V DC charger charging 12V bank is simple. But using the other alternator to charge the 48 volt main house bank is proving difficult and costly. I found a promising 12V to 48V DC charger, but as it is no name equipment( Foval 12V to 48V 800W charger for LiFePO4) i am cautious about not cleaning power output before dumping into my planned 48V EPOCH batteries. And as I can't find a 48V to 48V DC converter, I was wondering if I could run this through a stand alone Victron 48 volt solar controller? What say you experts?
Also my grand plan, is four 400V Bifacial panels hung off back of boat to get energy from both sides, on bespoke aluminum framed solar stand. Two strings in series to their own individual solar controllers. Tied into a victron distributor and all the other victron smart bits. 10000w 48V Quattro, 240V, which i was hoping could provide 240 for heavy energy appliances on one leg and 120V on other leg for existing 120V? Is that doable?

 

[sunshine_eggo]

Victron MPPT require the input to be +5V above battery to start charging and stay +1V above battery voltage to continue charging.

Victron does not make a split phase inverter for 120/240V power. You either need 2X 120V units configured to work in 120/240 split phase, or an EU model set for 60Hz/240V with an Autotransformer to get 120/240V power.

 

[AnarchyJet]

How much AC power do you need? With 1600w of solar and 1 80a alternator, I don't see a case to go 48v.
Staying 12v will allow you to use both alternators with DC-DC to charge the house bank.

 

[S/Y BLUE]

How much AC power do you need? With 1600w of solar and 1 80a alternator, I don't see a case to go 48v.
Staying 12v will allow you to use both alternators with DC-DC to charge the house bank.

Will sent me down the 48V rabbit hole. The more I looked into it the more convinced I am that it would be stupid to stay 12v as I have to replace my dead lead this year anyway. Two 300 Ah lithium will more than cover my 12 volt DC needs, I have two roof mounted 100 watt panels and a 12 volt solar charger already in place for the 12v existing system. So I will just leave it is my present thinking. I will sell the Victron 12V 120V charger/inverter i already have installed and upgrade to the 48V 240v. The capacity the 48V batteries will give me is a game changer. I plan a round the world sail with the wife in a few years. So a 12 volt system already in place as redundancy seems prudent. And the 48 is just the future, plus I figured I could find a way to rig a system that would allow me to charge the 12V bank from the 48V bank if called for.
Wife wants washer dryer, air fryer, convection stove top ect ect. So 240V will be more efficient and 48V will give me capacity without me having to stress about energy to much is the hope.

 

[S/Y BLUE]

Victron MPPT require the input to be +5V above battery to start charging and stay +1V above battery voltage to continue charging.

Victron does not make a split phase inverter for 120/240V power. You either need 2X 120V units configured to work in 120/240 split phase, or an EU model set for 60Hz/240V with an Autotransformer to get 120/240V power.

Sunshine so if I am following, it is possible? But once the battery bank hits capacity then the 12 to 48 charger from alternator won't be able to meet the requirements of the solar controller and it will stop charging?
So the multi phase from the inverter can't be split into 240 out one AC out and 120 out the second AC out?

 

[S/Y BLUE]

Sunshine so if I am following, it is possible? But once the battery bank hits capacity then the 12 to 48 charger from alternator won't be able to meet the requirements of the solar controller and it will stop charging?
So the multi phase from the inverter can't be split into 240 out one AC out and 120 out the second AC out?

I guess I am assuming the charger will be spitting out over 50V in charge cycle

 

[Backyard]

I think you might be confusing capacity and voltage or something. 4X 12 volt batteries is the same "capacity" whether it's connected in series or parallel. It's still 4 batteries

What series gets you is lower amp draw for the same load. Thus smaller gauge wire. Also, it's easier to find higher wattage equipment in higher voltage then 12V setups. But if you aren't drawing too much, 3K watts or so or less on your inverter then you can stay 12 volts and make the whole system easier on you. Take those four batteries and wire them in parallel. Or skip the dedicated 48V battery and buy 4X 12 volt ones. Once you start pushing past the 3k watt inverter load then jumping up to 24 or 48 starts to make more sense.

Maybe run a load calculation and let us know what you got, how much power you actually need and we can help you out better

 

[S/Y BLUE]

Victron MPPT require the input to be +5V above battery to start charging and stay +1V above battery voltage to continue charging.

Victron does not make a split phase inverter for 120/240V power. You either need 2X 120V units configured to work in 120/240 split phase, or an EU model set for 60Hz/240V with an Autotransformer to get 120/240V power.

Good to know I am thinking correctly about inverter as i was looking at the euro programed for 240 60Hz as you suggested. I also did look at the Autotransformer, but the auto has downsides for me. Space is main one as it's extremely limited on my cat and then there is the inefficient conversion of power again, going from 240 to 120 with another piece of expensive equipment.

 

[yabert]

What is the plan capacity of your 48V battery?
Seem like a 12V to 48V DC-DC or charger can do what you want, but it will become a critical component and you will have to decide how comfortable you can be in case of failure and long time before find a new one on a remote place.

About your 1.6kW of solar you plan, family with a Cat and 1.6 kW of solar installed generate an average of 5 kWh/day in the Antilles.
Up to near 7 kWh/day during best day, but anyhow it can be ''a lot'' of energy on a boat if your consumption is moderate.

 

[S/Y BLUE]

I think you might be confusing capacity and voltage or something. 4X 12 volt batteries is the same "capacity" whether it's connected in series or parallel. It's still 4 batteries

What series gets you is lower amp draw for the same load. Thus smaller gauge wire. Also, it's easier to find higher wattage equipment in higher voltage then 12V setups. But if you aren't drawing too much, 3K watts or so or less on your inverter then you can stay 12 volts and make the whole system easier on you. Take those four batteries and wire them in parallel. Or skip the dedicated 48V battery and buy 4X 12 volt ones. Once you start pushing past the 3k watt inverter load then jumping up to 24 or 48 starts to make more sense.

Maybe run a load calculation and let us know what you got, how much power you actually need and we can help you out better

Backyard let me clarify, one 48V 100Ah battery has the same(and my terms ain't scientific lol) Amp hour Ah capacity as four 12 volt 100Ah batteries, plus WAY more energy capacity as i understand. I don't know the terms yet, but I did the research. I plan on 3 Epoch 48V @100Ah batteries for my 48V bank. I really should do a load calculation but it just doesn't seem important to my thinking at the moment. I will explain, it's not about my current(pun?) needs but about putting in a system to meet any future needs. My thought process is if I am having to spend thousands anyway why not do it with expansion in mind for a few hundred more? My current 12v Victron 3k inverter couldn't handle my needs for example if microwave and air fryer were on together. Yes we managed but why have to manage if we can set up system to handle most things being used in a more friendly day to day manner?

 

[S/Y BLUE]

What is the plan capacity of your 48V battery?
Seem like a 12V to 48V DC-DC or charger can do what you want, but it will become a critical component and you will have to decide how comfortable you can be in case of failure and long time before find a new one on a remote place.

About your 1.6kW of solar you plan, family with a Cat and 1.6 kW of solar installed generate an average of 5 kWh/day in the Antilles.
Up to near 7 kWh/day during best day, but anyhow it can be ''a lot'' of energy on a boat if your consumption is moderate.

 

[S/Y BLUE]

Also have genset and don't forget the alternators. But idea is on long sail legs, think 3k nautical miles, 10 days at sea...not to lean on fossil fuels for daytime energy.

 

[yabert]

I plan on 3 Epoch 48V @100Ah batteries for my 48V bank

So, 15 kWh. Nice ''big'' battery for a boat.
As reference, family with a Cat and 1.6kW of panels have 7.5 kWh. Regularly battery was full before noon.
Still, panels placement and shade is an important metric to generate maximum energy quantity.

 

[Glock24]

The solar charge controller would work of you wanted to charge the 12V batteries from the 48V bank, but not the other way around. I know there are DC to DC chargers capable of charging 48V systems from 12 or 24V. You have to look into that.

 

[sunshine_eggo]

Good to know I am thinking correctly about inverter as i was looking at the euro programed for 240 60Hz as you suggested. I also did look at the Autotransformer, but the auto has downsides for me. Space is main one as it's extremely limited on my cat and then there is the inefficient conversion of power again, going from 240 to 120 with another piece of expensive equipment.

The AT conversion is very efficient. The only drawback to the AT is the hard limit on the neutral. The neutral can only carry 28A continuous or 32A for 30 minutes. This means that the imbalance in 120V use between legs is limited to 3360W continuous, 3840W for 30 minutes.

 

[Backyard]

Backyard let me clarify, one 48V 100Ah battery has the same(and my terms ain't scientific lol) Amp hour Ah capacity as four 12 volt 100Ah batteries, plus WAY more energy capacity as i understand. I don't know the terms yet, but I did the research. I plan on 3 Epoch 48V @100Ah batteries for my 48V bank. I really should do a load calculation but it just doesn't seem important to my thinking at the moment. I will explain, it's not about my current(pun?) needs but about putting in a system to meet any future needs. My thought process is if I am having to spend thousands anyway why not do it with expansion in mind for a few hundred more? My current 12v Victron 3k inverter couldn't handle my needs for example if microwave and air fryer were on together. Yes we managed but why have to manage if we can set up system to handle most things being used in a more friendly day to day manner?

Energy would be the ability to supply the current needed. Whereas capacity would be for how long

When it comes to batteries. Putting 4x 12V 100AH in parallel would get 400AH at 12V. 400X12 = 4800wh

4X 12V 100AH in series is 100AH at 48V. 100X48 = 4800wh

Both configurations give the same capacity or more accurately kWh

The difference between these two really comes down to ohms law. A 48 volt pack can deliver more energy to the same load or resistance. But with a load designed for 48 volts, it would in theory have 4x the resistance. Not always the case for inductive loads such as motors. But it gives you the idea

4X batteries in parallel has 1/4 the total internal resistance. A 4X in series pack has 4X the resistance of one battery. So it all cancels out

The difference is the external load. If the external load is the same then the 48V pack will deliver more energy. Since loads designed for their respective voltage whether it be 12 or 48 volts, if the same wattage will take the same energy. The difference really is in faults, shorts, etc where a low resistance path is created and high current is allowed to flow. A 48V pack will deliver 4X the current during this fault then a 12V battery. In this respect a 48V is more dangerous

The benefits and reason why people still use 24, 48 or even higher voltage packs is the reduced current needed to run an appliance for the same wattage used. This means smaller gauge wire. There can be a significant cost savings just in cables alone depending on how much batteries you have and the length of run for the cables

Another consideration is the SCC can have upper limits to the current it can provide. This can limit your total wattage used to charge your batteries. If you are limited to a particular current then doubling the voltage doubles the wattage. Similar issues apply to inverters. Often when you start getting into higher KW SCC' and inverters it's the maximum amperage that limits how much you can get or deliver. bumping up to the next voltage gives you more wattage.

It boils down to, if 12 volts can supply you the needed wattage then stick with 12V. If you run into a bottle neck then bump up the voltage

This is why we need to know your loads to be able to help on selecting proper equipment and voltage

 

[S/Y BLUE]

The AT conversion is very efficient. The only drawback to the AT is the hard limit on the neutral. The neutral can only carry 28A continuous or 32A for 30 minutes. This means that the imbalance in 120V use between legs is limited to 3360W continuous, 3840W for 30 minutes.

That's extremely useful information for me, the 120 side would have no heavy appliances on it, mostly phone chargers but I already have all the cabins wired with 12v USB outlets. Computers and maybe my CPAP machine, probably under 15A max load continuous. Ok so probably will have to budget in the AT to keep 120V viable if I decided to keep 120 on the inverter side instead of strictly Generator running to power the outlets.

 

[S/Y BLUE]

The solar charge controller would work of you wanted to charge the 12V batteries from the 48V bank, but not the other way around. I know there are DC to DC chargers capable of charging 48V systems from 12 or 24V. You have to look into that.

Block so you think I could use a solar controller on a switch running from 48V bank to 12V bank as a way to charge my 12V bank as needed? That would be awesome for me as my 12 volt loads are heaviest at night. Autopilot, running lights, navigation equipment, everyone in cabins with fans on. What safety would I need other than fusing it doing it that way? The batteries will have the usual safety systems so they should protect themselves i am thinking.

 

[S/Y BLUE]

So, 15 kWh. Nice ''big'' battery for a boat.
As reference, family with a Cat and 1.6kW of panels have 7.5 kWh. Regularly battery was full before noon.
Still, panels placement and shade is an important metric to generate maximum energy quantity.

Traveling family is usually wife and I plus 5 year old. But when stepkids and grandma's invade it's full house lol! Mainsail won't shade the panels off back of boat. Also will probably not sail outside of the mid latituds, pacific and Atlantic side.

 

[yabert]

Mainsail won't shade the panels off back of boat

That remind me a short trip between Martinique and St-Lucie on the family cat.
Full sun, but mainly in front port side, so mast and sail shade half of the panels in rear. Production difference between each side was impressive (2 MPPT for 4 panels). Pic below.

About DC-DC, you can find 48V to 12V from Victron or others and also 12V to 48V on ali, amzn, etc. There is no challenge to find them.
Charger from 230Vac or 120Vac to 12V is also possible and can be useful at dock. Or even 48V charger.
There is many choice and you have to choose wisely based on the complete system and needs.

I'm all for the 48V system, but at the same time, if your needs are relatively low, staying at 12V is easy, reliable (less components) and parts are common.
The only time I saw a power problem on the Cat of family and the 3 kW inverter is when inductive cooktop was at max and mother in law start the microwave.
Of course, we don't run vacuum or water maker all at the same time.

 

[S/Y BLUE]

That remind me a short trip between Martinique and St-Lucie on the family cat.
Full sun, but mainly in front port side, so mast and sail shade half of the panels in rear. Production difference between each side was impressive (2 MPPT for 4 panels). Pic below.

About DC-DC, you can find 48V to 12V from Victron or others and also 12V to 48V on ali, amzn, etc. There is no challenge to find them.
Charger from 230Vac or 120Vac to 12V is also possible and can be useful at dock. Or even 48V charger.
There is many choice and you have to choose wisely based on the complete system and needs.

I'm all for the 48V system, but at the same time, if your needs are relatively low, staying at 12V is easy, reliable (less components) and parts are common.
The only time I saw a power problem on the Cat of family and the 3 kW inverter is when inductive cooktop was at max and mother in law start the microwave.
Of course, we don't run vacuum or water maker all at the same time.

View attachment 284191

I like your design for panels mount. My cat is different design so going different way, but they all in the end do the same thing. My aft arch allows me to butt panel mount up to it and run my wires through arch into boat. 2004 leopard 47. Probably end up looking like this, kinda.

 

[yabert]

Probably end up looking like this, kinda.

Nice! You will produce quite a bit of energy then.

My current 12v Victron 3k inverter couldn't handle my needs

Why don't simply add another to have 6 kW splitphase 120/240?
Anyway, I can't wait to know your final choice of system voltage. Don't hesitate to plan and ask questions before buying anything. There is a lot of knowledge here on this forum.

 

[S/Y BLUE]

Nice! You will produce quite a bit of energy then.


Why don't simply add another to have 6 kW splitphase 120/240?
Anyway, I can't wait to know your final choice of system voltage. Don't hesitate to plan and ask questions before buying anything. There is a lot of knowledge here on this forum.

10k is just better in my mind , will probably just run one output through the transformer recommend above to get my 120v, especially as the 120V side will be low load.

 

[AnarchyJet]

+1 for running two 3000/12 victrons. It will give you redundancy on the AC side. Set up for split phase you get 120/240. Single 12v house bank to manage. As stated before the capacity is the same. As long as the inverters can be mounted close to the batteries, the current isn't really an issue.
I think the biggest advantage being PV voltage requirement for charging. A single panel will produce enough vs requiring 2 in series. All boats have major shading problems, that benefit from multiple SCC and parallel panels.
Just curious, have you brought this up on cruising forums, anyone else do this with success? The 48v installs i've seen are because of electric propulsion. What is your plan for the windlass or electric winches?

 

[yabert]

Good summary of all the good points to stay at 12V and 6kW.
Then add increase reliability because of fewer component and