Victron 24v to 12v converter or dc dc charger?

[Enyar]

Originally Posted by noelex 77

The requirements for charging a lead acid battery in cyclic operation are quite different to charging the same battery in standby operation (a battery that remains at 100% SOC).

DC to DC chargers are generally set up for charging a battery in cyclic operation. They have seperate voltage set points for bulk/absorption and float. Batteries in standby operation have different requirements, typically needing a constant voltage just below the float setting voltage set point. This is because the battery remains at 100% SOC and in this state the higher bulk voltage is detrimental.

DC to DC chargers are the better choice if the lead acid battery is subject to cyclic operation such as an engine start battery. The start battery does not remain at 100% SOC so the bulk/absorption and float algorithm is appropriate.

Some DC to DC chargers have the ability to select user settings that are suitable for standby operation, but otherwise for standby operation where the lead acid battery is kept at 100% (such as lead acid battery used to buffer the output) a DC to DC converter can be a better choice if it has adjustable voltage set points (most do). The stable voltage supply is also better for sensitive electronics. A higher bulk voltage when applied to a battery at 100% SOC risks a high voltage spike when large loads are turned off.

Thank you for the knowledge drop!

[Statistical]

Originally Posted by noelex 77

The requirements for charging a lead acid battery in cyclic operation are quite different to charging the same battery in standby operation (a battery that remains at 100% SOC).

DC to DC chargers are generally set up for charging a battery in cyclic operation. They have seperate voltage set points for bulk/absorption and float. Batteries in standby operation have different requirements, typically needing a constant voltage just below the float setting voltage set point. This is because the battery remains at 100% SOC and in this state the higher bulk voltage is detrimental.

DC to DC chargers are the better choice if the lead acid battery is subject to cyclic operation such as an engine start battery. The start battery does not remain at 100% SOC so the bulk/absorption and float algorithm is appropriate.

Some DC to DC chargers have the ability to select user settings that are suitable for standby operation, but otherwise for standby operation where the lead acid battery is kept at 100% (such as lead acid battery used to buffer the output) a DC to DC converter can be a better choice if it has adjustable voltage set points (most do). The stable voltage supply is also better for sensitive electronics. A higher bulk voltage when applied to a battery at 100% SOC risks a high voltage spike when large loads are turned off.

No battery charger should be applying bulk voltage to a battery at 100% SoC. If it is you should throw it in the trash now. That is the whole point of 3 phase battery charger to ensure higher voltage is not applied to batteries in high stage of charge.

I agree to all of those warning about high voltage applied to batteries in high state of charge but any charger doing that should be removed from the boat now. Even for a battery that is cylcing eventually it is going to end up in a high SoC and the charger will destroy it.

[noelex 77]

Originally Posted by Statistical

No battery charger should be applying bulk voltage to a battery at 100% SoC. If it is you should throw it in the trash now. That is the whole point of 3 phase battery charger to ensure higher voltage is not applied to batteries in high stage of charge.

The charging algorithm is not that sophisticated. It does not typically know the batteries SOC. Despite this lack of sophistication, charging algorithms work well for a battery under cyclic use, but unfortunately will overcharge batteries in standby use. There are exceptions, for example some Victron chargers have a “storage mode” and others have enough manual adjustment that satisfactory voltage set points can be selected, but this is far from universal and few users know the appropriate settings.

The bottom line is that for standby use most lead acid battery manufacturers specify a low constant voltage, typically around 13.4v. Few DC chargers will deliver this at least as a default, but this is easily achieved with a DC converter with an adjustable output.

As to throwing out chargers that will apply bulk voltage to a battery that is at 100% SOC, you will at least need to throw out all your solar chargers because they all start each solar day at bulk voltage, irrespective of the battery SOC.

[Statistical]

Originally Posted by noelex 77

The charging algorithm is not that sophisticated. It does not typically know the batteries SOC. Despite this lack of sophistication, charging algorithms work well for a battery under cyclic use, but unfortunately will overcharge batteries in standby use. There are exceptions, for example some Victron chargers have a “storage mode” and others have enough manual adjustment that satisfactory voltage set points can be selected, but this is far from universal and few users know the appropriate settings.

Fair enough. Are there any potential issues if the battery does become modestly discharged with a constant 13.4v charging? For example accidentally cutting off charger and a few weeks of self discharge or temporary high loads pulling SoC down a bit. Or will it simply just charge back up to full SoC slower than it would with bulk charging?

[noelex 77]

Originally Posted by Statistical

Fair enough. Are there any potential issues if the battery does become modestly discharged with a constant 13.4v charging? For example accidentally cutting off charger and a few weeks of self discharge or temporary high loads pulling SoC down a bit. Or will it simply just charge back up to full SoC slower than it would with bulk charging?

There are situations where it is difficult to know if the battery will be in standby or cyclic use. Leaving a boat over winter is a common example.

If there is no discharge, setting the charge voltage to a low constant voltage, say around 13.4v, would be a good choice. This will maintain the battery at 100% and replace any capacity lost from self discharge without overcharging the battery or causing too much water loss if it is a flooded battery. However, if the boat is in the water and a leak develops causing the bilge pumps to cycle, this battery may now be in a cyclic mode (depending on the charger output and bilge pump consumption) and the more normal bulk, absorption and float charging algorithm may be more appropriate. The standby charging settings are only appropriate for a battery that is staying at 100% SOC.

Note, the above only applies to lead acid (not lithium) batteries. Even within the lead acid family there are some variations. Some lead acid batteries benefit from a periodic very short (a few minutes only) absorption cycle even when 100% charged. This is said to “stir up and prevent stratification of the electrolyte” although in practice it probably helps more by equalising the cells.

In short, the normal default bulk, absorption and float charging set points are not appropriate for a lead acid battery that is kept for long periods at 100% charge. It will overcharge the battery and shorten the battery life. If the charger is adjustable, at least reduce the bulk, absorption and float voltage set points and the absorption time if this is possible. If you can set the charger to deliver a low constant voltage of around 13.4v, this is not a bad choice.

[CaptainRivet]

Originally Posted by s/v Jedi

As usual I don’t agree to most that was posted.

You can simply take a 24-12 converter set at the safe 12V level, which is 13.2V, plus connect a small motorcycle 12V AGM battery to that 12V circuit.

AGM will love the constant 13.2V and even buffer high demand spikes if any. It will also absorb transient surges, protecting sensitive equipment.

You only need 24-12 chargers if you intend to run 12V loads that take down a battery to low SOC before it gets charged again. This hardly ever happens.

That said, good units like the Victron Smart Orion can do both and are easily reprogrammed via a Bluetooth app so very versatile and ai recommend them.

Instead the worst chemistry for boats AGM use a small Lithium buffer battery, its BMS will shut off the converter if it fails. The AGM will get a thermal runaway and can cause a fire when the converter fails a deliver 24V or 30V...same the common mistake Alt reg failure.
The Lithium will deliver current spikes and also act as buffer.
It ultimate solution is an 20-50 AH LTO 12V battery that simply runs the whole 12V systems and get recharged by a converter, use Victron phoenix 2412 in 70A to buffer it as a LTO can do up to 10C constant dis-charge that can also act as emergency starter backup. The BMS will shut off converter if it fails.
The 2nd advantage as you run LTO at 12-15V (2v LVC, 2,5V HVC and they life litteraly forever) and mostly be in the area of 13,6V till 14,4V which is optimal for your pumps and all that contains amplifier. All 12V equipment can withstand 15,2V as thats the testing norm for it.
Thats what i am gonna do installing 6x40AH LTO Yinglong cells with active balancer and Electrodacus BMS (You don't need BMS but i have 2 spare onboard so use one as working spare...)when converting to 24V to run all 12V equipment.
Have a look at Alibaba&Co cheap class B LTO are more then enough here, even when the 35AH turn into 25AH that LTO can do 250A constant and is more then enough for that usage.

[CaptainRivet]

Instead of a FLA just get 4x40AH Winston LFP cells, put a jk BMS on it and you have a perfect buffer battery for 300Euro , that can in emergency act as starter (3C const, 6c peak).
Connect and charge (you don't need 3 stage DC2DC charging) it with a Phoonix 24 to 12V in 70A, that cost 170Euro and will always deliver enough charge, 2nd if the battery fails which is highly unlikly that 70A can supply the house directly without the bat.
The Orion DC2DC is 300Euro, the phönix 170 for double current. The money saved pays you 2 Winston cells.

[noelex 77]

Originally Posted by CaptainRivet

Instead of a FLA just get 4x40AH Winston LFP cells, put a jk BMS on it and you have a perfect buffer battery for 300Euro , that can in emergency act as starter (3C const, 6c peak).
Connect and charge (you don't need 3 stage DC2DC charging) it with a Phoonix 24 to 12V in 70A, that cost 170Euro and will always deliver enough charge, 2nd if the battery fails which is highly unlikly that 70A can supply the house directly without the bat.
The Orion DC2DC is 300Euro, the phönix 170 for double current. The money saved pays you 2 Winston cells.

With modern equipment almost everything will run on 24v directly. There is generally no need for a high powered 12v system, such as you are suggesting. Our total 12v house consumption is only for two devices and maxes out at less than 3A. This can be taken care of with a small 24v to 12v converter. If you want to add a battery back up, a small sealed lead acid battery would be ideal.

The exception is boats trying to convert from 12v to 24v with a large amount of legacy equipment, but even here the equipment will be gradually replaced with models capable of running from 24v.

[CaptainRivet]

Originally Posted by noelex 77

With modern equipment almost everything will run on 24v directly. There is generally no need for a high powered 12v system, such as you are suggesting. Our total 12v house consumption is only for two devices and maxes out at less than 3A. This can be taken care of with a small 24v to 12v converter. If you want to add a battery back up, a small sealed lead acid battery would be ideal.

The exception is boats trying to convert from 12v to 24v with a large amount of legacy equipment, but even here the equipment will be gradually replaced with models capable of running from 24v.

You have no 12V fridge, fresh water pump, bilge pumps....definitly in 20A region if all is on simulationiuosly and nothing of that is dual voltage.
Then you have your existing curcuits as not all can take 24V, if you wanna rewire everything for some small current less, well go ahead...i don't.

Maybe you not but i have plenty working and newish 12V legacy equipment, starting with a 12V watermaker HP35 or Autopilot Raymarine 12V linear drive Typ2 that will need plenty of current. Sure if the hp pump breaks it will be replace with a 24V one and connected to 24V bus but that will take time and till then it runs at 30-40A at 12V.

I have a 2005 FP Lavezzi, so 24V goes mainly for the inverters, energy storage and i will change the windlass motor to 24V.
So the rest is the old 12V legacy wiring spread all over the boat, eg fresh water pump is not running on 24V. Means I simply connect the old house legacy main wire to the 12V LFP or LTO and charge it with the 70A Converter from the 24V LFP. Job done converting for the change, and 95% out there will do it exactly like this too when changing from 12V to 24V.

Running a new seperate 24V main cable to main DC board at Navstation and there will be the small 12V LTO placed, together with the 24V to 12V converter so i have a 12V and 24V bus at the navstation and can easier switch it from 12 to 24V if it breaks or can run at 24V too (eg new Axiom plotter and quantum 2 radar). Then when i have time and mood i switch it to 24V and get load of the 12V curcuits...if not it works fine on 12V too.
Engine is 12V incl all around it, so having a 12V starter backup is adviseable.

[s/v Jedi]

No, not in a thousand years will lithium like to be held at 100% SOC continuously.

Rivet is giving the worst advice ever, even worse than his misguided comments in the short current thread. This is the bane on the forum and there’s nothing we can do to stop these comments that can cost people who believe it dearly.

[noelex 77]

Originally Posted by CaptainRivet

You have no 12V fridge, fresh water pump, bilge pumps....definitly in 20A region if all is on simulationiuosly and nothing of that is dual voltage.

Our fridge and freezer will run from 12v or 24v out of the box. The same with the autopilot computer, chartplotter, AIS etc. Naturally we run them 24v. All bilge, water pumps and water maker are also 24v. Most marine pumps come in 12v or 24v versions these days.

Originally Posted by CaptainRivet

I have a 2005 FP Lavezzi, so 24V goes mainly for the inverters, energy storage and i will change the windlass motor to 24V.

If I understand correctly, the only equipment you have running on 24v at the moment is the inverter with the windlass to follow. High powered inverters and windlasses demand a very substantial amount of current and it is difficult to supply this efficiently and safely via 12v so there are sound reasons for this. But in this case your primary house bank is 12v with few supplementary devices running from 24v. You require a substantial 12v house battery system to power most of your devices. This is quite different to a 24v boat.

[CaptainRivet]

Originally Posted by s/v Jedi

No, not in a thousand years will lithium like to be held at 100% SOC continuously.

Rivet is giving the worst advice ever, even worse than his misguided comments in the short current thread. This is the bane on the forum and there’s nothing we can do to stop these comments that can cost people who believe it dearly.

Where did I suggest that?
I suggested to run LTO HVC at 2,5V means around 90%SOC, offical cutoff is 3.0V.

[CaptainRivet]

Originally Posted by noelex 77

Our fridge and freezer will run from 12v or 24v out of the box. The same with the autopilot computer, chartplotter, AIS etc. Naturally we run them 24v. All bilge, water pumps and water maker are also 24v. Most marine pumps come in 12v or 24v versions these days.



If I understand correctly, the only equipment you have running on 24v at the moment is the inverter with the windlass to follow. High powered inverters and windlasses demand a very substantial amount of current and it is difficult to supply this efficiently and safely via 12v so there are sound reasons for this. But in this case your primary house bank is 12v with few supplementary devices running from 24v. You require a substantial 12v house battery system to power most of your devices. This is quite different to a 24v boat.

Its very seldom what you have that even pumps are dual voltage.
The standard setup when boat is older 12V and when you go 24V you just convert the high current draw items which is typically inverter,windlass, eWhinch (have manual) and keep the rest in 12V which is maybe 30-40A in total where you connect a 24 to 12V converter to run it.


At the moment i have 12V only boat running 6,5kW inverter at 12V, mostly they run at around 2-4kw when cooking. Safe and nothing gets more then handwarm under full load.
I installed all from beginning to go dual 12/24V easly. Issue are the inverters as the 3000 W Victron is a 2kw in realty if you have 30+ degree celcius, not running 450A.

I already have 24V 2x 3,5kw Studer inverters, which are real LF top notch ones that have 2x9kw peak and no issues in heat or massive heat derating like victrons. Lying at my parents and waiting for install which means converting dual voltage, one is covering what i need and 2nd is to reduce load and run all cooler/call it a working spare. I will never reach their 18kw peak but well they will run all 230V equipment i ever connect.

The bank is now 1100AH and will be 550AH/24V and will run mainly the inverters+Windlass.

The rest is 12V but only needs a 40AH LTO as buffer, that gets topped up by a Phoenix 24 to 12V converter 70A. The capacity is in the 24V house.
Don't have to be big if you use LTO as they can do 10C.
Also good would be Winston cells as their new rating is 3C cont and 6C peak so a small LFP buffer is ok.
Advantage of LTO they run mainly 13.8-14.4v as thats their flat curve helping to cover up the voltage drop in 12V.

[s/v Jedi]

Originally Posted by CaptainRivet

Where did I suggest that?
I suggested to run LTO HVC at 2,5V means around 90%SOC, offical cutoff is 3.0V.

In post 36:

Originally Posted by CaptainRivet

Instead the worst chemistry for boats AGM use a small Lithium buffer battery, its BMS will shut off the converter if it fails.

[noelex 77]

Originally Posted by CaptainRivet

Its very seldom what you have that even pumps are dual voltage.

Yes, you are correct. Many marine electronic items these days will run automatically on both 12v or 24v, but most equipment with motors has to be purchased as a 12v or 24v model although there are exceptions. However, virtually all marine water and bilge pumps models are available in 24v versions and usually work better on the higher voltage.

Originally Posted by CaptainRivet

The rest is 12V

It is obviously not ideal to have so much running on 12v when your primary house bank is 24v, but with time, as items wear out you can replace equipment with 24v versions. The ideal is to start from scratch as a 24v boat, or at least make the change when an extensive refit is needed. This way almost everything on the house side can run from a single, higher, 24v voltage bank. This is a much simpler system and simple is usually more reliable in the marine environment.