Charging 24V Lithium via a 12V to 24V buck converter from a 12V alternator/starter

[CaptainRivet]

My goal:

As said main charge source is solar (bifacial panels that are less prone to shading) plus a Honda gasoline gen with range extender tank permanently installed as backup which charges the LFP with 170A via the shore power charger which is much more efficent then the diesel engines ever can via alternator. THe alternator should just deliver what they can in stock config with minimal invest possible.
So it also makes more sense to have 2x80A buck converter in 90% of the time running full power as i get much more AH out of this setup and well in 10% its suboptimal but cannot cause an issue or damage. ANd in this 10% its only one engine running and I most like will be aware that i run the engine at low rpm eg 1300RPM for a long time and then manually shut off the buck converter as it doesn't make sense anyhow then or if I need the alternator charge raise the RPM by 200-400RPM (0.3-0.5l/h extra) to get full 80A charge.

And I have a 1100AH 12V bank (average daily consumption 250AH with 1400W real bificial solar that normally covers consumption to 140%), that then it will be a 24V 550AH bank which is massivly oversized.

[s/v Jedi]

Originally Posted by CaptainRivet

yes i have the Victron Orion TR Smart in 12/12 30A version in my 12V setup now. Well 2 sided sword:
Negativ:

- Gets extremly hot, then throttling down the amps
- how long will it live frying the condensator/semi conductors with 60-70 degrees celcius??=> you need active ducted cooling to keep it below 40 degrees celcius and not throttling the 30A...
- you cannot limit the amp output to eg 20A
- doesn't show in the BT app how much amp goes in and come out
- besides the battery type you can only adjust start and shut off voltage (no custom setup of battery type possible)
positive:
- its a victron...
- communication and app via Bluetooth
- does what a DC2DC should do
And this costs 250-300Euro for 30A....too much and I even have to DIY a solution for active ducted cooling additional to keep it below 40 degrees celcius and not throttling the 30A...and not cooking its internal electronic to death...too expensive for what they do. Would I buy them again...NO.

For 12-24A only a 15A version for 300Euro exists, I have 2 engine and would therefor need 4x means 4x300Euro=1200Euro...then its cheaper to get 2x 24V alternators which deliver around 2x45=90A instead 4x15A=60A from DC2DC.

Did you install these in the engine room? My 12-24V ones do not get extremely hot and they reduce output progressively as it gets hot. This mechanism is exactly what prevents your worries about component failure due to temperature. This unit has an 88% efficiency, which means that 12% is converted to heat, so that can be 50W at full output.

The throttling down is why you do not need to worry about components getting too hot. The only reason to improve ventilation is to get more power transferred, because as you improve cooling, the unit immediately increases output until the same temperature or maximum output is reached.

The Smart Orion supports full configuration of battery settings like absorption voltage, float voltage etc. If you don’t see that, you are in power supply mode instead of battery charger mode. See attachment.

[CaptainRivet]

Originally Posted by Jammer

Sure, you could make it work. I don't think it would be worth it.


On a boat, there are three possible benefits to using 24v rather than 12v as the main storage voltage for the house batteries:


1. You can operate a large bow thruster without running heavy and expensive high-current cabling and without setting up a separate bow thruster battery.


2. On the engine, you can use 24v alternators, which give you somewhat more power in the same amount of space and are less prone to overheating.



3. You can run smaller cabling between the batteries and the inverter-charger, and it becomes more reasonable to run very large loads, such as an electric galley or air conditioning.


If you have a 6.5 kw inverter and it is installed and working fine, and you don't have a bow thruster, and you don't want to change out the alternators, there is no good reason to switch to 24v unless you've run out of boat projects and just want to do a science experiment "4 the lulz."


When you add complexity you add potential points of failure and you add difficulty to future troubleshooting and maintenance.



My advice, if you really want a 24v bank for the inverter, would be to add one and leave your 12v system unchanged. Just have the 24v bank connected to the inverter and the 12v bank connected to everything else. If you want to charge the 12v from an AC source add a charger to do that. If you want to charge the 24v from the alternators then add a DC-DC converter to do that, just one.

There are many additional reasons for 24V house:
1) more security headroom: running 6,5KW on 12V means 600A through busbars and cabling. I do, have massiv cabling/busbars and fuses (all NH as nothing else is avaliable that can run more then 300A otherwise) and works but if you get a bad connection by eg getting loose that can get very fast very hot and cause a fire and/or damage cabling etc.
2) running 600A gets you into ripple problems, running 300A through a 700A continous rated install creates no riple at all.
3) to get 6,5kw I need to run a Victron multiplus 3000W (actually only 2,4kw) and feed via power assist function a 3,5kw inverter as fake shore power, so I get 6kw inverter power. Well in 24V a Victon 24/5000W Multiplus inverter is avaliable which delivers all i need, no tricks and simpler install. Forget to get anything above 3000W in 12V except of the very expensive Victron Quattro 12/5000. And in my case that is too huge in dimension, no space to install this...the 24/5000 multiplus fits.

4) for the 12V windlass the voltage drop in the 24m long cable (12m one way) is very high, even if its a 90mm one for a 12V/1000W windlass which is massivly oversized. With 24V or acctually 28,0V and a 20-28V to 13.8V buck converter at the end of that 24m windlass power cable and 1m before the windlass, the windlass gets full 13,8V. Spools like there is no tomorrow and motor lifespan is greatly improved.
5) I have a 2005 cat means part of the original install the cables are a bit oxidized. Not that much that you have to replace all but enough that a waterpump or other equipment with longer cable runs from 13,5V only get 12,5 or if bank is low from 13V only 12V. So again if I place a buck converter 20-28V to 10-15V after the long cable run from bank to Nav-station where main fuse panel is, I simply raise the voltage to 15V at the input of the main fuse panel, voila the waterpump or fridge compressor gets 13,5v-14V...again runs faster and lifespan greatly improved. All 12V equipment can withstand 15,0V and most like that, eg radio deilvers much more output and cleaner sound....
6) 24V means in my case instead a 4P4S 12V setup I will have a 2p8S setup means the BMS controlls more cells directly and less cells are in parallel. Negativ if one cell gets bad i loose 50% capacity, while at 12V only 25%.
7) getting install material and equipment (also as tool, backup or spare) that can do 600-700A is rare, very hard to source and very expensive...plus no room for error installing that, you really need to know what you are doing and execute 100%, means checking everything 5x before pulling 600A and regularly checks while doing it that nothing got loose or....
8) 24V alternator delivers more then a comparable 12V on...eg 115A Mitzi can do 60-80A in 12V, the 24V does 45-50A in 24V means 10-20% more output.

9) many more....
Buck converters are cheap, so keep 2 as spare is 200Euro Invest in case one dies...

[CaptainRivet]

Originally Posted by s/v Jedi

Did you install these in the engine room? My 12-24V ones do not get extremely hot and they reduce output progressively as it gets hot. This mechanism is exactly what prevents your worries about component failure due to temperature. This unit has an 88% efficiency, which means that 12% is converted to heat, so that can be 50W at full output.

The throttling down is why you do not need to worry about components getting too hot. The only reason to improve ventilation is to get more power transferred, because as you improve cooling, the unit immediately increases output until the same temperature or maximum output is reached.

The Smart Orion supports full configuration of battery settings like absorption voltage, float voltage etc. If you don’t see that, you are in power supply mode instead of battery charger mode. See attachment.

What do you think about my buck converter combined with a BMV 712 setup to charge the 24V bank from 12V alternators?
Do I miss something important?



DC2DC:

No mine are in a very well ventilated space (acutally one of the coolest places in my cat), installed vertically and have 30cm top and bottom to ventilate well. But if you run them >45min at full power my IR temp meter shows 50-65 degrees celcius depending of the ambient temprature and throttling down to 25 A from 32A when starting cold.
With the old software (before updating) when the 30A version where even going to 38-40A ouput it reached cooking temps >70 degrees celcius...and many complained to Victron.
So to solve the problem, Victron simply throttled the ouput to 32A and when people complained they got told "we deliver what we promised..30A".... known issue with them.

Maybe the 12-24 15A are better or more effectiv?? as the 12-12 30A

The 88% efficency and 50W heat is when they are at 20 degrees celcius. 50 degrees gives you 26A output or 70% efficency and 30% waste...for victron that costs triple compared to a renogy 30A thats bad...


Had the same problem with the new 50A phönix smart charger...got 80 degrees celcius after charging for 40min with full 50A....complained and Victron said thats normal...well I send it back and told them that standing nowhere and my existing cabling in the surrounding where i wanna install it are only rated for 60 degrees celcius, which is normal practice outside of the engine room. Plus with 80 degrees celcius operation temp I highly doubt the electronic inside will survive very long...
Victron accepted it and and returned money....but didn't change anything....

https://www.youtube.com/watch?v=xvXkdgln1NA

check out his test and what he done for active cooling, will do the same if I keep them.


The Smart Orion supports full configuration of battery settings like absorption voltage, float voltage => in which setting can you do that or which preset do you need to chosse?
if I choose Lithium nothing can be adpated like with eg MPPT where you have an expert mode to adapt what you want.
Where can I limit the current with the 30A version but my alternator only delivers 20A at low rpm? Actually nowhere due to Victron forum...chose the 18A version was the answer from victron...

[s/v Jedi]

Originally Posted by CaptainRivet

6) 24V means in my case instead a 4P4S 12V setup I will have a 2p8S setup means the BMS controlls more cells directly and less cells are in parallel. Negativ if one cell gets bad i loose 50% capacity, while at 12V only 25%.

WhileI completely agree with going to 24V (I did the same), the second part of this statement is not correct.

With 2 cells parallel, if one cell goes bad, you loose 100% capacity. With 4 cells parallel, if one cell goes bad, you also loose 100% capacity.

If you want redundancy, you have to adhere to my reference diagrams, which show two separate batteries of equal capacity, each with it’s own BMS, fuse, and main battery switch. Now if one cell fails, you still have 50% of capacity left.

[s/v Jedi]

Originally Posted by CaptainRivet

What do you think about my buck converter combined with a BMV 712 setup to charge the 24V bank from 12V alternators?
Do I miss something important?

I think you mean a boost converter, to go up from 12V to 24V. I show this and how to do this in my reference diagrams.

No mine are in a very well ventilated space (acutally one of the coolest places in my cat), installed vertically and have 30cm top and bottom to ventilate well. But if you run them >45min at full power my IR temp meter shows 50-65 degrees celcius depending of the ambient temprature and throttling down to 25 A from 32A when starting cold.

That is how they are supposed to operate and not extremely hot.

With the old software (before updating) when the 30A version where even going to 38-40A ouput it reached cooking temps >70 degrees celcius...and many complained to Victron.
So to solve the problem, Victron simply throttled the ouput to 32A and when people complained they got told "we deliver what we promised..30A".... known issue with them.

“Cooking temps”? I may not have had my Orions long enough because I never got 40A out of one, but everything you describe sounds normal except the cooking temps which isn’t a term associated with this. Also, if like you claim the heatsink got to more than 70C then this starts me wondering what the internal component temperature is. While I am fine with 60C, I wouldn’t accept 75C.

Also, you have a misperception of what they did: they didn’t throttle output down to 32A to “take amps away from you” but most likely found the endeavor of a tech who found the unit can deliver 40A for a while didn’t work as planned because of the delays caused by thermal mass after a cold start, resulting in overshooting target maximum temperature. A slower warm up fixes this.

I have spent many years doing thermal design of electronics and I can say that Victron did an excellent job with the Smart Orion products. They out the heatsink on the outside, which you may not be used to and in fact made the whole housing the heatsink. The negative is that the housing gets hot, but the advantage is that you have no active cooling with a fan that is noisy, accumulates dust/dirt requiring regular maintenance, wears out etc. and leads to a lower cost as the alternative requires another housing around the heatsink and fans.

Maybe the 12-24 15A are better or more effectiv?? as the 12-12 30A

The 12-12 30A is 87% efficient so only one percent less.

The 88% efficency and 50W heat is when they are at 20 degrees celcius. 50 degrees gives you 26A output or 70% efficency and 30% waste...for victron that costs triple compared to a renogy 30A thats bad...

No, that is not how efficiency works, you have it wrong. Efficiency is not varying to any significant degree with temperature variation. 88% efficiency means that when you put 100W in, 88W comes out and 12W gets converted into heat.

When the temperature has gone up and the unit throttles down to prevent overheating, the efficiency stays at 88% even though the output is reduced. The reason is that also the input is reduced accordingly. So lets say instead of 100W going in, only 80W is going in. Now you get 70W coming out instead of 88W but also you only get less than 10W converted to heat, which allows the unit to cool down a bit, or not get any hotter.

Had the same problem with the new 50A phönix smart charger

I have no experience with this unit.

check out his test and what he done for active cooling, will do the same if I keep them.

Like I wrote before: when you improve cooling, you get more performance from the unit at the cost of a lower efficiency, more maintenance and more noise. Also, you get more heat transferred to the ambient.

=> in which setting can you do that or which preset do you need to chosse?

I attached the page from the manual in my previous post. I suggest you read the manual

Where can I limit the current with the 30A version but my alternator only delivers 20A at low rpm? Actually nowhere due to Victron forum...chose the 18A version was the answer from victron...

The Victron forum does not decide on the features of Victron equipment, the designer engineers do. The reason for leaving this out is based on cost and simplicity as well as dimensions of the product.

You are complaining about how a 30A unit will not do more than 32A and now you only want 20A ?!

Have you tried the 30A model on your 20A alternator output? Tell us what happened?

[bikekite]

If you ran 24V alternators for the house and ran a 24V to 12V DC-DC converter to keep the engine 12V system charged, any guess on the steady-state draw to keep a common rail diesel engine running?

[smac999]

Originally Posted by CaptainRivet

I didn’t buy anything, I am just thinking through an alternative solution to convert from 12 to 24V.
I am having now Victron Orion Smart DC2DC but in 12/12 30A. And actually they do nothing else then switch on if 13.5V of starter lead is minimum available and kick in with full 30A without any possiblity to reduce/limit the current. If voltage drops below 13,5V it switches off, same when BMS switches it off via remote input.
My solution:
As discribed above the BMV 712 will switch the Buck converter off via it’s programmable relay output when starter lead voltage is below 13.5V. So I cannot drain starter beyond 13.5V. Above the buck converter converts 12 to 24V with 80A till the BMS shuts it off. I could even connect the ignition plus to the relay too .so the buck converter can only be on if engine is running.
Like this I only draw when excess power is available.

They will kick in 30a then throttle back. They need to be setup correctly to work good. Your lock out voltage is probably too high. So it shuts off before it can throttle. Set to 12.0v. And keep the shutdown voltage over 13v

[CaptainRivet]

@jedi: ca'not find your reference diagram for the boost converter. could you please send a link or just repost here, would actually fit well.

Regarding Victron DC2DC: For the expensive top line product I expect under normal conditions minimum
1) the rating means 30A charge 1ll the time and 35 degrees in summer in typical locations med, Caribbean is common. But definitely not already at 25 degrees celcius ambient throttling. means I consider it to be a 12 12 25A one and that makes it even a more premium price point
2)expect a full feature set means eg I can linit current, to eg compensate for a hot mounting location or simply because the alternator eg only delivers 50A constant instead 60A as planned so just 2 DC2DC running with 25A each.
3)in normal condition it overfill rating sowing some headroom.

[s/v Jedi]

Here is my reference diagram for 24V house batteries, 12V start batteries, a Smart Orion 24->12 converter for charging the start batteries from solar and a 12->24 converter for charging the house batteries from the alternator.

[CaptainRivet]

Originally Posted by smac999

They will kick in 30a then throttle back. They need to be setup correctly to work good. Your lock out voltage is probably too high. So it shuts off before it can throttle. Set to 12.0v. And keep the shutdown voltage over 13v

thanks will try that out. sure they throttle back but because they get hot themselves.
but if I have an old dumb alternator without Temp control I sometimes just know after DC2DC is installed how much Amp this old dude can really produce and need to adapt/limit output to that.

[CaptainRivet]

Originally Posted by s/v Jedi

Here is my reference diagram for 24V house batteries, 12V start batteries, a Smart Orion 24->12 converter for charging the start batteries from solar and a 12->24 converter for charging the house batteries from the alternator.

The Orion’s are DC2DC chargers, no pure boost converter that I would use.
As described controlled by a BMV712 monitoring the starter bank, that disconnects the 12V side and therefor the whole boost converter. Boost converter charges 24V house with 28,0V fixed voltage. I described in #1 and #5 how I would do it.
Reference diagram:
I don‘t see a 12->24V just 2x 24-12 Orion’s…

[s/v Jedi]

Originally Posted by CaptainRivet

The Orion’s are DC2DC chargers, no pure boost converter that I would use.
As described controlled by a BMV712 monitoring the starter bank, that disconnects the 12V side and therefor the whole boost converter. Boost converter charges 24V house with 28,0V fixed voltage. I described in #1 and #5 how I would do it.
Reference diagram:
I don‘t see a 12->24V just 2x 24-12 Orion’s…

Normally, when going down in voltage we call it a buck converter and when going up in voltage we call it a boost converter. I rather just list the input and output voltages.

The Smart Orions are both: in the configuration you can set them either as charger or as power supply with the latter being the behavior as expected from a standard converter.

You have to imagine one in my diagram goes this way and the second goes that way. You’re not supposed to be able to read the labels on the images, which some call “blue blobs” because they can hardly see anything

Yes, I saw some posts of how you proposed to do this, but I don’t agree with that at all and neither do the equipment manufacturers. My reference diagrams use equipment as fully supported by manufacturers and confirmed by me as working 100%.

[CaptainRivet]

Originally Posted by s/v Jedi

Normally, when going down in voltage we call it a buck converter and when going up in voltage we call it a boost converter. I rather just list the input and output voltages.

The Smart Orions are both: in the configuration you can set them either as charger or as power supply with the latter being the behavior as expected from a standard converter.

You have to imagine one in my diagram goes this way and the second goes that way. You’re not supposed to be able to read the labels on the images, which some call “blue blobs” because they can hardly see anything

Yes, I saw some posts of how you proposed to do this, but I don’t agree with that at all and neither do the equipment manufacturers. My reference diagrams use equipment as fully supported by manufacturers and confirmed by me as working 100%.

Ah ok, I thought they are in parallel to raise current. So with 2x400AH 24V you are having one 12/24 15A to charge your house and one 24/12 30A to charge AGM starter (you really use AGM?)….that takes days to charge your house, even as backup too small.
That’s my issue with the Orion 300Euro for 30A=10Euro per A is just outrage expensive. Then it makes more sense to right away get a 24V alternator with a regulator to charge LFP directly and the small amount of current with a DC2DC into lead starter…

Can you explain why you don‘t agree with it at all doing it the way I proposed to do?

[s/v Jedi]

Originally Posted by CaptainRivet

Ah ok, I thought they are in parallel to raise current. So with 2x400AH 24V you are having one 12/24 15A to charge your house and one 24/12 30A to charge AGM starter (you really use AGM?)….that takes days to charge your house, even as backup too small.
That’s my issue with the Orion 300Euro for 30A=10Euro per A is just outrage expensive. Then it makes more sense to right away get a 24V alternator with a regulator to charge LFP directly and the small amount of current with a DC2DC into lead starter…

Can you explain why you don‘t agree with it at all doing it the way I proposed to do?

The solar array is what charges the house batteries. The dc-dc converter taking 30A from the alternator is just for motoring through the night scenario. Also, besides the other 12V loads, the oem alternator won’t be able to supply more. I have upgraded my alternator and added a second Orion so I take 60A out of it, but I also have my autopilot still at 12V so a higher load.

When you don’t have solar panels, or don’t have enough of them and you don’t have a generator either, then you may have to charge batteries with the main engine alternator. This is a bad scenario but I did make a diagram for that as well. Now you need a new alternator with external smart regulator and a lithium BMS that can turn the regulator off before a HVC occurs. All that is costly and not preferred.

Your idea on charging the house battery is something to remember in a situation where normal charge methods with correct charge profiles have failed and you need an option to work until it can be repaired. To have correct charge profiles is a requirement in ISO and ABYC and for good reason. This is why a BMS isn’t a charge controller… it’s for when that controller fails or something else malfunctions.

Edit: the attached diagram is for a 12V house battery but with 24V components it also works for that.