Switching from 12V to 24V

[ka4wja]

Rom,
Thanks...
I'm learning even more...

Originally Posted by rom

(FYI cats do not necessarily have 2 starter batteries. Some cats e.g older FP start one engine with a dedicated starter batt and the other with the house battery)

Not being a catamaran owner (only cat I have ever sailed in my ~ 50 years of sailing was a 16' Hobie), I am learning something new here...

Thanks...

BTW, I don't want to drift poor Clive's thread too much, but can you tell me is this done because of the distances between the batteries and engine(s)??
I guess I mean, why not just start both engines with the house bank? Not done because of distance?

Sorry for asking a question that might be obvious to a cat owner, but those of us monohull guys it's interesting to see how the other half lives...

Thanks again.

Fair winds.

John

[john61ct]

You can of course use House to start your engine (s) rather than the conventional approach of dedicated Starter batts.

Redundancy & backup is then accomplished by having a smaller Reserve bank.

This could be another string, in this case at 24V, identical in every way to the others comprising the House bank, and perhaps even combined with it at high SoCs to minimize carrying "dead lead", maximize lifespan, take advantage of Peukert.

If so, as soon as SoC drops, an adjustable protective disconnect can isolate the Reserve bank to prevent House loads from pulling Reserve's SoC down.

A "1 / 2 / B / OFF" switch could be used to direct which bank is used for the Essentials circuits, i.e. cranking engine / safety / navigation gear.

[CatNewBee]

Originally Posted by ka4wja

Rom,
Thanks...
I'm learning even more...
Not being a catamaran owner (only cat I have ever sailed in my ~ 50 years of sailing was a 16' Hobie), I am learning something new here...

Thanks...

BTW, I don't want to drift poor Clive's thread too much, but can you tell me is this done because of the distances between the batteries and engine(s)??
I guess I mean, why not just start both engines with the house bank? Not done because of distance?

Sorry for asking a question that might be obvious to a cat owner, but those of us monohull guys it's interesting to see how the other half lives...

Thanks again.

Fair winds.

John

No problem,

I can tell you what Lagoon was doing, they installed one start battery per engine / generator and the house bank consist of 2 parallel batteries - optional 4.

So on my 400S2 there are:

a starboard start battery AGM spiral cell
a port engine start battery AGM spiral cell
a generator start battery AGM (port side)
four 120Ah Excide Equipment Gel house batteries (Port side)

The two engine start batteries can be combined by a transfer switch at starboard, so you can use either or both batteries together to start any engine, The generator start battery is completely disconnected from anything on board, so she will die if not running the generator or manually charged by a charger.

All in all a lot of redundancy.

Maybe they use the lead as ballast for the boat?

[john61ct]

Yes, a keel inset with a replaceable very powerful high-AH lead bank would be a great design.

Long as it never got flooded with seawater 8-)

[rom]

Originally Posted by noelex 77

The number of batteries or battery banks needed does not increase with a mixed voltage configuration. You are perceiving complications that do not exist.

You and I have a very different perception of redundancy and simplicity. Hopefully your redundancy strategy will only be called for in day light, calm weather.


Please have a look at this system. I would install it on a monohull or quadrimaran just the same. Redundancy is about turning a switch. Now show me a mixed voltage system offering the same simplicity and redundancy.


Note: by mixed voltage I mean start 12 and house 24V. As I said, if start & house are 24V then the design is a piece of cake even if there are still a few 12v equipment on the boat.

[rgleason]

If you are going to use LiFePo4, you'll need at least 8 cells in series and a BMS that supports 8 series for 24vdc. Most BMS choices (if you decide on a BMS) are for 4 in series or 16 in series. These parameters do add to the cost of using LiFePo at 24vdc.

Rom, your diagram below is a nice and simple concept, but cruisers have been trending towards connecting the alternator output to the House battery with the addition of a ACR Combiner between the reserve battery and house. (This is for a FLA setup.) I suppose your diagram would work so long as your external regulator sense wires were connected to the house battery directly, to avoid voltage drop problems while charging.

The three way then just becomes a means to switch the House Panel and Starter to a different battery, but not the Alternator. If you are going to leave the switch on Reserve for a long time, you should probably move the Regulator + and - sense wires to that battery and depending on the House bank status, disconnect the ACR Combiner.

The use of the ACR Combiner assumes compatible batteries for reserve and house banks. With mixed voltage, I guess you could have an ACR Combiner that powers a 24vdc/12vdc converter that goes to the 12vdc battery and charges it, but would that really be an appropriate regimen for keeping it charged? I don't think so. So then the next alternative would be perhaps something smarter that Sterling makes for DC/DC Battery charging, but I don't know if they do 24v to 12v.

Also is the alternator capable of charging both 12v and 24v, provided you switch the regulator program when you switch the regulator sense wires? All this leads me to believe that hybrid 12v and 24v banks are more difficult in an emergency situation. Simple is stupid but smart. Maybe both the reserve and house have to be 24vdc and perhaps the same type of battery, or compatible for charging (LiFePo4 and Gel?) and the 24DC/12DC converter just goes to the House Panel direct.

This is starting to look complicated to me, maybe it can work, but then you add the LiFePo4 HVD and LVD and BMS requirements and I am still trying to work it out.

[CatNewBee]

There are many ways to create redundancy.

You can use half of the 24V battery bank for an emergency start if the start battery fails. This is not optimal, but in a emergency situation it is justified.

You can later re-balance the batteries or whatever is necessary to recover the system when sorted out.

To run the 24V stuff if the 24V battery fails, you can use the charger logic and the alternator and run the emergency power supply this way.

[tarian]

Personally I think you are all over thinking the argument to eek out some more minimal power from batteries and thinking up large scale issues that are so far fetched its from Star Trek.
Wet cell batteries if taken care of (not sleeping with them) will give you 4 to 7 years, all dependent on the manufacturer , how you use them . etc. now over the life time of say 4 years a good 110 amp battery cost around 150 dollars/ 48 months = $3 a month X 6 batteries = $18 a month , now what are you trying to get more out of here saving an extra dollar a month getting as close to 100% efficiency as possible ,
If you have some intelligence , and know about power conservation and have some renewable power on board then really do you not have anything else to worry about.

My boat is full 24 volts with a 24 v to 12 v converter $70 it takes any 12 volt I need. I dont need 12 volt starters , why would I, I have a 24 volt one connected to the 2 starter batteries, my house is separate, this makes a fail safe easy to understand system , with one 12 volt panel.
Now to to OP if you are building from scratch why over complicate your design either go full 24 volts with two battery banks and run a separate 12 volt supply for any 12 volt gadgets. or go full 12 volts to save yourself grief, the only real advantage of 24 volts is smaller wire ,size ,less voltage drop and more powerful winches etc , but you boat does not really need these , but you choice , but I rewired my boat and stuck with the 24 volt system because it was there , if a choice I would have went 12 volts , just for the convenience of hunting down parts and equipment , not hard but more time consuming.

[rgleason]

Bruce Schwab shows a Sterling BB241235 24vdc out 12vdc in for 35amps that is user adjustible. So a 24vdc house and 12vdc reserve might be possible, but switching the starter might be a problem and switching the alternator might also be a problem and require some rewiring, not an emergency/quick recovery!


Tarian, I am done with long charging on an engine/alt with FLA. Massive Solar PV is not in the cards here.

[ka4wja]

CatNewBee,
Thanks for the details regarding the Lagoon's...


And, John, I know this was a tongue-in-cheek comment...but

Originally Posted by john61ct

Yes, a keel inset with a replaceable very powerful high-AH lead bank would be a great design.

Long as it never got flooded with seawater 8-)

But, remember this is actually similar to what the Dashew's did decades ago...

They designed a large battery bank, using either L16's or individual 2-volt cells, of "traction batteries" (very thick plate deep cycle batteries), right into the keel sump of their Sundeer's....and this battery weight was figured into the ballast design of the boats...
A rather elegant approach...



{Now Gerry Douglas, who designed my Catalina 470, did not figure in battery weight into the ballast calculations, but they did design in the batteries immediately in front of the engine and below the cabin sole (protected in their own "cabinet" / boxes)...they are immediately forward of the engine, and only 4' from the battery switches and breaker panel...making the sue of 2/0 wire adequate for them...and keeps the weight low and "centered", in the boat...}


BTW, with all the talk of electrical matters, redundancy, etc....don't forget they are sailboats...

Oh, and yeah I'm old school (or is that new age?)....I've been using one large battery bank (using either Rolls/Surettes, or Crown, 2-volt cells or 6-volt GC-2 sized batteries), for house and start, for decades now...
And, while I know some may wish to chastise me for this approach, to each their own...it (and large solar arrays) has served me well for many years of offshore sailing and ocean crossings, as well as weeks of hanging on the hook never listening to a genset...
{fyi, on my present boat, for the past 14 years....I do have a separate 12vdc AGM for my 6kw FP genset start battery, kept topped up by an "aux" output from my solar charger controllers....and do have long jumper cables to allow me to use this as an emergency main engine start battery (although I had planned on installing cables and switch to do this, never did...)...oh, and I also have a portable "jumpbox" which I've used to help others, but never needed it myself...}


Fair winds...

John

[noelex 77]

Originally Posted by rom

You and I have a very different perception of redundancy and simplicity. Hopefully your redundancy strategy will only be called for in day light, calm weather.


Please have a look at this system. I would install it on a monohull or quadrimaran just the same. Redundancy is about turning a switch. Now show me a mixed voltage system offering the same simplicity and redundancy.


Note: by mixed voltage I mean start 12 and house 24V. As I said, if start & house are 24V then the design is a piece of cake even if there are still a few 12v equipment on the boat.

Attachment 180014

Does the busbar with “everything connects here” mean that both the start and house loads always connect at one point?

This is similar to the very old system of wiring boats with a seperate “emergency battery” that was connected if the house bank was too low to start the engines.

This system has been long abandoned for seperate start and house banks. With these more modern wiring configurations the banks are seperate, but can be joined (or better still, switched if required) to start the engine in the event of failure of the start bank.

I agree that this should be ideally accomplished with the flick of a switch and this is easily done with mixed 24v house bank and 12v start bank.

You need to remember that a 24v house bank does not consist of 24v batteries in parallel (except in very unusual cases), but rather arrangments of 12v (or 6v or 2v for lead acid batteries) joined together. A high amperage 12v supply to start the engine is readily available from a 24v house bank. The batteries do not change, only the configuration. With a simple switch it is possible to supply the engine with 12v from the 24v house bank in the event the start battery fails.

[coopec43]

Originally Posted by rom

And also because I have the feeling that I=V/R, that R remains about the same, and that doubling the voltage would then double the current, not the other way round. But that could be completely wrong and they could be right. As I said, don't trust anyone until he/she can give a comprehensive explanation.

The watts required to start a diesel motor with a 12V or 24V starter motor would be the same. If you double the voltage from 12V to 24V you halve the Amps. (Amps = "current")

(That is hardly a comprehensive explanation I know).

Clive

[coopec43]

Originally Posted by ka4wja

Rom,

Not sure I should even write this....as it might be taken the wrong way??
But, there is much piece-meal work going on in this thread...which is fine...
but in my opinion, Clive would be better served with recommendations to look at things as a system, rather than a group of individual pieces...
I was trying to emphasize the advantage of designing a system, rather than just trying to "make things work"...
And then I got off onto tangents that diluted my point...

John

John

I accept your expertise in boating but I don't think you understand where I am at.

I have taught the "Scientific Method of Problem Solving" so I know the theory. The first thing you must do is establish where you want to end up and the problem is I don't know at this stage.

Will I have a de-salinator? (I think so, but not sure of size)
Will I have an auto-helm? (I think so)
Will I have radar? (I don't think so)
Will I have solar? (Yes but what size?)

All those things determine the size of the battery bank required but where will I put the extra batteries (if required). (Maybe in a couple of years lithium batteries will be the answer?)

The first thing I want to do is get the yacht in the water and go from there. I expect I will see other people's yachts and adopt some of their ideas so the yacht will evolve.

Right now my mind is working like a computer trying to fit things together. Very few components are mounted permanently as (for example) I have to watch the steering cables don't rub up against the fuel filters (which they will). Yesterday I had to dismantle a cabinet so I can route a bilge outlet hose loop through it.

Of course when I build my next yacht it will be easy.....

Cheers

Clive

[Thalas]

Lots of great info about the advantages of 24v consumption. Someone mentioned earlier that if you have more than 500W of solar, that 24v would have advantages in generation. What specifically would those advantages be?

I have 950W above the davits and 300W (3x100W) near the mast. Two sets of wiring with the 950W setup traveling further to get to the batteries in the salon. The 300W wiring has a straight shot down. Curious if mitigating losses of wire path length would be one of the benefits.

[coopec43]

Originally Posted by Thalas

Lots of great info about the advantages of 24v consumption. Someone mentioned earlier that if you have more than 500W of solar, that 24v would have advantages in generation. What specifically would those advantages be?

I have 950W above the davits and 300W (3x100W) near the mast. Two sets of wiring with the 950W setup traveling further to get to the batteries in the salon. The 300W wiring has a straight shot down. Curious if mitigating losses of wire path length would be one of the benefits.

Thalas

I'm certainly no expert but if you want a large inverter then 24V is the way to go. Apparently they are more efficient than 12v inverters.

What is the advantage of a 24v system over a 12v system? | Pangea ...
[url] https://pangeabuilders.com/what-is-the-advantage-of-a-24v-system-over-a-12v-system/
Sep 25, 2018 - You can get much bigger inverters on 24V or 48V than 12V. ... drop at 12v = 4.6% supply drop whereas 0.25 v line drop at 24v = 1.04% drop.


" If you want a small simple power system, 12 volts will probably be easiest. You can use 12 volt DC directly in very small systems, adding 120 volt AC with an inverter. 24 volts battery systems have some technical advantage. If you think you will have more than 500 watts of solar modules, consider 24 volts. http://www.backwoodssolar.com/learni...o-ask-yourself

I can't answer the second part of your comment. I googled "losses solar power wiring" and came up with a few relevant hits which I have yet to read myself.

Losses in the solar power system - ADITYA GREENS
https://www.adityagreens.com/.../the...olar-power-sys...
Mar 16, 2016 - The solar energy experiences many conversions and the losses in your solar ... loss within the components or as a transfer loss through wires.

DC and AC voltage drop and energy losses calculator
https://photovoltaic-software.com › Other solar tools
Losses in solar PV wires must be limited, DC losses in strings of solar panels, and AC losses at the output of inverters. A way to limit these losses is to minimize the voltage drop in cables. A drop voltage less than 1% is suitable and in any case it must not exceed 3%.

There may be other articles which could help.

Clive