Switching from 12V to 24V

[coopec43]

Originally Posted by rom

No you don't. Per your first message you have 150 Ah. @24V that is


And then you have a 3000W inverter, which makes me think you need a lot of juice for all sorts of house appliances (115 or 230VAC)


So either that inverter is total overkill, or you do indeed need to increase you battery capacity. I would say at least 400Ah@24V if you intend to use the full power of your inverter on batteries alone, that is without a generator running.

I won't argue with you. Thanks....

I had resigned myself to starting the motor everyday. Maybe I have to think of a small Honda 4ST generator? (as well as a stack of solar cells)

Clive

[Pete7]

Originally Posted by pcmm

Why do you want to switch to 24v? Almost 100% of the gear used on recreational boats is designed for 12v operation...

I found most of the stuff like chart plotters and fridges far more reliable when running off 24v. The only item I couldn't find at the time was a VHF that would take 24v so used a small dropper box to reduce the voltage down for that.

Pete

[a64pilot]

Originally Posted by Pete7

I found most of the stuff like chart plotters and fridges far more reliable when running off 24v. The only item I couldn't find at the time was a VHF that would take 24v so used a small dropper box to reduce the voltage down for that.



Pete

What do you mean by more reliable?
I ask as it’s very uncommon for either to actually run off of supply voltage, most electronics convert what is fed to them whether it be 120 VAC or 12VDC to something like 5 VDC, and most fridges convert power also.

My opinion is for high amp devices like windlasses etc, the higher voltage is beneficial for many reasons, but little things like fridges, and plotters etc., it’s irrelevant.

As far as whether the starter will take it, most likely it will. Nearly all the old Ford farm tractors were converted to 12V decades ago, and the starters are still fine. I assume it has to do with voltage drop and short term use?

To really reap the benefits though, we need much higher higher the better, but apparently there is a safety issue above 60V.
We were supposed to convert automobiles to 42 VDC in the 90’s, but we are still 12 VDC?
https://en.m.wikipedia.org/wiki/42-v...ctrical_system

[rgleason]

Noelex77 wrote:

The drive unit is considerably more efficient driven by 24v than the otherwise identical 12v model. For example, according to manufacturer’s specifications, the 12v drive unit consumes 13a @12v (156w) to develop 325 KgM of torque. The rotational speed at this torque is 2.5° per second. The otherwise identical 24v unit is only consuming 5a @24v (120w) to develop exactly the same torque. The 24v unit is also considerably faster with a rotational speed of 3.2° per second at this torque, so will need the power for a shorter time.

So the 24v unit will respond faster and therefore will work better and at the same time is consuming less power doing so. The savings add up to well over 30% less power.

The other advantage is the drive unit in 24v will run from the cheaper, smaller Simrad/B&G computer (the NAC-2) model because it only has to supply a maximum of 8.5A at full torque. If you run the same drive unit from 12v it needs 21a at full torque so the larger, more expensive (the NAC-3) computer is needed.

So in summary, the 24v autopilot is cheaper, (smaller computer, smaller wiring), easier to install (smaller wiring) and uses considerably less power for better performance (motors like higher voltages).

As a result, I think that 24v will result in a significant difference, particularly when at sea, 24hr/day, without self-steering vane.

For energy savings, it is also very important to have fully optimized autopilot software that utilizes a very good compass. Sean D'Epagnier's Pypilot (uses a raspberry pi)is a good example which uses significantly less power, even when driving Raymarine autopilot machinery (and others). Pypilot is also a plugin for OpenCPN although it can be completely independent. The point is that software optimization is critical and not always done.

[Cadence]

12V starter on 24v. Just a question, will the increased RPM damage the Bendix or flywheel since the camphor angle or even cog spacing may be for a particular engagement speed? That may be specific engine critical.

[rgleason]

The following ampere/hour capabilities are recommended for
the house bank, which serves the ColdMachine™.

We cruise for 2 weeks, with 225ah FLA, using 80 ah/day, and at sea 140ah/day, with Ozifrige Eutectic system, very little solar (20 watts) so far. Intend to improve electrical system with Alternator + Serpentine, LiFePo4 200ah + BMS, and 100 watts solar on the dodger. Then the next project is to replace the refrigerator insulation.

[rgleason]

Originally Posted by Cadence

12V starter on 24v. Just a question, will the increased RPM damage the Bendix or flywheel since the camphor angle or even cog spacing may be for a particular engagement speed? That may be specific engine critical.

Good question. I asked similar below.

Motor Starters at 24v it appears they run faster, when the solenoid kicks in and the start gear is engaged the motor will be running faster. There will be greater loads on the gear at start. It does not appear to matter if one starter ran 20 years.

The other question I have is with 24v starters will there be a likelihood of greater transients which can affect electronic gear?

[a64pilot]

Originally Posted by Cadence

12V starter on 24v. Just a question, will the increased RPM damage the Bendix or flywheel since the camphor angle or even cog spacing may be for a particular engagement speed? That may be specific engine critical.

From other vehicle electrical mods, it appears that whatever increases in stress there are, are within allowable limits.
A very, very common mod for starting a Garrett turbine aircraft engine is during starting, taking the dual 24v batteries and running them in series to boost voltage to 48V. This gets the engine started much quicker, and at lower peak temps. Starting a turbine is a very critical time, and you want to get through it as quickly as possible.
If your curious, I measured the actual starting loads for the G10 aircraft we built to be a little over 1000 amps at 24 VDC.
Feeding those 24 VDC starter/generators 48 V DC seems to do them no harm at all, even long term.

[NPCampbell]

Since you are halving the current to most devices you may want to reduce the ratings of the fuses/breakers protecting those circuits. Doubling the voltage means twice the wattage will be required before they blow/trip which may increase the chance of a fire in an overload situation.

I haven't figured out how some of the larger boats even manage with 12V while using a windlass that requires 1500+ watts. At 125+ amps you need to be using HUGE cables. A 15 ft run requires 1/4 inch thick #2 wires to limit the voltage drop to 5% and the steady state wire temp to 195F.

[ka4wja]

Noelex,

Thanks for the info on the Simrad corepaks being multi-voltage...I wasn't aware!
And, while I do know that Garmin now also makes multi-voltage corepaks, unless things have changed in the past few months, Raymarine doesn't...

Seriously thank you for this....and reminding me that things do change, sometimes for the better!

Although, for most of the mid-sized cruising boats, that are 12vdc boats, there is little need to change over to 24vdc....larger yachts, yes....and if building new, of course consider it....but, most on modest / mid-sized boats will deal with the larger wire size costs and stiffness, and stay with 12vdc...


~~~~~~~~~



Now, Clive...I'm sorry I did not understand that you were constructing a new boat....and I suspect others here were confused as well, with a title of "Switching from 12v to 24v" and writing this:

Originally Posted by coopec43

ALSO I plan to switch the yacht over to 24V completely but currently the interior lights and oscillating fans are 12V. I was planning to share the load of those items between each of the house batteries.
Clive

I assumed you already had the boat and all equipment installed and were in fact switching from 12vdc to 24vdc....but, it appears that I was incorrect...opps..

However, this makes it all the more important to answer the questions I posed earlier, as you are starting from scratch here!
Again, I may be wrong, but it appears to me that you are trying to make things work and getting a good deal of well-meaning advice/info from off-grid alternative energy sites?? Instead of taking a systems approach and designing your on-board energy system yourself, for your needs and your application??

I realize that your initial question was about starting batteries and whether you could "tap into" your 24vdc battery bank, from 12vdc....but, please have a look at what I wrote, 'cuz whether you believe me or not, it will help you...



Also, except for a 3000 watt inverter (mine is smaller) and the bread maker (I knead by hand), I have all equipment that you listed as "currently installed" and "intend to install", on my present 47' sloop, as well as a great deal more...but, as you'll see, you should design your energy system as just that, a "system", and all should work out well for you (whether someone goes 24vdc, or 12vdc & 24vdc, or even 12vdc only...they need a proper design, or they'll be chasing their tails and "solving problems", instead of enjoying life, sailing/cruising.. )



To be clear, there are 3 major parts of your on-board energy system design, and they should be fully understood and analyzed, so that you can design your energy system that meets your specific needs...these parts are:

1) Energy Storage (i.e. batteries....not just the A/H rating, but also their charge and discharge profiles, which are gotten from the manufacturer)

If, as you wrote, you have two 150 A/H batteries in your house bank, assuming they are 12vdc batteries (as you talked about tapping into this bank to access 12vdc), then you have a 150 A/H house bank (at 24vdc....which is like a 300A/H house bank at 12vdc)....and this is not only quite small, but will be unable to support a 3000 watt inverter for very long, before running the batteries very low (a very deep discharge) and even at 24vdc, a 75 amp current draw from a 150 A/H house bank is going to pull the battery voltage down while this is being drawn (this is not the voltage drop in the wiring, but in the battery due to the high current versus the battery capacity...

{BTW, "150 A/H's" is a quite small capacity for a Group 4D (which would typically be 180 - 210 A/H), and quite large capacity for a Group 31 (which would typically be 100 - 130 A/H's)....I don't know what batteries you're spec'ing out....but assume you've gotten the info from the battery manufacturer....just want you to be sure of the capacity of your house bank...}

And as I and others have mentioned, the higher current draw from the bank above the "20-hour rate" (7.5amps) the lower the actual capacity....a 50% increase in current above the battery's "20-hour rate", the capacity is typically 90% of "rated", and doubling of the 20-hour rate (15 amps) current draw capacity is typically 80% of rated....

But FYI, even more important for those looking to drive large appliances, if you draw a significant current, say 75 amps (@24dvc) to run your microwave....just 20 minutes will use approx. 30% of your entire battery bank's capacity....and that's assuming you started with batteries at 100% charge (which might not be possible, unless you have sufficient solar array, to handle your on-board needs and charge the batteries up to 100%, as well), so typically figure you're starting from 90% capacity....

Sorry to ramble on, there is just so much here to write, and I don't have the time now to write more....



2) Energy Sources / Charge Sources (for most mid-seized sailboats, solar is of course primary, these days...but some in very windy environs still get some effective use from wind power, too...and some that do long passages get a great deal of energy from towed-water-gens....of course there is also diesel gensets....and lastly, main engine alternators...)



3) Energy Consumption / Energy Budget (this is simply the power used by all of the devices on-board, times the amount of hours per 24hr day each is used....although we've become accustomed to using "A/H's per day", this does introduce a problem if you're using two different voltages on-board, as well as confuse many who are used to doing this only with 12vdc...so using "watt-hours per day" would allow you to easily compile a detailed energy budget...)


And, don't forget that many of us are able to live energy self-sufficiently, as long as the sun shines every few days....
We design our systems to not just "get thru the day" / "get thru the night" / "until we charge up", no....rather we design the system to actually run seamlessly, so we aren't just looking to charge, but the system is always operating as a system, where we use energy and it is replaced...we typically don't think along the lines of "charging", but along the lines of just providing power as needed, when needed, and the system handles it just fine...

{fyi, with ~900 A/H of battery capacity, 500+ watts of solar, and lots of extra frig/freezer insulation, and attention to detail in energy system design, as long as the sun shines every few days (every 3 - 4 days when at sea, and every 4 - 5 days when at anchor) everything is just seamless, and no "charging" is thought about....if there are many days of cloudy weather at sea, I use a towed-water-gen to supplement...or even my genset, or even the main engine....and at anchor, more than 4 - 5 cloudy/overcast days means I will probably crank-up the genset, but that's only happened once in many years... }



While I've listed these 3 criteria (used for designing your on-board electrical / electronics systems), in the generally accepted order of importance for most cruising boats....this assumes that the owner/designer has already done a complete energy budget...so, if you have, that's good (and it would be cool if you'd post it), but in case you haven't please stop and take the time to do this now....it will save you a LOT of time/effort and probably save much frustration along the way!!


If you look at your energy system on-board, as a system....and design it as such, you'll be a very happy sailor, whether 12vdc, 24vdc, 32vdc, etc.....but most that take a hap-hazard / piece-meal approach tend to run into trouble, and have a good deal of frustration...

Just as examples, there are quite pricey (> $500,000 USD) new sailboats that the factory made little effort to design an efficient / effective energy system on-board....also, I've anchored near slick, new, fancy sailing yachts that have to run a genset or main engine to keep their frig/freezer cold, and/or just to make water, etc....and even seen brand-new boats with piss-poor 2awg wire used for battery wire, and windlass wiring, at 12vdc!!! As well as the ubiquitous unfortunate issue suffered by almost all modern cruising boats = lack of adequate frig/freezer insulation!!

(remember, except for those sailing in cold weather, your frig/freezer will be the largest energy consumer on-board, followed by autopilot in 2nd place.....then generally followed by chartplotter/radar/computers/navigation system, in 3rd place...)

Fyi, most find domestic hot water to be their Achilles....if they run their engine, which almost always has a cooling loop thru the hot water heater, they get LOTS of hot water, but then they're burning diesel, same for running a genset and 110vac/230vac heating elements....and the power drain of 800 watt to 1200 watt heating elements is just too much for many on-board energy systems...so some sort of solar assist (water heated by the sun, not by electricity) is a great approach, as is a DC heating element to be used when you have sufficient sun shine...




Again, sorry I misunderstood....I thought you were "switching from 12vdc to 24vdc", but I now see that you are building a new boat....so, please know that it is even more important to design your own energy system / electrical system, according to your needs/desires, not mine...
(just remember that burning diesel, and running an engine and/or genset, gets old...real fast!!)

And, except for large amount of domestic hot water, most mid-sized cruising boats are (or can easily be) set-up to be energy self-sufficient, even on 12vdc!
The key is they design a system based on their specific energy storage capacity, energy generation/charging, and their own energy budget...(typically using large solar arrays...'cuz silence is golden!...nobody wants to listen to an engine run, nor smell diesel exhaust...)



Perhaps reading over the above, and the questions I asked earlier, and having a look at Maine Sail's site, etc., will show you how important taking a system approach is....learn about your batteries, charging sources, and make a complete energy budget...and you can easily design your energy system to best suit your on-board needs / application....not doing so is, in my opinion, a big mistake...




Fair winds....and wishing you good luck..


John

[Cadence]

I wonder why the 32V systems didn't last long. I suspect it was battery mfg. profit margin? Maybe driven by the 12v auto industry. Tooling for only 12v and not also 8V?

[ka4wja]

Yep, in the 70's it was being used on lots of bigger yachts, fishing boats, etc...and then it just disappeared...

Originally Posted by Cadence

I wonder why the 32V systems didn't last long. I suspect it was battery mfg. profit margin? Maybe driven by the 12v auto industry. Tooling for only 12v and not also 8V?

I know Rolls still makes 8v batteries and with the really big banks made up of individual 2-volt cells, you could make a bank any voltage you want..

John

[billknny]

Originally Posted by Thalas

I believe Delos is on a 24V bank. Brian seems pretty dialed in. Is it likely that Delos was wired that way when he bought it or did he convert? And if so, what would be the advantages? They recently reduced propane by moving to things like induction plates for cooking. I'm assuming that has to be 110V through the inverter, right?

All Amel Super Maramus (like Delos) were wired from the factory for 24V power. There are many heavy DC power users on the boat: Electric winches, windlass and a 5kW bow thruster. Trying to feed 5kW (>400 amps) of 12V power the to the bow of a 50 foot boat is just not practical.

These boats are designed and built around 24V DC power and 220V/50Hz AC power supplied by a genset. An inverter might have been added, but they do not have enough solar power to cook with, so they are running the genset to make electric cooking power. Seems silly to me, but everybody has their preferences.

[rom]

Originally Posted by ka4wja

Thanks for the info on the Simrad corepaks being multi-voltage...I wasn't aware! And, while I do know that Garmin now also makes multi-voltage corepaks, unless things have changed in the past few months, Raymarine doesn't...

As I said a few posts above, my brand new Raymarine EV1 does take either 12 or 24V. And so did the 10+ years old raymarine S3 AP it replaces... John, you should check before posting, that kind of information is very easy to find.


Edit: smaller Raymarine units (e.g. acu 100 and older S1) are 12V only though.

[rom]

Originally Posted by billknny

All Amel Super Maramus (like Delos) were wired from the factory for 24V power.

It would be interesting (for Clive at least) to know how Amel does that. Which components they use and if there is a 12V subsystem, how is it connected to the 24V system. Does the engine start on 24V ?