Switching from 12V to 24V

[HopCar]

What do you expect to gain by switching to 24 volts?
Boat builders are going with higher voltage because they can use smaller wires. They save money and weight. I don’t see any reason to retrofit a 12 volt system to 24 volts.

[atoll]

Originally Posted by HopCar

What do you expect to gain by switching to 24 volts?
Boat builders are going with higher voltage because they can use smaller wires. They save money and weight. I don’t see any reason to retrofit a 12 volt system to 24 volts.

if you goback a few posts,it sounds like 24v IS the existing system for windlass,fridge inverter etc the 12v engine is the retro fit

[Cadence]

Originally Posted by coopec43

Thanks Atoll
But I've ruled that out as I haven't sufficient room and engineering wise it would be a nightmare. Apart from that everything runs on 24V - fridge/freezer, inverter, macerator, anchor winch, mast/navigation lights so there seems little point in having 12V.

Clive

I hope you have verified what will and won't run on 24V verified closely.

[eyschulman]

I have been living with a 24/12 V boat for six years now. Where ever possible we use 24V which works for more than 90% of things. Where 12V is needed we convert sometimes a PITA but doable. Motors and house banks are 24V. Higher voltage has many advantages the only negative is the fact some things only come in 12V. If anybody in PNW is thinking of going 24V I have a new 24V Mastervolt Chargmaster 24/30/3 battery charger that will be a real bargain.

[guyrj33]

Here's one example of a 24v DC to 12v DC converter
DC/DC Converter Regulator Reducer 24V Step Down to 12V 10A 120W Waterproof Voltage Convert power SupplyTransformer Volt Module

https://www.amazon.com/Converter-Reg...onverter&psc=1

24v bulbs are easy to find.

West marine sells 24v fans.

[ka4wja]

Clive,
The 4-108 is a nice motor, and will last you a long time...good on you!
But, I'm really confused by what you are actually trying to accomplish, not to mention why??
24vdc is fine for commercial vessels, larger yachts, and even many mid-sized power boats....but for the average mid-sized (40' - 50') sailboat??
There is little to be gained....(yes, it can save $$$ on high-current wiring for windlasses, but that is a minor issue once you compare all of the other issues that present themselves....see below for details)


You asked for help, so here goes...

Contrary to what Alex (atoll) understood, I understood that you are convertering your yacht over to 24vdc??
As you wrote:

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.

So, I'm assuming you're converting your boat from 12vdc to 24vdc??
Yes??

1) And, you've already determined that you can run your existing "12vdc" frig and windlass on 24vdc??
2) Or, have you already converted your refrig/freezer and windlass to 24vdc??

3) Also, it isn't clear what you actually need on-board...I realize that your question was rather narrow and you didn't ask us to design your electrical system, but just your asking of this question and the limited info you provided, makes me wonder if you have thoroughly looked at your entire electrical / electronics system? As a whole system? And designed it as such, as a "system"? Or are you just "trying to get stuff to work"??


Notwithstanding your desire to just ask your question about tapping into your "24vdc house bank" for 12vdc systems (a bad idea), that you've already got answered... (it's best to use only one voltage battery bank and then use regulators/voltage converters for the low-current draw 12vdc devices, etc.)
The answer to these questions above matter here, in regards to the best approach for you to follow...

Also, the answer to these following few questions are even more important..

4) Are you not including a large solar array in your energy system for some reason??
And, you're going to rely on burning diesel fuel to charge batteries??
That just seems so very "1970's"??


5) Are the "two 150A/H AGM batteries" in your house bank, in fact two 12v, 150A/H batteries in series, giving you 150A/H, 24vdc house bank??
Or are you saying you have two 150A/H 24vdc batteries (?), in parallel, giving you a 300A/H, 24vdc house bank??
Or, is this a 12vdc house bank?? of 300A/H??

This is very important to clarify!!
{and fyi, even if you do have a 24vdc, 300A/H house bank, this is considered on the small end of the scale, of what is "typical" / "average"...usually 350A/H to 450A/H at 24vdc is typical (that would be about 700 - 900A/H at 12vdc)..}
'Cuz if you're writing about "heavy loads" (whatever those may be), remember two things:

a) higher current draws (above the 20-hr discharge rate of 15 amps for a 300A/H bank, or above 7.5amps for a 150A/H bank) will reduce the actual "A/H" capacity of the bank....
b) to survive any significant length of time (even normal current draws from normal cruising boat devices, refrig/freezer, autopilot, radar, etc., etc.) you will need a larger battery bank than you mention, unless you do have a large solar array??


6) How are you planning on getting your AGM batteries up to 100% charge??
You do realize that, while AGM's are an established battery design, they have one drawback for most cruising boats, their requirement to get back to 100% charge, or they lose capacity (10% to 20%) rather quickly...and this is almost never able to be brought back...
Now, if you do have a large solar array, that is great!!
And, a large solar array is almost an absolute for any cruising boat with AGM's...



7) Although this question might seem less important, it is actually an important question that I assume you have already answered for yourself, so for us here it's just curiosity...
Curious as to what you have on your 43' sailboat that draws so much current that 12vdc system will not work??
What are you trying to accomplish??

'Cuz...
--- Best overall refrig/freezer systems, for most small boats, are Danfoss-based....not the large 1/4-hp or 1/2-hp compressors freezing cold plates...but, even if you've chosen that less efficient route, there are many 12vdc high-current/high capacity compressors keeping food cold on many older cruising boats, without the need for 24vdc systems..
{now, of course, if this was a commercial vessel, fishing vessel, etc., where constant, very cold, deep freezing was necessary, then I see the desire for 24vdc system...but on a 43' cruising boat??}

--- How big anchor and chain to do have??
'Cuz, I've seen 55' - 60' boats, with Maxwell 3500 windlasses hoisting 110lb - 120lb anchors and 300' of 3/8" chain, all on 12vdc, just fine...
And, most 40' - 50' cruising boats, with 60 - 90lb anchors and 250' - 300' of 5/16" chain, running big enough windlasses, all on 12vdc just fine as well..

--- Of course in regard to "inverters", for high-power inverters, yes 24vdc to 110vac-250vac, is much better than trying to do this from 12vdc!!
But, what in the world could you be attempting to power thru an inverter that you'd have hooked up to a rather small 300A/H battery bank??
With that small of battery bank (yes, even at 24vdc, that is on the low end of the scale), you couldn't run a big inverter for very long...perhaps to run a microwave to make popcorn??
Just saying if you have large inverter loads, that require a 24vdc inverter, that is a great reason for a 24vdc battery bank....but a 300A/H battery bank is rather small to power large inverter loads...


Again, thinking you may not have really designed this all as a "system"??


8) And, while commercial 24vdc electronics are available (and of course almost all commercial vessels are 24vdc / 110-230vac), I've never seen them at reasonable prices or on the shelves / immediately available in remote areas....so the initial cost is usually more as are the costs of cruising with spares...
Which is why most will use either modern 12vdc electronics that will operate over a wide voltage range (typ 10-32vdc), or use 24vdc to 12vdc converters..

This doesn't apply to the "radios", as they are not usually designed for multi-voltage use...so, you will need to spend more on commercial 24vdc radios...or spend more on high-current 24vdc to 12vdc converters...
This may also apply to most autopilots...depends on brand and model...

FYI, as for radios....
--- 24vdc commercial VHF-DSC-FM radios are 3 - 4 times the cost of 12vdc consumer / yacht versions
--- 24vdc commercial MF/HF-DSC-SSB radios are 2 - 3 times the cost of 12vdc consumer / yacht versions

Using "12vdc electronics" (some will of course work from 10vdc to 32vdc, others will work with converters as needed) might seem inelegant, but is actually a good approach.
Except for the radios (and autopilots)...'cuz of their current draw...



Okay, enough of my ramblings for now...

Fair winds.

John

[coopec43]

Originally Posted by john61ct

Once you serial-join two 12V strings, you should treat it as a single 24V battery, one pos one neg point for all connections.

If the above is two separate 12V-only banks, that is OK but usually sub-optimal, because Peukert.

Simplicity rules for reliability, KISS.

Yes I suspected something like that - treating the batteries in series and as two separate batteries at the same time.

Thanks.

Clive

[coopec43]

Originally Posted by Colin A

I prefer the DC to DC converter myself. There are plenty of ways to center tap a 24V bank but my experience is they tend to have more downsides then a converter. For a while a number of boat builders used Equalizers to tap 12V from 24V they work OK until they don't. Used to do a lot of work on commercial boats which would be almost all 24V, they almost always just used a converter for 12V loads.

I will certainly be going through all responses but what you say makes sense to me. It is only the lights and oscillating fans that are 12V (I wonder how they would go on 24V!!!)

Thanks.

Clive

[coopec43]

Originally Posted by HopCar

What do you expect to gain by switching to 24 volts?
Boat builders are going with higher voltage because they can use smaller wires. They save money and weight. I don’t see any reason to retrofit a 12 volt system to 24 volts.

But Adler Barbour say you should use 24V on their "Cold Machine" as it is "too energetic on 12V" ????

Clive

[billknny]

Originally Posted by coopec43

I have established the starter motor will have no problem handling 24V

I would be really, really surprised if this were true. Double--and triple check--to be absolutely sure before you make these connections and turn the key the first time.

[coopec43]

Thank you for all your replies.

When I said I was building the boat maybe I should have mentioned solar panels, auto pilot and desalinator were on the plans. I should have also mentioned I have an infra-red microwave installed.

When I read

System Size
In the past we tried to reduce the cost of an off-grid system by limiting its size. This was achieved by using 12V or 24V appliances & lighting that do not require an inverter. In recent years, inverters and solar panels have become more efficient and a lot more affordable. In addition, most customers seem to want more power over the years. A 12V DC system with a tiny inverter is difficult if not impossible to upgrade/upsize. Not to mention that only very few companies sell extra low voltage appliances or lighting.

To summarise: Most systems we design are 24V or 48V with a 230V inverter. The criteria we use is power consumption and scalability. We would only suggest a 12V DC power system (like the Rainbow Power Cube) if you need a little light in a shed or caravan and wish to wire it yourself.

https://www.rpc.com.au/information/f...2v-or-24v.html

I am convinced I am going the right way by going 24V. (Adler Barbour says 24V is preferred for their freezer unit) I have checked and found I can buy 24V electronics at the same price as 12V . (24V is just an option)

Clive

[john61ct]

Originally Posted by coopec43

Yes I suspected something like that - treating the batteries in series and as two separate batteries at the same time.

Thanks.

Clive

Not sure, but your response causes me to think you did not get my meaning.

Always one 24V bank.

The 12V bank(s) if any comprise different batteries.

No switching or center tapping.

[john61ct]

Originally Posted by guyrj33

Here's one example of a 24v DC to 12v DC converter
DC/DC Converter Regulator Reducer 24V Step Down to 12V 10A 120W Waterproof Voltage Convert power SupplyTransformer Volt Module

https://www.amazon.com/Converter-Reg...onverter&psc=1

24v bulbs are easy to find.

West marine sells 24v fans.

No,

perhaps for a low amp unimportant device off in Siberia, but

otherwise stick with known-good robust units, like the Victron Orion discussed above.

[coopec43]

Originally Posted by john61ct

Not sure, but your response causes me to think you did not get my meaning.

Always one 24V bank.

The 12V bank(s) if any comprise different batteries.

No switching or center tapping.

Several others have suggested how to run my 12V "appliances" off a 24V bank so I'll look further into those suggestions.

But maybe I haven't got your meaning? Suppose I have X2 12V batteries in series as my house batteries. I could:

• start my motor using the house batteries.
• have X2 extra batteries in series (24V) to start my motor. Doing that I could use the alternator to charge the starting bank or the house bank by switching between banks. But then how would I power my 12V appliances?
• I could have a separate 12V battery (in addition to the house batteries) to start my motor and power my appliances but how would I charge the battery with 24V alternator?

Now where have I gone wrong?

Whatever I do I want someone to be able to manage the system without having a university degree in electronics.

Thank you for your response.

Clive

[john61ct]

Again.

You have one big Main bank, 12V or 24V depending on what **you** decide after answering the questions raised above.

Say that's, 24V for example, alternator and starter, all big current loads, maybe everything possible at 24V.

Then, you need a 12V load circuit for the rest, powered off the main 24V system.

A DCDC charger can keep a smaller 12V battery charged for that.

Or, use DCDC converters to feed load circuits directly as needed, no 12V battery involved.

Those are the **only** two choices I recommend, and can also be used if Main is 12V but some devices require 24V.

Tapping off half the 24V bank directly to feed 12V loads will reduce longevity of your Main bank due to imbalance issues.

Hope that helps.