Thinking of going 24 volt with the new boat

[Wolfgang.Schau]

Originally Posted by GILow

Just read what I wrote. I don't know why you are talking about weight.

What is the point of spending $$$ to convert from 12V to 24V, if it is not for saving weight?

[noelex 77]

Originally Posted by Wolfgang.Schau

What is the point of spending $$$ to convert from 12V to 24V, if it is not for saving weight?

The primary motivation for most monohull owners is often the ability to more easily and efficiently run high powered appliances (in GILow’s case electric cooking). The primary motivation for catamaran owners is often to save weight.

Of course no matter what vessel you own, both of these and other advantages that have been mentioned in this thread apply.

Originally Posted by Wolfgang.Schau

For example, replacing all 12V gage 10 wires to 24V gage 12 wires, weight saving may be 100lbs. Cost = $$$

Your comparison on weight saving was not really representative of the true gains.

With both 12v and 24v systems you sometimes end up having to choose a wire size slightly greater than is needed because the exact minimum size that would be acceptable is not manufactured, but on average the cross secional area of the wire can be slightly more than halved when voltage drop is the limiting factor (which it nearly always is). The only exception is very low current devices that require a minimum wire size based on their physical strength rather than the electrical characteristics.

10 AWG wire has a cross sectional area of 5.26 mm squared and 12AWG wire has a cross sectional area of 3.31 mm squared so on average the weight savings will be significantly higher than the difference between 10 AWG and 12 AWG indicates.

Originally Posted by Wolfgang.Schau

Matt,

Unless you are an ultimate racer who has to save every gram of weight, you are wasting your money :-(
What do you want to accomplish by switching from 12V to 24V?
You may save same weight for the smaller gage wires but spent thousands of dollars doing this.

Let' s do the math here for a lithium system:
600 Ah AGM batteries: 184lbs
300 Ah Lithium batteries: 72lbs
Please note: The usable energy from an AGM battery is about 50%,
for a Lithium battery about 98%, i.e., you need about half of the Ah's going Lithium.
Weight saving = 112lbs

The total weight reduction switching to 24v is of interest to many cat owners.

This will of course vary with the vessel, but Seawind did an analysis on their 1370 (45 foot) model and concluded the weight savings when changing from 12v to 24v would be between 150 to 200kg (330 to 440 lbs) depending on the options chosen.

So the saving are significant.

[ranger58sb]

Originally Posted by Wolfgang.Schau

What is the point of spending $$$ to convert from 12V to 24V, if it is not for saving weight?

And as I understand it, OP isn't "converting" from 12V to 24V... he's starting from scratch, no existing wiring or devices at all.

I think.

-Chris

[GILow]

Originally Posted by Wolfgang.Schau

What is the point of spending $$$ to convert from 12V to 24V, if it is not for saving weight?

What’s the point of responding to a thread if you haven’t read the question?

[GILow]

Actually, old Wolfie’s lack of grasp of mathematics may only be matched by their lack of grasp of reading the question, but it does bring up an assumption I’ve made about battery capacity.

I’ve survived for around five years with 675AH of Trojan T105s as my power storage. (6 batteries, 340AH useable@12v) In that time the lowest SOC I’ve seen was 68%, with the daily normal low around 85%. Despite the positive experience people have had with the Trojans I’ve never felt safe taking them below 50%.

But that was with a gas cooktop. I fiddled around with some numbers for the new boat, including the near double solar capacity, and came to the conclusion that, in terms of storage, the same size battery bank would be adequate.

HOWEVER, the voltage drop when drawing much over 1500 watts from the Trojan battery bank was pretty bad. At first I assumed I had a wiring problem, but a bit of time spent with the multimeter confirmed that the Victron batterysense was not lying, the problem was internal resistance of the batteries themselves. I concluded that I would need at least eight, or even ten T105s, not for their storage capacity but for their current capacity. (For Wolfie, that would be as much as 300 kg of batteries, and Wolfie, that’s kg, not lbs, I’ll leave you to do the conversion.)

Now, I’ve never used lithium batteries at this scale, but all I’ve read tells me they won’t have the same voltage drop issues. I guess I will find out. Fingers crossed.

(And yes, I know AGMs would be better than the Trojan T105s when it comes to current capacity, but I believe they are less suited to a boat that managed to be away from the dock for 300 days of the previous year. Getting back to 100% SOC on a regular basis is not guaranteed.)

[GILow]

Originally Posted by ranger58sb

And as I understand it, OP isn't "converting" from 12V to 24V... he's starting from scratch, no existing wiring or devices at all.



I think.



-Chris

Oooh yeah, definitely “from scratch”. See the photo in post #66 to see what that looks like, but I warn you, it ain’t pretty.

[rslifkin]

LFP (or AGM) will definitely help the current capacity issue. As will up-sizing the battery bank. Given enough solar to hit 100% SoC most days, AGMs would stay happy, but if you can put together a reasonable LFP setup, that's the way I'd go.

As far as how much battery capacity you really need, I'd say it's hard to have too much battery unless you're physically out of space.

[Dirk01]

Originally Posted by Jenta

We went all electric for galley and all, but in my case if I was doing this all over again I would probably go with 48 volts for my house bank instead of 24 because I am actually not running that much directly off 24 volts and the DC-DC converters are pretty effecient and reasonably priced all things considered. That would have allowed me to use less copper in my cabling and makes the bigger charger/inverters available to you.
Then I would just have the house bank at 48 and two busses fed by converters for 24v and 12v devices.

But heck no - I ain't redoing that project now! It's working so I don't need to break it

Don't forget that you need about 60VDC to charge a 48VDC LFP bank sufficiently. Hard to get on a boat. You've to put some two or three panels in series (depending on the panel voltages). Higher chance for shading. One shaded panel would kick the whole thing out of service.

Cheers
Dirk

[Na Mara]

That is a good point about the charging voltages of 48VDC and the need to series connect multiple panels to get up to those voltages and thereby make oneself vulnerable to shading. It’s a pretty good argument for either intermediary dc-dc chargers or buck boosters in such systems.

[mcon12000]

Originally Posted by coldfish

I have a fully electric boat, 72v x 100amp with step-down to 24v&12v. I am SOOOOO jealous of your beautiful clean box there. Honestly, that's just so beautiful I couldn't let it go without commenting. Nice job.

Thank you very much! It’s going to get pretty crowded in there so I have to be as neat as possible…

[coldfish]

Originally Posted by Na Mara

That is a good point about the charging voltages of 48VDC and the need to series connect multiple panels to get up to those voltages and thereby make oneself vulnerable to shading. It’s a pretty good argument for either intermediary dc-dc chargers or buck boosters in such systems.

I actually ran into that problem. I converted diesel to electric, got a 72v battery/motor and later realized that I couldn't charge it with my panels

They still do the house batteries, but that big 72v battery gets charged with shore power until I find a solution that makes sense.

[GILow]

Originally Posted by rslifkin

...

As far as how much battery capacity you really need, I'd say it's hard to have too much battery unless you're physically out of space.

So very true.

Anyway, I figure the solution will be to sail to somewhere it's nice and sunny.

[dutch-barge]

Originally Posted by GILow

Going to 24 volts has some big advantages. For a start you can get much bigger inverters, which matters with an electric galley. Either I get multiple inverters (3 or maybe 4) or I have to take care that I don’t use the coffee machine while the stove is on, etc etc.

Also, wiring 24 volts is cheaper and easier. Halve the cable thicknesses on the big stuff.

Solar regulator costs halve by going with 24 volts, a BIG item when you are looking at 1500 watts of solar.

WE went from 12V -> 24. cheaper cable, 1/2 the MPPT's needed. ( nice saving)
we did go for 2 3KV victrons.......
1 for the normal loads fridge, microwave , lights, washer
the 2nd only for the Induction oven
When we looked 2 3KV multi's were on sale and cheaper than a 5 KV Quattro,
WE decided to keep 2 separate systems. 1 charge / inver #2 ONLY invert and not put them parallel, JUST in case one of them was going to act up like a teenager.

All pumps changed to 24V, Shower pump, Blige pumps pumper water to the hea, all the same whale model so I only need 1 spare.
Old house alternator was dead, so a new 24V alternator
14 KW Lithium
2 KW Solar
all Led = 24V
BIG 220v sump pup under the engine
All equipment ( VHF, AIS with a cute small dc-dc victory converter costing around $15 or so 24 V all the way to the equipment and the dc-dc converter right next to the VHF etc)

[freeden]

Hi Jedi many thanks for the reply,
you are educating me 😄
I must thank GILow for the thread so much info
Thanks GILow

[FlyingScot]

It’s a familiar tale in some ways. I have heard so much about the benefits of raising the voltage from 12 to 24. Some have told me that you really save a lot with inverters at 24v vs 12v. It has to be great right? I mean, the science is clear, Mr. Ohm’s equation shows us that twice the voltage results in half the amperage (for the same power). This means cheaper and lighter wiring and/or better efficiency.

But then you start to draw out your system incorporating 24v along with 12v since it’s almost impossible to have a boat run entirely 24vdc.
This new layout will have to have 12v and 24v battery banks, chargers sometimes for each direction. Then you realize you have single point of failures so you add double of everything.
All of a sudden you look back and realize all of those gains come at some cost, more complex, more items to buy, install and maintain. More things to monitor. More things to keep spares of, etc.

We decided to build out a more robust 12v system.

It turns out that 24v inverters are barely more efficient as compared to 12v according to Victron’s specifications. (1-2%) https://Itwww.victronenergy.com/uplo...20V-US-EN-.pdf
Using DC-DC chargers to power your 12v loads or to recharge your 12v batteries incurs an 11-12% loss : https://www.victronenergy.com/upload...60-400W-EN.pdf

So how much more efficient will 24v be, if any, unless you switch almost everything to 24v?

Your proposed house bank isn't going to be huge, therefore your inverter use can be only so great, so I'd like to know how much your proposed galley will use in watts?

It is possible to get low voltage drop with 12v, but it will take large, heavy and expensive wires and busbars to do it.

24V may be the right answer for your situation but a 24v and 12v boat is inherently more complex than a 12v dc boat.