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Old 27-01-2019, 14:08   #1
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24v DC systems

The choice of 12 volts as the nominal voltage for DC systems is an accident of history. We persist in it because it has become a standard and because it's good enough for light loads -- lighting, electronics, bilge pumps, water pumps, fans -- and passable for intermittent motor loads like windlasses and starter motors.


24 volt systems have clear advantages for bow thrusters, larger inverters and inverter charges, and high-amp alternators. The amp draw is cut in half and the resistive losses are quartered.


Manufacturers of high-amp alternators, inverters, bow thrusters, LED lighting, bilge pumps, pressure pumps, and windlasses all have 24 volt versions of their products available, generally at no greater cost than the 12 volt versions. Most electronics also. The few loads for which a 24 volt equivalent is not available are easily enough served by converters, which are inexpensive and reliable.


I haven't come across a cruising yacht that has been built with a 24 volt system or been converted (or even partially converted) in a refit. I'm surprised.


Have you run into any yachts so equipped or been involved in a refit yourself? How did it go?


Have you considered a 24 volt conversion but decided against it? Why?


Do you think 24 volt conversions will become more common?
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Old 27-01-2019, 14:27   #2
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Re: 24v DC systems

There are many boats running 24V.

Many do both, since DC load devices are often only available at 12V.

DCDC converters are readily available, and only get expensive at high amp rates.

Some keep the main bank at 12V, and only use 24V as needed by some high-current load devices.

For those using inverters for AC load devices, no problem either way.

Those considering electric propulsion, 48V is a minimum starting point.
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Old 27-01-2019, 14:30   #3
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Re: 24v DC systems

I do not think 24v systems will become common for several reasons:
1. Cost to modify the existing supply chain. Manufacturers arenít going to spend money change unless they can recoup that somewhere. Yes there is an existing infrastructure for 24v, but expanding the market share of 24v will cost market share for 12v.
2. High voltage DC means a redesign of switches. Apparently the auto industry was all hot to convert to 42v a number of years ago (a decade?) but it fizzled out once the secondary effects were considered. Arcing at DC switches erodes the contacts. Special metals with expensive trace elements were needed to make reasonably long lived contacts and the added cost of the switches wasnít offset in the savings in copper wiring. AC doesnít have the same problem as DC. The boating industry probably isnít as sensitive about the cost of replacing switches but it tends to follow the auto industry.

If the cost of copper rises significantly in comparison to those of the needed alloying elements I could see a high DC voltage becoming standard but it would take a sustained period of this price differential for the various manufacturers to be willing to make the change.

When the auto makers made the change from 6v to 12v the savings in copper was significant at little cost.

The one place I expect higher voltage systems to make big inroads is in traction. Itís not clear to me what voltage will become standard but I really havenít researched this. I expect house service will remain 12v.
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Old 27-01-2019, 14:39   #4
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Re: 24v DC systems

Quote:
Originally Posted by john61ct View Post
There are many boats running 24V.

Many do both, since DC load devices are often only available at 12V.

DCDC converters are readily available, and only get expensive at high amp rates.

Some keep the main bank at 12V, and only use 24V as needed by some high-current load devices.

For those using inverters for AC load devices, no problem either way.

Those considering electric propulsion, 48V is a minimum starting point.



I've been living with 24v for 10 years now, including quite a lot of adding of electrical equipment during that time.


24v doesn't bring any great advantage if you don't use a charger/inverter and don't have a bow thruster or electric windlass.


Otherwise, 24v brings you much lighter and more manageable wiring and less voltage drop, better running equipment. I have a 10 horsepower bow thruster. I can't imagine the cables which would be required if I were trying to power it with 12v. 24v halves the amperage of everything.



There is no significant disadvantage of 24v that I can see. What few items of gear you can't buy in 24v, are low draw devices easily powered by cheap droppers.


I would think 32v or 48v would be a good idea on an electric intensive boat, but I'm not sure we can buy all the gear in that voltage. Droppers are fine for low draw gear, but for big stuff it starts to make less sense.
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Old 27-01-2019, 14:57   #5
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Re: 24v DC systems

We went to 48V (because we went with electric propulsion). It sure does make inverting nice though. Run a coffee maker and only 25 amps is going through the cables instead of 100.

We have a 600 watt DC-DC that produces 12V at 50 amps at 90% efficiency...enough for lights, radios, fans, radar, depth sounder. We don't have an electric windlass though.
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Old 27-01-2019, 16:01   #6
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Re: 24v DC systems

This subject was covered very extensively in a thread I started recently

Switching from 12V to 24V

I switched from 12V to 24V because people in the know said it would be better for the inverter and mandatory for larger solar systems. The manufacturer of the fridge/freezer unit said it would work better on 24V.


Maybe this is of interest?

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



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Old 27-01-2019, 16:26   #7
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Re: 24v DC systems

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Originally Posted by coopec43 View Post
This subject was covered very extensively in a thread I started recently.

I switched from 12V to 24V because people in the know said it would be better for the inverter and mandatory for larger solar systems. The manufacturer of the fridge/freezer unit said it would work better on 24V.
Its funny how quickly things can change. A year or two ago, i was inquiring about 24v and got blasted by people saying that a 38ft 24v boat was an absurdity. Now people are starting to say its a reasonable solution. i understand that diesel trucks use 24v. Is that right?

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Old 27-01-2019, 17:33   #8
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Re: 24v DC systems

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Its funny how quickly things can change. A year or two ago, i was inquiring about 24v and got blasted by people saying that a 38ft 24v boat was an absurdity. Now people are starting to say its a reasonable solution. i understand that diesel trucks use 24v. Is that right?

jon

I just did a search on Caterpillar alternators and starter motors and they were all 24V. Also a search on "Volvo truck starter motor" indicated they are all 24V. (Mack as well)


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Old 27-01-2019, 17:41   #9
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Re: 24v DC systems

Quote:
Originally Posted by coopec43 View Post
This subject was covered very extensively in a thread I started recently

Switching from 12V to 24V

I switched from 12V to 24V because people in the know said it would be better for the inverter and mandatory for larger solar systems. The manufacturer of the fridge/freezer unit said it would work better on 24V.


Maybe this is of interest?

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



Clive

Clive,


How did your fitout go? Are you pleased with the operation of the starter on 24v?


I ask because I have had poor results in the past using 6v starters on 12v. I found that it was necessary to have the field coils replaced with 12v ones by an automotive electric shop, otherwise the starter would overspeed and the pinion gear would fail early. That was with 1940s technology so your experience may differ, which is why I ask.
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Old 27-01-2019, 17:58   #10
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Re: 24v DC systems

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Clive,


How did your fitout go? Are you pleased with the operation of the starter on 24v?

I ask because I have had poor results in the past using 6v starters on 12v. I found that it was necessary to have the field coils replaced with 12v ones by an automotive electric shop, otherwise the starter would overspeed and the pinion gear would fail early. That was with 1940s technology so your experience may differ, which is why I ask.

Jammer

I still have a way to go as I'm only just finishing the HD wiring- still waiting for junction boxes, bus bar cover etc etc. Today I will be installing water tanks.....

Every mechanic I have spoken to says there is no problem running a 12v starter motor on 24V. My B-I-L Caterpillar Mechanic said they did it in the dyno-room for 20 years and there were no problems. (Of course a starter motor should only be run for a few seconds at most)

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Old 27-01-2019, 19:59   #11
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Re: 24v DC systems

I'm not "blasting" anyone, your rig your choice, but on a smaller boat I don't think the advantages outweigh the extra costs involved.

Eliminating dedicated thruster or windlass banks allowing consolidating everything into one big bank would IMO be a big reason to go to 24V.

To the extent you have high load devices that need the higher voltages, or long cable runs where the cost factor is huge, that may tilt in favor, but for normal load device categories getting away from a 12V bank means fewer choices and higher costs.
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Old 27-01-2019, 21:27   #12
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Re: 24v DC systems

My bow thruster, winches, and windlass are 24V, the rest of the boat is 12V.
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Old 28-01-2019, 05:57   #13
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Re: 24v DC systems

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24 volt systems have clear advantages for bow thrusters, larger inverters and inverter charges, and high-amp alternators. The amp draw is cut in half and the resistive losses are quartered.

Have you considered a 24 volt conversion but decided against it? Why?

It's apparently not uncommon to locate thruster batteries very near the thruster... and that bank would become available for windlass operations, too... so I'd expect difference between 12V and 24V in that situation would become moot.

I haven't really thought about conversion. Don't see any benefit, in a boat with many satisfactory 12V devices and with satisfactory wiring all ready in place (all over the place). Even if there were to be some benefit, comparing that to cost would suggest it's a losing proposition. I'd rather just go boating.

It happens we're looking at installing a bow thruster, and I did consider 24V for that... but the 24V thrust specs are exactly the same as for the 12V units... and I can locate batteries next to the thruster... and I can charge another 12V bank with an existing 3-bank charger that's currently only servicing one bank... et cetera. IOW, no useful reason to go to 24V for that, and a few reasons to stay at 12V.

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Old 28-01-2019, 06:03   #14
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Re: 24v DC systems

If the boat is big enough (new build or major overhaul) then go 120v/60 or 230v/50 for everything. There are a couple of big boys on the Trawlerforum who have done just that: huge battery bank; 48v --> inverters; lots of solar; generator of course.
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Old 29-01-2019, 04:39   #15
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Re: 24v DC systems

I just wish it were easier to go to 48V. Inverters and chargers are available, but alternators and regulators for them are scarce.


Plus there are enough loads that really want to be on 24V that you might need to keep that around. Windlesses, for example. So you end up with a small 24V system, plus 48V, rather than 48V replacing 24V. And of course you still need to keep a small 12V system around for the few things that are still only 12V.
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