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Old 06-12-2016, 21:51   #16
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Re: 12v to 24v conversion

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Originally Posted by Buckanear Bill View Post
As longjohnsilver pointed out, 125 A to the windlass is - my words - insane. Wouldn't a shock load like that to the batteries be detrimental to battery life?
Not at all. The bulk of the current comes from the alternator as the engine is (or should be) running when using the windlass. The windlass should also be powered by the house bank as all loads except engine starting are.
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Old 07-12-2016, 04:19   #17
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Re: 12v to 24v conversion

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I can't figure out the logic. I'm thinking about buying a boat and want to go from 12V to 24V? I guess you can buy a 24V starter and alternator. It may cost you as much as the boat? If it ain't broke don't fix it. I might see the sense on a larger vessel but not 38' sail boat. Starting a big ass diesel would make sense but not something on a 38' sail boat.
JMHO
Have you tried pricing a 24v starter or alternator for a Yanmar
3gm diesel?
i have.
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Old 07-12-2016, 08:04   #18
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Re: 12v to 24v conversion

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Originally Posted by Buckanear Bill View Post
As longjohnsilver pointed out, 125 A to the windlass is - my words - insane. Wouldn't a shock load like that to the batteries be detrimental to battery life?
125a from 4 golf carts in 12v vs 67a from 4 golf carts in 24v would be an intendical shock load... the c rating is the same for both.

125a from a 12v bank is nothing. Bow thrusters are in the 500a range. Inverters will draw 125a with a microwave.
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Old 29-12-2016, 20:58   #19
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Re: 12v to 24v conversion

I have 24v Starter motors and Alternators.
I suspect a 12v starter would work with 24v, but would not push it much further, the solenoid might burn out. 24v replacement starters are less than $200 on amazon.
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Old 30-12-2016, 05:40   #20
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Re: 12v to 24v conversion

Wouldn't mind reading longjon's progress report, if any.

Just saw an ad for Vetus rim drive bow thrusters, but looks like the smallest is 48V...

And then at the other end of the spectrum, a bazillion boats successfully use 12V thrusters and windlasses, so I expect that'd be the line of least resistance: a separate 12V bank up near the bow, and be done with it. Next least expensive approach is likely a 24V bank up near the bow. The former might be able to charge from an existing unit. Latter might needs its own dedicated charger. Either way, short primary wire runs.

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Old 30-12-2016, 06:09   #21
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Re: 12v to 24v conversion

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Originally Posted by Cadence View Post
I can't figure out the logic. I'm thinking about buying a boat and want to go from 12V to 24V? I guess you can buy a 24V starter and alternator. It may cost you as much as the boat? If it ain't broke don't fix it. I might see the sense on a larger vessel but not 38' sail boat. Starting a big ass diesel would make sense but not something on a 38' sail boat.
JMHO
Logic.. If you got to renew everything 35 years old, wires, starters et all are having their last breath why not. 24v gadgets rarely are more expensive compared to 12v. Lighter wires and fuses make some significant spare regardless of the size of the boat. Battery bank can be series only with cheap GC batteries, placed wisely no need for separate starting or windlass battery. For emergy starting there's small lithium thinghies if that's a concern. Chargers, inverters same price and if needed bigger ones availble for 24v. Can't see any reason not to
IMHO Teddy
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Old 30-12-2016, 08:00   #22
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Re: 12v to 24v conversion

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Wouldn't mind reading longjon's progress report, if any.
-Chris
i didn't buy the boat (yet). Still in the planning stage. Some things just dont seem to be available readily in 24v. This complicates things by needing two systems. How to charge both? How to operate both at same time? Run two separate 12v systems so the 24v charging charges all batteries evenly? Then one 12v system has a positive ground and one has a negative ground. i can't wrap my head around that one.

Another solution is to have a separate system in the bow just to run the windlass either 24v or 12v. (Remember i believe in BIG anchors and tackle, so a BIG windlass is needed for a 38'boat)

jon
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Old 30-12-2016, 08:14   #23
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Re: 12v to 24v conversion

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Originally Posted by longjonsilver View Post
Another solution is to have a separate system in the bow just to run the windlass either 24v or 12v. (Remember i believe in BIG anchors and tackle, so a BIG windlass is needed for a 38'boat)

Yeah, that's what I meant. Apparently quite common, especially for thrusters, although maybe not so much for windlasses. Often with AGMs for that bank, assuming within (under) living quarters. Often with separate/dedicated charger.

Anyway, given short duration loads, would think a hefty 12V windlass could be acceptabe, but haven't shopped for lifting capacities and so forth. FWIW, our 12V windlass works fine with our 50-lb anchor plus the chain weight. Manual says it's good for 850 Kg/1870-lb pull weights. Just runs off one of the house banks, not a special bank up at the bow. The breaker is rated for 135 amps.

But if you install a separate system up forward anyway, you could pick either 12V or 24V without regard to the rest of the boat. And that seems to be quite common, too (especially for thrusters, etc...).

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Old 30-12-2016, 09:01   #24
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Re: 12v to 24v conversion

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Originally Posted by longjonsilver View Post
i didn't buy the boat (yet). Still in the planning stage. Some things just dont seem to be available readily in 24v. This complicates things by needing two systems. How to charge both? How to operate both at same time? Run two separate 12v systems so the 24v charging charges all batteries evenly? Then one 12v system has a positive ground and one has a negative ground. i can't wrap my head around that one.

Another solution is to have a separate system in the bow just to run the windlass either 24v or 12v. (Remember i believe in BIG anchors and tackle, so a BIG windlass is needed for a 38'boat)

jon
What things?
What comes to some 12v electronic devices they are easy to run with DC/DC converter, there are upto 40A loads. Just a 12v busbar for those gadgets.. They also get better constant voltage through the converter not affected by the chargers etc.

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Old 31-12-2016, 07:18   #25
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Re: 12v to 24v conversion

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What things?
SSB radios for one. Yes, i had read the article that you posted.
thanks
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Old 02-01-2017, 15:24   #26
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Re: 12v to 24v conversion

Running a mixed voltage boat myself I understand the appeal of 24v. Wiring is all much smaller, easier to route, etc.

Running electronics off of modern DC to DC converters works well up to about 70a and provides very stable voltages.

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Old 02-01-2017, 15:25   #27
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Re: 12v to 24v conversion

Motors (like autopilot and water pumps) seem to last much longer.

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Old 07-02-2017, 20:19   #28
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Re: 12v to 24v conversion

Reading this with interest. I've done a good deal of DC wiring over the years including conversions from 6v to 12v on old cars.

The safe continuous load for lead acid batteries is usually given as C/4, that is, amp-hour capacity divided by 4 hours, so a typical group 27 battery rated for maybe 90 a-h would support a continuous load of 22.5 amps. Several batteries in series would be several times that. Short duration loads can exceed C/4, with the most extreme example being the starting motors on larger diesel engines which depending on circumstances can draw around C*2. So the windlass isn't going to hurt a reasonable sized battery string of 3-4 group 27s or equivalent.

I'm interested in 24v conversions because the choices are better for high-amp alternators and inverter-chargers, and because the cable management is so much easier. It is hard to run the very large battery cables in confined spaces, and with 24v you can typically drop down two sizes, sometimes more on longer runs.

A quick warning about trying to take 12v power from the middle of a 24v battery string. If more than a token amount it will lead to some of the batteries being less charged than others which will ultimately lead to the others being overcharged. For flooded cells this just results in loss of electrolyte, which can be replenished, but with AGMs or other sealed cells it can dramatically shorten the life of the battery.
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Old 07-02-2017, 22:14   #29
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Re: 12v to 24v conversion

It is just not worth the headache on smaller and midsize boats. Such boats typically do not have a bow thruster (nor they need one) and the windlass is designed to take the voltage drop.

Having two battery banks on the boat ends does not make much sense. Better put them amidships.
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Old 08-02-2017, 01:21   #30
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Re: 12v to 24v conversion

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Originally Posted by longjonsilver View Post
Well thats the beginning of my journey into 24v. i believe in having heavy ground tackle, anchoring out rather than a slip and its monthly drain on the budget, and that needs a powerful electric anchor windlass (Lofrans Tigre) that draws 1500 watt, and is available in 12v or 24v versions. Now a 12v version would draw 125 amps, while a 24v version would draw only half that or 62.5 amps. From the battery bank to the windlass would be about 60ft round trip, making for a huge loss of power especially with 12v. This would require 1 gauge wire for 10% voltage drop. Imagine the terminal ends for that! Might as well use welding cable.

So what to do? Have a second battery bank forward? Well, that would make about 20' round trip and require 4 gauge wire for a 10% voltage drop, which is the wire gauge needed for a 24v system, 60' run, 10% drop.

Or convert the boat to 24v. Modern electronics (Simrad 4G radar, chartplotter, sonor, and Icom SSB) all are dual voltage units, (if i understand it correctly), LEDs to retrofit the interior lights, VHF radio, refrigeration and solar panels are available in 24v versions.

So whats left? Engine starter, alternator, engine gauges, nav lights(?), stereo, bilge pump. It looks like 24v alternators are available at reasonable prices and could be made to work with a little fabbing of brackets.

So why not tap off the middle of the four 6v batteries to get 12v and the ends to get 24v and run two systems? Especially since the charging system (both engine and solar) would charge all four batteries at 24v.

Consider the problem of the terminal ends of the wires, that often are affected by corrosion, raising the resistance resulting in fires due to excessive heat loss. 24v, using the old 12v wires, would have 1/2 the current flow, and since Powerlost=I2*R, there would only be 1/4 the current lost at these terminal ends, resulting in a safer boat due to vastly less heating of the terminal ends. What am i missing here?

jon
This is an old post, so the OP has maybe already made all these decisions.

But I agree with his arguments above. 24v is better than 12v and brings similar benefits as going from 6v to 12v in cars -- remember that? Everything just works better and lasts longer with 24v.

Just a couple of tips (in case anyone else is reading this and going through the same thing):

1. It is tempting to use the old wiring, which will be oversized for 24v, but take a good, long, hard look at very old wiring, before deciding to reuse it.

2. You can deal with engine starting by having a separate start battery and alternator, which could be 12v. This adds reliability. The cost of adding a separate, heavy duty 24v alternator for the house bank may not be much more than changing starter and alternator to 24v. And you want the heavy duty alternator in any case, for producing bulk power, a function for which the car-type alternators marine engines are delivered with, are not designed.

3. As others have written above -- it is trivial to power the few things you can't get in 24v, using droppers, and droppers give the additional serious benefit of stabilizing voltage. Only significant issue may be SSB.
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