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Old 22-07-2014, 10:33   #16
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Re: My 12v set up

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Originally Posted by Matt sachs View Post
Another question. Assuming a daily cruising power budget of 300AH,
Wow that's a big power budget. Is that based on actual use, estimates or just a WAG? I would guess my budget around half that, maybe max 200 AH/day with fridge, autopilot, lights, stereo and running the invertor occasionally for whatever.


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Another question. Assuming a daily cruising power budget of 300AH, 900 in the bank .
Rule of thumb, unless you are on shore power or have significant excess charge from solar or wind then the practical available power from your battery bank is to charge up to 80% and discharge no less than 50%. So for FLA batteries you use about 1/3 of the total capacity. So you are in the ball park with 300 amp hours useable in your bank.

But if you have lots of solar and/or wind that will top off the batteries then you can get more.



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Another question. Assuming a daily cruising power budget of 300AH, 900 in the bank and 150 amp alternator, am I correct to assume I need to run the engine 2 hours a day to charge the bank.
Unfortunately is isn't that simple or that easy, for several reasons. First due to recharging inefficiencies you have to put back more amps than you take out. So 1 amp hour used will take more than 1 amp hour from the charging system to put that 1 amp hour back in the battery.

Second, with most battery types you can't just slam in amps as fast as you can or it will cook the batteries (yes temperature monitoring is good).

Finally, as the batteries charge up their voltage and internal resistance increases so gets harder to push more amps back into the batteries. So
even if you had a 500 amp alternator the batteries will only accept what they will accept.

NOTE: All these comments are aimed at mainly standard FLA (flooded lead acid) batteries. AGM, LiFePO and other battery chemistries can vary a little or a lot on some of these limitations.
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Old 22-07-2014, 10:37   #17
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Re: My 12v set up

Thanks Deep. One of the most rewarding things about this build it that I cut the trees myself a few years ago ( not the purple heart ) and now get to see the finished product. Im 6-3 and can stand up with out hitting my head anywhere except the vberth. I had to lower part of the sole 2 inches to accomplish this though.
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Old 22-07-2014, 10:44   #18
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Re: My 12v set up

Yes 300AH is a WAG, but I have 2 duaghters and a girlfriend. I made a list of everything on board and how long I would be using it during a 24 hour period while cruising, including plotter radar and the like then addad 20AH. At anchor it will be considerably less.
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Old 24-07-2014, 12:18   #19
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Re: My 12v set up

nuther question.
Im going with strategically located Buss bars in the electrical system to reduce clutter around the curciut box. The size of the wire going to the buss is much larger than the ones leaving it. The curcuit breaker is sized for the wire leaving the distribution panel. The small wires leaving the bus will heat up before tripping the circuit breaker, so Im fusing the smaller wires as they leave the buss with the proper size fuse for wire used. Sound reasonable? Is there a better way?
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Old 24-07-2014, 13:23   #20
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Re: My 12v set up

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Originally Posted by Matt sachs View Post
nuther question.
Im going with strategically located Buss bars in the electrical system to reduce clutter around the curciut box. The size of the wire going to the buss is much larger than the ones leaving it. The curcuit breaker is sized for the wire leaving the distribution panel. The small wires leaving the bus will heat up before tripping the circuit breaker, so Im fusing the smaller wires as they leave the buss with the proper size fuse for wire used. Sound reasonable? Is there a better way?
How small are the wires leaving your busbar? What size breaker are you using?

The circuit breakers on my panel are 10-15-20 amps. Unless you are using very small wires like 18-20 gauge or smaller and/or very long runs I think a 10 or even 15 amp breaker would be fine.

Otherwise, yes fuse the small wires. Instead of a bus and lots of little inline fuses I would instead use a fuse block for distribution. Something like this.
ST Blade Fuse Block - 6 Circuits with Negative Bus and Cover - Blue Sea Systems

Or if you don't want to keep boxes of fuses you can get a mini circuit breaker panel to hold 5-6 breakers and load it with 5 amp circuit breakers.
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Old 24-07-2014, 15:16   #21
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Re: My 12v set up

Skip. I havent made the drawings yet, but an example would be 5 - 50 milliamp LEDS and 3 12 USB outlets that draw 2.5 amps each. So I might have a 10 amp circuit breaker and several 1-3 amp circuits off the buss.
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Old 24-07-2014, 19:43   #22
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Re: My 12v set up

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Skip. I havent made the drawings yet, but an example would be 5 - 50 milliamp LEDS and 3 12 USB outlets that draw 2.5 amps each. So I might have a 10 amp circuit breaker and several 1-3 amp circuits off the buss.
Depends totally on the wire size. You fuse for the wire size not the load. Any quality panel I have installed or come across has 14 gauge wire and each circuit that is loaded with a fuse or breaker is 15 amps. As ABYC doesn't want to see any wire smaller than 16 awg additional fuses are not necessary.

What wire sizes are you planning to use?
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Old 24-07-2014, 20:13   #23
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Re: My 12v set up

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Depends totally on the wire size. You fuse for the wire size not the load.
Exactly. Fuse for the wire. If you have sensitive electronics you want to protect you can add a small inline fuse to cover that.

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As ABYC doesn't want to see any wire smaller than 16 awg additional fuses are not necessary.
My concern is for the current crop of LED lights and even some small electronics that come with a pigtail of tiny wire. I've seen some that looked like 24-26 gauge. Even if you run 14 from the panel to the fixture you have that short piece of light gauge wire. If possible I shorten it as much as I can and protect it with shrink wrap or something but I still see that as a potential weak point in the system.
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Old 24-07-2014, 20:21   #24
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Re: My 12v set up

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My concern is for the current crop of LED lights and even some small electronics that come with a pigtail of tiny wire. I've seen some that looked like 24-26 gauge. Even if you run 14 from the panel to the fixture you have that short piece of light gauge wire. If possible I shorten it as much as I can and protect it with shrink wrap or something but I still see that as a potential weak point in the system.
The good news is that the pigtail is short, and I agree if it can be shortened further it is better. I use heat shrink connectors and slip a long piece of heatshrink over the whole section if the wires will be in any way exposed.

Normally I use wire no smaller than 14 awg but have used 16 awg for low current interior lighting circuits.
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Old 24-07-2014, 20:33   #25
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Re: My 12v set up

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Normally I use wire no smaller than 14 awg but have used 16 awg for low current interior lighting circuits.
Did not know that was ABYC code but same here. The smaller stuff is just too fragile and I don't like the voltage drop on longer runs with the small stuff, even with light loads.
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Old 24-07-2014, 21:28   #26
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Re: My 12v set up

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Originally Posted by Matt sachs View Post
Another question. Assuming a daily cruising power budget of 300AH, 900 in the bank and 150 amp alternator, am I correct to assume I need to run the engine 2 hours a day to charge the bank (minus any input from wind and solar)

Do I need to monitor the temperature of the bank when using a high output alt? It seems the more I learn about 12 set ups, the more I dont know.
The bank and alternator "seem" reasonable. I think you might be over on the daily consumption calculation but regardless.

Getting 300 amps into a battery is not as easy as it seems. Batteries can only accept current so fast due to resistance. Resistance is cause by heat. Heat is cause by shoving amps in a battery. Basically - the faster you try to fill a battery the slower it accepts.

Fundamentally a charge profile fills a battery fast when it is "lower' and can accept faster, then it tapers off a bit in a mode called absorption (think about all these electrons in the battery trying to "absorb" back onto the plates. Kinda like a bunch of commuters on a train platform.

To get to absolutely 100% takes hours and hours and this is what solar is good at - finishing off the battery. The practicality is that you will likely not charge to 100% all the time and the batteries will live in some kind of less than full state all the time.

You may end up with a generator to meet your daily needs at 300 a/h unless you get tons of solar. but it's gonna take 4+ hours of fairly high amps to keep these batteries reasonably charged.

Now this have implications on battery life etc. but that's another topic and is largely just a cost of ownership issue.

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Depends totally on the wire size. You fuse for the wire size not the load. Any quality panel I have installed or come across has 14 gauge wire and each circuit that is loaded with a fuse or breaker is 15 amps. As ABYC doesn't want to see any wire smaller than 16 awg additional fuses are not necessary.

What wire sizes are you planning to use?
Yes you wire for the circuit but if using distributed panels you need to know the peak loads from that panel - You run, say, 10AWG to the panel and fuse the 10AWG for 30 amps (if that's the load) - then you wire 14-16AWG circuits from there with appropriate 5-15 AMP fuses.

It wouldn't work to run 20 feet of AWG16 for "one" circuit up front and size the fuse on the 10AWG circuit at 5amps (the smallest wire) if the total panel load can be 40amps...
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Old 24-07-2014, 21:45   #27
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Re: My 12v set up

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Yes you wire for the circuit but if using distributed panels you need to know the peak loads from that panel - You run, say, 10AWG to the panel and fuse the 10AWG for 30 amps (if that's the load) - then you wire 14-16AWG circuits from there with appropriate 5-15 AMP fuses.

It wouldn't work to run 20 feet of AWG16 for "one" circuit up front and size the fuse on the 10AWG circuit at 5amps (the smallest wire) if the total panel load can be 40amps...
Yes, if running distributed panels I would size the wire for 3% drop or less at max panel load. But I wouldn't fuse for max panel load but somewhere between panel load and wire ampacity. For a 30 amp max load and 10 awg I would fuse at 40 amps or so. 10 awg (105 C) wire is rated at 51 amps in engine spaces and 60 amps outside of engine spaces.

Basically fuse at the batteries for wire size and add a fuse whenever the wire size becomes smaller.
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Old 25-07-2014, 09:24   #28
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Re: My 12v set up

Thanks guys. I didnd atriculate my concern very well, but you picked up up on it. The LEDs have these little bity pigtails. I assume I need to fuse the circuit for that pigtail even if the rest of the circuit is a slightly larger wire.
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Old 25-07-2014, 17:01   #29
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Re: My 12v set up

I was going to put this in the blue pearl sinking thread, but didnt want to hijack the thread so I cut and pasted it here. I'm the OP so I can hijack it if I want to...

Im agree with Deep.
Its easy to calculate the known forces and build to meet those stresses.( I can't, but smarter folks can) Its impossible to build something to withstand unknown forces so we build in safety factors. Even then ,we can only guess what those stresses will be.
My thinking, and the way Im building my boat, is to look at the failures of other boats. Learn why they failed and be damn sure mine doesnt fail in that area. Is it convient? No. Is it economical? No. Is it smart? That remains to be seen, but thats what Im doing. Not having a price point to meet frees me to look at durability, not cost vs profit.
Seems to me, dirty tanks, clogged filters, rudder failures, and poor weather planning is the cause of most sailboat incidents. Im planning for that.
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Old 25-07-2014, 17:05   #30
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Re: My 12v set up

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The LEDs have these little bity pigtails. I assume I need to fuse the circuit for that pigtail even if the rest of the circuit is a slightly larger wire.
I don'y think that is necessary really. If you are using 16 awg wire for the run to the light from the panel fuse for that, not the 3" or 4" of smaller wire at the led itself.
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