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ProNautic 12-30C wire size for 38 foot round trip?
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Avidmagnum12



Joined: 23 Mar 2013
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City/Region: Ocklawaha
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C-Dory Model: 25 Cruiser
Vessel Name: C-Otter
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PostPosted: Sun Mar 18, 2018 5:32 pm    Post subject: ProNautic 12-30C wire size for 38 foot round trip? Reply with quote

Following Dr. Bobís advice Iíve decided to replace my Guest 2620A Charger with the ProNautic 12-30C and buy two larger house batteries. I intend to install it in the same location by the water heater on my 2011 CD-25. If I correctly follow the amp/distance computations, it seems to get a 3% drop Iíd need to use #4 wire. If I can accept 10% I could use the #10 wire that is already there.

What is acceptable and proper?

If you ran 2 #10 wires together what would the equivalent wire size be?

Thanks for the help to this electrically challenged C-Brat.

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Tom and Joyce Schulke

2011 CD 25 "C-Otter" 07/2015 to present
2011 CD 25 "My Girl" 06/2015 renamed C-Otter
2004 CD 22 Commuter "Out2C" 03/10 to 06/15
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thataway



Joined: 02 Nov 2003
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PostPosted: Sun Mar 18, 2018 7:09 pm    Post subject: Reply with quote

Tom,
To equate wire sizes you need to look at the wire cross section surface area. In boating we should be using AWG (American Wire Gauge). This is available in your handy "Boater's Pocket Reference" or the engineers "Pocket Reference by Glover". These make handy boat bed time reading. Or you can go to the internet.

#10 wire has a cross sectional area 5.26 mm sq, #4 wire would be 21.1 mm sq. So to get the equivalent, you would need about 4#10 wires, in each direction...and that is why the larger wires are so much more expensive! You could use a compromise at # 6 wire and only get about 6% voltage loss...

Two #10 would be equal to a #7 AWG (which would be difficult to find.

More after dinner.

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Thataway
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thataway



Joined: 02 Nov 2003
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PostPosted: Sun Mar 18, 2018 8:35 pm    Post subject: Reply with quote

You are really best off sizing wire for the Maximum current, (3% voltage drop @ 12 volts = 0.36 volts.) Considering that we are trying to get the most efficient use of our time and resources, you want to get the most voltage/current into those batteries.

There are two scenarios. One is you come back to your dock after a weekend out, and the batteries have been brought up to about 80% state of charge, by the outboard alternator. The batteries have to be topped off that last 20%. This is what the chargers which we get with our boats (typically a Guest 5-5-10 amps)

The other scenario--is closer to what Tom and Joyce use. They like to hang on the hook for days or weeks at a time. The charging is going to be mostly the outboard, but can be supplemented with a generator. I believe that Tom's 200 hp outboard puts out a theoretical 50 amps at WOT. We don't know exactly what the output is at his normal slower cruising speeds, nor do we know the exact amount available to charge batteries---especially if trolling. There is the amount needed to run the engine. Then there are the electronics, the refrigerator and another other appliances. There may be only 20 to 30 amps available.

What we do, is to force charge our 2 group 31 AGM batteries (about 110 amp hours each) from a portable charger, where we can put in 30 amps for a period of several hours. Then we stop charging when the charge rate drops to 3 to 5 amps. But it is that low amperage charging which tops off the battery last 20%. This takes considerable time. So we are often cycling our batteries between 50% to 80% state of charge. For example when cruising AK, we would stay at a marina every 3rd night if possible to top off the batteries, and get a hot shower (without steaming up the inside of the boat--alternate days were sponge baths)...

Overall my advice is to go with the heavier wire. Consider the effect of 10% voltage drop: At the Bulk phase of charging the charger is putting out 14.1 volts--but with 10% voltage drop, you are only getting 12.69 volts! That means that you are not really charging the battery--and it will take forever! Even with the 3% drop, the 14.1 becomes 13.67 volts. Enough to charge, but not at the most efficient rate. It would be good to check to see what the voltage is at the charger and the battery after the new battery and new charger is installed, with the present wiring. Then make a decision. It is very possible that your new charger will allow 14.8 volts, and then you are going to get a higher voltage at the battery.

I downloaded the manual for Tom's battery charger: great feature is that the output voltage and amperage is displayed, and there are good profiles. The "bad news" is that the manual, only gives the wire size up to 30 feet round trip run--and in that case it is #4. Interpolating, that it would be #2 for for a 40 foot run--and you have to round up--when using the wire size. #2 wire has a cross sectional surface are of 33.6 mm2 or 50% more than the #4 wire!

Also fuse the wire for the maximum current, at both ends--within 7" of the battery charger and 7" of the battery.

Also the best battery chargers have a temperature probe at the battery terminal, to avoid overcharging the battery. I have a Magnum inverter / charger on my RV which puts out 110 amps charging--the cables are only about 3 feet long, and are 00. There is a separate temperature probe and a voltage sense wire from the inverter charger to the battery bank of golf cart batteries.
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san juanderer



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PostPosted: Sun Mar 18, 2018 10:31 pm    Post subject: Reply with quote

Is there any way to get the charger and batteries closer together ?
Thataway is correct, don't compromise on the wire size.
Those big cables get very pricey per each foot.

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Avidmagnum12



Joined: 23 Mar 2013
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PostPosted: Mon Mar 19, 2018 8:57 am    Post subject: Reply with quote

Thanks for the great input. I figured out how I could cut the distance to the start battery to 33 ft total and the the house batteries to 25 ft total. Called the manufacturer today and they felt #4 AGW would be a good choice now with the shorter runs. So ....thatís what Iíll do. The charger is temperature controlled. Now all I have to do is figure out how to fuse it. The only maxi fuse holders Iíve found are on #8 AGW wire. Will that be a problem?

I listed the charger model wrong...itís a 12-30P. Should be better than the old Guest.

Thanks again Dr. Bob for helping me spend Joyceís Money. 💰😉

Tom
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alainP



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PostPosted: Mon Mar 19, 2018 10:33 am    Post subject: Reply with quote

Tom, I did pretty much the same thing a few months ago except the charger is the 40 amps model. I went thru the same dilemma with cable sizes.
I ended up using # 4 Ancor. The Pronautic puts out 14.6 v which seems to do the job even with the small voltage drop. Blue Sea System sells large in line fuses and holders (ATO/ATC) up to 40 amps I believe.
Lots of work but no regrets. Alain
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thataway



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PostPosted: Mon Mar 19, 2018 3:02 pm    Post subject: Reply with quote

One other item I found in my "research" last night, is the Sterling sells the identical charger, but has a far better manual. Here The 30 amp model requires 450 watts generator power--which is a useful piece of information for those running a Honda EU 1000. The remote looks like a great accessory to avoid crawling on the floor to look at the charger.

There is also a great article on installing this charger (with implications of other chargers)

Finally, one issue I failed to mention in my first post, is how hard it is on the factory supplied Guest chargers when you are running more power than the charger can supply at the dock--lets say, fans, 12 volt TV, incandescent lights etc--take 15 amps, and the charger leg that house battery is only supplying 5 amps. The other 10 amps are made up from the battery's reserve, and you are actually discharging the house battery. The small battery charger is working at max power to keep up--and these are not fan cooled, so they shortly overheat--and have premature failure. I did discuss this issue with Ryan from NMI..We will see if the chargers are changed in the future.
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Avidmagnum12



Joined: 23 Mar 2013
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PostPosted: Mon Mar 19, 2018 5:03 pm    Post subject: Reply with quote

Hi Alain....good to hear from you again and glad you like your charger. I ordered a couple 5191 Blue Seas fuse blocks and 40 amp MRBF fuses. These mount right on the battery post. Iíll take some photos when I get all the parts and begin assembly. Thanks.

Maybe you or Dr. Bob can give me an idea where to run the chassis ground cable on a C-Dory.

The article on installing the charger was excellent. I found a few minor problems with my present battery charger wiring. Good time to make things right.

Now if I can talk Joyce into the remote......hummmm

Tom
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alainP



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PostPosted: Tue Mar 20, 2018 11:20 am    Post subject: Chassis ground Reply with quote

I connected the chassis ground to an existing large negative terminal block located behind the starting battery in starboard side lazarette. I used a #8 cable left over from the old charger (10 amp) installation.
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thataway



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PostPosted: Tue Mar 20, 2018 7:34 pm    Post subject: Reply with quote

If you want the reference on the case ground, here is ABYC: 25.8.3 The inverterís, or inverter/chargerís, negative terminal and DC grounded (negative) conductor shall not be connected to the inverter case or chassis at the inverter
or inverter/charger itself.
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Avidmagnum12



Joined: 23 Mar 2013
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PostPosted: Sun Mar 25, 2018 1:11 pm    Post subject: Reply with quote

Alain and Bob....thanks for the information. I start the project later in the week. I have most of what I need and will have the rest mid week. The charger was about $300, the wire $70, fuses w/holders $60 and other stuff $60. So ......about half of a boat unit.

Then all I need is bigger batteries........priceless!

Tom
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localboy



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PostPosted: Sun Mar 25, 2018 10:44 pm    Post subject: Reply with quote

Quote:
5191 Blue Seas fuse blocks and 40 amp MRBF fuses


What are you using to mount fuses on the charger end? I've used the Blue Seas ATO/ATC holders on my relay install, but the wire size is #6.

https://www.fisheriessupply.com/bussmann-fuse-maxi-in-line-fuseholder-hhx

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Avidmagnum12



Joined: 23 Mar 2013
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PostPosted: Mon Mar 26, 2018 7:20 am    Post subject: Reply with quote

The installation instructions do not call for fuses on the DC wires leaving the charger but it has internal fuses next to the lugs. They are required by the battery connections. I do have some #6 fuse holders from Blue Seas like you used but am not sure how I would convert from #4 to #6. Iíll call ProNautic and see what they say. They have been helpful. The phone style cord for the temperature control was too short and they said to use an additional longer one with a connector. More investigation......

Thanks Tom
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Avidmagnum12



Joined: 23 Mar 2013
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PostPosted: Fri Mar 30, 2018 2:29 pm    Post subject: Reply with quote

Here is a photo of the new charger. So far so good. My batteries are over 3 years old but check out good under load. I will be ready for AGM's when the time comes to replace. Not a hard job, but it takes time to remove all the old stuff and run the new wires. The fuses for the old Guest Charger were in the middle of the wiring run.

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thataway



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PostPosted: Fri Mar 30, 2018 2:35 pm    Post subject: Reply with quote

Looks good!
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