3 strands of 12 gauge VS 1 of 4

[BugzyCan]

The real question here is, how many amps does the motor put out when charging (6?), how many amps does the solar panel put out when charging (6?), what is the length of wire from the A/B switch to each of the batteries (25 feet), and can 3 12 gauge wires handle this load instead of one 4 gauge.

It has already been determined that this is not going to work, so I do not see the point of the ranting lunatic post presented here.
Nobody is talking about directly shorting across a battery.
Advising to find someone else to do the task is also not helpful as I do not believe this is THAT complicated. All I requested was some advise, not a personal attack from some "boatwright".
So far, from the "constructive" people on this forum, I have learned
- 3-12G wires is not the same as 1-4G, I would need 6-12G wires to accomplish that, and the extra insulation could be a problem if it heats up.
- Having both motor charging, and solar requires a couple of diodes to prevent cross charging and back charging (at night). Solar panel has a charge controller, and it is my understanding that this should prevent back loading there, but I may install a diode on the line anyways.
- Solar panel has a fuse, motor does not. I may add one to it if I can find an easy way to do that.

Mr.Boatwright, if you think of something useful to suggest, please post again.

Originally Posted by Boatwright

Yikes!!!

This thread is a perfect example of why electrical fires on boats are tragically too common.

Extension cords from Home Depot?? Unfocused questions about solar?? Not a clue about fuses??

The problem here is way too many folks who think that since 12v won't give you a shock if you touch the positive terminal of a battery, no worries mate.The very real danger is a 12v battery has a large amount of energy stored inside. If you don't believe me, take your Mickey Mouse 12ga extension cord setup, put on a welders apron, gauntlets, and face shield. Next short it across the terminals and watch it get red hot, catch the insulation on fire and melt down in big blue flash.

The above is a very bad idea. Much better would be to find someone who is qualified to give you advice and is able to take a look at your setup in person, instead of asking (no insult intended) ignorant questions on an open forum.

[Boatwright]

I am sorry if you were offended by my characterization of your question.

However it is clear from the question itself that the person asking it has little knowledge of how to correctly and safely wire any system connected to a large storage battery. By large, I mean anything from a motorcycle battery on up. My tongue in cheek plan that you melt down 12ga wires was not meant to do more than make you realize the potential dangers of unsafe wiring practices. Paralleling conductors to substitute multiple smaller wires for a larger conductor as you have asked about is specifically prohibited by ABYC standards.

I did make a very good suggestion. That is: You should consult with someone locally who understands safe marine wiring practices and stop buying supplies at Home Depot.

This forum often has excellent advice. It is also frequented by folks with plans and opinions based on rudimentary knowledge. I am a retired professional boatbuilder, with extensive experience in marine wiring practice. You of course can choose who to believe.

[Thumbs Up]

The real question here, actually is simply the gauge of wire being used and installing appropriate fusing to protect it. Even if you use the extension cord, you could safely install only a 15 amp fuse (from what you have shown) if you have electric start then should actually have a #4 wire which takes what, a 50 amp fuse? No matter how you do it, if you fuse it near the battery (if your batteries are far apart then 2 fuses or breakers), it will be as safe as can be (might not be as efficient or last as long).

[BugzyCan]

Well, the short of it is, nobody in town seems to be able to supply 25 feet of 4 gauge wire at the moment. Apparently stock is way down due to Covid, so I am forced to be creative with this.
Turns out, the motor connection already has a blocking diode in the connecting wire, and the solar panel has a controller so there is no backflow there either.
I will get that second battery hooked up tomorrow, and then plug in the solar panel and monitor the cable to see if there is any heat generated.

BTW, my outboard motor does not have electric start.

[Thumbs Up]

Fuse?

[BugzyCan]

Originally Posted by Thumbs Up

Fuse?

There is a fuse for solar panel, and I believe the motor has one as part of its generator circuit, although I should verify that. Thanks for the reminder.

[Boatwright]

I keep coming back here because I sincerely fear for the safety of your setup.

1) No source for #4 wire?? Have you tried auto parts and welding eqpt. suppliers? Both should be able to supply (while not marine grade) suitable wire and will also be able to put proper crimped connectors on the ends. Welding cable used to be widely used for heavy conductors in boats because of its flexibility. Automotive battery wire would be an adequate second choice.

2) The fuse that others keep asking about is installed at the battery positive terminal and is designed to protect the wire from over-heating, not the eqpt being powered. This is a very common misunderstanding of the function of fuses. It is acceptable to use a [U]smaller[U] fuse to protect eqpt, but a fuse should never be larger than required to protect the wire. There is an exception to the fuse requirement for cable feeding a starter. The cable must short (I don't have my wiring standards book at hand, but i believe it's 6 feet max). It is also acceptable on smaller systems to use the starter positive lug as a fused connection for feeding a lighting panel. Fusible links or Maxi type fuses are used.

3) Why are your batteries 25' from your engine? Normally batteries are installed as close as possible to the high current demand of your engine starter to minimize voltage drop. Since you have a 26' foot boat, you seem to have chosen to put your batteries in the bow? This is also a bad choice as adding heavy weights in the ends of a boat puts unneeded strain on the structure and also affects fore and aft stability.

4) Have you considered using a smaller motorcycle or lawn tractor type battery close to your engine for starting only? Separating the functions of solar charged batteries for lighting, etc. from engine starting could solve the long conductor problem.

[smac999]

Originally Posted by BugzyCan

BTW, my outboard motor does not have electric start.

If the motor is pull start. Why do you need a 2nd bank?

If you need longer run time. Just add the 2nd battery in Parallel. 1’ of cable. Not 25’

[Boatwright]

Originally Posted by smac999

If the motor is pull start. Why do you need a 2nd bank?

If you need longer run time. Just add the 2nd battery in Parallel. 1’ of cable. Not 25’

Good question!

I'm throwing in the towel on this one. Facts gleaned so far:

6? + 6? amps charging current

No starter.

Poster believes he needs 25' of #4 cable to carry 12 amps and is having trouble sourcing same at Home Depot.

I just did the calculation for voltage drop based on 12 amps, 25' one-way.

A #10 wire gives a .59 volt drop, which is 5%, completely safe, and for a charging circuit will work just fine.

???? Am I missing something? Where did you get the idea you need a #4 wire to carry 12 amps safely?

[Thumbs Up]

.59 volt drop is actually a lot for charging circuits. He would be better of with his extension cord idea (#12x3) than a single #10. An inline spade automotive type fuse holder, some crimps, and a 20 amp fuse (2 if the batteries are not next to each other) and he will be up and running and perfectly safe.

[BugzyCan]

So now we are on message #26 and finally someone answers the original question. So it seems that 3 strands of #12 wrapped together, is OK for this application. thank you.

I did take the advice from smac99 and just hooked the two batteries together.

Why do I need two batteries? It is because I have a Raymarine ST2000+ tiller pilot, that apparently sucks a lot of juice, and not sure how effective a 100w solar panel will be at keeping a single battery alive. I also need enough power at night for my anchor light, so having two batteries makes sense. Is that wrong?

25' of #4 cable lets me use the second connection on my A/B switch (this is actually a 1/2/1&2/off switch), so I can keep one battery fully charged, while using the second battery, then I never run out, and I switch from 1 to 2 every morning. Seems kind of smart to me, but maybe I am wrong about that too?
I wanted #4 wire, since that is what is in place already, so adding anything except the same wire size seemed wrong. Guess I am also wrong about that.

Oh well, everything is hooked up, second battery is in, and the two of them are on a trickle charger now. I need to make a bracket to keep that second battery from slipping around under the sink. I may just zap strap it in place for this trip.

Thanks for all the replies everyone. It is my first time for a lot of this stuff, so your information is a great help. I am certain to have a lot more stupid questions in the near future.

[Sailorman Ed]

Bugzy, while marine tinned wire is preferred, lots of boats came plain copper wire originally.
Connect the two 12v batteries together into one larger bank, much more efficient.

I powered up my cabin (80 ft run) with the two hot leads of #10-2UF wire wired together and a second #10-2UF with two hot leads for the second lead to get 220v, this worked just fine for 10 years. You want each wire to be EXACTLY the same length as electricity will take the path of least resistance and could overheat 1 wire, that is why I tied both the black and white wires together in the 10-2. Legal? NO! but it worked just fine. The neutral was just the 2 ground wires.

You did not list distances only that you bought a 25 ft spool, I suspect your actual distances are much smaller so your voltage drop is not significant. A 100 watt panel is not going to put out enough amps to worry about, probably a single #12 wire is sufficient. I doubt your solar controller will accept a #4 wire anyway.

BTW, when you put multiple wires onto a terminal post, put the bigger wire (thicker terminal) at the bottom, thinnest wire(terminal) at the top, be sure all of clean and free of corrosion. And use a proper ratchet crimper, NOT the cheapo wire stripper/crimp combo tool.

[RJ 1946]

Please get a knowledgeable person to help you. Paralleling wires is a very quick way to start a fire, if impedance isn't the same between conductors one of them will end up carrying most of the load , over heat and start fire. Codes have very strict rules on multi conductors. People that haven't any ,or much, electrical knowledge and offer advice ("worked for me for years") are one good way to lose you boat. Fire is a very good way to ruin a very nice day. Should also check Coast Guard Rules, could also save a citation and fine

[mcon12000]

Your original question has been answered but the process pointed out that you should brush up on the ABYC code. In your defense It's hard to not be offended by a keyboard response of "no way!" vs in person. That said what you have proposed led many of us to tell you no way should you be attempting this but try and hear it more like we're having beer at the bar or I'm actually there helping you on the boat. This is why I hate Facebook and forums at times because things get sideways way to quickly.

Anyway you need a fuse at the battery post to protect the wire itself. Then you'll need fuses on each branch circuit or accessory. The manufacture will determine what size is needed to protect the "device" but YOU will need to calculate what is needed to protect the wire at its source. A fuse downstream at the device does not protect the boat from becoming a torch. Which might mean two fuses are in play. You will burn your boat to the waterline without proper fusing. Without fuses the wire becomes the fuse burning all the insulation off. It will continue to glow red hot/burn until the wire melts or the battery fails. Unlike your house the boat is vibrating and exposing its wiring to the elements which is why household rated wire doesn't work on a boat. The insulation on the cord you are cutting up likely isn't rated for exposure to fuel which can cause the wire jacket to literally dissolve over time. Also tinned wire reduces corrosion and lessens the likelihood of a poor connection overheating or failing. Regular copper wire will corrode quickly in a marine environment causing resistance, heat and premature failure.

Google Marine Ampacity Chart to determine wire sizes needed.

Some devices are fine at 10% voltage drop some are not but for the small price difference in 12 vs 10 gauge wire for example go with the 10 and fuse it properly at its source.

Also make sure the solar charge controller has the proper charge profile programed for your battery chemistry or expect a short battery life.

As your friend holding a beer here and not some dude attempting to scold you I'm also going to say DO NOT do the half baked version. Order the right parts, do it to code and never worry about it again.

[mcon12000]

Also the charge controller needs to connect directly to the battery terminals or it will never fully charge the batteries due to the voltage loss. If its charging through the AB Switch its not seeing the true state of charge/voltage of the battery. Especially true if you have a long 4awg cable run as you have eluded to here. So if your battery needs for example 14 volts for bulk charging it will only get 13v due to the additional cable induced loss. I do understand that you want to be able to route the solar charge controller to either battery but its unnecessary if you have the batteries in parallel. Make sense?