8 AWG alt wire?

[BravoVita]

I started re working my 12 volt electrical as it was a mess and some of the previous wiring was undersized for emergency starting off the house. Since I started upgrading wire, I have run into some questions about my repair.

The boat has a start and house battery, a selector switch is located 8 feet from the starter and an ACR is only 1 foot from this switch. The starting battery is 8 feet from switch to block and the house is 24 feet. Both were wired with 4 AWG and I replaced the 24 foot house run with 1 AWG. I plan on replacing my 3 pole switch with a 4 pole (emergency combine) however there is still 4 AWG running to the starter (from the battery switch), does this need to be upgraded to 1 AWG to match the house battery? If so would the 1 AWG introduced into the Starting circuit require replacing the 8 feet starting battery run with 1 AWG to match? Can I run my 20 amp house charger and 60 amp alternator to the ACR and jumpers to the selector switch? I don't understand why I would have to run the ACR and the rest of the power direct to the battery but I think I am being hard headed about this because this is turning out to be really expensive over what I originally thought however I don't want to skimp and die in a boat fire =( Also, the 60 amp alternator wire is 8 AWG and this seams very small to run 8 feet to the ACR and another 24 feet to the battery/block but I cant find a lot of information about sizing alternator wires on the internet.

[capt-couillon]

Many many ways to include an ACR in your charging circuits depending on the outcome you wish to achieve. The circuit below will do anything but your dishes...

Also find attached a wire selection chart... Remember circuit length is both b+ and ground legs.

Wire sizing for starter circuits will depend on starter size and type. A direct drive 4-108 starter will draw a heck of a lot more than a gear drive mitsubishi. Ck mfg for rated lock-rotor current and size accordingly

[Stu Jackson]

Originally Posted by BravoVita

1. I plan on replacing my 3 pole switch with a 4 pole (emergency combine)

2. ...but I cant find a lot of information about sizing alternator wires on the internet.

1. Here's why that is not a good choice for A SAILBOAT:

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries | SailboatOwners.com Forums

2. Nonsense. Power is power. If you know the amps you need to run and the length of the wire, what's the problem? Any wire sizing chart or graph will tell you the answer (round trip + & -, of course).

[DeepFrz]

Capt, why do you have the fuse at the starter end of the cable instead of the battery end?

[skipmac]

Originally Posted by Stu Jackson

1. Here's why that is not a good choice for A SAILBOAT:

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries | SailboatOwners.com Forums.

Strongly second this. When rewiring my battery system I found this on the BlueSeas website and thought it looked like a great solution until I read the specifications and realized the limitations. Eliminated this idea as an option and just went with two manual battery switches and a Yandina charging combiner.

[BravoVita]

Originally Posted by capt-couillon

Wire sizing for starter circuits will depend on starter size and type. A direct drive 4-108 starter will draw a heck of a lot more than a gear drive mitsubishi. Ck mfg for rated lock-rotor current and size accordingly

No idea what you are trying to say, its a Yanmar 2gmf, I think the starter is rated at 1000 watts but I am not sure Yanmar provides a "rated lock-rotor current" for the motor.


This again brings me to the point where I don't think its safe for my lack of knowledge to try and complete this without more help. I have already contacted local marine techs but it looks like a little 2gm is the last thing they want to be bothered with. Additionally, I found information like this (Universal Diesel Wiring Harness Upgrade Photo Gallery by Compass Marine How To at pbase.com) showing there may be issues outside of what I believed to be an issue.

Is anyone certified willing to spend some time through Facetime or in person (Bradenton FL) to walk me through what I should be doing? I would be willing to spend some money because I would really like to stop guessing and see my boat back in usable condition.

[capt-couillon]

Originally Posted by DeepFrz

Capt, why do you have the fuse at the starter end of the cable instead of the battery end?

Actually having a current protection device in a a switched primary starting circuit at all is in error (See AYBC Excerpts for explanation). If the primary starting circuit does not have a disconnect switch the 7" rule applies.

My bad...

[capt-couillon]

@ BravoVita...

Yeah, the starter for that motor is rated at 1KW with a nominal cranking current of around 80 amps (although the "inrush" current can be up to 200+ it only lasts on the order of 40 milliseconds or so) so 4 wire is adequate for the closer starting battery although I might go ahead and move up to #2 in the interests of "bigger is better".

An object lesson in why one attempts to keep all the batteries in close proximity to your aux engine and each other. Even with refrigeration, etc, it would be surprising to have a DC house draw in excess of 50 amps on a smallish boat (I gots one too) so sticking the house bank close to the starting bank minimizes the cost of large wire and associated Voltage drops if you are unable to mount your distro panels in the same proximity.

Make sense?

Branch circuits after the distro panel are sized as required. Long runs up the stick require not much to run modern led lighting. VHF radio in 25 W mode not more than 6 amps or so. Reefer around the same if its a big old one. On my 25 footer, I find it rare that I need to run more than #10 wire for the branches beyond the distro panel which is fed with #6 wire for an expected max 50 amp draw.

Might consider moving the house bank closer to the starting battery if possible? 6V Trojan 105 are an economical solution (2 in series for nominal 100A/hr @12V $100.00 ea) and their size allows for configuration in tight spaces. Just make sure service access is easy. Easier it is to access and service them, more likely you are to do so.

Hope some of this was a help or at least a basis for more questions.

David

[BravoVita]

Originally Posted by capt-couillon

@ BravoVita...

Yeah, the starter for that motor is rated at 1KW with a nominal cranking current of around 80 amps (although the "inrush" current can be up to 200+ it only lasts on the order of 40 milliseconds or so) so 4 wire is adequate for the closer starting battery although I might go ahead and move up to #2 in the interests of "bigger is better".

An object lesson in why one attempts to keep all the batteries in close proximity to your aux engine and each other. Even with refrigeration, etc, it would be surprising to have a DC house draw in excess of 50 amps on a smallish boat (I gots one too) so sticking the house bank close to the starting bank minimizes the cost of large wire and associated Voltage drops if you are unable to mount your distro panels in the same proximity.

Make sense?

Branch circuits after the distro panel are sized as required. Long runs up the stick require not much to run modern led lighting. VHF radio in 25 W mode not more than 6 amps or so. Reefer around the same if its a big old one. On my 25 footer, I find it rare that I need to run more than #10 wire for the branches beyond the distro panel which is fed with #6 wire for an expected max 50 amp draw.

Might consider moving the house bank closer to the starting battery if possible? 6V Trojan 105 are an economical solution (2 in series for nominal 100A/hr @12V $100.00 ea) and their size allows for configuration in tight spaces. Just make sure service access is easy. Easier it is to access and service them, more likely you are to do so.

Hope some of this was a help or at least a basis for more questions.

David

1. Yes that makes sense. Yet we kinda skipped over the actual specific questions I had about the starter wire or pretty much anything else I asked specifically.
2. I'm not too worried about anything after the panel, Its mostly the specifics to the battery, ACR and selector, starter and alternator wiring I am focused on.
3. The house bank will not fit anywhere closer in distance than under the aft berth where it currently resides and is already wired for the windless and 80 percent of what I believe needs to be done. At this point I am just looking for a bit of validation as to which theories are correct and which are incorrect assumptions.

As stated in one of my replies, I believe the opinion of a certified marine electrician is what is going to be required at this point.

[mitiempo]

Originally Posted by capt-couillon

6V Trojan 105 are an economical solution (2 in series for nominal 100A/hr @12V $100.00 ea).....

David

2 T-105 batteries in series is 220 AH @ 12 volts.

[mitiempo]

Originally Posted by capt-couillon

Actually having a current protection device in a a switched primary starting circuit at all is in error (See AYBC Excerpts for explanation). If the primary starting circuit does not have a disconnect switch the 7" rule applies.

My bad...

There is no reason not to fuse the starting circuit on a small engine (under 60 hp or so) and it is easily accomplished as long as wire sizing allows. I wire battery banks, starters, and main switches with large enough wire so it can be fused appropriately - 250 amp fuse for example. Alternator output should also be fused. Always close to the battery which is the power source that could be a problem if a wire chafes or there is another issue.

ABYC exempts dedicated starting circuits simply because a large diesel in a powerboat cannot easily be fused. On a small diesel it is not an issue.

The ABYC exemption is only in a "dedicated starting circuit" as well. If the battery switch is a 1/2/both/off switch the starting circuit is not dedicated purely to starting and needs to be fused.

[smac999]

if the 60a alt is 8 feet away from your switches / acr's should probably be about a 6 awg. this is assuming the engine ground is alredy pretty big.

if you already have 8awg I woudln't be too woried as you'll rarly see 60a anyways. especially if it's interal reg.

it's not a safty issue with the 8, just a charging efficiently issue. you'd want to aim for 3% voltage drop. it's gets a little trickier to use the chart when you have different size cables for the pos and neg. and also part of the run. (smaller alt cable, bigger house feed cable)

[BravoVita]

Thanks for all the input. No further responses are required. I decided not to chance anything and have found a certified marine electrician to complete an in person assessment.

[mitiempo]

Originally Posted by smac999

if the 60a alt is 8 feet away from your switches / acr's should probably be about a 6 awg. this is assuming the engine ground is alredy pretty big.

if you already have 8awg I woudln't be too woried as you'll rarly see 60a anyways. especially if it's interal reg.

it's not a safty issue with the 8, just a charging efficiently issue. you'd want to aim for 3% voltage drop. it's gets a little trickier to use the chart when you have different size cables for the pos and neg. and also part of the run. (smaller alt cable, bigger house feed cable)

14.4 volts with a 3% drop is 13.97 volts. That doesn't take any loss through connections into account either.

While there is always some voltage drop I try to minimize it as much as possible. I have used 2/0 wire for output on a 100 amp alternator before, depending on length of run. The higher the voltage at the batteries the faster the charge through bulk.

[capt-couillon]

Originally Posted by mitiempo

2 T-105 batteries in series is 220 AH @ 12 volts.

Correct, but figuring 50% max allowable discharge real world capacity is closer to 100