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Gone2long · 13-01-2017, 07:55

Brace yourselves for another naïve question,

The engine is a 3GM 30, a 3 cylinder, 27hp Yanmar, and the house bank is currently wired with 6 AWG Boat Cable rated at 600V. Does that seem sufficient for this size engine? The run to the engine is only about 2 meters.

Also, I would like to add a 3rd battery to my house bank and am wondering what size wire to use. I have not been able to find the same type 6 AWG wire where I am in SE Asia; however, I have some significantly larger, 1 Gauge Belden Starter Cable.

Any problem using the large wire to connect the last battery in the bank?

All input appreciated.

G2L

**a64pilot** · 13-01-2017, 08:41

The bigger, the better from an electrical perspective.
All wire has loss, the bigger the wire, the less the loss. There is a point of diminishing returns of course as with everything. I would replace the 6 Ga with the 1 Ga myself.
there are charts on line and I have an excellent app on my phone written by Blue Seas on wire, fuse sizing etc., but over sized never hurt anything except it cost a bit more of course

Gone2long · 13-01-2017, 08:56

... it doesn't do me much good if I don't know what the draw would be from the starter would be. Note that this file didn't transfer very well; there is a chart at the bottom showing 6 AWG amp capacity, but the columns did not transfer, so it is hard to read. Basically, it says that 6 AWG can handle 150 amps at 4.4 feet, which is about the distance I have.

Battery Cable By the Foot or Spool - 6 Gauge to 4/0 AWG

Battery cable is used to power your electrical system and is sized according to the American Wire Gauge, or AWG for short, specification for electrically conductive cables. Our battery cable is American made and comes in gauge (AWG) sizes of 6, 4, 2, 1, 1/0, 2/0, 3/0, and 4/0, with 6 gauge being the smallest, and 4/0 gauge being the largest. Battery cable must be sized to the needs of your electrical system, too small of a cable will cause excess heat that could pose a hazard. The size of cable you should use depends on two things: the amperage you need and the length of the cable. You can view our Battery Cable Selection Chart. to help you in determining the size of battery cable you need to use, as well as more information about how to properly size your cable and information about voltage drop. Our battery cable is SGT type and is available in either red or black. It is rated for use in 12 volt and 24 volt electrical systems with a maximum voltage rating of 60 volts. It meets S.A.E. specification J-1127 and has a temperature rating of -58°F (-50°C) to 221°F (105°C), and is RoHS compliant. Cable ends can be terminated using either battery terminals or copper cable lugs.

6 AWG Gauge Battery Cable

6 gauge AWG Automotive Battery Cable for 12 volt and 24 volt electrical systems. Rated for use up to a max of 60 volts. RoHS compliant. Made in the USA.

4 AWG Gauge Battery Cable

4 Gauge Battery Cable (AWG) for automotive and marine use. Made in the USA. Available in short lengths to 100ft. spools. Comes in either Red or black.

2 AWG Gauge Battery Cable

2 Awg gauge battery cable for low voltage DC electrical systems. Sold by the foot and spool. American made from 99.9% pure copper.

1 AWG Gauge Battery Cable

1 AWG Battery Cable. Made in the USA. Available in Red or Black. Copper core is composed of 133 strands of 22 gauge wire. Meets SAE J1127.

1/0 Battery Cable

1/0 Gauge Battery Cable (AWG). Rated for use up to 60 volts. 133 strands of 21 gauge copper wire. Durable PVC insulation. Meets SAE J1127. Made in the USA.

2/0 Battery Cable

2/0 Gauge automotive battery cable. For connecting batteries, starters, amplifiers, solar panels, etc. 133 strands of 20 gauge copper wire core.

3/0 Battery Cable

3/0 Awg Automotive Battery Cable. 259 strands of 22 gauge copper conductor wire. PVC insulation with anoutside diameter of 0.695 inches.

4/0 Battery Cable

4/0 Gauge Battery Cable. Outside diameter of 0.760 inches. Rated for use up to 60 volts. 19 x 108 strands of 30 gauge copper. Made in the USA.

Battery Cable Amperage Capacity Chart

Recommended Length and Amperage for Battery Cable while maintaining a 2% or less voltage drop at 12 volts Battery Cable Size 50 Amps 100 Amps 150 Amps 200 Amps 300 Amps 6 Gauge (AWG) 11.8 ft 5.9 ft 4.4 ft 2.9 ft 2.2 ft 4 Gauge (AWG) 18.8 ft 9.4 ft 6.3 ft 4.7 ft 3.1 ft 2 Gauge (AWG) 29.8 ft 14.9 ft 9.9 ft 7.4 ft 4.9 ft 1 Gauge (AWG) 37.7 ft 18.9 ft 12.6 ft 9.4 ft 6.3 ft 1/0 Gauge (AWG) 47.5 ft 23.8 ft 15.9 ft 11.9 ft 7.9 ft 2/0 Gauge (AWG) 60 ft 30 ft 20 ft 15 ft 10 ft 3/0 Gauge (AWG) 75.6 ft 37.8 ft 25.2 ft 18.9 ft 12.6 ft 4/0 Gauge (AWG) 95.2 ft 47.6 ft 31.7 ft 23.8 ft 15.8 ft.
When choosing the size of a battery cable to power your electrical system or project, it is important that it is sized appropriately. As electricity flows through a cable, there is an inherent resistance to the flow of that electricity which will generate heat in your battery cable and manifest itself in the form of what is called a voltage drop. Voltage drop is simply the voltage seen at one end of the cable minus the voltage seen at the other end of the cable. This voltage drop is influenced by the diameter of the copper conductors inside the cable, and the total length of the cable - The longer the battery cable is, the higher the voltage drop will be, and the larger the diameter, or gauge (AWG) of the battery cable, the less the voltage drop will be.
Why is voltage drop important? for example, let's say that your length of battery cable is connected to a 12 volt source and has a voltage drop of 2%, which is considered adequate for almost all electrical systems. At the source, or battery, you will read 12 volts using a voltage meter, but at the other end of the cable your voltmeter will only read 11.76 volts (12 volts -2%). If your circuit needs 100 amps of current, the battery cable will absorb 24 watts of power because of it's resistance. Now lets say that your voltage drop is 10%. Now your voltmeter at the other end of your battery cable will read 10.8 volts (12 volts - 10%) and that same 100 amp current draw will cause your battery cable to absorb 120 watts of power! Your cable will definitely get warm to the touch! This amount of voltage drop will cause other devices to not work properly - light bulbs will be dimmer, fans and motors will be weaker, and if the voltage drop is high enough computer systems can fail, and even the cable itself can be destroyed leading to a catastrophic failure and even an electrical fire!
When determining the length of cable you need for your circuit, both the positive cable, and the negative cable need to be considered, especially if you are wiring a vehicle that does not have a chassis ground such as a boat or other vehicle with a fberglass body. So if you have a 10 foot run from your battery, you actually have a total of a 20 foot run because the negative cable will also be 10 feet back to the battery.

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Gone2long · 13-01-2017, 09:09

Quote:

Originally Posted by a64pilot

The bigger, the better from an electrical perspective.
All wire has loss, the bigger the wire, the less the loss. There is a point of diminishing returns of course as with everything. I would replace the 6 Ga with the 1 Ga myself.
there are charts on line and I have an excellent app on my phone written by Blue Seas on wire, fuse sizing etc., but over sized never hurt anything except it cost a bit more of course

Yeah, that is what I figured, but I have also read that going from large wire to smaller can create friction and heat. Does it make a difference if the larger wire is at the end of the bank instead of at the beginning?

Pardon my overwhelming ignorance.

G2L

PS - Just found a manual for the engine, and, hopefully, it will tell me what the starter draws.

Frankly · 13-01-2017, 09:38

If you were starting from scratch I think something a little larger would be a better choice. If the 3GM is starting OK with the #6, I would be hard pressed to tell you to tear it all out.

You haven't mentioned anything about battery switches or fusing, but there is no harm (only to your wallet) in using something a little bigger for the additional battery.

One big bang for the buck is to put a section of extra insulation (often called split loom) over the starting cable in the engine compartment. Chafing through the insulation on an engine mount is probably one of the more likely scenarios for trouble with the starting circuit.

I have found wire any larger than about AWG #1 can be pretty hard to bend in typical boat situations. Good terminations and good tinned wire can also be just as important as the wire size.

Just my $2 worth

Stu Jackson · 13-01-2017, 09:56

Quote:

Originally Posted by Gone2long

Pardon my overwhelming ignorance.

None of us was born an electrician. What many of us do is point folks with questions like this to other resources so they can learn. Like this:

Wire Sizing Charts from West Marine http://www.westmarine.com/WestAdviso...e-And-Ampacity www.bluesea.com also has good material on this and fusing, but it's a PDF download and doesn't link. Here's the link to the page, scroll down for the PDF download of the Fuse & Wire Sizing Tables: https://www.bluesea.com/support/reference

Gone2long · 13-01-2017, 20:46

Quote:

Originally Posted by Stu Jackson

None of us was born an electrician. What many of us do is point folks with questions like this to other resources so they can learn. Like this:

Wire Sizing Charts from West Marine http://www.westmarine.com/WestAdviso...e-And-Ampacity www.bluesea.com also has good material on this and fusing, but it's a PDF download and doesn't link. Here's the link to the page, scroll down for the PDF download of the Fuse & Wire Sizing Tables: https://www.bluesea.com/support/reference

Yes; as noted in my "reply to self" written a few minutes after the initial post, I did find a sizing "chart", but I think I need to figure a bit more about how many amps are pulled by the starter.

Also, I read some of the fusing stuff suggested on a previous thread. Very interesting, as it also mentions other battery related principles that I needed to understand.

Still got lots to learn so, thanks for the links.

G2L

Gone2long · 13-01-2017, 20:57

Quote:

Originally Posted by Frankly

If you were starting from scratch I think something a little larger would be a better choice. If the 3GM is starting OK with the #6, I would be hard pressed to tell you to tear it all out.

You haven't mentioned anything about battery switches or fusing, but there is no harm (only to your wallet) in using something a little bigger for the additional battery.

One big bang for the buck is to put a section of extra insulation (often called split loom) over the starting cable in the engine compartment. Chafing through the insulation on an engine mount is probably one of the more likely scenarios for trouble with the starting circuit.

I have found wire any larger than about AWG #1 can be pretty hard to bend in typical boat situations. Good terminations and good tinned wire can also be just as important as the wire size.

Just my $2 worth

Thanks for the tips. So far, have not had any problems starting the diesel, and have experienced no heating of the wires; so, the good news is that, unlike me, whoever installed them and the solar seems to have known what he/she was doing. : )

All the best,

G2L

Paul L · 13-01-2017, 23:03

There's some info on current draw by the starter:
http://www.cruisersforum.com/forums/...e-76145-2.html

Gone2long · 14-01-2017, 02:47

Quote:

Originally Posted by Paul L

There's some info on current draw by the starter:
http://www.cruisersforum.com/forums/...e-76145-2.html

Thanks. That was a good read which helped fill in a lot of blanks in my understanding of the engine, batt types and sizes etc. Did a lot of other reading and poking around the system, so I now have a much better understanding of the situation.

Looks like my batteries and wire are OK. The 6 AWG may be a bit small, but the runs are short, and as noted above, and I've never had a problem so far with starting or wires heating up.

The extra 1 gauge that I have laying around the boat is probably left over from the original battery configuration which was re-done when the 420 watt solar array was added. I figure this is the case because the starter cable now being used is the same type, Belden 1 Gauge. It goes from the solar controller to the starter. The AWG is used only to connect the batteries in the two banks together and to run the batts maybe 2 meters to the controller.

Over the last two years, none of this has caused me a problem; so I figure it should be ok in the future. I am in a marina now, so tonight I will use shore power to keep the lights on while I add the third battery to the house bank, using the extra 1 gauge laying around.

Thanks for your help,

G2L

rwidman · 14-01-2017, 06:21

Quote:

Originally Posted by Gone2long

Brace yourselves for another naïve question,

The engine is a 3GM 30, a 3 cylinder, 27hp Yanmar, and the house bank is currently wired with 6 AWG Boat Cable rated at 600V. Does that seem sufficient for this size engine? The run to the engine is only about 2 meters.

Also, I would like to add a 3rd battery to my house bank and am wondering what size wire to use. I have not been able to find the same type 6 AWG wire where I am in SE Asia; however, I have some significantly larger, 1 Gauge Belden Starter Cable.

Any problem using the large wire to connect the last battery in the bank?

All input appreciated.

G2L

It doesn't matter to the engine or starter what size the wire for the house bank is.

Why not use the starter cable for the starter circuit?

Dave Lochner · 14-01-2017, 08:36

Quote:

Originally Posted by Gone2long

Yes; as noted in my "reply to self" written a few minutes after the initial post, I did find a sizing "chart", but I think I need to figure a bit more about how many amps are pulled by the starter.

Also, I read some of the fusing stuff suggested on a previous thread. Very interesting, as it also mentions other battery related principles that I needed to understand.

Still got lots to learn so, thanks for the links.

G2L

The instantaneous load on a starter will be around 200-250 AMPs for a fraction of a second. Once everything starts spinning the actual load will drop significantly. My starter is fused at 250 amps and it has not blown the fuse.

As others have mentioned bigger is better when it comes to wire size, especially on things like starter motors, refrigerators, and windlasses. Anything with a motor will have high instantaneous loads, it takes a lot of energy to get things moving, but once the motor is turning the actual load decreases.

If you have the 1 ga wire, then that would be a better choice than 6 ga.

Roger L · 14-01-2017, 09:45

Quote:

Originally Posted by Gone2long

Brace yourselves for another naïve question,

The engine is a 3GM 30, a 3 cylinder, 27hp Yanmar, and the house bank is currently wired with 6 AWG Boat Cable rated at 600V. Does that seem sufficient for this size engine? The run to the engine is only about 2 meters.

Also, I would like to add a 3rd battery to my house bank and am wondering what size wire to use. I have not been able to find the same type 6 AWG wire where I am in SE Asia; however, I have some significantly larger, 1 Gauge Belden Starter Cable.

Any problem using the large wire to connect the last battery in the bank?

All input appreciated.

G2L

That wire seems at the small end for this engine - however the run is short, and so the total heat caused by the resistance of having slightly smallish wire may be OK. If in doubt, simply feel of the wire when you are using a lot of battery power or charging the batteries at a high rate. If the wire is perceptibly warm then it is time for larger wire.

As to your question about using larger wire, there is no electrical problem with using the larger wire to connect the last battery - or to any battery for that matter. The only caveat is that if you are running two wires to the last battery - as I suspect you are - good practice says that you should use the larger wire for both of those wires.

Anytime that battery wiring varies in diameter, the resulting losses - as well as any local heating of the wire - are always going to be controlled by the smallest and longest wire (or worst corroded connection!) that you are using to connect to the bank.

Larger wire is difficult to bend, more expensive, and it can be hard to find proper fittings for it....those are the only noticible downsides to using larger wire where you can.
Keep your connections clean and tight!
rScotty - old sailor & retired engineer

reed1v · 14-01-2017, 16:07

Depends. Do you want minimal or ultra safe? We always went way oversized copper cables for any electrical transfers. Never had a problem.

**a64pilot** · 14-01-2017, 16:28

6ga will work fine for your starter, proof is it has. However if your bank is a little low, the bigger wire will start it where the smaller won't. Plus any motors brushes will last longer with less voltage drop that you will get with bigger cable.
If you have the wire, already and it's just laying around, I'd replace the starter cable.

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