Moderated Discussion Areas
ContinuousWave: Small Boat Electrical
Primary Battery Wiring
|Author||Topic: Primary Battery Wiring|
posted 12-14-2002 08:49 PM ET (US)
I'm changing the battery location for my outboard from the back of the boat to under the console. Do I need to [increase] the size of the wire? How much?
posted 12-14-2002 11:13 PM ET (US)
Try this site.
posted 12-15-2002 12:40 AM ET (US)
Do I need to [increase] the size of the wire?
I don't know... is it possible to buy TOO large a diameter battery cable?
posted 12-16-2002 05:25 PM ET (US)
I think you want 2-AWG. On recent Montauks, I have noticed the factory uses cable heavier than what comes with the engine. They use a terminal block to make the connections. You might try Boston Whaler customer service.
posted 12-17-2002 09:10 AM ET (US)
It basically depends on how much [current] your starter draws. The starter is typically the highest [current] device, and, if the wiring can handle that, all should be well. According to Ancor Products, if you use marine grade wire, which you should do, a 20-foot length of 6-AWG wire will carry 40 amperes at 12 volts with only a maximum of a 3% voltage drop.
You should be able to find the starter [current] in your owner's manual or you should be able to get it from the manufacturer. There is no need to use cable that is larger than your requirements.
Do not use automobile SAE cables for this application. Spend the extra money and get marine grade pre-tinned battery cable. Unless you have some kind of super-duty starter on your outboard, or unless your boat is 40 feet long, I seriously doubt that you need 2-AWG gauge wire for the job.
posted 12-18-2002 10:13 PM ET (US)
Voltage drop in the cable is directly proportional to current and to resistance.
To maintain the voltage drop at acceptable limits while making the cable longer you must use a cable with lower resistance (per-foot), which implies a larger cross-section conductor.
For a rough rule of thumb, increase one cable size for each time you double the distance.
posted 12-19-2002 11:58 AM ET (US)
I concur. AWG-6 would be ample for this job. Marine wire will make the grade and has my vote. Tinned copper with a thick and pliable sheath. Be certain to solder the ends on and do not forget the marine grade heat shrinking to make the recipe complete. Steve
posted 12-20-2002 08:45 AM ET (US)
I concur with AWG-6 marine grade. Used it on my 15 to run from console to motor. No noticeable loss at all.
posted 12-21-2002 04:14 PM ET (US)
The factory service manual for my 90HP
1-10 feet: 4 gauge.
11-15 feet: 3 gauge.
16-20 feet: 1 gauge.
It also says the no-load current draw for
posted 12-22-2002 11:20 PM ET (US)
I wonder what considerably higher means? Does it mean 25% more under load? 10% more? 50% more? I hate it when the manufacturers know the numbers but don't put them in print.
posted 12-23-2002 04:33 PM ET (US)
I'm working from memory here, and an
automotive application, but the draw under
load could easily be 2-3x the no-load draw.
posted 12-23-2002 07:43 PM ET (US)
Cable current carrying capacity is usually rated for use in conduit or other confined spaces. If the cable runs in open air, there is usually a signicant boost to the rating from the air-cooling effect.
posted 07-14-2005 11:01 PM ET (US)
I have been told that soldering is out for marine applications, replaced by crimping. Does this sound right?
Also, anyone know what a Honda Accord starter draws when starting? This is the same engine used in the marine applications. The postings above leave some doubt over the cranking current. Note that most automobile batteries are rated at 600-CCA. Is that because [the engine starter motors] really draw that amount of current?
posted 07-18-2005 09:05 PM ET (US)
The best advice for the recommended wire gauge to be used to connect a particular motor to its starting battery is found in the owner's manual or in the installation instructions that came with the motor. (I hope your dealer gave you the installation instructions when he delivered the motor to you.)
In all cases the size of the cable recommended is made in accordance with the required minimum voltage needed for reliable starting of the motor, assuming a battery with a decent charge and voltage level.
The longer the battery cable the greater the voltage drop that occurs in the cable. The greater the current, the greater the voltage drop. Thus, in the case of larger motors which have high current starters and whose batteries are located some distance away from the motor, rather large cable has to be used to maintain a properly low voltage drop in the cable.
There is no penalty for using a cable that is too large, other than the extra cost, the extra weight, and the lower flexibility of such a cable. On the other hand, the penalty for using a cable that is too small can be failure to start, poor starting, excessive heating of the starter motor, and a voltage drop so great that engine electronic systems will not function properly.
The ANCOR company has a wire size calculator online:
You can use this to make estimates of the necessary cable size.
If your engine manufacturer has recommended a specific cable size for particular lengths of cable, you should follow those recommendations if they require a larger size cable than other sources suggest would be adequate. It may very well be that the engine needs special protection against low starting voltages in order to run properly. It is often mentioned that the Mercury Optimax engine is particularly sensitive to battery voltage fluctuations during starting; these engines may need larger battery cable than otherwise thought necessary.
The recommendation against soldering of large wire gauge connections is often made because of concerns for the durability of those connections in an environment where there is vibration. Also, the size of large wire often makes it difficult to get a good solder connection without special soldering equipment. If a crimped connection is used, it is very important to prevent the connection from becoming corroded due to water.
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