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ContinuousWave: Small Boat Electrical
Moving Battery To Console From Stern
|Author||Topic: Moving Battery To Console From Stern|
posted 04-27-2012 02:57 PM ET (US)
[The author wants to move the batteries on his OUTRAGE 18 to the console from the transom. He estimates the new circuit will be 40-feet in total length of conductor, and he plans to use 1-AWG, replacing the original cables with a one-piece run. He solicits comments. He also inquires about the fit of larger wire in the engine cowling grommet through which all the electrical and mechanical cables pass.]
posted 04-27-2012 08:20 PM ET (US)
You should select the wire size based on the voltage drop. There is a good wire voltage drop calculator at ANCOR's website. There is a prior discussion on this topic here in the CONTINUOUSWAVE website SMALL BOAT ELECTRICAL archive. There is a lot of good information on this topic in the prior discussion.
I suggest you calculate the voltage drop and use the conductor size recommended. If you use a bigger size that is okay, but you'll pay more for the wire.
As for the wiring grommet on the engine, I imagine you will not have much trouble. The wiring grommet usually provides for a secondary path intended to isolate the fuel line. If the main path is crowded, move the fuel hose to the secondary path through the grommet.
posted 04-27-2012 08:21 PM ET (US)
Interesting question and direction. I am doing the same modification on my 1987 Outrage 18, but I have chosen to use 4-AWG wire from the console to the 150 Mercury. And 6-AWG for the major feed lines to buses and fuse blocks. I am completely re-wiring the boat. New bilge wires and nav light wires and lamps. My major issue is the electric down-riggers. I have planned on installing 16-AWG wire to them, but wonder if that will be to small. Each side will have its own feed line, but they will share a 15-Ampere circuit breaker.
As far as entering the motor wire boots, I am a little concerned with 4-AWG wire entering my Mercury; 1-AWG would not fit into my engine as near as I can see.
posted 04-27-2012 08:31 PM ET (US)
If the distance between the battery and the engine is 20-feet, you enter 40-feet in the wire calculator, as the wire has to run to the engine and back. Using a figure of 40-feet, I found that a 1-AWG conductor can only handle 60-Amperes with a 3-percent voltage drop. You can figure the engine cranking motor is going to be about 150-Amperes. So 1-AWG is out of the question. The calculator says for 150-Amperes and 40-feet, a 3-percent voltage drop will mean 4/0-AWG.
How did you figure the wire distance was 20-feet? The center console can't be more than 10-feet from the engine.
posted 04-27-2012 11:08 PM ET (US)
I did this project on my Outrage 17.
For the engine grommet, if it is the pre-formed type with defined holes, you can cut out the hole for the battery cables. It worked for my 2 AWG wires.
posted 04-27-2012 11:47 PM ET (US)
How do you determine whether to use the 3% voltage drop charts or the 10%? Also, do you use the maximum current that would be momentarily drawn during a start or the current output of the alternator? I understand wire size is based on heat(or how much the sheathing can handle) and resistance.
On my Outrage 18, with batteries in the console, the cables are around 31ft, round trip. Most new outboards come with 4ga cables, 12 feet long(24ft round trip). This leads me to believe that 2ga should easily be acceptable for the extra 7ft. I'm running 4ga, which I realize is on the small side. My boat has had this size on it since new in 1983, with no issues. I have not felt any heat on the cables even after multiple starts.
Having said all that, I do believe that bigger is always better when it comes to wire size.
posted 04-28-2012 03:26 AM ET (US)
Thank you to all who replied.
I estimated, generously, at 20 feet each way, since I have 18-foot control cables, and there will be some additional cable length between the Perko switch, and the batteries.
posted 04-28-2012 10:38 AM ET (US)
Re the current drawn and the voltage drop:
The maximum current drawn by an electrical starter motor used to crank over an outboard engine will most likely occur at the initial application of power to the starting motor. At the instant electrical power is applied to the electrical motor, its load will probably be at a peak, as the motor is stalled and has not yet turned the outboard engine flywheel.
The power of the motor will also be proportional to the voltage applied to it. The more voltage, the more power the motor will have to turn the outboard engine flywheel.
The voltage at the motor will be determined by the resistance of the connecting cables and the current being drawn. The more voltage lost in the voltage drop in the connecting cables, the less voltage delivered to the cranking motor, and the less power it will have to turn over the engine.
The primary purpose of the battery in a small recreational boat is to start the outboard engine. The engine starting load is the greatest load applied to the battery, and the most important load. For those reasons you will find that the battery is generally located as close as possible to the outboard engine.
When a decision is made to move the battery farther away from its primary load, the resistance of the connecting cables must be carefully considered. Any electrical power lost in the connecting cables will reduce the ability of the battery to provide sufficient power to start the engine.
If you are comfortable with reducing the electrical power available for engine starting, then use electrical cables of marginal size and tolerate the loss of engine cranking power. If you want to maintain the battery-to-engine connection with the least loss, you must increase the cable size.
In this particular application we need 40-feet of cable between the battery and the outboard. In the typical installation with the battery at the transom the cable length will be more like 12-feet. The new installation has increased the cable length by a factor of 3.3-times. To maintain the same resistance in the new cables as was in the original cables, the conductors size must be increased in a proportionate amount.
It is fairly typical that the OEM cable supplied with an outboard motor of 40-HP or more will have a conductor size of 4-AWG and be no longer than six-feet. If we make the cables 3.3-times longer, we probably need to make the wire 3.3-times larger, e.g. 1-AWG or larger. One outboard engine manufacturer (Evinrude) specifies use of 1-AWG cable for the battery connection for cables 16 to 20-feet long. Note that you must also include the length of cable in the connections to the primarly power distribution switch. If there are other connections, such as power distribution bus bars, all of these connections must be extremly well made and have extremely low resistance.
This winter I bought a clamp-on DC Ammeter with a peak recording function. I have not had a chance to use it, yet, but I plan to do some testing with a few different boats and motors, to see what sort of current is drawn by the outboard engine during cranking. I had to get a peak-hold meter because my E-TEC engine starts so rapidly you couldn't read the current on a normal meter.
posted 04-28-2012 10:55 AM ET (US)
According to the wire calculator
a length of 40-feet in a 12-Volt system with 3-percent voltage drop requires the following:
70-Amperes = 1-AWG ("one gauge")
A length of 40-feet in a 12-Volt system with ten-percent voltage drop requires the following:
70-Amperes = 6-AWG ("six gauge")
posted 04-28-2012 11:02 AM ET (US)
When you turn the ignition key, will the engine crank over? This is an important question for most outboard engine owners. In the electrical system there are three factors which determine if the engine will crank over:
--the state of charge of the battery;
--the stored electrical energy in the battery; and
--the power loss in the electrical wiring between battery and load.
If the battery is fully charged, is in excellent condition, and the electrical wiring has extremely small power loss, we have the greatest chance of successfully starting the outboard engine. As the state of charge of the battery decreases, we lose power. As the battery ages and its ability to store electrical energy decreases, we lose power. As electrical power is lost in the wiring, we lose power. These three areas represent the margin between starting and not starting.
To give the greatest margin for starting, we should
--keep the battery fully charged
--use a battery will sufficient capacity to store the electrical energy needed
--provide the lowest possible loss in the wiring
If we neglect any of these areas, we compromise or reduce the margin between starting and not starting.
posted 04-28-2012 11:19 AM ET (US)
The typical battery cable with a new engine is a six-foot long duplex cable with 4-AWG conductors. We analyze this as a 12-foot conductor for three-percent voltage drop in a 12-Volt system. We find that the conductor can handle 110-Amperes before the voltage drop exceeds three-percent.
Now we use this same current value, and increase to 40-feet. To maintain the three-percent voltage drop the conductor must be increased to 2/0-AWG.
This seems to contradict the OEM recommendations which use 4-AWG for the 12-foot circuit and 1-AWG for the 40-foot circuit.
My conclusion from this: the OEM 4-AWG cables in the 12-foot circuit have more margin than the 1-AWG cables in the 40-foot circuit. Or, said in another way, using a 1-AWG battery cable in a 40-foot circuit is marginal.
posted 04-28-2012 02:31 PM ET (US)
I have not checked any outboard engines yet, but with my FLUKE 374 Clamp-On DC Ammeter I just checked the peak current during engine start of my vehicle, a modest little 2.4-liter in-line four-cylinder engine. The engine starter motor drew a peak current 346-Amperes during cranking. That is a lot of current. The engine was also warm. I think it might take more current to crank over a 3.3-liter V6 outboard that was cold on a cold morning
posted 04-28-2012 09:02 PM ET (US)
Jimh, thanks for the excellent and well presented response. I am presenting the following information not to be provocative or disagree, but rather to get your thoughts on it. Based on the information you provided, I am seriously considering upgrading to 2ga wire on my boat.
According to information obtained here:
Reading into the charts, it seems on lengths up to 30 feet, 4ga wire is limited by temperature, not resistance or loss. The max that 4ga can handle is 160 amps. So if engines come with 4ga wire on them, we can conclude that 160 amps is the most the wire needs to be rated for, and we can use that number for our calculations. So using the chart, we see that 2ga wire is necessary for a 40ft length with a 10% voltage drop.
On the BlueSea web site, information there leads me to believe there is more to cable ratings yet. It leads me to believe that 4/0ga wire can handle at least 1000 amps for 10 sec, and 650 for 1 min, 450 for 5 min, and 300 continuously. The linked site above tells us 4/0 is rated for 445 amps, so this is a bit of a contradiction.
Mercury outboards ship with 12ft (24ft round trip) of 4ga cable. Using this as a basis for your previous findings, how do the numbers come out then?
Going into the 3% chart we see that this would be acceptable for only 55amps and the alternator alone puts out more than that on many Mercury outboards.
Do you think in an application with 35 ft(more realistic for an Outrage 18 than 40) that using 4ga wire is creating a loss in the wiring or is the risk just overheating and melting the sheathing? Is there a point where using too big of wiring creates a loss?
All of this is interesting to me because I have worked on large aircraft for years and much higher current loads are carried in much smaller wire over longer distances.
posted 04-28-2012 11:38 PM ET (US)
Eric--The first thing that comes to mind with aircraft electrical systems compared to boat electrical systems is the system Voltage. I believe that it is almost universal that aircraft use 24-Volt systems, and boats use 12-Volt systems. As a result, aircraft power distribution is able to tolerate more voltage drop in the conductor.
Let's look at an example. Assume we have a conductor of a certain length and size such that when 30-Amperes flow through it there will be a voltage drop of 0.5-Volts. If the system voltage is 12-Volts, then 0.5-Volts is a drop of 0.5/12 = 4-percent. If the system voltage is 24-volts, then 0.5-Volts is a drop of 0.5/24 = 2-percent.
As the system voltage becomes lower, the concern for the voltage drop in the conductor becomes more prominent. As a general rule in a 12-Volt system you can say that the voltage drop in the conductor will become a factor sooner than the current carrying capacity of the conductor. That is, you will reach the limit of a voltage drop tolerance before you reach the limit of the conductor's current carrying capacity.
The current carrying capacity of a conductor--its ampere capacity or ampacity--is generally defined by the heat rise that will occur as a function of current flow. The heat comes from the resistive loss in the wire, which creates a voltage drop. The voltage drop in the conductor multiplied by the current in the conductor is the power lost in the conduct. That power is in the form of heat.
The rating of a conductor to tolerate heat is typically measured by the amount of temperature rise over the ambient temperature. A number of factors come into play. If the conductor is not bundled in a cable with other conductors, an assumption is made that there will be more air flow around the conductor to carry away heat. If the conductor has insulation that is particularly tolerant of heat, such as a Teflon insulation, the conductor may be rated for more heat rise. And if the ambient temperature is low, the conductor can probably tolerate more heat rise.
posted 04-29-2012 11:21 AM ET (US)
ASIDE: Aircraft electrical power systems also tend to use alternating current with a frequency of 400-Hz instead of 60-Hz. This reduces the weight of transformers because the primary windings do not need to have as much impedance to self-magnetizing. Although today we think of AC power as being universally 60-Hz (or 50-Hz), power distribution in Canada was done at 20-Hz for a period of time. The transformers necessary for use on 20-Hz AC power were huge and heavy because of the low frequency. My father told me stories of how the lights in Ontario had a flicker because of the 20-Hz power. He also built some of his own radio equipment using surplus transformers from Canada that were designed for 20-Hz power. Those transformers were very heavy and had lots of iron in them.
posted 04-29-2012 04:52 PM ET (US)
Marko: wires for your battery should be larger than required, I made a set of 1/0 battery cables (10 ft) for my whaler back in 1985 I crimped the ends and soldered them as well, covered them with heat shrink and then dip them in liquid rubber. I'm still using them today with no problems. The larger wire allows the current to flow easier and there will be no stress on the starter (which mine is still original) trying to pull a load. The most important thing is to make sure there are no breaks/cuts in the wire and that your ends are protected from corrosion...
|L H G||
posted 04-30-2012 12:43 AM ET (US)
Boston Whaler has been rigging the Post Classic Outrages and Montauks with console located batteries for some time now. So I would think a simple check with them (Chuck Bennett perhaps?), a dealer or an owner, would give you the size battery cables required. I'm sure they have already done all the work, in consultation with Mercury engineers, to properly size this wire.
posted 04-30-2012 07:55 AM ET (US)
There is no question that Boston Whaler has been rigging boats with the batteries located a long way from the engine. They probably began to do that when they changed over to the VERADO engine. The VERADO engine weight was probably so much higher than the outboard engines previously used that the weight distribution had to be changed to accommodate all the extra wieght on the transom. The VERADO also needs the electro-hydraulic boost pump for its steering, and this usually is located near the engine. That probably took up room near the transom that normally would have been used for the batteries.
But I don't see much value in letting Boston Whaler become the exclusive electrical consultants. The rules of good electrical installation are not something known only to Boston Whaler. Electricity behaves in a predictable manner. You can easily calculate the voltage drop in a conductor without calling Chuck Bennett.
posted 04-30-2012 08:30 AM ET (US)
The electrical cable used with outboard motors to connect to the battery is typically a very high strand count cable in order to provide flexibility. Also the cable usually has a rubber jacket (as opposed to a vinyl jacket) to further improve the flexibility. This sort of cable is often called "welding cable."
When moving the battery to the console from the transom, the cables obviously have to be lengthened. Whether or not the cable run ought to be one-piece is another question for discussion.
If the new installation is to use a one-piece cable from the console to the engine, the new cable must be of the high-strand-count and rubber-insulated type to provide the necessary flexibility. Such cable becomes rather large in diameter, and, as mentioned, there is concern if the cable can pass through the rigging grommet in the engine cowling.
If the new installation permits using two-piece conductors for the circuit, the welding cable type conductor can be used at the engine where the flexibility is needed, and a non-welding cable, that is, a cable with vinyl insulation and lower strand count, can be used for the extension of the circuit. It might be possible to re-use the original battery cables from the engine for the short portion of the circuit. If that is done, the cable size in the extension may have to be a big larger than calculated, to prevent too much resistance from getting into the circuit.
posted 04-30-2012 08:44 AM ET (US)
Re the criterion of how much voltage drop to tolerate in the battery cable during engine cranking, the decision is a matter of how much electrical energy you have to spare. If the battery is fully charged and in excellent condition, the starter motor will still be able to turn over even if ten-percent of the voltage is lost in the cables. The real concern is to know how much margin there is in the system, that is, how low can the battery voltage become before the voltage drop in the cables prevents the engine from starting.
In a perfect installation there would be no voltage drop in the cables. In the real world, the cables have some resistance, so there is some voltage drop. To minimize the voltage drop the cables have to be larger.
Let's look at the ten-percent drop criterion. In a 12-Volt system a ten-percent drop is 1.2-Volts. This means that even if the battery is fully charged, has a terminal voltage of 12.9-Volts, and does not sag at all under load, the starter motor is only going to see 11.7-Volts at best. In terms of the battery state of charge, we have already gone from 100-percent charged to only about 20-percent charged with the voltage being delivered to the starter motor. To lose 80-percent of the battery voltage in the cables seems like a lot of lost power.
posted 04-30-2012 08:55 AM ET (US)
In looking at other arrangements of battery location and the starter motor they power, one sees that almost universally the battery is located as close to the starter motor as possible. There are a few passenger vehicles with low hoods and very small engine compartments where the battery has been moved away from the starter motor, but those are the exception. Typically, as the engine becomes larger and the cranking load larger, the battery is moved closer. The battery to crank a large diesel is usually just a few feet from the starter motor.
posted 04-30-2012 09:50 AM ET (US)
I agree with Jimh that closer is better for batteries to be used for starting engines. Howeever it is interesting to note that some automobiles have batteries located in the trunk supposedly as a safety precaution in a crash. In particular some (perhaps all) Mercedes Benz and BMW models.
Aircraft electrical systems typically utilize 115 volt 400 hz and 28 volt dc systems although there is a future move to 270 volt dc systems.
I have read that automobile systems are moving to 42 volt systems.
The higher voltage systems all permit the transfer of power with lower losses or with smaller gauge wire.
posted 04-30-2012 12:47 PM ET (US)
I can imagine a meeting at an American automobile company:
Designer: With this new, aerodynamic, low-hood design the customer will be delighted.
Mechanical Engineer: There won't be room under that hood for the battery. We'll have to move it to under the back seat.
Electrical Engineer: If you move the battery away from the engine, we will have to double or triple the size of the battery cables, and that costs more.
Accountant: How much will the larger cable cost per car?
Project Manager: If the bigger cable costs more than $0.75 per car, we have to find a better way.
|L H G||
posted 04-30-2012 02:37 PM ET (US)
Way before the Verado, in the mid to late 1990's, Boston Whaler started putting the battery in the console on the white Classic Montauks, and probably larger boats as well. I remember seeing such an installation, and they ran the standard battery cables of the Merc 2-stroke 90 to a pair of [terminal] posts on the starboard side of the hull, then used a much heavier gauge wire into the tunnel and up to the battery in the console.
This information should be easy to obtain from a dealer.
posted 04-30-2012 02:40 PM ET (US)
To clarify the term "Aircraft" and try to explain that it is as generalizing as the term "vehicle" would be in a general claim of conformity.
Light aircraft are generally manufactured with 12-volt systems. The 24-Volt systems do not usually enter the picture until turbo-prop-sized aircraft, or approximately 12,000-lbs gross weight That said, some of these light aircraft have the battery location aft of the cabin or in the tail. Some of the older aircraft have them within the engine cowling. The battery cables used (in all the aircraft in which I have been associated) carried cables that never exceeded 4-AWG sizes--even when the batteries exceeded recommended distances from the starter and largest electric motor or draw.
There are many reasons for these wire choices, and all make sense when broken down into fact. However battery cable sizes and wire sizes are set by our liability criteria, not by the facts brought forth by our electrical engineers alone--just as most of our manufacturing laws have been contrived. Wiring installed during manufacturing has a huge safety margin, sometimes even 300-percent of actual load carrying capacity.
posted 04-30-2012 07:41 PM ET (US)
The method of installation by Whaler that Larry describes make sense; the battery cables provided with the outboard engine are used instead of being discarded. The flexible wire is used only where needed.
Gus--Thanks for the information on aircraft. I think aircraft like to use light-weight batteries, too.
posted 05-01-2012 05:02 AM ET (US)
Not to get to far afield from the threads main goal, older light aircraft use small lead acid batteries, with low CCA abilities, where as today the sealed, AGM and Gell Cell Batteries, still using lead acid battery technology, the Nickel Cadmium battery or NiCad are almost all 24 volt and are extremely dangerous. They can run away (melt down) and catch fire fairly easily.
I have some concerns with some of my wire choices thanks to your awesome wire sizing lists. However some of the choices on the list are exaggerated for some ulterior motive. .
posted 05-01-2012 08:15 AM ET (US)
Another concern with moving the battery a distance from the starter motor and connecting it with very large conductors should be over-current protection and fusing. When the battery was only three feet from the starter motor, we could reasonably ignore the usual practice of fusing or providing a circuit breaker for the engine starter motor circuit. In the proposed installation above, we will have 40-feet of unprotected 1-AWG conductor running from the battery to the engine and back. These conductors are also going to be run through a below-deck tunnel, which will have water sloshing in it at times. And there will be no fuse or over-current protection provided. Is this a good practice?
posted 05-02-2012 12:39 PM ET (US)
The following document from Blue Sea System explains the issues in detail. As always Blue Sea has excellent resources for boat electrical systems: http://bluesea.com/viewresource/98
Directly related to your question jimh, here is the relevant text for the above document:
"Notice that wires intended to carry engine-starting currents between the batteries, the switch, and the starter, are not required to have main-circuit-protection devices installed.
This exception is based on the notion that the starting battery would have just enough power to handle starting the engine, and the wiring would be appropriately sized such that the full capacity of the battery would be unlikely to overstress the wire. It was also assumed that the batteries would be very close to the engine.
Some modern installations violate some or all of these assumptions with very large house banks that may include an emergency cross connection switch, making them part of the starting system. The house banks may be some distance away from the engine in different compartments. Some experts believe that all circuits on a boat should be protected - including the start circuits. However, at this time, this is not an ABYC recommendation."
So I would say there is no clear answer as the experts are not in agreement. There is no question adding an appropriately sized fuse or breaker to the starting circuit would make it safer to some degree, but as with all over-current protection (and all safety devices) there is a cost benefit factor to consider and the cost for a large enough breaker or fuse for a starting circuit is quite high for the low probability that the starter wires will short and not be able to handle the full battery current causing a fire.
I still may consider adding a high current fuse to my starting circuit on my Montauk at some point. However based on the fact that Whalers where rigged from the dealer using batteries in the console with wire through the rigging tunnel to a post on the rear splash-well, then smaller more flexible wires to the motor, I am confident my similar setup with 2 gauge wires to rear post, then 4 gauge wires to motor(the originals from when that battery was in the rear) is a well tested proven setup without significant safety issues.
Photos of my electrical system can be seen here: https://picasaweb.google.com/107007622155886602752/ WhalerProject?authkey=Gv1sRgCOHiqYL_38ejFw&feat=directlink
posted 05-02-2012 01:03 PM ET (US)
Re the risk of the wire in the rigging tunnel:
In the case of an insulated electrical conductor with insulation rated for exposure to water or oils, in the case of a conductor of size 1-AWG or 2-AWG, there is probably more risk for other components in the rigging tunnel from contact with the conductor than vice versa.
posted 05-02-2012 05:37 PM ET (US)
Whaler dealers have installed the battery inside the console as early as the 1980s.
My Dad had Larry Russo mount both the VRO oil tank and the battery inside his 1984 Montauk 17 on delivery. I still have the boat today. Russo credited him with starting the practice on all his later boats. We never had to cut out the deck, and he simply used the kevlar strap provided as OEM.
I had the pleasure of meeting Mr. Russo again this past fall after many years outside of New England and after my Dad's passing. Larry Sr. remembered him quite well as my Dad was a tough negotiator in addition to having meticulous attention to detail and he did most of the salesmanship back then.
posted 05-03-2012 09:34 AM ET (US)
Equally important to wire size for minimizing voltage drop is making a proper crimp termination. Be sure to use a crimp tool with a die set that is designed for the ring terminal you are using. I've seen some crimpers that you use with a hammer and this is definitely NOT the way to go. You need a "gas tight" crimp to the cable which can only be done reliably with a proper crimping tool. Don't solder the connection, this is a bad idea especially for a high vibration environment. A "gas tight" crimp will not have any gaps for solder to penetrate so you risk annealing the wire and terminal, degrading the connection.
posted 05-03-2012 09:39 AM ET (US)
ASIDE to Mombo: I enjoyed reading your historical recollection about the rigging of Boston Whaler boats. I think there is no question that the notion of moving the boat battery to the center console from the transom of Boston Whaler boats has been in the minds of many users in past. Our present discussion is focused on some of the electrical concerns and the need for proper design and installation to make that sort of historical rigging work best. Your historical anecdote gives a good perspective on this topic.
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