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Author Topic:   Battery location--options and dangers
Highwater posted 07-19-2002 11:30 PM ET (US)   Profile for Highwater  
Is there a danger that marine electronics and a laptop computer could be damaged if located too close to a battery?

I want to move my battery under a modified center console in a 15' Whaler. The top of the battery case will be 4" from the bottom of a laptop computer. Could the magnetic charge from the battery damage the computer? If so, how far away would the battery have to be from the computer to be "safe?"

Boston Marine posted 07-19-2002 11:37 PM ET (US)     Profile for Boston Marine    
Maybe that question is best left for your computer manufacturer.
Highwater posted 07-19-2002 11:46 PM ET (US)     Profile for Highwater    
No doubt. Time is of the essence.
Highwater posted 07-20-2002 12:16 AM ET (US)     Profile for Highwater    
I contacted a friend who is a computer expert and he answered my question. I apologize for bringing up a question that is only tangentially related to Boston Whalers. If anyone else is interested, here is the answer:

"A battery does not put out a magentic field, only an electrical one. You would
have to worry if you were around an alternator, but not a batter, especially a
DC batterty. A home computer usually has its power supply right next to the
disk drive and that is 120V AC for comparison."

smgrogue posted 07-20-2002 03:16 AM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Highwater--are you putting in a new console or simply modifying the stock console, and if so, what are the specific mods. Will the console be raised? hinged for access? Is this battery for your elec start or for a forward mounted trolling motor?
Boston Marine posted 07-20-2002 08:25 AM ET (US)     Profile for Boston Marine    
And current being drawn or transmitted also puts out a magnetic field along the wire path.
Highwater posted 07-20-2002 08:44 AM ET (US)     Profile for Highwater    
It is a completely new console, made out of mahogany. The battery is for the electric start. I have been working hard on the design and will post a picture in a month or so. Thanks for asking.
jimh posted 07-20-2002 10:03 AM ET (US)     Profile for jimh  Send Email to jimh     
In a typical lead-acid battery there is not much magnetic material. Thus a battery, of its own structure, is not likely to be very magnetic.

Current flowing in a wire creates an eletro-magnetic field, but the field strength is proportional to:
--number of turns of wire
--amount of current
--distance from wire.

Thus a modest current of an ampere or two flowing in a single wire at a typical distance of six inches is not likely to produce much of a magnetic field, at least not enough to affect a laptop computer.

The field from a wire might affect a nearby compass. To minimize this effect it is suggested that wires carrying current be run in twisted pairs, one conductor carrying current to the load and the other carrying it away from the load. This will tend to cause the fields created by the wires to cancel each other, and the resultant field from the wires will be minimized.

This same technique--twisted pair circuits--was employed in the wiring of the telephone system and allowed thousands of twisted pair circuits to be carried in a single cable with very little crosstalk among them.

I was quite surprised when I read this thread that the question was to batteries and computers. I think there are much more important issues about battery location on a boat and possible dangers.

In terms of location, the stern has traditionally been the place for a battery, but increased weight of outboards has led to a trend to move the battery more forward in the hull. This gets some weight out of the stern, but it puts the battery farther from its primary load, the starting motor.

The eletrical implication of this is the need for longer and larger cables to connect the engine to the battery.

Distributing more weight forward in a boat is acceptable, but only if the weight is kept close to the center of gravity of the boat and the center of pitching resistance.

Imagine two identical boats. One has all of its heavy components, the engine, the battery, etc., tightly grouped and at the point of the boat's center of gravity and close to the boat's center of pitching resistance).

The other boat has the same weight, but the heavy items are located either at the extreme bow or extreme stern. This boat will have a much different motion in a seaway than the first boat.

When a planing boat is on plane there is only a small portion of the hull in the water, perhaps only the rear 25% of the boat. Any weight that is located forward of this area is going to have a considerable moment and will tend to create more pitching motion.

The battery can be a producer of gases. During charging a battery can emit hydrogen gas. If the case is damaged and cracks, the battery can release acid. These dangers are generally mitigated by locating the battery in a well ventilated area and enclosing it in a secondary container ("battery box").

Highwater posted 07-20-2002 07:17 PM ET (US)     Profile for Highwater    
On my 15' the battery was originally located in the stern, on the port side. I wanted to reduce weight in both the stern and on the port side. I needed less weight aft because I carry a lot of fuel that is located toward the stern of the boat, and the 72 qt ice chest is also in the stern (where the battery use to be). I wanted less weight on the port side because the propeller's torque is making the boat list to port when I am on a plane. So I am putting the battery just aft of midship, slightly to starboard of the centerline.

I realize that in heavy seas, things will bounce around less in the stern of the boat, and we definitely do not want the battery bouncing around, but it is strapped down. So I assumed that it would be okay under the console. And there is wood under it (embedded in the fiberglass). I increased the gauge of the wire (from 4 gauge to 2) to compensate for the increased length of the run.

What I have learned from you valuable input, Jim, is that I can reduce the effect that the battery might have on the compass if I twist the red and black wires (like a telephone wire). I assume that I would only have do this near the compass. Thanks!

63WHALER posted 07-20-2002 10:18 PM ET (US)     Profile for 63WHALER    
I'm interested in how long of a run of cables from motor to the console where the battery will be located. Thinking of doing same , that is installing two batteries in center console of a 16'. Is 2ga. wire what I should use? Since the wire should be tinned this may be pretty costly. Any ideas or problems you may be aware of I should know before doing this rigging?
Highwater posted 07-20-2002 11:12 PM ET (US)     Profile for Highwater    
Unfortunately, this is not my area of expertise. I choose the 2-gauge wire because I wanted to go one step better than the 4-gauge wire I was replacing. I do not know if it will be just right, too thin, or overkill. I bought 12' of wire (times two) from West Marine. It was about $2.80 per foot.

Since I have only owned the boat for a month, I'm going to take out the battery and put it in my spare car (which needs a battery) and install a brand new marine battery on the boat. Since Jim mentioned the danger of spilled acid, I may replace the old battery box as well.

Instead of having two batteries on board, I am opting to back up my one battery with a Prestone "Jump It!" portable battery jump starter which I bought at Wal-Mart. It is the same size as a battery but weighs much less, has a built-in light, a built-in "cigarette lighter" outlet, and it is portable (in case I have the opportunity to render assistance). Best of luck in your project! David

Jerry Townsend posted 07-20-2002 11:56 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Highwater - you are doing things right. The comments made by Jimh are all right-on too. The 2 gauge wire is not really over-kill - just prudent as the current flow from the battery to the starter when cranking the engine might be of the order of 200 to 600 amps - depending on the size of the engine - but this is just a wag but it will be high. But, in any case, there is a lot of power flowing in that cable. The heavier cable reduces the resistance so that more power is available at the starter.

Someone also mentioned the 'tinning' of the cable - but the term tinning only applies to the connections at each end - and not the entire cable.

And a bit further on the subject of battery cables - when you make your connections to the end of the cables, smear some vasoline or grease around the cable at the end of the insulation - prevents corrosion problems in the cable. ------ Jerry/Idaho

whalerron posted 07-21-2002 01:03 AM ET (US)     Profile for whalerron  Send Email to whalerron     
When you buy the battery cable, you can buy "tinned" cable. It is tinned from for the entire length of the cable and it is readily available and made by Ancor. The new Coast Guard regs for boat wiring require all wires to be pre-tinned for their entire length.
jimh posted 07-21-2002 09:13 AM ET (US)     Profile for jimh  Send Email to jimh     
Although the price of ANCOR "marine" wire is rather high, it is good wire.

Marine wiring requires some special considerations. Because of the vibration and motion likely to be experienced, the wire should be flexible. This comes from having many strands of small diameter wire. You can find large gauge stranded wire which has only a few strands; marine wire should have hundred and hundreds of tiny strands cabled into large gauge conductors.

Marine wire is also "tinned" copper. This protects the bare copper wire from corrosion. It also makes soldering easier, but it is often recommended NOT to solder large gauge wires in marine applications. This probably stems from the idea that soldering stiffens the wire which may lead to fatigue failure from vibration. If properly done, I personally think soldering improves connections, but you have to be careful not to let the solder wick up into the wire and cause it to stiffen.

The insulation used on marine wire is important, too. Sunlight (UV radiation) causes many wire insulation platics to alter their characteristics, so marine wire is made with insulation that is resistant to UV degradation. Of course the insulation should also resist water and oil, too.

All of these factors make marine wire more expensive than common insulated wire.

Obtaining good marine grade wire in small lengths and in different color insulating jackets is difficult other than at the boat store, so sometimes you just have to pay the high-dollar price.

When buying wire remember this collarary to Murphy's Law which is used in the electrical industry:

"Any wire cut to length will be too short."

whalerron posted 07-22-2002 09:03 AM ET (US)     Profile for whalerron  Send Email to whalerron     
jimh, you are so right about the precut wire being too short. I repowered in the spring and the dealer gave me controls, cables and battery cables with the package. The battery cables were whatever length I needed. I painstakingly measured and remeasured the battery cable length to be 13 feet back to the transom outer edge. When the dealer asked how long the battery cables needed to be, I told him "13 feet from the battery to the transom and then add on whatever the Johnson needs for routing under the hood." His response was "Ok, 13 feet plus another 4 feet should do it." The following week, I picked everything up and took it out to my brother's house (2 hours from the dealer) for the installation. When we got ready to route the battery cables, you guessed it, they were cut to exactly 13 feet.
jimh posted 07-22-2002 07:28 PM ET (US)     Profile for jimh  Send Email to jimh     
Maybe you can get the dealer to swap out the battery cables. I would hate to see them spliced. That would be a poor installation.
Jerry Townsend posted 07-23-2002 02:03 AM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
When twisting wires around the compass or other instruments to negate the magnetic field - the twist should be tight rather than loose. And try to have the twisted pair at least 3 feet from the instrument. ------ Jerry/Idaho

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