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ContinuousWave: Small Boat Electrical
Battery Connection Problem
|Author||Topic: Battery Connection Problem|
posted 03-25-2015 08:57 AM ET (US)
While I was connecting the assortment of cables to a replacement battery yesterday I ran into a problem.
I first connected all the negative cables to the battery as they were the deepest into the console and the most difficult to reach. I then began connecting the positive cables saving the small GPS and VHF cables for last.
When a touched the ring connector of the GPS and the VHF cables to the battery post I saw a very small spark. In order to be certain I tried again. The VHF connector sparked again but the GPS connector did not. I put both connectors aside to think about the problem.
I didn't believe I had made any mistakes when connecting the negative cables that would have caused an error or damaged the wiring. I then connected the GPS and VHF cables to the battery and called it a day.
I concluded, without a good reason, that the GPS and VHF both consume small amounts of power even when switched off. Since I've not experienced anything like this before my conclusion is based on hope rather than knowledge.
I've decided that I should have disconnected the VHF and GPS negative cables from the negative bus and connected them directly to the battery and then checked to see if the sparking problem remained. If so that would have proven my conclusion. However, I was too tired and discouraged to do so. Before trying the direct connection approach I would like to hear what you folks think.
posted 03-25-2015 04:45 PM ET (US)
I am not an expert on electrical connections, but with batteries, one always connects the positive cable first and the negative cable second, and removes the negative cable first and the positive after that. The reason is that the positive pole of a battery is your power supply, and the negative is just the ground. So, when you connect the negative first, you have established your ground and as soon as the positive connector gets close to / touches the positive post, the power jumps to the connector.
Try reversing your procedure and you should have no problem.
posted 03-25-2015 06:23 PM ET (US)
Thanks for your observation and suggestion. I believe you may be right. But in my experience when a hot connection is completed at either end of the circuit a spark is usual.
The connection is now complete so I'll give it a few days and see if my battery discharges.
If I decide to disconnect the negative power wire from the negative bus and connect the devices directly to the battery I will be doing exactly what you suggest. If that test does not create a spark I'll reconnect the negative wires to the negative bus thus doing as you suggest a second time.
None of the other devices I connected to the battery positive terminal after connecting them to the negative terminal generated a spark. However, none of the other devices were electronics unless the DTS and SmartCraft are considered electronics.
posted 03-27-2015 06:57 AM ET (US)
Butch, since you sound like a careful person, I'm sure your positive wires each have a fuse in them, right? Assuming that is so, don't worry about the spark - it's probably just as you surmise, that the device has some part of the circuitry "always on" and with the initial connection it's trying to fill up one or more capacitors.
As long as you're protected from a real short via a fuse or breaker, finish the hookup and see how it works. I'm betting you'll be fine.
posted 03-27-2015 07:53 AM ET (US)
Regarding which cable, the positive or negative, ought to be connected or disconnected to a battery first or last, I believe the habit or recommendation or usual practice of disconnecting the negative cable first and connecting the negative cable last has arisen because of this: in automobiles where there is a connection of the negative terminal of the battery to the metal chassis of the vehicle, the practice of disconnecting the negative terminal first or connecting it last has come into being because one wants to avoid creating a short circuit from the terminal to the chassis with the metal tool that is used to loosen or tighten the connector. The negative terminal is already bonded to the metal chassis, and if the metal tool comes in contact with the chassis while the cable is being connected or disconnected from the negative terminal, there is no harm; the terminal is or will soon be in electrical contact with the chassis.
Once the cable is removed from the negative terminal, the battery is no longer connected to the chassis of the vehicle. When the positive cable is then connected to or removed from the positive terminal, if the tool should happen to come in contact with the chassis there would be no short circuit current at all, because the battery is then not connected to the chassis for its negative circuit.
On a fiberglass boat where the surrounding area of the battery is all fiberglass and electrically an insulator, the worry about the tool being used to loose or tighten the battery terminals accidentally coming in contact with the boat's fiberglass surrounding area is no longer present.
Of course, one must always worry about the tool making a short circuit directly across the battery terminals, no matter if in a conductive environment like a vehicle engine compartment or in a non-conductive environment like a fiberglass boat. The order of connection or disconnection makes no difference if a dead short across the terminals is created by a metal tool.
posted 03-27-2015 08:06 AM ET (US)
I expect you'd see a small spark on either the positive or negative cable, whichever one is connected last, if there is some current being drawn at the time of connection of the circuit to the battery.
I also suspect that in the radio there is probably a filter capacitor that is being charged up when you apply power to the power leads. The filter capacitor is probably there as part of a brute-force power line filter to remove or smooth out any AC ripples on the DC power.
It is the nature of a capacitor to present a very low impedance to change in voltage. When a capacitor that is discharged to 0-Volts is connected to 12-Volts, the instantaneous flow of current into the capacitor to charge it up to 12-Volts will be a very high current. It is this high current that creates the visible spark you are seeing. As soon as the capacitor is charged to 12-Volts, the current flow decreases to practically nothing, just he leakage current in the capacitor, which should be extremely small, on the order of less than one one-thousandths of an Ampere.
posted 03-27-2015 09:02 AM ET (US)
Thank you to all. Both the VHF radio and GPS are fused quite closely to the positive terminal connector. After observing the spark and making a final connection to the battery I checked both fuses and they were intact.
After completing all the connections I checked every electrical device on the boat and all were functional.
I guess this was a lot of fuss over nothing but I am nothing if not a bit OC.
I intend to add a positive battery insulating boot soon to help avoid an accident when working with the battery connections. Of course this does nothing to protect the small screw post terminals mounted more closely together on the battery. Perhaps I will see a protective insulating boot for those as well.
PS: Many years ago while working on the batteries of a stern drive powered boat I owned I managed to establish a direct short circuit between a battery terminal and the engine through the wrench in my left hand which was in contact with my wedding band. I had to have the ring repaired as it melted almost through. Burned my finger rather badly, too. I no longer wear a ring or watch when working on batteries.
posted 03-27-2015 09:42 AM ET (US)
Re wearing a ring, especially a ring made of gold, the best electrical conductor there is, when working on electrical circuity: it is a good practice to remove any metal rings when working on electrical circuits, particularly when working on DC circuits where there is a lot of current available. In the instance cited above, Butch was fortunate to survive with only a burn on his finger.
ASIDE: In the past ten years or so, I have had the opportunity to watch while a factory-trained and certified technician replaced 40 12-Volt AGM 80-Ampere-hour batteries in a large UPS several times. The first time this occurred, ten years ago, the technician was using standard tools which he had himself wrapped in electrical tape to insulate them. The last time, a few years ago, his entire tool kit was replaced with new tools, all of them encased in plastic insulation. He explained that his employer insisted on re-fitting all their service technicians with these new insulated tools and insisting they only use these tools when working on the batteries. He also had to don a protective suit and wear a face mask, both new work rules for working on batteries. He had always removed all his jewelry and wrist watches, but those were also now mandatory procedures. I think he wore gloves, too.
posted 03-27-2015 10:03 AM ET (US)
Be very careful of sparks around lead acid batteries as the hydrogen gas produced by these batteries is very explosive. Face protection is a must, I've seen 8D batteries explode from this and it was not pretty.
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