Fuse for iPhone Charger

[LCnSac]

I want to install a simple [cigar lighter accessory outlet] by Attwood for charging my iPhone 6, USB to Firewire. I know most of the chargers for this model put out a maximum of 2.1 amps, but I cannot find any recommendations for the size of an inline fuse between the [cigar lighter accessory outlet] and the deep cycle house battery. What fuse have you installed?

[Acseatsri]

I believe you're referring to a USB charging port. The outlet only puts out 2.1 amps at 5 volts, so the draw is about 1 amp @ 12 volts. I would fuse it at 3 amps, but definitely no larger than the wire that feeds the device is safely capable of handling.

[LCnSac]

I think the 3-Ampere fuse is a good suggestion. That's what Lowrance recommends, and I've never had a problem with those with the 3-Ampere inline. I haven't gauged the wire, but it's probably 10 or 12-AWG, so the capacity is larger than any fuse I'd use for the iPhone.

[jimh]

If the USB port on the device you are installing provides 5-Volts at 2.1-Amperes, that is 10.5-Watts of power. If the source of the power is a nominal 12-Volt circuit, then the current in a 12-Volt circuit that is equivalent to 10.5-Watts is only 0.875-Amperes. However, that calculation presumes that the conversion of the voltage to 5-Volts from 12-Volts is done with no loss, which may not be the case. Better to assume that at least 2.1-Amperes may be flowing in the 12-Volt circuit.

If you are to use the now most common ATC cartridge fuses, it is hard to find them in values of fine increments of Amperes, so you will have to choose from the common values. ATC cartridge fuses are available in ratings of 1 to 5-Amperes in one-Ampere increments, but to find fuses below 3-Amperes can be difficult from the usual mass-market suppliers.

Here is an interesting case of another color coding of numerical values in ATC fuses identification:

COLOR = AMPERES
Black = 1
Gray = 2
Violet = 3
Pink = 4
Tan = 5
Brown = 7.5
Red = 10
Lt. Blue = 15
Yellow = 20
Clear = 25
Green = 30
Amber = 40

[jimh]

Also, regarding the charger port on an iPhone 6: I very strongly doubt that the connector is a Firewire port. The iPhone 6 has the Apple LIGHTNING connector for charging. Compare at

https://en.wikipedia.org/wiki/Lightning_(connector)

versus

Firewire, the Apple trademarked name for an IEEE 1394 port

https://en.wikipedia.org/wiki/IEEE_1394

[jimh]

Also, I am not at all clear about the device you are planning to install.

Is the device just a CIGAR LIGHTER SOCKET (these days more often known as a CIGARETTE LIGHTER RECEPTACLE) as universally used in automobiles to provide 12-Volt battery power for the past 50-years?

Or, is the device some sort of USB outlet that fits in approximately the same size hole as would a CIGAR LIGHTER SOCKET?

If you are installing a CIGAR LIGHTER SOCKET, I recommend fusing at its rated current, which will probably be around 15-Amperes. I installed a CIGAR LIGHTER SOCKET at the helm panel of my boat. I also use it as a place to plug in various power cords for various devices which employ the very common CIGAR LIGHTER PLUG connector. One of the devices I plug in, on occasion, is a hand-held search lamp, which draws about 15-Amperes.

The general concept of the cigar lighter power socket is that there is a lot of 12-Volt power available there. If you were to fuse it at only 3-Amperes I suspect that many devices that could plug into that socket would blow the fuse.

On my boat, I have the CIGAR LIGHTER socket fused at 20-Amperes. I used a Marinco socket. I probably should reduce that to 15-Amperes.

Also see this prior discussion:

http://continuouswave.com/ubb/Forum6/HTML/002209.html

[LCnSac]

Also, regarding the charger port on an iPhone 6: I very strongly doubt that the connector is a Firewire port. The iPhone 6 has the Apple LIGHTNING connector for charging. Compare at

https://en.wikipedia.org/wiki/Lightning_(connector)

versus

Firewire, the Apple trademarked name for an IEEE 1394 port

https://en.wikipedia.org/wiki/IEEE_1394

Lightning is correct, sorry for confusing the two terms. It's a cigar/cigarette lighter, yes.

I've considered the reduced utility, but these are inexpensive recepticles and I think I'd dedicate one to the iPhone with a 3 amp inline. Unless I'm misunderstanding low voltage current, I'd think that fuse would act to protect a power surge? I had planned to pick up another with battery clips and a 10-15 amp fuse for the searchlight or whatever else might require 12V power. My Rule air pump for the float tubes (I use boats as mother ships at times) has to be a direct to battery connection.

[jimh]

A fuse in a branch circuit only opens when the current in the circuit exceeds the fuse rating for a predetermined amount of time. Generally with a fuse there are two factors that determine when the fuse opens:

--the amount the current exceeds the fuse's rating, and

--the duration the current exceeds the fuse's rating.

For example, if you have a 1-Ampere fuse and 1.2-Amperes flows in the circuit, the fuse may open after a minute or more at that current flow. If the current in the circuit is 10-Amperes, the fuse will open much faster, perhaps in less than 0.1-second.

The term "power surge" is a vague term. Power is a product of voltage AND current. A fuse only protects against current, not voltage. There is more damage likely to a connected device if the voltage provided to the branch circuit suddenly experiences a surge. Of course, in most cases, when the voltage surges, the current that will be drawn by the attached loads will increase in proportion, so the fuse will blow. But a big over-voltage surge could cause damage to connected devices before the fuse opens.

To protect against voltage surges one typically uses a voltage surge suppressor, not a fuse. These devices operate instantaneously to shunt the over-voltage away from the loads attached to the branch circuit. Of course, one of the best surge suppressors is a big lead-acid battery in good condition with a full-charge. Some of the most damaging voltage surges occur when the boat battery is temporarily disconnected due to a loose connection. Without the battery there to absorb voltage transients, there is nothing to stop them; this is when they cause damage. For that reason, keep battery connections solid and secure.

[jimh]

As I mentioned earlier, when one sees a cigar lighter socket there is an assumption the power available there is sufficient to power an electrical cigar lighter, that is, quite a bit of power, not just a couple of Amperes. As long as you never plug in a load that needs more than 3-Amperes, the 3-Ampere fuse will remain intact. I suspect, however, that, sometime in the future, some load will be connected that will need more than 3-Amperes. I recommend you carry a supply of replacement fuses and make the fuse accessible.