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I am using a fan hub that is connected to my PSU with a Molex connector. I would like to know how many amps the Molex connector can handle, and hence how much current the fan hub can draw. Wikipedia says it is rated for 11A per pin, and the Molex connector has 4 pins. Does this mean it has an ampacity of 44A?

Michael Scheper
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avg9957
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From referenced Wikipedia page:

Max. current 11 A/pin (18AWG w/30 °C rise)

So 4 pins at 11A/pin leads to the 44A of OP. The problem is a little bit more complicated than that.

The maximum current that can be carried is a function of the maximum temperature of the housing (105°C) and the maximum temperature of individual connection (30°C) (and maximum temperature of wire insulation) (and length of wire) (and ambient temperature). More wires, the less total current.

From Tyco data sheet for Amp connectors.

enter image description here

Table shows number of circuits vs size of wire. Larger wire = more current. Less wires = more current. Derating connector due to adjacent conductors.

The wiki page is wrong (and right). With every circuit energized, for a 4 in-line connector, with 18 AWG wire is 9A/pin. 36A per connector theoretical maximum, if 105°C and 30°C are maintained. That is 18A supplied and 18A sunk (Ground).

As Tyco says:

...are intended to be a guide in the selection of a connector family. All applications should be tested by the end user.

As in designer is responsibe. There are other factors: Ambient Temperature. Insulation on wire. Wire length. Odds are that no actual circuit will have 18A sourced due to other factors.

Increase wire size to 14 AWG and you do get 11A/pin. And OP 44A/connector.

From SuperUser (but no reference to external source) Is this a floppy disk connector to the power supply?:

enter image description here

With the 14 AWG cable, you could get 11A on 12V circuit (Pins 1 and 2), 132W, and 11A on 5V circuit (Pins 3 and 4), 55W. Assuming power supply could source it.

Typically, power supplies supplied half that for peripherals (5A for both comes to mind). You try to avoid theoretical maximums for production.

A good reference on connector capabilities: All about the various PC power supply cables and connectors

StainlessSteelRat
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You've mentioned that you have the larger MOLEX connector that is used for 3.5" and 5.25" devices (not the SATA ones).

Their pinsizes are the larger ones and allow for 8.5A per wire.

Depending on what voltage goes over the wire will determine how much watt goes over the wire, as watt = voltage * amps. The Red wire has 12 volts, so it will draw 102watts maximum, where the Yellow wire has 5 volts, so it will draw 42.5 Watts maximum.

Keep in mind that even though this is supported, it is not meant that it will actually be used. 8.5A is quite a bit of amps for any device. Phone chargers for example usually have only 1.2 Amps and upto 2-3 Amps for fast charge.

I bet a pc fan will use about 12 watts maximum, which is quite a bit lower, but if you look for how much watts the fan use combined and you leave a bit of headroom for the controller itself, you should be fine. In worst case, the fans will spin a little bit slower.

LPChip
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