Current capacity of wire

[iceisfun]

Hello EEVBlogers

I have a question about a project I'm working on

I am trying to connect some stepper driver + encoder boards with a DB9 interface to a control box, but I don't know how much current I can carry on one of these wires?

The current requirement is 3A @ 5v per phase of the stepper motor

http://www.ebay.com/itm/370423582662

[Monkeh]

Not 3A by a long shot.

[IanB]

Two things constrain the amount of current you can carry in a wire:

1. Voltage drop
2. Heat generation

With smaller circuits and lower currents voltage drop is the main thing to be concerned about. Simply take the wire you are considering, find out its size (gauge) and length, determine the resistance and then use Ohm's law to find the voltage drop for the current it will carry. See if this voltage drop is within allowable limits. If not, use a thicker wire.

[8086]

Google homework:

Resistivity

Ohm's law

[M. András]

get the db9 connectors and solder some 0.5mm2 wires or 0.75mm2 to it that rs232 or god knows what cable from ebay will have maximum 0.25mm2 wires in it or even thinner

[Monkeh]

get the db9 connectors and solder some 0.5mm2 wires or 0.75mm2 to it that rs232 or god knows what cable from ebay will have maximum 0.25mm2 wires in it or even thinner

Because 0.75mm² is totally adequate for 5V 3A at 10 feet.

[Rufus]

The current requirement is 3A @ 5v per phase of the stepper motor

This http://www.powerstream.com/Wire_Size.htm is a useful reference.

[FoXX]

Very nice link Rufus, thanks

[M. András]

get the db9 connectors and solder some 0.5mm2 wires or 0.75mm2 to it that rs232 or god knows what cable from ebay will have maximum 0.25mm2 wires in it or even thinner

Because 0.75mm² is totally adequate for 5V 3A at 10 feet.

i like to oversize things just to be sure

[Monkeh]

get the db9 connectors and solder some 0.5mm2 wires or 0.75mm2 to it that rs232 or god knows what cable from ebay will have maximum 0.25mm2 wires in it or even thinner

Because 0.75mm² is totally adequate for 5V 3A at 10 feet.

i like to oversize things just to be sure

Oversize? That's undersized. Do the calculations next time.

[M. András]

well yeah. my mistake its a serious voltage drop