Wire Lengths?

General discussion of the MCP motion controller product line
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boston
Posts: 3
Joined: Mon Mar 15, 2021 6:40 pm

Wire Lengths?

Post by boston » Mon Mar 15, 2021 8:17 pm

I just received my MCP233 and I need some clarification on wire length. Before purchasing I skimmed the manual which states:
1.0.4 Wire Lengths
Wire lengths to the motors and from the battery should be kept as short as possible. Longer wires will create increased inductance which will produce undesirable effects such as electrical noise or increased current and voltage ripple in the DC Link capacitors. The power supply/battery wires must be as short as possible. They should also be sized appropriately for the amount of current being drawn. Increased inductance in the power source wires will increase the ripple current/voltage which can damage the DC Link capacitors on the board and/or causing voltage spikes over the rated voltage of the motor controller, leading to controller failure.
However, I just happened to glance at the data sheet which states the following:
Warnings
The following guidelines should be followed when using the MCP or damage will occur. There are several factors that will affect the
operation of the MCP.
1. Battery wire should be no longer than 20 inches in length.
2. Motor wire should be no longer than 20 inches in length.
The data sheet is much more restrictive than what the manual indicates. 20” is useless to me and I’ll need to return the units if that’s the case. I have two automotive use cases. I don’t have exact wire lengths because I’m prototyping this on the bench first.

USE CASE ONE – DOOR OPENERS
The motors have a stall current of 20 AMPs. The MCP233 will be under the dash, the actuators are in the doors and the battery is in the nose (maybe two feet).

USE CASE TWO – SWAY BAR ACTUTORS
The motors have a stall current of 5.5 AMPs. The MCP233 will be under the dash, the front actuator will be at the front axle (maybe two feet), the rear actuator will in at the back of the car (maybe 12-15 feet) and the battery is in the nose (maybe two feet)

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Basicmicro Support
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Joined: Thu Feb 26, 2015 9:45 pm

Re: Wire Lengths?

Post by Basicmicro Support » Wed Jun 02, 2021 11:44 am

The datasheet it being very conservative. Power wires should be kept as short as possible. Use larger gauge wire than you think you need. The longer the wire the larger the wire gauge should be. 3 feet of wire and the power wire being at least the same gauge as the motor wire is ok.

Using large lengths of wire with out compensating with wire diameter will increase inductance/impedence which will cause excessive ripple current in the motor controller and damage it.

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