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4QD series controllers - Current limits

Contents, this page

• Introduction
• Earlier Controllers
• Control board layout (issue 13 shown)
• Later Controllers

Introduction

The control board current limit resistores have changed frequently, as MOSFET improve the Rds generaly decreases. This increases the current, but it has to be constrained within safe limits.

Earlier Controllers

The 4QD series controllers were originally aimed at golf buggies and similar terrestrial applications where reverse is not used much and reverse current does not need to be as high as forward current. The 4QD series use a full bridge circuit and since the forward hiside is conducting forward current all the time and is not chopped, this is where most heating will occur and if MOSFET current limits were ever pushed to the limits, this is the first place than should fail. So the bridge included one extra MOSFET in this arm to reduce the dissipation here.

The reverse current in the standard controllers was therefore set to about 75% and the forward current.

Later Controllers

The 4QD series controllers now have symmetrical current limits - this actually simplifies the current limit circuitry as there are now in general only two versions of the control board;

1. All 36v controllers (lower Rds MOSFETs)
2. All 48v controllers (higher Rds MOSFETs)

The chart below shows the values in use August 2012.

Control board layout (issue 18 shown)

The drawing shows the issue 18 control board: greyed out components are not fitted. Earlier boards may vary slightly.

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