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4QD controllers
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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
(up to and including issue 15 before April 2004)
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
(issue 15 April 2004 onwards)
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;
The chart below shows the values in use August 2012.
| Resistor | 36v | 48v |
|---|---|---|
| Ri(a) | 4K7 | 4K7 |
| Ri(b) | note | note |
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.
