Wednesday, November 09, 2016

Vindication Monday!

'twas disappointing to see a short in the motor after rebuild, but perhaps that could be explained.  The controller label still wasn't visible, but a document search said that the Sand Star E Plus offered regenerative braking.  That could only mean one thing on a brushed motor with four terminals labeled A1, A2, S1, S2..... SHUNT WINDINGS.  The shunt wound motor is another old workhorse, but rarely seen on golf carts.  It's prime characteristic is that speed is controlled by varying the voltage on the 'shunt' that energizes the electromagnetic fields.  At a certain shunt voltage, the motor will give its all to maintain a particular speed, until the load is too much to bear.  Conversely, if a shunt wound motor is 'overhauled', or forced to turn at a faster RPM than the shunt dictates (rolling down a hill), it will generate current back into the battery.   This revelation comes courtesy of a little consulting and measurement by Dan Bentler, who walked me through the diagnosis.  The motor couldn't go through a full bench test, as the output shaft bearing is integral to the transaxle, but it turned just as expected once bolted back on.  Reconnect the controller, and a dead short appears.  So we have a bad controller, and that's not so hard to replace.  Removal of the controller confirmed that it was an uncommon but affordable shunt motor controller.

On the Grumman project, we got the motor mated back up to the transaxle, but discovered a different bolt spacing on the end bell that didn't match the other motor, but it will match if we simply remove and 're-index' the adaptor plate (rotating the motor housing 90 degrees).  We need practice installing motors anyway, right?

No comments: