Welded contactor checking systems and methods

A method comprising:

• providing a plurality of batteries that are electrically connected and that collectively output power for an electric motor via first and second nodes;
• providing a first relay that is connected between a first output of the batteries and the first node;
• providing a second relay that is connected between a second output of the batteries and the second node;
• providing a third relay that is connected between the first output of the batteries and the first node;
• controlling the first relay and the second relay;
• commanding opening of the first relay during a first diagnosis period;
• commanding closing of the second relay during the first diagnosis period;
• measuring a first voltage difference between a voltage at the first node and a voltage at the second node during the first diagnosis period, the first voltage difference being measured while the first relay is commanded open by the relay control module and the second relay is commanded closed by the relay control module;
• outputting whether the first relay is welded closed based on the measured first voltage difference during the first diagnosis period;
• commanding opening of the first relay during a second diagnosis period;
• commanding closing of the third relay during the second diagnosis period;
• commanding opening of the second relay during the second diagnosis period;
• measure a second voltage difference between a voltage at the first node and a voltage at the second node during the second diagnosis period, the second voltage difference being measured while the first relay is commanded open by the relay control module, the second relay is commanded open by the relay control module, and the third relay is commanded closed by the relay control module;
• and
• outputting whether the second relay is welded closed in response to the measured second voltage difference during the second diagnosis period.

A system comprising:

• a plurality of batteries that are electrically connected and that collectively output power for a load via first and second nodes;
• a first relay that is connected between a first output of the batteries and the first node;
• a second relay that is connected between a second output of the batteries and the second node;
• a third relay that is connected between the first output of the batteries and the first node;
• and
• a battery control module comprising:
• a relay control module operatively connected to the first and second relays and configured to open and close the first and second relays;
• and
• a welding indication module operatively connected to the relay control module and configured to (i) command the relay control module to open the first relay during a diagnosis period, (ii) command the relay control module to close the second relay during the diagnosis period, (iii) measure a first voltage difference between a voltage at the first node and a voltage at the second node during the diagnosis period, the first voltage difference being measured while the first relay is commanded open by the relay control module and the second relay is commanded closed by the relay control module, and (iv) output whether the first relay is welded closed based on the measured first voltage difference during the diagnosis period,
• wherein the welding indication module is further configured to (i) command the relay control module to open the first relay during a second diagnosis period, (ii) command the relay control module to close the third relay during the second diagnosis period, (iii) command the relay control module to open the second relay during the second diagnosis period, (iv) measure a second voltage difference between a voltage at the first node and a voltage at the second node during the second diagnosis period, the second voltage difference being measured while the first relay is commanded open by the relay control module, the second relay is commanded open by the relay control module, and the third relay is commanded closed by the relay control module, and (v) output whether the second relay is welded closed in response to the measured second voltage difference during the second diagnosis period.