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Unread 10-13-2018, 11:10 PM
philso philso is offline
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Re: Huge voltage drops and hot battery wires

Quote:
Originally Posted by Tamas_907 View Post
My team and i are preparing for an offseason competition with our 2018 robot and bumped into some problems with the electrical system. The robot is drawing too much voltage from the battery and also heating the battery wires up.

We've tried trouble shooting the problem by disconnecting the compressor, because we have a minor leak in the pneumatic system, but that's another fix for another day. This decreased the load on the battery, but we could only drive for about 30 seconds before dropping to 5 volts.

When we went to disconnect the battery, we've discovered the battery wire was burning hot. The wire that connects the main power switch wasn't warm at all. Also, there were no other warm wires on the robot.

We've tried 7 different batteries from different years including new ones, but they started to dip below 5-6 volts about 30 seconds after driving around only with the drive train.

There were no modifications to the robot before we went on summer break. Before that, we had no problems with it.

I just wanted to ask for some ideas what the problem could be, so when we go back to fix the robot Monday, we have a place to start.
I just reread your original post. Wre the battery wires hot just near the SB50 connector or along their whole length? One or both of the crimps for the lugs in the SB50 connector may be loose if the wires are hot mainly near the connector.

If there is a short across the 12V, you would not have any voltage to run your robot. Also, those connectors are designed to make it very, very difficult to short from one side to another.

Look inside the two SB50 connectors on the wires going to the battery and on the wires going to the robot. Are the contacts deformed?

Lastly, use a small screwdriver to depress the spring steel latch that holds the contacts in the SB50 connector and pull the wire and lug out. Look at the area on the contact where it makes contact with the the other connector. I have noticed that the silver(?) plating is physically worn off many of the contacts. This may lead to a high contact resistance and heating where the two contacts touch.

If you can get access to a thermal camera like the one phargo used, it will lead you to the problem area very quickly.
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