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  #16   Spotlight this post!  
Unread 10-14-2018, 02:35 PM
GeeTwo GeeTwo is offline
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Re: Huge voltage drops and hot battery wires

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Originally Posted by Tamas_907 View Post
The batteries weren't hot themselves, only the battery connector cable. It got more hot towards the end of the connector and it was normal temperature after the main breaker's battery connector.
That sounds like bad crimps inside the battery's SB50 connector. The resistance from the contact inside the connector to the lug at the battery should be a bit over a milliohm on each side.
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Unread 10-14-2018, 05:29 PM
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Re: Huge voltage drops and hot battery wires

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Originally Posted by GeeTwo View Post
That sounds like bad crimps inside the battery's SB50 connector. The resistance from the contact inside the connector to the lug at the battery should be a bit over a milliohm on each side.
If you measure the resistance of a contact with a normal DVM with a normal PAIR of probes, and you get a reading of under anything around 4~5 Ohms, it is a good connection. It requires a 4-probe technique with a higher end DVM to properly measure anything below 10 Ohms.
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Unread 10-15-2018, 09:15 AM
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Re: Huge voltage drops and hot battery wires

You can pull up driver station logs and trend voltage drops and current draws to find out what is using current and how much. You can also go back and look at earlier times when you were not having this problem and see what has changed. This feature is an often overlooked diagnostic tool. These logs stay on the driver station computer until you specifically delete them.
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Unread 10-15-2018, 09:42 AM
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Re: Huge voltage drops and hot battery wires

I bet that you have a contact/spot resistance issue in a battery connector, likely on the robot. Carefully inspect any crimps or contacts (metal pads inside the Anderson, for example) in this area. Ideally, post pictures of all of these!

Also, if you decide to probe this contact for resistance with a DMM or Ohmmeter, DO NOT PROBE THE CONTACT SURFACE DIRECTLY. You risk raising a burr on the contact, which could turn into a significant spot resistance on its own. Use a dummy connector and probe the wires off of each end of the connector (added benefit of testing the as-used Anderson connection) or probe the bottom/crimped area of the Anderson terminal.
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Last edited by JamesCH95 : 10-15-2018 at 09:46 AM.
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Unread 10-16-2018, 02:36 PM
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Al Skierkiewicz Al Skierkiewicz is offline
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Re: Huge voltage drops and hot battery wires

Quote:
Originally Posted by Tamas_907 View Post
The batteries weren't hot themselves, only the battery connector cable. It got more hot towards the end of the connector and it was normal temperature after the main breaker's battery connector.
This could still be a bad SB50 connector on the robot side if it occurs with more than one battery. Remember that temperatures on the inside of the battery will not transfer to the case immediately. That being said, that battery internal could be hot while the case seems cool.
I have seen students modify (bend) the spring steel under the SB50 contacts to make insertion easier. This will reduce the contact pressure and ultimately lead to high resistance and heat at the terminal. If you crimp your own SB50 pins and do not use a valid crimper, what method do you use? Over the years, teams have reported that they used a hammer, pliers, etc. I have a good method for crimping using a bench vise but we (WildStang) use the AndyMark crimper and then solder our connections.
A worn SB50 will allow the contacts to move quite a bit inside the connector. (side to side) If you wiggle the wires and the contacts move a lot compared to other connectors, it is time to trash that connector, shell and contacts please. A high temp terminal will show color changes to indicate the terminal is the source of the heat.
I have seen many robots that have the conditions you describe. In worse case, the SB50 shells melted and fused together.
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Last edited by Al Skierkiewicz : 10-16-2018 at 02:49 PM.
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