Finding a electrical short

At Seneca this past weekend we experienced some battery drainage during a match. We beak every battery and have never experienced this sorta issue in our other 2 events this season. Below is a match where we are having trouble moving towards the end… In the last second though our robot seems to recover. I looked at the driver station during these issues and the battery was spiking and would drop to about 8v. This happened earlier in the day except our Rio rebooted. We looked over all the wiring and found the Rio power cable was loose and our main breaker red terminal. We tightened them but all that fixed. All the connections look solid and no strans are frayed or sticking out of the pdb, vrm, and pcm. We use Anderson power poles for most our connections from the talons to the motor. Is there a way to track where the voltage drop is coming from?

What drive-train are you using? We had an issue with our drive-train having too much grip, causing our voltage to drop to ~6V. This would make the rio go into brownout protection (I think) and we would chatter while turning.

We fixed the issue by putting electrical tape over the wheels to reduce friction.

Also in the driver station in the power tab (looks like a lightning bolt) you can see what type of short (if any) that you are having, and which rail it came from. (12V, 6V, 5V, 3.3V etc.) it will be highlighted red if there are any.

I agree it sounds like typical robot load, not a short. Batteries are interesting things…they work well, until they don’t. Maybe you are loading the battery too much with the drivetrain, maybe the battery is getting weak, maybe it was not really fully charged. Maybe there’s a loose connection in the power distribution system.

Generally when there’s a short circuit, you’ll experience a circuit breaker opening, and part of the robot not working at all until the breaker cools and resets.

We are using a 6 mini cim 6" 60a medium grippy wheels from andymark. I thought of this at first, however we never had this issue at our 1st 2 events and that’s what makes me think otherwise. All we added between then is a climbing winch which uses 1 775 pro and it isn’t used until the end of the match. We were dying before we even went to climb.

It is possible they were not charged fully as we realized 2 of our batteries had leads which were to short so we were stuck to using 4 batteries. We plan to hav 8 by next event.

Also, make sure all the 6ga connections are fully secured.

Check everything:

  • Battery Terminals(Both the bolted connection and the crimps)
  • 120a Breaker
  • PDP Connections

Loose connections in any of these places can cause issues

As it appears to be normal load, the easiest way is to retrieve and log or display the current meters in each channel of your PDP.

Low voltage problems like this without tripping breakers is usually indicative of either bad (uncharged or dead) batteries or loose main power connections (between the battery and the PDP). Check all of your connections, and make sure that the wires are as short as possible. If you can wiggle the connections, they need to be tighter.

If you’re going to another competition this season, ask the local CSAs to check your wiring and logs to see if they can help pinpoint the problem.

You seemed to be running right up to the point that you made a solid hit with another robot. About 100% of the time the result is intermittent battery connection which is exactly how your robot is acting. You were lucky, most loose wiring will result in total reboot of the RoboRio or radio. It does not seem that is the case. When a connection is loose, voltage will be dropped across the connection. The amount of voltage drop is dependent on the current through the connection and the resistance of the connection (which is very high for loose connections.) The offending connection will also become very warm. See my recent post in the “not Al’s annual inspection” thread.

BTW, the Battery Beak will tell you the state of the battery under certain conditions at the time of the test. If the battery is old and has limited capacity, the Beak may show the battery to be good. However, if you use the internal resistance test, you need to know the the results of the test on that battery when it was new to see a change in today’s test. The Beak may not show a loose connection and it will definitely not show a problem in other parts of the robot since it isn’t connected there.

You should always use a battery beak before a battery change. Before you go to the competition make sure the resistance of the batterys isn’t to high (measure when fully charged). You could get a battery tester so that you can measure the robot battery at load but that isn’t necessary (we don’t even do that). Check that the battery cables are screwed to the terminals securely and use a lock washer. Check the crimps at both ends of the wires, make sure when you plug the battery into the robot that the andersons are locking together correctly.

Always? We’ve never used a battery beak. But we do keep track of which battery we are using, and whether it’s been fully charged, and sometimes we even look at the battery voltage on the laptop. And haven’t been affected by low battery charge on the field, for a long long time.

Maybe this newfangled instrumentation technology is necessary, maybe it isn’t.

I always check the battery charge just to make sure that the battery isn’t going to be a problem because it is one less area for something to go wrong.

The Battery Beak is a load tester, so it will say if the batteries are in good condition and if they’ll hold up under load. Granted, if you’re at a competition with brand new batteries that you know are good, you could get away with a $10 multimeter, an AM BattHawk, or the green light on the charger.

hmmm…our batteries are getting to be a few years old, I think they are from the 2015 season and newer.

Then again, maybe we just don’t build power hungry robots, and that’s why we’ve been ok without load testing batteries.

A battery beak does give you one more indication when things are not right, but you might not be able to tell if everything is indeed good, by using it? You still need to have good procedures in place, to make sure that you don’t put a partly charged battery in the robot before a match.

If the battery beak says the battery is %100 or higher I trust it for the competition robot. We buy 5 new batterys every year so that we will always have the best batterys in our robot(no older than 1 or 2 years for competitions).

We use a battery Beak and find it useful. Keeping note of the internal battery resistance help to decide when they are on the decline. We survived long before we had one by battery tabs in the charged batteries and pulling batteries when they started to seem flaky on the robot. Many ways to skin a cat.

As documented here on CD in other threads, beak is not totally immune to false positives (saying the battery is good when it’s actually not… especially for older batteries), but it is very unlikely to give false negatives (saying the battery is bad when it’s actually good).

There’s really no quick and easy test with rare false positives.

Low-amp long-duration tests are probably the most reliable test that is affordable for FRC teams. But that sort of test cannot be done as you’re cycling batteries off the charger at a competition, and you don’t want to run that sort of test too many times during the season because if you do it too many times it takes its toll on the battery.

Some teams use the low-amp long-duration testing at the start of each season to weed out the batteries that need to be retired from competition use, then use beak at competitions.

Actually recharging these batteries takes almost a day according to a reliable source I’ve talked to.

Actually, no. A load tester would put a resistance load across the battery to measure actual terminal voltage and current across a high power load. In our case, that resistance would need to be in the order of 0.5 ohms just to get just over 20 amps and the resistor would need to be rated at 200 watts.
The Beak uses resistors to give a quick indication of battery health and internal resistance.
However, batteries generally do not go bad all of a sudden unless dropped or damaged as shown in the video. The video shows a very typical loose connection somewhere in the primary (battery, breaker, PDP and 6 wire) electrical system.

We experienced a similar challenge this weekend at Hatbro- Horsham and found that it was loose battery terminals and a broken dart actuator.