Batteries Plus

[karin_fisher]

Has anyone taken their FRC batteries to Batteries Plus to have them tested? Our batteries are less than a year old. Our chargers show fully charged but when resistance is put on the drive train the load on the Classmate goes below 9v. What is the best way to trouble shoot?

[Ether]

Originally Posted by karin_fisher

Has anyone taken their FRC batteries to Batteries Plus to have them tested? Our batteries are less than a year old. Our chargers show fully charged but when resistance is put on the drive train the load on the Classmate goes below 9v. What is the best way to trouble shoot?

You can kill a battery in less than a year with improper handling and/or improper storage.

Here's a link to one of the most thorough and accurate battery testers on the market.

How much "resistance" are you putting on the drivetrain? 4 stalled CIMs can pull a LOT of current and cause a low voltage reading.

[Al Skierkiewicz]

Karin,
It is not unusual for the battery to fall to 9 volts with a fresh battery while driving around. Short duration dips to 5 or 6 volts are not uncommon. It is important to note the battery voltage after two minutes or more. If the battery generally stays above 6 volts while driving, the batteries are likely OK. If you can't make it through a complete match without resetting the Crio and/or the radio, then you might have a bad battery.
The battery checker that Ether has linked can duplicate the testing done by the manufacturer and give you a plot and amp hour calculation. I recommend a discharge of 7 amps and a test stop voltage of 8 volts. The curves can then be saved and each test you make of the same battery can be overlaid with the previous tests to show if your battery has changed or has reached end of life.
Please remember that the 12 volt connection to the Crio analog module and the jumper on that module are used to sense the battery voltage and provide the reading on the dashboard. If the voltage dips to about 5.5 volts, the Crio disables all output, which temporarily stops all motor function. If the battery voltage falls to 4.5 volts for a short duration, the power supplies that feed the Crio, camera and radio will reset and so too will the devices they feed.

[Mark McLeod]

Originally Posted by Al Skierkiewicz

Please remember that the 12 volt connection to the Crio analog module and the jumper on that module are used to sense the battery voltage and provide the reading on the dashboard. If the voltage dips to about 5.5 volts, the Crio disables all output, which temporarily stops all motor function. If the battery voltage falls to 4.5 volts for a short duration, the power supplies that feed the Crio, camera and radio will reset and so too will the devices they feed.

Not quite right.
The battery voltage fed in through the Analog breakout to the cRIO is not used by the cRIO to cut power at low voltage. The cRIO isn't involved at all. That's why your robot will run without power to the Analog breakout-you just get a 0.00 volts reading at the Driver Station.

At low voltage the Power Distribution Panel is the element that lets power drop to the regular red/black wago connections on the PDP, while sustaining full power through just the two special 12v radio and 24v cRIO outputs. The power to the 5v (nominally the camera connection) is not protected. The motors lose their power, at least momentarily until the battery recovers, while the radio and cRIO resist rebooting until the battery falls below the minimum threshold.

[Al Skierkiewicz]

Mark,
I have been told that low voltage is sensed by the Crio and motor control outputs are disabled below 5.5 volts to protect the PD supplies and hopefully keep the Crio and radio alive. We need to get this nailed down.

[Mark McLeod]

You were given misinformation.

It's very easy to refute.
Try it at home when you get the chance.
Just pull the breaker for the Analog module power.
Everything still runs fine.

[Joe Ross]

The UnderVoltage Lockout on the 5v supply on the Digital Sidecar is 5.5v. That would shutdown the PWM, Relay, and Digital outputs.

[Mark McLeod]

Might lead to the misunderstanding about the cRIO controlling power brownouts.

I wonder how the power bleed through the 37-pin cable affects this, since that supplies enough power to keep the PWMs operating without the 12v power source, unless too many PWMs are active.
Although, with a power brownout and PDP diverting the power to the protected outputs, there is only a trickle of voltage coming off the PDP to supply the speed controllers in any case. Trying to drive the normal complement of things will make the robot seem dead on the field anyway.