Warming up the batteries

[Al Skierkiewicz]

Originally Posted by thelittlesister

Our battery will drop from 12-13 volts to 9-8 in 1 minute of just being plugged in no matter what the temperature is.
-Ally
316

Ally,
You have left a lot open to question. Does the battery drop with the robot turned on but not moving? It is normal for a battery to read 8-9 volts under load (while the robot is moving) after a minute of operation particularly if you are running the compressor and using a lot of air. When you stop moving and the compressor turns off, does the battery come back to 11-12 volts on your dashboard? Again this is normal.

If the battery draws down to 8-9 volts with nothing else running and stays there or gets worse, then you have a short or bad component on the robot. Start by pulling all the breakers and then putting them back in one at a time to determine which device is drawing the battery down.

[thelittlesister]

We only have the one robot because we have to carry previous parts over to new robots. Could it be possible that all 7 of our battery chargers are bad? We have batteries dating back to 2006, but we have the one from every year. We haven't load-tested it. How would I do that?

The battery drops just from the time we take it off charge, put it in the robot, and turn it on. It will drop to an unfunctionable 6ish by the end of a match. The compressor takes a lot, but our battery dies just by plugging the robot in and not even turning the robot on. At comps we plug in the battery then walk to the field and by the time we get connection it has already dropped from 12-9 and we can watch it drop by not even moving(without the compressor running)(and we'll be disabled). But our volt meter will read something along the lines of 13 before it goes in the robot. And then once the voltage drops it does not come back up. We only had this problem during off-season competitions and practice this year, but never before that.

Thanks for your help!

[JamesCH95]

It seems most likely that there is a problem with your robot's electrical system. I would disconnect everything: the battery, main breaker, all the power distribution board breakers, etc. Measure battery voltage, connect ONE THING ONLY, measure battery voltage again, and repeat until you find out what component is draining your power.

If the battery is draining while just sitting there it may be a fault with the main breaker, Anderson connector, or all of your chargers/batteries were exposed to the same damaging conditions.

[thelittlesister]

I'll have to try it. Thank you so much!

[Alan Anderson]

Originally Posted by thelittlesister

The battery drops just from the time we take it off charge, put it in the robot, and turn it on. It will drop to an unfunctionable 6ish by the end of a match. The compressor takes a lot, but our battery dies just by plugging the robot in and not even turning the robot on. At comps we plug in the battery then walk to the field and by the time we get connection it has already dropped from 12-9 and we can watch it drop by not even moving(without the compressor running)(and we'll be disabled). But our volt meter will read something along the lines of 13 before it goes in the robot.

Those symptoms suggest either that your robot is drawing significant current when it should not, or that something bad has happened to all of your batteries. Did they get frozen or baked at some point? (A frozen SLA battery will not have much capacity afterward, especially if it was discharged at the time.) Do you have one charger that has failed and keeps pumping current into fully-charged batteries? (We boiled a bunch of batteries that way a few years ago.) Does someone on your team have a habit of carrying them by the wires? (That is very bad.)

The possibility of faulty robot wiring is actually the preferable option here. Without a battery connected, use an ohmmeter to look for (and with luck, find) a connection between the power connector and the frame of the robot. Or you might just be getting physical contact between the battery terminals and some metal structure.

[Mike Betts]

Ally,

The chances that you have a bunch of bad battery chargers is very unlikely.

I agree with the suggestions of turning on one thing at a time to identify a fault.

Another possibility: I have seen are loose connections at the battery causing high resistance and large voltage drops. Last year, I had a team at WPI with bad connections on all of their batteries...

Regards,

Mike

[Al Skierkiewicz]

Ally,
There are a few answers here. The batteries that are from previous years, 2007 or earlier have likely reached their maximum life. If they cannot hold a charge, it is time to recycle them. Our batteries have a useful life span of a maximum of 400 charge/discharge cycles. If they are run hard (drained in one match) you can expect that to be much less. If you have used them for a significant number of demos and off-season play then it is likely that even this year's batteries could be at the end of their life. A battery load tester can tell you for sure. A voltmeter cannot tell you anything about the battery without a load. The one I recommend is the CBA-II from West Mountain Radio. It is expensive but worth every penny. it even allows you to test the battery and overlay it with last year's test of the same battery to track age differences. We have been using mine since 2004.
For those that might be wondering, yes batteries can fail right out of the box. Dropping, holding by the wires and poor storage can kill batteries. Over charging, higher than 6 amps, will also kill a battery no matter how much you think you are monitoring it. With AGM batteries, the higher voltage encountered with high current chargers, can punch through the glass mats and cause hot spots inside the battery.

[thelittlesister]

Alright, I'll check these things too, but I won't be able to get into our workshop until January so it'll take some time to find out what it is. I really hope we can find the problem before it accidently gets recycled and put on our new 2011 robot!

[SammyKay]

Originally Posted by JamesCH95

It seems most likely that there is a problem with your robot's electrical system. I would disconnect everything: the battery, main breaker, all the power distribution board breakers, etc. Measure battery voltage, connect ONE THING ONLY, measure battery voltage again, and repeat until you find out what component is draining your power.

If the battery is draining while just sitting there it may be a fault with the main breaker, Anderson connector, or all of your chargers/batteries were exposed to the same damaging conditions.

We have tried just having it plugged into one thing at a time. We tried all this during the elimination rounds at Ramp Riot this year. We currently have one or two batteries that actually work. The 2010 battery we got is one of the worst ones. I don't remember exactly which battery works the best, but it was the only one consistently working for us.

[Al Skierkiewicz]

A sharpie is a good thing to have on you at all times. Mark the suspect batteries as "practice only!" Mark your new ones with the date you opened the box and put them on the charger. Mark the side or the top, never the bottom. You will wear off important info if you mark the bottom.

Sammy,
Remove all the snap action breakers and then see what happens. The only thing running should be the Crio and the wireless access and the camera if you have one. If you have a camera, pull the plug on the bottom. If the battery doesn't discharge, then add two breakers that feed your drive train and see what happens when you drive. If the battery stays up, add two more breakers and repeat. Typical electrical problems are frayed connections at the Crio power input connector or the power output connectors on the PD. The same is true for power feeding the sidecars and Crio interface cards. Check all the wiring on the PD as this is another area where a frayed wire will contact and adjacent lead.
Another common problem is through the camera which has a power supply common to the camera case. Plug the camera in last if you have one. When you are telling us the battery is falling to 8-9 volts is that reading on the dashboard/Classmate or with an actual voltmeter across the battery terminals? It is not uncommon for there to be a failed 50 amp battery connector on the robot side that could be dropping the voltage. A bent contact, a poor crimp, a damaged terminal on the PD all could give the effect of low voltage to the robot.

[SammyKay]

Originally Posted by Al Skierkiewicz

Ally,
There are a few answers here. The batteries that are from previous years, 2007 or earlier have likely reached their maximum life. If they cannot hold a charge, it is time to recycle them. Our batteries have a useful life span of a maximum of 400 charge/discharge cycles. If they are run hard (drained in one match) you can expect that to be much less. If you have used them for a significant number of demos and off-season play then it is likely that even this year's batteries could be at the end of their life. A battery load tester can tell you for sure. A voltmeter cannot tell you anything about the battery without a load. The one I recommend is the CBA-II from West Mountain Radio. It is expensive but worth every penny. it even allows you to test the battery and overlay it with last year's test of the same battery to track age differences. We have been using mine since 2004.
For those that might be wondering, yes batteries can fail right out of the box. Dropping, holding by the wires and poor storage can kill batteries. Over charging, higher than 6 amps, will also kill a battery no matter how much you think you are monitoring it. With AGM batteries, the higher voltage encountered with high current chargers, can punch through the glass mats and cause hot spots inside the battery.

I believe we have tried using a batter load tester. I'm not totally sure, but I think so. As Ally said, we are unable to get into the workshop until January to test the batteries any further.

Thanks everyone for all these ideas! We've been kinda lost about what is wrong and where to go from there, but these should really help us out

[SammyKay]

Originally Posted by Al Skierkiewicz

A sharpie is a good thing to have on you at all times. Mark the suspect batteries as "practice only!" Mark your new ones with the date you opened the box and put them on the charger. Mark the side or the top, never the bottom. You will wear off important info if you mark the bottom.

Each battery has a number (as well as the year we got them) and we are planning on keeping a record of the voltages of each battery/how they ran when we tested them.

[Doug G]

In 2008, we did 2regionals and a scrimmage before atlanta, and had the battery mounted on it's flat side in the robot. We then lost two matches at Atlanta because two of the six batteries we had been using would die during a match. They would read 13volts on a meter before a match, but under load it dropped to 6 volts or so. We eventually figured out that one or more of the glass plates within the battery must have cracked or have been compromised. We now use a 50 dollar load tester from napa auto parts to make sure the batteries are still ok when at competition.

New students see those batteries as industructible heavy objects and don't realize how careful they need to be with them. I also recommend mounting them as vertical as possible to reduce the stress on the plates inside.

[DonRotolo]

Originally Posted by thelittlesister

We haven't load-tested it. How would I do that?

You have any of several issues:
1. The chargers are all bad (unlikely)
2. The batteries are all bad (very likely)
3. The robot has a fault (possible)

You've read several suggestions to eliminate #3.

#1 is indeed unlikely, but possible. After a full charge (as indicated by the charger) measure the battery voltage with a multimeter. A normal reading for a battery just off the charger would be over 13.5 volts. Let the battery sit for a day, to eliminate the 'surface charge' and a normal reading should 12.6 volts.

#2 is easily determined with a load test. Al's recommendation of a West Mountain Radio CBA is excellent, but they are not free.

Instead, take about 10 feet of #10 wire (or 8 feet of #12), which should be about 1 Ohm. Measure the length of wire with an Ohmmeter (be sure to comensate for the resistance of the meter's test leads) to verify about 1.0 Ohms. (A high-wattage 1 Ohm resistor (25 Watts capacity) will do as well)

While measuring the voltage across the battery terminals, connect the 1 Ohm load (the wire or resistor) also across the battery's terminals. Count exactly 15 seconds. Write down the battery voltage at the 15 second mark.

A Very Good battery will read over 10 volts. An OK battery will read over 8.5 volts. Bad battery will drop below 8.5 volts. (NOTE: These numbers are debatable, but that's what I use).

If in 15 seconds with a 1 Ohm load your batteries all drop below 8.5 volts, and start above 12.5, they're bad. Buy new ones.

What causes a Lead-Acid battery to go "Bad"? Other than usage, sitting in a discharged state (terminal voltage less than 12.4 volts) for any period of time. Like over the summer. This kind of battery loses 50% of its charge in 90 days. On our team, we make sure they don't go more than 60 days without getting charged. Even then, we lose 3-4 batteries each year.

[Al Skierkiewicz]

OK Sammy,
We will be waiting for a report in January. There is a possibility that you have one or more failed chargers and that in the normal course of events, all batteries have been touched by the bad charger. That is unfortunate but should not be ruled out. I am going to guess that the batteries have been used often and are just dying of old age.
Doug, the glass is a woven mat between the plates so there is really nothing to break. The lead plates can become dislodged with abuse and break off the common terminal inside a cell. In this case, the battery will test normal even with a momentary load tester. The CBA will show this damaged cell by a drop of 2 volts after a period of time. Black in the attached plot is a normal (2 year old) battery showing 16 amp hour capacity, the blue shows a two cell failure, green shows a single cell failure and the red shows the signs of intermittent plate connections within a cell followed by several cell failures.