MK Battery Problems

[ebarker]

The new charger is a little wierd.

If you pull the charger off a battery that has reached full charge and immediately connect to a battery that needs charging the charger goes stupid and does nothing.

If you reboot disconnect and reconnect and/or reboot the charger then you will be back in business.

You really have to pay attention to see if it is really charging.

[eugenebrooks]

You might want to check each bank of the charger to confirm
that it is executing its three stage program properly, and that
the parameters are reasonably close to what MK specifies.

The suggested charge rate is C/5 amps, about 3.6 amps.
Yes, FIRST specifies the limit at 6 amps and this is reasonable
for our usage of the batteries.
The suggested absorption voltage is 2.40 to 2.45 volts per cell.
The suggested float voltage is 2.25 to 2.35 volts per cell.
There are 6 cells in the battery we use.
The last parameter is the length of time the charger sits
at the absorption voltage before kicking down to float.
The typical standard for this is 4 hours, and this is fine
for a deeply cycled battery, but is not good for a battery
that has been shallow discharged.

The Interacter charger, www.batteryweb.com,
implements timing on the absorption cycle that is proportional
to the length of time spent bulk charging. This is desired
behavior for batteries that are shallow discharged and
rotated to the charger every match, as they should be.

There is no need to trickle charge these batteries for long
periods, and if you do, the survival of the battery depends
critically on the charge voltage. The self discharge rate is
3% per month. All you need to do is store them fully charged
in a cool dry place for the summer, and then give them an
overnight charge when school starts again.

Below is a link to MK's technical manual for their GEL and AGM
batteries, the one we use is an AGM battery.
http://www.mkbattery.com/images/VRLA_TechManual.pdf

Eugene

Originally Posted by Cory

The charger is an AutoMeter Professional BusPro-600S. 6 station, 5 amp per station smart charger.

The 6 in question probably had 40 or so charge cycles, tops, on them.

The charger had one station in question which had been charging slightly warm since Atlanta 07. About a month and a half ago we noticed that it was charging extremely hot, saw one very swelled battery, and 5 more that had minor swelling.

We immediately discontinued use of the banked charger and went back to the vintage kit chargers (Xenotronix HPX-60) and have not noticed anymore issues.

[Cascade]

We think we had one battery fail this year as well. We will be testing this again in a couple weeks. We left this battery at home so as not to get it confused and put in the robot.

Please see the attached battery testing we did between the 2006-2007 seasons. Please keep in mind the data presented is based on the old Exide batteries; however, I imagine the new MK batteries will respond in a similar way. We use this in the pit to estimate when a battery will be fully charged based on the charging voltage. If you have any questions, we are happy to answer them.

About the two chargers teams are using: The old charger with the single LED was a pain to use until we understood them. When we tested the batteries we had a current meter in series with the charger and battery to see what the charger was doing during the change in color from amber, to green, to blinking. Amber means the battery is charging. As you can see from the graph as the voltage goes up, the charging current goes down. A solid green light means the battery is charged. This occurs at 14.2 vdc like clockwork. The blinking light back to amber to green means the charger has entered a trickle charge mode. You can see this happen on the current meter as the meter will momentarily show current then go back to zero. The blinking coincides with the momentary current shown on the meter.

The new charger is better since it shows the percentage of charge. It is a little quirky on startup and you do have to make sure to hit the current button twice to get to 6 amps and if the red light is lit unplug the charger and plug it back in. By the way, you can also see from the graphs, no charger is actually applying 6 amps to any battery.

Other tips we have learned the hard way:
1. Put Anderson connectors on your battery charger leads. This prevents arc welding in the pits and gets you a 100% good connection every time. Think we have post on this through my handle.
2. Make your own battery cables. We have a post on this you can find, too. This tip has eliminated battery cable problems for us.
3. Carry batteries by the battery, not the cables. Take care of the cables, also.
4. Be nice to batteries and treat them like a laptop or your favorite tool.
5. Check to make sure the spring that clicks onto the pin in the Anderson connector is engaged. We found one had slid off the spring and not making full contact with its mate on the robot end of the Anderson connector. To fix this, simply push or poll the cable until you hear or feel the click of the pin snapping back onto the flat spring.
6. Clean any corrosion from the battery posts or cables and make sure everything is tight.
7. Buy a load tester. We got a cheap one at Harbor Freight Tools for about $20. Don't forget to use a DMM to measure battery voltage.

Feel free to use our battery information or share with other teams as you wish.

[Al Skierkiewicz]

Tom,
I looked over your data and it is pretty much what you should expect to see. There are a few issues in the data. Your calculated battery resistance is flawed since it does not take into account the output impedance of the charger. The actual resistance goes down as the battery charges and is normally around 11 mOhms. It is normal for the current to go down as the voltage goes up simply because of the difference in charge voltage compared to battery terminal voltage. It is quite common for lead acid batteries to be charged with a constant voltage style charger. With that type of charger, the terminal voltage is low when the charge current is high. It rises as the battery becomes charged because lead acid battery terminal voltage rises with charging. As that is the case the only way to get the battery to take any current during charge is to force the charger to a higher voltage than the battery. Another charachteristic of lead acid cells is that when they reach full charge, any additional current forced into the battery is given up as heat. Since the charger is capable of a higher voltage than the battery, this will be the case unless the charger is smart enough to turn off when it senses the battery is at full charge. I am guessing the time scale is reversed in your graphs as the graphs represent typical charge and terminal voltage for these batteries. Nice work and it represents quite a bit of time commitment to bring this data to the group. Note that there is also a difference in starting current and this likely due to the different discharge conditions on the batteries you were testing. If I can figure a way to include this in my electrical presentation, can I use some of your data?
What may be at issue here is the difference between gel cell technology and AGM which is slightly different construction but uses the same chemistry. The suggested max charge current on the MK sheet for our battery 5.4 amps. The supplied charger is designed to output up to 6 amps. I wouldn't think that would be a problem but time will tell. I have given the MK rep all the data on the chargers teams were given over the past few years. He has not indicated a problem yet but others are still investigating the issue.

[Cascade]

Thanks, Al

You are right; I did not take into account the impedance of the charger. We were simply looking for a way to understand what the battery and charger were doing and be able to explain to the kids how to use the chargers. Yes, the time base is reversed because we wanted to know based on the charging voltage how long it might be until a battery would be charged enough to use in a match if we got into a situation like the championship rounds, where batteries may be needed quickly.

Here is how we tested each battery:

1. We put together 5, 200 mA, 12 vdc bulbs in parallel to equal a 1 amp load.
2. Attached the load to a battery until the load voltage dropped to 10 vdc.
3. Attached the battery charger to a battery with 1 DMM in series to measure the charging current and 1 DMM across the battery to measure the charging voltage.
4. We recorded the voltage and current readings every 10 minutes.
5. Enter the data into Excel. Each test took about 4 hours, so be patient.

Why I thought this was a valid test is the repeatability of the data. Look at the last graph where all 6 batteries just about end up right on top of one another. This validated for me, anyway, we had a new tool to use, share, and learn something from. Best part is it seems to work close enough as we have used this at three regional’s now and the kids are using it and are successful with it!

Thanks for the feedback. Yes, feel free to use the data for any purpose. We like to help where we can.

Please remember the data is based on the former Exide batteries, not the new MK brand.

[IndySam]

Hate to bring up an old thread but...

Last year we had nothing but trouble with the batteries. One by one they all failed until we were left with one good battery and that was from 2007.

I just got done running the six new batteries we purchased this year with our CBAII in preparation for IRI and they all still check out as good as they were new.

What are other teams experiences? Was the low friction less hard contact game responsible for not shorting out batteries or are these just a better batch.

Thoughts?

[ATannahill]

We only had problems with one battery all season. A battery leaked acid during the minnesota regional. We had no problem with batteries shorting out or dropping charge.