Re: MK Battery Problems
 

This battery issue seems to be pretty common. Maybe FIRST received a bad batch for the KOP? Has anyone informed FIRST?

Re: MK Battery Problems
 

We're not going to Atlanta, but when you get a chance, look at the contacts in the connectors, see for yourself. As far as I know they were all pre-terminated connectors. I don't have access to the batteries and chargers and robots right now, or I'd take some pictures.

I think Al S. is looking into this. I doubt it's the cause of all the battery problems, but we did notice a definite difference between the performance of the older and newer connectors when we were wiggling wires around at the AZ regional (when we also had another serious wiring problem).

Re: MK Battery Problems
 

We have 8 of the new style battery's. This year 2 of them went bad with the same symptoms as everyone else has, the voltage drops to nothing when a load is applied. We have 2 other that are down about 20% when load tested and we won't use them unless we absolutely have to. We are using the Excide chargers from prior years. The new charger is still sitting in the box.

Re: MK Battery Problems
 

i remember in Vegas team 4 asked me if i could check out there batts. for the sam reason they had a full charge but the battery would not work for more than a minute maybe that could have been why.....

Re: MK Battery Problems
 

We have not had any voltage problems with the new batteries, but have lost 6 batteries due to swelling this season. We believe that the swelling problem is due to our bank charger which we have now discontinued use with, prior to the swelling we had noticed that it was charging hot.

We did have a voltage problem in 2006. The battery in question read 13.5+ volts off the charger where it had been for an hour. But once the match started it failed to even move the robot and read something like 7 volts.

Re: MK Battery Problems
 

Colin,
Can you give me manufacturer and model number or a link to the charger? Yes I am still working toget a handle on these issues and I need hard data on battery, charger used, approximate life span (#of matches).

For all, remember that these batteries have a specified life span of about 400 charge/discharge cycles. When high current in charge or discharge is used, then that life is severely decreased. Repeated 80% discharge can lower this to almost 200 cycles. This is also affected by charging a warm/hot battery.

Re: MK Battery Problems
 

How is battery life affected by sitting for a long period, discharged? I know this kills car batteries....

Re: MK Battery Problems
 

Kill these batteries too. They need charging periodically. I think it is at least every three months.

Everyone,
Please remember to recycle these dead batteries !!

Re: MK Battery Problems
 

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.

Re: MK Battery Problems
 

Leaving Lead Acids discharged leads to a process called
Sulfation effectively messing up the Batteries ability to charge
fully the next time.

We have been wondering about our performance lateley also.
Haven't had any burn up or lose a cell yet.

Re: MK Battery Problems
 

The battery brochure for this battery can be found here...http://www.mkbattery.com/images/ss.pdf
It implies that float charging can keep these batteries going for a while. With IRI we end up charging batteries during the summer for practice. Then we don't really start using them for several months and do not leave them on float. Over the years, we have not noticed any serious deterioration. We use a CBA-II from West Mountain Radio to track batteries and compare them from one year to another. We have generally been getting usable service life for practice of three years or more.

Re: MK Battery Problems
 

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.

Re: MK Battery Problems
 

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

Re: MK Battery Problems
 

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.

Re: MK Battery Problems
 

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.