Re: MK Battery Problems
 

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.

Re: MK Battery Problems
 

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?

Re: MK Battery Problems
 

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.

Re: MK Battery Problems
 

we dropped one of our 08' batteries during a demo this year, It dident crack or leak or anything, But it no longer holds a charge...

Re: MK Battery Problems
 

We load test our batteries at 20A, with a cutoff voltage of 11 volts. It is easy to build a load tester using some high power resistors, a fan, some relays, a resistor divider for voltage sense, and that aging EDU controller you probably have laying around. The cutoff voltage is high to avoid wear and tear on the battery from the load testing. We record the number of seconds that the battery remains above 11 volts with the load applied. We also use a 5 bank three stage charger and don't fall into a situation where a battery is used for two matches before charging. We do note good years, and bad years, for batteries from the load testing performance. The capacity can vary by 20% or more, but we have never had a battery fail during a competition event.

Eugene

Re: MK Battery Problems
 

Sam,
I didn't see this post until this morning or we could have talked at IRI. We set the CBA for 7.5 amps and 8 volts terminal voltage (end) to simulate the manufacturer's specs and get a good amp hour calculation. Are you keeping your sweeps so you can compare the same battery over a period of time and overlay them? I have many teams that claim bad batteries, but most when they show them to me, have obvious external damage, indicating rough handling.
I cannot stress enough, do not lift or carry by the wires, do not carry with one hand and do not drop into the robot or onto to the floor in the heat of battle. The terminals are soldered internally (no other mechanical connection) and are not designed to handle the full weight of the battery. Lifting or carrying by the wires is a death sentence and it may cause injury if the terminal fails while you are carrying the battery. A battery that has been handled by the wires will show some opening between the terminal and the red or black sealant due to the movement of the terminal. Two hands please for safety sake. These batteries are smooth and heavy, one hand is not enough even for a big guy like me. Dropping the battery can force two plates together causing a short or will cause fractures in the plates and connecting bars causing reduced capacity or failure with temperature.

Re: MK Battery Problems
 

I just received word from West Mountain Radio that they have a new tester, the CBA III available in August for $149. It will do up to 40 amp testing.
http://www.westmountainradio.com/CBA.htm

Re: MK Battery Problems
 

I should have asked you when we talked Saturday. We are very careful when handling the batteries and I do save the tests from our batteries.

It just seamed like last year was a bad year for batteries. We never had problems like we did last year. Of the six from this year 5 are just as good, or better than when they were new and the 6th is only slightly weaker and still very usable.