Battery Beak

[Mike Copioli]

Originally Posted by Siri

So just to make sure I understand, if I use the Beak on a battery I just finished charging in the pit, the Good ones will read "Fair" because of the higher Rint? (Do Fair batteries read "Bad"? Bad ones still read "Bad"?)

Not necessarily, the batteries Mark tested had a higher than normal internal resistance it just so happened that the last battery was right at the threshold between 'Good' and 'Fair'. I would reserve that battery for practice only. A good rule of thumb for surface charge in SLA like the ones used in FRC is 10%. What this means is; if you take a battery directly off of a charger and then test it you get a 10% increase in the internal resistance and SOC from the surface charge that has not had time to penetrate the lead plates. For a healthy, new FRC battery this should not cause a 'Good' battery to read 'Fair'

Originally Posted by Siri

What's the minimum percent Charge that still indicates a surface charge to you (somewhere between 130% and 113%, I take it)? Is surface charge ok in actual use of the battery?"

Surface charge is a result of the chemical reaction inside the battery being slower than the rate of charge provided by the charger. There is always some surface charge when a battery is first removed from the charger due to this reaction, it is perfectly normal. Again it accounts for apx 10% of the total charge in FRC. In other words the surface charge is deterministic and not unpredictable. So if you wanted to test your battery right after removing it from the charger just deduct 10% from the result. Or let it rest for about 5-15 minutes.

Originally Posted by Siri

Thanks! I suspect these are stupid questions to anyone with a modicum of practical EE knowledge, but I regret I'm not really one of those people. I do need to fix this.

These are valid questions that we asked ourselves during the time spent developing this device. As it turns out surface charge is not a large of a variable as we expected.

[Mike Copioli]

And just to clarify one point:

Surface charge will NOT cause the Battery Beak to read a 'Bad' battery as 'Good'. I would stake my reputation, my company and my NON ANONYMOUS user name on it.

[Ether]

Do users need to be concerned at all about the battery temperature affecting the readings (e.g. cold trailer in the winter, hot trailer in the summer)?

[Mike Copioli]

Originally Posted by Ether

Is this true even if the battery has been charged at a rate higher than 6 amps, and is hot?

Yes, surface charge is weaker than deep charge. This behavior causes a small increase in internal resistance as measured by the Beak. This increase, if the battery's internal resistance is within 10% of the threshold between 'Good' and 'Fair' or 'Fair' and 'Bad', could only cause a battery's status to appear worse than it would be if the battery had been properly rested. This is one of the reasons the 'Fair' Status exists, otherwise it would just be 'Good' or 'Bad'. If a battery is that close to the threshold you should probably reserve it for practice only.

[sanddrag]

I know some other teams have used the CBA III from West Mountain radio as a battery analyzer, and I'd speculate there are others available. I like that the Battery Beak is all self contained and does not need a computer interface. Is there anything else that compares? I just want to look at all available options before I go buy one.

[Mike Copioli]

Originally Posted by sanddrag

I know some other teams have used the CBA III from West Mountain radio as a battery analyzer, and I'd speculate there are others available. I like that the Battery Beak is all self contained and does not need a computer interface.

The CBA series of testers measure battery capacity by applying a load until a specified cutoff voltage is reached and then calculating capacity in Amp Hours, the Beak measures battery internal resistance by applying two different loads and then calculating internal resistance. Both tests are of value and important to understanding the health of your battery. What the beak provides is a quick way of assessing the health of your battery between capacity tests at competitions without completely discharging your battery.

Originally Posted by sanddrag

Is there anything else that compares? I just want to look at all available options before I go buy one.

Internal resistance testers have been around for years, but most of them are very expensive. As far as I know the Beak is the only internal resistance tester that was specifically designed around the types of batteries used in FRC, VEX and FTC.