Re: First: 2008 Batteries are D-Y-I-N-G.
 

http://www.batteryuniversity.com/index.htm

very cool battery link.

Re: First: 2008 Batteries are D-Y-I-N-G.
 

I would like to know what people are using to test their batteries and what standard they are using. Thank you.

Seth

Re: First: 2008 Batteries are D-Y-I-N-G.
 

We had quite a few batteries die on us. We think it is because, during a demo, we drained them very low, like 5 volts on the OI low, causing the plates inside to corrode.

When "charged," the voltmeter says the battery's voltage is fine, but it cannot deliver enough current to run the robot. So as advice to all teams, NEVER discharge your battery to the point where, on the OI, it reads a very low voltage.

We wasted a few practice rounds at SVR last year because we were putting batteries that said 13+ volts on the voltmeter on them, but couldn't deliver current, so the robot couldn't move.

Re: First: 2008 Batteries are D-Y-I-N-G.
 

Seth,
We use the CBA II battery analyzer from West Mountain Radio. If you look earlier in this thread you will see actual curves from actual batteries.

Pikat,
I know that this will sound weird but teams who draw lot's of current during driving can easily draw the battery below 5 volts during those high current demands. The internal resistance of the battery is 11 mOhm so a 400 amp draw will drop the terminal voltage of a fresh battery by 4.4 volts. At the end of a match where the internal resistance rises, this resistance will cause a further voltage drop.

Everyone,
A voltmeter only tells you the "open circuit" voltage of the battery. A voltmeter does not draw current (not enough to change the reading) to cause a drop across the internal resistance of the battery and therefore is not a good indicator of battery health. A current tester will show what the battery is capable of delivering under a load. The CBA II will draw up to 7.5 amps and West Mountain makes a high current device as well. However, one must know what the data tells them. It is possible that the battery has reduced capacity in that it can only deliver current for a fraction of the time a good battery can, the battery cannot supply current at full voltage or a combination of the two. A battery that cannot supply current for a normal length of time has some internal condition that prevents correct operation. I know that this is a foreign concept, but the data sheet specifies these batteries to have a 400 charge/discharge cycle life. It is very easy for a team who only keeps a few batteries in their inventory to run 400 cycles in a season between practice,demos and events. Charge when the battery is hot, store at temperatures near or below freezing, or deplete a battery in just one two minute match will shorten that 400 cycle life by half or more.

Re: First: 2008 Batteries are D-Y-I-N-G.
 

Good point. I was referring to the fact that we were running our robots for hours at a time (not high load, just driving it around) without changing the battery. In other words, these lead-acid batteries don't like to be fully discharged.

Re: First: 2008 Batteries are D-Y-I-N-G.
 

We load our batteries at 20 amps, and measure the time that
it takes to drop to 11 volts. We don't go all the way to 10.5 volts
because deep discharge is not good for the battery. We load
using a constant current device, but you can do a reasonable
job with high power resistors from digikey. We qualify our
batteries every season, tracking their performance year to year.

You can make yourself a tester with high power resistors,
a fan to keep them cool, and a spike. It is not a constant
current load, but it is close enough. You can measure the
voltage using a voltage divider hooked to an analog input.
The old EDU RC is very good for this. It is a great project
for your robot team to do, producing a load tester that will
get used every year.

Eugene

Re: First: 2008 Batteries are D-Y-I-N-G.
 

I would like to disagree with the bold in this statement. It is taken a touch out of context, but I will explain why. In the world of engineering, we buy parts to meet a specification...

Semi-Tangent:I happen to work in the military engineering world where the standards are extremely high - could you imagine dropping a cellphone off a 3 story building and have it work when you pick it up? Our radios are required to do this. Could you imagine leaving your car stereo underwater for 3 days, expect to pull it out, let it dry for an hour and have it work? One of our radios DID that during Katrina & saved lives... Could you imagine exposing your robot to -30degreesF or +120degreesF and expect the electronics to still work? Our radios have to. They have to and we design them to meet that. We cant use parts in them that dont allow us to meet our -30degree requirement. We cant use a battery that will only last in our product for an hour, or our soldiers wouldnt be able to carry enough batteries to last a mission.

Yes, these are extreme examples, so whats my point? My point is that FIRST is FORCING us to use this vendor and this battery, they have lain the specifications for us. We dont really know why MK... did they get a better discount/donation or a sponsorship donation from MK? did the old battery vendor not want to donate anymore? did they think that these batteries were actually better? Who knows. But the reality is that these batteries ARENT as good as the old ones, and teams SHOULD be comparing them. If there is something better out there, that meets the specification of a FIRST event better, we should be allowed to use it. Teams are right to raise an eyebrow because they are spending a lot of money on batteries. Some try to keep up to 10 at a time alive, and thats a BIG expense. At bare minimum you need 4 if you are going to end up in the finals (unless you beg & borrow), and having to buy new ones put us all on edge. Now it appears that there is evidence that they arent as robust and dont hold up to the riggors of a FIRST team's usage as well as the old ones. So maybe we/they should revisit the options...

My point being that Cellphone & Radio designers alike, we all design/engineer FOR our users. We are using motocycle batteries... they are not designed to be taken in and out, dropped, handled incorrectly, charged and discharged over and over again... so if we are using something NOT for its intended use, we need to find the part that most closely matches our specifications and will last the longest so teams dont have to take on that expense over and over again.

Re: First: 2008 Batteries are D-Y-I-N-G.
 

so were all in the shop the other day with the batteries on the chargers i leaned back on the table and burned my arm (not really bad, but it left a mark) i quickly turned around to notice that one whole cell of the battery had bulged out and the battery had gotten up to 165 degrees and was leaking out the top


For all those who are thinking this the battery was fully dead when we put it on and hadn't been on the charger for 2 long before this happened

Re: First: 2008 Batteries are D-Y-I-N-G.
 

It sounds like the charger is messed up... I bet Thomas broke it. Tell him Ryan Nazaretian sent you.

Just remember to dispose of the battery properly, and also keep a close eye on that charger. Is it one of the new smart chargers, or one of the older chargers?

I'm not too fond of 'Smart' chargers after one almost burnt down my work shop. Mine had an automatic trickle charge cycle that was meant to keep on a battery. Unfortunately, it failed with a deep cycle marine battery and burnt through the large charging cable (designed to carry 70AMPS). I was very fortunate that it was lying on the concrete instead of on top of my workbench.

Re: First: 2008 Batteries are D-Y-I-N-G.
 

We have also had a problem with the newer batteries. I have been in FIRST since 2002 and have had TWO Exide batteries go bad,(not including the oldest ones which have been retired when they lost the ability to hold a good charge) and to date We have had FOUR MK Batteries go bad on us. Just the other day I had one start to heat up and leak out of the top while charging. We order 10 every year and over the years we have a large stock of Exide batteries that still work. I understand that FIRST is probably getting them discounted and all but if the batteries are not holding up as well as the old ones.... Maybe one solution would be to still supply and offer MK batteries, but lift the restriction of using other batteries so those of us that want to pay a little more for batteries that last longer can do so. I do not think that the MK batteries are a bad product, but I do think we are using these batteries in a way they are not designed to hold up to as well as the batteries of the past have proven to.

Re: First: 2008 Batteries are D-Y-I-N-G.
 

My team has never really had many batteries to our name, but from my experience, the exides DID hold up better.

Re: First: 2008 Batteries are D-Y-I-N-G.
 

Reading through all these posts, Al and Don make some excellent points here. I want to add a little information for those that don’t go to the battery university website or want to spend hours researching battery characteristics.

If you discharge a lead acid battery too far, you hurt the battery and its amp hour capacity will be reduced.

Typical discharge to levels for batteries, or don’t go below this charge level.
Automotive batteries 80%
Marine batteries 50%
Deep cycle batteries 20%

Automotive batteries should not be discharged below an 80% charge level or you’ll hurt the battery. There is only 20% of the charge that is usable but the automotive battery will deliver more amps for the same physical size when compared to Marine or Deep cycle battery. In an automotive application the battery is discharge a small amount very shortly starting the engine and then is recharged by the alternator.

The FIRST battery seems to fall into the Marine category as the cycle life is greatly reduce if the charge drops below 50%.The information below is from the MK Battery website.
Life expectancy:
Cycle Use: 100% depth of discharge 250 cycles
80% depth of discharge 350 cycles
50% depth of discharge 550 cycles

What this means is that if you continually run your batteries down to low charge levels, you WILL significantly reduce the capacity of the battery.

On a side note, I don't like the battery charger FIRST supplies but they are better than the older non-smart chargers. I've seen these not sense properly and over charge batteries. This was probably due to a defective battery. I prefer the Black and Decker (used to be Vector) Smart Chargers. They use a three stage charging technology that helps extend battery life. I've given away or thrown away all my old battery charges for these new chargers, they are that much better.

FYI Some AGM batteries have platinum on the glass mat. This helps as a catalyst to recombine the oxygen and hydrogen bubbles if the battery is over charged or charged at too high of a current.