Re: 2013 EnerSys Genesis NP18-12B KOP Battery/FIRST Choice Weak?
 

I am assuming everyone has already checked this...but.

In my experience at least, poor performance of a new battery is generally caused by a poor connection with the battery terminals. If you haven't already, clean the terminals with an abrasive and re-seat all of your connections.

Re: 2013 EnerSys Genesis NP18-12B KOP Battery/FIRST Choice Weak?
 

Ether and Others,

Here is the data from the graph I posted earlier in this thread.

-Hugh

Re: 2013 EnerSys Genesis NP18-12B KOP Battery/FIRST Choice Weak?
 

Hugh,

Thanks for posting that data.

I played around with it and was able to fit a logarithmic model as Garrett suggested, with a little bit of coercing.

The blue is your data, the red is the model.

It still doesn't like that sharp bend in the curve, so it's not following the model exactly.

@Garrett: if you have suggestions for changing the model let me know and I'll try it to see if it gives a better fit.

Re: 2013 EnerSys Genesis NP18-12B KOP Battery/FIRST Choice Weak?
 

The AH rating of the batteries are listed at a 20 hour rate. The Spec for a 17HR battery is .85 amps for 20 hours and the 18HR is .9 amps. The higher the rate of draw the less you get out of them. I have been using this type of batteries Amateur radio for years. I have ones from 12HR to 55HR and they all are rated at using the 20 hour draw test. My 4 year old 55HR batteries tested at only 45HR this year. Time for 2 new ones.

Re: 2013 EnerSys Genesis NP18-12B KOP Battery/FIRST Choice Weak?
 

Had the kids leave the new battery on one of our 8 step chargers for the week. Retested it Saturday and it did fine.

Re: 2013 EnerSys Genesis NP18-12B KOP Battery/FIRST Choice Weak?
 

JDL,
Just to be sure, I would run it on last years robot for a while and see if charges and discharges normally.

Re: 2013 EnerSys Genesis NP18-12B KOP Battery/FIRST Choice Weak?
 

I have given it some thought, and I have a few reasons why it wouldn't match correctly, but I'm not sure how to model them. I'll stop by one of my professors (hopefully) by the end of this week and see if they have any input. My current thoughts are:

1. As current is flowing the concentration gradient will not be constant. The higher the current the more skewed the gradient will become.
2. The effective surface area may change. As the battery becomes more and more discharged, each terminal will have lead sulfate on it, which will not react and will hinder the reaction.
3. As the electrolyte becomes more dilute its resistance may change. The plates also will have a changing resistance, especially with sulfation.

If anyone has a battery beak from crosstheroads, or a similar device, could you post what it thinks the internal resistance is of a battery at multiple voltages? I know its alot to ask, but if you could give a sweep from like 13 to 11 at like half a volt steps that would be awesome.

I feel like something is going to have to change which has to do with the rate of reaction. Maybe the plates are not uniform after several cycles.

My team has a battery with a dead cell, I may open it up in a lab and see if I can test some things. I'd discharge the remaining 5 cells and at certain points stop the discharge and measure the resistance of the battery. I would also look into making some of the plates viewable, and either take video or pictures of it at different stages of discharge.

Re: 2013 EnerSys Genesis NP18-12B KOP Battery/FIRST Choice Weak?
 

Garret,
There are several views on the battery internals here and on other areas of the internet. I would not recommend opening the battery. Disposal and cleanup of the electrolyte and the exposure of lead in uncontrolled environments makes me cringe.

Re: 2013 EnerSys Genesis NP18-12B KOP Battery/FIRST Choice Weak?
 

Before this thread I was able to get West Mountain to donate an older CBAIII to our team since they are no longer selling them and only selling CBAIVs. We have been testing our batteries from last year and have already found some dead ones. I don't know if they will do this for more teams but they were very nice about it when I sent them an email.