Re: Be aware of battery and charger inconsistencies!
 

we give them a charge and shelve them until needed again. though hey see periodic use throughout the year anyway

Re: Be aware of battery and charger inconsistencies!
 

How long do they typically sit on the shelf without any maintenance, and is the shelving area air conditioned?

Re: Be aware of battery and charger inconsistencies!
 

As others have already stated, the charger you are using is designed for automotive batteries where the value for C, in Amps, is much greater than the C value for the 18 Ahr batteries used in FRC. Automotive batteries rarely give an Ahr rating but they would typically be in the range of 35 to 85 Ahr. The claim about automatic charge rate selection is relevant ONLY when the charger is connected to an automotive battery. Using an automotive charger in the "automatic mode" would almost guarantee that you are charging your FRC batteries at currents well above the manufacturers recommendations for part of the time. This excessively high charging current leads to premature failure of the battery. The failure modes can consist of reduced battery capacity, shortened life and rupture of the case (possibly explosively) due to boiling of the electrolyte.

The automotive chargers use charge currents that are appropriate for automotive batteries and they change charge currents and transfer to trickle charge mode based on the battery voltage. Since the voltage at full charge is related the same for all the 12 V (nominal) batteries, irrespective of their Ahr rating, the automotive chargers are able to properly charge all automotive batteries no matter what their actual Ahr rating is.

Each week, where I work, we literally use tons of batteries just like the ones used in FRC (different Ahr rating) to build large Interruptible Power Supplies for industrial applications and data centers. These are sourced from one of the FRC legal suppliers. We CALCULATE our charging current based on the size and number of batteries in a battery bank and recommendations from the battery manufacturer. Neither we, nor any competitor that I know of, has the technology that would allow a charger to distinguish between batteries of different sizes and what charge rates are appropriate for that battery.

Re: Be aware of battery and charger inconsistencies!
 

I believe the RCM (reserve capacity in minutes) rating of automotive batteries follows an industry standard of 25 amps load until voltage drops to 10.5V.

If so, you could multiply the RCM by (25/60) to get an Ahr rating (at 25 amps down to 10.5V).

For many automotive batteries, the RCM rating is available.

Re: Be aware of battery and charger inconsistencies!
 

I'm still not sure how using a >6A charger after you've used some other charger adheres to the rules. But by all means, you should put in a Question on the Q&A to see what the answer is; that's absolutely the right approach. Good luck; I'm pretty sure I know who's going to process that question, and he's the one that tells the LRIs & his inspectors when he's the LRI to tell teams to remove chargers >6A.

So to answer this another way, and avoid illegal chargers: what is it about this charger that is apparently improving the OP's robot performance? Is there a process to follow with the "standard" chargers that should achieve the same result, but safely?

Re: Be aware of battery and charger inconsistencies!
 

There's no apparent competitive advantage. The issue is that charging over 6 amps is unsafe per manufacturer direction and can decrease the life of batteries.

Re: Be aware of battery and charger inconsistencies!
 

because the rules state nothing about chargers, the only rule that mentions anything about charging is the one that states they shouldn't be charged at a higher rating than manufacturer recommends, which is 6A. Using a 6A charger to do bulk charge, then the 15A charger for top off will be within the rules because the charge rate will never be higher than 6A. these new chargers will only top them off which will only draw a few amps at max, so we will be explicitly within what the rule states.

Re: Be aware of battery and charger inconsistencies!
 

How do you know that? Have you tried this proposed process and measured the current?

Re: Be aware of battery and charger inconsistencies!
 

the main issue we suffer from is inconsistencies, not necessarily any kind of improved performance over other good chargers. All of our previous chargers get different performance because they all charge the batteries to a different level. The max charge current is actually irrelevant to us, what matters is the state the batteries are in when they get taken off the chargers. These Stanly provide a consistent charge every time and every charger is the same. That is the key element we need, a consistent charge level that actually fully charges the batteries. We do not get that out of the 6 old ones we had(which there are three different types) but we do with these new ones.

Re: Be aware of battery and charger inconsistencies!
 

Because the old chargers can't put out more than 6 so they will charge them as much as they can until hey reach a fully charged status(which isn't really fully charged it seems like). At that point we will move over to the stanly, there is actually a current readout of the charge rate so yes we did measure it and once it reaches a certain point it goes into float charge which documentation states is not more than a few amps. So we can indeed for a fact know and guarantee that we will always be within this rule. This is what we were going to do from the start anyway. Just because we have 15A chargers doesn't mean they will ever be charging at that unless we put a dead battery on which there is no need to.

Re: Be aware of battery and charger inconsistencies!
 

How do you know that the charging rate will not be above 6A?

Also, 6A is pushing it for these batteries. You should charge your batteries at the lowest charging rate you can get away with to maximize the lifespan of the batteries. The only thing charging at a higher rate gives you is less time to charge.

Re: Be aware of battery and charger inconsistencies!
 

My tentative working hypothesis, based on the presently insufficient information available, is that the Stanley BC1509 is overcharging the FRC battery (for which it was not designed).

Some "smart" battery chargers are not smart enough. If you interrupt them in the middle of a charge cycle and then try to continue, they may mis-read the state of the battery and fail to complete the charge cycle. I know my Schumacher SC-1200A sometimes does this.

Re: Be aware of battery and charger inconsistencies!
 

we are aware it will decrease the battery life but we don't care. From the information I found online here "http://www.powerstream.com/SLA-fast-charge.htm" there is absolutely no danger what so ever in using this charger with these batteries. Possibly through missuse or abuse but under normal conditions nothing dangerous should happen.

Re: Be aware of battery and charger inconsistencies!
 

Note:

The Ahr rating will increase if measured with a lower current.

So be careful when comparing FRC Ahr to automotive Ahr computed from RCM*(25/60).

I eyeballed some data from the discharge curves in NP-18-12 datasheet and plotted the actual Ahr of that FRC-legal battery vs discharge current.

At the RCM 25 amp rate, the FRC battery appears to be less than 7Ahr, which would correspond to an RCM of about 17 minutes.