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  #31   Spotlight this post!  
Unread 06-03-2014, 12:30
sanelss sanelss is offline
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by Ether View Post
How do you store your batteries during the off season?


we give them a charge and shelve them until needed again. though hey see periodic use throughout the year anyway
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Unread 06-03-2014, 12:33
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by sanelss View Post
we give them a charge and shelve them until needed again
How long do they typically sit on the shelf without any maintenance, and is the shelving area air conditioned?


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Unread 06-03-2014, 14:22
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by sanelss View Post
It's not that we set the charge rate to 15A, the charger states: "automatically selects charge rate from 0 to 15 AMPS to maximize battery life, charge speed and maintenance" it also makes no claims as to a rating of battery it can/can't charge. From other online documentation I found there is no danger at charging up to 1C other than shortening the battery life, which you may consider damage I suppose though. Honestly i'm no worried since we can work around it by bulk charging on 6A then cycling to these for top off
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.
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Unread 06-03-2014, 15:03
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by philso View Post
Automotive batteries rarely give an Ahr rating but they would typically be in the range of 35 to 85 Ahr
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.


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Unread 06-03-2014, 15:15
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Re: Be aware of battery and charger inconsistencies!

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I'll post on the QA and look for an official response but regardless I believe we can easily adhere to the rules to there shouldn't be any problems.
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.
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Unread 06-03-2014, 15:46
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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?
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Unread 06-03-2014, 15:53
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by GearsOfFury View Post
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?
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.
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Unread 06-03-2014, 16:02
sanelss sanelss is offline
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by Jaxom View Post
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.
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.
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Unread 06-03-2014, 16:06
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by sanelss View Post
...because the charge rate will never be higher than 6A
How do you know that? Have you tried this proposed process and measured the current?


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Unread 06-03-2014, 16:07
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by GearsOfFury View Post
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?
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.
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Unread 06-03-2014, 16:10
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by Ether View Post
How do you know that? Have you tried this proposed process and measured the current?


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.
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Unread 06-03-2014, 16:11
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by sanelss View Post
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.
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.
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Last edited by Chris_Ely : 06-03-2014 at 17:16. Reason: correctness
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Unread 06-03-2014, 16:11
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Re: Be aware of battery and charger inconsistencies!

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Originally Posted by GearsOfFury View Post
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?
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).

Quote:
Is there a process to follow with the "standard" chargers that should achieve the same result, but safely?
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.


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Unread 06-03-2014, 16:19
sanelss sanelss is offline
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Re: Be aware of battery and charger inconsistencies!

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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.
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.
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Unread 06-03-2014, 16:20
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Re: Be aware of battery and charger inconsistencies!

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


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