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Old 2018.11.26, 08:21 PM   #1
RFick73
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Question Proper care & maintenance of your NiMH AAA's

So, this past weekend I was a little let down by the performance of some of my batteries. I bought the batteries about 1 1/2 years ago & use them typically once to twice a month or so year round. I'd say they have somewhere in the ballpark of ~50 cycles on them & that # is probably a bit high.

I currently charge my batteries in a SkyRC NC2500. The last few times I have purchased 5 sets of batteries, I have run them through the "Break-In" process labelled the batteries with their finished mAh & voltage levels. I then use that information to typically match them by mAh or by the voltage. What's the better way? I guess it depends on what I want. I used to be ALL about run time, but the brushless have an insane run time as it is, so I've been gravitating towards end voltage matching. I usually mark the groups with a letter or number & keep them together. Does any of this really matter?

It was mentioned that my care & maintenance may be the culprit, so, I wanna make sure what I have been doing is correct or change my bad habits.

Now, I swear I've read charging batteries at a lower amp rate is the way to go but is that the case? Maybe that's just for longevity sake? Do higher amp charging rates help with higher discharging rates. I really don't mind getting less cycles out of them if I get better performance, I know there has to be a tradeoff. I typically run my batteries & then store them for about a month or so until the next usage, at that point, because I'm in no hurry to use them, I charge them at .5amps. But seeing I only have 5 good sets & we run for like 8 hours, I typically run them, charge them & potentially use them again later that day.

I was asked how often I discharge my cells. Well, I don't.. Other than when I run them in my car. I knew it was a thing, but I've just never done it outside of my typical running the batteries through a 'Break-In" process every 6 months or so. The charger has a refresh setting, but I figured because I have the time, I would just use the Break-in process.

I typically bring 10 sets of batteries with me to the track. They are all the same but 5 sets are 3 years old, the others are all 1.5 years old. The set of 3 year old ones I really only keep in case others need a set to use or I really run low. I bring 2-3 chargers with me to the track so I can charge what I need how I need to. I try to go through the 5 newer sets & once I get to about the third set toss my original ones back in. I've often let them go at .5 amps or bumped them up to 1 or even 1.2amps if I knew I'd wanna use them sooner. What should I be doing, should I be discharging them first in the charger then charging up at 1-1.2amps? If I'm not using them should I discharge them, let them sit then charge them the day or two before using them? Should I be running them through the "Break-in" every 4-6 months or using the "Refresh" option more often?

What have others found worked for them? Help!
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Old 2018.11.26, 09:37 PM   #2
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Start by doing a full charge, discharge, charge cycle. Then you can start to analyze data.

Does the charger have and adjustable cutoff voltage for discharge? If so, raise it to 1.1v or so, and discharge the cells. It doesn't matter if the cells have loads of capacity at lower voltage, because that will hurt performance to run with the lower voltage.

After the cells finish the discharge, look at the capacity at that voltage, and remove the lowest ones. Then raise the cutoff to 1.2v, and run the discharge again. Remove the highest results and keep them for race packs, the others group for practice packs. This will ensure that you have cells that will maintain the highest voltages for the longest amount of time.
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Old 2018.11.26, 10:00 PM   #3
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Quote:
Originally Posted by EMU View Post
Start by doing a full charge, discharge, charge cycle. Then you can start to analyze data.
What Amperage rating should I charge them at, 1C? They are 900mAh, so .9? What about discharge? I believe the highest the charger can discharge them is at 1amp

Quote:
Originally Posted by EMU View Post
Does the charger have and adjustable cutoff voltage for discharge?
Yes it does, it looks to be set @ .9 currently. What should it be typically set to, after I run the 1.1v & 1.2v test? I like using this method, TY for the idea.
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Old 2018.12.09, 12:41 PM   #4
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Sorry for a late response, I missed the notification of your reply.

750mah cells i charge at 500mA, 800-900mah cells i charge at 700mA.

Discharge should be at the maximum rate that you can discharge at, with a higher cutoff of 1.1v or even 1.2v. I find after a quality run, my cells are usually around 1.15v to 1.2v, so this data is much more useful than capacity of the entire discharge curve.

I don't see an advantage to charging aggressive besides the first minute or two being fast and then a larger drop off in power through the run. A lower charge rate will give a little less initial punch right off the charger, but the cells discharge will remain flatter than an aggressive charge. This will give you a car that feels similar in thr first minute as it does in the last minute of a race.

I don't think that nimh cells really need regular discharge/cycles if you use them consistently. If anything, constant full cycling wears them out a little faster. I only discharge my cells to extract data on their health and to group them into packs. I find that using a higher cut off as explained earlier gives you the more useful data, since capacity at a lower voltage does not help racing.
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Last edited by EMU; 2018.12.09 at 12:44 PM.
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