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View Full Version : Another Post on Batteries: Clearing up some confusion???


Spoon
2007.01.01, 05:32 PM
I have been doing a little bit of battery research and I was going to post my findings on my blog but I want to get a little bit of feedback before I do so. A lot of the information comes from two articles online and applies mostly to Sub-C packs but I tried to filter down to the information that would be relevent to us in the smaller world of AAA's. Read on and if you can provide any insight, please do. The reference articles are linked at the bottom of this post.

The first reference is an article written by Steve Pond (Radio Control Car Action) and Jim Dieter (Team Trinity). It looks like it was written around the time 3000mAh Sub-C cells became available. I think the SubC cells are up to 4000+ but some of the info is still relevant. I'll try to distill some of it here.

Charge Rate:
Jim Deiter (JD) recommends a charging rate between 3 to 5 amps. That's about 1 to 1.5 times the capacity of the battery. For our smaller capacity (700-900 mAh) cells, this would translate to roughly 700 to 1400 mA charging rate.

Here are a few tidbits from the article that I found interesting...

* Trickle charge should be avoided when charging NiMH packs, it tends to have a flattening effect.
* Packs should be "re-peaked"right before a race.
* Linear charging should be used for NiMH

A whole bunch of tidbits regarding discharging/storage

* If a pack will be used within a week, discharge to 0.9 volts
* Rate of discharge does not seem to impact performance
* If batteries are to be stored for more than 2 weeks they should have at least a 50% charge

From reading the discharging information I can only assume that the Team Trinity guys store their batteries discharged. I don't really understand why they wouldn't store them charged. My best guess it that they would want them discharged and peaked right before a race so storing them discharged saves the batteries one full cycle.

The second reference is from the Team Novak site. There's a lot of information on what to do and not to do when charging and discharging your cells. Conveniently, they provide links to a Novak product that will do just the right thing for your cells!

The Team Novak article reinforces the idea that trickle charging NiMH is bad for them; something that I didn't know. There is also a small amount of information on discharging and storing. Basically packs used weekly can be discharged to 0.9 V per cell and stored that way and packs stored for more than two weeks should have a couple of minutes of charge put into them before they are put away. One more subtle bit of info that we glean from the Novak article is that the "stored" batteries should be discharged to 0.9 V, allowed to cool and then charged right before the race. The discharging before the charging will give the best performance.

Both Novak and JD (of Team Trinity) agree that packs can be run more than once a day. Novak recommends no more than 2 cycles per day.

One last bit of information is from an informal chat with Bullithatch. One of his sources claims that the way to get the best performance out of our little cells is to dicharge them completely, let them sit for 10 minutes, then charge them up. I imagine if they are not stored for too long in the fully discharged state, that doesn't contradict anything that I have summarized so far.

References:
http://www.teamnovak.com/products/batteries/battery_care.html
http://www.rccaraction.com/articles/NiMHbatcare1.asp

Spoon
2007.01.02, 10:51 AM
Hmmm... lots of views but no replies. I guess I'll ask some specific questions, or at least highlight the stuff I found interesting.


First, trickle charging. It seems that trickle charging is bad for NiMH (at least for our applications) has anyone else found this to be true either through research or actual (informal or formal) testing?

Second, battery storage. If the batteries are used regularly, these guys recommend storing them partially discharged (0.9 volts) then charging them up just before you need them. Does anyone else do this? I have been storing my batteries charged and sometimes use them a week after I fully charged them.

Last one. Cycles per day. Apparently the first charge of the day will produce a somewhat "flat" response, so 2-3 cycles in one day of racing is not a particularly bad thing.


If you guys and gals think any of this info isn't relevant to AAA's and Mini-Z's in your experience, I would like to hear that too.

onrailz
2007.01.02, 12:05 PM
Hmmm... lots of views but no replies. I guess I'll ask some specific questions, or at least highlight the stuff I found interesting.


First, trickle charging. It seems that trickle charging is bad for NiMH (at least for our applications) has anyone else found this to be true either through research or actual (informal or formal) testing?

Yeah, My understanding is that trickle charging isn't necessarily BAD for NIMH's it's just that these cells act like they've been charged- ie, you charge them hard and fast, thats how they'll put out. Slow and low, thats also what they'll do which isn't ideal for racing. Also, you are quoting these guys off a site that the public can see. They are being quite reserved about what they say on there. You go to a big race and peek at their chargers and you'll see that nobody is charging @ 3-5A... more like 6,7, and 8A depending on motor type.

Second, battery storage. If the batteries are used regularly, these guys recommend storing them partially discharged (0.9 volts) then charging them up just before you need them. Does anyone else do this? I have been storing my batteries charged and sometimes use them a week after I fully charged them.

Again, a very reserved answer from these team guys... more like discharge it, then solder the positive to negative and forget about it. Thats big in stock class racing anyway. Lots of punch but a little sacrifice in run time.

Last one. Cycles per day. Apparently the first charge of the day will produce a somewhat "flat" response, so 2-3 cycles in one day of racing is not a particularly bad thing.


Yeah, they seem to feel better and better throughout the day for me...

If you guys and gals think any of this info isn't relevant to AAA's and Mini-Z's in your experience, I would like to hear that too.

It's very relevant, Spoon. I've used all these tips and tricks for years in 1/10 racing and all of them seem to have the same great results with the AAA's. Thanks for posting!

EMU
2007.01.02, 01:48 PM
I allways try to avoid trickle charging. The Energizer 15 Minute charger automatically goes to a trickle when the cells are peaked (a function that I hate). As far as I know, the Duracell 30 minute chargers do not trickle when they finish a charge (light goes out, but I havent seen any documentation that states whether it trickles or not).

Most of the time after I race, I will leave my batteries half charged... in the condition that they were in after the last race. Before the next race night I will discharge my cells. Sometimes I do it the night before, sometimes I do it while I am at the track. I charge with one of my Duracell 30 minute chargers until they are charged and let them sit. Before my heat/race I will repeak the set in my Energizer 15 minute charger, and monitor them to make sure I pull them as soon as they are done. Usually only takes a couple minutes...

I do not discharge my cells after each run, I only discharge them before the initial run. I use one group of cells for my practice, and one group for my races (about 4 sets in each group). I dont match my cells, but I keep my race cells in numbered sets... practice cells are loose and un numbered (used to keep them numbered, but since they are retired race cells, there are many that are no longer usable).

I have noticed that cells that have been trickling are slower/flatter than cells fresh of the charger without a trickle.

The Energizer 15m charger is harsh on the cells, and I only use it for races. The difference in punch is minimal compared to the long term damage that occurs with the cells.

Another thing to not is the temperature of the cells when charging. They should get warm, borderline hot. If they dont, then they will be a flat when running. Batteries perform best when they are warm/hot and the internal resistance drops, of course with an increase of temperature you have a decrease of lifespan. So you have to choose what you are going to use the cells for, and charge/discharge appropriately.

For transmitter batteries, you dont need them to have punch, you need them to last a long time... so a slow charger is best suited, and you want to keep them fairly cool. Race cells you would want to charge fast, and heat up the cells a bit. You would want to run the race cells almost right off the charger, while they are still warm for the best punch.

I look at batteries as a short term investment. Charge them fast, get the most speed out of them, when they stop performing well, get new ones.

bnwhtlw
2007.01.02, 02:34 PM
My duracell 15 minute charger has a built in fan and when its done, its done, it does not trickle. It cuts off 100%. I have a lacrosse charger coming this week so I can take better care of my bats.

Good thread though!

pinoyboy
2007.01.02, 09:12 PM
I've got some Atomic 750s and I want to get the best performance out of them. So far, I've charged them with an 8 hour charger, but i'm guessing that is bad since that is considered a trickle charger correct? My only other battery chargers are an Energizer 15 min and a Radio shack Xmod charger.

Which charger do you guys reccomend me to use to get as much punch out of them for a 5 minute race?

lfisminiz
2007.01.02, 10:03 PM
Like EMU said, the duracell 30 min charger seems like a good all around, not real technical charger, without getting in to all types of extra stuff.

lfisminiz
2007.01.02, 10:04 PM
GOOD questions. i would like to know this myself.

pinoyboy
2007.01.02, 10:08 PM
Geez, so another charger? The thing about the Duracell charger is that i've found it at Best buy for $40. I have a gift card for that much, but I heard the La Crosse Battery charger is pretty good, and it costs about the same.

But what I'd really like to know is will going to a better charger give me better performance in running 5 minute mains, or would people who run longer races benefit more?

bnwhtlw
2007.01.02, 10:23 PM
I dont know why I said I have a duracell, I have a dynex...not a huge difference, but there is some I suppose.

EMU
2007.01.03, 12:12 AM
I've got some Atomic 750s and I want to get the best performance out of them. So far, I've charged them with an 8 hour charger, but i'm guessing that is bad since that is considered a trickle charger correct? My only other battery chargers are an Energizer 15 min and a Radio shack Xmod charger.

Which charger do you guys reccomend me to use to get as much punch out of them for a 5 minute race?
I would use the Xmod charger and charge your cells up with that for the first charge (Can be done the night before). Right before the race use the Energizer 15 min to repeak the cells before practice. After you run it, take the batteries out and wait till about 15 minutes before your race and put them back in the Energizer to peak for the next race.

If you are charging up from a full discharge, you would want to run it at a little lower amperage to have the batteries last a little longer. From what I remember the RS Xmod charger charged in around an hour or so...

Charging on a slow charger will give you longer runtime and lifetime of the cell, but you wont have as much speed. Fast charging will give you faster speed for a shorter period of time. And will kill the cells much faster.

imxlr8ed
2007.01.03, 01:59 AM
Just want to remind all who use the Lacrosse... try to use a fan on it at all times. I have a computer fan usually hooked up to a controller pack. (done with a 9 volt connector from the local R. Shack.) I forgot my fan for my last event and I went ahead and charged a set anyways... about 20 minutes later, I thought it was strange that those cells weren't done yet... went over and found the screen all wacky and a ton of heat coming off the thing, I quickly unplugged it, whacked it on the back to get the cells out... the thing got so hot, the plastic was all mushy ! The cells actually melted into the extra tile of RCP I had laying there !

After shedding some tears over my dumb decision, I got home... hooked the thing up the usual way (with a fan), and it worked fine. I'm cycling some cells on it now.

Even with this issue, I still think it's a great charger. Affordable and the refresh cycle is perfect for starting cells out. (and the cells you sometimes get with it are really good batts.) Just remember...

USE A FAN WITH IT !

The only downfall is linear charging... obviously can't do it with a charger like this. I know linear charging will keep cells matched longer, less chance of one going astray. We've done alot of experimentations... with all kinds of cell brands. I'm curious though... who's using what ? I have actually found Rayovac 750s to be quite punchy and durable. (even that set I baked still works, but probably not too much longer) Intellects seemed to die out too quickly. I saw all kinds of cells up at the World Cup... didn't really notice anyone with a battery that gave them an upperhand though.

Oh... and yes, all my cells get more voltage into them as the day goes on... from my AAAs up to my 10th scale cells. (no more than 3 runs a day though... they don't get as much in them after the 3rd run !)

EMU
2007.01.03, 02:14 AM
For practice and some racing I use Intellect 750, races I use the 900mah cells from @tomicmods, AWD I use Duracell 1000. I have a few sets of Sanyo 800s that I am waiting to open when my @tomicmods cells start going... I really dont notice any difference in punch between these cells. I used to run Atomic 800, Maha 800, PN 900, but they all had less punch than the Intellects.

briankstan
2007.01.04, 02:04 PM
This is a post that Shuter wanted to post and quote. I'm just helping him out.


The issues of battery discharging/charging have been talked about in various threads with conflicting information for some time. It reminds me of when I was into CB radios a few years back. I discovered that if I asked the same performance questions concerning antennas and radios at 10 different custom CB shops I would get 10 different answers. CB seemed to stand for “Constant Bull$hit” rather than Citizens Band. The issues of charging, discharging and storage of our batteries is not much different. There is constant conflicting information. Builthatch recently jarred me out of complacency with his unhappy report on his defective PN discharger. Since I had been using a PN discharger for months on EMUs recommendation (a highly valued source of information) I became concerned. I bought a multi meter and learned how to use it so I could test my batteries, charger and discharger thinking that would settle the issues for me. Boy was I wrong. It instead launched me into a journey searching for the holy grail of battery usage as it applies to Mini-Zs. I talked with and read information from electronic design and repair technicians, battery manufacturers, battery distributors, college professors and battery testing equipment manufacturers. In the end the best information came from the design/manufacturers of battery testing equipment and Academia. The best source of accessible written information in plain English I found comes from the Isadore Buckmann book “ Batteries In a Portable World” A condensed version can be read free on the web at Battery University.com and is a wealth of information.

The information I gathered was sometimes technical and crossed boundaries of charging/discharging/storage. It applies to the care and feeding of rechargeable Nickel Metal Hydride (Nmih) batteries only. Our Mini-Z fuel. I will try and sum up the information and provide conclusions rather than complete explanations. Even so, this will be a lengthy thread.

Definitions – “C’ is used to express a batteries capacity and comes into play in discharging and charging of our batteries. A 1000 mAh battery when discharged at a rate of 1 C (1000 mA) will provide 1000 mA of energy for one hour. A discharge rate of 2 C (2000 mA) will deplete this battery in ˝ hour. A discharge rate of .2 C (200 mA) will deplete the battery in 5 hours.

A 700 mAh battery when discharged at a rate of 1 C (700 mA) will provide 700 mA of energy for one hour. A discharge rate of 2 C (1400 mA) will deplete this battery in ˝ hour. A discharge rate of .2 C (140 mA) will deplete the battery in 5 hours.

The reverse is true for charging. A 1000 mAh battery will receive a full charge in 1 hour at a 1 C charge rate of 1000mA. A 700 mAh battery charged at a 1 C charge rate of 700mA will become charged in one hour.

THE SHORT ANSWERS

Charging our batteries – Our Nimh batteries should be rapid charged at a C rate of 1- 2. For a 1000 mAh battery that is a minimum charge rate of 1000 mA (1 Amp) for one hour. Maximum recommended charge rate is 2000 mA (2 Amps) for ˝ hour.

For a 700 mah battery that means a minimum charge rate of 700 ma (.7 amps) for one hour with a maximum charge rate of 1400 ma (1.4 amps) for ˝ hour.

Discharging our batteries – While it appears that discharge rates are not as critical to battery health as charge rates, a discharge rate of .5 C (2 hours) to 2 C (˝ hour) is recommended. A discharge rate of .5 C may yield a slightly higher battery capacity than a discharge rate of 2 C but it is probably negligible for our purposes. My PN discharger discharges at a rate of between 1 and 2 C or and discharges each cell within a few hundredths of a volt to each other. It also cuts off at the proper point.

Battery storage – The recommended state to store our Nimh batteries is at 40% of capacity. Not Fully Charged. If we use a set of batteries for practice or to run a race we should not charge them for storage. Leave them as they are and charge them just before their next use. Storing your batteries in a cool or cold environment is best for them. You can even store them in your refrigerator for long periods. Put them in a zip lock bag to reduce condensation.

NiCad’s are just the opposite. Store them Fully Charged.


These are the short answers to charging, discharging and battery storage. I believe they are correct as far as they go. I hope they prove helpful. I am not sure of the rules on length of threads so I will start new threads for the longer explanation and discussion of discharging/dischargers and what I expect may be a fairly contentious thread on charging/chargers. There is a lot of information to be discussed for those of us that want to further explore.

Spoon
2007.01.04, 02:18 PM
Brian, Thanks for posting that information from Shuter.

Actually, thanks to everyone that has contributed. We are getting some really good information from both academic and practical use sources. The best thing is that each post seems to reinforce a little bit of the previous information. Correct me if I am wrong but I am not really seeing any conflicting information so far.

shuter
2007.01.05, 10:40 PM
Hmmm... lots of views but no replies. I guess I'll ask some specific questions, or at least highlight the stuff I found interesting.


First, trickle charging. It seems that trickle charging is bad for NiMH (at least for our applications) has anyone else found this to be true either through research or actual (informal or formal) testing?

Second, battery storage. If the batteries are used regularly, these guys recommend storing them partially discharged (0.9 volts) then charging them up just before you need them. Does anyone else do this? I have been storing my batteries charged and sometimes use them a week after I fully charged them.

Last one. Cycles per day. Apparently the first charge of the day will produce a somewhat "flat" response, so 2-3 cycles in one day of racing is not a particularly bad thing.


If you guys and gals think any of this info isn't relevant to AAA's and Mini-Z's in your experience, I would like to hear that too.

Trickle Charging

Trickle charging with a C rate of .1 to .3 (most inexpensive battery chargers fall into this catagory) should be avoided to charge a depleted NiMH battery for a number of reasons. The low rate of charge does not produce enough voltage or heat variation for the battery charger to reliably recognize and it may continue to apply the charge. Overcharge can result. Overcharge when trickle charging can occur even if the battery is cool or only slightly warm to the touch. If you are using an inexpensive charger that fully charges your batteries and then goes to trickle mode it is recommended that the batteries be removed rather than allow them to remain in the charger overnight. NiMH batteries do not tolerate overcharging well and the continued trickle charge will actually cause crystalline formation inside our batteries. (rock) The crystal formation displaces a functioning portion of the battery reducing cpacity. :(

As with most things there is an exception.... New unused batteries. They may well have been produced months before you open the package. Having been sitting around for months they may have developed dry spots where the electrolytes have drained to the bottom. (Gravity) The most effective method to rejuvinate them and maximise their potential is to trickle charge them. First fully discharge the batteries then trickle charge them for 24 hours at a .05 C rate. They should then be fully discharged and recharged at a rate of .5C to 1C a few times. This should make your batteries very happy and maximize their capacity. :D

We all know that none of this has to be done. Most of us have probably just charged our new batteries and gone racing. The purpose of my gathering, distilling and posting this information is an attempt to dispel some of the battery myth floating around so those that are interested in getting that last little bit from their batteries can do so.

Cycles per day - There is no limit to the number of times per day our NiMH batteries can be cycled as long as proper battery protocol is observed. Charge at a rate of .5C to 1C. Allow batteries to rest/stabilize a few minutes after discharging and after charging.

Deep discharging - NiMH batteries have very little cyclic "memory". Current NiMH battery construction has practically eliminated "cyclic memory" thereby reducing the need to deep discharge on a frequent basis. In addition, our NiMH batteries do not recognize or count a usage or depletion of less than 70% as a cycle. If our batteries are getting regular use (at least once every two weeks) there is no need or advantage to deep discharge more frequently than once every three months. Deep discharging, while necessary to form/condition new batteries and batteries that have been sitting for a few weeks, is hard on the battery and reduces battery life a little each time.

lfisminiz
2007.01.05, 10:50 PM
Im glad to read information on batteries. Its nice to get a better idea of the do's and dont's of charging and discharging. :)

shuter
2007.01.08, 03:21 PM
Spoon - I also had been charging my batteries before storing them. WRONG! They should be stored in a partially discharged state of 40% of capacity. This is not a critical number so storage after using them to race is about as good as we can do. A battery analizer is needed to establish the exact capacity anyway so unless you have one, there is no way to tell exactly what % of battery capacity is left after racing. Charge them just before racing to assure your batteries are charged to maximum capacity

Battery self discharge - Our AAA NiMH batteries will self discharge as much as 15% of capacity in the first 24 hours after charging! Additional self discharge will occur at a rate of 10%-15% per month thereafter. These self discharge rates will be accelerated if the batteries are stored in a hot enviroment. Like leaving them in a hot car. The self discharge rate will increase with battery age. Factors that accelerate self discharge of our batteries are damaged seperators. (induced by excess crystalline formation, allowing the batteries to cook while charging, and high discharge cycle count which promotes swelling of the cell.) Once a battery exibits a high self discharge rate it can not be repaired, even with a smart charger/analizer.

Discharging a AAA NiMH battery to 1 Volt leaves only a small portion of battery capacity in the battery. Possibly as little as 1%. Discharging beyond that to .9 Volts is risky and should be avoided, especially at high discharge rates. The risk of cell reversal is substantially increased if the batteries are being discharged is series since the average discharge state may be significantly higher than the weakest battery. The weak battery can be damaged.

shuter
2007.02.21, 02:48 AM
Trickle Charging

Trickle charging with a C rate of .1 to .3 (most inexpensive battery chargers fall into this catagory) should be avoided to charge a depleted NiMH battery for a number of reasons. The low rate of charge does not produce enough voltage or heat variation for the battery charger to reliably recognize and it may continue to apply the charge. Overcharge can result. Overcharge when trickle charging can occur even if the battery is cool or only slightly warm to the touch. If you are using an inexpensive charger that fully charges your batteries and then goes to trickle mode it is recommended that the batteries be removed rather than allow them to remain in the charger overnight. NiMH batteries do not tolerate overcharging well and the continued trickle charge will actually cause crystalline formation inside our batteries. (rock) The crystal formation displaces a functioning portion of the battery reducing cpacity. :(

As with most things there is an exception.... New unused batteries. They may well have been produced months before you open the package. Having been sitting around for months they may have developed dry spots where the electrolytes have drained to the bottom. (Gravity) The most effective method to rejuvinate them and maximise their potential is to trickle charge them. First fully discharge the batteries then trickle charge them for 24 hours at a .05 C rate. They should then be fully discharged and recharged at a rate of .5C to 1C a few times. This should make your batteries very happy and maximize their capacity. :D

We all know that none of this has to be done. Most of us have probably just charged our new batteries and gone racing. The purpose of my gathering, distilling and posting this information is an attempt to dispel some of the battery myth floating around so those that are interested in getting that last little bit from their batteries can do so.

Cycles per day - There is no limit to the number of times per day our NiMH batteries can be cycled as long as proper battery protocol is observed. Charge at a rate of .5C to 1C. Allow batteries to rest/stabilize a few minutes after discharging and after charging.

Deep discharging - NiMH batteries have very little cyclic "memory". Current NiMH battery construction has practically eliminated "cyclic memory" thereby reducing the need to deep discharge on a frequent basis. In addition, our NiMH batteries do not recognize or count a usage or depletion of less than 70% as a cycle. If our batteries are getting regular use (at least once every two weeks) there is no need or advantage to deep discharge more frequently than once every three months. Deep discharging, while necessary to form/condition new batteries and batteries that have been sitting for a few weeks, is hard on the battery and reduces battery life a little each time.

Spoon - I added information on discharging and cycles per day you had asked about using the edit feature. The info came from George Mathew the Applications Engineering Manager at Cadex Electronics.

Flashsp-2
2007.03.02, 12:12 AM
After reading through this (and Battery U, and the other battery threads), I am curious if the antiquated NiCD cells would actually work better for qualifying runs. I realize that they have a lower energy density (i.e. lower capacity), but according to Batt U they have a significantly lower internal resistance. This would leave me to believe that these would be very good for running low lap qualifying, where you would only need the speed for less than a couple minutes. Maybe I am wrong, I don't know, I haven't had any experience with NiCD since 1700's were the big thing in 1/10th scale...

Sinister_Y
2007.03.02, 01:40 AM
I agree was talking to one of my friends, a big tech guy and he said to do just that. Run Ni-Cd. They have alot less internal resistance. Try and find a AAA though with a good capacity is very difficult.

He so far as to say to tape the cells so no one could see what cell it was...he made my laugh. Try it and let us know. It probably would only work for stock heats and then only maybe a 5 min run max.. if that.

Flashsp-2
2007.03.02, 05:28 AM
Yeah, the highest mAh NiCD I saw so far was 400. Definitely not good for anything other than qualifying, but if they do perform better in the first few minutes then they just might be enough to push a B main guy into the A main. Of course, it would require going back to the NiMH for the actual heat. Now to find some NiCDs to try out :D

EDIT: I found some ultralast 700s on the bay, now that may be worth looking into...