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Battery and charger advice please - 1/20/2005 9:58:55 PM   
GTee


 

Posts: 32
Joined: 12/31/2004
From: Newcastle, UNITED KINGDOM
Status: offline 		Hi Every1

A quick question or two on batteries and charges.

First, I am new to the wonder full world of RC so I dont know much about alot of it...lol. I have purchased radio gear for fixed wing, ic flight, second hand so I dont know about the history of the batts the RX bat is 700mah 4.8v, the TX is 700mah 9.6v and the charger is a 70ma. Am I right in thinking that I would need to charge them both from discharged for 10 hours to reach their max (700 divided by 70 = 10)?

Second, I am quite tempted to buy a Pro-Peak Mercury EX charger as someone at my local club charged my RX batt this week (after I left it on, oops) in about 30 mins, I have seen a few people with these charger so they must be good but will it damage the batts if I fast charge them every time?.

thanks.
       Post #: 1

RE: Battery and charger advice please - 1/21/2005 1:28:20 AM   
Flying Geezer



Posts: 1049
Joined: 4/12/2003
From: Bowling Green, KY, USA
Status: offline 		Charge for 14 hours. You need 40% more going in. capacity/charge rate X 1.4. As for fast charging, it won't hurt your battery pack to fast charge every time. Some will argue that fast charging shortens battery life. Probably does, but the difference is not going to be noticeable.
It's a choice, do you want to wait hours for charging, hoping for 10-15 years out of a battery pack, or are you willing to replace in 5-7 years for the convenience of fast charging.

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Hughes RC

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       Post #: 2

RE: Battery and charger advice please - 1/21/2005 4:46:04 PM   
Rodney



Posts: 4782
Joined: 12/8/2001
From: FL
Status: offline 		You did not say what type of batteries, NiMh or NiCad? In any case, check out Red's site at www.rcbatteryclinic.com for some good honest advice on how to care for your batteries. There is probably more misinformation given in these forums on battery care than any other subject. Two reliable sources otherthan the manufacturers (always first choice) are Red's site and radicalRC.com.

(in reply to Flying Geezer)
       Post #: 3

RE: Battery and charger advice please - 1/21/2005 6:55:10 PM   
GTee


 

Posts: 32
Joined: 12/31/2004
From: Newcastle, UNITED KINGDOM
Status: offline 		Thanks people for the advice.
I cant belive that batts last so many years I was expecting about 1 year max "wow"
So if I bought a 1700mah batt and charged it with my 70ma charger it would take 34 hours to charge right?

btw. Their nicd batteries

(in reply to Rodney)
       Post #: 4

RE: Battery and charger advice please - 1/22/2005 1:36:09 AM   
Flying Geezer



Posts: 1049
Joined: 4/12/2003
From: Bowling Green, KY, USA
Status: offline 		Actually, you'll never get a full charge at 70 mAh charge rate, but you can charge with the wall mole and use what capacity you get. There is more mis-information given given on battery care than about any other subject.

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RE: Battery and charger advice please - 2/16/2005 6:43:13 PM   
redbirdy


 

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Joined: 1/20/2004
From: kingsport, TN, USA
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quote:

ORIGINAL: Flying Geezer

Actually, you'll never get a full charge at 70 mAh charge rate, but you can charge with the wall mole and use what capacity you get. There is more mis-information given given on battery care than about any other subject.


Anyone mind explaining this? Why wouldn't a 70ma charger eventually charge a 1700 ma battery pack? Is the rate of natural discharge greater than what's being delivered after the battery reaches a certain threshold capacity? Does anyone know what the discharge rate for idle nimh packs are? Is it a certain percentage of what the capacity is? Is this rate of discharge independent or dependent on what the capacity of the battery is?

(in reply to Flying Geezer)
       Post #: 6

RE: Battery and charger advice please - 2/16/2005 7:08:29 PM   
Red Scholefield



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From: Newberry, FL, USA
Status: offline
quote:

ORIGINAL: redbirdy

quote:

ORIGINAL: Flying Geezer

Actually, you'll never get a full charge at 70 mAh charge rate, but you can charge with the wall mole and use what capacity you get. There is more mis-information given given on battery care than about any other subject.


Anyone mind explaining this? Why wouldn't a 70ma charger eventually charge a 1700 ma battery pack? Is the rate of natural discharge greater than what's being delivered after the battery reaches a certain threshold capacity? Does anyone know what the discharge rate for idle nimh packs are? Is it a certain percentage of what the capacity is? Is this rate of discharge independent or dependent on what the capacity of the battery is?

Actually it probably would charge it eventually. The rule of thumb has been that the minimum charge to reliably recharge a pack is C/20, which for a 1700 mAh pack would be 85 mA. 70 mA is not that far off. For some reason people seem to think these rule of thumb numbers for batteries are sacred. They are not, but the further you get away from them the less chance of success. Another rule of thumb is that C/50 is required to maintain them at a full state of charge. Nature does not work with nice round numbers nor is it consistent all the time. Things like age, temperature, previous charge/discharge history come into play here.

A number of things come to play in the charge scenario, not the least of which is the charge efficiency and the rate of self discharge. Self discharge can vary, again depending on a number of parameters from 1%/day to 5% or more and is not linear, meaning it loses more in earlier than later. Charge efficiency can also vary from battery to battery again with a number of parameters coming to play with efficiencies varying in the range of 70 to 95%. Then add in the fact that the actual capacity of the cell can vary as much as 20% and I think you can see that hard numbers just won't work. Stick as close as you can to the rule of thumb numbers and you will be much happier. Wander far off and things can start to deteriorate.

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RE: Battery and charger advice please - 2/17/2005 12:21:24 AM   
Flying Geezer



Posts: 1049
Joined: 4/12/2003
From: Bowling Green, KY, USA
Status: offline 		Well, EXCUUUUUSSSSe me. It might, might not, rule of thumb, hard numbers!! I think it is pretty good advice to tell a newbie to stay away from a marginal situation. Make up your mind Red. Several months ago you posted that you posted that lab tests showed charging to be ineffective below C/20.

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Hughes RC

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RE: Battery and charger advice please - 2/17/2005 12:47:48 AM   
Red Scholefield



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quote:

ORIGINAL: Flying Geezer

Well, EXCUUUUUSSSSe me. It might, might not, rule of thumb, hard numbers!! I think it is pretty good advice to tell a newbie to stay away from a marginal situation. Make up your mind Red. Several months ago you posted that you posted that lab tests showed charging to be ineffective below C/20.


When someone posts "you'll never get a full charge at 70 mAh charge rate" I feel obligated to step in and give as much information as I can. I have never posted anything that said lab test showed charging ineffective below C/20. What I said is that charging below that can get a bit marginal in some cases. Pick a number C/19 or C/21.5. We can nit pick this to death. I just want to get people off the hard number kick and make them think a little, observe results under varying conditions, learn something and apply it. Now if you would like to belabor the issue of 7% - 9% Castor/sythetic with 9.6% +/- .55% nitro there is probably a forum where you can debate that also.

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RE: Battery and charger advice please - 2/17/2005 1:05:49 AM   
Flying Geezer



Posts: 1049
Joined: 4/12/2003
From: Bowling Green, KY, USA
Status: offline 		Seems to me your comments are "nit-picky", and arrogant. I'm tired of guys showing up at the field with 1700 mAh packs, charged for 10 hours on a 50 mA wall mole, thinking they can fly all day with their big battery pack. I could have written the guy an essay, too. instead I gave him some solid advice. Excuse me for saying "never" instead of "probably never" or "maybe never" I didn't know it was going to turn into a court of law. What I resent is your attitude toward my comments. Arrogance is not a virture.

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RE: Battery and charger advice please - 2/17/2005 1:14:20 AM   
echobot



Posts: 314
Joined: 10/30/2003
From: Sturgis, MI, USA
Status: offline 		Red,

I have a question for you. How high does the number go for the C rating. Is it from 1 to 100 or higher? I have seen so many different definitions for this C rating that I really don't know what is what anymore.

Oh, and to make sure that I understand the C rating do you always divide the battery mah by the C number?

Damn I confused.

Thanks,

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Ed

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RE: Battery and charger advice please - 2/17/2005 2:37:19 AM   
Red Scholefield



Posts: 4980
Joined: 12/8/2001
From: Newberry, FL, USA
Status: offline
quote:

ORIGINAL: echobot

Red,

I have a question for you. How high does the number go for the C rating. Is it from 1 to 100 or higher? I have seen so many different definitions for this C rating that I really don't know what is what anymore.

Oh, and to make sure that I understand the C rating do you always divide the battery mah by the C number?

Damn I confused.

Thanks,


The term C defined.

C designates the declared rated capacity of a cell (battery). All cell charge/discharge current is specified in terms of a multiple of C. For example the 0.1C or C/10 current for a 1.2 amp-hour cell is 1.2 divided by 10 or .12 amps (120 mA). This could apply to either charge or discharge. We use _C or C/_ to specify either charge or discharge rates since it normalizes the rate regardless of the capacity . If we say you should charge at C/10 we don’t have to specify the actual capacity. It will work for any capacity pack. A 600 mAh pack charged at C/5 would be charged at 600/5 or 120 mA. Similarly discharging a 1500 mAh (1.5 Ah) pack at 10C would be at 15 amps.

Hope this clears it up for you (and any others that are confused).

< Message edited by Red Scholefield -- 2/17/2005 2:44:08 AM >

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RE: Battery and charger advice please - 2/17/2005 1:27:35 PM   
echobot



Posts: 314
Joined: 10/30/2003
From: Sturgis, MI, USA
Status: offline
quote:

Similarly discharging a 1500 mAh (1.5 Ah) pack at 10C would be at 15 amps.


Red,

Well I'm still comfused on your example of discharging. If the battery is 1500 mAh divided by 10C it comes out to be 150 not 15 amps. So do I convert ma to amp when calculating discharge rates to get the 15 amps or did I miss something here?

Thanks,

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Ed

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RE: Battery and charger advice please - 2/17/2005 2:22:41 PM