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working age of Ni-Mh

Old 02-01-2012, 07:24 AM
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Default working age of Ni-Mh

I have a couple of large Ni-Mh's and they are 4 years old.

The 1500 which has not been charged much does not seem to have much capisity and the 2500 is acting about the same.

Is there a rough time frame for these battery, I don't mind replacing them at 4 years but wondered about it.

sticks
Old 02-01-2012, 07:34 AM
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Rodney
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Default RE: working age of Ni-Mh

Chances are good that they have deteriorated to much to be reliable. the only way to tell for sure is to make two tests. first charge them at 0.1C for 16 hours and the discharge them down to 0.9V/cell at 0.33C measuring the mahs you remove. If it is 80% of the rated capacity, they are probably good. If it passes the first test then recharge for 16 hours at 0.1C and leave them set unconnected to anything for at least 24 hours then do the discharge test again. If it approaches the same mah capacity as the first test gave, you have good batteries. The second test is to see if there is excessive self discharge which is often a problem as NiMh's age.
Old 02-01-2012, 07:42 AM
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jester_s1
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Default RE: working age of Ni-Mh

Great info from Rodney. I'll add that if you'll do those tests when the batteries are new with maybe 5-6 cycles already on them, that will give you a baseline for how good new batteries should perform. When you start to notice in regular testing that they are dropping off, that's your signal to replace them.
Old 02-01-2012, 08:16 AM
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Default RE: working age of Ni-Mh

ORIGINAL: Rodney

Chances are good that they have deteriorated to much to be reliable. the only way to tell for sure is to make two tests. first charge them at 0.1C for 16 hours and the discharge them down to 0.9V/cell at 0.33C measuring the mahs you remove. If it is 80% of the rated capacity, they are probably good. If it passes the first test then recharge for 16 hours at 0.1C and leave them set unconnected to anything for at least 24 hours then do the discharge test again. If it approaches the same mah capacity as the first test gave, you have good batteries. The second test is to see if there is excessive self discharge which is often a problem as NiMh's age.
I forgot about this, I have been running them down and recharging . I will try this, but may replace the one battery anyway. The one went to a tx that died and the other goes in my main tx.
thanks a lot, I will try and get back about this and let everyone know.

sticks
Old 02-01-2012, 08:42 AM
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Default RE: working age of Ni-Mh


ORIGINAL: Rodney

Chances are good that they have deteriorated to much to be reliable. the only way to tell for sure is to make two tests. first charge them at 0.1C for 16 hours and the discharge them down to 0.9V/cell at 0.33C measuring the mahs you remove. If it is 80% of the rated capacity, they are probably good. If it passes the first test then recharge for 16 hours at 0.1C and leave them set unconnected to anything for at least 24 hours then do the discharge test again. If it approaches the same mah capacity as the first test gave, you have good batteries. The second test is to see if there is excessive self discharge which is often a problem as NiMh's age.
I struggle with "C" , but went back to my notes and figured this out. Is this right, its a 2500 NiMh tx battery and I came up with.
.1c = .25 amps
.33c = .8 amps

sticks
Old 02-01-2012, 09:14 AM
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Default RE: working age of Ni-Mh

Run, don't walk - Replace them both now.
Old 02-01-2012, 10:47 AM
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Default RE: working age of Ni-Mh

your saying my figures are not right, or is that just a funny?????

sticks
Old 02-01-2012, 11:44 AM
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Default RE: working age of Ni-Mh

No sir no 'funny' stated or intended. Your original question seemed to be should you replace the batteries based upon just age?

I was just expressing my opinion in reply that yes you should based just on age and it needs to be done soon. Sorry I will refrain from any further reply.

John
Old 02-01-2012, 11:52 AM
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Default RE: working age of Ni-Mh

that's alright, I was more wondering if my figures are right.

I am trying to get the hang of the "C" and would like to know if I had the right figures.

I do plan to replace one of them, the other is just going away don't need it. I will put the 2500 in a little land TX for the grand kids.

thanks for the reply.

sticks
Old 02-01-2012, 11:56 AM
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Default RE: working age of Ni-Mh

I have to agree with John, if there is any question then just replace them. Everytime I have questioned the reliability of a battery and not replaced it, it has bit me in the butt. Over 35 years that is about 4 airplanes lost and1 kitchen cabinet door.
Old 02-01-2012, 12:24 PM
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Default RE: working age of Ni-Mh

I beleve I am in agreement with Rodney only I like to keep things simple. Since I only have just a few Lipo's but a very large number of Nimh as well as some Nicd I prefer to keep things simple and I do that by charging all of them (Nimh-Nicd) in the same way and that is the overnight rate.

Yes the Overnight rate is the C.10 thing, heck I might have written that incorrectly but heck we are talking of the same thing and that is I charge all of them at about 1/10th of the the rated capacity. In other words Your 2500mah gets charged at 250 mils. Thats what works for me.

Now on to the cycling thing. All I can say is I abandoned that practice long ago Simply because it never made any real world differance for me, Perhaps others? I do not beleve I have been any worse the wear for my omission though.

I do attempt to replace batterys at around two years. This is difficult at times so I attempt to keep a good fresh supply on hand for replacements at all times. There have been a few occassions where some may not get flown in that period but unused or not the pack gets replaced next time out. Batteries should be treated as expendables and receive regular replacement.

I do beleve the figures you expressed are right on though.

John
Old 02-01-2012, 12:34 PM
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Default RE: working age of Ni-Mh

thanks on both counts.

I was wondering what others thought about age of our battery and when to replace and if my figures were right.

I do think 4 years is long enough, but it will work great in the grand kids land car.

sticks
Old 02-01-2012, 12:37 PM
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Default RE: working age of Ni-Mh

Cool[8D]
Old 02-01-2012, 12:59 PM
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Default RE: working age of Ni-Mh

I agree with johnbuckner. After two years, use the batteries for something other than aviation.
Old 02-01-2012, 01:16 PM
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Default RE: working age of Ni-Mh

Evan age isn't a particularly good indicator for NiMh...even new ones are subject to the seemingly random sudden death syndrome that affects this particular battery technology. I know several people who have given up on NiMh for flight packs for this reason and have gone back to NiCd.
Old 02-01-2012, 01:31 PM
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Rodney
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Default RE: working age of Ni-Mh

Yes, your numbers for 0.1C and .33c are correct.
Old 02-01-2012, 01:38 PM
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Default RE: working age of Ni-Mh

I have no problems with the suggestion to replace the batteries with new if you can. However, even new Nixx based batteries need to be checked out by charging at 0.1C for 15 to 16 hours and then checked for capacity. Some will require a repeat of this slow charge/discharge cycle before they come up to full capacity. I have had new batteries that were not at all reliable and I have also had some NiCad's that performed well for 10 years. If in doubt, replace them.
Old 02-01-2012, 02:51 PM
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Default RE: working age of Ni-Mh

I am using a very good peek detection charger for this trial. I would think this should work, or isn't that the case.

Its the Thunder Power TP-1010c


Old 02-01-2012, 03:08 PM
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Default RE: working age of Ni-Mh

ORIGINAL: JohnBuckner

Now on to the cycling thing. All I can say is I abandoned that practice long ago Simply because it never made any real world differance for me, Perhaps others? I do not beleve I have been any worse the wear for my omission though.
Icycle nimhs a couple times a year. It's not for memory issues, but as a way to monitor the charge holding capability of each battery.

Old 02-01-2012, 03:19 PM
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Default RE: working age of Ni-Mh

I run em a max of 2 years....that being said i got away from em except for ignition batteries this year. new batt technologies are impressive.
Correct me if i am wrong but I was told when a nimh batt hits full charge it will be warm, if it is not it is not fully charged. Always used that for a method to see if it false peaked on me.
Old 02-01-2012, 03:52 PM
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Default RE: working age of Ni-Mh

from what I have seen, they don't get warm until over charged at a fairly high charge rate. The extra current has to go some where and heat is one way for the battery to vent extra current.

I would guess that a really fast charge could cause the batter to get warm, not real sure about that.

I know that when I raced cars we charge fast and hard and we would take them off charge when warm.
Old 02-01-2012, 04:01 PM
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Default RE: working age of Ni-Mh

I pulled this off Red's battery clinic.... it has alsways served me well:
Q: How do I know if my pack is fully charged?

*

Temperature is the key.. always, always, always! IF THE PACK AIN'T WARM AT THE END OF THE CHARGE ROUTINE, IT AIN'T CHARGED! Note I said 'warm'. Not HOT! Hot is NEVER GOOD at the end of the charge routine.. but warm is OK. If using a temp probe, set it for 10 degrees above AMBIENT. If it's a peak controlled charger and the charger shuts down before the pack is slightly warm to the touch.. IT AIN'T FULLY CHARGED. If it's a timer controlled charger and at the end of the charge period the pack is not warm.. it's NOT fully charged yet! By far and away the biggest reason for low capacity numbers is undercharging.. if you have a 5 gallon pail with only 3 gallons in it, your only gonna get 3 gallons out of it. Engage your brain.. check temperature at the end of the charge routine!

*
here is the link. http://www.hangtimes.com/rcbattery_faq.html
Old 02-01-2012, 04:32 PM
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Default RE: working age of Ni-Mh

ok, I went and read it. I guess the warm part as to hot is the key

. I can see how warm won't hurt, we really warmed up our battery for outdoor racing our cars. We even got them HOT off and on and they did not die on the spot, even though it was not good for them.
Old 02-01-2012, 08:25 PM
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Default RE: working age of Ni-Mh

My experience is that the lifetime of battery packs varies wildly. I have some old low-capacity NiCd packs that are 8 years old that I still fly and still have good capacity and low self-discharge rates. I've had some higher capacity NiCds that barely lasted 3 years. I've had NiMH packs that were no good even when new, and some that are still good after 5 years.

I think the best advice is to buy high quality batteries and replace them every 2 years or so. Someone who has the equipment and desire to check capacity and self-discharge rates and knows how to interpret the results can safely use them for longer. But that starts to become another hobby in itself.

I think that peak detect chargers and higher charge rates tend to shorten battery life. In my opinion, C/10 is the kindest charge method for NiCd and NiMH. I think that even C/10 may be too high for some high capacity cells. I like to charge my Eneloop NiMH packs at C/20.
Old 02-01-2012, 08:27 PM
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Default RE: working age of Ni-Mh

By the way, the warm effect only works for charging at higher rates. If you charge at a low rate they will not get noticeably warm.

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