Popriv

I picked up a hobby king Turnigy accucell 6 charger Just for the ability to cycle my RX NiMH batteries.
I set up an old 2000 mAh battery to test the cycle.
I set it to charge at .200 amps then it would start a discharge... I think at .500amps
But the charger timed out at 120 min. Looks like a safty feature...
Do I have to disable the timer for the cycle option??

documentation is limited... any info on cycling these packs would be appreciated..

Thanks

Steve

alan0899

G'day Steve,
I had the same problem with mine, it is a safety feature, just go into the "User selects" & find safety timer, it will be set at 120 minutes, increase that to whatever you require, I used the maximum.
Do you have the instructions, if not they can be found here. http://www.sparkfun.com/datasheets/P...ual%282%29.pdf
There is a quick procedure for calibrating these chargers, here. http://www.hobbyking.com/hobbyking/s...4f0fd641f2b5c5

Cheers

tacx

My Feedback: (1)

You should be charging at a full 2.0 amps not .2 amps. It timed out because at .2 amps it will take forever.

alan0899

G'day Mate,
2 amps for a NiMh pack will kill it really quick, OK for LiPo, not for NiMh.
Stick to slow charge, & remember, with NiMh, you need to put in 140% in, to get 100% out, because of losses, inside the battery pack.

Cheers.

jester_s1

1c is fine for NiMh, which would be 2 amps for that pack. But if this is a new battery, you are doing exactly the right thing to form charge it at c/10 and do a couple of cycles.

countilaw

Have you tried calling Hobby King's customer service to get some tech help?


Frank

KW_Counter

1C for a NiMh can be done but it will shorten the life of the pack.
You are better off with a milder 1/10C for normal charging.
You are correct charging at 200 mAh.
Discharging at 500 mAh is fine.
Discharge to .9 volts per cell.
However, at the field, stop flying/driving at 1 or 1.1 volts per cell.

Have Fun,
KW_Counter

acdii

Agreed, high charge can kill a pack. I have a 5 cell Nimh that has a bad cell in it, I had charged it at 1.5 amp, and did several discharge/charge cycles, and now have a bad cell. It could have been faulty to start with, but it didnt last very long, less than a year, in fact I had picked it up last February, and have less than 10 cycles on it total.   I have since switched to Life packs, I found i get much longer times between charges with them.

Rodney

You are correct in charging at 0.1C when checking out a pack especially if it has not been charged at that low rate for a while or if it has sat dormant for a few weeks. Charge at 0.1C for 16 hours then do you discharge test. You do not have to discharge it before doing this 16 hour slow charge as an overcharge will not damage it at this low rate of charge. If you can not set your charger down to this low a rate, use the wall wart that came with the system and just charge over night with that. If comparing to factory specs, limit your discharge rate to about 0.33C and discharge down to 0.9 volts/cell. If you discharge at a higher rate than that or only down to 1 volt/cell you will get a smaller value for the capacity. Your Nixx cells will always benefit from the slower charge rate when you have the time to do so. However, if you are in a hurry and have to use a peak detecting fast charger, you must use a higher charge rate to insure that the peak detection kicks in, usually at least 0.5C or higher.

jaka

Hi!
NiMH batteries don't need cycling!

alan0899

G'day Jaka,
No they don't, but cycling every now & then, will tell you if there is a problem, ie, low capacity, bad cell & so on.
As I said in post #2, go to "user selects", & change the safety timer setting.
That was the original question, & before you know it, we are discussing the merits or otherwise of cycling NiMh cells.

Cheers.

RCKen

My Feedback: (9)

Correct, Ni-MH batteries do not require to be cycled

However, us poor humans require Ni-MH's to be cycled in order to determine their capacity and what condition they are in. When a pack is new I will cycle it several times to determine it's initial capacity. Then over time I will periodically cycle the battery to check it's current capacity. When the current capacity drops below 80% of the initial capacity I will pull the pack from use as a flight pack battery and start using it for something else, or throw it out.

Ken

Rodney

Those who think NiMh do not need cycling are sadly mistaken. They are a nickle based chemistry and do suffer the same problems with balancing and reverse charging as NiCad do. It is usually very helpful on NiMh's that have been fast charged to get an occasional slow charge (defined as charging at 0.1C for 16 hours) to regain balance and full capacity. Here is some good info if you are seriously interested in the facts.

Battery information
http://www.hangtimes.com/redsbatteryclinic.html
http://www.camlight.com/techinfo/techtips.html
http://www.whenshtf.com/showthread.php?t=2153
http://www.srbatteries.com/nimh.htm
http://dansdata.com/gz011.htm
http://users.frii.com/dlc/battery.htm

Popriv

OK, I set the shut off timer to its max. and started a test on an old 4 cell Nimh 2000 mah pack.
set to charge at .2 amps and discharge at .5 amps
I ran this cycle 2 times.
Everything seemed to work as advertised.
Not sure what to make of the resulting cycle log numbers?
2nd cycle dicharge was a higher number than the 1st cycle.
I want to try this on a new pack as I'm hoping to see a pattern and the numbers will mean something to me.

Mainly want to condition a new pack before using and check on the condition of older packs. I gave up on using a light bulb and meter to discharge so this is great for $25 bucks....

thanks for the tips

acdii

Higher numbers on the second discharge is a good thing. Thats the amount of Mah removed from the pack.  When the numbers go down on each cycle, that means time to toss the pack.  The amount of mah on a charge is how many mah has been put back into the pack. Usually the charge mah will be a bit higher than the discharge mah, but sometimes can go the other way depending on the temp of the pack and amount of time between the discharge and charge cycle.  Batteries can recover some mah on their own after sitting and cool down, but not always, depends on the draw. 

Popriv

HydriMax ultra 2000, 4.8v NiMH, a couple of years old..

charge 1 at .2 amps - 2000 mah
discharge 1 at .5 amps - 1580 mah

charge 2 at .2 amps - 2000 mah
discharge 2 at .5 amps - 1649 mah

charge 3 at .2 amps - 2000 mah ( 10 hours )
discharge 3 at 1.0 amps - 1610 mah ( I raised the load to 1 amp )

I'm watching the 3rd discharge cycle now. Its been running for 90 min. at 1.0 amps.
Its gone down to 3.45v
It just dropped to a .8 amp load and the voltage went up to 3.6v
Still a .8 amp load, voltage down to 3.4
Now it dropped to a .6 amp load, voltage up to 3.7 again.
Dropped to a .4 amp load, voltage up to 3.8v.
I'm seeing a pattern here... but I thought it would stop at .9v per cell or 3.6v
It appears to taper off the load at the end of the discharge cycle?
about 110 min. for discharge cycle.

What is the better discharge rate?
I notice the last discharge was less than the 2nd cycle.
What kind of a load does my 4 servo, .46 sport plane draw? per flight?
That 1610 mah is not all available for use? that would drop the voltage to low. ( I have spektrum. lol )


I'll put this battery on a walwart and test another old battery to compare the numbers
Great to finally see the numbers. lots o old batteries that are probably still good.

steve

Popriv

So I should do this cycle with my new pack until the discharge number stops increasing.
The highest discharge number is my baseline for my new pack in the above example it would be 1649mah.
The condition of that pack can be tested by cycling it and when the 1649mah drops 80% to 1319mah the battery is ready to retire.

do I have this correct?

steve

alan0899

G'day Mate,
Your cutoff voltage should be 1 volt per cell or 4 volts for a 4.8 volt pack, if you go too much lower than that, you run the risk of reverse charging a low cell.
I don't know if anyone realises what happens if you discharge that much, that one cell goes completely flat, no voltage at all.
See diagram, I hope I have explained it well enough.

Cheers.

jester_s1

Popriv - a .5 amp discharge load is good. The load really isn't crucial, but as you've seen you'll get a slightly higher number for your capacity by going with a lower load. That's because the charger terminates the discharge when the pack reaches the preset threshold under load. The more load you have, the more capacity it will have left when it reaches that threshold. The important thing is to be sure that you use the same load every time in order to have meaningful numbers for comparison, and that the numbers are fairly close to each other when doing your initial forming charges and cycles.

Popriv

yes, I just happened to be there to watch the discharge cycle and was surprised to see it drop as low as 3.45v.
I think it is set to discharge to .9v per cell or 3.6v.

I could increase the cut off point?

Steve

alan0899

G'day Mate,
Increase your cutoff to 1 volt per cell or 4.00 volts for a 4 cell, 4.8 volt pack, or 5 volts for a 5 cell, 6 volt pack.
If you always use the same cutoff voltage & the same discharge rate, & keep records,
I number my packs, you will get consistant, & reliable info on each pack.
I use 80% as my cutoff point, when a pack will only discharge to 80% I throw it away.

Cheers.

Rodney

The value that was established many years ago by some of the testing labs is 0.9Volt/cell for the end of discharge for NiCad and that is the value that most manufacturing specs relate to. On 4 or 5 cell packs, there is very little risk of reverse charging if you use the 0.9 volt/cell limit. If using larger packs (more cells in series), you can get more of a chance of one cell getting a reverse charge at the end of such discharge limits, the more cells in the pack, the higher the risk of reverse charging the weakest cell near the end of the discharge cycle. If you are comparing to factory specifications, the cut off voltage on discharge needs to be 0.9 Volts/cell. NiCad and NiMh are very similar in this respect.