Jump to content
burakol

NiMh Health

Recommended Posts

Hi, 

I have a handful of these 5 year old Onyx 5000NiMh. These probably seen less than 15 cycles total. It was stored for 3 years. I do have a clone b6 charger, which I suppose is not that great when  charging other batteries than a LiPO. So I took out my older Duratrax Intellipeak Pulse charger and seems to work better for the NiMH. I did notice however, that 2 out of the 3 packs I fully charged last night, discharged itself. When I tried to run it on my stock GF01, the low voltage on the TBLE02S kept kicking in right at the bat. However, I was still able to run the 1 pack for a few minutes but it noticeably lacked the punch of a fully charged battery. Does this mean these NiMH packs have deteriorated and possibly developed a bad cell already? Can it still be recovered? 

Although I want to try a LiPo, I am still not in the position to do so. I think it requires more involvement when it comes to charging and storing it, plus the dangers of misusing/mishandling it scares me, given that I live in a townhouse... and I dont' want to cause any hazardous situation for my family and my neighbors..

Thoughts? Thank you. 

Share this post


Link to post
Share on other sites

My first guess is your NiMH packs have gone bad, but since you have a B6 clone you might be able to cycle those packs a number of times and rejuvenate them.  Just repeat full charge/full discharge cycles maybe 5-10 times and see if the pack then holds a charge better.  NiMHs should be stored with a full charge for best long-term results.

  • Like 1

Share this post


Link to post
Share on other sites
4 minutes ago, speedy_w_beans said:

My first guess is your NiMH packs have gone bad, but since you have a B6 clone you might be able to cycle those packs a number of times and rejuvenate them.  Just repeat full charge/full discharge cycles maybe 5-10 times and see if the pack then holds a charge better.  NiMHs should be stored with a full charge for best long-term results.

How long should they keep their charge for if they are not put into use? I'm assuming that it shouldn't lose half of it's charge overnight right? 

As for the B6 clone, I'm not so sure I can rely on it... when I do a discharge/charge cycle, I anticipate it to take at least a number of hours to finish... mine goes through a full 2 cycle for less than 2 hours... sometimes shorter... when I observe the discharge cycle, it literally seems that it sucks all the charge out of the battery in a zap... like from 8.4 volts down to 5.4 in less than 5 minutes... I am not sure that's accurate... 

 

  • Like 1

Share this post


Link to post
Share on other sites

Correct.  Per Battery University (https://batteryuniversity.com/learn/article/elevating_self_discharge), NiMH might lose 10-15% of charge in the first 24 hours, and then 10-15% per month thereafter.

If your B6 is showing a low voltage relatively quickly, then it's possible one of the six cells in your battery pack is weak and isn't holding a charge at all.  Since all the cells are wired in series, one weak cell becomes the weakest link in the chain and affects overall performance of the pack.  If a few cycles doesn't rejuvenate the pack then it's time to replace it.

  • Like 1

Share this post


Link to post
Share on other sites
5 hours ago, speedy_w_beans said:

Correct.  Per Battery University (https://batteryuniversity.com/learn/article/elevating_self_discharge), NiMH might lose 10-15% of charge in the first 24 hours, and then 10-15% per month thereafter.

If your B6 is showing a low voltage relatively quickly, then it's possible one of the six cells in your battery pack is weak and isn't holding a charge at all.  Since all the cells are wired in series, one weak cell becomes the weakest link in the chain and affects overall performance of the pack.  If a few cycles doesn't rejuvenate the pack then it's time to replace it.

I am now using my older intellipeak pulse charger... I think this one is more accurate but the problem I have is the discharge voltage as it is fixed down to 2.6v. I am taking my chances with it since it seems to be the better charger for reviving the packs compared to the b7 clone. I can feel the packs get warm to the touch but not hot. 

I have a total of 6 5000mah nimh packs. 1 of which I think may have a bad cell.  A 4500mah nimh, 1 2000mah nicd, and another 2700mah nicd. I am going to cycle all of the packs at least 3x each. 

It would be a waste to toss them away. Hopefully most of them can still be put to use. 

  • Like 1

Share this post


Link to post
Share on other sites

I have a feeling NiCd survives better than NiMh.  But NiCd is toxic and low in capacity. I had them recycled most by now.  

Going from 8.4v to 6v means it's got 2 cells gone rogue.  Their + and - sides have flipped.  If you are familiar with the concept of "almost dead" and "all dead," flipped cells are "all dead."  They don't come back.  

fwCKTAP.jpg

If there is a way to find defective cells, replacing them could revive the pack.  But, it's sort of a time consuming surgery.  Also, because the new cells are more powerful than older cells, it causes one of other 5 to die.  So it's not really worth the time, in my opinion. 

Having said that, just as Speedy said, cycle several times to see if they come back alive.  

Charge it, cool it, discharge it, cool it ... 4-5 times.  If you leave it to Intellipeak's cycle function, the pack could die of heat-stroke.  (I've killed like 2 packs -- I'm a slow learner, apparently)  Each cycle, the pack should take more charges.  After 3 years, though, the best you might get is 85% of what it was.  If it was 3300mAh then, I'd count myself lucky if it held 2850mAh.  

 

Share this post


Link to post
Share on other sites

Thanks for the reminder about letting it cool during the cycle... I think that is a key important thing to note... I have all the packs fully charged today and will monitor the voltage drop tomorrow and see which of them are holding fine... 

So what I'm really confused about is on two batteries, when I check the voltage, it indicates a full charge, but when I run it, the esc cuts off... meaning it already drained out... when I take it out, voltage shows ok. So I guess that's a pack with a dead cell? 

Share this post


Link to post
Share on other sites

When you measure the voltage it's under no load, so almost no current is being drawn out of the pack, and there's no voltage drop as a result.  But as soon as you start to put a meaningful load on the battery, the current flowing out of it causes a voltage drop on the battery, especially in old/weak cells.  This is a phenomenon known as "internal resistance."  It's the characteristic of a battery's voltage dropping while under load.

Share this post


Link to post
Share on other sites

Is there a more quicker way to check if the pack has been revived? I'm currently cycling 3 packs that I think has gone bad. I did notice that after the initial cycle, the discharge time has increased. It now takes longer to reached the set discharge voltage of 2.6v. Does this mean that the weak cell could have now been awaken? 

Share this post


Link to post
Share on other sites

It’s simply not worth the agro. Just chuck em in recycling and get new ones

Share this post


Link to post
Share on other sites

Out of the 8 total packs I have... 

I have 5 healthy ones and 3 that I'm currently reviving. With the time I have right now at home, I think it is well worth trying to recondition them and save some extra dollars for something else. I dont have plans using LiPo anyway so I think the packs I have now should serve my purpose. 

If I cant revive the 3, I might open them and look for the bad cell and replace it with a healthier from the other weak pack... since they are the same brand/type/capacity, I should be able to get away in inter mixing them. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...