Cold weather + NiMH

[OoALEJOoO 3663]

Cold weather is giving me a hard time. My toes hurt and my hands are stiff. Worst of all, my NiMH batteries are mostly dead. I need some help

This is the first time that come winter my NiMH batteries are having issues. Back in December, I fully charged all of them for storage, come March I top-charge one of them, take a car for a spin and its dead. Tried other batteries, same thing.

These are the symptoms and what I've tried so far:

• I have x8 NiMH 3600mAh batteries and all of them are having the same issue, which makes me think it's a NiMH thing and not particular to a damaged battery.
• Ambient temperature is about 8 degC. I charge my batteries in a room at 12 degC.
• My charger reports batteries have about 7.8V when fully charged. However, when placed in any car, power is very low and after maybe 30 seconds of running the ESC starts hitting the low-voltage cut-off.
• I place them on the charger again, 7.8V and they won't take any further charge.
• When doing a discharge cycle, they discharge about 1500mAh of their supposed 3600mAh capacity. Then charge again those 1500mAh. I recall back in the summer they did charge to about 3400h mA.
• I always charge at 0.5C, so 1.8A.
• I did a 5-cycle discharge/charge on a few of them. No effect.
• I also have x4 5000mAh batteries and they seem less affected, but definitely off. They do have what appears to be normal punch, but they charge/discharge about 2500mAh only.

Was fully charging for storage a mistake? This is driving me nuts...

[skom25 2677]

Quite strange. Year ago, I left them fully charged and just recharged once per month.

This year I ran my RC also during winter, sometimes below 0 C. Totally no issues.

However, one of my NiMhs some time ago started to behave more or less as yours. It was fully charged, but car was absolutely slow like with almost empty pack.

[Kowalski86 5026]

22 minutes ago, OoALEJOoO said:

Was fully charging for storage a mistake? This is driving me nuts...

I try to keep mine fully charged when I'm not using them, but I usually charge them at 2.2a and I don't use LVC, I just quit running when I can sense the power level dropping.

What I can say is that heat really hurts NiMHs, for a time I had a Stampede that wasn't geared correctly, and my 5000mh battery became too hot too touch. Now that battery behaves just like yours does.

[alvinlwh 8068]

Cold weather??? You no longer in SG? 

[Ferruz 13732]

Quite strange, indeed, especially that it happened to all of them at same time. I don't think that fully charging before storage was a mistake, as far as I know it's the right thing to do. I would rule out cold weather as well: where I live temperatures get to the extremes in both winter and summer, I often run my cars at -20 / -25°C and if anything the NiMHs seem to "like" it and last quite a bit longer in the cold. 

So, not sure what the culprit could be. Are those batteries all the same brand, and did you get them together in the same bundle? I did experience similar issues from time to time with some batteries, where they would just lose their punch even when fully charged. When running, they would only last a few minutes with lower performance, then cool off, back to the charger and it would show them as charged within minutes. I thought the cause would be some defective cells in them, as fair enough this happened after a few years of intense use. Then again, I have some Nicads from the Ice Age that still perform well.

Anyway, I kept the defective ones (one of which somehow got back to life) with the idea of frankensteining up some home brew packs out of them in the future, but moved on to new batteries for the time being.

Last year towards the fall I purchased a couple NiMHs packs, I believe it was on scamazon, and was pleasantly surprised by their performance. High discharge rate makes a big difference for people that are still on NiMH... that, plus they haven't skipped a beat so far and behaved well throughout the winter months. It you want I can find out what they are later and send you a link.

[sosidge 782]

Sounds like false peaking. 7.8v just off the charger is not charged. Charge them again, they will be warm to the touch when charged.

Also NiMHs are an inferior battery chemistry, life will be much easier with Lipo.

[Hypoxic 836]

21 hours ago, sosidge said:

Sounds like false peaking. 7.8v just off the charger is not charged. Charge them again, they will be warm to the touch when charged.

Also NiMHs are an inferior battery chemistry, life will be much easier with Lipo.

I have to do this with mine. The charger will stop and reads, “FULL”. Then I start it again and when finished it reads, “CAPACITY” and the pack is warm.

[Gratuit 192]

Maybe try another charger? Or first check it and his connector... If every battery has the same symptoms, that could be the cause of your problem

[ThunderDragonCy 9114]

I would agree on charger. When I ran nimh batteries the full charge voltage was way over 8V. 

[Twinfan 2479]

34 minutes ago, Gratuit said:

Maybe try another charger? Or first check it and his connector... If every battery has the same symptoms, that could be the cause of your problem

Yep, I must admit this is my thinking.

[OoALEJOoO 3663]

Thanks for all the help!

Adding more details on my setup and what I have done:

• 3600mAh batteries are 2x Zeee, 2x Awanfi, 4x Champion. 5000mAh are 4x Champion. All have deans connectors.
• I have 3 charges: SkyRC B6 (clone), Onyx 210 and Onyx 110.
• Normally the SkyRC is used for discharging, then the two Onyx for charging. I always charge at 0.5C to 0.6C tops.
• Good points about the chargers perhaps being the problem. I've tried randomly all 3 to charge with similar results but I need to check them systematically for any patterns.
• Indeed, as many of you mention, there are regular instances of false peaking with batteries still cold. I charge them again until they peak when warm.
• When charging, charge voltage starts at around 8.5V, then climbs all the way to about 10.5V before peaking (for a true peak). Can't remember if these voltages are normal or not, or if its suggestive of battery internal resistance has gone bad.
• Once charged, they are a warm to the touch. I let them cool a bit and their voltage settles at 7.8V or so.
• When discharging, the SkyRC B6 can only do 10W, so that's 1.2amps right when the battery has 7.8V. The 3600 mAh batteries can sustain a discharge rate of about 1.2amps for 1000mAh or so before the voltage starts dropping. Once it reaches 6V, the discharge stops to charge again to reach around 1500 mAh.

What I'll try next:

• Charge noting which charger is used to verify no charger has kicked the bucket.
• I wonder if charging at 1C will make any difference. It would probably make the voltage reach over 11V when charging.

I understand my chargers are on the crappy end of the spectrum but seems odd that suddenly everything went off. I'll probably need to buy another charger at some point, although it would suck to buy a new charger only to realize the issue is the batteries.

[sosidge 782]

10+ volts at the end of the charge means the battery is shot (or was not good to start with). 9-ish at peak would be normal.

NiMH cell quality is very poor nowadays, the cheap Chinese cells in most packs are intended for cheap power tools.

[Twinfan 2479]

Nothing wrong with my Overlanders , they've been superb and still are.

[El Gecko 1673]

3 hours ago, OoALEJOoO said:

• Normally the SkyRC is used for discharging
• When discharging, the SkyRC B6 can only do 10W, so that's 1.2amps right when the battery has 7.8V. The 3600 mAh batteries can sustain a discharge rate of about 1.2amps for 1000mAh or so before the voltage starts dropping. Once it reaches 6V, the discharge stops to charge again to reach around 1500 mAh.

NiMHs don't need to be discharged, in fact they shouldn't be discharged because they don't like to dip into the lower percentages of battery capacity, and this could have prematurely damaged all your batteries. You will notice more when it's cold since their capacity would already be diminished, but most likely the discharging is the root cause. I have an old Traxxas NiMH that I used until it was flat a few times, and it has never charged up and been able to output the same potency after that.

 

1 hour ago, sosidge said:

NiMH cell quality is very poor nowadays, the cheap Chinese cells in most packs are intended for cheap power tools.

MEH, this is just your bias showing. The cheap Chinese 6-cell packs that I bought 5 years ago are still going great. Conversely it's the expensive Gens Ace one which has dropped off significantly since new. There is nothing wrong with NiMH cells unless it's just a randomly bad pack to begin with, or they are mishandled/mischarged etc.

[Kpowell911 2640]

Why is LVC turned on on your ESC if youre not using Lipo?

[Kowalski86 5026]

1 hour ago, El Gecko said:

NiMHs don't need to be discharged, in fact they shouldn't be discharged because they don't like to dip into the lower percentages of battery capacity, and this could have prematurely damaged all your batteries. You will notice more when it's cold since their capacity would already be diminished, but most likely the discharging is the root cause. I have an old Traxxas NiMH that I used until it was flat a few times, and it has never charged up and been able to output the same potency after that.

Good point, running a NiMH battery down to the last drop does wear them out fast. That being said, I've found Traxxas NiMH batteries to be lower quality compared to others.

[El Gecko 1673]

1 hour ago, Kpowell911 said:

Why is LVC turned on on your ESC if youre not using Lipo?

Most brushed ESCs like the Hobbywing 1060 and its clones have a built-in LVC for NiMH at a lower voltage than the Lipo LVC. The NiMH cutoff is always enabled regardless if the Lipo one is enabled with the jumper.

[No Slack 622]

My NiMH packs work always (different brands) however two HPI packs were gone in a year. I always discharge my packs after use with a discharger to 5.4V, let the packs rest for a few hours and charge them again for storage (or use). Mostly with 2C. If not in use I cycle the packs every 2 months. Of course over the years there is some loss but it is marginal. The point is: use the packs and they will be good. And buy recently produced packs as they have a shelf live.

[OoALEJOoO 3663]

Thanks for the comments.

I see mixed feedback about whether discharging is good and bad. I have only done discharges during this trouble shooting, and that is to 6V, which I understand is not 100% discharge & still safe. Before that, I've only run the batteries until the cutoff triggers, then charge them after they have cooled down.  

9 hours ago, sosidge said:

10+ volts at the end of the charge means the battery is shot (or was not good to start with). 9-ish at peak would be normal.

The charge voltages on my batteries end at around 10.5V right before the peak triggers. Once the battery is removed from the charger, it's about 7.8V when the warmth is out. This is charging at 0.5C. Your experience of 9-ish, at what C is that?

22 hours ago, Ferruz said:

Last year towards the fall I purchased a couple NiMHs packs, I believe it was on scamazon, and was pleasantly surprised by their performance. High discharge rate makes a big difference for people that are still on NiMH... that, plus they haven't skipped a beat so far and behaved well throughout the winter months. It you want I can find out what they are later and send you a link.

I'm tempted to try those, do you remember their brand or have a link?

[Ferruz 13732]

Sure! I'll search for the link and PM it to you (I never understood if posting links  to sellers is ok or not), anyway the brand is Flylinktech, way less good sounding than how good the product actually is 

[Tamiyastef 3086]

Well, I used (and abused) NiCd packs BITD without any trouble. When I got totally back into the hobby there were only NImh packs available, we never got along. They charged or they didn't (I guess depending on their mood of the day), they worked somehow (but never at the level of the old NiCd's) It was totally random in my experience. I'm now really enjoying the Lipo progress.

[OoALEJOoO 3663]

Thanks for all the comments. Looks like I was able to revive almost all the batteries, not to their former glory but certainly close. The 2x Awanfi 3600mAh are dead though, all others seem to be back to their original punch while having a tad less capacity.

What I did was perform 2 discharge & charge cycles at 1C, which is higher than the 0.6C max I did in the past. I guess the heat helped.

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