Charging / cycling NiMH batteries (4.8V, 2000mAh)

[dr wogz]

Help needed: Battery charging 101 / for dummies

OK, so my other hobby I’m trying to get back into is R/C flying. And I have a new battery charger that I initially got for my other toys. I hate charging batteries. All I’ve found to read either deals with big batteries, theory, or just seems so convoluted, that I give up. (My head is mechanically oriented, so batteries & other assorted “electronics” seem to be just fuzzy magic.)

I just have one type of NiMH battery I want to charge.. a 4 cell 4.8V 2000mAh battery; typical of R/C Radio receivers (4x ‘AA’ sized 1.2V cells)
(I have LiPos, and these are no issue.)

I am trying to charge / cycle this battery. My charger is a recommended “B6 V2” by HT-RC. Based off the popular IMAX B6 style..

I’m also trying to put together a “settings & procedure list” for charging these.

I’ve been told to (once I receive them / new batteries):
Fully charge them
Cycle them 3 - 5 times
Use them,
But discharge them before fully charging them again. And the discharging can be done periodically.

I’ve been told to charge them at 10% of their rated capacity. So, at either .2A or .4A for a fast charge.
I’ve also been told that these batteries don’t’ peak detect too well, so to set my ‘capacity cut off’ to just over their rated capacity. Over-capacity is set to 2100Ma

Discharging should be set to 1.1v/cell.
The charger 'discharge rate' is 2A, and the voltage / cells seems hard fixed to 4S / 4V: 1V/cell

But, after a full charge, I try to do a discharge, but it immediately times out as the rated voltage at this point is below some threshold: it blinks 3V / 3.76V. Are these considered DOA? Did I strike out, and actually have 3 straight ‘bad’ batteries?!


I’m also trying to figure out what:
NiMH ‘Sensitivity’ / D-Peak is, it’s typically set to 7mV. How does changing this affect charging; discharging?

NiMH Discharge TVC is, it can be changed, but jumps in steps, from 500mV to 1000mV in 100Mv steps. And I assume this is where I would set my cell discharge voltage to 1.1V/cell. It seems to be set as 1V per cell, not the 1.2V it should be set to. And there doesn’t seem to be a way to change this.

Is it the charger? And is there is some other setting I am missing?

Any and all help is appreciated..


http://ht-rc.com/productshow.asp?id=185

 

[OverTheTop]

AFAIK NiMH has a full cell voltage of 1.2V. A "discharged" voltage of 1.1V sounds a little high, but I can't remember the final voltage on those. Google should be your friend.

I would target a final voltage if 1.2V and charge at the 0.1C rate. Full charge will take over the ten hours due to efficiency of charging. That has been my experience with NiMH batteries in the past.

[edit] If you want good information on batteries you can go to something like the Eveready website and read up on the chemistry and how you need to care and feed it.
Here is some info on NiMH:
https://data.energizer.com/pdfs/nickelmetalhydride_appman.pdf
Yes, the end voltage they specify is 1.0V, so 1.1V mentioned earlier in the thread is too high.

 

[dr wogz]

@OverTheTop
thanks for the reply. (I was hoping more would chime in. but I guess it's the nature of the beast..)

"Google is your friend".. yeah, I did a lot of that, and found that other user forums provided more / better answers. But the amount of ads on the internet these days is just astounding. I have a hard time weeding thru all this crap.. so much so, that I just give up.

I'm also trying to figure out what questions / queries I need to ask in order to get the answer / info I want. Its great on the theory & such, little on the practical or help in troubleshooting..

I kinda feel like I'm trying to learn how to swim, and the instructor has gone over all the techniques, buoyancy in different water types, swim-suit styles, strokes, kicks, etc.. but we have never / will never put a toe in the pool..

/rant off

I do appreciate your response, and I'm just frustrated..


OK, so I still seem to have the same issue, a new battery, put on charge @ 0.2A and have D-Peak set at 6mV. It charged, for a few hours.
(the wife unplugged the charger once it started beeping, so I have no idea to the mA it got.)

I put it on discharge, and it immediately reads at 3.00v / 3.76V. So, my question here is: is this [another] failed pack? is it something in the charger? (Some setting set too high? too low?) Is this right? is this to be expected on new / fresh packs? this is the 3rd in a row, so I am suspecting some setting in the charger is off.. but what?

How do you determine if the pack is a DOA pack?

I have the discharge set to 2A and 4S: 1v/S, so it should discharge to 4.0V. But since it initially reads 3.76V, it's below that threshold.

Is it a dead pack, or just really drained, and I should set the discharge to 800mV/S or lower? (It's at 1000mV/S right now)


(and another case of a product manual that is barely useful to the the end user..)

 

[BEC]

If your pack is already at 3.76V with no load, it's pretty flat now. No further discharging needed.

Delta peak is a charging approach for nickel-based chemistry cells that takes advantage of the characteristic of these, under a fast charge (1C or more, typically 4C), for the terminal voltage to drop as they pass 100% charge. So, the "delta voltage" is how much you let that voltage fall (usually set on a per-cell basis). As the voltage drops, the cells start to heat up quickly and past a certain point they will be damaged.

NiMH cells are less robust, generally, than NiCds and so picking a delta peak level is dicier. They also self-discharge faster (just left sitting around) and they seem to be less tolerant of being left like that. I have some really old NiCds that still respond well (as in decades) but I've never had NiMHs last long....and now that LiPoly has taken over electric power I've stopped messing with them in other than consumer electronics like shavers and such. Here I get the slow-self discharge types (Eneloops and so on) and use the chargers sold for this purpose. I don't try to peak charge them or fast charge them using any approach.

Delta peak detection does NOT work at low charge rates such as the 1/10C rate you were using on your 2000 mAh cells. That's more of a just plug it in and leave it overnight kind of charge rate.

As for "forming" the packs—cycling them when new—I can't say as I stopped messing with NiMH cells when I started flying LiPolys (this is nearly 20 years ago now). And since what I was flying was electric powered, I haven't messed with receiver batteries for much longer. For transmitters, I just used the wall wart 1/10C chargers supplied by the makers or—in a couple of cases—replaced their packs with LiFe or LiPoly packs and used one of my FMA Cellpro 4s to charge them when needed.

What is the discharge rate of your discharger? A supposedly charged 4-cell pack falling to 3V under load right away sounds either overloaded or is made of junk cells with really high internal resistance or has at least one bad cell.

What is your actual application? Are you really using this 4-AA cell NiMH battery for a receiver pack? Your model is happy with lugging that 1/4 pound pack around? If you're comfortable with LiPolys, look into using a single cell for receiver/servo power. Most modern receivers and servos work fine at the ~4V of such a "pack".

 

[davel]

BEC gave you a good summary. If you haven't already been there, Battery University is a good site for info on all battery types. https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride

 

[dr wogz]

Hi All,

so I reached out to the battery manuf, and i got a reply (Yeah!!) now to decipher what they wrote.

any & all input is appreciated!

they wrote:

We think charging for several hours at 0.2A, the peak value of D is 6mv. It is unreasonable.
If the battery pack is out of power, it will take more than ten or more hours to charge at 0.1C.
We suggest to Set at 20-40mv.


OK, so.. D-Peak of 6mv is unreasonable, and they say 20-40mV, which I assume is their recommendation for D-Peak
I did mention I have charged it, yet they seem to say it is out of power..

I have read to not over charge it. I don't want to put it on charge again, after a number of hours already under charge.

2 likely faults / short comings with my charger:

• The timer is limited to 720 minutes / 12 hrs. Their cells say 14hrs at .1A
• D-peak is 20mV max. or "default" (whatever that is..) I can set it as low as about 2mV

Another local source says discharging at 2A is also likely an issue. discharge it at something much lower..

So, a lot to theory, and a lot of speculation & variables to play with.. Not too sure which to start with..

I am about to try:

• a discharge rate set to 1v/S, at 1A. maybe also at .5A to see what that does..
• Charging it with a D-peak of 20mV, with a cap cut-off of 2100mAh
• Plugging it into a wall charger, and set my cell phone timer for 14hrs..
• start looking for a new charger!
• start looing for LiPo 6V batteries with the 'JR' connector..

 

[dhbarr]

The way I read it was:

"If your pack is discharged and you set D-Peak at 6mv ( ~0.1C ) it will take > 10hrs to charge."

So next time you need to charge, if you set it at 30mv you should be in good shape, right?

NOTE: Not responsible for battery asplode.

 

[dr wogz]

OK, so it looks like discharge rate might have been too high. I've reduced it to 1A and they seem to be at a better level & are able to discharge.