I haven’t really used the accucell to charge NiMh because I have a basic 4x NiMh charger, but I think the accucell missed the termination. It is set at default Delta Peak Termination. I read some old discussion on how a low C rate will cause this to happen more frequently. It was at 114F when I got back from running errands so I put a fan on it. It dropped to 102F pretty quickly.
I am discharging another cell, this time at 1.0A, 1.0V and I will try another charge at 2.4A for 1C. Any further tweaks I should try?
It was at 114F when I got back from running errands so I put a fan on it. It dropped to 102F pretty quickly! It read 1.46V on my meter.
Excess voltage is shed as heat during NiMh charging. Charging is a completely unreliable way to determine capacity. You have to discharge to determine capacity.
Think about those devices you have around the house hooked up and charging all the time (mobile phones for example). Those are charged at a very low rate and simply ‘shed’ the excess as a minor bit of heat. They never stop charging. There is no termination.
If the cell starts warming up during charging, it’s done.
IMO, absolutely do NOT charge those cells at 2.4A. These are high capacity, therefore high resistance. That’s simply asking for trouble.
Yes, if the charge rate is too low, the charger will miss termination. A lot of that depends on the quality of the charger, and the quality of the cell.
[note-a lot of NiMh cells and chargers are complete crap. This makes people have poor results and think the chemistry is terrible. What’s unfortunate is the junk that is being distributed and the wholesale lack of knowledge of how the chemistry works.]
I charge my Eneloops at 0.6A. I would never go over 1A, ever.
These are not high power cells, they are high capacity. Think of them as ‘fragile’.
I haven’t messed around with the accucel 6 for a while, but I vaguely remember there being an option for delta peak sensitivity. If you find it, try lowering the value to around 5mV/cell. I also suggest plugging in values for capacity and charge time just to play it safe.
Also, I’d avoid the fan cooling while you’re charging the cell. The cell should remain reasonably cool to lukewarm while charging without any assisted cooling; if the cell’s hot, there’s a good possibility that you’ve either missed termination or that there’s something wrong with the cell.
And until we can establish that the charger can properly detect charge termination at a lower charge rate, I’d leave the charge current at 1.4A or raise it as you mentioned earlier.
I just grabbed a fresh cell from the package. I will charge it from 1.26v full at 0.6A. Then, I will discharge at the two rates you recommended above for Capacity and Amps.
It is at Default setting now, it has a range of 5mw to 20 mw. I switched it to 5mw.
edit - Default Username - Thanks for the info. I just saw that you posted while I was typing. I guess I made one change you suggest and one change Flydiver suggested. I will try to get over this learning curve so I can post some reliable info. I didn’t expect so many snags along the way…
Sometimes encountering snags is part of the fun! Just exercise a little bit of caution and be aware of the charger’s surroundings; don’t keep the charger in an area where a fire could cause trouble, and keep in mind that the fumes released from a vented cell are not particularly healthy
Somehow people seem to have the idea that Lithium charging is difficult and NiMh is easy.
It’s actually the opposite. The nature of termination for NiMh using smart chargers is quite a bit more difficult than lithium.
But, if you screw up the consequences for lithium are much higher.
Having said that SLOW charging NiXX at 1/10C is very easy and quite safe. But people think it’s slow and unreliable. Yeah, it’s slow, but it’s VERY reliable and often superior, especially for forming new cells and balancing out packs.
It will always miss the dv/dt termination for one nimh cell, but 4 in series is fine
I also use a temp probe and that will cutoff charging as the cell/s heat up - but I'm using that as a backup to dv/dt. I haven't changed from the default dv/dt setting for nimh as that works.
see this thread for huge amounts of info about the Accucell 6
there are 228 pages in this thread and it's worth reading if you have a Accucell.
I do single cell testing with mine all the time. Works fine on ‘most’ cells, for me. On old ‘crapped out’ cells…not so much. But, that’s generally what I’m trying to determine.
I am aware that on these low cost hobby chargers there can be variations in quality of components and certainly in assembly. I may have lucked out with a good unit.
In the case of the IMAX B6 there are a lot of fake copies of that charger out, and some of those are simply junk and won’t charge NiXX at all.
The thread I mentioned has many comments about it not being consistent with a single cell, which I had accepted as my main use of nimh is to charge sets of 4 AAs for the camera.
Ok, I am working towards helpful info but I don’t think I am there yet. I tried to use 0.6A for the charger but it just hung around 1.46V while charging for a long time, I had to interrupt it to leave the house, restart it etc. So I don’t think that was a good charge. I decided to discharge it anyway. It was at 1.39V after resting, so I discharged it at 1.0A, 1.0V (is 1.0V the intended final voltage?). As you can see, it discharged for 2 hours, releasing 1971mah to a detected Voltage of 1.39. It terminated here. I didn’t stop it. When I checked it with my meter, I found it was at 1.22V.
I am going to discharge (1.0A, 1.0V) another cell that I charged on my Mach1 Speed Charger. http://www.lenmar.com/Uploads/File/Manuals/MSCAA.pdf.
When I started this discharge, it was at 1.349V. I think I found it had terminated it’s charge to 1.39V yesterday. Isn’t this a little low?
not sure about what all that testing means. Has anybody bought any of these? They look sufficient, or better possibly, and much cheaper than Loops. I will either try some of these or get the ones at IKEA, which I think were recommended.
I got some of the EBL 1100mah AAA. On the first 700ma discharge through the OPUS BT-C3100, I got 1007mah from 1.4v to 1.13v. The 2nd discharge got 1096mah. I believe that makes this truly the highest capacity AAA around, so I have little doubt that the AA is truly 2800mah now. That is very impressive in itself, but even moreso when you consider these are priced very low.
The EBL 18650 2600mah did not do as well. They are the worst-performing 18650s I’ve ever gotten as they only got ~2150mah @ 1A discharge.
First discharge at 700ma via Opus has minimum of 2513mah and max of 2602mah.
Second discharge at 700ma via Opus has minimum of 2582mah and max of 2617mah.
I cannot say whether or not these are low self-discharge or not, but I did retest a couple of the EBL AAA after 3 weeks. They had 950mah left with 700ma discharge. I don’t think I cycled these batteries though, so I don’t know how helpful that is.
