A good nimh charger doesn't rely on the actual voltage, but on how the voltage change over time. When the battery is close to full, the voltage increase starts to slow down, then when the battery is fully charged the voltage actually drop a little. A good charger detects this and halts the charge then. Look up -dV/dt for more information. Search for "Negative delta V nimh".
So the same battery charged to a slightly higher voltage may have less charge than the same battery charged to a slightly lower voltage, because the charging was halted too early. Or there never was a voltage drop detected and instead the charge stopped when the battery started to heat up, and perhaps take damage, because it couldn't take any more charge.
However there may not be any dip in voltage when the nimh battery is full. That depends on the charge current and the battery. A higher current may help to make the dip more noticeable, charging a nimh using a lower current may lead to overcharging and overheating and even damage to the battery. Older nicad had a more pronounced negative delta V.
A few years ago no one knew how to charge lipos. Now it seems knowledge of NiXX charging has gone out the window.
SINGLE cell NiXX can be discharged to zero and be fine. (NOT packs, that can lead to permanent damage).
By definition a fully charged NiXX gets that way be being OVER volted until it’s full. You can’t set the voltage, the charger figures that out. You just set the current, and the termination if the charger has that setting.
Apology-I missed that. So much for careful reading.
All those batteries appear to be charged and fine at that capacity and voltage. Have you tried checking voltage 24 hours later? Even with LSD they will drop noticeably.
Accuracy of the capacity ‘meter’ on any of these chargers is speculative IMO. I have found reasonable consistency for capacity (as defined by me as good enough…. :bigsmile: ) on the same charger, but not between chargers. My Opus and Accucel-6 are in the ballpark but certainly not consistently similar. OTOH if I do a number of cycles on either charger I can get different capacity results on the same battery. Having said that the inconsistency seems to be related to the quality/age/use of the battery > the older and higher the IR > the more inconsistent the results. This makes sense to me.
I also have an Turnigy 80W hobby charger and a Piranha dedicated NiXX charger. Both do a good job charging batteries. The Piranha only charges so I can’t do discharge testing on it but it’s a solid and versatile NiXX charger. The Turnigy is just a slightly ‘hopped up’ Accucel.
Frankly, and I would suppose this shows, I take all capacity measurements on these somewhat loosely as long as the charging is done well and safely and the capacity is is the vicinity of what it is supposed to be. For NiMh I allow quite a bit of slop, less so for Lithium but even for that the specs and reality often don’t line up. In addition IR goes up > and performance goes down before the actual capacity is much impacted. Capacity is not irrelevant but with lithium, and to a lesser extent NiXX, performance is my key parameter.
Ok, I re-ran some batteries through the Opus. It gave lower mAh that the Lacrosse on the AAA and AA batteries. I had to use 200mA discharge on the Opus as it was the closest I could get to the 250ma discharge on the Lacrosse. As before, the Lacrosse AA and AAA batteries tested out at the voltage the charger read while the Opus AA and AAA batteries tested higher than the charger’s voltage readings. I ran some 18650’s through the Opus and their final charge voltage read 4.18-4.2v but my two DMM’s read about 0.03v lower than the Opus showed.
I wonder how much cell resistance has to play in the voltage reading. Just seems weird it under reads the NiMh but over reads the Li-Ion. I actually have another charger on the way and I’ll compare the two.
