Can keeping charging cells too cool cause end-of-termination problems?

[Turbo DV8]

Oops. Can't edit a title, and I realized I meant "termination" or "end-of-charge" problems, not "end-of-termination!"

I have three La Crosse BC-900's and a Maha 808 charger. Because of the old BC-900 overheating issue, I have a muffin fan installed over the Maha and another directly over the bank of three BC-900's. I am not worried about the Maha overheating, I just figured that cooler is better, right? I am noticing with some frequency that cells in both brands of charger will not terminate until I turn the cooling fans off. It is easier to track on the BC-900 due to the voltage display. For example, with cooling fan on, my AA Eneloops will charge up to about 1.53v then just hang.. and hang, and hang some more at that voltage. Within five minutes of turning the fan off, they all terminate. Once or twice could be coincidence, but it is too frequent and repeatable. I now do not use the fan on the Maha, and when using the fan on the BC-900, I monitor the voltage and when it gets close to 1.5 volts, I turn the fan off. If I can't be around to monitor the BC-900, I don't use the fan at all. Which kinda defeats everything!

I know that the BC-900 has temp sensors to cut charging if temperature exceeds some value, but any ideas why keeping the cells cool might cause end-of-charge detection?

 

[VidPro]

i am the one that suggested that a cooling fan might not be the best thing to put on these chargers that are "calibrated to work without one".

ya see the ammount of change of the voltage drop and all, is a time/quantity thing, if the battery doesnt heat (as much) the battery doesnt v-drop as much, and it could cause missed termination.

NOT because you cant make a charging alogrythm that works with a fan cooling, but just because the unit isnt designed with a fan in mind at the time.

so here is the basic idea and logic (which might be totally wrong, but thats how it seems to me).
at the end of the charge for the battery, the cell goes into a overcharge state, Temperature rises, Pressure rises, and the voltage drop, IMO this is BECAUSE the battery is starting to get damaged, its not taking the charge, and HEAT is being expeled instead of the energy going into chemical changes. the heat and pressure (probably due to gas) causes the chemicals to change the resistance or something, whatever it causes an Anomaly.

so which comes First? the Heat, the temperature , or the pressure, or the overcharge state?
Well who cares which came first the problem is if you change that somehow , then the computer will not see the MINOR change in the battery, in the time it allots for doing that, and it will not terminate properly.

BUT , if the pressure didnt rise, and the temperature didnt rise, and the Voltage Didnt drop, DID the battery even REACH the overcharge state?

well the battery IS still fully charged, your just dissipating the HEAT off the battery, the energy going in that is still no longer being "stored" in the battery, its just pouring out as heat, and your dissapating that heat off of it.

i think of it a BIT like a teakettle boiling, it probably isnt that way, but the pressure rises , when the temperature (from the heat) gets to high, and the battery internally changes. if you cool the teakettle it will never whistle.


analise:
1. did you get a Voltage drop that the computer can see? NO cause the voltage is still high.
if the voltage was still dropping it could drop as far as 1.3v even with the charge on it.

2. is there a Limit on the total voltage that the unit can put out into the battery ? Yes, the total voltage the curcuits put out is limited. that mean the voltage differential between the battery and the charge voltage will be smaller, because of that at SOME voltage point the current to the battery will be slightly reduced.

3. is the battery being Damaged? #1 question. probably, the battery is still probably overheating in the part tight in the center, where your cooling isnt reaching. your cooling is not internal, there is still heat being produced in the battery, its probably getting very hot (baking) in the center. i have seen the center part of a ni-mhy cell get Brown from the heat.

TERMINATE ON TIMING:
so what can you do? use old timing methods, and stop the entire charge process, when there is nothing but heat comming out.
if the battery IS already fully charged, and your cooling is keeping the v-drop from occuring, WHY would you want to continue the charge till the pressure rises the temperature rises and the battery begins to faulter?
IF you knew it was charged and just not terminating, then terminate it Manually, there is no reason to smoke it so the stupid computer can read an occurance.

TERMINATE ON TEMPERATURE:
Monitor the temperature, when the temperature increases at an increasing level (even with the fan) , then your producing more heat than charge, and its done, terminate the whole process not just the fan.

TERMINATE ON VOLTAGE HIGH
when the voltage reaches a specific HIGH point, the charge IS basically complete, if you terminate the charge anytime it reaches 1.50V this would be charged for most good modern batteries. bad weak batteries with high resistance will go higher than that, better low resistance battereis will not even get that high.

RATE:
Increase the charge rate, in the 15 minute chargers Designed with a Fan, they put SOOO much energy in, that when that energy turns to heat, Even the fan can not remove the heat.
If your not getting terminations, and have a very low rate, then increase the rate, so a visable occurance occurs. of course with the risk of causing even more damage if it still does not terminate .

COOLING:
Decrease the flow of the fan, dont try and remove ALL the heat, so the damage is still done, so the teakettle still boils, problem is you cant recalibrate the computer to detect what now might be a Slower voltage drop.

the computer needs to see the battery faulter in a Time/quantity reduce this time or the quantity and the Present charger that your working with will not work right.

in there there is no Answer, only the puzzel itself.

the built in temperature sencors on most this stuff are not "connected" to the battery enough to be usefull in a temperature termination, they are only good enough to reduce a total disaster, and any cooling, even say putting it outside in the snow, would render the already almost useless temp seoncors , completly ineffective, even in a disaster.
only if they put the sencor very well connected to the battery will a temperature sencor have any value , like they do with ya "PRO" battery charge stuff.
even then, cooling the outside of the battery will cool the sencor, and the inside can still potentially bake , while the temperature sencor doesnt see a problem.
only if they put the Temp sencor IN the battery, could you cool everything and still read the heat deep in the battery itself.

 

[VidPro]

ahh one more

DECREASE THE RATE:
if you decrease the rate, to say c/10 or about 200ma, AND keep the cooling, you will have basically a "dumb" charger, and you can charge your average good modern battery for 16+ hours or so, and it will act like a dumb charger , and charge up and stay within spec for the cell and the cell will be able to handle the overcharge rate, without going into an overcharge state.
so it wont get to hot, or be to hard on it, it will not terminate, and it really wont have to.

this of course wont work for AAA batteries unless you can get even lower, like say 100ma (with the extensive cooling)