Thanks for the tips and keep them coming please. I thought I remember reading a while back about not using your batteries right after they come off the charger? Something about waiting one day to let the voltage drop a bit???
This only really applies to situations where you are using a battery chemistry that has a tendency to have some voltage settling after charging, IN CONJUNCTION with a direct drive bulb setup that is pushing the bulb to the limit anyways. Resting cells, especially NiCD and NiMH cells, will reduce the likelihood of burning out that bulb prematurely. I have personally observed a voltage settling tendency in my collection of 10 Emoli 18650 size LiMn chemistry cells. After ~24 hours they tend to settle to ~4.10V, another few days and they settle to ~4.08V. I have tested their runtime into various loads and they are performing as they should be, so the cells are in decent condition. As a result of my observation of this voltage settling tendency, I have made the suggestion to users of LiMn cells who are planning to drive something like an MN21, to let the cells rest to reduce the chance of blowing that expensive bulb...
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niconical said:
I have a question along these lines. It was never worth it's own thread, so here will do nicely.
I often see people mentioning "pull them off the charger when they reach xx volts", but how do you do that? I am in the habit of fully charging, then using a light to drain them a little, check cells after they have rested, drain some more, repeat, then get them resting at 4.1v that way.
Can I touch the + and - ends of the battery with my multimeter while it is still being charged?
I saw something in a thread a while back that implied I could, but I've never really been sure.
I use my DSD more often than not, it actually has the contact pins for the cells "exposed" from the top, so I very frequently just take the probes from the multimeter and put them right on those pins on the charger to see what the charging voltage is at. Keep in mind that the actual cell voltage will almost always be at least a few hundredths lower than the charging voltage, depending on cell size and charge rate and what charging phase it's in. Small cells charged fast, like an RCR123 in a Pila IBC, will have a charge voltage of probably 0.1V higher than the actual voltage of the cell through the Constant Current phase of the charging. A larger cell, like say, an 18650, on a slower charger like the DSD, will only be like maybe 0.03V lower than the charge voltage... It will take some experimenting, but you can get a feel for when to pull them by testing on the charger, seeing what voltage it is at, then just go ahead and yank the cell to see where it's really at, then resume charging is you want to... On the Pila charger, since you actually have a Constant Voltage phase, once the charging voltage reaches 4.20V, it will just hold it there, and the current flowing into the cell will taper off as the actual cell voltage tries to find equilibrium with the 4.20V of the charger.
I find myself checking charge-voltage mostly just to keep mental track of how much longer before I need to come back and check on them again. I will usually pull cells when they are over 4.15V charging voltage if I catch them in time. The very end of the DSDs charging algorithm brings em to about 4.22V, after which point they usually fall to ~4.10-4.16V depending on the size of the cell and how new it is.... so that's plenty acceptable to me.
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etc said:
I will try timing charging AW cells with Pila, e.g. the cell is at 3.5V and it should take 2 hours to charge to 4.1V (as an example, I don't know the exact charge time).
Problem is, the cell will be discharged to various capacities, sometimes 3.5, sometimes 3.8V, whatever. So there is no constant time.
Maybe there is a formula you can come up, say charging every 0.1V takes xx minutes.
I am afraid however it's not a linear equation so probably wouldn't work very well.
You're right, it's not perfectly linear, and there probably isn't any perfect way to setup a timer to prevent a full charge. Best way to do it is to get a feel for charging time, check cell voltage during the charge from time to time, and yank them before the charger has a chance to top em up all the way manually. Or get a more expensive charger...
In theory, one could probably set up a pretty simple circuit that would cause a voltage drop to the cell, such that the charger would terminate normally, but the resulting cell voltage would be a little lower. Maybe one of the Electrical Engineers on here could tell you how to do that. I doubt it's hard. Probably just a certain type of diode would do the trick.
Eric
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