charging nimh
- Thread starter roadie
- Start date
Help Support Candle Power Flashlight Forum
Carpenter
Enlightened
Not an expert here, but an AC/DC converter will not have a charging circuit required to properly charge NiMh batteries. You'll need a charger.
If you want to do it right, look for a charger that uses single channel instead of dual channel, that way every battery gets proper attention from the charger.
If you want to do it right, look for a charger that uses single channel instead of dual channel, that way every battery gets proper attention from the charger.
You actually can, the slower the better. Some newer radios and phones that come with NiMH instead of NiCad are still using the same trickle charging circuit. You calculate the charge rate at 1/10th the battery rating IIRC then put a series resistor to limit the current and time the charge so as to not overcharge. Its not the best for the batteries and you will overcharge them some, which is hard on them, but the slow charge rate makes it less bad for them. Just don't expect 500-1000 cycles from them charging them this way.
MrAl
Flashlight Enthusiast
Hi there,
Normally you would use a smart charger, or even better yet one of the 15 minute
chargers out there, which charge up the cells in 15 minutes which is really nice.
You can use a dc wall wart to charge the cells by using a series resistor to
limit current, but you must watch the time carefully so that you dont overcharge.
The resistor would be set for something like a 20 hour charge time.
You can use a faster charge rate if you monitor the temperature of each cell in
the pack. If one starts to get very hot, stop the charging.
You can also charge faster if you are willing to monitor the terminal voltage
and you can use a constant current circuit with your wall wart. With this
method you look for a drop in terminal voltage while the cells are charging.
Once you see about 30mv you stop the charging.
This method is a bit more complex because it requires a constant current
circuit that connects between wall wart and cells.
Normally you would use a smart charger, or even better yet one of the 15 minute
chargers out there, which charge up the cells in 15 minutes which is really nice.
You can use a dc wall wart to charge the cells by using a series resistor to
limit current, but you must watch the time carefully so that you dont overcharge.
The resistor would be set for something like a 20 hour charge time.
You can use a faster charge rate if you monitor the temperature of each cell in
the pack. If one starts to get very hot, stop the charging.
You can also charge faster if you are willing to monitor the terminal voltage
and you can use a constant current circuit with your wall wart. With this
method you look for a drop in terminal voltage while the cells are charging.
Once you see about 30mv you stop the charging.
This method is a bit more complex because it requires a constant current
circuit that connects between wall wart and cells.
I don't care for the 15 minute chargers, got to handle a couple in stores and the batteries were quite warm, I'm not sure if they exceeded the specs or how close they were to the max temp spec but I prefer to charge slowly to extend the lifetime of my batteries. My 1 hour charger was getting batteries too warm for my comfort so I bought a maha which can charge in an hour or 5 hours and normally use the 5 hour setting.
My circa 1998/1999 HP CapShare came with a simple charger which just plugged into the wall and slowly charged via a simple resistor, and would keep charging as long as it was plugged in. Those old 1650mAH original batteries it came with are still in use today. Newer cells with higher capacity are more picky on overcharging but the basic rule of thumb is the lower the overcharge current and lower the temp the more they can tolerate. So if you design your circuit to achive full charge after say 16 hours you can pretty much leave them on for many more hours.
My circa 1998/1999 HP CapShare came with a simple charger which just plugged into the wall and slowly charged via a simple resistor, and would keep charging as long as it was plugged in. Those old 1650mAH original batteries it came with are still in use today. Newer cells with higher capacity are more picky on overcharging but the basic rule of thumb is the lower the overcharge current and lower the temp the more they can tolerate. So if you design your circuit to achive full charge after say 16 hours you can pretty much leave them on for many more hours.
MrAl
Flashlight Enthusiast
Hi again,
I didnt like the cells getting hot either, but in the 15 minute chargers they have a
fan and that helps. After being able to charge in 15 minutes i would never want to
go back to 4 or 8 hour charges...never.
I didnt like the cells getting hot either, but in the 15 minute chargers they have a
fan and that helps. After being able to charge in 15 minutes i would never want to
go back to 4 or 8 hour charges...never.
Last edited:
VidPro
Flashlight Enthusiast
you can dumb charge with a proper voltage of wall wart, as long as when it gets to the top voltage its at a rate that is well below overcharge for the cells, AND the cells are in ok shape. just takes time.
