|   battery charger question | EP
Jan 23, 2003 9:49 AM | | ok, one more question, pulling a whole system together.
What V & Amp parameters matter when choosing a charger for a 6V 4500 mah NiMH battery pack ? Chargers usually indicate the output and I've noticed the voltage is higher than the pack, like 7.25V charger for a 6V pack. I mean, would a 9V or a 12V work too ? What are the limits to be aware of ?
And btw, what would happen if one uses a nicad charger on a NiMH battery ? |
| the pressure in the charger has to be higher than the pressure.. | clary.
Jan 23, 2003 11:58 AM | | in the battery or the electrons will not flow in the direction desired. A fully charged 6v 4500ma battery will exhibit a peak voltage of up to 7.3 volts so the charger must be rated higher than 7.3 volts in order to allow the battery to reach that voltage. Supplying too high a voltage, higher than the battery pack's voltage rating will damage the battery pack by trying to build up voltage higher than the battery's capability. Because of little resistance in a battery, you must also limit current. Attaching any DC power source will supply electrons to the battery at full capability, possibly destroying the battery if that capability is too high. NiMH can be recharged between 200ma (for like 16 hours of charging) to well over 600ma (for shorter recharging times) with proper circuitry to protect the battery from overcharging. Without limiting the current, a charger with high current output will heat and damage the battery pack and a charger with low current output will take longer to recharge the battery pack. Therefore chargers are supplied with a specific voltage and current capabilities to suit the batteries they are meant to be charging. |
| thanks very much for the info nm | EP
Jan 23, 2003 1:19 PM | | |
| re: last Q... | clary.
Jan 23, 2003 12:40 PM | | a NiCad charger will work on NiMH batteries if the NiCad charger is a dumb simple one (although the current is usually smaller than an equivalent NiMH charger). If it has detection circuitry (a smart higher powered NiCad charger), it might not know when to shut off or limit current (trickle) while charging NiMH batteries.
My idea is that it is better to purchase cheap dumb chargers ($5-10) than to pay for expensive smart chargers ($100s). The money saved can be used to build more batteries that can be fully charged and waiting to be used immediately rather than trying to recharge the exhausted one quickly and damaging them in the process (quick chargers reduce battery life). Slow charging allows the battery pack to attain maximum voltage while keeping the battery from any damage caused by quick charging. My 200ma charger will take 16 hours (from 10pm to 5pm next day) but the battery isn't even warm from the experience and receives a full 7.3 volts of charge. When I connect to a stronger charger (400ma) I get roughly 7 to 7.1 volts before the battery is hot. |
| have as many chargers as you have batteries you will use (nm) | clary.
Jan 23, 2003 2:00 PM | | |
| re: battery charger question | neng
Jan 23, 2003 2:30 PM | | EP
I've been following your posts, it seems like you are getting more and more into making battery packs.
You might want to think about getting this charger. Better value then the microbrute, can charge multiple voltages up to something like 19 volts, nimh, nicad, lithium-ion. It also has a timer and temperature monitor so its charge and forget. etc etc etc.
http://www.nimhbattery.com/mh-c777plus.htm
Although its $82 and then you have to pay shipping. I have found it to be my charging workhorse because its quicker and safer. I don't know what to do with all my other cheap chargers that are laying around. |
| wow, the Cadillac of chargers, thanks nm | EP
Jan 23, 2003 9:19 PM | | |
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