bradford336
New Member
Hey all! I am trying to come up with something better than a halogen bulb and a timer to discharge my NiMH battery packs. I use 6 Volt 5 cell packs ranging from 1400 mA to 2400 mA in R/C airplanes. I understand that they need to be discharged to 1.1 V per cell so 5.5 V total. I want the discharge to take around 2 hours. (if the pack is fully charged) This way I can judge the flight time I can get out of them.
I have seen circuits using 7805 regulators and just having them operate a load through a relay until they reach 5 volts and unlatch due to the regulator losing power to operate.
I have seen comparator circuits which I like but am unsure about which calculations I need to do in order to get what I need. They are a better choice for me though since I can use trimmer pots to adjust my load.
Can anyone help me come up with a happy median? I would like something fairly inexpensive and simple but still be able to adjust the load for which ever pack i am discharging. A circuit which would allow me to add a timer and possibly a charging circuit later on maybe.
Let me just say I know a lot of people say not to discharge NiMH packs because they only have so many usable cycles. I do not use them for electric motors I use them to power radio equipment. Although they do not have the memory issues like the old NiCd packs I still like to occasionally check run times. The purchase of a new pack is better than watching my gas powered plane fly into the sunset with dead radio batteries.
I was wondering about doing the 7805 regulator circuit with simply putting a resistor between the pack and the regulator to make the 5.5V cut-off I want. Would this suffice for now? If so what would be the best way to calculate the R value?
I would really prefer the comparator circuit though.
Any help would be so greatly appreciated. Thank you for looking at this post.
I have seen circuits using 7805 regulators and just having them operate a load through a relay until they reach 5 volts and unlatch due to the regulator losing power to operate.
I have seen comparator circuits which I like but am unsure about which calculations I need to do in order to get what I need. They are a better choice for me though since I can use trimmer pots to adjust my load.
Can anyone help me come up with a happy median? I would like something fairly inexpensive and simple but still be able to adjust the load for which ever pack i am discharging. A circuit which would allow me to add a timer and possibly a charging circuit later on maybe.
Let me just say I know a lot of people say not to discharge NiMH packs because they only have so many usable cycles. I do not use them for electric motors I use them to power radio equipment. Although they do not have the memory issues like the old NiCd packs I still like to occasionally check run times. The purchase of a new pack is better than watching my gas powered plane fly into the sunset with dead radio batteries.
I was wondering about doing the 7805 regulator circuit with simply putting a resistor between the pack and the regulator to make the 5.5V cut-off I want. Would this suffice for now? If so what would be the best way to calculate the R value?
I would really prefer the comparator circuit though.
Any help would be so greatly appreciated. Thank you for looking at this post.
