NiMH Charging/Discharging questions

[noremacyug]

everyone talks about how to charge lipos and i understand why, as it can certainly be confusing. however, i just received my new multifunction charger today and need to know how to properly charge/discharge my 7.2v NiMH sticks. i've binged this issue as well as looked through the sticky here, but as i said, most everything these days are geared towards lipos. i think i have some idea and i might even be right. i just want some guru approval before i blow up a battery pack.

battery packs i have are, of course, both 7.2v 6 cell NiMH packs. one is a 3300 mAh pack and i'm awaiting a second 5000 mAh pack.

-first off, do i ever need to discharge the packs to a mimimal voltage for any reason? i've read that you don't want to over discharge them but i have seen safe numbers such as 1.0v per cell. so in my case i would assume 6.0v. from what i've read it is a good idea to cycle them from time to time and from what i gather that involves discharging them. am i wrong?

-second, what rate should i discharge the packs? my charger only discharges at a max of 1.0A. i would assume that would be no prob for the packs since my 3300 mAh would be 3.3Ah? and the 5000 mAh will be 5.0Ah? again, if i'm wrong or misunderstanding this please correct me. also, what is the rule of thumb here as i'm obviously just guessing.

-i guess lastly i need to know how best and what rate at which to charge them. i've read that c/10 is a very safe rate but is that necessary? my old charger that is being replaced is a radioshack "fast charger" and when i flipped it over out of curiousity regarding the power output it said that @ 7.2v it's output was 8.0A. my pack got a little warm when charging with the radioshack charger, but it never felt too hot, just warm. so i'd assume the max output of 5.0A of my new charger would likely be safe. however, i want to know my options for charging the packs, how they affect them and when to do what. for instance, if i'm not going to be running again for a day or two, i would assume a slow trickle charge would be better for fully topping off the cells.

hopefully someone can set me straight here as i've looked everywhere i can think of to get some solid info.

thanks

[WIDELOAD]

Answers in green mate.

Originally Posted by noremacyug

i just want some guru approval before i blow up a battery pack. Im not a guru, but if you blow up a nimh...GOOD WORK!

-first off, do i ever need to discharge the packs to a mimimal voltage for any reason? i've read that you don't want to over discharge them but i have seen safe numbers such as 1.0v per cell. so in my case i would assume 6.0v. from what i've read it is a good idea to cycle them from time to time and from what i gather that involves discharging them. am i wrong?

Nimh's ideally shouldnt be discharged past 0.9v/cell (5.4v for a 6cell pack).

Be aware as well that if this is a stick pack DO NOT discharge down that low (stick to 5.9-6v total). Or a cell will most likely end up dead and then you have a useless pack.
Race dischargers are designed for ladder packs and therefore could discharge each cell individually.

Cycling is exactly that, charge & discharge. Most modern chargers have this built in, but you can make a discharge rig up out of light bulbs (google it)

-second, what rate should i discharge the packs? my charger only discharges at a max of 1.0A. i would assume that would be no prob for the packs since my 3300 mAh would be 3.3Ah? and the 5000 mAh will be 5.0Ah? again, if i'm wrong or misunderstanding this please correct me. also, what is the rule of thumb here as i'm obviously just guessing.

If you discharge packs, most chargers only do it at 1A. The dischargers available for hardcore use do it at up to 30A.
Again, if in doubt make you work discharge rig.

-i guess lastly i need to know how best and what rate at which to charge them. i've read that c/10 is a very safe rate but is that necessary? my old charger that is being replaced is a radioshack "fast charger" and when i flipped it over out of curiousity regarding the power output it said that @ 7.2v it's output was 8.0A. my pack got a little warm when charging with the radioshack charger, but it never felt too hot, just warm. so i'd assume the max output of 5.0A of my new charger would likely be safe. however, i want to know my options for charging the packs, how they affect them and when to do what. for instance, if i'm not going to be running again for a day or two, i would assume a slow trickle charge would be better for fully topping off the cells.

The higher the amp rate you charge at the more punch you batteries have. Now with this it also shortens the life span of the pack as well.

Slower charge rate will increase you run time slightly but you will loose some punch. You cell's will also have the longest life span.