NiMh battery/cells query

[Damo666]

Hi guys. Since i've received some real good answers to my previous subject, i though i'd post another question in the hope for some " real life " answers; I have some NiMh pp3 batteries here that i'm charging at 1/10c as i believe this is the best charge rate for longevity if i'm not mistaken. They've only had 3 charges upto date. My question further to this is; Should i be completely depleting these batteries prior to charge just like the good old NiCd variants, or should i just bung 'em on charge after little use? Googling for answers brings a variety of answers all of which i can't weigh up! All the best regards from Manchester, UK. Damian.

 

[RCinFLA]

NiMH are charged similar to NiCads. There is no crystaline memory issue with NiMH so you don't need to discharge them down like NiCads.

They can take continous 0.1 C charge but it is better if you can take time to do them at a little lower rate or knock down rate after fully charged.

They last longest if used between 30% and 80% charge capacity. They have higher capacity for same sized battery then NiCad and a little lighter in weight.

NiMH have an even higher self discharge rate then NiCads (which are bad enough). They don't reach their full capacity until five to ten cycles when the cells are new.

 

[MrAl]

Hi,

Lets not forget the low self discharge NiMH cells, which have very very low self discharge so can stay charged for a year or more and still be usable.

 

[edeca]

There are some good pages that discuss this in much better detail than we could here:

Charging NiMH Cells
Battery Chargers and Charging Methods
How to charge Nickel Metal Hydride Batteries.

There are also a number of very cheap charger ICs if you are building a proper circuit. Let me know if you'd like me to dig out details of the ones I've got.