Optimal Cycling Rates for New NiMh's...

[EX Con]

For new NiMh cells/packs, MRC suggests a charge rate of 1/2C. For example, 4200Mah=4.2 amps, 1/2(4.2)=2.1 so charge at 2.1 amps for the first time. This sounds right to me compared to what I've read. My question is about cycling the same new batteries. What is the the ideal discharge rate for them after that initial 1/2C charge? How many cycles would you do before putting them into regular service? And, for future cycles, what rates would you suggest for both charge and discharge(say, a few months down the road or after several uses in the model)? For that matter, after the packs have been put into service, how do you determine when to cycle again? If there is a definitive link you could show me where most people can agree on the information they provide, please let me know...

[SPISHAK]

My question is about cycling the same new batteries. What is the the ideal discharge rate for them after that initial 1/2C charge?

I would also like to know the answer to this. I can't afford to make the lipo jump yet. Is a 1 amp discharge rate OK for nimh battery cycling? TIA

[Eggy]

The first charging should be done at 1/10C (4200Mah pack = 420mA) this is to balance the cells, and not 1/2C.

[Flying Scotsman]

Hate to say it lads buy lipos and a decent charger. Your credit card company will dislike you though
Douggie

[Fluid]

NiMH cells have no memory effect, so cycling only reduces the pack's life. However, Ni cells should be periodically balanced at 1/10C until all cells are warm - one cool or hot cell tells you the pack is not yet balanced. How often this needs to be done depends on the quality and original matching of the cells in the pack. Store partly discharged at 0.9 to 1.0 volts per cell.

I usually charged at 2/3C, otherwise cell temps could get excessive here in the South in summer. Anything over 150F is bad, at the beginning or end of a run. I've set plenty of SAW records with Ni cells and my packs lasted a long time, so my regimine works, but I'm not saying others don't.



.

[sjslhill]

Jay,

Did you really store them over the winter at 1.0V per cell and this worked? No lost capacity?

thanks,
Steve

[Fluid]

Hi Steve - I never stored more than a few months at a time. I always raced all year long, both in Alaska and here in Texas. I noticed no degradation of performance after storage once they were balanced and run once or twice at full discharge rates. But since they are self-discharing, if not checked periodically when stored their voltage could drop too low and they could have permanent damage. It's never a discharge-and-forget-it scenario like LiPos.


./

[SPISHAK]

I got a nimh 6 cell pack from my TC-3 that hasn't seen a charge in 4 years and still measures 7.5 on my volt meter. It won't fit in my boat, but is it still good? ima dummy....i admit ;>}

[Jimmy Sterling]

Spishak,

Although the pack may read as having a normal voltage on your meter, once under load I think you will find the pack struggles to maintain a nominal voltage if any.

The most prificient way of testing this would be to set up a rig so you can monitor the voltage of the pack whilst under load eg. small 12v light bulb and see how the pack handles.

You may find it is still O.K

Also, depending on how the pack is configured (stick or with bars) you maybe able to monitor each cell individually and find out which are 'duds'

Good luck.

Jimmy

[sjslhill]

I think that many of us will run a bunch of times and put the boats on the shelf for maybe months at a time. If you do this, I suggest you store your packs with some charge in them. Once you run again, do the C/10 charge and balance as Jay states. Our lakes freeze over here and I don't have an indoor facility to run in.

However, I have been considering what I am going to do....I think I am going to run either NICAD or A123 mayself. I don't like NIMH and I really don't like the idea of LiPoly. I know that LiPoly has the most power for weight, I just don't want the risk right now. I am going to run some 700 and 800 powertool motors, Astro 40, 05's on gearboxe(s) and 27T in my CB.

thanks,
Steve