Need help with Ni-Mh cells

[whiplash]

Sup guys, everyones converting to lipos, but I cant afford that right now, I just got into boats, I used to fly, when I got in, Lipos where the way to go, so I did research on lipos every night and all I know is lipos. So my buddy gave me some ni-mh for the time being, and Id like to care for them properly till the lipos come in.
I also got some new 6 cell packs in pairs, and Im going bonkers trying to find the best way to cycle,charge, and discharge them. All inputs would help. Can you charge say a 3600mah pack less than 3.6 amps? someone told me the amps flows down so you need to charge 3.6 and above........huh? Thanks guys.

[ED66677]

Here are some basics you need to know about Nimh... I'm not an expert but still, 25+ years in RC!

Charging : assuming that you have a DeltaPeak charger (that detect when the battery is full), max charge is 1C, 1C means if you have some 3600mAh (3,6Ah) the max charge current is 3,6Amp, so you can't (you can but should not) charge in less than 1 hour, for a new pack I'd recommand to charge at 1/10C so 360mAh, you will need to cycle these cell for 3 or 4 times before they are fully charged

Discharge : in the best case Nimh cell are given for 10C so that's 36Amp constant for a 3600mAh cell, if you pull more than 10C you will reduce the lifetime of the cell, that's the major issue in fast RC boat, because these are those who pull the highest amp compared to RC car or RC plane, but very often we pull more than 10C because we don't have other solution... except Lipo's witch are up to 30C $$$

Maintenance : some guys use balancing device ( i.e 10 every charge) to have every cell of a single pack at the exact same voltage, voltage difference in a single pack cause higher voltage cell to be over charged compared to lower voltage ones, I personnaly don't do it, but cycling 3 or 4 times batteries at low amp (charge/discharge) tend to balance them as well

Once a battery is full, I keep it charging at 1/100C to 1/50C, Nimh cells tend to discharge while stored!

[whiplash]

God I hate metric....Im usually good at this...ok 3600mAh is 3.6Ah, = 3.6amps. So for new cells 360mAh = .360Ah = .36amps per hour?

Now I have noticed that when I charge my used packs at their 1C rate, It finishes
inunder an hour at 3.6 amps. and there hot, which leads me to believe that I should drop the charging amps. which means that 20-30 min. charges at the lake is out of the question?

is that why guys come to the pond with plastic cases filled with match pairs of
ni-mh packs? Like 6-8 pairs. They go home and charge during the week? heh heh.

[ED66677]

you got it Whiplash!

when I charge my 4000mAh pack @ 1/10C they are cool and get more than the nominal, very often I get 4200mA!!! but at 1C they only get 3,8A

Nimh cell like to be hot or warm when discharging, that's where they provide more power, so some guys do charge them, as you said during the week @ 1/10C and "boost" them at 1C just before using them, that's what I do, I think one guys down here did show a picture of the inside of his truck, he's got a little oven to keep packs warm!!!

[bobswworld]

Thank You for this whiplash and Ed66677, This sounds like it will fix my problems as well, I was just using what my mrc959 charger was picking for charging. But I noticed a severe decrease in run time and just overall power. My posts are under Aquacraft775 prop selection.
I will take and try this info,
Thanks

[ED66677]

glad to help!
that's why are all here, help or be helped!

[Fluid]

Now I have noticed that when I charge my used packs at their 1C rate, It finishes inunder an hour at 3.6 amps. and there hot, which leads me to believe that I should drop the charging amps. which means that 20-30 min. charges at the lake is out of the question?

The cells should be hot when charged at 1C, around 120F for a good pack. This is perfectly normal and hurts nothing - no need to charge at a lower rate (see below). Charging at 1C means a dead pack will be recharged in about an hour. There is no safe way to hurry this up. BTW it is best to charge right before you run because NiMH cells have a higher voltage at higher temperatures. Just do not exceed 150F on the cells at any time.

It is a very good idea to balance packs periodically at about 1/10C. If you do not do this, eventually your packs will be so out of balance that individual cells will overheat when charging. Store your packs fully charged, and recharge them every month if not used. Do not trickle charge NiMH cells for long periods of time.

.

[whiplash]

Ok i think I got the charging down, Im sure of it, but I want to be sure that my new packs are prepared corectly, for longevity.
So, when I first get them I should charge at 1C....discharge.....charge 1C..... discharge......than charge at 1/10C till full?
If this is corect what should be the discharge rate, and min volts per cell? and do I let cool in between cycles? (refering to same 3600mAh 1.27v /cell).
Thanks guys on this...

[whiplash]

check out thread by Doby, "lets see what we all look like"
if you care to see what whiplash looks like..............one of the last post. heh heh

[Rex R]

when you get your cells, the 1st charge should be 1/10c. this will let each cell reach full charge w/o overheating any that may already be at or near full charge. 5 to 10 amp discharge till you reach 1volt per cell(6volts) measured under load. recharge at up to 1c. note you may notice that the packs don't have full capacity the 1st few times you run them in your boat, this is fairly common and should go away after 3-4 runs. also bring the boat in when you 1st start to notice it slowing down don't wait for the esc to 'cut out'.

[whiplash]

Thank you Rex, I like all these infos, anyone else got more they want to add?
please do, all this info can save alot of newbees like me alot of money. Thanks guys.

[ED66677]

Just follow what RexR said!