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-   -   Charge rate for NiMH AAs in Tx (https://www.rctech.net/forum/radio-electronics/421691-charge-rate-nimh-aas-tx.html)

G33Kster 07-31-2010 04:18 PM

Charge rate for NiMH AAs in Tx
 
I just went and got some rechargeable NiMH AAs at Target (didn't want to wait for a HobbyKing order, and the cost of shipping would make them near-equal $). They are 2450mAh so I figured I'd use the charge port on my Tx and hook it up to my RC charger with the NiMH mode, then charge at 2.4A (pretty much 1C). However, I looked on the side of the AA and it says "Standard charge 245mA for 16h." Can these AA cells really only be charged at 0.1C, or do they just charge at a low rate to save energy/draw low power from the charger? I'd rather not wait overnight for a charge on my Tx, but I guess it isn't the end of the world if I do :rolleyes:

bluechucky 07-31-2010 04:31 PM

I bought some from aldi and have been charging them at 1C with no problems through my transmitter (DX3S)

Xmod_Racer 07-31-2010 04:32 PM

I charge all my AA's at .8 amps, that seems pretty good. Theyre warm when they come off the charger

G33Kster 07-31-2010 05:20 PM

Thanks guys. I'm starting out charging in Auto mode with a max of 1.2A (0.5C). In your experiences, how long do NiMHs last in a Tx per charge? Since the nominal voltage of an 8 AA Tx pack is 9.6V, and the Tx starts beeping (at least for me) around 9.4V I think not long. What's the fully charged voltage of an NiMH cell anyway?

Duster_360 07-31-2010 05:50 PM

Rechargeable AAs fast charge is 1.0amp, slow charge is 0.5. You can charge them at 1C, but exepct life to be short, these small cells don't tolerate the heat well and you basically cook the life out of them at 1c rates charging at 2+amps.

I get 5+ yrs use out of my AAs charging at much as I can at 0.5amps. I fast charge at 1amp only when I'm in a pinch for time.

G33Kster 07-31-2010 06:01 PM

Thanks, I'll keep that in mind. Should I be doing a discharge/charge cycle every time to combat the memory effect, or are newer NiMHs better about this? I don't have much experience with Ni-cells because I first got my Evader when I was around 7 years old and I ran it on NiCd 6-cell packs, but never really payed attention to how I was charging them (I also think that I would put the 1500mAh packs on the quick charger and turn the knob to 6.0A because everyone knows more amps is always better :sweat:). When I recently got into the hobby for real at the beginning of the year, I switched to BL and LiPo, hence my lack of experience with this stuff.

Duster_360 07-31-2010 06:15 PM

If you're only disch them less than 1/2way, then I would finish disch before I re-charged. These still have a memory prob if you treat them the same over several cycles. I disch mine to more than 80% most times, so I don't disch them every time.

I do disch them about every 4th or 5th cycle though.


When these are fully charged, NiMh cell voltage will be 1.4+v and good ones will be close to 1.5, so that 8 cell pack will start out at 11.6+v. It will last a while, longer than you thought anyway. The 1.2v/cell value is a nominal value, a lot like lipos 3.7v/cell. Both charge to higher values.

If you really want your NiMhs to last between charges, buy some of the new low self discharge rechargeable NiMhs. I've been using them since Feb and have only charged them twice. The main prob with rechargeable NiMh is their self discharge. LSD NiMhs eliminate that, now voltage drop is pretty much just what you actually use.


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