NiMh or NiCd?

NiMh or NiCd?
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NiMh or NiCd? - 5/30/2006 5:30:54 PM

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From: Berwick, NS, CANADA
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Hello guys.

I have always used NiCds for my reciever batterys. Now I am looking into getting a 2100Mah NiMh from HiFlight R/C. What are the differences between NiCds and NiMhs? Can I use my Futaba wall charger to charge a NiMh battery? What about my quick charge? Also I am wondering if the 2100Mah NiMh is going to be a big heavy brick. Got to keep things light.

Thanks for any help.
Shane

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RE: NiMh or NiCd? - 5/30/2006 5:57:50 PM

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You get more mA for the ounce and size with NiMh and it's well worth taking advantage of this. If you can get sufficient mA for your day's flying from NiCd and handle the weight and size OK then it may be worth sticking with them as they seem to take more abuse and last several years as against two or so for NiMh.
I have generally moved to NiMh for the capacity advantage for both Rx and Tx and have no problems. The downside for me is that they self discharge more than NiCds and you have to adopt a habit of topping them up before a day's flying, whereas I'd fly with NiCds several days after a charge but the extra capacity /ounce/cell size of NiMh, wins hands down in gliders.
Your Futaba wall charger will do the job fine but a full charge of a 2100 mA pack will take 40 odd hours at 70 mA. They fast charge fine, up to 1C (2.1 Amp for a 2100 mA pack and many charge faster) but the first two or three charges should be done at 1/10C (210 mA or less to balance and form the pack)

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RE: NiMh or NiCd? - 5/30/2006 6:10:19 PM

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OK. That sounds reasonable. So I could just Plug my plane in on charge Thursday morning and then be ready to go fly for the day on Saturday. lol

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RE: NiMh or NiCd? - 5/31/2006 10:26:48 AM

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Yes but that's a full charge. Most of the time you won't need that, just a top up, unless you fly all night! Stop charging if they get very warm. Slightly warm comes towards the end of the charge, even at these low rates. I get about 2 1/2 hours from 3 servos + Rx from an 800 mA pack so you are going to get a long time from this pack. A charger will tell you what you have used when you recharge the pack and you can figure out the safe capacity time from a full pack for future reference.

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RE: NiMh or NiCd? - 5/31/2006 1:11:04 PM

rajul

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You'll find a good comparison of NiMH and NiCd characteristics here http://members.aol.com/davthacker/nimhfaq.htm

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RE: NiMh or NiCd? - 6/1/2006 1:49:23 AM

mirwin

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quote:

ORIGINAL: marcellus ". . . . . They fast charge fine, up to 1C (2.1 Amp for a 2100 mA pack and many charge faster) but the first two or three charges should be done at 1/10C (210 mA or less to balance and form the pack) . . ."

Marcellus, I switched over to NIMH late last season, and I'll never go back to Nicads for XMTR or RCVR. This year I bought a new 2,700 mah nimh RCVR pack for a new plane (10 servos) but I think I might have ruined it. I didn't realize that one must slow charge a new pack the first few times. I charged it at - as near as I can remember - about 1,000 mah and it got extremely hot, and took a long time to cool down. Should I trust that battery, or write it off as a lesson learned? I'm inclined to toss it.

Thanks much,
Mike

P.S.: I bought a 4,200 mah nimh to replace it already. The extra weight shouldn't affect my 18 pound P-47 much.

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RE: NiMh or NiCd? - 6/1/2006 2:25:38 AM

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The insturctions to my nicd/nimh battery charger said for the first 5 charges to charge at .5C, so your battery should have been fine if you only charged it at 1000 mah, The highest mah my charger goes to is 2000 mah so it may change once you get to a higher mah. hope this helps.

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RE: NiMh or NiCd? - 6/1/2006 7:53:32 AM

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mirwin,
will your charger let you know the capacity by telling you how many mA come out on a discharge and go back in on a charge? 90% + of the 2,700 mA should be ok. You could also check the voltage of each cell whilst under load to see if they are all around 1.2V, though it might be difficult to get at the individual cells with the packaging. I pierce this with a pin to check! Before you trash them, form charge a couple of times at 1/10C. 1000mA is about 1/3 C which should not have harmed them but if they got very hot, they may well have been damaged or even vented. It doesn't sound as though you are usig a peak detection charger, which would have shut off at full charge.

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RE: NiMh or NiCd? - 6/2/2006 2:39:16 AM

mirwin

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quote:

ORIGINAL: marcellus

mirwin,
will your charger let you know the capacity by telling you how many mA come out on a discharge and go back in on a charge? 90% + of the 2,700 mA should be ok. You could also check the voltage of each cell whilst under load to see if they are all around 1.2V, though it might be difficult to get at the individual cells with the packaging. I pierce this with a pin to check! Before you trash them, form charge a couple of times at 1/10C. 1000mA is about 1/3 C which should not have harmed them but if they got very hot, they may well have been damaged or even vented. It doesn't sound as though you are usig a peak detection charger, which would have shut off at full charge.

My charger is a peak detection but it has no display. they didn't get so hot that I couldn't hold the pack in my hand, but they were hot enought that I worry about them. I'll put the pack under load, and check each cell.

Thanks much!

mike

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RE: NiMh or NiCd? - 6/5/2006 2:03:30 AM

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From: cork, IRELAND
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did any of you have trouble with nicads causing corrosion of the black or negative wire on either the tx or rx? fortunately i didnt myself but i have seen it to happen a few times to other club members in my area. one case was so bad the tx battery plug in connector was welded to the transmitter and the wires were so rotten they fell apart very easily. nimh batteries are not supposed to have this problem so i converted just in case.

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RE: NiMh or NiCd? - 6/5/2006 12:54:52 PM

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Yes, lots of problems a few years ago with NiCds but I stored the models outside in a wooden shed. I'm convinced that the dampness was part of the issue. I've had no problems for several years and whether that is because the cells have changed or I now store things inside, I know not. It will creep all along the black wire through switches and around the Tx, so it is good policy to disconnect the battery if you are going to leave things a while, to limit it's progress if it's going to happen.
Judging by where you live you are at a slight disadvantage!! Perhaps someone else will know if NiMh are less prone to black wire corrosion.

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RE: NiMh or NiCd? - 6/5/2006 3:31:45 PM

Rodney

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Black wire disease is almost always associated with NiCad batteries and always starts at the negative terminal of the battery. It will slowly progress up the wire until it hits an open area like a switch or sometimes a splice. The wire becomes very brittle and will not accept solder. This is usually caused by a leaking NiCad and was more prevalent when we used a lot of wet cell NiCads. There is a good writeup on this problem in rcbatteryclinic.com. You cannot repair a wire that has started this chemical process, the only cure is complete replacement of the affected wire.

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RE: NiMh or NiCd? - 6/5/2006 6:25:20 PM

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something you guys/gals may want to take into consideration, under load a NiCd will provide higher voltage then the NiMh. this is very important if your using high current digital servos. at a 2 amp drain most of my NiMh batteries drop slightly below 4 volts, the NiCd will keep a good 4.7 or better (4 cell setups). allot of receivers will 'drop out' at 4 volts and you'll loose control over the receiver until the voltage picks back up. as you progress in size (such as AA to Sub C) the voltage drop under load is less but still not what a NiCd can provide. with that in mind if you are running a high current setup you may want to step up the cell size (physical size not mAH) to keep voltage at an acceptable level during flight.

kc

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