NI-Cd and Ni-MH discharge amounts  
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NI-Cd and Ni-MH discharge amounts - 1/20/2007 1:11:20 AM   
fastplane


 

Posts: 271
Joined: 7/24/2004
From: Houston, TX, USA
Status: offline 		I have been using only Ni-Cd batteries so far. No problems but now that I have larger planes, high torque/digital servos I need larger capacity batteries.
I was told to go to Ni-MH because of the discharge curve at the end doesn't drop off suddenly like Ni-Cd.
Then others told me that there was a problem with Ni-MH because they discharge twice as fast as Ni-Cd.
This is quite confusing to me.
Given the same RC plane setup and same load at the battery --- how/why would the Ni-MH discharge faster than the Ni-Cd?
And if so what does that mean relative to flying time?
So, which type battery is better/best to go flying most of the day?
Thanks
       Post #: 1

RE: NI-Cd and Ni-MH discharge amounts - 1/20/2007 2:29:18 AM   
Trogdor the Burninator



Posts: 554
Joined: 11/29/2003
From: Ashburn, VA, USA
Status: offline 		After going nimh, i've never looked back. I think what someone was meaning is that the self-discharge rate of nimhs can be higher.. so if you charge tonight but don't fly for a week the nimhs will discharge more juice than a nicd. If you charge the night or day before no problem with that. I went from a few flights on a 40 size plane and 600 mah nicd to flying all day on the 1800 nimh... well as much as I could fly 7 or 8 ten minute flights or so. And now they have 2200+ nimhs...

oh and try a nimh tx pack.. then you really can fly all day.

(in reply to fastplane)
       Post #: 2

RE: NI-Cd and Ni-MH discharge amounts - 1/20/2007 11:45:48 PM   
Gerald8272


 

Posts: 18
Joined: 1/4/2002
From: Friendsville, TN, USA
Status: offline 		I agree with Trogdor on the NiMhs. If you decide to go that route, be sure to form charge and cycle them about three times before use.

(in reply to Trogdor the Burninator)
       Post #: 3

RE: NI-Cd and Ni-MH discharge amounts - 1/21/2007 1:05:11 AM   
Geistware



Posts: 12946
Joined: 4/9/2002
From: Locust Grove, GA, USA
Status: offline 		I will recommend that you stay with NiCads unless you use NiMH packs with low internal impedance.
I can go into a list of reasons lets just say that with my two 5 cell 1800maH NiCad packs and 10 digital servos, I can make 7 flights before the voltage is too low. I find that my ship averages about 2 amps in flight. It is estimated that it peeks as high as 11 amps. (Knife Edge Snaps). Just make sure that your packs can deliver the load at or above 6 volts (4.8 volts) at the servo.
quote:

ORIGINAL: fastplane

I have been using only Ni-Cd batteries so far. No problems but now that I have larger planes, high torque/digital servos I need larger capacity batteries.
I was told to go to Ni-MH because of the discharge curve at the end doesn't drop off suddenly like Ni-Cd.
Then others told me that there was a problem with Ni-MH because they discharge twice as fast as Ni-Cd.
This is quite confusing to me.
Given the same RC plane setup and same load at the battery --- how/why would the Ni-MH discharge faster than the Ni-Cd?
And if so what does that mean relative to flying time?
So, which type battery is better/best to go flying most of the day?
Thanks



_____________________________

Aircraft Proving Grounds
http://www.rcaircraft.net/
Information on the building and flying of Radio Control Aircraft.
Site for hobbyist in the R.C. Aircraft modeling world.

(in reply to fastplane)
       Post #: 4

RE: NI-Cd and Ni-MH discharge amounts - 1/21/2007 4:14:32 AM   
fastplane


 

Posts: 271
Joined: 7/24/2004
From: Houston, TX, USA
Status: offline 		Geistware, I get several recommendations to use both types. Each person has their own reasons that prove their point.
In my long experience every time I receive many divergent views with proof it usually means that either case will work. Each method has it's merits and detractions. The real key for any solution is to be aware of the good and bad points of both cases.
I am not an expert in batteries and am not aware of all of the good and bad points about either type of battery.
I have read some articles and most seem to lean toward the Ni-MH.
I will be using 4.8v packs either Ni-Cd or Ni-MH. In either case I would want about 2400 mAh packs.
I would not know about low internal impedance. Nor do I know how to assure above 4.8 volts at the servo, (in use in the air I presume?).

(in reply to Geistware)
       Post #: 5

RE: NI-Cd and Ni-MH discharge amounts - 1/21/2007 7:21:57 AM   
Trogdor the Burninator



Posts: 554
Joined: 11/29/2003
From: Ashburn, VA, USA
Status: offline 		I think geist has a good point.. I have heard of the problems he was describing but I'm not 100% on the technical details. I think it comes down to sticking with quality packs made specifically for the load you intend to put on them. Try talking to a place that makes up packs like cheapbatterypacks.com or a large scale place like Don's hobbies...

(in reply to fastplane)
       Post #: 6

RE: NI-Cd and Ni-MH discharge amounts - 1/21/2007 2:15:42 PM   
Rodney



Posts: 4998
Joined: 12/8/2001
From: FL
Status: offline 		From my experience, Giestware has given you good advice. I have also found that NiCads will give you twice as long a life as NiMh will in terms of number of cycles of reliable use.

(in reply to Trogdor the Burninator)
       Post #: 7

RE: NI-Cd and Ni-MH discharge amounts - 1/21/2007 6:40:58 PM   
fastplane


 

Posts: 271
Joined: 7/24/2004
From: Houston, TX, USA
Status: offline 		Rodney, I am sure that Giestware has given good advice as always.
I have also received good advice from those that say Ni-MH are the better battery to use for RC airplanes.
I think it is odd that there is no comparison chart/table/data of the different types of batteries. Which would note their good and bad points relative to RC airplanes.
I believe that rechargeable batteries have been around since about mid 1960.
I have been looking for such data but have not found it yet.

(in reply to Rodney)
       Post #: 8

RE: NI-Cd and Ni-MH discharge amounts - 1/21/2007 7:32:20 PM   
Carpilot


 

Posts: 30
Joined: 9/13/2008
From: Lakewood, CO, USA
Status: offline 		most of the problems you hear about with Ni-Mh batteries are related to older ones, the modern Ni-Mh batteries perform as well as Ni-Cd.

I think the Ni-Cd batteries may have an advantage when operating at high current levels, All my cordless tools still use Ni-Cd batteries.

but I use all Ni-Mh RX packs in my planes and in my transmitters now and I think they are great. the biggest reason I switched is because a 1500mah Ni-Mh RX pack weighs less than a 1500mah Ni-Cd pack.

(in reply to fastplane)
       Post #: 9

RE: NI-Cd and Ni-MH discharge amounts - 1/21/2007 7:39:13 PM   
Geistware



Posts: 12946
Joined: 4/9/2002
From: Locust Grove, GA, USA
Status: offline 		I am not going to generalize but look at NiMH usage in two lights.
Those who have used 2700maH AA packs in 1400maH Sub C installations.
You will get more flight time with the NiMH. You should, you have twice the capacity.
You are also drawing current at a fraction of the rated capacity. Less percentage load, better your flight time.
You also have those who have used the low impedance NiMH packs.
They are as good as NiCads of the same cell size. (A,AA,AA,C, etc)

I will not argue the point. Do the test yourself.
Load the pack at "C" down to 0.9 volts per cell.
Find out the capacity removed at load, then see which chemistry can deliver current, under load, and still have the required voltage.
Unless it is a low impedance NiMH pack, the NiCad will win every time. Don't believe me. Do it yourself.
Those who have used 2700maH packs in 1400maH installations are going from loads that are C/3 (500 ma) to loads that are C/5 (500 ma)

Of course it is going to look better!

quote:

ORIGINAL: fastplane

Geistware, I get several recommendations to use both types. Each person has their own reasons that prove their point.
In my long experience every time I receive many divergent views with proof it usually means that either case will work. Each method has it's merits and detractions. The real key for any solution is to be aware of the good and bad points of both cases.
I am not an expert in batteries and am not aware of all of the good and bad points about either type of battery.
I have read some articles and most seem to lean toward the Ni-MH.
I will be using 4.8v packs either Ni-Cd or Ni-MH. In either case I would want about 2400 mAh packs.
I would not know about low internal impedance. Nor do I know how to assure above 4.8 volts at the servo, (in use in the air I presume?).




_____________________________

Aircraft Proving Grounds
http://www.rcaircraft.net/
Information on the building and flying of Radio Control Aircraft.
Site for hobbyist in the R.C. Aircraft modeling world.

(in reply to fastplane)
       Post #: 10

RE: NI-Cd and Ni-MH discharge amounts - 1/21/2007 9:30:46 PM   
fastplane


 

Posts: 271
Joined: 7/24/2004
From: Houston, TX, USA
Status: offline 		Geistware, I have nothing to argue about. I am asking about Ni-Cd & Ni-MH of the same capacity.
Please go back and read my original question.
I have no Ni-HM batteries. If I did I would already have my own experience and opinion.

I cannot do the tests.
I have nothing to load a battery pack at "C", (whatever that is), to any desired volts and no way to measure individual cells.
I have no equipment to determine capacity removed or anything else. I only have a digital voltmeter that can put a 250 mAh load on a battery pack.
I am also searching for equipment, (battery discharger/charger) to help me maintain any current battery I have or will have.
That is one reason I posted the original note. I don't want to go out a buy batteries just to determine which is better for me.
I was hoping to get this technical data from RC Universe.

(in reply to Geistware)
       Post #: 11

RE: NI-Cd and Ni-MH discharge amounts - 1/21/2007 10:25:57 PM   
dick Hanson



Posts: 10265
Joined: 12/12/2001
From: slc, UT, USA
Status: offline 		OK- here is where it can get confusing--
you need to know at least these things about the batteries you are going to use
A --the amp hr rating -- that tells you how how much you get
B- the impedance --and some batt people don't want you to know this because it tells you how fast you can suck power from th e battery.
for example the 2700 ma Sanyo NiMh 2700 EVO cells are small lightweight and incredibly good cells !
what is the catch?
- the catch is -they have extremely high impedance --25 .
so they are terrific for cameras and little electronic lightweight devices.
Your servos will suck as hard as they can to get current and the wires and the TYPE battery and all the connections - all restrict current to them.-If you use high impedance cells - the real volage to your servos drops off at the servo and the RX (very important!)
You want batteries which flow current easily
Old Nimh cells all had lots of impedance - NiCads were better -
Now , new Nimh are available with very low impedance -4-8 on many packs available.
So why use these ?
well -new technology has more mah packed in a smaller and usually ligher package-and still allow the servos to easily suck power (low impedance)
So what to buy?
look at price and weight of course but pay most attention to ampre hr rates and impedance - on Nimh you can easily get tricked .
I use 6v packs exclusively -no regulators . NiCad /NiMh I don't care as long as they have very low impedance
I am now trying out a new cell called 123 LiIon which is lighter and smaller but two (2) of them deliver almost same voltage as 5 NiMh! and very low impedance --
they are more bucks but the weight is down vs Nimh or NiCad (a 6 v 2300ma pack is 5 ounces ) No regulator needed .
In your case -if you have low drain (std sport)servos and don't have the surfaces flapping all over the place all the time -- a smaller higher impedance battery may be just fine but be forearned
MA rating is only 1/2 of what you need to know.

< Message edited by dick Hanson -- 1/21/2007 10:48:29 PM >

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(in reply to fastplane)
       Post #: 12

RE: NI-Cd and Ni-MH discharge amounts - 1/22/2007 4:27:15 PM   
BillS


 

Posts: 3100
Joined: 9/6/2004
From: Greensboro, NC, USA
Status: offline
quote:

ORIGINAL: fastplane

Geistware, I have nothing to argue about. I am asking about Ni-Cd & Ni-MH of the same capacity.
Please go back and read my original question.
I have no Ni-HM batteries. If I did I would already have my own experience and opinion.

I cannot do the tests.
I have nothing to load a battery pack at "C", (whatever that is), to any desired volts and no way to measure individual cells.
I have no equipment to determine capacity removed or anything else. I only have a digital voltmeter that can put a 250 mAh load on a battery pack.
I am also searching for equipment, (battery discharger/charger) to help me maintain any current battery I have or will have.
That is one reason I posted the original note. I don't want to go out a buy batteries just to determine which is better for me.
I was hoping to get this technical data from RC Universe.


You received very well thought out answers to a general but complex question. Fussing at the responders is not likely to produce answers more to your liking.

If you didn’t like or didn’t understand the answers consider rephrasing the question.

Bill

(in reply to fastplane)