Nimh batteries downside???
11-20-2004, 12:39 PM
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RE: Nimh batteries downside???
I've been using two 2700 mAH 5-cell NiMH packs without regulators in 35% planes for 3 years now without issues. These are A-cells, chosen because I wanted to have the current capacity available for a bunch of Hitec digitals. The only time I had a current issue was with the ailerons - 4 digital servos pulling at once. The problem only showed up after a year of flying. I changed the aileron extensions and Y-harness to heavy duty and the problem went away.
11-20-2004, 01:41 PM
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RE: Nimh batteries downside???
I have also been nimh in my 35% Radiocraft for 4 years now using all 5900 digitals with 2 2700 s from Radical rc. No problems at all i also use the I4c Isolater with it. I have 11 other big birds using combo of 5900 s and 5600 Hitecs digitals using 1650 mah metal packs no problems. I use the Hughes charger + and Orbit charger for these packs.
11-20-2004, 01:44 PM
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RE: Nimh batteries downside???
ORIGINAL: scottfl78
leave my NiMH's alone [:@] NiMH's and digi's work don't believe the hype, Lithiums burn down houses..
leave my NiMH's alone [:@] NiMH's and digi's work don't believe the hype, Lithiums burn down houses..
No, improper charging, storage, and use of Li-po/Li-ion burn down houses(none that I know of - FWIW). If they're handled right, they're great. They just don't like to be abused as much as we're used to with Nimh or Nicds.
I use them all the time, and the only problems I've ever had were my own fault - not the battery.[&o] Nimh will work fine with digital servos, and yes, they can carry the load. How else would they be able to power electric aircraft, especially drawing dozens of amps at full power? The digitals draw more than standard, but nowhere near as much as powering a motor! True, they are more suspeptible(sp?) to temperature, but not that bad. They hold their charge for longer at a higher level under "normal" usage, like powering our radios. Also, when they do finally give up, the discharge curve is very steep compared to other types of batteries(generally speaking). No "memory effect"? Hogwash. It's also referred to as "voltage depression" and does affect Nimh as well as Nicd. The cure for this is easy - discharge, then SLOW charge(C/10, C/15 or less, depending on battery)
As for useful life (number of cycles), if the overall capacity starts significantly decreasing, it's gone. I would rather buy new batteries than a new plane. I don't worry too much about how many charge/discharge cycles it's been through- it's irrelevant. You gotta measure it to be sure!
I'm not an expert by any means, just some stuff learned by experience and somewhere between 10-15 years of research, and much learning via the "hard way"....
Just my .02
11-20-2004, 01:49 PM
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RE: Nimh batteries downside???
ORIGINAL: Diablo-RCU
...changed the aileron extensions and Y-harness to heavy duty and the problem went away.
...changed the aileron extensions and Y-harness to heavy duty and the problem went away.
11-20-2004, 05:42 PM
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RE: Nimh batteries downside???
Been operating 2, 4 cell 2700mah nimh's with jr8411's and get about 3 12-15 min flights before I recharge, as a precaution. Flying style is mixed but not much in the way of continious 3D flying.
I'm operating 9 servos total with two matchboxes and one receiver. The only problem I have encountered is that over the winter the battery's seemed to die a slow death. I charged them on a Sirius charger and it showed a good charge but based on another nimh I decided to cycle them prior to flying this summer. Lucky that I did so because they showed a full charge at 5.4V but they fell right off the cliff when the controls were operated (on the ground in my house). I tried everything to get these battery's back to life. They would false peak and would not take a charge now matter what we threw at them. Wall wort, Sirius nor Triton could bring them back.
My suggestion, especially with the larger battery types, is to keep a sticky note on each plane/pack with a date and the MAH's that go into them (assuming a full charge prior to storage) with each charge and to charge them at regular 30 day intervals to a fully charged state. Do not let these big ones loose their charge during storage.
Also, an excellent place for information would be the web sites for Sanyo and or Panasonic. They can put your mind at ease...good luck.
I'm operating 9 servos total with two matchboxes and one receiver. The only problem I have encountered is that over the winter the battery's seemed to die a slow death. I charged them on a Sirius charger and it showed a good charge but based on another nimh I decided to cycle them prior to flying this summer. Lucky that I did so because they showed a full charge at 5.4V but they fell right off the cliff when the controls were operated (on the ground in my house). I tried everything to get these battery's back to life. They would false peak and would not take a charge now matter what we threw at them. Wall wort, Sirius nor Triton could bring them back.
My suggestion, especially with the larger battery types, is to keep a sticky note on each plane/pack with a date and the MAH's that go into them (assuming a full charge prior to storage) with each charge and to charge them at regular 30 day intervals to a fully charged state. Do not let these big ones loose their charge during storage.
Also, an excellent place for information would be the web sites for Sanyo and or Panasonic. They can put your mind at ease...good luck.
11-20-2004, 06:01 PM
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RE: Nimh batteries downside???
They will "fall" all the way out if left for too long, as they have a tendency to self-discharge. Beyond a certain point, the chemical balance in the battery gets screwed up somehow(don't ask, I don't know), and it becomes just about impossible to revive them(without very $$$ equipment). [&o]
11-20-2004, 06:59 PM
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RE: Nimh batteries downside???
I usually charge my metal packs every 2 months during the winter or more often. I had a Radical RC sanyo 3800 pack 5 cell Metal go 2 years without a charge. I recentily charged it on my Ace Constant volt charger for 16 hours on c-10 and cycled it down on my Orbit and it still showed 90 % capicity. Not bad , i was surprised.
11-20-2004, 08:03 PM
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RE: Nimh batteries downside???
I keep mine on trickle charge all year with my Alpha 4 with no problems so far..Im about to get 3 more 2150 packs for my WH Edge..I like them so far...
11-20-2004, 11:02 PM
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RE: Nimh batteries downside???
Hi Gents!
In the intrest of dispelling myths and oft re-told tales of 'unsitability' regarding the various technologys we commonly use in R/C allow me to suck up a bit of bandwidth here..
NiMH, Nicad and Lithium are ALL viable technologies for our hobby. However, just as we select servo's for their output power and speed and engines for their weight vs power output we need to consider what's appropriate as battery power for our models. There are situations and circumstances that directly impact the suitability of NiMh or Nicad OR lithium for the task you expect them to do..
The hobby buys packs based on the 'capacity' number.. relevant to the amount of energy stored. What's most often missed is impedance.. the ability of the cell to deliver that stored energy and the resultant amout of voltage drop that occurs while the loads are applied. The key is' how much load, for how long'.. in other words; the bigger the load, and the higher the impedance number; the more dramatic the voltage drop.
Data Point: For many years, as a general rule (there are exceptions) NiMH and Lithium had higher internal impedance than Nicad.. in other words, Nicads had more 'grunt' and could sustain a higher voltage level while loads are applied. Where these diffrences remain most apparent are in cell sizes and types SMALLER than sub-c.. NiMH AA and A cells in particular carry higher impedance values (bigger voltage drops) than their Nicad brethern of the same dimensions. Thanks to the demands of the tooling market, NiMH impedance values have come down dramaticly in recent years; sub-c NiMH cells like the GP 3300 SCHR now have impedance values that are almost identical to the venerable 'big gun' sub-c nicads like the Sanyo CP2400SCR. A quick comparision of impedance values between an 'A' sized 2700 HRAUL (20mOhms) vis a Nicad 1400 'A' (10mOhms) shows a pretty big gap.. and it's worse on AA cells. The popular Sanyo 1650 and 2100 NiMH AA cell has 25 mOhms impedance vs only 12 mOhms on a Nicad 1100 AA.
Whats all this mean? It means that little AA sized NiMH 4 cell packs ain't the right choice for an IMAC 40% aircraft running digital servos. It should also be noted that the hobby has gotten very very concerned about dependability regarding airborne systems and the aforementioned 40% aircraft would not be flown on a little 4 cell AA pack of any kind anyway.. these aircraft usually fly with 5 cell packs (sometimes regulated) and also quite often use a parrallel pack system for extra security.. and these two simple moves further reduce the negative effect of impedance being an issue with NiMH packs.. parallel packs cuts the impedance of the system in half, and using a 5 cell pack effectively removes voltage drop from being a threat to Rx regardless of impedance.
There's even more good news for the folks wanting more capacity, less weight and more current handling ability from their airborne system packs.. NiMH continues to improve. Sanyo has at last released a 4/5 height 'fat A' cell NiMH cell with the same impedance value as a Nicad Sub C.. an outstanding advance in NiMH development... a smaller footprint with the same punch as a Nicad sub-c pack. KAN and GP both have out small 2/3 'A' size NiMH cells that whip the pants off of BIGGER AA nicads in both impedance AND capacity... and more improvements are coming all the time.
The gist of all this... while NiMH still lags a bit behind Nicad in duty cycle lifetimes and at temperature extremes, they have turned the corner regarding impedance and have even surpassed Nicad in some types and cell dimensions. Nicad still (and will always) enjoy faster recharge times and more resilience to overdischarge and overcharge abuse, but the big gulf of difference between the two as far as reliability and suitability for our larger aircraft has vanished.
Advice: the more agressive the aircraft, the more appropriate the use of 5 cell setups and parallel packs (regardless of technology). Never sacrafice dependability for weight.. an extra 3 ounces of battery 'insurance' on a 20 lb (320 ounce) aircraft is an excellent tradeoff.
Hope this helps!
In the intrest of dispelling myths and oft re-told tales of 'unsitability' regarding the various technologys we commonly use in R/C allow me to suck up a bit of bandwidth here..
NiMH, Nicad and Lithium are ALL viable technologies for our hobby. However, just as we select servo's for their output power and speed and engines for their weight vs power output we need to consider what's appropriate as battery power for our models. There are situations and circumstances that directly impact the suitability of NiMh or Nicad OR lithium for the task you expect them to do..
The hobby buys packs based on the 'capacity' number.. relevant to the amount of energy stored. What's most often missed is impedance.. the ability of the cell to deliver that stored energy and the resultant amout of voltage drop that occurs while the loads are applied. The key is' how much load, for how long'.. in other words; the bigger the load, and the higher the impedance number; the more dramatic the voltage drop.
Data Point: For many years, as a general rule (there are exceptions) NiMH and Lithium had higher internal impedance than Nicad.. in other words, Nicads had more 'grunt' and could sustain a higher voltage level while loads are applied. Where these diffrences remain most apparent are in cell sizes and types SMALLER than sub-c.. NiMH AA and A cells in particular carry higher impedance values (bigger voltage drops) than their Nicad brethern of the same dimensions. Thanks to the demands of the tooling market, NiMH impedance values have come down dramaticly in recent years; sub-c NiMH cells like the GP 3300 SCHR now have impedance values that are almost identical to the venerable 'big gun' sub-c nicads like the Sanyo CP2400SCR. A quick comparision of impedance values between an 'A' sized 2700 HRAUL (20mOhms) vis a Nicad 1400 'A' (10mOhms) shows a pretty big gap.. and it's worse on AA cells. The popular Sanyo 1650 and 2100 NiMH AA cell has 25 mOhms impedance vs only 12 mOhms on a Nicad 1100 AA.
Whats all this mean? It means that little AA sized NiMH 4 cell packs ain't the right choice for an IMAC 40% aircraft running digital servos. It should also be noted that the hobby has gotten very very concerned about dependability regarding airborne systems and the aforementioned 40% aircraft would not be flown on a little 4 cell AA pack of any kind anyway.. these aircraft usually fly with 5 cell packs (sometimes regulated) and also quite often use a parrallel pack system for extra security.. and these two simple moves further reduce the negative effect of impedance being an issue with NiMH packs.. parallel packs cuts the impedance of the system in half, and using a 5 cell pack effectively removes voltage drop from being a threat to Rx regardless of impedance.
There's even more good news for the folks wanting more capacity, less weight and more current handling ability from their airborne system packs.. NiMH continues to improve. Sanyo has at last released a 4/5 height 'fat A' cell NiMH cell with the same impedance value as a Nicad Sub C.. an outstanding advance in NiMH development... a smaller footprint with the same punch as a Nicad sub-c pack. KAN and GP both have out small 2/3 'A' size NiMH cells that whip the pants off of BIGGER AA nicads in both impedance AND capacity... and more improvements are coming all the time.
The gist of all this... while NiMH still lags a bit behind Nicad in duty cycle lifetimes and at temperature extremes, they have turned the corner regarding impedance and have even surpassed Nicad in some types and cell dimensions. Nicad still (and will always) enjoy faster recharge times and more resilience to overdischarge and overcharge abuse, but the big gulf of difference between the two as far as reliability and suitability for our larger aircraft has vanished.
Advice: the more agressive the aircraft, the more appropriate the use of 5 cell setups and parallel packs (regardless of technology). Never sacrafice dependability for weight.. an extra 3 ounces of battery 'insurance' on a 20 lb (320 ounce) aircraft is an excellent tradeoff.
Hope this helps!
11-21-2004, 11:47 AM
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RE: Nimh batteries downside???
Well put, and 100% true! This thread is going into my "archive".
Best website I've seen for batteries, charging, etc:
http://www.rcbatteryclinic.com/
Best website I've seen for batteries, charging, etc:
http://www.rcbatteryclinic.com/
11-21-2004, 01:41 PM
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RE: Nimh batteries downside???
Excellent analysis Steve! I started this thread for two reasons:
1.) There is always a certain amount of apprehension when dealing with new technology such as NiMH and Li- Poly versus the tried and true Nicad that I have used reliably since the mid 1970's.
2.) I was somewhat curious as to why the Nicad cell has not been relegated to the R/C boneyard if the newer
cells are so superior. I think I have my answer. Like everything in life there are tradeoffs and it appears
that this is one of those areas where you have to balance the pros and cons.
Based on all this discussion, I have decided to stay with nicads for my 30% Comp-Arf Extra. I will go with twin packs, wired in parallel with two heavy duty switches to obtain a degree of redundancy. I am investing about $2600 - $3000 in this project, and while that may be chump change to some, it's not to me. The few ounces I can save with the newer cell technology is insgnificant compared with system reliability which is my primary concern. Just my .02!
jmw
1.) There is always a certain amount of apprehension when dealing with new technology such as NiMH and Li- Poly versus the tried and true Nicad that I have used reliably since the mid 1970's.
2.) I was somewhat curious as to why the Nicad cell has not been relegated to the R/C boneyard if the newer
cells are so superior. I think I have my answer. Like everything in life there are tradeoffs and it appears
that this is one of those areas where you have to balance the pros and cons.
Based on all this discussion, I have decided to stay with nicads for my 30% Comp-Arf Extra. I will go with twin packs, wired in parallel with two heavy duty switches to obtain a degree of redundancy. I am investing about $2600 - $3000 in this project, and while that may be chump change to some, it's not to me. The few ounces I can save with the newer cell technology is insgnificant compared with system reliability which is my primary concern. Just my .02!
jmw
11-21-2004, 03:13 PM
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RE: Nimh batteries downside???
Great info here!! Im going with 2 6v 2150 Nimh packs for my 28% edge and Im going to run 5 Jr 8611's. I will definitely be paying attention after each flight to see how they perform..If not then Im going to go back to Nicads..
11-21-2004, 03:31 PM
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RE: Nimh batteries downside???
Yup.. Red's R/C Battery Clinic is an excellent resource, and we've also added a FAQ page to our site that expands the knowledge base a bit and deals with NiMH & impedance with a bit more detail.. You'll also find a 'white paper' that details some interesting points relevant to Lithium vs Nicad and NiMH in big birds.
the links:
[link=http://www.hangtimes.com/rcbattery_faq.html]R/C Battery FAQ[/link]
[link=http://www.hangtimes.com/weightcompare.html]Lithium, Nicad & NiMH Weight Comparison[/link]
Thanks for the kind words gents!
Steve
the links:
[link=http://www.hangtimes.com/rcbattery_faq.html]R/C Battery FAQ[/link]
[link=http://www.hangtimes.com/weightcompare.html]Lithium, Nicad & NiMH Weight Comparison[/link]
Thanks for the kind words gents!
Steve
11-21-2004, 07:17 PM
#44
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RE: Nimh batteries downside???
[8D]Glad to hear that you are experiencing the same readings that I do. I have a 1450 MAH
nimh in my transmitter and charge it at the 1500 MAH rate from where it then goes into the
trickle mode. By the time that I get to the field from charger disconnect (approx 35 min),
the reading is around 11.0 or just below and then drops down to 10.4/10.3. About six months
ago, I turned on my transmitter at home (antenna extended) to see how long it would take
to reach the warning beep on my transmitter. It read 10.4 for 5-6 hours and then slowly moved
down to 10.2 after 6-7 hours.
I use an Ace Digipulse which charges at C/10 for 14 hours and then goes into trickle.
nimh in my transmitter and charge it at the 1500 MAH rate from where it then goes into the
trickle mode. By the time that I get to the field from charger disconnect (approx 35 min),
the reading is around 11.0 or just below and then drops down to 10.4/10.3. About six months
ago, I turned on my transmitter at home (antenna extended) to see how long it would take
to reach the warning beep on my transmitter. It read 10.4 for 5-6 hours and then slowly moved
down to 10.2 after 6-7 hours.
I use an Ace Digipulse which charges at C/10 for 14 hours and then goes into trickle.
11-21-2004, 10:05 PM
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RE: Nimh batteries downside???
Redrum you wont have problems with your set up as long as you have 22 guage wiring extensions and good switches and use a good charger for your packs.
11-21-2004, 10:32 PM
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RE: Nimh batteries downside???
I have an Alpha 4 for charging and all my extensions and switches are hevy duty from Cermark..Cant wait to try out those 8611's
11-22-2004, 11:14 AM
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RE: Nimh batteries downside???
All this talk about impedence and voltage drop doesn't mean much if your not drawing enough current for it to matter. Does someone have a graph that plots voltage vs. current, and a chart that gives pretty accurate current draws of servo systems? I ask because I run 5 Hitec 5945's and 1 Hitec 5475 digital servos in a 28% Laser 200 (87" wing, 16-lb, 52cc gas engine) with 5-cell 2700 mAh NiMH and have never had a problem. What I want to know is how many digital servos before I have a problem?
