TT2

My Feedback: (13)

I know this is probably going to get ugly and I realize that this subject has been discussed to DEATH. My reasoning for posting this is recent developments in NiMH capacities.

There are new Sanyo AA NiMH cells available that are 2500mAh! A 5-cell 6V pack would tip the scales at about 4.4 oz and cost around $20 assembled with a connector. A 2400mAh 7.4V lipo pack weighs 3.3 oz and costs $27. Add a 6V regulator for 1.5 oz and $40. Here's what you end up with:

NiMH: 568.18 mAh per oz; 125.00 mah per $
Lipo: 500.00 mAh per oz; 35.82 mah per $

The numbers don't lie. The energy density is actually higher for the NiMH packs (with the new Sanyo cells).

One of the biggest factors is the cost and weight of the regulators. They aren't required with NiMH packs even though some guys choose to run them...I don't but that's just me...the eternal minimalist.

Multiply the cost and weight times two if using a redundant system. Did I mention that I've never seen a NiMH pack burst into flames? Oh yeah...and the Lipos need to be charged at 1C whereas the NiMH packs can be charged at 2C.

Three 2500mAh NiMH packs (2 Rx, 1 ignition) would cost you $60. The BEST deal I've seen on this type of Lipo package (Fromeco's) costs $201.00. The NiMH package would actually save you 1.2 oz and $141.00!

If you need larger capacities then simply gang the 2500mAh NiMH packs in parallel. You could have (2) 5000mAh Rx packs and (1) 2500mAh ignition pack for 22 oz and ONE HUNDRED BUCKS! The BEST deal I've seen on this type of Lipo package (Fromeco's once again) costs $255.00. The Lipos save you one oz. This one oz. costs you $155.00. If you are concerned about one oz. on a 40% plane, there are MUCH cheaper ways to lose the weight (CF wing tube, etc.).

Did I mention that I've never seen a NiMH pack burst into flames?
It's your money guys!

-Tom

JohnVH

My Feedback: (38)

I prefer the LIION, I have never seen one burn.

I like the added flights I get before needing to charge, weight and money have nothing to do with it for me.

Matt Merciez

My Feedback: (34)

Tom,

Would you please provide links to websites that provide price and details on the new NiMH batteries you discuss as well as links to the websites you reference for prices on the regulators and batteries for the lipos.

Thanks

DKjens

My Feedback: (50)

Tom,
I see your point(s). However, I have been much more comfortable with my batteries, since changing to Li-Ion. I never seemed to be able to get the volume out of my NiMH when using those batteries. When starting this hobby, I started with helicopters, and this made me somewhat anal about checking battery packs prior to every flight. It seemed, that no matter how large a NiMH pack I put in my plane, after 2-3 flights of 10 minutes each (3D) the capacity checked at 60% or less, which I was not comfortable with. Also, NiMH and NiCd batteries need to be charged immediately prior to using them, where Li-Ion will hold their charge for a long time. I changed to Li-Ion when moving to 33% planes and above, actually, when getting my second 33% plane. I have never had to recharge at the field (I would do that constantly with NiMH), and it just seems one can pull much closer to the capacity out of the Li-Ions than the NiMHs, before reaching the cut-off voltage.
Another factor becomming increasingly apparent, is that more and more servos suitable for the giant scale planes, are designed to run on higher current tha 6 Volt. Many of the new Hitec digitals can run straight off a 2-cell Li-Ion, the large Seiko PS-050 servo can run straight off a 3-cell Li-Ion.
Finally, when looking at your numbers above, I don't get the same results as you for the Li-Ion pack. You say a 2400mAh Li-Ion pack is $27.00 and weighs 3.3 oz, 6V regulator: $15.00 and 1 oz, this makes: 558 mAh/oz and 57 mAh/$, so weight wise similar to your wonder NiMH cells and about twice as expensive per mAh.
DKjens

NeoGenesis

My Feedback: (27)

Lets just say that the 2500 Mah cells that are supposed to be in my packs barely get over 2100mah when cycled. They are brand new. Yes I saved some $$$ but now wish I just would have broke down and purchased lithium 2300 packs from TBM.....




Neo

TT2

My Feedback: (13)

NOTE: When I started typing this up I was comparing against Lipo (lithium polymer) instead of the much cheaper Li-ion (Lithium Ions). The Fromeco cells are Li-ion NOT Li-poly...so it's a slight slip in terminology but the numbers still apply. Li Ion cells are supposed to be more 'stable' than Li Poly cells, but have been known to ignite.

Matt:
[link=http://www.fromeco.org/]Fromeco[/link]
[link=http://www.battlepack.com/loosecells.asp]BattlePacks loose cells[/link]
The $20 for an assembled pack is a guesstimate...but that's about what assembled AA 6V NiMH packs run. If you DIY the cells are $3 each.

DKjens:
1. It sounds as if the NiMH packs either weren't being properly peaked, had one or more degraded cells, or just weren't good to start with. I've had tons of NiMH packs and have found that only the Sanyos are reliable. The cheap packs that people buy off of e b ay are really bad. I used Tekin BC112C and BC112A chargers on my NiMH packs and they loved each other! The Tekins have a positive-negative pulse charge method that seems to keep the cells in very good condition even after hundreds of charges.

I agree that some NiMH packs don't hold a charge very well...then again, some hold their charge exceptionally well. Lithiums don't seem to lose their charge at all which can be a great benefit for some guys. It just depends on their charging habits. I tend to charge the night before then top-off the packs before I head to the field. Lithiums would certainly save me the topping-off step!

2. If using unregulated power for servos then Lithiums might be the best option for stand-alone power. I'm going to try some of the teeny 1 cell Lithiums for powering hand launch gliders in the near future.
3. I adjusted the regulator cost and weight to reflect those available from Fromeco.

Don't get me wrong guys, I'm not bashing Lithiums...matter of fact I just had two Lithium packs arrive yesterday. I'm just presenting a much cheaper alternative for the guys who aren't the 'money is no object' type.

NeoGenesis: I'd be calling the place I bought the packs from.

-Tom

Panzlflyer

My Feedback: (15)

I just got a new 5 cell nimh from Radical and theres no way that it is even close in weight to my Fromeco 2 cell Lion.
One problem Ive had is that the smaller Nimh packs are pretty lousy when it comes to current draw...hence the Nicad standouts wont use them. The Lions while not as good as Lipo in that department seem better.
I have had 2 Nimh short out on me and meltdown. One did catch fire.
I constantly worry about my Lithiums after reading all the stuff here but after 3 years have yet to see a reason to go back.
i guess if I really want to fret I should junk my pda,cell and laptop as well.

JohnVH

My Feedback: (38)

7 flights over 3 days (5 today) on my 1/4 scale with a single fromeco 2400 in it, and still lots of battery left.. I should be able to get over 15!! Never had a nicad or nimh do that for me.

CDignition

My Feedback: (9)

I agree...They are the ticket. You can get a 2 cell 2350 Mah pack for 23 bux from TBM.. fairly light, and lots of volts..

famousdave

My Feedback: (61)

The only reason you would not want to go with Li-Ion is if you did not want to save weight or fly longer between charges.


Li-Ion truly is a liberating technology. I can SAFELY fly my planes over the course of several days without charging or topping off. I can pack nearly 2X the density in the same weight, I can leave them for weeks and not have to "refresh" them either..

There are plenty of those who will argue but the switchover to Li-Ion was about as much of a no brainer as it gets.


As far as fires - if you have a good charger and follow instructions you won't have issues. A full gas can can blow up too.. but with care and handling there are very few fires... with the exception of those Darwin Awards winners...

DP

CDignition

My Feedback: (9)

lol @ DP

Touchdown

My Feedback: (1)

Hi All,

The main thing you all are not adding to your posts is the plane setup (digital servos, two receivers, ect), more of these equals more power use. Lithium batteries look great. The setup would cost me 3 times a nimh setup so I havn't changed yet. (maybe when the price drops). Plus I run a 2100 nimh in my 30% with one reciever and digital servos and get 8 - 12 minute flights (imac and 3d) before recharging. Why change (thats a fairly full day at the field).

Mike Bogh

My Feedback: (14)

I get 28 flights per charge on my Fromeco LIONS on my 28% WH/DA~50/all digital mg's.
28 freekin' flights, every single time!!!.
I now have over 200 flights, and have charged my Fromecos 7 times.
4400 on the reciever, 2200 on the ignition.
Did I mention that I never bring ANY field chargers to the field anymore?
Never, not once.
That one reason alone, is why I will only fly LIONS, from Fromeco, period.

TT2

My Feedback: (13)

Wouldn't a 5000mah pack provide more flight time than a 4400mah pack? 1mah = 1mah regardless of battery chemistry, right? Are the cell capacity ratings different for NiMH than for Li Ion and Li Ion Polymer? Has anyone done a practical comparison using a discharger? My LiPos are used unregulated for electric motor power. I don't have any Li Ions or regulators or I would perform the test myself.

28 flights between charges is amazing. If that were my plane, the engineer in me would say that is too much battery and something smaller could be used. I'm not saying it's wrong, it's just different than the way I've programmed myself over the years (charge plane, go fly, charge plane, go fly, etc.). If I have enough capacity for one afternoon at the field (8 flights max) then I'm happy.

-Tom

TT2

My Feedback: (13)

OK, now I get it. I was thinking in terms of mAh instead of Watt Hours. Since the voltages of the Lithium packs are higher the total energy produced for a given capacity is higher:

4800mah or 2400mah Li Ion (without regulator) Watt Hours per Kilogram: 190
4800mah Li Ion (with regulator) Watt Hours per Kilogram: 155
2400mah Li Ion (with regulator) Watt Hours per Kilogram: 131
2500mah NiMH (without regulator) Watt Hours per Kilogram: 120
'Old' 1650mah NiMH (without regulator) Watt Hours per Kilogram: 79 (just thrown in for comparison)
'Old' 1100mah Nicd (without regulator) Watt Hours per Kilogram: 42 (just thrown in for laughs)

Also the self-discharge factor is something to be considered. Li Ions have a self-discharge rate of 5% per month where NiMH self-discharge at 25% per month (and I've experienced VAST differences here with NiMH from pack to pack).

So, to answer my original question...Do Lithium batteries REALLY make sense? Yes! The larger the packs, the more attractive the Li Ions become. Remember that this comparison was based on the NEWEST NiMH AA cells available...the Li Ions are still better.

There are also new Lithium Ion and Lithium Sulphur batteries looming on the horizon that increase the Watt Hours per Kilogram up to 350 and 500!

-Tom

Hammbone

My Feedback: (309)

I switched to Lithiums years ago, but I understand both sides of this discussion.
You can save some money and keep using NiMh or NiCad's. You can spend a little more money and have the Lithium's that have no memory, hold their charge, and require less charging.
Both ways will provide successfull flying and enjoyment in this hobby.
That's what's nice about this hobby..... You can do whatever you want to do.


Jim

NeoGenesis

My Feedback: (27)

agreed



Neo

cassidy

My Feedback: (5)

I currently fly Large old time freeflights such as the Powerhouse and Majestic Major as well as a Sr Cadet all on Nicads. Haven't moved over to LiPo yet because of two factors.
I already have about 25 large Nicad packs.
This type of plane needs a good deal of weight upp front to balance.
Must admit the multiple flight and long endurance of the lipo are things that are pushing me to research more. I have been flying electric since 1995 and every year it gets better with the advancing technology.

jongurley

My Feedback: (29)

It all comes back to the old adage, 30 more dollars is nothing when it could save a 6000 dollar plane,

drandles

My Feedback: (8)

TT2,

Thanks for starting this thread. I've had Duralites for years in my small plane. Most of my planes currently have NiMH batteries in them and yes I am disappointed in the number of flights I get in before I feel the need to recharge. I have installed Lion batteries in my rejuvenated Sukhoi which I will maiden flight whenever the weather breaks. I thought I was installing them for weight savings. Thanks for reminding me that it is capacity and recharging that is the other advantage.

With my little plane I charge it every third time I bring it out to the field... just because.



Dale

TT2

My Feedback: (13)

The thing I'm looking at the most closely is the 2500-ish sized packs...which I use the most. When you factor in regulators for the Li Ions, the WH/Kg between the 2500mah NiMH and the 2400 Li Ion is negligible...about 4% favoring the Li Ions. BUT...this comes at an ADDITIONAL cost of 200%-ish. $60 per Li Ion pack / regulator vs. $20 per NiMH pack. Sure, you get regulated power with the Li Ions, but I've never experienced jittery servos on dual 6V NiMH systems...even running 8 digitals and 2 analog servos through one receiver.

The thing that bugs me the most about using Lithiums for Rx packs is the regulators. Their weight is low but not insignificant, they cost more than the battery itself, and they add two more connections in the power chain...wires never seem to break in the middle. I don't trust 'failsafe' systems and would only consider running two packs, two switches to the Rx on any plane with a gasser on the nose...it's very cheap insurance.

-Tom

Hammbone

My Feedback: (309)

Like I said...... we all get to use what we want.
It's just personal preference.

I used to use two RX packs on 35% planes for redundancy.
I've recently changed my mind and decided to use only one RX pack on 35% and smaller planes. I've decided that the weight savings is more important to me and I'll take the risk. This is my decision and it fits my needs. We are all a little different. Others do not want to take the risk.

We each can do what we want.


Jim

TT2

My Feedback: (13)

Hammbone, you're absolutely right! It's nice to have multiple options to consider! BTW, did you steal drandles' plane? Both of you guys' avatars are quite similar.

-Tom

Hammbone

My Feedback: (309)

They do look similar in the avatars.
If my picture was bigger, you'd see the difference.


Jim

SAL98

My Feedback: (6)

I see your getting beat up about using NIMH over Lithium Ions. You have to remember your talking to the giant scale crowd and there usually not that concerned with price if it can be justified with some type of performance gain. Just flying $2000.00 to $8000.00 dollar models attest to this fact.

I setup my Wildhare Edge with 2 1650 Nimh packs running in parallel off of 2 separate switches into my receiver. I have 6 Hitec 5625 digitals and 2 standard servos in that plane and I have consistently flown over 15-18 full 3d flights before recharging the packs. I also have a 1650mah Nimh pack in my transmitter (futaba 9C) and I can get roughly 7 hours of use before recharging.

Your absolutely right, when NiMh were only up to the 1600-1800mah range, the lighter and denser Lithiums was a dream come true. Know that you can get 2.5A Nimh, You can budget in a cheaper electrical source and fly Giant scale. But that will never happen because Lithium technology is expanding as well. Know people are running 2-4400 packs and charging up there planes once a week. Not to mention when someone invest 3-8 grand in a model, they are not going to skimp on something that cost less than 10 percent of there
total purchase if like i said " It can be justified with some type of performance gain".

I believe that the Nimh are the best choice for planes up to a 50cc gasser but after that Li-ions should be a no brainier