every time I show up at the flying field I get pummeled by the ‘believers’ that insist the lithium’s are
‘the way’, and they turn a deaf ear to any information to the contrary. Same goes for the folks that prefer to
stay with the ‘traditional’ packs.. they are no more inclined to listen to the facts than the ‘other’
team. Still, I shake my head and smile; like republicans and democrats, the two ‘warring’ factions seem to enjoy
the debate even to the exclusion of flying at times! Me? When I get out of the shop I try to avoid talking ‘religion
or batteries’. Politics... well, keeping the theiving cretins in Washington outta our wallets is a different story.
I have absolutely no doubt that those
that have already invested in new packs or chargers will not be switching based on the content of this comparison report,
nor is it intended as an assault on their choices... I have great respect for those that in effect put cash on the barrel
head and then 'risk it all' to help develop new technologies for the hobby. It's thanks to those brave souls that these
technologies are as refined as they are, and it's thanks to their support and input that we enjoy the choices we have
today.. But for the folks that are still sitting on the fence or are contemplating their first IMAC or Giant Scale project,
perhaps this white paper will be of assistance in making a decision.
Where it all Started
The ‘storm of debate’ on batteries has been with us from the start of radio control.. and the
focus of the debate has it's roots in weight. Everybody knows, ‘lighter is better’ when it comes to model performance,
and some of the hobby’s greatest improvements in performance are relative to power and weight in the aircraft we all
fly. Ever in pursuit of ‘weight savings’, the builder often gets to the end of his project, weighs up the fruits
of his efforts and discovers he ‘needs’ to cut the weight buildup by revising his selection of on-board equipment
in pursuit of his magic number. I’ve discovered that about the only thing you can do to a model that does not add weight
is look at it. Everything else is weight gain. Everything!
Next, having established
a train of logic that has ‘weight’ as the core of the debate, the modeler looks for servos, receivers and control
components that reduce the deficit of weight gain that appeared in the building process. By the time we’ve finished
the control system and are looking at batteries, there seems to be a willingness to compromise both common sense and an inordinate
amount of money to assuage the guilt of ‘missing the magic number’.
Crunch The Numbers...
Let’s have a
look at a typical IMAC 'Big Bird' scale IMAC or Giant Warbird project. We’ll pick an all up weight number of 15lbs (240oz)
for this exercise, less batteries and switches. Our project is powered by an ignition engine, and has digital high
torque servos so we’ll need to deal with that too. All the technologies compared are fully capable of flying the subject
aircraft equally well, with similar system ‘safeties’ and backups.* (see note at bottom of page)
Duralite Plus (TM) Li-Ion Basic Parallel System, Total Capacity; 5200ma. Total Rx
pack load rating: 30 amps
|Quan||Desc||Weight ea||Cost ea||Total weight||Total
|2||#7262 2600ma-7.4 volt RX pack ||3.9oz||$51.95||7.8oz||$103.90|
|1||#7262 2600ma -7.4 volt (ignition)||3.9oz||$51.95||3.9oz||$51.95|
Chargeport switches|| .3oz||$17.95|
Fromeco Relion (TM) Li-Ion Basic Parallel System, Total capacity; 5200ma Total
Rx pack load rating: 30 amps
ea||Cost ea||Total weight||Total Cost |
volt RX pack
2600ma 7.4 volt IGN Pack
| HD Chargeport
A123 LiFe Basic Parallel System, Total
Capacity; 4600ma. Total Rx pack load rating: 60+ amps
|Quan||Desc||Weight ea||Cost ea||Total
weight||Total Cost |
6.6v Rx packs
6.6v Ign pack
(required on some ignitions, not all)
| 3|| HD Chargeport Switches|| 0.3oz|
Sanyo NiMH HR-2700AUX Parallel System, Total Capacity, 5400ma. Total Rx Pack load rating: 20
2700 ma 5 cell 6.0v NiMH (HR-2700AUX)
GP 1350 ma 4 cell 4.8v NiMH
HD charge port switches
| || || || |
Sanyo NiMH** 1950 FAUP Parallel System, Total Capacity, 3900ma , Total Rx Pack Load
Rating: 45 amps
1950ma 5 cell 6.0v NiMH (HR-4/5 FAUP)
GP1350ma NiMH High Rate 4 cell 4.8v
HD charge port switches
| || || || |
Sanyo Nicad Parallel System, Total Capacity, 4800ma.
Total Rx Pack load rating: 45 amps.
2400 ma 5 cell 6.0v Nicad (CP-2400SCR)
1600 ma 4 cell 4.8v NiCad (KR-1700AU)
HD charge port switches
| || || || |
And, the winner
Now, a quick look at the numbers would indicate
that all three Lithium based systems shown are in the ‘ballpark’ as far as weight goes.. the Nicad system is a
beast in the weight comparisons, but that can be an advantage in some scale warbirds looking for weight in a strategic area
of the plane to get CG in range without adding lead. The Lithium systems are less than one ounce different
in weight, there's a 4 ounce difference with the NiMH setups. With the two Li-Ion systems, if you factor
in the additional weight of a voltage monitor and the recommended low voltage cutoff modules, then the Li-Ion weight
advantage is reduced to less than 1 ounce over the NiMH setups, and the A123 system easily becomes the 'lightness
leader'. While A123 comes in below the Li-Ion and NiMH in the capacity race, whatever small capacity advantage
a Li-Ion and NiMH system would enjoy is usually eaten away by the A123's much lower impedance, larger
usable percentage of capacity and faster potential recharge times.
Folks; if you sit down and figure out what the equipment
costs for the more exotic Li-Ion systems (Power Boxes, regulators, etc) and then have a close look at the cost per ounce
of system weight, you really gotta ask yourself just how much of a difference that 1 ounce will have on the
way our 16lb (256oz) airplane is going to fly. . For that matter, ask yourself how much of a difference four ounces
will have on the way our two hundred and fifty-something ounce plane will fly! Now,
normally, it's not a wise thing to thump folks about the head and shoulders with tire irons or numbers,
but just off the cuff here, I'd say "taint no winner, folks; my scale
cain't read less than 1%".
What it all means...
Now, if you’re on or near the top of the heap in aerobatics world, and you
intend to compete on the nationals level in pattern and aerobatic events, possibly I can see the weight point, (and you’ll
probably get your packs for free at that level) but at this point in comparative technology development
and in the vast majority of today’s sport aerobatic ARF IMAC aircraft, the one to four ounce weight difference
don’t amount to a hill of beans in aircraft performance. I humbly submit that picking a better prop is a whole lot more useful exercise in better power to weight
than throwing a ton of cash into your battery system!
...if not weight... then Why??
dependability, reliability and field serviceability points of the great debate, A123, Li-Ion, Nicad and
NiMH all have their foibles. Nicad, NiMH and Li-Ion all share relatively 'short' service lifespans (2-3 seasons).
Li-Ion and most NiMH systems rate poorly under intense loads compared to NiCad or A123. At this point A123 has the
durability and relability edge with the best performance under load and longest operational lifespan of all technologies
tested. It shares with Li-Ion the obvious requirement of compatible chargers and field equipment and for folks familiar
with NiMH and Nicad, what could be considered a daunting new knowledge base and most likely; new field equipment/chargers
will be required. (to ease the learning curve see our A123 Setup and FAQ pages)
I pursue critical application radio system setup with one motto: "Every component between the battery
and receiver adds risk, weight & reduces reliability." My best advice for folks contemplating the move to the big
birds and the various battery technologies used in them.. keep it simple.Consider and
provide for ease of access to the pack(s) for evaluation and charging at the field and equip yourself with competent serviceable
pack checking & charging equipment that's easy to use, appropriate for the type system you intend to use and become
familiar with it so you can make competent "fly; no-fly" decisions before each and every flight. Buying good high
quality field gear the first time might be a bit more expensive out the gate, but in the long run costs much, much
new technologies eventually completely 'take over'? Certainly!! Just about the same time we switch over to solar heat,
windmills, safe nuclear power and cars that run on hydrogen. Regardless, every month that goes by, there are fewer
Nicad and NiMH cell types in production; more Lithium types coming on-line. In the short term, don't look for the changeover
to be complete over the life of your next new battery pack.. whatever type you choose! :)
Edited, April 2011
*It should be noted that with the Lithium Ion systems a Voltage Regulator is commonly
used for each pack. Should you chose to improve the ‘Spaghetti Factory’ wiring situation and further improve current
handling and system safety in these systems, there are several types of ‘Power Boxes’ available from several
distributors that greatly simplifies system installation.. and it adds several hundred bucks (at least, most cost
$400+) to the cost and 5 or more oz to the system weight. You'll also note I did not price in the (much more expensive)
'recommended' regulators and switches sold by Fromeco and Duralite.. I used the pricing and weights of the ElectroDynamics
UltraSwitch II's and common standard HD 10amp system adjustable regulators (when I need one) that I sell here.
REGARDING REGULATORS: With the Nicad & NiMH and A123 systems, using
a voltage regulator is not usually a required piece of equipment. I generally avoid the use of regulators and
select ignition systems and servos that will tolerate the full voltage of the packs that I select for that model. Whenever
you use a regulator you are adding a component that adds weight, complication and another possible mode of system failure,
and they are not used in the comparison except where commonly used. All 3 lithium setups shown have redundant Rx switches,
chargeports and packs.
LiFe systems (commonly referred to as LiFe PO4) do not share A123's load carrying capability or A123's extremely
long calender/duty cycle lifetime advantages. If it does not say A123 on the label, for comparison purposes
it's at best just a lower voltage Li-Ion pack in terms of loading capability, relaibility and lifetime expectations.
**** We've showcased the Sanyo 4/5 'A' 1950 FAUP High Rate NiMH cell in this comparison rather than the more
commonly flown (slightly lighter) Sanyo HR-2150AU. Why? Because we liked the load performance, durability and fast charge
capability of the heavy duty 4/5 A FAUP High Rate cell. And; we preferred to place dependability just a hair higher on
the order of priorities than weight when we chose a cell for IMAC Rx applications.