Seems like 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 ‘politics, religion or batteries’.
I have absolutely no doubt that those that have already
invested in the new technologies will not be switching back 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 the technology is
as refined as it is, and it's thanks to their support and input that it's improving at a remarkable rate. 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. Every thing 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’.
We Crunch The
Numbers...
Let’s have a look at a typical IMAC 'Big Bird scale
IMAC 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
Plusä Li-Ion
Basic 2S2P System, Total Capacity; 3800ma. Total Rx pack load rating: 15 amps
|
Quan |
Desc |
Weight ea |
Cost ea |
Total weight |
Total Cost |
|
2 |
#7194 1900ma
4 cell-7.4 volt
RX - Flat pack |
4.4oz |
$68.95 |
8.8oz |
$137.90 |
|
1 |
#7092 950ma 2 cell-7.4 volt
RX - Flat pack (ignition) |
2.1oz |
$36.95 |
2.1oz |
$36.95 |
|
3 |
Voltage regulators, Switched. |
1.2oz |
$46.95 |
3.6oz |
$140.85 |
|
|
|
|
|
14.5oz |
$315.70 |
Fromecoä Li-Ion Basic
2S1P System, Total capacity; 4800ma Total Rx pack load rating: 8 amps
(data submitted by MaudDib, RCU post 1/24/05)
|
Quan |
Desc |
Weight ea |
Cost ea |
Total weight |
Total Cost |
|
2 |
2400ma 2 cell-7.4 volt RX pack |
3.3 oz |
$27.00 |
6.6oz |
$54.00 |
|
1 |
2400ma 2 cell-7.4 volt IGN Pack |
3.3oz |
$27.00 |
3.3oz |
$27.00 |
|
3 |
Smart Fly TM
Failsafe regulators w/switches |
1.5oz |
$45.00 |
4.5oz |
$135.00 |
|
|
|
|
|
14.4oz |
$216.00 |
Sanyo NiMH HR-2700AUX
Redundant System, Total Capacity, 5400ma. Total Rx Pack load rating: 20 amps
|
Quan |
Desc |
Weight ea |
Cost ea |
Total Weight |
Total Cost |
|
2 |
2700 ma 5 cell 6.0v NiMH (HR-2700AUX) |
7.2oz |
$32.95 |
14.4 oz |
$65.90 |
|
1 |
GP 1100 ma 4 cell 4.8v NiMH |
3.3oz |
$23.95 |
3.3oz |
$23.95 |
|
3 |
HD charge port switches |
0.3oz |
$14.95 |
0.9oz |
$44.85 |
|
|
|
|
|
18.6oz |
$134.70 |
Sanyo NiMH**
1950 FAUP Redundant System, Total Capacity, 3900ma , Total Rx Pack Load Rating: 45 amps
|
Quan |
Desc |
Weight ea |
Cost ea |
Total Weight |
Total Cost |
|
2 |
1950ma 5 cell 6.0v NiMH (HR-4/5 FAUP) |
7.2oz |
$39.95 |
14.4 oz |
$79.90 |
|
1 |
GP1100ma NiMH High Rate 4 cell 4.8v |
3.3oz |
$23.95 |
3.3oz |
$23.95 |
|
3 |
HD charge port switches |
0.3oz |
$14.95 |
0.9oz |
$44.85 |
|
|
|
|
|
18.6oz |
$148.75 |
Sanyo Nicad
Redundant System, Total Capacity, 3000ma. Total Rx Pack load rating: 30 amps.
|
Quan |
Desc |
Weight ea |
Cost ea |
Total Weight |
Total Cost |
|
2 |
1500 ma 5 cell 6.0v Nicad (KR-1500AUL) |
5.75oz |
$29.95 |
11.5 oz |
$59.90 |
|
1 |
1050 ma 4 cell 4.8v NiMH |
3.0oz |
$19.95 |
3.0oz |
$19.95 |
|
3 |
HD charge port switches |
0.3oz |
$14.95 |
0.9oz |
$44.85 |
|
|
|
|
|
15.4oz |
$124.70 |
...and the winner is..... Nobody!
Now, a quick look at the numbers would indicate
that all three systems shown are in the ‘ballpark’ as far as weight goes.. the Nicad system and the Li-Ion systems
are less than one ounce different in weight, there's a 4 ounce difference with the NiMH setups. Add to the
Li-Ion systems the weight of a voltage monitor and the recommended low voltage cutoff modules and the Li-Ion weight advantage is
reduced to less than 1 ounce over the NiMH setups, and the Nicad system becomes the 'lightness leader'. While Li-Ion
comes in a close second and NiCad seems a distant third in the capacity race, whatever flight time advantage a Li-Ion
system would enjoy is eaten away by the NiCad's much faster field recharge time.
Folks; if you sit down and figure out what the field support
equipment costs for Li-Ion (Chargers, ESV's, Cyclers, Power Boxes, 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; mah 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??
On the dependability, reliability and field serviceability points
of the great debate, Li-Ion lags behind the others simply because of the safety outcry.. all those safeguards add expense,
weight and significant complexity. I pursue critical application radio system setup with one motto: "Every
component between the battery and receiver adds risk, reduces reliability." As long as Rx's and servo's fry at 7.2v I
can't see how anyone can produce a more reliable system than a simple parallel NiMH or Nicad setup with dual
HD switches.
Is the new technology going to 'take over'? Certainly!! Just
about the same time we switch over to solar heat, safe nuclear power and cars that run on hydrogen. In the meantime,
don't look for the changeover to be complete over the life of your next battery pack. :)
Steve Anthony
NoBS Batteries
Edited, Jan 2005
*It should be noted that with the lithium
system a Voltage Regulator is absolutely required for each pack. Should you chose to improve the ‘Spaghetti Factory’
wiring situation and further improve current handling and system safety in the Duralite Plus system, they have an outstanding
item called the ‘Power Box’ that greatly simplifies system installation.. and it adds $325.00 and 5.24 oz to the
system weight.
With the Nicad & NiMH system,
unless JR coreless servos are installed in our aircraft, using a voltage regulator is (in my opinion) a superfluous piece
of equipment that adds weight, complication and another possible mode of system failure, and they are not used in the comparison.
All 3 setups shown have redundant Rx switches, chargeports and packs.
**** We've showcased the new 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 new heavy duty 4/5 A 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.
