First off, why? The simple answer is that I already had 3S 2200mah packs for use in my speed 400 prop planes and smaller 55-60mm jets. Rather than buy 4S 3700-4000mah packs that would only be used in jets, I decided to experiment using 6S 2200mah packs.
As it turns out, the weight of a 6S 2200 battery pack (2 3S 2200’s in series) is the equivalent weight of a 4S 3700-4000mah pack.
Also, whether you use 4S or 6S, you’ll need either a receiver battery or switching battery eliminator circuit (SBEC), so it’s not as if there is anything extra needed. Most ESC’s that have a SBEC also can accommodate 6S.
The other advantage is efficiency with higher voltage. For roughly the same watts as a 4S set up, you’ll be pulling 20C, but at much less current, so there will be less resistance losses. For every amp drawn, you’ll get about 22 watts in, as opposed to about 15 with a 4S set up.

The Set-up

2 3S 2200 packs in series. I used either Spyder 25C 2200’s or Billowy 50C 2250’s. The Spyder’s weigh 6.4oz and the Billowy’s weigh .1 oz more. Both were tested by “everydayflyer" in the “Batteries and Chargers” section and are close in resistance with less than 10mOhm for the pack.
I used a Castle Phoenix 80 with Hyperion “cool” SBEC (med timing)
I also used an ARC 28-47-2 (kV=2170) for all fan testing.
All fans were mounted vertically in a test stand, and were open exhaust (no thrust tube). All fans had rounded intake lips that either came with the fan or fit the fan housing for the purposes of testing.
The test stand was placed on a kitchen scale with .1 oz. accuracy.
PLEASE NOTE: The numbers tended to fluctuate at full throttle, so everything has a margin of error of about 1 amp and .5oz thrust.
CAVEAT: the edf calculator http://www.s4a.ch/eflight/fancalc_e.htm gives very mis-leading results for 6S and cost me some time and money when I bought the wrong kV motors.

On to the results:

HET 6904
Amps=37
Watts=850
Thrust=54
Grams/watt=1.83

DF70 “sickle fan”
Amps=31
Watts=700
Thrust=47.5
Grams/watt=1.9
-The sickle fan has an unreinforced plastic rotor, so 800 watts would probably be it’s limit.

Eflite Delta V-15
Amps=33
Watts=750
Thrust=51
Grams/watt=1.93

WM400 MKII
Amps=35
Watts=790
Thrust=50
Grams/watt=1.79

Other non-standard tests

DF70 housing with Eflite Delta V-15 rotor (cut down a few mm)
Amps=29
Watts=650
Thrust=44.5
Grams/watt=1.94

AFA 68mm fan with Neu 1112/1.5Y (kV=2350). Review here: http://www.rcgroups.com/forums/showthread.php?t=1337010
Amps=35
Watts=800
Thrust=51
Grams/watt=1.81

The Grams/watt is really system efficiency and the number goes down with the higher the wattage; not a true fan efficiency. As I used the same power system, I think the results can be compared.
You do need “true” 20C packs to get these results and not worry about puffing batteries. FWIW, the Spyder 25C 3S 2200’s are $30 and the Billowy Power 50C 3S 2250’s are $33.
Though I used the ARC motor, any 2200 kV motor will get similar results, depending on actual kV and efficiency.

I hope this helps those with 3S2200 packs wanting to get into 70mm EDF’s

Terry

interesting stuff, many thanks

You're welcome.
I will add more results after I test them.

ex-racr
one thing that matters too is how much can squeeze the outlet before the results turn negative.
the exit velocity also have something to say!
and how is the motor used compared to the fan wheel used.
Right now i am working on a comparison of a 3 blade and a 5 blade fan.
But more will come..
Claus

Claus,
These tests were carried out primarily to get amp readings, so as to confirm a motor around 2200kv would be suitable for 6S.
The thrust measurements were icing on the cake as they took very little effort to record.
Some of the fans tested may do better with poor ducting or a reduced outlet, but I wanted a consistent test standard between fans.
FWIW, I don't consider any fan tested to be the "best". They all have benefits and disadvantages to me.

Best regards,

Terry

Hi Terry,

For what it's worth, I'm posting the EagleTree graph of a 6s test I did for a customer. The wattage is not all that high, but the customer wanted a low amp setup. I was surprised to see actully how low the amps were. Seems to be pretty efficient.
I thought you might be interested.
Gary


.................................................. .......
Motor: ARC 28-47-2
ESC: hobbywing 60A
batt: XPS 30c 3200 (the smallest 6s I have)
EDF: Skyworld 70mm (w/ 8 blade rotor)
.................................................. ........


The first chart is on MEDIUM TIMING...... (1012w....42.7A)
The second is on HIGH TIMING............... (1081w...44.5A)

I got this a few days ago and ran it up.
Details of the fan are here:
http://www.rcgroups.com/forums/showthread.php?t=1359237
The set up: 6S 2200 50C with Mega 16/25/2E (kv-2300, Rm .015)

Amps: 35
Watts: 760
Thrust: 48 ounces
Grams/Watt: 1.79
I suspect the mediocre G/W reading is because the ESC was losing sync with the motor at full throttle a little.
Never the less, it's in the same ball park as others.
One important thing to note is that the motor used has a higher kv than the ARC 28-47-2 used for most testing.
For my goals, this is a perfect match of motor and EDF unit, as my goal is to get about mid 30 amps static, without a thrust tube. That way I get 900-1000 watts installed.

Terry

Would be interesting to add the following:

Change Sun 70mm 10 blade
WeMoTec Minifan

Slaanesh,
I tested the CS 70 10-blade with the available motors I had. The simply didn't have the torque to make efficient use of the fan.
As for the Wemo, it is the same/similar load as the DF70.
As I still have more fans and motors than available airframes, I won't be adding to my inventory for a while
If you look at the Change Sun 10-blade 70mm thread, some have used the HET 3W-25 with good results on 6S with amp ranges appropriate for using 2200 batteries.

Respectfully,

Terry

Wow, this is good stuff!!!
Thanks for the hard work on this!!!

Hi Terry,
Good thinking,
I have been increasing efficiencys for over a decade now and have been spamming HV setups to boredome at this forum. HV is the way to go for decent flight times and better performance. i did even extensive research for SHV setups in 70mm edf class. It's even a good remedy for chosing the more silent"amp hog" rotors which are trending right now.
If you really enjoy increasing efficiencys you'd probably end up designing your own edf jets too
Please keep an eye on the older units. new products aren't always always an improvement.

best regards!
Erik

Martin and Erik: Thankyou!
With 6S 2200, you lose nothing over a 4S3700-4000mah set up.
Despite the sound, the EFlite fan is one of the better units.
Also, as far as HV and SHV, I think 6S 2200 is probably the best solution for 70mm, in terms of performance and weight.

Originally Posted by Erik v. Schaik

If you really enjoy increasing efficiencys you'd probably end up designing your own edf jets too
Please keep an eye on the older units. new products aren't always always an improvement.

best regards!
Erik

I already have a jet design and a "new" rotor design in my head. Don't know if either will ever materialize.
Also, the Change Sun 10 blade 70mm, as well as the 90mm and 120mm is a rip off of the STUMAX rotor design. It needs a big motor to have good system efficiency.
Some have had success with it.

Regards,
Terry

Originally Posted by ex-racr

I think 6S 2200 is probably the best solution for 70mm, in terms of performance and weight.
Regards,
Terry

Personally I am very keen on 8s setup. 4x2s kan make a jet very narrow which is needed for high speed projects. a 7s setup (2s+3s+2s) would create a very aerodynamic fuselage. Personally i do like the Jeti spin55 very much which has great specs and dimensions. Without cooling ribs this one is amazingly thin.
Latest controllers have 12s+BEC which makes one wonder why one should't buy 12s 1350mAh cells. The only reason which puts me off is the KV tolerance which makes it very hard to pick a suitable motor.

Originally Posted by Erik v. Schaik

Latest controllers have 12s+BEC which makes one wonder why one should't buy 12s 1350mAh cells. The only reason which puts me off is the KV tolerance which makes it very hard to pick a suitable motor.

-lowering the KV enough for 8+S means going to higher turn windings (more resistance) or heavier motors with lower turns, which I'm sure you know
Don't forget all the added stuff to the cells (balance leads, tape, shrink wrap, battery connectors) tends to add up when using multiple packs.
I figured out I could use 12S 2200mah for a 90mm Midi fan, but the weight of all the cells is actually more than 2 3S 3800-4000mah batteries. Weight-wise, it makes more sense to go 6S or 9S on larger packs.
I have a couple other set ups that I have data on, but it is installed data; not the test stand. I need to charge up some cells, measure and post data.

Terry

For a high efficiency setup I would not prefer a modular pack to begin with. I do solder the packs in series, including balancer cable. Unfortunately the specs of a pack don't mention the weight of the leads. Keep in mind SHV setups have thinner dia wiring and smaller connectors. Lower C-rated packs are lighter too.

Don't get blinded by the inner resistance of a motor. If the voltage is higher, the current will drop which reduces heat waste and increases flight times. An other side effect to be noted is you can recharge the cells with high current and continue the flight without the classic cooling down time of approx 1hr we used to do to avoid a demagg.
On a 2007 project I was able to recharge my pack within 8 minutes and take off for the next flight. At a turbine event the recharge time has been used to create a time gap for turbine flyers 3 times in a row
you cannot do this on a High Amp/Low Voltage setup.

if the motor stays cool, there is no reason to add more iron unless it lacks torque or you have to start doing math with other fan+motor diameter with identical FSA to increase torque. That's why the 80mm class has been introduced.

If I were to design an other speed edf racer I'd go SHV for sure. Not only because of eliminating heat waste but the design layout of the airframe would not be "in the box" to start with. Unfortunately, there are no high performance edf jets available to match high power setups. A good edf jet design is a key factor as well, not only the drive system.

br,
Erik