Hannu Vuorinen

Hi,


Some photos of our experiments using litium-polymer flight
pack while towing 1/4 scale gliders.

Tug is 1/4 sc. Piper J3 originally made from Sig kit, till last year
it was powered by Saito .130 4-stroke engine.

Electric conversion includes Actro 40-6 outrunner with Actronic
70-32 controller, and flight pack configuration 10s2p Kokam
3270mAh litium-polymer cells.
AUW is 6,35 kgs, prop normally used is Menz 19x8" 5700rpm
at 32A static. However, in tow operation I use Menz 20x11"
at 5000rpm.

So far biggest glider towed has been 4 meter of wingspan,
and 4,6 kgs weight.

Hannu Vuorinen

Piper and 3,8 meter Ventus in take off

Hannu Vuorinen

..

Hannu Vuorinen

1/4 scale A-S K-8 behind Piper , AUW 4,6 kgs

Hannu Vuorinen

And higher..

Greg Covey

Hannu,

Great photos!

Thanks for sharing.

Hannu Vuorinen

Thanks Greg,

Below pic of 1/4 Piper powerplant, Actro40-6 outrunner
and Kokam 3270mAh 10s2p -flight pack, photo from
last winter "flight endurance" test, flight time reached then was 32 minutes continously. In tow operation average power consumption seems to be around 650mAh/ tow/200 meter altitude, when taking up 4 meter size glider.
This would mean roughly 7-8 tows per one charge.

Matt Kirsch

My Feedback: (21)

I'm intrigued by your pack configuration. You're sucking 32A out of a 2P pack of 3270 Kokams, and they're holding up ok?

Let's see... 3270mAh at 5C maximum is roughly 16A... I guess you could do it with throttle management.

Hannu Vuorinen

Hi, Matt,

Right, Piper flies normally average power setting of only 9 amps (1, 4C
discharge)
in normal flight, in tow operation average power setting through
hold tow sequence is roughly 18amps ( 650mAh/tow up to around 200 meter altitude and landing).

As in normal flight C -values are very low, it means also that Kokam pack is holding its voltage in very high value, would
estimate somewhere 38-39V region in flight (apprx 340 - 350 W of power)
Continous C values in 2P-pack 3270mAh is 26A,
and 6C peak just below 40A


Please note that this is just average value, in first seconds
tow take off amps are little bit over 40A.

I have used this certain pack now roughly 30 charge cycles, and it
works perfectly, only thing is to remember balance cells after every 4-5 charge cycles

Hannu Vuorinen

And this is easy way of balancing packs at same time,
all 10 packs in parallel charge at 1 cell setting

d_wheel

Please explain your reason for charging all cells in parallel. This type of charging has been considered bad for batteries for many, many years. If one cell is defective, it may be destroyed, or even worse cause the charger to be confused and destroy all of the other cells. I would personally not use this method of charging unless you can explain why it is safe and effective.

Later;

D.W.

Hannu Vuorinen

Hi, DW


Lipo cells has a tendency to go unbalance in series
connected pack, and it is happening more you draw higher
C-values(like also NiCd/Mh cells). At the end of the day, unbalanced pack wont
give you anymore the performance out, so it must be
balanced somehow. also, if it is badly in unbalance,
it may damage your cells during series charge.

So, we have to balance them somehow occasionally.

While all packs are connected parallel into balancing bar
(1 cell setting, 4,2V), we treat them like they are 1 cell,
in this case it means one pce of 66.000mAh cell.

So, there is no chance of getting voltage higher than accepted,
charger will keep it in 4,2V.
Even if some of the cells are not in same voltage, connected in bar
they are charging and discharging inbetween cells depending on their condition, heading to balance. Ofcourse we can speculate about charger failures etc, but will leave that now out of this.

Few things to monitor while pack is in parallel charge:

1. If you connect empty and full cells in bar, there is a risk
that charging currents in between cells can go too high. If you
suspect this, check amps between cells before connecting to
charge bar. Minor unbalances will cause only few tens of milliamps currents between cells, ie. much below 1C currents, so it is OK.

2.
When they are connected in parallel charge, charge current will
rise by multiplying cell number. So, if one cell damages during parallel charge, and circuit opens, other cells will get too high charge current. This is anyway very hypotethic situation bearing
in mind that even most efficient commercially available charges can go only up to
5-7amps charge current, at 150-180W power.
Example: When having for eg. 10 pces of 2000mAh cells,
1C charge current would then be 20 amps.
It would be quite a powerfull lipo-charger getting that power out!
So, in parallel charge currents are anyway very low, in Piper pack
full charge current is 3,1A (power of my Spectra II charger is 150W) This means 1/22C charge current for individual cell(66.000mAh:3,1A=1/ 22).

3.
If cells have different quality connections, solderings etc,
it is posible that resistance may vary. This would cause different
charge current for cell. It has to be quite a difference, that it really
hurts cells.

Greg Covey

D.W.,

Yes, Hannu is right, charging Lithium Polymer cells in parallel is just fine. Check out some of my large e-conversions on my Aerobatics page like the Graupner Extra 300S. It uses a 5s5p pack of Kokam 1200HC cells.

More recently, my Graupner ShowFlyer has been converted from a 26-cell NiCd pack to two packs of 4s5p Kokam 1500HD cells. I charge each pack as is in the 4s5p configuration.

Regards.

d_wheel

Thank you Hannu. I am happy to see that you are aware of the potential problems and are monitoring for them. I still would not recommend that anyone who is not proficient with electronics try this form of charging. Although it is a lot more trouble, I would recommend charging each cell individually to obtain an equalization of all cells. This way, there is less danger of damage or personal injury. Also, it would be much easier to identify any cells that are having a problem.

I can't argue with your success, however, and have always believed that if something works for a person they should stay with their method.

Later;

D.W.

d_wheel

Hello Greg,

In your pack configurations the cells are always connected in parallel. This keeps each set of cells more or less equalized. My concern with Hannu's method is that he is taking 10 individual cells that have been operating in series, and then connecting them in parallel to equalize them. This is where I see the potential for problems. As he said in a later post, if one cell is defective, it might draw the bulk of the current during charge which could be disastrous.

However, as I stated to Hannu, if it is working for him then stay with it until signs of problems occur. My biggest concern is that an electronics newbie might hook something like that up and walk away without monitoring for the potential problems.

Later;

D.W.

Hannu Vuorinen

Hi, DW

Few comments about parallel charging/balancing,

1. Lipo cells always needs to taken seriously while handling them

2. Series charge is always more risky than parallel charge.
This is simply becouse of possibility of too high voltage.

3. If short circuit occurs, short circuited cell has the lowest
internal resistance, so it wont damage any other cell
(only possibility, if close region, heat can hurt neighbour cell)
becouse this cell will suck the highest current.

Ofcourse individual cell charge for balancing is very good
and safe method, but thinking about large size cells and lots of
them to treat, single charge is not very effective way.
BTW, in lap-top PC´s litium cells are also always treated in parallel charge.

Below some closer look photos about Piper powerplant

Actro 40-6 outrunner

Hannu Vuorinen

Kokam cell pack in their flight condition.
It is easy to slide this box into fuselage

Hannu Vuorinen

.

d_wheel

Hannu,

What is your opinion of the outrunner motors? I am thinking about trying one on my next project and would like some comments.

Later;

D.W.

Hannu Vuorinen

Hi, DW


I have used outrunners for something like two years now,
and they are great in scale type applications.

On the other hand, if you need short burst of highest possible
power, conventional brushless motors give the best efficiency.

Outrunners are best in their efficiency in the sport/scale
type flying, where power settings vary a lot, so outrunners
wont give you the highest efficiency in full throtttle, but
beat conventional motors in lower power settings.

Also low weight and small size is a great benefit in outrunners.

Below pic of my Torcman 430-30 (1500W power)outrunner
installation in my 1/5 scale FW44 Stieglitz, motor weight is only 540 grams. It fits smoothly in relatively small space inside dummy motor.

d_wheel

That is a very nice model Hannu. I don't have the patience to build scale projects. If I can't have something flying in a few days, then never mind. I am trying to learn to hover and torque roll now, and having a good time with it. Getting better but still can't hold it for very long. Thank you for your impression of the outrunner motors.

Later;

D.W.

Hannu Vuorinen

Thanks, DW


I took a part last weekend in Finnish Stand Off Scale
3rd cup competition at Kuopio with my Piper , and on last
flight round we made also aerotow as last optional
maneuver, it went just OK, scoring 8 points on that
tow maneuver. Total result was 1st, second time on this season..
Very close to win Finnish Championships now, first time with
electric among glow & gasoline powered models!

Hannu Vuorinen

Hi,

below link to 3 flightvideos of Piper, video by C. Walsh

http://www.kolumbus.fi/sxh/video.html

daveslats

Hannu,
That was an outstanding thread, concluding with some excellent videos. Well done! I have a piper cub, too, but a much smaller Sig version (1/8 scale, I think). I have it converted from a 25 glow to a Jeti brushless. It flies well, even off floats, but flight times are only around 6 minutes with a ten cell NiCD pack. I like the idea of those LiPo packs you discussed earlier, but it seems like you have to have a degree in electrical engineering to figure out charge rates etc., and I've heard the up-front capital cost is pretty heavy too. Any comments?

Hannu Vuorinen

Hi Dave,

I really dont have any degree in electrics!! Jus few years flying electric, so
just learning by doing...
Nowadays there is so much info about lipos available, that it is much easier
than 2 years ago, when I started playing with Li-cells. Your Sig Cub would fly
easierly 25 minutes with lipos, or much more if you want..
Thinking about my tug combination, Actro 40-6 outrunner powered Cub and K-8 glider is total weight of 11 kgs (is that closer 24lbs?) while taking off, and it goes smoothly
up, I would not anymore even think about NiCd/Mh cells, Kokams are just great!
OK, initial investment is much higher, but... planes just fly so much better!
And 5 times longer. But also a big step onforward is motor technology, especially
in scale/pattern/3D planes, where lots of flying is on partial throttle setting.