crashparry

Hi I am running a dragonfly with seperate esc/mixer and gyro, with a Johnson250 motor and like90 blades.

I' am going to buy the Apache 1-4 cell charger, any good?

Also can't decide on cell config...

either..

a) 2 cell at 1200 mah
b) 2 cell at 1500 mah (nearly twice the weight)
c) 3 cell at 1500 mah


What do you think would be best?

Regards

Crash.

crashparry

Come on, I know some of you are running LiPO's....

What are you running?

biggerswede

The problem seems to be that with 2 cells you probably can´t use more than a small part of the charge before the voltage will be too low to fly. Guess you wouldn´t get off the ground below 7 volts or so.
3 cells might either be great or fry your electronics with the 12 V or more voltage at full charge.
Wonder if it is possible to design a lightweight switching step-down voltage converter with high efficieny and 5-6 amps current capacity to deliver a stable 8 volts or so from a 3-4 or any number of cells Li-poly pack? As an electronics engineer I would say that it can be done. The design might resemble a high frequency high power ESC.

biggerswede

On second thought I would use 4 Lipos and set the output to about 9.5 volts. That is about what you initially get from a freshly charged stock battery. When the Lipos go below 11.5-12 volts the converter output will start dropping too indicating that it´s refueling time but until then you have the constant performance of a battery hot from the charger. Sounds tempting?
I believe that the converter could have at least 90 % overall efficiency and weigh below 10 grams. Low on-resistance FET, Scottky power diode, air-core inductor wound with Litz-wire and high operating frequency, maybe in the 100 kHz range.

RickyT63

Crashparry,
There are reports that 3-cell lipo cooked main board due to higher voltage. Best bet for using lipo with stock main board is 2-cell.
Here are some great 2-cell lipo pack:
- Kokam 1500mah 2-cell pack.
- ThunderPower 1320mah 2-cell pack. <--- (I use this and it's average ~ 15mins continuous hovering)
- E-Tec 1200mah 2-cell pack.
As for charger I've bought BEL 2-3 cell Lipo charger and hooked it up to an old PC power supply.
Hope this help.

thiswillfly

Kokam 1500 is the best in my aerohawk. Have tried e-tec 1200 also to compare, but the kokam wins in my opinion. Kokam fits in the original battery mounting clip so no need to design an alternative battery mount - and still heavy enough to maintain good CofG. Kokam with it's higher capacity has more power to keep the voltage up for longer. The slightly heavier weight of the kokam is not a problem as it's still lighter than the stock battery. I also bought an apache 1215 charger which is excellent and at a low price.

Freakazoid

My Feedback: (1)

This site boasts a lipo upgrade for a dragonfly, and it seems only 1cell? [&:]

Im thinking of going lipo aswell, but the weird voltage has me puzzled.

magic man

Yes it does look like a esc. There is a voltage regulator for li-po's that you can purchase from hobby-lobby

crashparry

No, that is a two cell lipo at allerc.

Looks like The favorite Is 2 cell at 1500 mah then!

Cheers guys

Super-Hornet

Hi

2 or 3 Cells? Hmm... difficult to decide.

Get 2Cell, it is lighter but if u calculate Wattage, W = V * I where V = Voltage, I = Current, that means to get the same wattage for both 2 Cells and 3Cell, 2Cells need to pull more current. Therefore it is hotter.

In theory 3Cells will have longer flight time but 3Cells is 1/3 more weight than 2Cells (On the same AH rating). With that extra weight, your main motor need to spin faster in order to lift it (Therefore more wattage needed). Due to main motor spin faster, your tail also have to spin faster to counteract the main motor...again more wattage... both motor become hotter also. At the end, u might get the same flight time for 2Cells and 3Cells comparison.

The indirect good point of 3Cells is that your main motor spin faster and therefore more stable and also extra weight will make your chopper more stable BUT if u do crash, it will hurt more.

Super-Hornet

crashparry

...and 2 cells is cheaper than 3

2 it is