flyingchaos

Hi,

Does anyone know what is the maximum amperage on the mains and the tail esc on the GWS/FEDA dragonfly esc/mixer board? It is the separated mixer. non all-in-one.

After analyzing the circuit, it looks to me that the tail and the main FETS are identical, except that the mains use two FETS(one on each side of the board) in parallel for added amperage capability...

The FETS are lableled as:
MK3L
9123
I'm am having a great deal of trouble trying to find specs for these chips!

The point is, I was thinking of using of using a 3-cell lipo, but am afriad to burn the board. The board is a nice design for simplicity and provides use of a 4 channel radio.

Anyone tried using 3cell on the standard esc? or 2-cell and how does it run then?

Any help is appreciated. Thanks!

-Dan



I guess I could replace these FETS with popular higher current capable FETS that are out there for cheap. (for instance: for a little over a buck a peice, IRF7832 can handle 20A by itself! probably burn the traces on the board before burning your motor! )

Super-Hornet

Hi dragon-dude

I'm using the same board as yours. I also tries to find the spec for it. Let me know if u got it.

I recently upgraded my Dragonfly tail rotor to a EDF50B. It is 5 blades CN12-R-LC motor. So damn powerful and it can even lift itself up. (The whole ducked fan) So far my Mixer can withstand it. If i feel the FET with finger, it doesn't feel hot. Guess it can take in more current.

Now according to my GWS Dragonfly box, it does mention that you can upgrade the Main Motor from EM150 to EM350 and never mention about u need to replace the mixer for higher current. And in the GWS website, it also mention u can upgrade the Tail Motor to CN12-R-XC motor and never mention about changing the Mixer. From that maybe we can assume that the Mixer can withstand/supply quite high current.


Oh.. btw.. I once connected the tail motor to a 4Ampere 3V motors can it can run it. The whole wire that connected to the tail motor turn hot so does the FET. I didn't try long to avoid damaging the FET.

Super-Hornet

Linz

Hi Dan,

Did you ever find any information about the FETS MK3L 9123?? My speed controller got hot and now there is a nice brown spot on one of them...

Thanks in anticapation,

Linz

flyingchaos

Hi Linz,

Unfortunately, I did not find anyspecs on that chip :-(
However, I do remember reading a post somewhere that said the gws all-in-one is capable of 4.2 Amps, which led me to beleive that our mixers (the main&tail esc mixer only) probably uses the same FETS. I this assumption is right, this means that the tail is 4.2 A and main is 4.2 X 2 = 8.4 Amps max...

From your interest, you're probably going to try a 3 cell lipo or have already burnt your board :-)
You can look at this posting...

http://www.rcuniverse.com/forum/m_15...tm.htm#1546211

mcdoong tried a FET that I advised and it sounded like it works...perhaps works too good :-)

So if anything, atleast someone has tried a off the shelf FET(for cheap) and it works.
I'll be ready to fry mine up soon, I'm waiting on so Lipo's.

-Dan

Linz

Hi Dan,

Thanks for the speedy reply. Forgive my lack of knowledge but what do you mean by 3 cell lipo?? (Sounds like something a plastic surgeon would use!!)

I ordered a few logic level FETS form our Farnell on monday - pinouts look ok, I'll let you know how it goes...

Thanks Again

Linz

flyingchaos

lipo=lithium polymer

It's great for this hobby because its lighter and usually double the flight time of conventional nimh(birdseed) packs.

Lipo is just a different chemistry battery as opposed to nimh or nicads.

Lithium-Ion are similar to li-po's and are perhaps more well known(they are primarily used on cellphone, and camcorders)
From what I know, Li-po's have a higher C level or allowable amperage drainage and are lighter than Li-Ions, that's why we use them here.

each Li-ion/po cell is equivalent in voltage to 3 nicd or nimh batteries( so 1.2v X 3 = 3.6)
so 3 cell li-po is = 10.8 but the actual voltage measured is more like 11.1 volts.

I just thought you may have broken your board by using a 3-cell... ;-)
Some people have sucessfully used a 3-cell on stock mixer boards, and some have fried it on thier boards...I want to give it a try on my heli sometime and see what happens :-)

-Dan

BTW what is the FET chip model number that you have...a dual FET has the same pinout and I'm afraid to say that it probably will not work. (in fact I'm positive it will not work, if you have a gws main/tail mixer board)

Linz

RE: MK3L 9123

Hey nice one Dan,

thanks for the info about the batteries, I'd not heard of lipos.

Its interesting what you say about people frying their boards. Does this mean popping tracks off the board?? I'm convinced my Main Rotor FET popped through using a newly charged power-pack - after the first time it had been charged - when I measured voltage off-load it was about 10 - 11 volts. My board has a piece of thick (for the miniture application) wire running across the top to the main motor supply, as if the track wasn't ever designed to carry enough current...

As regards the FET, I was piviliged enough to have our doctor in electronics (no - really!) pass by whilst I was trying to choose one and although I've only used the Heli with its replacement for 1/2 hour it still seems ok... I only changed the one that popped (wrt to your thread about current imbalance - thanx)

for an IRF7401, N Logic MOSFET, SO8b case style, 8.7A pulse 35A. Farnell Pt No 167988. They are £2.50 tho, about $4.

The device is a single transistor type so the pinouts are the same as the original but my only worry is if the problem re-occurs it will pop the next weakest link. There are other lower amperege devices in the series though, and they are all readily available. (Happy to help if anyone can't source them)

My last thought is how interesting it was to find that the Heli MOSFET failed in such a way that the throttle on the Main Rotor was effectively stuck at full. My girlfriend found it most amusing as did the cat, but only 10 minuites after the danger had been neutralised and everyone had been accounted for...

Thanks Again!!

Linz

flyingchaos

>>My last thought is how interesting it was to find that the Heli MOSFET failed in such a way that the throttle on the Main >>Rotor was effectively stuck at full. My girlfriend found it most amusing as did the cat, but only 10 minuites after the >>danger had been neutralised and everyone had been accounted for...

I'll put my background to use while being laid off....
I think what happens here is that when a high current flows from the MOSFET's source(N+ dope) through the substrate to the drain(N+ dope), two things can happen:

1. the source and drain doping is so close together that they can melt together at high temp causing a Permanent ON case. ( and stays this way until it burns up.)

2. the source has melted through the silicon oxide layer to drive the gate and turns itself ON possibly damaging other chips at this state.

Does this describe it? ;-)

-Dan

chuckstarck

My Feedback: (1)

I had the same issue with a HB II just today. I can't find the IRF7401 in the US. Got any ideas? THis is a hummingboard, both sides burned out of nowhere and full throttle into a pile. Tell the cat...

flyingchaos

try the irf7821. Another member here got a hold of them from digikey and verified that it works...
You can read up on the thread here:

http://www.rcuniverse.com/forum/m_15...tm.htm#1546211

Good Luck. Oh...just a reminder, you have 8 tries left with the cat. :-)

Dan

chuckstarck

My Feedback: (1)

got the original in the USA at Mouser Electronics, same Zetex original part.

www.mouser.com

chuckstarck

My Feedback: (1)

for all who care...

The fet isn't the real culprit. After you replace it, one of the D4 diodes is probably bad. I killed 4 fets, testing this to see what really was happening. Actually, those fet's should do 8.9amps each and there are two of them, that 17.8 amps! You could stack more on top of each other if you wish as well, that's what they are doing on the board but put them on each side to make it look otherwise.

Looking for a source. I found the fet's at mouser.com, $1.35 each but the diode that parallels the fet is bunk. Can't find a source as yet. Says S7 D4 on it.