HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 03, 2012, 09:24 PM
Registered User
Daydreamin's Avatar
New Zealand, Taranaki, New Plymouth
Joined Dec 2011
60 Posts
Help!
EDF Motors

I've been researching EDF power systems for the last few weeks and so far everything has made sense, all except one thing.

In my current jet I have a 2W-20 Het motor, 6904 fan unit, 60A esc and 3S 2650mAh 40C zippy battery. Cold this set up pulls 42A at around ~12V so will be producing ~450Watts which is what I want for my foamy jet. But eventually I would like to upgrade to a heavier jet and being able to re-use gear would save some $$.

From what I've read if I upgrade to a 4S battery the current draw is likely to increase slightly or stay the same, but unlikely to reach the motors max rated amps of 60A. So my question is: if this motor is rated to 60A but limited to a 3 or 4S battery (and current draw on 3S is only 42A) what is the limiting factor preventing the motor from drawing more amps?

Is the max amps rating on the motor just for spikes? Is it due to the efficiency of the fan unit? Is my zippy battery lying to me when it says its 40C? or is there some other reason/explaination?
Daydreamin is offline Find More Posts by Daydreamin
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 03, 2012, 09:31 PM
Bypass Ratio = Infinity
scatsob's Avatar
United States, NC, Jacksonville
Joined Apr 2006
1,653 Posts
If you go to a 4s battery your current will rise. Max amp ratings are typically continuous unless stated otherwise. To answer your first question, the only thing limiting current draw for a given KV is load. If you increase the voltage the rotor will spin faster increasing load and therefore current.
scatsob is offline Find More Posts by scatsob
Reply With Quote
Old Jan 04, 2012, 07:23 AM
High Dynamic Thrust
stoneenforcer's Avatar
United States, FL, Mt Dora
Joined Feb 2007
2,304 Posts
a couple fast quality 4s motors for 70mm applications are

Mega Motors. 16/25/1.5r 3750kv or the 16EDF 3600kv
stoneenforcer is offline Find More Posts by stoneenforcer
Reply With Quote
Old Jan 04, 2012, 07:53 AM
Registered User
Nederland, NB, Waalwijk
Joined Sep 2006
236 Posts
Hi,
I run a 2W20 motor in a Minifan pro at 4 cells. Current draw is around 70Amps, motor is very happy with this. Its a gread combo. I think your fan is very similar to the Minifan. I am sure someone here will correct me if I'm wrong.
MrBlobby is offline Find More Posts by MrBlobby
Reply With Quote
Old Jan 04, 2012, 10:01 AM
Da' Cajun
Boogie_'s Avatar
Lake Charles, Louisiana
Joined Jun 2009
2,876 Posts
The HET 6904/2w-20 on 4s is is a tried and true set up. Depending on the ducting it will consistently give 700-900 watts @ 60A-70A.

what is the limiting factor preventing the motor from drawing more amps?
As scat said, the motor kv is a constant. The ducting (restictions) will cause the amp draw to vary from one plane to the next.

Is the max amps rating on the motor just for spikes?
The amp rating is there to absolve the manufacturer from any blame if the motor fails due us EDF power hungry freaks blowing it up.
But this motor is golden on 4s.

Is it due to the efficiency of the fan unit?
Yes.

Is my zippy battery lying to me when it says its 40C?
Probably. ...just a little.
Most guys run their ESC/batts at about 60% of the rated max current just to give themselves a cushion against some catastrophic failure.
Boogie_ is offline Find More Posts by Boogie_
Reply With Quote
Old Jan 04, 2012, 01:02 PM
Build'em and Crash'em
Ken Lapointe's Avatar
Narragansett, RI
Joined Oct 2000
3,211 Posts
The current drawn is based on the load and voltage supplied, not the amp rating of the motor.

The amp rating is just how many amps the motor can take.

the Kv of the motor tells us about the design of the motor and helps us figure out the power it will use to spin a fan for a given rpm. Mostly its about fan, which is the load, and volts in which tell the fan how fast it should try to spin for that Kv number and the the amps used is the end result. As long as the amps used is lower than the rating of the motor you are good to go.
Ken Lapointe is online now Find More Posts by Ken Lapointe
Reply With Quote
Old Jan 04, 2012, 02:17 PM
Registered User
Daydreamin's Avatar
New Zealand, Taranaki, New Plymouth
Joined Dec 2011
60 Posts
Thanks guys, I guess now I need to get a 4S battery and give it a go. This is all going into a HK 70mm T45 air frame, the ducting before the fan is pretty useless (1st picture). Would you recommend that I add some foam (2nd picture) to help smooth the flow of air prior to entering the fan? I would assume this would increase the load on the fan but unsure whether this would have a positive effect on the amount of thrust produced?



Daydreamin is offline Find More Posts by Daydreamin
Reply With Quote
Old Jan 04, 2012, 02:52 PM
Registered User
Si Goodchild's Avatar
Lincolnshire, UK
Joined Oct 2009
522 Posts
I say go for it. I did a similar mod to an F18 which had poor inlet ducting and that flies really well. Poor inlet and outlet ducting kills performance. You need to make sure that the ducting doesn't get sucked flat under the load (and a 2w-20 on 4s will do that quite easily. Ask me how I know that.).

Your proposed setup should go really well, just make sure that your ESC is up to it. Also, batteries make a huge difference at this sort of power level. A weak batt will sag voltage under load and the RPM will drop off noticeably. A good strong battery will hold up under load and the thrust will be much better. The difference between a 4s 2200 30C and a 4s 3300 30c or 4s 3000 40c is huge.
Si Goodchild is offline Find More Posts by Si Goodchild
Reply With Quote
Old Jan 04, 2012, 07:12 PM
It's like an addiction!
Downwind3Zero's Avatar
NY, Rochester
Joined Oct 2003
1,506 Posts
I agree, you will have to reinforce the foam strips you are adding to prevent the ducts from collapsing. Apart from that I think it's a good idea.
Downwind3Zero is offline Find More Posts by Downwind3Zero
Reply With Quote
Old Jan 09, 2012, 11:09 PM
Registered User
Renton
Joined Jan 2009
77 Posts
2w20

I currently have been running the HET set up on 4S 2700 20C and it is producing a lil better than 800W. The set up is in an Exceed F/A18 Blue angel with no mods to the inlets or exits and I would estimate the WOT somewheres around 90MPH but could be more or less. Flights are 5 mins with and extra min for backup approach. I have been running this setup for a season now with an est 50-60 flights. I have a new Red Viper Exceed 70MM with metal retracts and the Hoffman beast with wemo and 125A CC ESC not had a chance to get her in the air yet but I am expecting 100-120MPH as was told to expect from this setup. That setup will be with nanotech 4S so guess I'll see. If anyone has any input on the beast please let me know!
sethmattox is offline Find More Posts by sethmattox
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Found x2 used 64-69mm EDF's with motors Pickle72 Aircraft - Electric - Power Systems (FS/W) 2 Sep 21, 2011 08:57 PM
Sold 4 Motors for sale, 2 64mm EDF motors, 2 parkflyer propeller motors -= GYRO =- Aircraft - Electric - Power Systems (FS/W) 3 Sep 21, 2011 01:10 PM
Sold 3800kv EDF motors 3s - 4s New in box MiG-3 Reno Rocket Aircraft - Electric - Power Systems (FS/W) 0 Sep 19, 2011 05:56 PM
Found x2 used 64-69mm EDF's with motors Pickle72 Aircraft - Electric - Jets (FS/W) 1 Sep 19, 2011 12:50 PM
Sold 2 x 64mm edf fans and brushless motors,and servos and landing gear!!!! tc3wins Aircraft - Electric - Jets (FS/W) 7 Sep 13, 2011 08:49 AM