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Old Dec 12, 2014, 11:53 AM
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PoorDad57's Avatar
United States, VA, Smithfield
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3S or 4S Difference for Ducted Fan

I have a 70mm 3000KV ducted fan, well two actually, that I'm installing in a scratch built RA-5C Vigilante. I believe they will draw about 43 amps. I used 45 amp ESCs (cutting it close). I have 3S 2200 25C 11.1 volt batteries. Should I spring for 4S batteries? The plane can handle additional weight. Would I get more thrust from the fans using the higher voltage batteries? I apologize if my newbie question is stupid and has been answered a couple of hundred time previously.
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Last edited by PoorDad57; Dec 12, 2014 at 11:58 AM. Reason: add pictures
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Old Dec 12, 2014, 12:12 PM
Mulit-Platform Pilot
barracudahockey's Avatar
United States, FL, Jacksonville
Joined Sep 2004
3,501 Posts
Well KV is RPM per input volt so if you up the voltage you will see more RPM's and theoretically, more thrust. Can the fan motors handle the voltage? Check the specs. Can the ESC's? You're already pushing your luck with the ESCs. Also, 25c isn't much for EDF use.

On the other hand, thats a bad a$$ project!! Looks great! Please PLEASE send me some pictures when you get it going.
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Old Dec 12, 2014, 12:18 PM
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PoorDad57's Avatar
United States, VA, Smithfield
Joined Dec 2014
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Thanks! Yes, the motors list 4S as recommended battery. I didn't do a good job of research before buying everything. Got the amps matched ok Battery 55A, ESC 45A, Motor 43A, but didn't understand the 3000KV thing and how that related. That's good news if I can gain some thrust (It is already pretty good). Plane weighs a touch over 4 lbs. Here's a couple more pics. I'm reworking the flight controls right now. When these photos were taken I had internal servos, but there is too much play in the linkage. I rigged it for Elevons, so the entire surface moves. I'm going to put the servos outside and connect directly to the Elevons. Won't be as pretty but it will work far better. I want this thing to fly twice. I think it's going to be pretty fast.
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Last edited by PoorDad57; Dec 12, 2014 at 12:26 PM. Reason: Add comments
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Old Dec 12, 2014, 12:32 PM
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turbonut's Avatar
upland CA
Joined Dec 2004
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Your amps will go up with 4s so you will need a larger ESC. What fans and motors do you have? How much battery do you think the plane can carry? on most of my 70mm jets i use 3600kv and 4s as a base line but I also use use 4s 4000 mah batteries.And 70amp ESC this gives about 800 watts. We need to know what the motors can handle. If they are Mega 16/15/3 you dont want much more than 45 amps or they wont last long. What do you think the plane will weigh?..
OK your post came in as I typed this...Do you have a amp meter?
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Old Dec 12, 2014, 12:48 PM
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PoorDad57's Avatar
United States, VA, Smithfield
Joined Dec 2014
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No, don't have a meter. Here's the motor information. I'm cutting it close on the ESC, and apparently not turning up to rated RPM with the 3S?

Specification
70 mm duct Fan
3000 KV brushless Duct Fan motor for 70 mm Duct Fan
Recommend to use 14.8v 4s lipo battery
For most RC Jet EDF Model
Weight: 44 grams (70mm Duct Fan) / 98 gram (Motor)
the max thrust :1250g
max current : 43A
recommend esc : 50A
recommend number of cells : 4s lipo battery


Package included:
2x 70mm Duct Fan Unit with 3000KV motor
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Old Dec 12, 2014, 03:03 PM
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turbonut's Avatar
upland CA
Joined Dec 2004
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I recommend that you get a watt meter and 4s batteries...And go from there. But they should work for your project. Just try to have a bit of extra size in the ESC. if not you may over heat them.Even if you have to go to 60 amp . And get 40c batts or better if you can
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Old Dec 12, 2014, 04:57 PM
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St. Martin's Avatar
Skunk Water, Rhode Island
Joined Jul 2002
12,478 Posts
3000Kv is good for 4s. If...you are running a low count blade fan. With a average 5 blade fan, WeMoTec, Eflite, etc you will get around 30-35A and 415-430W. And you will only need 2200Mah packs. If you use a high blade count fan, that motor will burn up on 4s.

Fuzz
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Old Dec 12, 2014, 05:55 PM
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So I will get more thrust with the 4S vice 3S?
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Old Dec 12, 2014, 08:00 PM
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turbonut's Avatar
upland CA
Joined Dec 2004
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Yes if the parts can handle the extra current/Amps
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Old Dec 12, 2014, 08:25 PM
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Willoughby, Ohio
Joined Jan 2002
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If you are getting 43 amps on 3S which is approximately 477 watts. Going to 4S will result in the watts going to at least 850 watts which is 57 amps. So make sure all your gear can handle the new power level plus 10% to be safe.
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Old Dec 12, 2014, 11:21 PM
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Joined Jan 2014
568 Posts
I'm loving your Vigilante. I want it! A 64mm, 70mm, or 80mm version would be a treat.
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