watt meter reading questions    Gallery
View related threads: (in this forum | in all forums)

Logged in as Guest



Users viewing this topic: none
    Search This Thread  
 
Printable Version


Scale Mustang Exhaust - Kit
Seller:  tony-howard
Details:   $35.00   |  5/1/2013   |  Classified Ad
We will rotate YOUR AD in this spot if you select "Forum Featured" when placing or editing your ad!

All Forums >> RC Airplanes >> Beginners >> watt meter reading questions
Page: [1]

Tower Hobbies Get Coupon Codes Brands  
Login
Message << Older Topic   Newer Topic >>
watt meter reading questions - 11/22/2012 1:38 AM   
Popriv


 

Posts: 801
Score: 216
Joined: 5/5/2008
Last Login: 6/19/2013
From: bellingham, MA, USA
Status: offline 		Just trying out my watt meter on a

.10 supertiger motor, kv1250.
max current -29A, surge - 33A.
max watts 320, surge - 370.
prop size 10x7E - 11x7E (I mistakenly bought the SlowFly Props, whats the difference?)

30 amp hobbyKing ESC

3s hoppy people 20C lipo...

Using this combo to pull a 28 oz. Yak.

Using the 11x4.7 prop, full throttle = 35amps 375 watts

Using the 10x4.7 prop, full throttle = 30 amps 320 watts


Sooo, dont use the 11" prop as it exceeds the esc and motor specs?

The 10" prop looks good although its pushing the esc at full throttle. hopefully the esc is not overrated at 30amps?

I should avoid prolonged full throttle?

Do I have this right? anything else the watt meter can tell me?

Thanks

Steve

_____________________________

Excuse me while I touch the sky...

Hide Signatures
       Post #: 1

RE: watt meter reading questions - 11/22/2012 8:03 AM   
JeffinTD


 

Posts: 449
Score: 110
Joined: 4/23/2011
Last Login: 6/18/2013
From: The Dalles, OR, USA
Status: offline 		Though I'd expect current to be lower when flying as opposed to static testing, personally I would use a bigger ESC for a bit more of a safety margin.

Hopefully one of the experts here will chime in.

Hide Signatures

(in reply to Popriv)
       Post #: 2

RE: watt meter reading questions - 11/22/2012 8:54 AM   
Popriv


 

Posts: 801
Score: 216
Joined: 5/5/2008
Last Login: 6/19/2013
From: bellingham, MA, USA
Status: offline
quote:

ORIGINAL: JeffinTD

Though I'd expect current to be lower when flying as opposed to static testing, personally I would use a bigger ESC for a bit more of a safety margin.

Hopefully one of the experts here will chime in.




Yes, I forgot about the fact it was a static test and should pull more amps.. How much more?

I was flying this plane with a 400 motor ( about 170 watts) and it flew like a sport plane.
Now I will have 300+ watts so I don't expect to need much full throttle?
I'll probably order another larger esc to be safe but I'm thinking I would be ok until then to fly....?

Steve

_____________________________

Excuse me while I touch the sky...

Hide Signatures

(in reply to JeffinTD)
       Post #: 3

RE: watt meter reading questions - 11/22/2012 9:48 AM   
JeffinTD


 

Posts: 449
Score: 110
Joined: 4/23/2011
Last Login: 6/18/2013
From: The Dalles, OR, USA
Status: offline 		I would think it would be ok, but I've seen ESC's burn up, which when the BEC goes with it is a sure crash.

Hide Signatures

(in reply to Popriv)
       Post #: 4

RE: watt meter reading questions - 11/22/2012 11:31 AM   
guver


 

Posts: 14852
Score: 174
Joined: 3/7/2003
Last Login: 6/19/2013
From: LaGrange, OH, USA
Status: offline 		I'm no expert at picking power systems either , but I do have some experience with the ST .10 and I think that's what I'd worry about. Your 10x4.7 is probably gonna be ok as long as the SF prop doesn't get over rpm. It has to be close , if not over the max.

_____________________________

and airplanes were in

Hide Signatures

(in reply to JeffinTD)
       Post #: 5

RE: watt meter reading questions - 11/22/2012 12:17 PM   
mike109



Posts: 1436
Score: 148
Joined: 7/25/2004
Last Login: 6/19/2013
From: DubboNew South Wales, AUSTRALIA
Status: online 		G'day

I like to have a bit of "headroom" in the size of my ESCs. If the motor draws a max of 30 Amperes, I would use a 40 to 50 Ampere speed controller. And on more expensive planes with large batteries, I think using a separate receiver battery is good sense. This way if the ESC goes FOOM, the plane will not be out of control.

As for the props being "slow fly", I think they are recommended on motors which deliver relatively low revs, say less than about 10,000rpm - motors with kV ratings up to about 800. Your motor is a 1250 kV motor which means that on a three cell LiPo it will be turning about 10 x 1250 or 12,500 rpm. This is probably a bit more than the slow fly props are intended for. You can probably find the details on the site of the prop maker. I would not use a slow fly prop on that motor with a 3 cell pack. Two cell would probably be OK.

The battery C rating is also something to be considered. At my club last weekend, a pilot who usually flies pylon racers was thrashing a small cheap glider around like a pylon racer. All was well for a few minutes then VOOOMP - the wings were blown off the plane and the fuse trailing smoke headed for the ground where it crashed in flames. It was quite spectacular. I suspect he was pulling too much current out of the battery for too long. He needed a battery with a higher C rating. And or better cooling. The C number (say 25) times the battery capacity in Ampere Hours (say 3Ampere Hour or 3000mAh) can give a constant current of 75 Amperes but I like to use batteries at about half the C rating to keep them cool. Especially if they will be operating at near full power all the time. They last longer too.

Have fun.

Mike in Oz

_____________________________

"I just had no control. Must be the radio." Club Saito #597 Kadet Brotherhood #66

Hide Signatures

(in reply to guver)
       Post #: 6

RE: watt meter reading questions - 11/22/2012 2:32 PM   
Edwin


 

Posts: 5961
Score: 156
Joined: 2/8/2002
Last Login: 6/18/2013
From: Leander, TX, USA
Status: offline 		I would run the esc at 70% of its rated power. Just my rule of thumb.
Edwin

Hide Signatures

(in reply to mike109)
       Post #: 7

RE: watt meter reading questions - 11/22/2012 2:47 PM   
mscic-RCU



Posts: 1100
Score: 100
Joined: 3/29/2002
Last Login: 6/6/2013
From: New London, OH, USA
Status: offline
quote:

ORIGINAL: Edwin

I would run the esc at 70% of its rated power. Just my rule of thumb.
Edwin

Very good rule of thumb, I do the same.

Hide Signatures

(in reply to Edwin)
       Post #: 8

RE: watt meter reading questions - 11/22/2012 5:52 PM   
Popriv


 

Posts: 801
Score: 216
Joined: 5/5/2008
Last Login: 6/19/2013
From: bellingham, MA, USA
Status: offline
quote:

ORIGINAL: Edwin

I would run the esc at 70% of its rated power. Just my rule of thumb.
Edwin



For now , can I adjust throttle set point so I can't over rev the motor?
Would that's keep my amps down? ( I'll test when I get home )

Goin flyin tomorrow and this is all I've got for now....

Should have more than enough power even at less than full throttle.

Also, can I use a glow prop in place of the E prop?


Thanks

Steve



_____________________________

Excuse me while I touch the sky...

Hide Signatures

(in reply to Edwin)
       Post #: 9

RE: watt meter reading questions - 11/22/2012 7:47 PM   
JeffinTD


 

Posts: 449
Score: 110
Joined: 4/23/2011
Last Login: 6/18/2013
From: The Dalles, OR, USA
Status: offline 		I don't see why you couldn't limit the throttle on the radio to keep the amps down.

Personally I'd stick with electric props on electric motors.

Hide Signatures

(in reply to Popriv)
       Post #: 10

RE: watt meter reading questions - 11/23/2012 1:52 AM   
Popriv


 

Posts: 801
Score: 216
Joined: 5/5/2008
Last Login: 6/19/2013
From: bellingham, MA, USA
Status: offline
quote:

ORIGINAL: Popriv

Just trying out my watt meter on a

.10 supertiger motor, kv1250.
max current -29A, surge - 33A.
max watts 320, surge - 370.
prop size 10x7E - 11x7E (I mistakenly bought the SlowFly Props, whats the difference?)

30 amp hobbyKing ESC

3s hoppy people 20C lipo...

Using this combo to pull a 28 oz. Yak.

Using the 11x4.7 prop, full throttle = 35amps 375 watts

Using the 10x4.7 prop, full throttle = 30 amps 320 watts


Sooo, dont use the 11'' prop as it exceeds the esc and motor specs?

The 10'' prop looks good although its pushing the esc at full throttle. hopefully the esc is not overrated at 30amps?

I should avoid prolonged full throttle?

Do I have this right? anything else the watt meter can tell me?

Thanks

Steve



OK, Setting the high throttle end point to 75% and It only pulls 25 amps. I'll see how it flys. I could open it up a bit...

Not having a servo to drive the throttle I hadnt thought of adjusting the "endpoint" this seems like a good way to not exceed the system?
Assuming I dont need the extra power....

Steve

_____________________________

Excuse me while I touch the sky...

Hide Signatures

(in reply to Popriv)
       Post #: 11

RE: watt meter reading questions - 11/23/2012 2:41 AM   
Bozarth


 

Posts: 1035
Score: 156
Joined: 4/30/2004
Last Login: 6/19/2013
From: Aurora, CO, USA
Status: offline
quote:

ORIGINAL: mscic-RCU


quote:

ORIGINAL: Edwin

I would run the esc at 70% of its rated power. Just my rule of thumb.
Edwin

Very good rule of thumb, I do the same.



If an ESC is capable of sustaining a certain amount of amps, why are you adding your own reduction factor, and how did you come up with 70%? Have you experienced failures at the advertised amp values?

Kurt

Hide Signatures

(in reply to mscic-RCU)
       Post #: 12

RE: watt meter reading questions - 11/23/2012 3:14 AM   
Edwin


 

Posts: 5961
Score: 156
Joined: 2/8/2002
Last Login: 6/18/2013
From: Leander, TX, USA
Status: offline 		Technical school. I'm a test engineer by trade. We were taught to design to an RMS value thats roughly 70%. In higher power current draws I will sometimes double power capacity of the components.
Edwin

Hide Signatures

(in reply to Bozarth)
       Post #: 13

RE: watt meter reading questions - 11/23/2012 4:43 AM   
opjose



Posts: 12307
Score: 284
Joined: 11/26/2005
Last Login: 6/18/2013
From: Poolesville, MD, USA
Status: offline
quote:

ORIGINAL: Popriv


OK, Setting the high throttle end point to 75% and It only pulls 25 amps. I'll see how it flys. I could open it up a bit...

Not having a servo to drive the throttle I hadnt thought of adjusting the ''endpoint'' this seems like a good way to not exceed the system?
Assuming I dont need the extra power....

Steve


This gives you a FALSE sense of security.

The prop can still make the motor draw more AMPS than the ESC and motor permits even at less then full throttle ( e.g. nose straight up ).

Your best bet is to adjust the prop size so the draw never exceeds any limits.

All of that said, the HK ESC's normally do have nominal overhead... so your 30A ESC will deal with momentary draw up to 40A.

As your plane "unloads" in the air the amp draw DROPS, as static draw is usually a worst case senario.

That means even the 11" prop might be OK, but why risk it?

I'll bet you'll have no problems with the 10" prop with that combo.

With the 10" prop you'll have no worries.

However, some novices inist on flying the plane full throttle all the time... something that you really should not do.
Consider full throttle to be a power reserve. At level flight keep 70-80% throttle and use more when climbing, etc... when you really need it.

-

As for props.

Slow Flyer props are for that "slow flyers". They are most efficient at low airspeeds with lighter planes.

The "E" props are good general props to use, particularly with the KV rating of the motor you have.

DO NOT use a glow prop. Your setup is already boarderline. A glow prop draws more current, but does so less efficiently on an electric setup, so you are wasting energy, and sacrificing performance, with the risk of higher draws ( normally about 20% versus an "E" prop ).

And yes as others have stated it is ALWAYS a good idea to design in a 20% or so overhead into your electronics.

Electrics are not like glow/gas. With the latter you may bog the engine down but the engine will still run fine.
With an electric the motor and ESC have NO LIMIT to the amount of energy they consume except for the "thermal limits" ( burns out or catches fire! ).

On electrics the prop determines power consumption.



_____________________________

Don''t worry, be happy and fly something!

Hide Signatures

(in reply to Popriv)
       Post #: 14

RE: watt meter reading questions - 11/23/2012 6:08 AM   
2walla


 

Posts: 289
Score: 100
Joined: 3/29/2003
Last Login: 6/12/2013
From: walla walla, WA, USA
Status: offline 		10x4.7 is maxing everything out.. Remember most all of the ratings for amperage for your equipment are in free air, or with 5mph of cooling air flowing over them.. Put the motor and esc in a tightly cowled plane without good cooling flow and it will overheat and melt down. You may want to go up a size on the speed control to prevent if overheating..

The other thing is for static testing a setup I like to use a parallel dual battery setup that way I know I don't have sagging battery voltage giving me a false reading.. This way 6 months later you don't find out when you buy the latest 50c lipo and charge up and put in your plane you don't have a meltdown because when you first set it up your battery was actually limiting the current draw..(THis is why a you see a lot of people have stuff meltdown when they get a new battery pack)

On batteries and c rating C rating is the measure of the ability of a battery to hold rated voltage.. a 1000ma 10 c pack will deliver 10 amps at rated voltage.. same mah 20c pack would deliver 20amps at rated voltage... if you are using a 20c 1500mah pack at 30 amps you are maxed out.. It may deliver more current than that, but the voltage will start to sag.
C rating has notrhing to do with the ability of the battery to reject the heat it generates.. For all practical purposes going beyond a 30c battery doesnt get you much because if you continually pull that much amperage it will certainly overheat the battery. Most setups can't keep a battery cool at a continuous 15c output.

Setting the limit on the transmitter for the throttle is a bad thing to do because some speed controls auto calibrate for endpoings and you could end up with it still going to full power but with less throttle stick resolution..

Hide Signatures

(in reply to opjose)
       Post #: 15

RE: watt meter reading questions - 11/23/2012 11:51 AM   
Popriv


 

Posts: 801
Score: 216
Joined: 5/5/2008
Last Login: 6/19/2013
From: bellingham, MA, USA
Status: offline 		Setting the limit on the transmitter for the throttle is a bad thing to do because some speed controls auto calibrate for endpoings and you could end up with it still going to full power but with less throttle stick resolution..



I understand what your saying, but in this case, it appears the throttle limit has reduced the amount of amps and watts at full throttle?
I agree with having the extra safety margins built into the system. But I don't think I'm in a NO FLY situation.

_____________________________

Excuse me while I touch the sky...

Hide Signatures

(in reply to 2walla)
       Post #: 16

RE: watt meter reading questions - 11/24/2012 2:03 AM   
Popriv


 

Posts: 801
Score: 216
Joined: 5/5/2008
Last Login: 6/19/2013
From: bellingham, MA, USA
Status: offline 		Plane flew fine today, more than enough power even at 3/4 throttle.. gonna change to the E props though

_____________________________

Excuse me while I touch the sky...

Hide Signatures

(in reply to Popriv)
       Post #: 17

Page:   [1]
All Forums >> RC Airplanes >> Beginners >> watt meter reading questions
Page: [1]





Jump to:


 
Google 



Search | Marketplace | Event Calendar | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

Photo Gallery | Instructor Search | Field|Track|Marina Search

Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

SITE MAP!   : :   FORUM RULES

RC Universe is a service of Internet Brands, Inc. Copyright © 2001-2013.

Charities we support that also need your help
Yorkie Rescue | Humane Society | ASPCA | Crohn's-Colitis America


0.922RCU1