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drawing too many amps?

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Old 10-01-2011, 04:31 AM
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rcjetflyer0718-RCU
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Default drawing too many amps?

I purchased a Model Tech Mini Mach Racer, the motor, prop, and esc called for in the instructions. A KMS 2208/09 motor, a 18amp esc (a Castle instead of the KMS), and an APC 6X4 prop. According to the info sheet that came with the motor it should draw 12 amps cont and 16amps for 60 secs.When I set it up with my watt meter it would draw 18.9 amps. So I tried a KMS 2212/09 and an 7X5 prop and it draws 16amps which is within specs of the manufactures.
The plane flies ok with the 2212 but with the 2208 it flies like a bat out of he!!. I decided to try the 2208 with a Castle 36 amp esc because I didn't want to fry my esc. when put on the watt meter it now says its drawing 21 amps. Both props on both motors are below KMS suggested size.

So my questions are:
1. Will my 2208 burn up drawing the 21 amps?
2. How do you know what size prop an esc to use when the manufactures info is BS?
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Old 10-05-2011, 03:56 AM
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Default RE: drawing too many amps?


ORIGINAL: rcjetflyer0718-RCU

I purchased a Model Tech Mini Mach Racer, the motor, prop, and esc called for in the instructions. A KMS 2208/09 motor, a 18amp esc (a Castle instead of the KMS), and an APC 6X4 prop. According to the info sheet that came with the motor it should draw 12 amps cont and 16amps for 60 secs.When I set it up with my watt meter it would draw 18.9 amps. So I tried a KMS 2212/09 and an 7X5 prop and it draws 16amps which is within specs of the manufactures.
The plane flies ok with the 2212 but with the 2208 it flies like a bat out of he!!. I decided to try the 2208 with a Castle 36 amp esc because I didn't want to fry my esc. when put on the watt meter it now says its drawing 21 amps. Both props on both motors are below KMS suggested size.

So my questions are:
1. Will my 2208 burn up drawing the 21 amps?
2. How do you know what size prop an esc to use when the manufactures info is BS?
Alwaysprovide links to the motors, batteries, props and ESCyou are testing. I have no information about them and can'tassume you have reported this correctly.But your statement about what themotor should draw sounds like typical and maximun allowed, not what you should expect for a given prop.

12 Amp continous and 16 amps for 60 secondsit is the maximums allowed with that motor. Actual will vary by prop and battery used. Change the prop or the voltage of the battery or the C rating of the batteryand the draw will change. And an APC 6X4 will be different than a GWS6X4.

Were you using the EXACT same battery on all tests? If you vary anything then the results will be different.

Net net, at 18 to 21 amps you should expect the 2208 motor to burn up pretty soon.


Everyting you wanted to know about electric flight
http://www.rcuniverse.com/forum/m_7100376/tm.htm

Look at chapters 2, 3 and 4

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Old 10-06-2011, 05:16 PM
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Default RE: drawing too many amps?

So my questions are:
1. Will my 2208 burn up drawing the 21 amps?
2. How do you know what size prop an esc to use when the manufactures info is BS?



1. Probably......... since it is a motor rated for only 12A

2. Try smaller props until you get to an amp draw well within the motor's limitations.. a 2208 is probably ~40g... so at the "rule of thumb" of 3W/g... it should not be asked to cope with more than 120W (10-11A on 3s).... a 2212 might be 50g... so for it.. 150W (12-14A on 3s)
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Old 10-22-2011, 06:55 AM
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Default RE: drawing too many amps?

Where do you stand with this problem.  Were you able to get a combination that worked well?
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Old 10-25-2011, 11:41 PM
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Default RE: drawing too many amps?

1st off I stated the ESC and prop were both the most common brands so why is a link required? The motor is a KMS brand that were imported by Global (Hobby People) they now use their own name brand and I could not find a KMS website. The battery I used on all the wattmeter tests was a Hobby People 3S 2200mah 20C battery. I gave the data for the motor from the sheet that came with the motor. My main concern is I have a few of KMS motors and none of the suggested props even comes close to the motors current draw.
This is one of the main reasons that I and my flying buddies don't fly electric because all the different manufactures gives differnet specs and usually its marketing BS and nowhere near the real specs. I know that E Flite and Rimfire information is close to being right but these off brands are so far off you end up burning up the components.

my solution to the orginal problem was to set the throttle throw so the motor wouldn't draw over 16 amps. I haven't flown it yet becuase I'm still rebuilding the orginal plane.
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Old 01-19-2012, 08:38 AM
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Default RE: drawing too many amps?

Actually, the Hobbico Rimfire motors are grossly over rated.  They are good motors but you need to take the performance ratings with a grain of salt.  It is important for you to know that reducing the throttle doesn't reduce the current.  It merely reduces the amount of time the motor can draw the current.  Reduced throttle should keep your motor from frying but, for your information, it won't do anything to help an ESC from frying.

It is folly to overprop a motor and/or ESC.  Nothing good can come from it.  If you want to use the motor you have, then use less prop so that you can fly full throttle if you want to.  Doing anything else will result in premature failure.  If you want the enhanced performance then use a motor adequate for driving the prop you prefer.  Understand that this adds weight and nothing good can come from adding weight either - CG issues, wing loading etc.

KMS are pretty overrated as well, by the way.

The reason I don't fly fuel is cost, mess, noise, smell, inability to restart in flight etc. etc. etc.
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