HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Sep 15, 2012, 05:14 PM
LiPo-Sucker & Airframe EMT
pugsam's Avatar
Charlottesville, Virginia, USA
Joined Aug 2010
3,173 Posts
Discussion
ESC -- amp rating / amp limit

I have a Parkzone F4F Wildcat, with the stock 18 amp ESC.

Recently, I changed the stock 2-blade prop to a 3-blade (the Corsair/T-28 3-blade) and decided to run a wattmeter on the ‘Cat, to see what the 3-blade draws.

With a fresh 3s 1500 30C, and also with a 2200 25C, at full throttle it maxes-out at a fraction over 17 amps -- just below the ESC’s 18A rating.

Here's my question: Is there some sort of built-in protection, to limit the draw to under 18A?

Or is that just coincidence?

pugsam is online now Find More Posts by pugsam
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 15, 2012, 05:29 PM
Dude, I do fly all day long!
rcalldaylong's Avatar
San Jose, California
Joined Dec 2007
5,764 Posts
Quote:
Originally Posted by pugsam View Post
I have a Parkzone F4F Wildcat, with the stock 18 amp ESC.

Recently, I changed the stock 2-blade prop to a 3-blade (the Corsair/T-28 3-blade) and decided to run a wattmeter on the ‘Cat, to see what the 3-blade draws.

With a fresh 3s 1500 30C, and also with a 2200 25C, at full throttle it maxes-out at a fraction over 17 amps -- just below the ESC’s 18A rating.

Here's my question: Is there some sort of built-in protection, to limit the draw to under 18A?

Or is that just coincidence?

Unless you're hearing the motor cut in and out, I doubt it. more likely just a coincident. I gear all my ESC 20% below ESC limit, but I have tested some of my ESC where when going above threshold, the motor will cut in and out.
rcalldaylong is offline Find More Posts by rcalldaylong
RCG Plus Member
Old Sep 15, 2012, 05:57 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,318 Posts
They don't seem to provide any info beyond saying that it has a LVC or low voltage cutoff. And that you should end the flight before that happens to cut the motor off (good advice!).

Like rcalldaylong, I don't normally use ESC's at or near their full ratings. I downrate them about 25% also and would want to use about a 25A ESC on a plane that was pulling 17A at full throttle.

You can get an idea as to whether it will survive or not, you can test that by holding the ESC between your fingers and running it up to full throttle. If it does not get too hot to hold onto after 15 seconds or so, you may be OK. If you can read the ESC temperature with a thermometer that would be even better.

It is not unusual for some ESCs to get that hot or a little hotter in use, especially so if they have a linear power supply for the BEC and a few servos in use.

As a comparison, my Thunderbird 18 ESCs, with a 19A load, get to about 155F with the BEC in use. If I am not using the BEC (using an external switching mode BEC instead) the same ESC with the same load only gets to about 100F.

So you are smart to have checked it and upgrading to a little larger ESC would be a good idea.

Jack
jackerbes is offline Find More Posts by jackerbes
RCG Plus Member
Old Sep 15, 2012, 06:18 PM
Registered User
pda4you's Avatar
USA, TX, Trophy Club
Joined May 2002
14,442 Posts
The ESC has no ability to limit the current. You have to do that. The motor, propeller battery, battery voltage all contribute to the load.

I disagree that you need to change that ESC out. I have flown over 200 flights with the stock combo with zero issues. I fly in relatively hot TX and mine has remained well behaved. I now use a slightly larger prop - for just a tiny bit more draw than the stock - again with no issues.

Now that said - if you are worried - feel free!

Just remember the ESC does NOTHING to limit current. They will run till they cook .

That is why you have to select one that is up to task. Some will say you can limit the throttle in the radio system (limiting throw for example) so it stays below the amp limit - but that isn't a great idea either as the ESC is really just a switch that is "On" or "Off". It sees the full current every time it is "On" so damage can be done. When you are at partial throttle the ESC simply turns the motor on off on off on off to approximate lower power.

Mike
pda4you is offline Find More Posts by pda4you
RCG Plus Member
Reply With Quote
Old Sep 15, 2012, 09:58 PM
Registered User
United States, NM, Las Cruces
Joined Jul 2012
510 Posts
esc's usually post a continuous current and a burst current (usually for no more than 15s). For example my eflite pro switch 60 is rated at 60amps continuous and 75 amps for up to 15 seconds. There are some exceptions to this. PROPER AIRFLOW IS REQUIRED TO RUN AN ESC AT OR NEAR IT MAX CONTINUOUS CURRENT. As long as you don't leave it there for the whole flight and you have good airflow, I would not worry. A simple esc upgrade is good insurance though.
erikc641 is offline Find More Posts by erikc641
Reply With Quote
Old Sep 15, 2012, 10:29 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,258 Posts
Remember that the current draw in flight will drop a bit due to the prop unloading. As long as the ESC has some decent cooling, it'll be just fine.

Quote:
Some will say you can limit the throttle in the radio system (limiting throw for example) so it stays below the amp limit - but that isn't a great idea either as the ESC is really just a switch that is "On" or "Off". It sees the full current every time it is "On" so damage can be done. When you are at partial throttle the ESC simply turns the motor on off on off on off to approximate lower power.
In fact, at partial throttle the actual instantaneous current draw spikes are HIGHER than full throttle current. The ESC will tend to run hottest around 75% throttle or so due to this in combination with the additional heat of the FET switching.
C₄H₁₀ is online now Find More Posts by C₄H₁₀
Reply With Quote
Old Sep 16, 2012, 09:09 AM
LiPo-Sucker & Airframe EMT
pugsam's Avatar
Charlottesville, Virginia, USA
Joined Aug 2010
3,173 Posts
Thanks, everyone, for the good feedback.

pugsam is online now Find More Posts by pugsam
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Battery C rating/ Esc AMP draw. rene21 Electric Power Cars 5 Aug 09, 2012 10:35 AM
Question ESC rating much larger than motor rating? iamtheone Power Systems 2 May 29, 2012 03:27 PM
Found WANTED FS/FT 60 + Amp Brushed ESC and 3 cell Lipos rated 40 Amp continuous or higher dgfisher2004 Aircraft - Electric - Helis (FS/W) 0 Jul 25, 2005 10:29 PM
Wattage limit on the B40L series and Megas above amp ratings... Admiral_Red Power Systems 1 Jun 17, 2003 06:29 PM
What limits possible amps through an ESC? Nicke Power Systems 16 Feb 13, 2003 08:41 AM