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Old Jul 30, 2006, 05:25 AM
nooobama
United States, PA, Stroudsburg
Joined May 2004
984 Posts
Help!
Why is my 40amp ESC so hot at 25 amps??

I'm using an E-flite 40 amp ESC with 2 hs-81 servo's, Mega 16/25/3 on an APC 7x5 prop and a 2250 Vammy 3 cell pack. The ESC got so hot the covering melted off. The battery is barely warm. I them swapped out the ESC with a new in the package one...same thing. There is pretty good air flow through the plane but I have been flying at about 1/2 to 3/4 power.
What am I missing here?
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Old Jul 30, 2006, 05:40 AM
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LenBFP's Avatar
Melbourne Beach, Florida
Joined Jan 2002
3,863 Posts
When you say 25 amps is that at full throttle? The ESC is always seeing the full throttle numbers, it just switches off a little sooner when you run at partial throttle.

Len
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Old Jul 30, 2006, 06:30 AM
nooobama
United States, PA, Stroudsburg
Joined May 2004
984 Posts
Sorry, forgot that part. At WOT I'm pulling 29 amps max on a fresh pack. That's the weird part, The ESC's are way hot but I'm staying under their rated max amps by quite a bit. I really don't want to have to mount this thing on the outside of the plane.
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Old Jul 30, 2006, 06:52 AM
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LenBFP's Avatar
Melbourne Beach, Florida
Joined Jan 2002
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That ain't right. I would contact the vendor or manufacturer.

Len
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Old Jul 30, 2006, 09:26 AM
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JimNM's Avatar
Las Cruces, New Mexico, United States
Joined Jun 2002
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As I understand the issue... the esc works most efficiently at full throttle - the three outputs cycle through off and on at "full" speed. When run at partial throttle, the off part of the cycle is elongated and/or the on part is shortened - making the AVERAGE amp draw less. The battery and the ESC and the motor all see FULL amperage all the time. This is why "just runing at 1/2 throttle" to avoid overamping the system doesn't work. I think of a garden hose with a sprayer handle on it - the WOT is like holding the handle down and letting the water go without stop, as opposed to partial throttle when you pulse the water jet by opening and closing the sprayer. The slower the throttle setting, the longer you have the sprayer closed. The water comes out of the end of the hose just as fast as WOT - but at a slower average rate.

I have read here several times that the heating associated with the ESC is most severe at partial throttle - due to the electronic parts working overtime to turn on and then reverse state to turn off - repeatedly, really really fast.

If it't any consolation, I've burned off the shrink wrap on two Eflight 40 amps esc's running them in gliders - wot for 30-60 seconds and then 5-20 minutes gliding. I re-covered them and am still flying them 2 years later.

JimNM
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Old Jul 30, 2006, 10:46 AM
Since 1952
Harry D's Avatar
Canada, AB, Edmonton
Joined Oct 2004
1,246 Posts
Finishman, are you using the BEC in your setup? You should be fine with only two servos and a 3S lipo, but if the servos are drawing more current than they normally would (because of a defective servo, binding linkages, etc.) the BEC (as against the motor speed controller) part of the ESC might be causing the overheating. Can you measure the current draw when you move the servos continuously, with the motor off? If it's more than an amp or two, that may be your problem.

Harry
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Old Jul 30, 2006, 11:24 AM
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Mark Wood's Avatar
United States, CA, Bear Valley Springs
Joined Feb 2000
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Quote:
Originally Posted by JimNM
...When run at partial throttle, the off part of the cycle is elongated and/or the on part is shortened - making the AVERAGE amp draw less. The battery and the ESC and the motor all see FULL amperage all the time. This is why "just runing at 1/2 throttle" to avoid overamping the system doesn't work... I have read here several times that the heating associated with the ESC is most severe at partial throttle - due to the electronic parts working overtime to turn on and then reverse state to turn off - repeatedly, really really fast.
Exactly, Jim.

mw
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Old Jul 30, 2006, 12:29 PM
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pilotpete2's Avatar
The Northeast Kingdom, Vermont
Joined Jun 2004
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JimNM,
While you are correct that an ESC runs hotter and less efficient at partial throttle, the "system" only sees the average current, no way does it see the full throttle current at all throttle settings. At half throttle with a pack that is nominally 12V, the effective voltage is now only 6V, we'll let Mr. Ohm take it from there
Please do not take my comments to mean that you can fly a system that is overcurrent at WOT by flying below WOT, no way Personally I tend to use ESCs that are rated at double my max anticipated draw.
Pete
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Old Jul 30, 2006, 12:34 PM
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pilotpete2's Avatar
The Northeast Kingdom, Vermont
Joined Jun 2004
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Finishman,
I use a CC Phoenix 45 in a very similar setup, 3S Lipo, 2 HS-81 and it barely gets warm, but since it's in a 2M sailplane I only use 20-30 sec full throttle bursts for climbing.
Pete
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Old Jul 30, 2006, 12:37 PM
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JimNM's Avatar
Las Cruces, New Mexico, United States
Joined Jun 2002
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Pete - I think I'm based in reality..., but I'm wrong at least twice a day.

You cannot reliably use a wattmeter to measure the real partial throttle stress the battery/esc/motor see during partial throttle operation due the switching frequency of the esc and the much slower sampling/display rate of the watt meter. I'm going to shut now - 'cause I really don't know what I'm talking about...

"...It is preferable to remain silent and be thought a fool,
than to open one's mounth and remove all doubt."

JimNM
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Old Jul 30, 2006, 02:22 PM
nooobama
United States, PA, Stroudsburg
Joined May 2004
984 Posts
I heard this line of thought before about 1/2 or so power and how tough it is on the esc's. But what are you to do? At some fields I can only fly at that speed, others I can go wide open. Maybe I'll try one of my cheap 30amp esc's and see what happens.
I have a meter and without the motor on I pull almost nothing at standby.
Thanks for the replies, CWK
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Old Jul 30, 2006, 02:28 PM
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scratchandbash's Avatar
Grove City PA basement/park
Joined Feb 2005
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The ratings on many ESC's seem to be utter bulloney. You can get the infor off a the fets, with good eyesight or a mag glass. Get the manufacturer's data sheets, and do the math for your ESC's fet bank. I've found their ratings are nonsense. They list continuous ratings that are supposed to be peak ratings. In addidtion to that, many in the electronics industry of high quality power devices, do not believe in pushing fets as high as their ratings. They rate their devices responsibly, and add more fets if they want to rate higher. I haven't used very many brands of ESCs, but I've found the Castles to run reasonlbly cool at their max cont ratings. Not so, for some other brands.
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Old Jul 30, 2006, 02:54 PM
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9LIVES1968's Avatar
Birmingham,Al
Joined Dec 2001
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Quote:
The ESC is always seeing the full throttle numbers, it just switches off a little sooner when you run at partial throttle.
How does an esc know full throttle numbers? Does it know when I change from one prop to another what the new amp pull is? I have seen the above quote before, but I have a hard time beliving it. SO once I give full power to a given prop/motor combination, the esc is always pulling the full amp current no matter what my throttle setting is? If I dont have a prop on it, does it still remember the previous amp figures?
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Old Jul 30, 2006, 02:58 PM
nooobama
United States, PA, Stroudsburg
Joined May 2004
984 Posts
hmmmmm....maybe an O.S.25 on a twinjet
simple but dirty
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Old Jul 30, 2006, 03:05 PM
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LenBFP's Avatar
Melbourne Beach, Florida
Joined Jan 2002
3,863 Posts
The ESC just switches the voltage that is supplied by the batteries on and off. The losses in an FET (heat) are mostly when switching. There is no partial voltage going to the motor. The on time is just shorter.

The current (amps) varies dependent on the load. No prop, almost no load. Power is watts or volts times amps, so the power changes as the load changes.

Len
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Last edited by LenBFP; Jul 30, 2006 at 03:19 PM.
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