By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by CML

low throttle bad for the esc ?

All Topics | Latest Posts

Search for:  in Thread Title in  
john haz02/05/2011 11:48:11
360 forum posts
32 photos
Hi chaps
 
maybe somebody can clear up this conflict of information I keep getting ?
 
i keep reading that the esc should be run as near to max throttle as possible, anything less will cause problems with it overheating.
 
Then in the next breath, experienced modellers are saying "use the throttle" .
 
I only ask because one of my 500 heli's has a high (1900kv) motor & to get the headspeed I want with a 12t pinion, I run a flat 70% curve in stunt. Most seem to favour 80-90% but this gives me too much headspeed (for my preference).
 
I appreciate that 90-100% might be more efficient, but 2 people (both experienced heli and plane pilots) have told me that running max 75% will kill my esc !!!
 
My "theory" is that when i was learning to hover, i ran just over 50% throttle on a linear curve & never burnt one out. And .... flying my edf's, I spend half the flight at 40-60% throttle, again no problems.
 
Am i missing something, or is it acceptable to run an esc at a continuous 75%, or a varying 60-85% ???
 
 
 
 
birdy02/05/2011 12:06:34
avatar
1423 forum posts
110 photos
This is a link worth reading if you are interested, and gives a good explanation as to why esc get hot at mid throttle.
 
If your esc had ok cooling though it shouldn't be a problem.
 
Birdy.
Steve W-O02/05/2011 12:06:48
2775 forum posts
310 photos
Did you ask them how it would kill your ESC?
 
Why should a helicopter be different to a fixed wing plane, I'm sure the ESC has now way of telling where it is, and on fixed wing you often fly 30% and up.
 
I'm sure there can be some illogical explanations (such as cooling air flow) and maybe some logical ones if the ratings are borderline.
 
The heat in an esc is generated when the FETs are in the on state and also in the transition stage., which is very short.
 
I'm interested to hear of any good answers to
Sparks02/05/2011 12:11:21
avatar
261 forum posts
55 photos
A decent quality ESC should be capable of running at any throttle setting.
 
The ESC has more work to do when running at part throttle so will dissipate more heat than when running at 100% throttle .
 
Ensure that the ESC heatsink is well ventilated and that it is running well within the specified voltage and maximum current ratings. Use a wattmeter so that you know what current you are drawing and that it is within the ESC's capabilities.
 
Choose an ESC that exceeds the max current requirement by 25>30% to provide an adequate safety margin (and allow for sales hype). Also, don't extend the ESC/battery lead lengths. If you need longer leads, extend the ESC/Motor leads.
 
 
 
 
 
 
Tim Mackey02/05/2011 12:28:11
avatar
20919 forum posts
304 photos
15 articles
All good info
john haz02/05/2011 12:45:24
360 forum posts
32 photos
excellent, thanks chaps
 
Cooling: I am pretty good with this, tend not to mount them under the canopy of heli's - have them strapped on the side to catch downwash from blades.
 
exceeding max current: I usually do that one pretty well too - both 500 heli's have turnigy Platinum pro esc's, rated @ 80A / the 600 heli has the same @ 100A
The two EDF's & the Roo all pull around 350w & have 40A esc's, but although nearer the mark, they are air cooled very well & don't get more than warm.
 
thanks again for all the advice - It just didn't make sense to me that running les than 80-90 would kill the esc when a lot of us run planks at 50% for a lot of the flight.
 
Appreciate the quick replies too
 
 
Plummet02/05/2011 12:47:54
avatar
1403 forum posts
41 photos
I think that we may have a several conflicting stories here.
 
I suspect that all ESCs nowadays will be "Switched Mode". What this means is that they either allow current to flow unrestricted, or not at all, just like a light switch. The effective control of the amount of current flowing is governed by the on-off timing. More on and less off means more current (on average). More off and less on, less current.
 
Heat is generated when current flows across a volt drop. The equation is W=VI, where W is the heat in watts, V is the volt drop, and I is the current flowing. From this, you can see, that if V or I are zero, then W is zero.
 
When the switch is off, no current flows, so no heat is generated. When the switch is on, there should be no voltage drop across it, so again, no heat.
 
That story is, of course, not really true.
 
An electronic switch cannot really go instantaneously from on to off or vice versa. A current cannot instantly go from zero to lots. It is while the switching is actually happening that heat is generated. Also the electronic switches are never quite perfect conductors. There will be a small volt drop when they are conducting, so a bit of extra heat creeps in (or out).
 
Now I am getting to stuff I know even less about. There is a difference between brushed and brushless motors and their ESCs.
 
Brushed motors first. With these there are just the two wires from ESC to motor, and the current flows only one way. The rapid switching of the power, and the ratio of on and off times control the motor speed. I am guessing that the actual speed of the switching, that is, how many ons and offs per second will be fixed, and only the ratio of on to off times will vary. Since most of the heat is generated during the transition from on to off or back again, the heat generated will be more or less constant. That, of course, is ignoring the slight volt drop, which will cause extra heat, in proportion to the average current. So I am guessing that the heat will be maximum at the highest speeds, but not by a lot.
 
Now brushless motors are different. With these, I think that the speed of switching varies with the motor speed. The currents in the coils are sent back and forth, so that the coils are sometimes north magnetic poles, and sometimes south. These will attract or repel the little magnets on the rotating bit of the motor. So for higher speeds the currents have to be switched faster. So my guess would be that for a brushless motor the ESC will get hottest when the motor is running fastest.
 
But then we have the cooling problem. The faster the model is flying, the more cooling air there might be.
 
Of course, I could be typing piffle.
 
Plummet
 
p.s. It took me so long to type this that I needn't have bothered.  Ho Hum.

Edited By Plummet on 02/05/2011 13:08:02

john haz02/05/2011 12:49:07
360 forum posts
32 photos
Steve - i don't think it was a heli specific comment from him, just that with the heli in stunt, it really is a flat throttle curve, whereas a plane would be used with the throttle moving more.
 
i think it's a case of people thinking that a given figure (85% or 90%) is correct without understanding why they say it.
Steve W-O02/05/2011 13:09:28
2775 forum posts
310 photos
Posted by Plummet on 02/05/2011 12:47:54:
I think that we may have a several conflicting stories here.
 
I suspect that all ESCs nowadays will be "Switched Mode". What this means is that they either allow current to flow unrestricted, or not at all, just like a light switch. The effective control of the amount of current flowing is governed by the on-off timing. More on and less off means more current (on average). More off and less on, less current.
 
Heat is generated when current flows across a volt drop. The equation is W=VI, where W is the heat in watts, V is the volt drop, and I is the current flowing. From this, you can see, that if V or I are zero, then W is zero.
 
When the switch is off, no current flows, so no heat is generated. When the switch is on, there should be no voltage drop across it, so again, no heat.
 
That story is, of course, not really true.
 
An electronic switch cannot really go instantaneously from on to off or vice versa. A current cannot instantly go from zero to lots. It is while the switching is actually happening that heat is generated. Also the electronic switches are never quite perfect conductors. There will be a small volt drop when they are conducting, so a bit of extra heat creeps in (or out).
 
Now I am getting to stuff I know even less about. There is a difference between brushed and brushless motors and their ESCs.
 
Brushed motors first. With these there are just the two wires from ESC to motor, and the current flows only one way. The rapid switching of the power, and the ratio of on and off times control the motor speed. I am guessing that the actual speed of the switching, that is, how many ons and offs per second will be fixed, and only the ratio of on to off times will vary. Since most of the heat is generated during the transition from on to off or back again, the heat generated will be more or less constant. That, of course, is ignoring the slight volt drop, which will cause extra heat, in proportion to the average current. So I am guessing that the heat will be maximum at the highest speeds, but not by a lot.
 
Now brushless motors are different. With these, I think that the speed of switching varies with the motor speed. The currents in the coils are sent back and forth, so that the coils are sometimes north magnetic poles, and sometimes south. These will attract or repel the little magnets on the rotating bit of the motor. So for higher speeds the currents have to be switched faster. So my guess would be that for a brushless motor the ESC will get hottest when the motor is running fastest.
 
But then we have the cooling problem. The faster the model is flying, the more cooling air there might be.
 
Of course, I could be typing piffle.
 
Plummet
 
 
 
 
The brushed and brushless work in roughly the same way (as far as speed control goes)
 
The brushless have the additional job of controlling polarity and timing of the pulses.
 
The full on internal resistance is fairly low (depending on mainly price of the ESC), so the voltage drop and hence heat generated is also fairly low. In comparison more heat is generated when the FET is not fully on, and has a higher internal resistance, so the more times it switches on and off, the more heat could be generated.
 
Instead of just controlling the width of the on pulse, it is usually split into more narrower pulses, which means more on and off cycles (this increases efficiency), and possibly more heat.
 
It can be looked at like a microwave on 50% power. Microwaves can only operate at 100% power, so to get 50%, you turn it on for 15 seconds, then off for 15 seconds. the ESC would do that by switching on for 1 second, then off for 1 second (which would not work with a magnetron) Both 50%, but one the pulse are shorter, and so change more often

Edited By Steve W-O on 11/09/2011 18:24:02

John Privett02/05/2011 14:17:08
avatar
5988 forum posts
239 photos
Plummet - have a look at the link in birdy's post above. It gives a good account of what is going on in the brushless ESC.
john haz02/05/2011 15:05:22
360 forum posts
32 photos
I have just read birdy;s link & am now a little wiser.
 
I can now understand why they heat up when used at less than 100% throttle, although it seems the only downside of doing this is the heat & if the ESc is running quite cool, there shouldn't be any problems looming (as others have said).
 
the part i wasn't aware of was the ESC to motor matching. i had (wrongly) assumed that if I fitted a max 45A motor, had a max prop load of 35A then a 40A ESC would (just about) do the job ! It seems that the motor might still draw intermittent high current, therefore cooking the ESC.
 
Better get some 50 + 60A esc's on order soon for upgrade purposes LOL
 
Thanks again to all that have contributed. I often come across snippets of info but rarely take anything as correct unless it's been posted on here - once others have picked holes in the theory, I reckon it's good enough for me to base my choices on.
 
 
Steve W-O11/09/2011 18:26:07
2775 forum posts
310 photos
Forum issues, look at my post a couple up and see when I edited it.
 
Only PM how to will be answered
Tim Mackey11/09/2011 18:44:31
avatar
20919 forum posts
304 photos
15 articles
John Privett11/09/2011 22:18:45
avatar
5988 forum posts
239 photos
Tim, I think Steve is just pointing out how trivially easy it is to go back and edit our previous posts, even from long, long ago. Just because the link isn't there doesn't mean it can't be done... The context to this being the discussion elsewhere about the forum software, and specifically here its "security by obscurity" - never something to rely on!
Steve W-O12/09/2011 16:28:14
2775 forum posts
310 photos
Posted by John Privett on 11/09/2011 22:18:45:
Tim, I think Steve is just pointing out how trivially easy it is to go back and edit our previous posts, even from long, long ago. Just because the link isn't there doesn't mean it can't be done... The context to this being the discussion elsewhere about the forum software, and specifically here its "security by obscurity" - never something to rely on!
 
 
 
Yes, the software is as watertight as a colander with all the holes drilled out to 3/4"

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E! 

Support Our Partners
electricwingman 2017
CML
Slec
Cambridge Gliding Club
Gliders Distribution
Wings & Wheels 2019
Pepe Aircraft
Sarik
Advertise With Us
Do you use a throttle kill switch?
Q: This refers to electric-powered models but do you use a throttle kill switch?

 Yes
 No
 Sometimes
 Rarely

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us