ESC cooling ?

I'm still trying to get my little "Wattage brand, Pitts" together ... new to
electric ... and am wondering about cooling for the ESC. I realize that the
motor and battery have to have a lot of it. How about the ESC ? It's a
"Castle Creations Phoenix-35". Can I just wrap it in foam and tuck it out of
the way? The plane will be about two pounds with a Himax 3510-1000 motor and
Thunder Power battery, (LiPo 2100 mah 11.1 V). I guess the battery is
supposed to be good for a 30 amp draw and the motor only needs or can use
about 25 comfortably. From what I've been reading, I can probably run it at
half to three quarters throttle and still zoom. Soooooo .... does the
controller have to have a lot of air flow or can I treat it pretty much like
the receiver? Thanks.
Reply to
Forrest
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Sounds like you have made some good choices for a power package. Don't wrap the CC Phx 35 in foam. Stick it to the framework with a strip of servo tape or Velcro, in a place where the air can flow over it. It is pretty darned efficient but still dissipates some power as heat; un-intuitively, it's less efficient and relatively more heat is dissipated at lower power settings than when balls-to-the-wall.
Abel
Reply to
Abel Pranger
dont worry to much, make sure that the esc has 1a2 cm free space. after first flight put your finger on it and feel. If your finger burns to it you better get some extra cooling or check the real amps. But my little brain voice tells me it will be just handwarm. +-40 50°
TM
"Forrest" schreef in bericht news: snipped-for-privacy@comcast.com...
Reply to
dingo
Ditto Abel's reply...
The big reason for foam wrap is vibration protection from glow/gas engines. Unless you have a seriously out of balance prop or bent shaft, this is a non issue for electric.
No foam, definetly some airflow. Many of us use either double stick servo tape to mount them, so at least one side is open to air, or Zip ties . PCPhill
Reply to
PCPhill
Yes. The ESC will work, but the BEC may easily heat up and die on 3s LIPO..its NOT a switching regulator. How many servos are you tagging in this thing? Make sure they are low current..if you lose the BEC you lose everything..DAMHIKT
Reply to
The Natural Philosopher
I'm not sure what this statement means but I have a Phx 25 and you can switch it from 2 cell lipo to cell lipo or upgrade it's software(LHS did it for me) and it will switch automatically. The motor will cut out at low voltage, move throttle to off and it will power up again. Again, I'm not sure what TNP means by " but the BEC may easily heat up and die on 3s LIPO..its NOT a switching regulator" because my Castle Creations phoenix 25 will absolutely detect how many cells you plug into it! BTW, just secure it and fly it. It'll do fine. mk
Reply to
MK
It doesn't have anything to do with the cell count, it has to do with how the voltage is controlled to your RX. Almost all ESCs are limited in the amount of current they can supply to your servos and RX, and pulling too much current will overheat the BEC portion of your ESC. That said, if you're using 3 or four micro servos such as are typical for the Wattage Pitts, you're safe. Just make sure your linkage is moving freely, or you'll be pulling more current than you think. A single fully stalled servo might be able to overheat your BEC.
PCPhill
The higher your cell count, the fewer servos you can use with a BEC. The BEC will be generating more heat to hold the RX voltage to 4.8 as the supply voltage goes up, which means heat less dissapation available for the servos. If you get to 4S LiPos you have to disable the BEC on CC ESCs.
Reply to
PCPhill
I have a Hitec HS-81 for the elevator and a couple of Cirrus micros for the rudder and ailerons. The elevator is a little stiff but not all that bad.
Reply to
Forrest
| It doesn't have anything to do with the cell count, it has to do with how | the voltage is controlled to your RX.
Well, yes, but the higher the cell count, the higher the voltage, and the higher the heat released in the BEC ...
| Almost all ESCs are limited in the amount of current they can supply | to your servos and RX, and pulling too much current will overheat | the BEC portion of your ESC.
True, except for the `almost' part. :)
Here's a little math that might make things a bit more clear.
Suppose you're putting 12 volts (from a 3 cell LiPo pack, if you care) into a BEC/ESC, and suppose that the BEC puts out five volts to your RX and servos.
If your servos and RX are drawing 500 mA, that means that your BEC is converting (12v - 5v) * 0.500A or 3.5 watts of electricity into heat. That may not seem like very much, but it's probably all coming out of one chip and it may not even have a heat sink. To compare, your soldering iron may use 25 watts, but the tip is probably larger than the chip on your BEC, and it's not insulated by anything, and consider how hot it gets.
(Of course, to be fair, 500 mA is a bit on the high side for average current draw on a small plane.)
The other source of heat in a ESC is the ESC itself. If we look at a Sprite 25 brushed ESC
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, it's rated at 25 amps/40 amps surge and the rated resistance is 0.0025 ohms. Heat produced = I^2 * R, so for 25 amps that's 1.6 watts.
... which seems too low. I suspect that this internal resistance figure is the lowest possible value, when the ESC is at 100% output. As you lower the throttle, the effective internal resistance probably increases signifigantly. Certainly, in most cases an ESC will get hotter at 50% throttle than at 100% throttle.
In any event, if you wrap the ESC in foam, that heat will have a hard time getting out, and it'll get hotter, and hotter and hotter -- probably until something fails.
Airflow is your friend. Your RX doesn't dissapate much power at all, so cooling isn't needed. Your battery, motor and ESC are not so lucky, and you'll definately want cooling for them, and may even want to design your plane so some air flows over them. (Your servos probably don't dissapate too much power so they probably don't get too hot, but they do probably use a lot more power than your RX, so while you probably won't have to go out of your way to make sure they get good airflow in most cases, you probably don't want to wrap them in foam either.
Note that there are some BECs out there that do not use a simple voltage regulator and instead have a full switching power supply. While these still aren't 100% efficient, they're far more efficient than the standard voltage regulator type BEC, and so the math I gave above doesn't apply. But this sort of BEC is usually not included in a ESC -- it's usually a seperate unit, and somewhat expensive at that -- so unless you know otherwise, you should probably assume that your BEC is of the more common voltage regulator variety.
Reply to
Doug McLaren
To which Doug M. replied:
Until recently I had been under the mistaken assumption that the BEC is a switcher sharing the same timebase with the motor-controller switcher. After all, that seemed like the "logical" way to do it. Ha ha. Not so. Turns out the BEC uses a linear regulator in almost every instance, and linear regs work by dumping heat. Thus, unlike a switcher, they're sensitive to higher input voltage (cell count) at a given current draw. So the higher the cell count the fewer servos you can safely run. There are outboard BECs now available that *are* true switchers, enabling high cell counts without a waste-heat penalty. And they're a lot cheaper than a new ESC. Bill(oc)
Reply to
Bill Sheppard
I realize that, I was referring to the part of the post where he was confused between a switching power supply and the need to use switches to set the cell count. No switches, so its not a switching power supply ;) I did address the heat vs. voltage issue in my reply.
Although the brand eludes me, I read about an ESC recently with a "doubled" BEC circuit to provide more current. Still limited, but much less a factor... I was trying for simplicity, so didn't get into Ohm's or watts law. An excellent BEC is available from Jeff Meyer's (Mr. SEFF): The Ultimate BEC @
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. I've used the 6V version on my 10S lipo Extra, with zero problems. I belong to an all electric club and there are many of these in use in the big E birds.
PCPhill
Reply to
PCPhill
| Although the brand eludes me, I read about an ESC recently with a | "doubled" BEC circuit to provide more current. Still limited, but | much less a factor...
Well, the cheap BECs are strictly just voltage regulators. You could just go down to Fry's and plop down $1.19 for a 5 or 6 volt voltage regulator and use that. If you want more capacity, put a few in parallel, though I wonder if the load would still be spread out enough if regulators weren't all exactly alike (i.e. one at 5.01 volts, one at 4.98 volts, etc.) Perhaps bolt them to a small heat sink to make sure they don't get hot.
Personally, I'm surprised that more people don't do this.
| I was trying for simplicity, so didn't get into Ohm's or watts law. | An excellent BEC is available from Jeff Meyer's (Mr. SEFF): The | Ultimate BEC @
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. I've used the 6V version | on my 10S lipo Extra, with zero problems. I belong to an all | electric club and there are many of these in use in the big E birds.
Yup, that's one of the switching BECs that I (and others) was/were referring to.
It's cheaper than I thought, however ... starting at only $30. Kind of heavy, though (20 grams.)
Reply to
Doug McLaren
It is a bit heavy for a small plane, but the built in BECs are usually adequate for them. I'm flying a 4 Star .40 and a Multiplex Magister, both with 3S packs and standard servos, using Phx 45s and the integrated BEC. No heat issues to date. In the size plane they're typically used in, 20 grams vs. 90+ grams for a seperate RX battery is more the issue.
PCPhill
----- Original Message ----- From: "Doug McLaren" Newsgroups: rec.models.rc.air Sent: Tuesday, January 03, 2006 4:11 PM Subject: Re: ESC cooling ?
Reply to
PCPhill
You have entirely missed the point.
Go to castles web site and see how many servos they can drive off various voltage inputs.
I am talking about the 5v regulator that powers the receiver and teh servos off the main battery. If it gets hot and shuts down, and many have, you lose everthing.
Reply to
The Natural Philosopher
You were confused, I wasn't. I merely stated that the BEC was not a switched PSU/regulator. IN my world that means its a linear regulator. And therefore its heat loss is proportional to the Vdrop across it times the current through it.
AND at 6v and an amp, thats 6W, about 3 times what a un heatsinked packaged chip can do in free air, let alone packed in a foam fuselage.
I've crashed a model on 4 HS55 on 3s LIPO PRECISELY because of this effect. With extra cooling and the next sized ESC up, it seems to hold up..constant wiggling of the two ailerons servos was netting me about 300mA average..that chip on te board is good for about 1W only. I was pushing 1.8W through it. Net result - regulator went failsafe and pulled down to about 0.5v...JUST enough to send the servos to full travel, and stop the motor..., and that was that.
The smaller castles aregood for 3 servos on 3s LIPO provided they aren't binding and speeds are not too high. 4 is pushing it - one hot day and thats that. Even with cooling.
Reply to
The Natural Philosopher
Get some cooling. Mine went ,in a fully enclosed fuselage, after 6 minutes in the air. cool day. 4xHS55. Wasn't a Castle tho. The chips on those are a little bigger. You should be OK on just three.
Reply to
The Natural Philosopher

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