View Full Version : How hot is too hot?
10-18-2005, 12:29 AM
Looking for some info out there on motor and batt temps. Since I am new and this is my first wing that I am consistently flying, I dont know if I have a problem or if its normal -
Setup - 48" Windrider EleBee EPP Wing, Zagi reverse timed Speed 400 spinning a 5x5 carbon prop, Zagi 20A esc, 8cell 1700 NiMh from Cheapbatterypacks. Battery has Deans Ultra, ESC is soldered direct to motor. Motor and battery have maybe 10-12 flights now.
Issues - On windy days (10mph or so) I have to run this bird at full throttle to make headway. It does OK, but nothing fantastic. I just muscle it up through the wind slowly then turn her around and have some fun. Well today it happened again - the battery and motor are freaking hot! I mean the battery was hot enough that it softened the velcro sticky tape backing enough that it pulled right off the battery's shrink wrap when I pulled it out of the canopy. After I pulled it, the battery was almost too hot to hold on. The motor - Forget it! Even after waiting several minutes, its way too hot to touch. I mean burn your fingers hot. The canopy does have a cooling hole cut into it right in front of the motor and the back is open to let air out. I also have a small slit (tried making a NACA duct) up front for the battery.
Is this normal?!? Today was the second day the battery got hot enough to lose its velcro. It was a nice cool 65 degrees out too. I also notice that I am just losing power after 5 mins or so of wide open throttle. You can hear it slow down and I just cant gain any altitude. Now, if it sits for several mins I can toss her back up for another 5 mins maybe less and then it dies again. If I run a mixed bag of full throttle and 1/2 thottle cruising I can get 15 mins easy of air time.
Getting frustrated because the winds just wont die down lately. I dont mind flying in wind, but the 5mins of flight time is getting me peeved.
Lastly - anything better I can use to glue/stick the velcro on the battery and inside the plastic canopy? I am using the heavy duty velcro with the sticky tape on the back. Its not holding up...
10-18-2005, 01:20 AM
The batteries and motor should be kept under 150F. 150F is way too hot to hold for more than a second or less. The NiMH cells will soon die from overheating and the motors magnets could demagnitize. Try oiling the motor bearings and getting some cooling air to the components.
10-18-2005, 04:15 AM
Batt and motor are both overloaded. You need to go down a prop size. Maybe 5-3 prop.
10-18-2005, 04:54 AM
Anyone please tell me how to water breakin brushed motors
10-18-2005, 06:32 AM
Oil the bushings/bearing and hook the motor to a 2-4 cell pack and run it fully submerged in a glass of water. I run it until there is a light layer of black stuff on the surface of water. Take it out and dry it best you can. oil it again, and then run it until it is warm to hot so that the h2o inside get worked out (maybe a minute or two's time). I then take the time to "time" the motor.
To time the motor, you have to loosen the back plate of the motor. This may need the little "tabs" around the edge to be bent back or dremel'd off. Make sure you know which direction the motor will be run in it's final application! Mark a spot on the can and back plate for reference. Hook up the same 2-4 cell pack with a multimeter hooked between the + of the motor and the + battery cable so that the motor spins in the correct direction needed. I use the x.xx resolution setting on teh mueter. Run the motor and record the amp draw. Move the endplate in a direction and watch the amps. If it goes up, wrong direction (even if RPM increases). If the amps goes down but rpms stays the same, your in the right direction. (If rpms goes down, the motor is probably already timed right from the factory.) As you continue to turn the end plate, you will see the amps go down a little then rise back up with the rpms going faster. You can A) set it at it's lowest amp draw, or B) keep movig it until you have the same amp draw as when you started with an increase of rpms. (what I do) If you go very far past that pont (more rpms and amps) then the motor will start to not work, or the amps will be really high and the rpms will be realy low- OOPS! Too far. :) Mark the new spot on the can and crimp the edges again or put a couple spots of solder so nothing moves. All done!
Did I miss anything guys?
Hope this helps. :)
10-18-2005, 08:22 AM
Your working your motor and battery pack too hard. 5 min at WOT in the wind is enough to put any electric system to the test. Your overdrawing and overamping your battery and motor. Pretty soon, your motor just wont quite make power anymore in or out of the wind because the windings and brushes are getting burnt and overheated. Overheating your windings causes massive resistence to be induced in the motor. Your battery pack isnt gonna take much more of it either. Overheating the pack will cause the cells to break down and either not charge or will disipate rapidly.
If your gonna stay brushed, mabey go to a gear box with the Speed 400 so you can swing a bigger prop. If not, go brushless geared or outrunner. Either will give you more power to cut through the wind and throttle back. You can still over do it with a brushless Lipo setup. Its just more expensive to replace. But the power to weight ratio makes it worth it. Instead of spending your time trying to climb to an acceptable altitude, your model will get there quickly allowing you to throttle back and still maintain altitude. More flying, less climbling.
Hope this helps,
10-18-2005, 02:52 PM
I figured I was pushing it too hard. I have been wanting to try brushless, so maybe this is the time. No LiPo yet, I have 3 of those NiMh packs that are new and the charger I just got on sale doesnt handle LiPo so I would need a dedicated one. I know I should have bought one that handles all 3 batt types, but I couldnt pass on the sale. The other issue I have with LiPo for me at this stage is my flying ability. I may feel like I am consistent, but I dont want a hard nose in to destroy a brand new $$ LiPo and possibly burn my plane! For now I think NiMh is better for my wings.
I am going to try a couple diff props on it, the Bee kit came with 2 sizes of the cheap plastic ones that I have no idea the pitch and prop of (one is close to the carbon, the other is larger but looks like it has less pitch). I am also going to open up the canopy more to get more air over the battery tray and motor mount area. Hopefully that helps a little.
Thanks for the help! I need to accept that its just not powerful enough on windy days. On calm days, she flies wonderfully. The windy ones are kind of like drag racing a Yugo. Sure, it will go down the track - but do you really want to??
10-19-2005, 05:50 PM
I did some google searching and found out that the recommended combo of 1700mah, rev timed Zagi 400, and the 5*5 carbon prop will pull over 15A measured on a bench. Thats whats cooking the motor! Seems there are several people with the EleBee that are running into the exact same issues I am.
What options do I have if I stay brushed a little longer? Ray mentioned going with a gearbox, are they standard for a 400 motor? How would I pick a gear ratio and then the correct prop? I have a online version of motocalc saved, but to be honest I dont really know what I am looking at or what I should be changing. I used to change gear ratios on my rc buggy and carpet cars, but that was trial and error... Would just changing out the pack or prop help?
Sorry for so many questions...
10-19-2005, 10:32 PM
That's a fairly fast type plane as opposed to a cub type plane that would benefit with a gearbox. I'd stick with the direct drive and go to a lower pitch prop. Another way is to wack a 1/2 in. off each prop blade if you want to experiment. If you're staying with the hobby, a good investment is a Wattmeter. Takes the guesswork out of things. If it saves you from cooking a batt., it's paid for itself.
10-25-2005, 09:04 PM
You will know when its too hot if it gets hot enough
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