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Am I having a 'brown out"?

#1
Hi guys. I'm quite new to the game and had a problem with my mini viggen that I Maidened last night.

I'm running a 2200 3s and an eBay 4500 kv edf http://pages.ebay.com/link/?nav=item.view&alt=web&id=201269756781&globalID=EBAY-GB sorry I can't do the link thing on my phone

The edf recommends using a 30A esc so I have. Now after about 2 mins of flying, I lost a lot of power. Luckily I was high up so could bring it on for a landing but the power loss was significant enough that I could not maintain altitude.

I put in my second battery and it happened again. I had just assumed I was draining the batteries quickly at first but then I realised that, when running the same setup but with a 70A esc in the old full size plane I would get over 4 mins flying and

A bit of research and I have come across this brown out issue. Does this sound like it could be the cause of the symptoms I'm describing?

I'm using 2 9g servos on the plane too.

Also the plane looks really nice and I have installed the esc in the place David shows in the build vid so I would have to cut the plane up to change it and I'd rather avoid that if I can. But if needs must...

Thanks
Chris
 

razor02097

Rogue Drone Pilot
#2
No. A brownout is a term used for a loss of control due to the receiver losing power temporarily and rebooting. What is the C rating for your battery? There is always 3 specs that need to be provided. Cell count, C rating, and mAh rating. That will determine the max current you can draw from your battery without damage.

Was the battery puffy when you landed? EDF motors are VERY power hungry... especially at full throttle they consume a lot of power. 30A ESC sounds kinda small for a 64mm but I could be wrong. If it is too small the ESC will get mighty hot after a while.
 
#3
Thanks for replying. The battery was fine. Not puffy or hot they are turnigy 2.2ah 3 cells. My charger didn't have balancing on it. I'm charging them now with my new charger then gonna go and fly / time the runs. Hopefully I won't crash as I'm still a bit of a noob ��

I'll try to check if any heat is coming off the esc after but it's not easy to get to.

By my calculations tthe batteries should last over 4 mins at 30 amps.

Just looking at these eBay edf adverts, it looks like they are rated at 28 amps so maybe I'm pushing it with a 30a esc. I'll see what happens tonight
 

quorneng

Active member
#5
My guess would be the ESC is over heating. I have had exactly this problem. The ESC was not over loaded (but probably quite close to its limit) but it had insufficient cooling airflow.
Once this was improved it can now run the battery down in the normal way!

By the way if you run a 2200mAh battery down in 4 minutes you are drawing over 30A! :eek:
A Watt meter is a useful tool if you are working the electrics hard - as you usually are with a EDF.
 

pressalltheknobs

Posted a thousand or more times
#6
one possibility is that the ESC failsafe is kicking in due to a lost connection - which could be caused by range, interference or a brownout. The default failsafe mode for a lot of ESCs is to reduce throttle to some percentage.

ESCs might also behave like that if they detected the battery had reached the lipo cuttoff threshhold. These things are usually programmable

I would check the failsafe configuration of you ESC and Receiver and make sure you understand what they are set up to do and if they work as it is supposed to. You should also make sure the BEC that is in the ESC is up to the task for powering you servos. If not you can uses a standalone BEC and wire it in from the receiver which is hopefully easy to get to.

In theory a 2.2mAH 20C battery can provide up to 44 Amps so it should be good enough. If the motor can draw 28A then a 30A ESC does not leave a lot of room but unless you are flying this thing full throttle all the time it is probably going to be ok if it is a reasonably good ESC.

quorneng's suggestion of overheating is also something to check f you mounted the ESC and some interior compartment that is not properly ventilated.
 
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#7
Thanks for the info. It's really useful.

Both the edf and esc are no name eBay jobbies. Although the vendor of the esc said they are also sold under the brand "mystery"

i took it out again tonight and I got 3 mins flight time out of it. An improvement which I was going to maybe put down to the cooler temps and/or the new charger with balancing.

The drop in power seems to be a step rather than a gradual thing which makes me think it is the esc fail safe.

The esc is mounted internally but it is at the point where the 2 intakes for the edf meet so I don't think the airflow is the cause of the problem. It's basically in a wind tunnel :D


I will check those configs knobs.

Thanks again for the advise. I'm still very much in the learning curve.

By the way I was getting some sweet high speed rolls in tonight. Going from a mini 4 channel trainer to the viggen is quite a step up. My first time doing more than just "clinging on and not crashing" with this plane.... Loving it. The trainer had a tiny 1 cell brushed motor and would lose about 7/8 meters of altitude when rolling, and I had to use rudder and ailerons to get it to roll fast enough. his plane twist like a spinning dart. It's awesome. <3 Just hope I can find the cause of the problem
 

razor02097

Rogue Drone Pilot
#8
one possibility is that the ESC failsafe is kicking in due to a lost connection - which could be caused by range, interference or a brownout. The default failsafe mode for a lot of ESCs is to reduce throttle to some percentage.

ESCs might also behave like that if they detected the battery had reached the lipo cuttoff threshhold. These things are usually programmable
in my experiences that ESC failsafe is zero percent throttle. Both the LVCO and the lost signal. Unless the ESC is programmed for NiMh batteries in which case there is no LVCO.

Honestly I would hope the ESC would cut the motor completely in the event of loss in signal. Otherwise the model will fly away.

To me it sounds like either the ESC is overheating or the battery is having a lot of trouble keeping up with the demand. If the battery is indeed 20-30C that would mean the esc is pulling more than 44 amps continuously. The second number indicates how much the battery can supply for a very short period of time without damage.

Do you have access to a watt meter? Something like a Watts-Up or maybe this? http://www.hobbyking.com/hobbyking/store/__10786__HobbyKing_HK_010_Wattmeter_Voltage_Analyzer.html
It would be nice to see what that ESC is actually pulling.
 

quorneng

Active member
#9
If the ESCs are cheap 'no name' types they work perfectly well but you really should not run them at their maximum. They are cheap because they use cheaper components which tend to be less efficient so you get more heat that needs to be removed. To make matters worse they tend to skimp on the thickness of the heat sink as well!
As a rule I run mine at no more than 2/3 their claimed maximum and even then I try to arrange better cooling.

Mounting the ESC in the duct is good but how is it positioned? The electronic bits that do the work are all under the heat sink so that is the side that needs most cooling.
Bizarrely shrink wrap is a splendid heat insulator and it this property that limits the rate at which the heat can be dissipated. Really high speed airflow actually adds little extra cooling.
Now if you can get that air flow directly onto the surface of the heat sink.......

This is the heat sink mounted flush in the top of the inlet duct of my DH Venom.
ESCinDuct.JPG
The ESC shrink wrap has been removed (the heat sink is now retained by a single tie) so the majority of the heat sink surface is bare aluminium that is directly exposed to the air stream but with no significant restriction to the flow.
 
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#10
I have access to a multimeter but the screen is broken. I should get a new one given that I am an electrician but I have job specific meters coming out of my ears. Anyhow I have put the 70A esc from the old plane in. I mounted it on top of the fuselage (see pic) for access and cooling. Although I don't think airflow was the problem.

The weather looks good again tomorrow so I'll test it out and get back to you guys.

I just hope I haven't messed up the way it flies by chopping/taping/gluing it :) I guess I'll find out soon &#55357;&#56842;
image.jpg
 
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quorneng

Active member
#11
Nice job!
The 70A ESC should cope fine and I wouldn't worry to much about the changes you have made. I doubt it would make any difference at all.
Hope all goes well.

If you are going to keep playing with EDFs you really do need a dedicated model plane Wattmeter so you can really get to know exactly what is going on. It will pay for itself very quickly if you can spot something is running close to its limit before it actually fails in the air!
 

pressalltheknobs

Posted a thousand or more times
#12
in my experiences that ESC failsafe is zero percent throttle. Both the LVCO and the lost signal. Unless the ESC is programmed for NiMh batteries in which case there is no LVCO.

I agree that a cut to zero is generally better.

I checked my ESCs (different brand than this) and the signal loss failsafe slowly reduces throttle to zero and is not programmable so that may be usual as you say.

But also on my ESC the default voltage failsafe is softcut and reduces power to 31%. It may be changed to a cut to zero. Probably what I had remembered.

Mine also has thermal protection that will reduce throttle until the ESC cools down also not programmable. This does seem the most likely candidate here if the ESC has that as a feature.

Worth noting that RX failsafes can be programmed to reduce throttle to a % on signal loss. Probably these are typically off by default so unlikely to be a factor here but that does depends on what "off" does.

Really the point though it to make sure you understand what the programmed failsafes do (default or otherwise) and make sure they work as you expect. Then you know what to expect if they kick in and if the model acts that way it's probably what's going on.
 
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Julez

WOT and going nowhere
#13
At full throttle you will get minimum 3.52 minutes. If you give me the amp draw from the EDF I can give you a more accurate flight time.

I didn't entirely understand the rest of the conversation on this thread, but with a 30A speed controller if you pull continuous 30A from it on a 2.2Ah pack (Usable capacity 1.76Ah) that pack will give you 3.52 minutes. I believe someone else stated that if you're getting 2 minutes of flight time you're overdrawing the ESC.

I can see that you've replaced the ESC at this point by previous posts. I'd still be interested to know how many amps the EDF draws and what throttle setting you tend to use though- just for fun. ;)

Happy flying!
 
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#14
Ok so a status report as promised.

The plane flew like a dream for over 5 mins on both batteries... Yay!!

I went to the field opposite my dads place so he could see it before I most likely crash it while he's on holiday. Just as I was about to launch 4 of the neighbours came out to watch too! Anyway, under all that pressure I forgot to time it but I think it was about 6 mins or more. I did I a lot of partial throttle and just got a feel for the plane.

On the second battery I flew mostly full throttle doing aerobatics and brought the plane down at the first sign of the power dropping. It was almost exactly 5 mins.

By my maths a 2.2Ah lipo with a 28 amp load should last 4.7 mins so I'm pleased with tonight's performance

The batteries were ever so slightly warm and the esc had barely raised temperature.

I'm so glad I change the esc based on your advise, thanks a lot and happy flying!!
 
#15
Just saw your post Julez. The edf is 28 amps. That's how I did my calculation in the post above. is the usable Ah usually stated somewhere or is that just based on 80%? I can't see it on the battery.
 
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quorneng

Active member
#16
CrossedupChris
Some battery specifications claim you can use the full capacity printed on the label, however the safest option is to limit it to about 80%.
The problem is how long that gives you depends on how you fly.
The best way of finding out how much you have used on a particular flight is to use a charger that records how many mAhs has been put back in to reach full charge. If it only takes 60% you can fly next time a bit longer (or use more full power). If it requires close to full capacity then cut down the flight time a bit.
After recording the results for a few flights you will get an idea of a 'safe' setting on your timer to avoid relying on the ESC low voltage cut off. You should really consider the LVC (normally set at 3.3V per cell) as a 'back stop' as drawing a LiPo to that level regularly can shorten its life.
 
#17
Thanks mate. There's loads of kit I need to buy. Just got a new charger though so might not be replacing that soon. The first sign of low volts was 5 mins so I'll set my alarm for 4:20 or so next time. I'm not flying too far away at the moment as in still very much learning so I should be able to get it down comfortably before the power drops off after that time.