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Old May 05, 2012, 12:43 PM
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South Africa
Joined Feb 2010
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What's happening to my batteries ?

Ok guys got something strange going on:

First of all an answer from an expert who knows about overpowering / overpropping motors the right way would be nice to get a reply from for the general bloke who never overpropped anything in his life can't help.

I've been flying this motor: (though mine is 890kv don't know where they get 800kv from, anyway) for too many flights to remember now, it won't quit... !!!

http://www.cthobbies.co.za/pTR35-48C...-AXi-2826.aspx

Now what i do is i overprop the motor by using a 15x13 folder, works like a charm, the motor
purrs nicely like a kitten, with no problem doing 15 second full power runs on 3s batteries, then
of course gliding periods in between to cool the motor and let the batteries recover. Been doing this for months on end.

The other day a bloke passes by the field, tells me he fly's quads, hex's and oct's and i can have his (used (perhaps well used) 4s turnigy 2600 mah nano batteries, all 6 of them)

So i charge them up thinking that on 4s i will have to be careful especially because i already am over propping my plane, bench test gives me full power at 60-70 % throttle.

Took 3 of the 6 batteries to the field to test and first one, power was good as expected and the plane flew very nice, afterwards i remove the wing and see the battery swelled, and it was warmer than my 3s cells normally are,

second battery,

same thing swelled, but performed nicely

third battery, after launch almost lost all power, i cut throttle and maneuvered in for a landing

as i disconnect the battery one of the esc wires broke right at the connector as if it was taking too much current and was hanging on a few strands of wire before broke off.

battery voltages after flights

pack 1. 14.9 v
pack 2. 14.9 v
pack 3. 15.9 v

So could it be that my motor is giving too much resistance for the batteries/wires to handle,
could it be that i just need thicker gauge wire ? Could all this be because of a faulty wire connection to esc ?

The motor gets almost hot at the base, the bell is just above mild, you could say almost warm afterwards but far from hot.

However point being that batteries swelled, wire came loose, motor warm than usual (or could it be that it was loose before and just needs re-soldering ?) will that solve the problem ?

Like mentioned i only go up 60-70% on the stick 15 second full power run and let cool, always worked with 3s on full power. However could it likely be that i had a bad motor connection to start with or did it "burn loose" and why ?

(like mentioned the last battery died almost 15 seconds into the flight, it was then when i discovered the "loose wire" hanging on 5 or 6 strands of wire that broke off when i removed the connector (t-60 turnigy connectors from the esc) after landing, the batteries still have lots of power left so i assume it must be the wire ?
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Old May 05, 2012, 01:14 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,429 Posts
It sounds like the packs have been abused in the past. Swelling and heat are signs of high current and/or high internal resistance. What's the C rating on the packs, and how much current does the motor draw at full throttle? Did the previous owner take proper care of them?

The additional motor heat is due to the motor pulling far more current than it used to; higher voltage means it'll try to spin at higher RPMs, which will make it draw more current and produce more heat.

Also, what ESC are you running? It sounds like you're on the fast track to damaging it.

You're really best off just sticking to 3S operation. Bumping up to 4S virtually always requires additional changes to the power system, the most common being a smaller prop.
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Old May 05, 2012, 01:36 PM
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South Africa
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I think the cells have been worked hard, however all cells seem to be well balanced. So they are not dead cells i would say probably 65% into it's lifespan.

its turnigy nano tech 25-50c discharge 5c charge.

However could it be because maybe without me knowing the esc wire was not fully making contact, therefore adding a considerable amount of resistance to the batteries, causing the batteries to heat up ?

Esc is not of concern of burning out lol.... i am suppose to use a 40-50 amp esc on this motor, however i am using an 80 amp esc.

I wonder now if i should first reconnect and resolder the esc joints then go and fly the packs again (assuming it could've been a faulty wire because of what happened after the 3rd flight) or rather try and make 3s out of the 4s packs and use like that.

Also like mentioned, i'm not running at 100% throttle with 4s, only at the end when the battery gets a bit weaker i'l push it up to 100% for a while.

can't say how many amps i'm drawing, all i know is this setup works well on 3s, and maybe it could on 4s if it is/was a faulty wire issue...?
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Old May 05, 2012, 01:47 PM
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eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,436 Posts
Using just part throttle still puts big full current pulses through everything, it's just that a meter will average out those pulses and show what appear as less, and looks therefore 'safe'.

The picture below may explain it better. Basically it's like using a switch you turn on and off quickly to control a motor, while 'on', it still draws the full voltage and current, but just for a short time.

So your motor, ESC, and batteries are still seeing, (and 'feeling'), some pretty hefty currents.
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Old May 05, 2012, 01:50 PM
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dedStik's Avatar
United States, VA, Virginia Beach
Joined Feb 2012
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You should not fly with any swollen packs. Any of them that swelled should be disused.
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Old May 05, 2012, 02:10 PM
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Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
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Simply put, the batteries are puffing because too much current is being pulled from them and they are overheating. The bad wire connection will not cause that and it will not increase the resistance of the battery. The only thing it will increase the resistance of is the wire itself. That increased wire resistance, being external to the battery, will actually decrease the amount of current being pulled from the battery by a small amount, but not a whole lot.

Larry
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Old May 05, 2012, 03:19 PM
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Space Bat's Avatar
United Kingdom, England, Cambs
Joined Oct 2011
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The problem sounds as others have said that the C rating was not correct due to the fact that the batteries were possibly already cycled and used where the C rating had diminished due to increased internal resistance...Especially as you are using a larger prop than what is typical on a 4s - which with that motor will be happier on a 12X6 - 13X6.5 being pretty much the maximum before crossing that over heat your lipo territory as your efficiency is crashing down the graph...

I am over propping a 1130kV on a 3s with a 13X6.5 - the batteries do not like this at all - however I am keeping the setup so as to evaluate the new Zippy compacts...but have to be extremely careful what I can and can't do - and can always drop to a 12X6 or 12X7 depending on what I want to do...
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Old May 05, 2012, 07:58 PM
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South Africa
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You see now that's why i'm a member of Rcgroups, exactly the answers i wanted to know !

(better reply before you people go to sleep it's 2:57 in the morning here) usually when i wake up in a normal day 7:00 for me and reply, i get little response lol...)

Thanks for the informative information !
Eflightray very nicely explained
Lnagel good to know that the bad wire would not cause it.
Spacebat, thanks for reminding me that i'm actually working my motor harder than i should and that is why i should stick to 3s.

The batteries still give good power and the capacity is still good even under swolen conditions. looking at the packs now 2 of the packs have gone almost to normal again also.

because i have 6 of them, don't just want to bin them, i think what i'll do is make 3s batteries out of all of them and enjoy 6 more flights at the field...! (hopefully ) I will then use the packs that continues to give me 4 minutes per pack ( 6 minutes if you add gliding time and good conditions) like my other 3 cell packs, any of the remainder packs giving less flying time than that i will not use.

Having said that i never really discarded a pack in my 13 years of flying electrics due to its llifespan that diminished, only because of accidents (where they were crashed to smithereens) before they got old due to actual usage. few and far between considering how much i've flown over the years though.

So i'm not too sure how far i can push it before i will get "sudden power losses" which can be disastrous

Will the lipo slowly warn me (ie.. lose power gradually over time) or will i get a surprise one day and the pack just dies mid-air... Or would this be different for everyone each time this happens.

I'm someone that will take a bit of a risk and fly the packs as long as i can and more, but what are the final sign to look for if you are willing to take that chance ?

I believe the packs aren't at the final stage yet, certainly not the plane has good power with good capacity but eventually i suppose i will hit that threshold.
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Old May 06, 2012, 10:28 AM
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United Kingdom, England, Cambs
Joined Oct 2011
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You don't have to give up on the 4s

Just need to prop down - so 12X6 will be fine and provide more than enough - if as I suspect you are a power junky you can go to a 13X6.5 but sparing with the WOT but you should be able to keep that going....but yeah will be providing a hotter running system - however shouldn't be puffing the batteries - unless at WOT for longer than the odd 5-10 sec bursts....
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Old May 06, 2012, 11:07 AM
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United States, WA, Seattle
Joined Jan 2007
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Last comment-why knowingly over prop? The efficiency of the motor drops way off and the extra lost power merely becomes waste heat?
Yes, you can milk some extra power out of it but it exacts a price on all components. If you don't seriously need it for some good purpose you are straining EVERYTHING in the power train and it will come back and bite you.....sometime.
As stated, doing it with 4S just seriously compounded all the problems you barely had under wraps.
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Old May 06, 2012, 12:43 PM
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South Africa
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I've had smaller props, they don't give me the bite i require, not much noticeable difference in temperature going to the 15x13 prop when still using 3s, in fact the plane takes longer to reach the altitudes i desire when using smaller props there for bursts are longer than 15 seconds which i found drained more battery power.

So letting the motor work a bit harder for 15 seconds instead of taking ages to get to desired altitude puts me up to altitude quicker, and as mentioned flying times are the same, but i have the added speed and more than enough torque to get me up to height quicker,

And no, the power system is all mild when i land, that's why i've been able to do it for so many years, i've never had a motor/esc failure due to doing it because they don't overheat, far from it.

Anyway i have changed all packs to 3s, spent the whole afternoon doing it, so will see how it goes hopefully next weekend...

Remember It's not full punch from start to finish, i cut throttle at altitude, use a folder so it folds and fly around a bit and when at low altitude
punch it for 15 seconds again etc. Sometimes i'll do speed dives or loops and need to quickly add power again when low however the battery takes a bit of a punch when not completely recovered, doing it consecutively like that.
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Old May 06, 2012, 09:11 PM
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United States, NJ, Lodi
Joined Jan 2012
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Sounds like you may have missed this post. Here it is again to help explain part of what you are saying here
http://www.rcgroups.com/forums/showp...35&postcount=4
Quote:
Originally Posted by Axefly View Post
I've had smaller props, they don't give me the bite i require, not much noticeable difference in temperature going to the 15x13 prop when still using 3s, in fact the plane takes longer to reach the altitudes i desire when using smaller props there for bursts are longer than 15 seconds which i found drained more battery power.

So letting the motor work a bit harder for 15 seconds instead of taking ages to get to desired altitude puts me up to altitude quicker, and as mentioned flying times are the same, but i have the added speed and more than enough torque to get me up to height quicker,

And no, the power system is all mild when i land, that's why i've been able to do it for so many years, i've never had a motor/esc failure due to doing it because they don't overheat, far from it.

Anyway i have changed all packs to 3s, spent the whole afternoon doing it, so will see how it goes hopefully next weekend...

Remember It's not full punch from start to finish, i cut throttle at altitude, use a folder so it folds and fly around a bit and when at low altitude
punch it for 15 seconds again etc. Sometimes i'll do speed dives or loops and need to quickly add power again when low however the battery takes a bit of a punch when not completely recovered, doing it consecutively like that.
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Old May 06, 2012, 10:38 PM
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Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
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Quote:
Originally Posted by Axefly View Post
I've had smaller props, they don't give me the bite i require,
But you are now running 33% higher voltage, so the smaller props will spin faster and draw more power. Try propping down to 12x8. This should give similar performance to the 15x13 on 3S, but the batteries and motor will be a lot happier.
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Old May 07, 2012, 01:31 AM
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South Africa
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It all ,makes sense Bruce thanks, (i used a 12x10 before) on 3s, and i found the motor running hotter than i was comfortable with, (probably because i had to run it hard and long to get to altitude (however on 4s it could've worked definitely by not having to run it for a long period to get up to height because like you say the prop will spin faster !)

Darn if i only was given this hint a bit earlier i already converted my packs to 3s ! I would've loved to see what it does with 4s and a 12x10 !


Syner no i have not missed that one thanks, i agree with that post.

(practically mostly due to the way i manage my throttle my results slightly differ ie i don't do full power runs throughout the flight, letting the motor cool in between) But what has been said is all true in that post.
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Old May 07, 2012, 09:15 AM
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South Africa
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Now that i think about it, it might've ran hot on the 4 cells as well anyway even though if i used a 12x10. Just not as much as the 15x13, however still hotter because of the extra volts.

Or i'm trying to sooth the conscious because of what i did, changing all the packs to 3s lol......
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