How warm should a lipo get ?

[Nick Farrow]

Hi,

I have an evo1800 on the back of a tower pro a2409-12t. I tried a 9*5 prop which should pull about 24 amps and noticed that the battery back was warm (not hot). I reduced the prop to the optimum of 8*4.5 which should pull ~20amps and the battery was still the same. I know with nimh my packs got hot, but assumed my lipo would not (even get warm) given that it should provide 36A Ok.

Any thoughts!

Thanks

nick

[Tim Mackey]

Warm is fine, - I can still bring the feelings back into my fingers on a cold winter day by grasping the packs as they come out of the planes !
PS any electric flyer who has more than a passing interest in this elecktrickery stuff would be well advised to get a "whattmeter" or similar, to KNOW what amps are being pulled from any given combo.

[Nick Farrow]

Thanks Timbo,

I have thought about this, but BRC hobbies motor/prop datasheets are cheaper !

Given the dosh I spent on this pack, I just want to check I'm not stressing it

nick

[Tim Mackey]

yes, but as you get deeper into the dark side....datasheets will not cover every possible combo.
The meter also accuarately monitors the onload voltage of the pack - which is very indicitave of its "quality". Plus it calculates the wattge input too...saves you having to do it, and rememebr wattage is the way to assess the power to weight ratio of your aeroplanes, aiming for around 100Watt per pound is a good start.

[Jonathan Lewzey]

Your pack should be fine as the current draw is within the pack's capabilities. If you feel the pack is getting too hot, which it shouldn't, try a bigger pack if it will fit in your model.

Also provide good ventilation on the pack, ESC and motor to keep all the drive train components working well.

Speaking from personal experience, my shock flyer has the tower pro A2406/12t outrunner which is rated at 12.5 amps max. i use a 20C 540mAh pack which gives only 10.8 amps constant, but because it has bursts of up to 30C (16.2A) and I rarely use full throttle, the pack comes out barely warm.
Jonathan

[Tom Sharp]

to paraphrase a certain television show.
Ventilation; Ventilation; Ventilation:

[Nick Farrow]

Thanks for all the comments.

The pack died at the weekend, the charger kicked the evo18000 even after the balancer had done its work. The pack is around 18months old and I did drop it on the shed floor.It does not appear to be malshaped. I will comparer it with its replacement in terms of its heat. I have to get another one of these as they fit neatly into the fuse of the easyglider. Otherwise I would have gone for a much cheaper pack from BRC hobbies own range!

[scott cuppello]

Oh yeah, as you get deeper into EF.....a watt-meter becomes essential....particularly for EDF [where all manufacturers claims, not to mention a lot of shops, fall between innacurate.....and just miles out], and IC conversions....which I'm well and truly into these days.....CM-Pro Zero just about finished.....how much nose-weight!!!!!!

[Danny Fenton]

The innacuracy of most of the data we get with Lipos, motors and ESC is amazing. Some manufacturers parts can be pushed much harder than they say, others are very marginal. Friends and I have discharged lipos and A123's at very large currents (we have pulled over 100A from A123's) checking the C rating and capacity is as per specs using heating elements in water (please don't do this unless you know exactly what you are doing!) and they very rarely are as good as they say. I have a very well known brand lipo that wont deliver anywhere near the C rating without the voltage dropping way too much. I have found that Lipos perform better when warm, the first flight on a cold pack is never as good as a fresh off the charger still slightly warm pack.
You are totally blind without a wattmeter, and it is essential, just remember a motor/prop will unload an incredible amount in flight. So what appears to be 50A static will drop to The best way to check this is with an onboard flight monitor such as Eagle Tree. This is an essential piece of kit to work out how hard you are pushing your equipment.

[Tim Mackey]

Hi Danny. I have often wondered about the eagle tree device, but somehow never got around to splashing out on one. I tend to just use the astro flight "whattmeter" on any new / modified installations, and then deduct 10% as a likely reduction for unloading factor in flight. One thing to note however is that EDFs tend NOT to unload that much, if at all, in flight. having said all that, as far as my LiPos are concerned, I aim to not use them at any more than around 50% of their claimed C rating, and it is more the ESCs that I am checking capability for.

[Tony Jones]

Hi Timbo

I have an Eagle Tree Micro Logger with all the bells and whistles in an 'electrocuted' Black Horse Chipmunk. It shows that due to the prop unloading with increasing airspeed, the static amps of 48 fall back to 35 before the model is even off the ground. Amp draw at any given throttle setting is much less that I thought it would be, too. So I could go up an inch in prop diameter if I wanted to. (I don't in this case as the motor is plenty powerful enough anyway). Doing so would exceed the motor's max amp rating for only about 4 secs during the early part of the take off run. But I now know just how far I can push without blowing things up if I ever want to extract max grunt from this motor/battery combination.

I've just bought a cheap (£100) second hand on E-Bay and can now download and replay flights at the field rather than waiting 'til I get home. Or would be able to if the weather would allow any flying...

[Tim Mackey]

second hand what ? Laptop ??
I see our fav web seller is doing the eagle tree logger at a tempting price, but would prefer it if I could see for sure that they are also stocking the altimeter attachment...really fancy that one :-)
Interesting about the amount of unloading experienced...I always worked on around 10% but it seems you are experiencing closer to 25%+ !!
Have you tried it in an EDF yet ?

[Tony Jones]

Hi Timbo

The Laptop is a P3 IBM Thinkpad. Not fast, but it doesn't have to be. I also use it to programme my Castle Creations speed controllers occasionaly.

Only flown it in the Chippie so far. It will shortly be transferred to my 3.5m Thermal soarer. I don't expect the same degree of prop offloading, but it will interesting to see if my estimation of altitude is anywhere near accurate!

[Tim Mackey]

So have you got the altimeter add on then ?

[Danny Fenton]

Hi Timbo I would say that Tony's figures are pretty good, the more slippery the model the more the unloading, I think your 10% is a bit conservative. The temp and rpm sensor I would find more important. A friend of mine did indeed get his Eagle Tree from our favorite supplier and has all the whistles including temp, pretty sure he got it all from them, but can check if you wish.

Just spent most of this afternoon at the Greenacres Fun Fly as an A123 Evangelist LOL showing my Wot 4 off on 6x A123 while friends threw about an Edge on 10x A123 as well as a pair of 3Demons on 6 cells. My Hurricane on 12 cells and a Spitfire on 13cells, weren't able to fly but they still were visible as what can be done. I think some are finally seeing the light on these cells!
Several people were amazed that I could fly again after just 10 minutes charge, and at how simple my charging gear is LOL. Really flattered, I was asked to visit their club in Kent and do a talk on the cells. Guess they were impressed.

[Tim Mackey]

Yes I think I am going to have to get a bit more enlightened on these A123s myself :-)

[Bladerunner]

Hi Nick

As LiPo's age(time and usage) their internal resistance increases unavoidably - i.e. there is nothing that can be done to prevent it. So you will eventually end up with a pack that charge's fine and still has usable capacity, but will no longer sustain high discharge rates, or will overheat at high discharge rates. If you find that your battery pack appears to be running progressively warmer, then it may be that you are beginning to witness the age of the pack.

Trust that helps.

[Tony Jones]

Timbo

Yes, plus the airspeed gizmo! Once I've checked on the first couple of flights that the engine and battery temps are OK, I usually remove them.
IMHO, this gear is really of most use in checking out the data for a new model. After all, who wants to download and replay every flight?

[Danny Fenton]

I agree Tony, would you really want to risk leaving it in a model? we get the first few short test flights out of the way, then use it to check performance, and work out safe flight duration times, then it goes safely back in the box LOL