PlanePlanter

My Feedback: (9)

OK So I'm new to the brushless/Li-Po craze so here we go.
How warm do your batteries get? I was testing my system out the other night, and after the ESC shut down I unplugged the battery. It was not "hot" but warmer than I thought it would be. It wasn't to the point that you couldn't hold it just purdy dang warm! I'm guessing all is OK, just want to make sure

Greg Covey

That's as warm as they should ever get. Typically, they should not get that warm.

Try to design your Lithium packs so that the continuous current rating of the pack is equal to the motor current draw at max. throttle.

Good luck!

PlanePlanter

My Feedback: (9)

Thanks Greg! Still on the learning curve with this stuff.

PlanePlanter

My Feedback: (9)

OK so I know this has been asked a million times but here I go. I just want to make sure I understand this.
Set-up
Axi 2208/34 running 10X4.75
Jeti advance 18
Apogee 830 mah 2S1P ( Rated 9A cont. 12A Bursts )

Looking at the motor specs with that prop it should have only been pulling 6.6A ( Per H.L. website ) So why did the pack get that warm?
Do I have to big of a ESC? ( 18A )
Am I getting overly concerned about nothing?

When I say the pack got warm, it was a little warmer than those hand wrmers you use in the winter. Like I said it was not "hot" but right on that border line. Thanks a million in advance for your answers!

d_wheel

It is very difficult to tell another person how to judge heat by "feel". An item might feel warm to one person, and not to another. For instance, the motor on my RappE reads around 120 degrees immediately after a flight. I can not hold my finger in it for more than a second or two because to me it feels HOT. My friend holds his finger on the same motor and says, "It feels slightly warm.". My point is that you really need to pick up some kind of thermometer. These are priced very reasonably and take all of the guess work out of checking temps.

http://www.reliabilitydirect.com/tem...Y-minitemp.htm

As for LiPo batteries, I understand that 140 degrees F is the limit. Anything hotter than that and they might go into thermal runaway... Not good.. Mine usually run around 100 to 110 at the hottest. The newer TP cells run about 10 degrees cooler even at higher currents.

Later;

D.W.

latch66

The ratings from the Hobby-Lobby website (or any website for that matter) do not apply to everywhere. They are for general information only, to be used as a "guide". Your altitude above sea-level has a great impact on the performance of your motor/prop combination. Props which will be unusable at altitudes closer to sea-level due to amp pull, will become usable at certain altitudes above sea-level.


My advice would be to put a Watt-meter on your plane and find out for certain what the motor/prop/battery combination is pulling.

Also, when they say bursts to 12 amps, that's what they mean. Bursts only. If you are flying at full throttle and are above the 9 amp rating for the pack, then you are risking damage to the pack.


Please keep in mind that you will pull more amps from a motor on the "bench" than you would if you were flying. I have seen this number be as much as 5 amps or more depending on the motor/prop/battery combo.


The Lipo packs should not be "hot". As said earlier 140F is about it. Anything hotter and you are risking losing the battery or worse.

I think your ESC is fine.


I hope this helps.


If you find out what the problem is, please post it so we can all benefit from the knowledge. Thanks.

PlanePlanter

My Feedback: (9)

d_wheel, Good point! Never thought of it that way when I posted. Thanks for the 140 deg info. I will pick up a thermometer.

Latch, Will do, I didn't know that a bench run pulls more amps I don't have a watt meter but may pick one of those up also. I doubt I do a "full" bench run again ( till the ESC kicks off ) as I don't want to hurt anything.

Theres alot to learn w/this Ltric' stuff!

Matt Kirsch

My Feedback: (21)

You can't have an ESC that's "too big" except in the sense that it's physically larger and heavier than the plane can carry. The ESC has absolutely nothing to do with the current draw. That's determined by the motor/gearbox/propeller combination, and the batteries themselves.

I'm not sure where Hobby Lobby gets their data, but the modelmotors.cz website lists the current draw on the AXi 2208/34 with a 2-cell Lipoly and a 10x4.7 prop at 7.8 Amps. I'd believe them over Hobby Lobby, mostly because I've caught major mistakes in the AXi motor ratings on HL's site before.

"Continuous" ratings are simply the rate at which the battery can be discharged without immediate, obvious damage. There is generally a signifigant loss of capacity when the cells are pushed to their continuous ratings (i.e. you only get 80% of rated capacity at the continuous rated current draw), and some heat. At 7.8 Amps, you're pretty close to the rated continuous capacity of 9 Amps.