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Puffed LiPo?

Old 06-16-2010, 05:09 PM
  #1  
Thermalrunner
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Default Puffed LiPo?

Hi,

I have a question, please. I flew another sailplane with this setup we talked about. 550, Turnigy 30 amp ESC, and a 2 cell Lipo, 7.4v 1800Mah, and it flew great. Up 5 times. But when I was done and the battery was run down, the motor was too hot to touch and the battery was swollen. I'm afraid to charge it. The motor and ESC are fine, I tested them. And the sailplane "has" air ducts, in and exit, so there should have been cooling.
Any ideas? Maybe I drained the battery too much?
Thank you.
Dean
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Old 06-17-2010, 02:54 AM
  #2  
Sky Sharkster
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Default A Goner?

Hello Dean,
Yes, I'm afraid the bad news is your battery is a goner. Dispose of safely.
There are two main ways to kill a LiPo, aside from puncturing it in a crash.
One, discharging it too fast.
Two, discharging it too low.
I am far from an expert on LiPos, but I'll try to explain this in the terms I understand it.
(1) LiPo batteries have a "C" rating, this is a way of determining the rate at which the electrons can safely be pulled out of the battery. Just as there is a maximum safe rate of CHARGE, there is also a maximum (or safe) rate of DISCHARGE. C Rating.
Briefly, the C rate multiplied by the Mah capacity = discharge rate.
So, your 1800Mah battery (regardless of the number of cells, or total voltage, cells X 3.7 volts per cell) has a C rate, let's say it's 15C.
15 x 18 = 27(0). Twenty-seven amps is the maximum safe discharge rate.
If your motor pulls more than 27 amps (most likely at full throttle), and this is entirely possible with a 30 amp speed controller, the battery will overheat, permanently damaging it. Sometimes the thermal overload function of the ESC will shut it down, sometimes not.
The battery overheats, puffs and is damaged. Theoretically you could still use it, but it's dangerous and dumb. It could easily cost you your airplane and a lot more, if it ignites.
(2) LiPos are also subject to problems when they are discharged too low. Even when the amp draw is within limits (C rate), it is possible to drain it below the maximum safe level. This figure is (variously) 3.3 volts per cell, 3.5 volts, I've even seen 3.1 volts quoted. Most experts agree that a LiPo discharged below 3.0 volts is permanently damaged.
So, you either ran it too hard (too much amp draw in a short time) or for too long. There is a low-voltage circuit built into most modern ESCs and it SHOULD catch the latter, but they're not all set the same and don't always keep up with a rapidly-changing situation.
A wattmeter will tell you the exact amp draw at any throttle setting. This is the safest and most reliable way to calculate your power system.
Here are a couple of links that explain LiPos better than I ever could;
http://www.rchelicopterfun.com/rc-lipo-batteries.html
http://www.rchobbies.org/lithium_bat...eakthrough.htm

Good Luck!
Ron

Last edited by Sky Sharkster; 06-17-2010 at 11:47 AM.
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Old 06-17-2010, 01:51 PM
  #3  
Mike Parsons
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Originally Posted by Thermalrunner View Post
Hi,

I have a question, please. I flew another sailplane with this setup we talked about. 550, Turnigy 30 amp ESC, and a 2 cell Lipo, 7.4v 1800Mah, and it flew great. Up 5 times. But when I was done and the battery was run down, the motor was too hot to touch and the battery was swollen. I'm afraid to charge it. The motor and ESC are fine, I tested them. And the sailplane "has" air ducts, in and exit, so there should have been cooling.
Any ideas? Maybe I drained the battery too much?
Thank you.
Dean
Dean,
I am afraid I agree with Ron, it is toast. Ron gave a great explanation and if you don't have a wattmeter, it is an invaluable asset in your arsenal of tools. Mine has saved me hundreds of dollars in possible damage.

It would be interesting to know the amp draw, but it could be as Ron said overheating (get a thermal temp guage too (great tool)), battery drained too low or over amping.

With the motor being as hot as you say, I would guess either over amping, or over heating. Since sailplanes are short run (throttle for climb only), I want to lean towards over amping.
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Old 06-17-2010, 02:32 PM
  #4  
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Definitely take it to your battery recycler. Do NOT attempt by any means to charge it or use it again. I had a puffed battery catch fire on my last week. Luckily it was on a fire-proof surface and was already destined for the dumps...
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Old 06-17-2010, 06:22 PM
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Matt Kirsch
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If the motor is HOT to the touch, then you're drawing too many Amps.

It's very likely that you exceeded the rating of the battery, by a LOT. That's why it puffed.

Cooling air only goes so far. It can only prevent damage when the parts are used within their capabilities.
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Old 06-17-2010, 10:52 PM
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Thermalrunner
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Anybody have a recommendation for a "brushed" motor that would handle the Turnigy 30a ESC (brushed) and the lipo 12C 1800Mah? The one I had was a 550 out of a Sportsman glider, that overheated.

thank you
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Old 06-17-2010, 11:06 PM
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Mike Parsons
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Originally Posted by Thermalrunner View Post
Anybody have a recommendation for a "brushed" motor that would handle the Turnigy 30a ESC (brushed) and the lipo 12C 1800Mah? The one I had was a 550 out of a Sportsman glider, that overheated.

thank you
I wish I could make a recommendation...I haven't messed with Brushed motors in 5+ years.
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Old 06-18-2010, 02:18 AM
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Sky Sharkster
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Default Brushed Replacement?

Hello Dean,
Wish I could say there was a brushed replacement, but honestly, I don't think there is. Brushed motors are primarily used in "Beginner" or Starter planes because of their low cost. The downside is, they're fairly inefficient, heavy for the power output and don't last long.
Since the cost of brushless has gone down so far, they're hardly more expensive than a brushed motor and last (almost) forever.
Hobby-Lobby.com lists several "500" and "600" brushed motors (but no 550's) and most are $18.50 US. They also have a "Turbo Ball Bearing 600" brushed motor for $35.00, but you could easily find a brushless motor for that price.
Now the speed controllers for brushless are more expensive and since you already have a brushed controller, I'd like to find a motor that would work. About the only idea that comes to mind is to use a geardrive. This reduces the amp draw greatly while increasing efficiency. It allows you to use a large prop for more thrust.
The downside there is that a Sailplane needs a planetary gearbox, not an offset one. Planetary gearboxes are more complex and expensive. I have an MP JET "400" sized planetary 'box and it's great, beautifully machined and provides "600" power out of a "400". Problem is, it cost more than $30.00.
If you want some links for any of these ideas I've presented, let me know.
Overall, I think you would be better served by buying an inexpensive brushless outrunner and ESC. You can still use the 30 amp brushed ESC with a "Speed 400" pylon racer or smaller brushed model.
Good luck, whatever you decide!
Ron
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