3 years charging these lipo battries and no problem. 8-16-2013 my luck ran out.
I was charging a 3 cell 2200 mah lipo while I worked at the computer.
It caught FIRE near me. Got it out the door just in time.
It burns HOT and long.
I was charging a 3 cell 2200 mah lipo while I worked at the computer.
It caught FIRE near me. Got it out the door just in time.
It burns HOT and long.
Could have burned the place down to the ground.
Be CAREFUL.....PLEASE !
Be CAREFUL.....PLEASE !
Earl
It Caught FIRE near me. Got it out the door just in time. It burns HOT and long.
Be CAREFULL.....
Be CAREFULL.....
Comments
Interesting points. On the ESCs that are shipped by 3D Robotics, the default low voltage cutoff is 2.85V. Basically, what I saw in my experiment is that by the time the batteries get to 2.85V, they're pretty much out of juice and the quad is either already on the ground or a couple of seconds away from falling out of the sky.
I do agree with your point, which is that if having one of the ESC shut off before the others is a very very bad thing to be avoided. I didn't see this behavior in my experiments, and I have been flying on the default ESC settings since my experiment and haven't seen it in flight, but then again, I take precautions to land before my batteries get too low. Also, I buy the more expensive batteries with high C ratings. I imagine that having a low C rating battery or bad wiring could cause a temporary voltage dip, causing one of the ESCs to failsafe before the others. I would love to hear from others whether they've had this sort of thing happen.
It's probably ok to disable the voltage cutoff on the ESCs if you have some other way to guarantee that you're not going to run the batteries too low, like a forced auto-land once they get below 3V. I haven't tried this myself yet. But I think if people are flying with no low voltage protection for LiPo batteries at all, they're asking for trouble... either damaged cells or in the worst case a fire. I'd rather crash my drone than burn down my house, but that's just me ;-)
Good discussion.
IIya, the thing about the voltage cutoff, is that it is better to destroy the battery, than to destroy the battery AND the quad. Using the low voltage cutoff will usually cause the quad to crash, as invariably one of the ESC's will reach LVC before the others. However, this does not mean that we fly with no LVC at all. The key is to use telemetry, or a voltage failsafe auto-land. You should land when voltage gets low, don't keep flying until it won't fly anymore. That's not what it's about to disable the LVC in the ESC's.
Now, the perennial question is: How low is too low?
I typically fly until the in-flight hover voltage is 3.5V/cell. This typically results in a post-flight at-rest voltage of about 3.7-3.8V/cell. This seems to be nice. I normally put back the typically recommended 80% of the stated capacity.
However, sometimes, I've gone past 3.5V accidentally, even to as low as 3.0V/cell. It can sometimes drop VERY fast once it gets past 3.5V which is why it's pretty pointless to do this anyway. But as I say, sometimes it happens. I wonder how much damage I do when this happens?
i have some Unused reputable phone company batteries that i made into 3S batts for powering ground equipment. These batteries cut out internally at 3.5V as over discharge protection. They take 1200mAh of charge from that voltage (classed as 1200mAh). You can really see that the phone companies are not going outside that range. Also if you try and pull large current they have over current protection, and cut out.
We don't do any of that in RC, and people, without using telemetry or low voltage audio alarms are simply over discharging, and pulling more current than the battery can handle. You probably only have 100 to 150 charge cycles (maybe less)before you need a new battery.
I think it really important to see how much charge your batteries are accepting (not whats written on side;-)), and not pulling out more energy than you put in. You will then maximize the finite<\b> lifetime.
I think incorrect ESC settings could be contributing to some of these lipo fires. A few months ago, I did some experiments to test whether setting ESCs to NiCd and reducing the cutoff voltage (as recommended by many web sites) was a good idea. To test this, I tethered my drone and ran it at 50% thrust until the batteries ran out, with a voltmeter attached. What I discovered was that if I turned off these safety mechanisms in the ESCs, I only got about five extra seconds of flight time, but I invariably caused damage to the LiPo (in the form of gas discharge). Many of the sites that recommend these ESC settings say it's worth it to kill a battery in order to save a drone, but based on my experiment, the extra 5 seconds may not really help to save your drone, and will definitely lead to damaged batteries that may have a higher chance of catching fire. I now fly with my ESC settings at the default level, and just take other precautions to keep the batteries from running low like a low battery alarm set at a 3.5V threshold, and landing whenever I notice that I need over 75% thrust to keep the drone aloft.
I charge my lipos on a glass table, on our deck. For storage, I place the batteries in fire proof bags, then into a steel ammo box, and last, in the fireplace.
It is stories like this that keep me doing what I have been doing. For me, it is easy to get careless and over confident at times. - Not safe.
Thanks.
My very first LiPo (ThunderPower=not so cheap) burnt spectacularly on my very first flight with it lol. This was when they were kind of new and the first cars/rooms had just started getting burnt during charging.
Anyway, my excuse is I had previously used NiMH in the plane and replacing with LiPo made the LiPo a kinda loose fit in the airframe. I made up the spare space with tightly-packed (I thought...) foam, and of course the LiPo fell out due to inadequate anchoring and burnt on the ground. Plane sorta glided down OK.
I charge my LiPos in Visions (glass) cookware. It's the kind of cookware single guys (??) bought maybe in the mid '80s I think, haven't actually cooked in it in at least 20+ years. You can likely find it at garage sales, nice for charging because you can see through it. In Canada, for those Canadians who followed the news here lately, know you'll likely be able to find a lot more of it at garage sales soon...haven't seen it in stores for a very long time.
BLEVE?
My wife gets annoyed when I talk about rapid deflegration vs. detonation, when we watch something on TV or a movie. One needs to get ones terminology straight, and too often the entertainment industry gets it wrong. HAHA!
I guarantee you any firefighter since that event occurred has seen this video somewhere in their training's.
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