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Old 12-26-2008, 12:25 PM   #1 (permalink)
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Arrow LiPos and Cold Weather...My Solution

It all started last week.
It was 27 degrees f, and I tried to fly my CP Pro. I had kept my batteries warm, but after about 2 minutes of flight time, they chilled to the point that they lost power, the heli lost head speed and I had a rather hard landing.

A few days later, my oldest son came home (Southeast Missouri) from Dallas. He owns a T-Rex 500 ESP and he was delivering my Christmas present, a brand new T-rex 500 ESP!

We took his 500 for a little flight in about 25 degree weather. His battery came out of the pocket of his hoodie and directly onto his helicopter. By the time he ran it up, it didn't sound right and could barely hold itself in a hover. He landed and we called it quits.

This is our first winters in electrics and helis and we weren't sure what was happening. We did some research online and found that basically, LiPos use a chemical reaction to both store and release electrical energy. Cold temperatures interfere with the chemical process, which is why LiPos discharge poorly in the cold and if you try to charge them in the cold you will ruin them.

We built my 500 and hovered it several times in my garage, but we were scared to try to fly it outside because the temperature was still in the 20's.

The next day we came up with an extremely simple solution:

Just don't let the LiPos know it's cold!

Here's how we accomplished that:

I slightly pre-warmed the batteries. I placed them on top of a warm (not hot!) part of my furnace. You could also do this either by placing them over a heat register or giving them a top-off charge.

Then I made a crude transporter out of a small stirofoam cooler. I placed foil in the bottom to reflect the heat back towards the batteries. Then I laid 3 small "Hot Hands" hand warmers on the foil in the bottom. I then placed a small face towel over the warmers. I did this for insulation and because I didn't want to place my batteries directly on the warmers. I placed the batteries in the cooler then folded the towel and the foil over the top to hold the heat in.





To use a battery, we laid another small "Hot Hands" warmer directly on a battery. we then wrapped the battery in foil (leaving the velcro side of the battery uncovered). Be sure to always keep the shiny side of the foil in towards the battery. Our T-Rex 500s came with 2 sets of velcro wraps, one large and one small. We wrapped the 2 small wraps around the battery to secure the foil and hand warmer in place. We then used the large straps to secure the whole thing to the helicopter.









Incidentally, my batteries are FP 3300mah 25c. I did the cut-away battery tray mod on my 500 to accomodate the larger batteries.

The sacrificial lamb was my Blade 400. We strapped a heat pack and foil to it's battery and banged it around (as well as 2 novice heli pilots could) for 5 minutes. It never lost any performance and when it landed, the entire power system was just pleasantly warm. Nothing was hot.

Our next test was with the new T-Rex 500 and was a 3 minute hover at 22 degrees f (the coldest temperature we have tried to fly in yet). Upon shutdown, the battery, motor and esc were lukewarm at best. The second battery was 6 minutes of sport flight, cruise, rolls, loops etc. Same result, battery, motor and esc warm, not hot. So we put the heat pack on a third battery and took right back off again. After 6 minutes of sport flying on the third battery, it, motor and esc again were just lukewarm. Although this was my first time flying a 500, my son said that it performed just as well as his did in 70 degree weather.

I especially liked not having to wait for the motor and esc to cool before flying again!

My local shop deals mostly with cars and not even very much of them. I had them order me one of those IR temp sensors. After it comes in, and it gets cold again, I am going to do some more extensive testing and will report actual temperatures of the equipment after flights.

I finally figured out how to load pics, but they're kinda big...
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Last edited by RotorJockey; 12-27-2008 at 07:53 AM..
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Old 12-27-2008, 11:17 PM   #2 (permalink)
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Guys, this was simple and easy to do. Those heat packs stayed warm all day, and it was nice while I wasn't flying to keep my hands warm in my hoodie pouch. I was a bit skeptical before our test flights, but I couldn't be happier with the results. I don't have to deal with that very often at all in dallas, but it sure was cold in Cape Girardeau that day. I'm surprised no one has posted something like this before, or they have but I didn't find it when I searched HF.
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Old 12-28-2008, 08:16 AM   #3 (permalink)
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Got my IR temp sensor.

It's 31 f this morning.

After 6 minutes in the T-rex 500 I recorded the following temps:

Battery: 99 degrees f
Motor: 75 " "
ESC: 70 " "

CP Pro battery simply wrapped in foil, after 5 minutes was at 98 degrees f.
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Last edited by RotorJockey; 12-28-2008 at 09:18 AM..
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Old 12-28-2008, 08:45 PM   #4 (permalink)
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sweeeet...thanks for the info!
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Old 01-04-2009, 03:00 PM   #5 (permalink)
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Very sweet. I'm flying an AXE CPv3 which *might* have the room to have the battery wrapped in aluminum foil prior to flight, but the hand warmers.. even the super thin boot inserts for toes, will not fit. I'll have to figure something out, although keeping the batteries in the house or pocket and loading them directly into the heli usually gives 5 or 6 minutes of flight time.. painfully short, but enough to satisfy in between RealFlight training sessions.

Thanks for the idea!
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Old 01-04-2009, 10:57 PM   #6 (permalink)
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Default Hello darkhaven

I have run several tests with just the foil and from what I can tell, just starting off with a warm battery and reflecting the heat back to the battery with the foil, the difference is only a couple of degrees with the hand warmers.

When you get to the point of EXTREME cold, the foil may no longer be enough, but for up to 5 degrees below freezing (f), the foil does an outstanding job of holding in the heat.

I intend to test lower temps as the winter progresses.

the results for anyone else who tries this will be welcome.
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Basic Flying Rules: "Try to stay in the middle of the air. Do not go near the edges of it. The edges of the air can be recognized by the appearance of ground, buildings, sea, trees, and interstellar space. It is much more difficult to fly there."
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