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Old 12-26-2008, 12:25 PM   #1 (permalink)
RotorJockey
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Join Date: Dec 2008
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...
__________________
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."

Last edited by RotorJockey; 12-27-2008 at 07:53 AM..
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