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Lipoly Battery questions

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Old 02-11-2006, 01:55 PM
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6pack
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Default Lipoly Battery questions

I am new to electrics..
I have a Cessna 182 by ParkFlyers, Mulitplex Permax 480 motor - stock 50amp ECS - and use a new 7.2V 1800Mah LiPo

1. How soon can I throw the LiPo Battery on a charger just after a flight? I have a 12VDC Car Charger for my LiPo and After I fly The battery is still warm to the touch. I was told by someone at the park that flies electrics that I should first wait til the LiPo cools down then charge.
2. Does the LiPo Loose some, how do i state it?, Charge... Like i have been using the orignal LiPo also that I bought with the kit, And it does not seem like it is getting a full charge like the new one that I bought. I can put the new LiPo in and the Full Throttle sounds a whole lot different from when i throw in the Old LiPO and goto Full Throttle.
3. The Gent that flies Electric at the park also mentioned going to a 3cell LiPo 11.1V 2100 MAh for longer flights and better Reponse at full throttle. But he never stated that I should change out the 480 motor or ECS.
4. I was also told that the LiPo Battery should never be ran til dead or Drain battery. Why?

I have 2 ParkFlyer's Cessna 182. One that I am keeping orignal and one that I am looking to Mod or Test for new motor ecs bat config.
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Old 02-11-2006, 03:15 PM
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Default RE: Lipoly Battery questions

Hi 6pack-

1. To maximize the life of your lipos, it is best to let them cool down before charging. If you understand that you may be shortening the life of your lipos, charging a slightly warm battery is OK. Do NOT charge a battery that is hot to the touch. In fact, if you have batteries that are getting hot, you should find out why and correct the situation.

2. Lipos slowly lose capacity over time. Abusing them by drawing excessive current or discharging them too far will speed up the loss of capacity. A properly cared for lipo will last hundreds of flights.

3. The electronic speed controller (ESC not ECS) can probably handle the higher voltage of a 3-cell lipo; you should be able check with the manufacturer. The motor is more of a question. Sometimes, you have to run a smaller prop to reduce the current if that type of motor is to survive the move to 3S lipos.

4. Over-discharging a lipo is probably the worst thing you can do to it. It causes permanent changes in the cells that often cannot be undone. A lipo sould never be discharged below 3V per cell. That's 6V for a 2-cell lipo, 9V for a 3-cell lipo.

The 3V per cell rule is for UNDER LOAD conditions. In other words, you don't want the voltage to drop below 3V per cell at any time, including in flight. An obvious problem is that most of us don't have a way to measure the in-flight voltage.

The solution is to check the battery voltage after flying and after giving the pack a few minutes to recover. This so-called "resting" voltage gives you a good idea of how far your lipo has been discharged. Borrowing from the table [link=http://www.rcgroups.com/forums/showpost.php?p=3272601&postcount=11]here[/link], if the resting voltage of a lipo is near 3.6V per cell (7.2V for a 2-cell pack), it is fully discharged. If the resting voltage is less that 3.6V per cell, the lipo has been over-discharged.

By comparison, a fully charged lipo will be about 4.2V per cell, or 8.4V for a 2-cell pack.

- Jeff
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Old 02-13-2006, 11:17 AM
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lozza
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Default RE: Lipoly Battery questions

I know this plane. If you use the stock prop, the stock ESC and the stock Speed 480 with a 3 cell lipoly, motor life will be very short but glorious! I think your Permax might have the same problem. The ESC will handle it but the motor will fry quickly. You could either try a smaller prop, as suggested by the other poster, or use your 2 cell lipoly with a prop with longer pitch. I would think a 7 x 4 should be enough. If that doesn't meet your power expectations, try a 7 x 5, but I would recommend measuring the current, and be careful it is not too much more than the stock setup draws from the standard 7 cell NiMH battery. I think it could tolerate 25% more current though. The stock motor runs fine with good life on 8 cell 1000 mAh NiMH, in my experience, with a similar prop to the standard one for the Cessna, which is I think about a 7 x 3 or 7 x 3.5.

The two cell lipoly with longer pitch prop is in my opinion a better option than the 3 cell, as it is nice and light and fits in the battery bay well, though snug.

Your lipoly should be getting barely warm with this setup, and in fact they do not heat up as much NiMH batteries can, at least they shouldn't! If yours is getting hot not just slightly warm something is not right. It is important to have a good quality lipoly charger, and be extremely careful that your settings match the battery you are charging.
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