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Old 05-16-2009, 12:18 AM   #101
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Thanks, will do.
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Old 05-16-2009, 03:30 AM   #102
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Originally Posted by noffey View Post
If I have a plane that takes 18volt battery, is there any advantage to having a single 18 volt battery over a 7.6 plus a 11.4
The only advantage is you only have one battery to charge. Unless you get a battery charger that can handle 2 batteries at once, then you will have to charge each battery by itself and that takes longer, or you could buy 2 chargers. The problem with a 5 cell battery is that not very many planes use them. Most planes use a 3 or 4 cell battery unless you get into the larger ones. Also, each cell is 4.2V when it's fully charged, so a 2 cell would be 8.4 and the 3 cell would be 12.6V. Now that is not the working voltage of the battery, that is the fully charged no load voltage. A 2 cell will be 7.4V and the 3 cell will be 11.1V under load or nominal voltage. A 5 cell battery will be 18.5V under load. Each cell will change to 4.2V on the charger, but the voltage will drop after you put a load on it. What plane are you flying that takes a 5 cell battery??

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Old 05-16-2009, 07:28 PM   #103
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I have no plane yet, but was looking at the 64" corsair. I am flying gas now, and was comparing costs.
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Old 05-17-2009, 02:53 AM   #104
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One thing that is a little different then gas or glow is the fuel cost. In a battery, you pay for all your fuel up front where in gas or glow you buy a little at a time. You can figure about 200 to 500 flights on a battery depending on how you take care of it. You can also fry a battery in one flight of your not careful. Run your battery to about 80% discharge and you should get about 500 flights out of it.

As for the number of cells, you would be better off going with a 6 cell battery if you can. That way you can buy 2 three cell batteries and use them in different planes. The most common battery is a 3 cell in most of the smaller planes, but you can put 2 of them together and make it a 6 cell battery. If you really need an extended flight time, you can go 6S2P and use 4 packs to make up a battery pack for a bigger plane. That's 4 batteries altogether with 2 hooked up in series to make a 6 cell battery using 2200mah batteries and then using 2 of these hooked together in paralle to give you 4400mahs total. Each 3 cell battery would cost you about $19.00 unless you have to have the big name brand batteries. That's $76.00 for a pack and you can break that down and fly a smaller plane using 1 2200mah battery.

If you are going to be flying big planes ALL the time, then you would be better off getting a 5 or 6 cell battery and flying on that. Just make SURE that is what you want. Once you buy one of these big critters, you can't break it down later to fly smaller planes. Also, you want the biggest battery you can get in there for flight time, but you need to watch your weight too.

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Old 05-17-2009, 03:45 PM   #105
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A comment on voltage vs amperage. This is covered in one of the e-book chapters but let me bring it out here.

We often talk about watts/pound as a good starting point for sizing power systems for our planes. But you can get to the watts you want in one of two ways.

If I am flying a 5 pound plane and would like good aerobatic performance, 100 watts/pound is probably a good target. So, if the plane is 5 pounds I need a battery/motor/prop combo that will produce 500 watts.

Now, how do you get to 500 watts? I am going to use round numbers here so forgive me if the multiplication is a tiny bit off.

While a 3 cell lipo has a nominal rating of 11.1V, under heavy load its voltage will drop closer to 10 volts. So I am going to use 10 volts to represent a 3 cell pack.

So, if I want 500 watts, I need 10 volt and 50 amps out of my battery pack.

Another way would be to use a 6 cell pack, 20 volts, and draw 25 amps. That also gives me 500 watts. This can be a single 6S pack, or it can be two 3S packs hooked up in series. They sell connectors just for this purpose.

Now, you will get various opinions as to which approach is better, high voltage or high amperage. But I find most experienced power system designers will favor higher voltage and lower amperage.

There are a variety of reasons:

In order to handle high amps you need BIG FAT wires. They are heavy and can be a bit hard to handle.

You need a BIG ESC rated for high amps. They are expensive

Batteries are rated in amp hours, meaning how many amps they can deliver over time. So the higher the amp draw, the faster you drain them.

So, if we are producing 500 watts.

A 3S 2500 mah pack, producing 50 amps, will last about 3 minutes, assuming you could use the full 2500 mah capacity. And you would need at least a 20C pack. A 25C or 30 C pack would be even better so you are not running the pack at the edge of its capabilities.

A 6S 2500 mah pack, producing 25 amps will last 6 minutes and you get the same 500 watts. For this set-up you could use 10 to 15C packs which typically cost less then 25 to 30 C packs.

You could go to 5000 mah 3S pack for longer duration, but typically a 5000 mah 3S pack costs more than two 2500 mah packs you would use to make the 6S pack.

Chargers = There are lots of fairly good and reasonably priced chargers that will charge a 3S pack. If you get two of them you can charge the two 3S packs in an hour or less.

The chargers that can handle a 6S pack are much less common and can be pretty pricey. You get one of these chargers and you charge your 6S pack in about an hour.

So, there are are a variety of ways to get to the power level you want. And the different approaches have different cost factors.

A 6S 5000 mah pack can be pretty pricy. But 4 3S 2500s might be a lot less expensive simply because this is a much commonly used pack. AND, as Ed points out in his other post, you can take those 4 3S 2500 mah packs and use them to fly smaller planes. That big, fat 6S 5000 mah pack is only going to be good in a big plane.

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Old 05-17-2009, 04:37 PM   #106
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Originally Posted by AEAJR View Post
You could go to 5000 mah 3S pack for longer duration, but typically a 5000 mah 3S pack costs more than two 2500 mah packs you would use to make the 6S pack.
Of course you could just as easily use the two 2500mAh packs in parallel to produce the 3S 5000mAh pack. And then you'd still have two packs for smaller planes if you needed them. And if you're going to use packs together which have had varying usage (i.e. used in other models not just the large one) it's a lot safer using them in parallel rather than series.

There are good reasons to prefer higher voltages for high power but that really isn't one of them .

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Old 05-17-2009, 05:21 PM   #107
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Thanks for your comments Steve. Could you elaborate? I don't see your point. What is unsafe about taking two 3S 2500 mah packs, connecting them series to create a 6S 2500 mah pack?

The only concern I can see, and a valid one at that, would be if the packs were not matched to some degree. In my examples I make an assumption, but should have stated it, that when I talk about putting packs in series or parallel, I am talking about matched sets. Two of the same pack.

While one could use dissimilar packs, and be electrically valid, dissimial packs put an unknown into the equation as to quality of the pack, resistance and the like. So I would always use matched packs for this kind of set-up.

Perhaps this was what you were thinking.

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Old 05-17-2009, 06:03 PM   #108
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I've been discussing with Aeajr about collecting all his work in a single file. Done, here is the pdf file of his work.



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Old 05-17-2009, 07:34 PM   #109
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Red,

Thanks for the work you put into this.

My goal for this e-book was to have it be a living document with input from you, the readers and provide the ability for constant updates. However many have asked if there was a single file that had all the chapters.

Red took on the work of creating such a document. He discusssed it with me and I asked him to post it here for your benefit.

This community is full of helpful people. Red probably knows more about batteries than anyone else, so post your questions because that is all part of the purpose of this e-book. It started out as mine but it is mine no longer. It belongs to the community now, to live and grow and help all those who come here for help.

I will continue to add when I think I have something worth adding.

Enjoy guys!

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Old 05-17-2009, 10:35 PM   #110
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I read your article on electric motors and stuff and found it very interesting, but either I missed it, or you left it out, but I saw nothing on safety. On thing that everyone needs to know about electric motors is that they should never have a prop attacked to the motor while you are working on it, unless you are working on changing out a prop or checking the current draw or anything that needs the prop installed. If you are working on the control surfaces and getting them lined up, there is no need for a prop and in fact can be quite dangerous to have one on. I have seen more then one accident because the prop was on when it shouldn't have been.

A glow engine can be stopped kind of easy with a finger without to much damage to the finger, but an electric motor can cut you to ribbons. Now I am talking about the smaller engines, like a .46 to .60 or so, not a 2.20 4 cycle or a big gas engine. The problem comes in on an electric motor in the fact that as long as the battery is hooked up, the motor will draw current and try it's best to continue to run. Most of the time at your expense by cutting the daylights out of your hand or finger.

We talk about 500W or 600W motors as if they are nothing, but in fact are quite powerful. I'm going to round things off a bit to make it easy, but a 1HP motor is around 760W and that is a lot of power. A 500W motor which is used quite often is running around .7hp and that is more then enough to carve you up good. The props we use are also very sharp and can slice and dice you faster then you can blink. Put a good APC prop on an electric motor and you could very well have a slicing machine with a .5hp motor behind it cutting you faster then you can react.

In then end, it boils down to this. Never put a prop on an airplane you are working on unless you NEED the prop for some reason. If you are working on a plane with a prop attached, make sure you don't have anything around that can get caught up or sucked into the prop. Also, make sure nothing in back of you is going to get blown around. Make sure your pets are safe from props also. Some are quite brave and think they are defending you and will attack the prop for what ever reason.

The best thing you can do is remove the prop any time there is a battery in the plane unless you are planning to fly. Talk to anyone that has been cut bad by a prop and they will tell you the same thing. If you don't need it, take it off. If you need it, be VERY careful around it. Also, don't get in the plane of rotation of a spinning prop. I have seen blades thrown for one reason or another and they could smart if one hit you.

Ed
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Old 05-17-2009, 11:04 PM   #111
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Originally Posted by AEAJR View Post
Thanks for your comments Steve. Could you elaborate? I don't see your point. What is unsafe about taking two 3S 2500 mah packs, connecting them series to create a 6S 2500 mah pack?

The only concern I can see, and a valid one at that, would be if the packs were not matched to some degree. In my examples I make an assumption, but should have stated it, that when I talk about putting packs in series or parallel, I am talking about matched sets. Two of the same pack.
The assumption I was making was that if you used the packs separately in other models as you seemed to be recommending then, even if they were originally well matched, they would soon become unmatched because they would have been used differently. Only if you keep them together and only ever use the pair as a 6S will they stay well matched.

That only applies to series connected pairs since exactly the same current must always flow through both. Unmatched packs connected in parallel are much less of a problem because, if necessary, they can share the current unequally according to their relative "strengths".

Steve
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Old 05-18-2009, 12:36 AM   #112
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Originally Posted by mred View Post
I read your article on electric motors and stuff and found it very interesting, but either I missed it, or you left it out, but I saw nothing on safety. On thing that everyone needs to know about electric motors is that they should never have a prop attacked to the motor while you are working on it, unless you are working on changing out a prop or checking the current draw or anything that needs the prop installed.
Ed

You didn't mention how useful it is to clean off the work bench while you are setting up an electric model. Gets rid of all those pesky screws and small parts you probably would forget to put back on anyway.

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Old 05-18-2009, 04:09 PM   #113
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I know I missed some things, but that would take another article to cover all the safety aspects of electric flight. I wasn't in the mood to write a whole article on it last night as I had a bad headache. There are a lot of things that need to be done not only with electric planes, but glow and gas too. I just covered what I thought was the most important points. There are a lot of things that need to be covered to keep someone from burning their house down or their airplane too. Like I said, it would take a whole new article.

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Old 05-18-2009, 04:48 PM   #114
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Ed,

Your contributions are always welcome and valuable. Thanks for taking the time to share your insights.

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Old 05-30-2009, 04:22 PM   #115
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A few safety tips when flying electric powered planes.

Propellers

The first thing you need to learn is NEVER put a prop on you motor with a battery installed unless you are ready to fly. Any time you are working on the plane the only time a prop should be on your motor is when you need the prop to check the spinner distance or something of that nature, but the battery does not need to be hooked for that. The only time a motor needs a prop and a battery hooked up is if you are checking the amp draw. More accidents happen when the motor is turned on by accident than you would believe. Planes fly across the work shop, hands and fingers get cut and pets are in mortal danger of spinning props and children are especially vulnerable to accidents with electric planes. Always think when you are working on a plane with a prop on it and never take anything for granted. New people should be especially aware of this as they are not yet familiar with the workings of electric planes yet.

Electric motors like a lot of things in our life are very easily taken for granted and things can happen faster than you can react. A motor looks small and not very threatening. Most motors are armed when power is applied to the ESC(Electronic Speed Control), yet some are not armed until you deliberately do something, such as go to full throttle and then back to off, or push an arming button or something like that. The problem with motors arming when power is applied will bite you faster than most of the others simply because the motor is armed and ready to turn on as soon as power is applied and it figures out how many cells are connected to it and that does not take long. Some have a slight delay before arming, but are still armed when this delay has times out and the delay is not very long. Most can be programmed to play a little tune when power is applied and some do not. It just depends on the manufacture of the ESC. Why am I going threw all of this seemingly meaningless warnings? Well, it's like this . You apply power and your ESC emits 3 beeps to tell you how many cells are connected to the ESC and it sets the cutoff voltage by the number of cells it finds. After it finds the number of cells and sets the low voltage cutoff, it is ready to go. You are working on the ailerons and trying to get them lined up at zero and you accidentally bump the throttle to 3/4 throttle and the motor starts running. Now if you have the prop off, nothing bad happens, but if you have a prop on, it takes off. The natural reaction is to reach for the plane to try and restrain it. Some times you grab it buy the body of the plane around the nose and nothing bad happens, but if it happens to be heading for your child, you may not be as particular as to where you grab it. After returning from the emergency room and 20 stitches later, you don't feel much like working on your plane any more.

You say that all you have to do is turn the motor off with the throttle, but those unfamiliar with electric planes don't always do the right thing. Also, the plane is moving rather fast and all you are thinking about is stopping it, so you grab it some where. That's nice IF you grab it in the right spot. If not, it's time for that trip to the emergency room again. It also depends on how hard you grab it as to the damage that can be done to your plane. Grab it to hard in the wrong place and you are in for some repairs even before you got that nice new plane out to the park to fly it for the first time.

Motors seem small and from the looks of them they are not going to hurt you very bad. Lets look at the motor and see just what it is that we are using. I am going to use approximate numbers and round them off to an even value, so please don't get on me because I didn't get the numbers exactly right. A 1 HP motor runs about 746 watts, so a 500 watt motor is running around .7 HP and while it doesn't have as much torque as some motors, it has enough to do a lot of damage.

In the old days of flying .60 powered planes using wood props, I have had my finger caught in a prop more than once and it hurts, but doesn't stop your day of flying. These engines are fairly easy to stop and your finger can stop that engine rather easy. You may get a small cut, but most of the time we didn't. Just a smack on the finger to let us know we did something stupid. The new props from APC are a different matter. I have cut my hand on a new prop before I even go it put on the engine. That trailing edge is sharp. Most of the people in my club take an X-Acto knife and scrape the back of the blade to take the razor edge off. Then we balance it and mount it.

On electric props, they are even sharper both on the leading edge and the trailing edge. We can take some of the edge off the trailing edge, but we are stuck with the leading edge unless we want to mess up a good prop. Now when an electric motor hits your hand, it is still drawing current from the battery and if it was not a good solid hit, the motor will continue to run. That means it is going to be slicing up you finger or hand and can send you to the Emergency room fast. If it hits you wrist or arm, it can slice open a vain, or worse and you can bleed rather badly and require a few stitches to repair. That's if you are lucky. If your not lucky, you may spend some time in the hospital and that's not fun either. If you are alone and this happens (and it has) you could be in for a life threatening situation.

Another problem with electric systems is this. If you get a solid hit and by chance the motor stops, it is still drawing current from you battery through the ESC. In another section, you were told about the KV rating of a motor. What that means is this. If the motor is running, it is drawing current and trying to run at the KV rating. It can at times run at this rating and at other time it may not. Here is what I mean. An 800KV motor will try and run at 800rpm for each volt applied, so if you apply 10 volts it will try and run at 8,000rpm. If it has the correct prop, it will run very close to this rpm and everything is fine. If however you put a 14X6 prop on a motor that can only turn a 12X6 prop, the motor may not be able to turn at the rated rpm, but the motor will still try to and this amounts to heat and a LOT of current. That is why we prop our motors with the correct prop and why we need a watt meter to check this.

Playing around with different props is fine as long as we stay within the limitations of the motor, ESC and battery. Now take that same motor with a 12X6 prop and stop it with your arm. I don't think you will, or even want to try, but for sake of argument let us say that you did. Now your motor is turning "O" rpm and trying it's best to go to 8,000 rpm. Needless to say, the current draw is going to be very high and the ESC will NOT like you. More than likely it burn up and let the smoke out. In the process of burning up, it shorts out the battery and now you have a battery that is trying to put out max amps. The first thing you will notice is the smoke coming from the battery followed closely by the flames coming out of the battery. I saw this happen once, although he did not hit his arm, he hit the ground and stopped the motor. Very shortly the smoke started coming out of the front of the plane and then the flames. Burned up the nose of his plane and took out the motor, ESC, and the battery. Over $200.00 damage because his plane flipped over on it's back on landing and he didn't go to low throttle. He was an old glow guy and figured the motor stopped, so there was no need to retard the throttle. Guess again.

Working on a Plane with the prop on it

There are times that we do need to put a prop on our planes during setup in our shop and there are some precautions that need to be taken. The first things that needs to be done is make sure you shop area is clean and free of anything that can be sucked into the prop or blown around the shop by the prop. You now have a good reason to clean your shop up and put everything back where it belongs. Anything that is close to the prop can either be sucked into it or blown around by it. Some pieces can become flying objects that can damage other things besides you. Small nuts and bolts can be thrown quite a distance and damage your prop and anything it may hit, including you and other people or property. I don't mean to sound sadistic with this, but it can and has happened. Most of the time nothing bad happens, just a bit of a scare, but it only takes once to hurt someone else and it can follow you for the rest of your life.

Motors coming to life on their own can make for some interesting fun and games. That is until you find out that you now have a wing to repair and a dent in the wall of your shop. I have seen it happen. We still don't know why the motor came on, but it was on 72MHz and all we can think of is something from outside hit us. His wife was not very happy with the dent in it wall either. Planes are FAST in the shop and can cover a surprising distance faster than you would think they would. Make sure the plane is tied down good or have a friend hold it so it can't move while you are making any checks you need to make. The best place for this kind of work is outside where you can put a stake in the ground and tie the plane to it so it is not going anywhere. Try your best to pick an area that is free from sand and small stones. They can very easily be picked up by the prop and thrown with quite a lot of force. Never stand in the plane of rotation of the prop or allow anyone else to stand there. A thrown blade is about the worst thing you want to get hit by.

I use a metal tent stake to hold mine and it works great. I tie a soft rope around the tail and then make my run ups. That way, I know the plane is not going anywhere. This may sound extreme, but how may times have you started a .60 powered plane in your shop? Well I treat my electric planes the same way. Most of mine are 400W up to 1000W and I don't want to take a chance of them going somewhere I don't want them going. On smaller motors (50W or 150W or so) you can very easily hold them in your hand. Also, building gliders with motors on them are not able to be tied down like a regular plane. In that case, you can hold it if it is a small glider or build a stand for a larger glider to hold it for you. Just be very careful and use your best judgment. These things are meant for fun, lets keep them that way. It's hard to hold a plane, watt meter and work the transmitter using only two hands. There are better ways to do it. Please do it safely.


Using an ESC that is to small

I am sure that this has been covered in another section, but I would like to go over it again from a safety aspect. You all know, or should know that an ESC that is too small for the intended use is going to cause problems. Here is why. The motor is driven by a square wave put out by the ESC. The duration of the square wave determines how fast the motor runs. For instance, if the square wave is at half duty cycle the motor will run at half throttle. That means that the square wave is on half the time and off half the time. Now don't call me and tell me I am wrong, I am rounding things off so it is easy to understand, not going through the math and getting into the full depth of it. If the square wave is running at 25% duty cycle, the motor will run around 1/4 throttle and so on. Now, if you are using a motor that draws 30 amps and you only have an ESC that will take 25 amps you figure you can run this motor at 3/4 throttle or less and stay in the current range of the ESC and everything will be fine, right?? Not really. The square wave is ALWAYS running at full power and if the motor is pulling 30 amps at 10 volts it will pull 30 amps any time the square wave is on. Even though the watt meter says you are running the motor at 20 amps, you are really running it at 30 amps. Here's why. Without getting into the math, the watt meter is seeing 30 amps while the ESC is on, but during the off cycle it sees "0" amps, so it averages the reading and comes up with a lower number. Even though there are 30 amps at the time the ESC is on, it cannot read anything but "0" while it is off, so you cannot get a true reading of what is going through the ESC when it is on. The only time a watt meter will read the true 30 amps is when we are at full power and that is over the rating for the ESC. Now then, while the watt meter is reading a lower watt reading, the ESC is seeing the full 30 amps while it is on, so you are driving the ESC over it's rated power handling capacity. Doing this will lead to one thing, a burned out ESC. If this is the only thing that happens and you happen to be in a position to glide in for a landing you are lucky. There is a very good chance that when the ESC burns out you may loose the power to the radio, so now you have no control over the plane. Now what are you going to do?? Watch your airplane fly into the windshield of a parked car?

For one thing, a LiPo cell cannot take a hard impact without getting damaged. If this impact happens to start a fire and you are in some farmer's field of wheat and it catches on fire, how are you going to put it out?? Say you do get it put out and nothing more than a few square yards of wheat are burned, do you think he is going to be happy? What if you can't get it put out at all and you have to call the fire department. The wheat field mostly burns up and the local farmer decides your going to pay for his wheat. Do you expect the AMA to pay for the farmer's field? Were you flying your plane in accordance with the AMA guidelines at the time of the crash? (AMA Safety code step 3) Where established, I will abide by the safety rules for the flying site I use, and I will not willfully and deliberately fly my models in a careless, reckless and/or dangerous manner.) Flying a plane with an ESC rated smaller than what is needed is being reckless to me. You can check with the AMA on this one, but I would never take the chance.

LiPo Safety

Probably the most important part and the most neglected is the care and feeding of LiPo batteries. Most people that I talk to do not REALLY understand the LiPo battery as good as they should. First of all, you will need to buy a changer that is made JUST for LiPos, or one that can handle LiPos in addition to the other batteries you intend to charge. Never use a NiCad charger to charge a LiPo battery, with one exception that I will cover later. NiCad and NiMh batteries are no where near as volatile as a LiPo battery. First of all, you never charge a LiPo on a combustible surface. Use SOMETHING that is fire PROOF to set the battery on while charging. Using a LiPo charging bag or putting it on cement or something of the sort is the best thing you can do. NEVER leave a LiPo alone while it is on charge unless the area you are using to charge on is of no consequence if it burns up, including your house. If you value your house, do NOT leave it alone until it is off the charger and properly stored. There is more than one house that has burned down because of charging a LiPo battery and that includes cars too. I have gone to large events for electric airplanes and saw many people put their LiPo on charge using their car battery and walk away while it is charging.

If a LiPo battery or the charger has a problem it can vent with flames. That does not mean it will, I said it can. If a LiPo battery is punctured it can vent with flames. That means that those little screws holding your motor on and sticking into the battery compartment can puncture a battery in a crash if they are long enough to stick into the battery compartment. If you don't have something to stop a screw from puncturing a battery in a crash, it may vent.

One particular battery charger that can charge different kinds of batteries has an auto setting for LiPo batteries has been known to reset themselves for some strange reason and cause a battery to vent because it decided it was a 4 cell battery on the reset instead of a 3 cell battery. This battery charger counts the cells of the battery after you hook it up and sets the charge rate according to this count. By putting a battery that is partly charged on can make it get a wrong reading and it thinks it is 4 cells instead of 3. This is an accident waiting to happen. This particular battery charger has had it software changed to stop this from happening, but I still would not trust ANY battery charger and leave it along while it is charging.

Never over charge a LiPo battery for any reason. If you need more power, get a bigger battery. Each cell of a LiPo should charge to 4.2 Volts when fully charged. The best way to make sure it does this is to buy a battery charger that balances a battery while charging and has a readout for each cell. FMA has a very good battery charger that I use that can charge 2 to 4 cells and I use it most of the time, but that is by no means the only good battery charger on the market. Just make sure that the battery charger that you buy can handle LiPo batteries and it's nice to have one that will charge any kind of battery.

The second best thing is a battery balancer. They are fairly cheap and will balance a battery by discharging the high cells down to the low cells. Some of these can be used while charging your pack so when it finishes charging it is balanced. At least buy something that will balance you battery. If you never balance you cells, sooner or later you will wind up with one cell that is lower than the other 2 and guess what happens. You over charge the other cells trying to bring the pack up to the voltage that it is supposed to read. If you are lucky, you just puff a cell or two..

If a cell becomes puffed up, it's time to replace it. Throw the old one away and get a new one. A puffed cell is a bad cell and is just waiting to cause you problems. The best thing you can do is just get rid of it and buy a new one.

Some people will tell you that you can discharge a cell to less than 3 volts. DON"T DO IT. Never discharge a pack below 3 volts per cell and really this is to low. For the best battery life, I would stay above 3.2 volts and some people stay higher. Also, that is under load, not resting voltage. If you are getting this far down on your battery before it is discharged, you need a higher capacity rating on your battery. As you get near this voltage, the battery is almost discharged anyway and any further use will discharge it rather fast. There is not really much left in a battery when it gets this low.

Make sure the battery is tied down in the plane so it can't move around. Stuffing foam around the battery is not a good idea. I use Velcro tape to hold mine in place with a strip on the bottom of the battery and a strip on the bottom of the battery compartment. That keeps the battery from sliding around and at least changing the CG. Then I tie it down using Velcro tape using 1 or 2 strips depending on how big the battery is. Air needs to circulate around the battery while in use to help keep it cool. If you are pulling a lot of amps out of the battery, it will get warm and it's nice to have air flow to help it cool off. Foam insulates it and helps it retain heat and stops the air circulation. That is at best not good for the life of the battery and at worse, can cause problems with heat buildup in the battery to the point of problems.

Crashing your plane is a good time to take the battery out and take a VERY good look at it. If it shows any signs of being damaged, it is best to just get rid of it. I have heard of people putting their plans in a car after the crash with the battery still in the plane and it started a fire after a few minuets. I have also heard of people flying their batteries after a crash and never having problems with it even though there was obvious damage to it. I leave that decision up to you, but I will NOT take a chance of my car burning up from a damaged battery. The battery is cheaper to replace than a car is. It is best to let it sit on the ground for awhile after a crash even if there is no damage showing just to make sure. I carry my batteries in an ammo can while in my car to make sure nothing happens to cause a fire in the car I cannot control.

I also make sure the leads do not have any way to short out while in storage. Never short a battery of any kind. That is a fast way to burn up the wires attached to the output and once the insulation burns off, the wires may and probably will short out good. The only thing to do then is get rid of the battery as fast as you can. Never puncture a LiPo battery or any other kind for that matter, but a LiPo battery will more than likely vent with fire. The metal inside the battery burns very nicely and will put out a nice big flame. Yes some types of metal will burn. Ever see a rocket booster? Gurss what's inside that booster.

To dispose of a battery that is no good, discharge it to "0" volts. The best way to do this is to use your battery charger to discharge the battery as low as you can get it. Then put a light load on it to discharge it the rest of the way. Make sure it is at "0" volts and then twist the wires together and put it some place for a couple of days just to make sure nothing happens, then throw it away. Some people say puncture the battery and put it in water for 24 hours and others don't. I'll leave that up to you to decide. Don't just throw a charged or partly charged battery in the garbage can. It can very easily cause a fire.
For the new people in this hobby, I would very strongly advise you to read ALL of this information on LiPo Batteries and if you are new to batteries, read everything. They have some very good information on the different batteries.
http://www.fmadirect.com/tech_data/index.htm


This is the one time that you can try and charge a LiPo battery using a NiCad charger. On thing I will tell you right now. You are on your own and don't come blame me if it starts a fire. I bought a new battery and used it one time. When I went to put it on the charger, the charger refused to charge it because the voltage was to low. I looked at it with a volt meter and 2 cells read 3.1 volts and one cell read 2.8 volts. My charger refused to have anything to do with this battery, so I set it to NiMh and adjusted the current to 100ma and put it on charge. This was the lowest setting on my charger. I did this in my shop with a cement floor and the battery and charger sitting on the floor. There was no way for anything to catch on fire if the battery decided to vent. I charged it until I got the battery up to 3.2 volts on the weak cell and then put it on LiPo and charged it the normal way using a balancer along with my charger. It charged all the way up and when it finished the weak cell read 4.2 volts. The next morning the cell read 4.0 volts while the other two read 4.2 volts and 4.19 volts. I talked to the people I bought it from and was told to run it until I got to about half voltage. I checked the cells and they read 3.65, 3.21, and 3.66. The battery was replaced under warranty. If you try and repair a battery using this method, take everything outside and charge it there. That way there is no way to burn down your house if something happens.

I tell you this because some ESC’s do not have the right low voltage cutoff or you set it wrong. This may work to get your battery back up and running again. Some chargers have what they call a repair charge and it will charge a low battery using this method and bring the battery back up to charge. The best way to use a battery is to discharge it to 80% and then recharge it. That means if your battery is a 2200mAH battery, don't use more than 1750mAH out of it. Some people use voltage to determine the lowest voltage they will go. I use the mAH reading when I charge it. I find this by flying the plane for awhile and checking the battery to see what the charge is that I put back in. If I can fly longer than that, then I limit my time to that and recharge my batteries. That means you must be aware of how long you have been flying. I use the timer on my transmitter for that. If I am flying a powered glider, then I know how many climbs I can make before I have to stop flying and that is always less than 80% of the battery charge. As long as you take care of your batteries, they will last a long time. If you abuse them, then you can expect a short life. Sometimes as short as one flight.

I have seen some ESC's that set the cutoff voltage to 67% of the voltage. That's around 2.8 volts on a full battery, but if it's not at full charge, it doesn't know that and will adjust the cutoff to 67% of THAT voltage. That is why I never trust an ESC cutoff voltage and why I use the 80% of capacity instead.



Storage of LiPo batteries

.
Some chargers have a storage charge section. What this does is charge your battery half way. This is the same condition you should have received your battery in. If you are going to be storing your batteries over the winter then you will need to put a storage charge on them. If it's just for a week or two, I would not worry about it, just leave them charged. If you are not able to do a storage charge on your charger, then just run it on the model until it goes to about 3.5V per cell. Balance the cells and put them away. If it is only going to be for a week or two, don't worry about it, put them up with a full charge on them and don't top them off before you go fly. They don't need it for short term storage.

Put it in a refrigerator to keep it cool. NEVER freeze a battery. If you don't have a refrigerator, just find a nice cool place to store them and wrap them with something to make sure the leads don't short out. For storage over the winter, this is the way you should put your batteries up.


That's about it for now. I'm sure there are other things that I didn't cover, but this hits the main points and should give you an idea of how to take care of your batteries and the rest of the electronics in your plane. Take care and enjoy the hobby. It's a great hobby and if a little care is taken, can be just as safe as any other activity.

Ed
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Old 05-30-2009, 06:04 PM   #116
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Originally Posted by slipstick View Post
Of course you could just as easily use the two 2500mAh packs in parallel to produce the 3S 5000mAh pack. And then you'd still have two packs for smaller planes if you needed them. And if you're going to use packs together which have had varying usage (i.e. used in other models not just the large one) it's a lot safer using them in parallel rather than series.

There are good reasons to prefer higher voltages for high power but that really isn't one of them .

Steve
I would disagree to some extent on the packs never being used for anything else. I have two 2S packs that I, on occasion, put together as a 4S pack and never had a problem doing this. I try and make sure that they both get about the same use so that they are at least close in balance, but no where near perfect. Don't get me wrong, I don't use one pack that has 300 cycles and another that has 50 cycles on it. What I mean is. I bought both of these packs at the same time and about 15% of the time I plug them together into a 4S pack. The rest of the time I use them as 2S and go back and forth between packs so they get about the same usage. So far, everything is working out fine and both packs take very close to the same charge and work great as a 4S pack also. I would never use two unknown packs for this type of connection, but I also don't see a problem using them alone or together. They are both 2S 2500mah 20C packs and I don't think there is a problem using them in other applications as well. Right now I have 49 cycles on one battery and 50 on the other and yes I do log these batteries just to make sure they can be used together as a 4S when I want to. I don't log all of mine, just these and until I see a noticeable difference in them, I'll continue to use them as a 4S pack.

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Old 07-21-2009, 08:57 PM   #117
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This is a great aid to newcomers like me, Thank You
Now for some questions that may have been answered already but I havnt come to yet.
Which way does the prop go on?
What determines interchangability on motors, ESC, Recievers and servos? Mfg? Size? Capability limits? How much of this stuff has to match as far as brand names go?
Thanks
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Old 07-21-2009, 09:05 PM   #118
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Originally Posted by Stryker 1 View Post
This is a great aid to newcomers like me, Thank You
Now for some questions that may have been answered already but I havnt come to yet.
Which way does the prop go on?
What determines interchangability on motors, ESC, Recievers and servos? Mfg? Size? Capability limits? How much of this stuff has to match as far as brand names go?
Thanks
Label/size markings on the prop typically face forward.

Servos, ESC and motors are pretty interchaneable with the exception that brushed motors need brushed ESC and Brushless motors need brushless ESC. Chapter 33 ( TOC is in the first post ) is about receivers.

Most servos and receivers can be interchanged as far as plugs go, but some use unique plugs so you do have to check. But the "universal" plug is used my most makers.

Read the chapter on receivers as there are some specifics to brand.

72 MHz PPM - also called FM - is not brand specific but there are shift issues you must know about - read the article on receivers.

72 MHz PCM (which is also FM) is brand specific

2.4 GHz is brand specific except that JR and Spektrum equipment can be interchanged as they use the same standard.

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Old 07-22-2009, 12:38 AM   #119
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I am still taking all of this in. Still thinking that I went wrong , after 20 of not flying. Was talked out of going E-flight. And kept the nitro stuff. Now have to work around the expense of changing over.
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Old 07-22-2009, 12:57 AM   #120
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Why get rid of everything you have now just to change over to electric. There is nothing wrong with flying both. I still fly glow and love it. In fact I just finished one plane and am working on another one. I love glow and electric. They are just two different ways to fly, but that doesn't mean you HAVE to give one up for the other.

Ed
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Old 07-22-2009, 01:18 AM   #121
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Default Still trying to get set up on elec. flight

Hello gang. This is a great group of flying floks.
Trying to get my head on stright as what is the correct elect. stuff to get started with.
Was at Topeka < Ks. flying field over the weekend. Lot of nice e-flight .
What about multiplex [easy star].
What about the Berg-4 receiver
What about the Rim fire motor

What kind of charger do I need to start with

What about batteries?? Just do not know what kind , size, etc. to go with for a starter.
What about the fire hazord with all batteries

I understand that there is a lot of stuff made in China. Some good. Some not so good?

As you can see, I need to still do a lot more reading. I have been flying nitro for 35 years. Hung everything up. For 20 plus years. Now back to flying nitro. Sure wish I would have started over with e-flight stuff.
Thanks. everyone.
Sarg 5 from Kansas
SEEING THE COUNTRY WE DEFEND.
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Old 07-22-2009, 01:41 AM   #122
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You have your own filed on your farm, do ya??? What's it like??
Sorry, I couldn't pass it up.
Sounds like you have a million questions just like every other new guy.
About the best thing I can tell you is, start doing a bunch of reading. As for the Chinese electric stuff, a lot of it is good and I can give you brand names if you like, but some of it is junk too and I can give you a few names to stay away from. It just depends on the size of the electric you want to fly as to the motors and such that we can recommend. Let us know the area you are interested in and maybe we can help point you in the right direction.

Ed
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Old 07-22-2009, 06:52 AM   #123
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I also would like info on good/bad chinese stuff, any help here will save a lot of grief later as it seems chinese is a way of life now. I am interested in mostly parkflyers at this time. Thanks
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Old 07-22-2009, 01:51 PM   #124
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What I am looking for guys and gals
Give me the product names of the Junk China stuff
The good China Brand Names
Stuff to stay away from.
I STILL NEED TO GET THE STRIGHT INFORMATION ON THE BATTERY FIRE DANGER. I HAVE BEEN TOLD THAT THE [NICKEL-METAL HYDRIDE BATTERIES are about as safe as one can get. WHY??!!
Leaving for the lake to fish for about 10 days. See everyone later.
ONE MORE
Yes, I did build my own flying field. I live 10 miles out in the country on family farm. The Russell RC club kept loosing their flying field.
I went out into my pasture, found a nice flat space next to a good country road. Took the big brush hog, mowed down a 200 yeard / 200 yard area to see what was below the high pasture grass. Found only a small number of pot holes, or we call them OLD BUFFALO WOLLS. Filled them in with fresh dirt. seeded. Still work in progress. Put up a wind sock. Build a new gate 30 feet off of the roadway. rounded up a couple of large wood wire spools. Building a couple of run up tables, that I saw at the Topeka RC park.
BEST OF ALL. THERE IS NOT A HOUSE WITHIN ONE MILE OF THE FIELD. I OWN MOST ALL OF THE LAND BETWEEN THE FIELD AND HOUSE. The flyers tell me that this is the best spot they have seen. GREAT OPEN AIR VIEW . Do have a power line on the north end. But the touch down area is some 150 yeards from the wires and there is also a somewhat high hill beyound that. Which gives you a great view of your aircraft. No problem, even for me.
I AM STILL LEARING [ALL OVER AGAIN].
Take care. The fish are calling.
later
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Old 07-22-2009, 03:30 PM   #125
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This is an E-BOOK titled EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC FLIGHT.

THIS IS A KNOWLEDGE DISCUSSION, NOT A DISCUSSION ABOUT SPECIFIC PRODUCTS OR SPECIFIC COUNTRIES OF ORIGIN. PLEASE TAKE ANY DISCUSSION ABOUT CHINESE PRODUCTS SOMEWHERE ELSE.

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