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Posted by Rhea | Oct 03, 2013 @ 06:46 PM | 2,497 Views
There is some confusion about what happens in the electrical world when things are connected in different ways. For instance most LiPo batteries I have seen and used are labeled as 2S or 3S or 4S etc. I think nearly everyone knows that tells us the number of cells in a battery and they are connected in a series configuration. 2P or 3P on the other hand mean the cells are configured in a parallel connection. I have seen some questions arise regarding voltage and current in these different configurations.

Two simple rules to remember when considering series or parallel connections:
1 Power sources in series; voltage adds and current remains constant.
2 Power sources in parallel; current adds and voltage remains constant.

I like analogies so letís look at this in another way. Using pennies to represent the voltage letís put a stack of 100 pennies in one pile. A penny weighs 2.5g. so letís say each penny is 2.5 volts. The area is ĺ of an inch and letís say thatís ĺ amp (750mA). This stack would be 250 volts at 750 mA.
Now letís put all those pennies in a single layer in a line. That would represent a power source of 2.5 volts at 75 amps. So we see rule number one is the stack (series) configuration and the single layer in a row is rule number 2 (parallel).

That was looking at voltage and current from the viewpoint of the battery providing power. When charging that battery the rules above are still in effect. I have seen many questions about charger settings when charging batteries in parallel. If you have two 2S, 1300 mA batteries you could charge them in a serial or a parallel as well as one at a time.
In series you would set the charger for 1.3A and 14.8V or 4S, 1P.
In parallel you would set the charger for 2.6A and 7.4V or 2S, 2P.
Posted by Rhea | Oct 03, 2013 @ 04:44 PM | 2,477 Views
I wrote something about how Watts will show up when you connect your battery to the motor in your plane. Now your battery is run down to its low limit. Hopefully, if it’s a LiPo it still has enough voltage to be recharged safely.

I started writing this blog because when I went to get some answers about LiPo batteries I found that so many people in the threads didn’t even have a clue what a volt is. So I am going to try to do a DC Electrical Theory 101 here. The purpose is not to explain LiPo batteries—I have seen that there are others who know more than I do about that. I also will not discuss chargers—that gets into way too much confusion. I will try to explain the cause and effect of charger settings to the battery being charged.

So, you have a new battery or you have one that has just powered your plane around the park for the last 5 or 10 minutes. It’s as good as a paper weight right now. Let’s make it a viable power source again. You have a charger that can safely do that and you have read and understand how to use it.

Here’s what has to be done to refill that spent battery. What has been used is the current so that’s what the charger will put back in. Of course the voltage is low as well because that’s the thing that got the current out of the battery. If this doesn’t make too much sense let’s look at it this way. You started with a full bag of potato chips, say 16 ounces. You eat half of the...Continue Reading
Posted by Rhea | Oct 03, 2013 @ 01:03 PM | 2,100 Views
Or should we ask who was Watt? Interestingly James Watt was an early developer of the steam engine but the unit of electrical power was named after him by the British Association aka British Science Association or BA long after his death.

So if a Watt is a unit of electrical power how do we get it and what is it in our model planes (or other electrically powered models)? It is the result of applying a voltage to a load and out comes power.

Like every other physical action we can write an equation to explain it. So the basic equation for electrical power is, P=EI.
P is the power or Watts.
E is the volts or Electromotive force.
I is the current or Amps (and there isnít any alphabetic alternate name for this like for the other two).

The E comes from the battery, of course and the I is the combination of motor and prop size. The voltage typically determined by a LiPo with a voltage somewhere between 3.8 and 4.2 volts per cell and wired in seriesóyes there are exceptionsówill give you the voltage.

The I can be determined, somewhat, by the data sheet or specs. for the motor and prop you are using. The wattage is also stated as a maximum value on the motor data sheets. That is because since a Watt is a unit of power and power is heat you need to know how much heat the motor can tolerate.

So, you see, you can use this information to determine the size of battery you would need for a particular size plane etc.
Here is a link to a calculator that can help you with motor, prop and battery combinations.
Posted by Rhea | May 09, 2013 @ 08:40 PM | 2,781 Views
I fly electric.

I retired at the beginning of 2008. It seemed like a good idea to get back to the hobby of my youth; flying model airplanes. I knew things had changed a little since 1960 because along the way I tried RC car racing in the 1970s and I had seen some of the earlier electrics for RC planes too.

So when I went to the Local Hobby Shop to inquire what I could get to power a small plane that was sitting, unfinished, in the closet I was amazed. The clerk pulled out something he called an “Outrunner” and a “LiPo”. “What!!” I exclaimed is this? It’s what we have now. Well that was 2008. In the few short years since then I went from the first motor, an E-flite Park 250, to my largest Power 46. I have four Power 46 size motors from four different manufacturers. I also have a smaller motor then the Park 250. I have a Park 180 also and of course the Micro Fliers like a Night Vapor a Champ and a Blade Scout.

Wow! This electric stuff is amazing! In the 1950s we dreamed of something like this and tried to make small planes but we didn’t have materials or the mechanical technology for small like there is now. And what about the radios!? That’s a whole other topic.

The reason I am writing this, however, is to put something here that could help someone understand electric theory behind all of this. I am a retired EE so it was easy for me to pick up the concept behind this electric power. During my career I either...Continue Reading