E-Power 201

Discussion in 'General Plane Discussion' started by TManiaci, Sep 9, 2008.

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  1. Sep 9, 2008 #1

    TManiaci

    TManiaci

    TManiaci

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    Okay, for the graduates of E-Power 101, I thought we could advance on to the next level. :p

    I have to confess, I am no expert of advanced E-Power systems or issues. So, I will gather some intellegence and ask that others contribute and bring topics to discuss.

    The last segment of E-Power 101 covered the use of the Wattmeter to test Amp loads and select the right propeller to get the most out of your power system. There are some other very handy uses for the Wattmeter that you might not be aware of... Let's take a quick look at that.
     
  2. Sep 9, 2008 #2

    TManiaci

    TManiaci

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    In our previous discussion, we showed how the Wattmeter is used in-line with our power source to monitor Wattage, Amperage, Voltage and accumulating Amp-Hours of energy. These measurements are taken when the aircraft is in a ready to fly static state, and the feedback we gather allows us to make intellegent decisions about equipment selection.

    Wattmeter Wiring Load.jpg
     
    Last edited: Sep 9, 2008
  3. Sep 9, 2008 #3

    TManiaci

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    But that's not all it's good for... check it!

    If you want to verify your charging, place the Wattmeter between your Battery and Charger to see all the important data for that process too. Amperage, Voltage and Amp-Hours are really nice to see, partcularly if you have a Charger without a data display.

    Wattmeter Wiring Charge.jpg

    But HEY... think about using this on all your other batteries too.
     
    Last edited: Sep 9, 2008
  4. Sep 9, 2008 #4

    TManiaci

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    Now most of you have chargers, and most of those chargers do Discharge. What is Discharge? It's a Controlled load to test your battery capacity. Do you use it? I bet not. Why? Because you're a lazy ass! :boxing:

    Seriously.... batteries decay and lose the ability to perform over time and due to cycling, storage and exposure to extreme temperatures. We always "trust" our batteries.... don't we?

    So, you should probably consider checking your battery capacity once in a while. It might save a treasured aircraft. The Wattmeter can help if you don't have a fancy charger with a data display.

    Wattmeter Wiring Discharge.jpg

    Notice that the Wattmeter has a second power source attached. This provides power for the Wattmeter when the Test Battery that is attached drops below a certain threshold (around 3V). The connection is a conventional Servo Lead style like in your Rx. Just grab an old 4AA 4.8V battery pack from your nitro plane crap and plug that in there, you're good to go.
     
  5. Sep 9, 2008 #5

    TManiaci

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    Now here is one of the coolest uses for the Wattmeter. This applies to any aircraft, not just E-Powerd toys.

    We always worry about Servo Loads, and how much power our flight systems draw. Guess what? You can measure all that with the Wattmeter!

    I like to use the Wattmeter to set up my max throws in 3D rates. If you connect the Wattmeter between your Battery and Rx, or Battery and ESC for an Electric, you can SEE the Amp draw of your Servos.

    Wattmeter Wiring Servo.jpg

    As you move each surface, you can see the load increase. When you have a servo that is binding with resistance, the current draw goes up rapidly. When you hit a hard stop where control surfaces are hitting throw limits, you can see it clearly! If you use the Wattmeter to set up your throws, you will avoid undue overload from straining servos that are fighting hard stops.

    This is all very important stuff. Generally speaking, a failure in a flight system is probably most often brought on by some stressful condition. This is one that you can eliminate if you take a little time and tune-out the high-draw conditions in your setup.

    Also, when you are matching Servos where you have multiple servos and a common surface, this method can show you how well you are matching, and allow you to better tune the match.

    Knowledge is POWER...
     
  6. Sep 9, 2008 #6

    TManiaci

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    I see you out there Sandman. Care to discuss your experience with Flight Data Recording on E-Birds?
     
  7. Sep 9, 2008 #7

    sandman

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    Now it's getting interesting. Static testing with a Wattmeter is a good first step. To really find out how much power you are using in flight, particularly at various stages in the flight a datalogger becomes a very useful tool. Now you can see amps, volts, prop rpms and even battery or motor temp measured 8 times a second. This really lets you see the differences between props, batteries, motors, and ESCs. You will know at the end of the flight how many Amp-hrs of battery you consumed and which parts of the flight used the most power. If you fly a set pattern like IMAC patterns, you can associate the power with a particular maneuver - how much to climb on a vertical line, how much in level flight, etc. And you can fine tune those pesky ESC settings like advance, PWM frequency to optimize power and/or efficiency.

    Using an Eagle Tree logger, I was able to optimize this setup:

    Extreme Flight 74 inch Yak-54 - about 11 lbs auw
    Neu 1515/3D motor with 6.7:1 gearbox
    Mejzlik 20x12 E prop
    Castle HV-85 esc
    EvoLite 5350 or 4350 10S-1P battery
    Peak Power 70 amps at 38 volts - 2660 Watts
    Capacity used for an 8 minute flight with two IMAC Sportsman sequences - 3400 +/- 200 mA-hr.

    From this, I know I can practice with the 5350 mA packs and have capacity for a couple of retries at less than perfect maneuvers - but compete with the 4350 packs to save 10 ounces of weight.
     
  8. Sep 9, 2008 #8

    sandman

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    Another handy trick for determining the quality of your motor is to run it as a generator. I have a small milling machine so I moake a simple fixture to hold the motor and turn the shaft with the spindle at say 1500 rpm. Next, measure the voltage across each of the three possible combinations of wire pairs. A prefect motor would show exactly the same voltage on any pair of wires. Remeber that the back EMF of the motor is used to help the ESC set the advance and power to the motor. If the three phases are not well matched, then the ESC will not bea ble to respond as precisely of predictably as we would like.

    Of the motors I have tested this way, Neu motors are the best by a significant margin with matching of 0.1 to 0.2% between phases, followed by Axi and Hacker tied for second at 1 to 2% matching, Hyperion a bit further down and DualSky at 7% error that is so bad that I would never put one in a plane.
     
  9. Sep 9, 2008 #9

    sandman

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    When I get home I'll dig up some results from the logger and post them - very interesting results.
     
  10. Sep 9, 2008 #10

    TManiaci

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    Just so we're clear...

    When we test power on the bench, we are in Static conditions. That testing leaves us a margin of error, or cushion. When a plane is in the air, the loads on the power system are generally lower as the system "unloads" as the aircraft moves. There are probably only a few moments, even in radical 3D stunts, where we load the system as much as we do static with a fresh battery.
     
    Last edited: Sep 9, 2008
  11. Sep 9, 2008 #11

    TManiaci

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    Thanks Sandman!

    Do you have some static test data to establish a benchmark too... it would be very interesting to see the differences.
     
  12. Sep 9, 2008 #12

    TManiaci

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    Tech note... really good stuff Sandman!

    For those that want to know... "Back EMF", back Electro-Magnetic Flux or Force.

    Back electromotive force is a voltage that occurs in electric motors where there is relative motion between the armature of the motor and the external magnetic field. One practical application is to use this phenomenon to indirectly measure motor speed as well estimate position. A good ESC "reads" this feedback on the motor leads to adjust timing advance of the Output signals.
     
  13. Sep 9, 2008 #13

    Showtime

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    Tman you are the man.
     
  14. Sep 10, 2008 #14

    bdavison

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    I wish Align would hurry up and release a new E-meter. WE NEED THE E-METER!!!.

    That little thing was perhaps the best device ever made for electric pilots.

    There are tons of rumors floating around about the new e-meter.
    Digital servo programmer, tach, amp/watt/volt meter, data logging, ESC programmer, and other diagnostic tools.

    I sware whenever it comes out...Im rushing to the hobby shop to get one.
     
  15. Sep 10, 2008 #15

    TManiaci

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    I was checking out the Bantam e-Station tWo Meter. This one does all the stuff that the other Wattmeters does, and it includes a cool built-in cell-balancer system for up to 6-cell Lipos. I like that... and it's only $80.

    TWO balancing.jpg

    balance setup.jpg
     
  16. Sep 10, 2008 #16

    Mithrandir

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    So... who makes the gnarly charger for 10 and 12 S systems?
     
  17. Sep 10, 2008 #17

    TManiaci

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    Doomed,

    The only one I see talked about out there is the Schulze 636.

    Looks to me like most everyone is moving away from 12S packs, and using the far less expensive 6S in series setups for 12S motors.
     
  18. Sep 10, 2008 #18

    Showtime

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    he called you Doomed... HA Tearsim my eyes
     
  19. Sep 10, 2008 #19

    TManiaci

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    Which brings us to the topic of high voltage systems.... Why do we need Series Wire multiple 3S, 4S, 5S and 6S packs together to make these absurdly high voltages?

    Simple explanation... POWER.

    Remember that P = I x V.

    Now, look at I (current in amps), and consider the commonly available Lipoly Battery pack. Notice as you browse all the Lipo manufacturer websites that the largest ones are 8000 mAH. Also note that these fatty packs cost more than several tanks of gas in a big SUV.

    The large capacity cells get really expensive. Not only that, but they get really HEAVY too. So, if you look you'll find it's cheaper to buy a pair of 5S packs and wire them in series than it is to buy a special purpose (low volume) 10S pack. Do the math...

    Now consider the POWER part of the equation. Assume you have a 20C 8000mAH pack. At 3S the POWER potential is:

    11.1V x 8.0AH x 20C = 1776 Watts.

    Now, think about the Wattage needed to fly a big 40% wieghing in at maybe 42 lbs. We need at least 10 W/oz (160 W/lb) to fly 3D, and better 12+ W/oz (~200 W/lb) for nice performance. So, how much power do we need?

    P = 200 W/lb x 42 lbs = 8400 Watts!

    So, you can see that going big on the battery capacity becomes a limit, and to increase the POWER you have to increase the VOLTAGE, instead of the Current.

    That means you MUST Series wire batteries to get enough juice for high-power applications.

    Also note... look at the Outrunner Motors for big applications. They have really low kV ratings. They are designed for High Voltage systems, because they know that nobody is gonna make a 3S1P 40,000 mAH pack, LOL.

    Also, consider the Amperage you would need to manage if you were to use 3S or 4S at over 8,000 Watts, remember I = P / V:

    8,400W / 11.1V = 757 Amps on 3S Pack
    8,400W / 14.8V = 568 Amps on 4S Pack

    Amperage equates to weight, in wire gauge and in component size. Motors and ESC would have to be monsterous to manage current this big. Not practical for a light build on any aircraft.

    So, you can see that super-high output systems must run on high voltage to manage all the key factors: Weight, Cost, Efficiency and Power.
     
    Last edited: Nov 8, 2010
  20. Sep 10, 2008 #20

    bdavison

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    There's another reason to use multiple smaller packs vs one large one...
    If a cell bombs out in a large pack....your out LOTS of money.
    If a cell bombs out in a multi pack setup - just replace that one much smaller cheaper pack.
     

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