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Old Nov 18, 2012, 12:46 PM
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Bad Batteries??

I have a S.E.5a Slow Flyer. I am using the recommended motor and batteries. It is 2 or 3 years old. The motor runs with a pulsing sound with either of two batteries. I am sure this is responsible for somewhat sluggish behavior. I don't recall if it was this way, initially, but I think not.

I have tried recharging several times, but it doesn't help. None of my other planes/batteries behave this way.

Is this a battery problem?
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Old Nov 18, 2012, 01:38 PM
PGR
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United States, CA, Costa Mesa
Joined Jun 2004
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The pulsing you described sounds like a "soft" low voltage cutoff (LVC). If so, that would mean that your battery voltage is sagging too much (a symptom of weak battery packs) or the LVC is incorrectly set for the battery packs you are using.

Pete
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Old Nov 18, 2012, 01:55 PM
Wake up, feel pulse, be happy!
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Joined Aug 2009
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Are the batteries as old as the plane? If so, it's probably time to get new ones... Especially if they've been stored for extended periods of time above storage voltage.
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Old Nov 18, 2012, 01:58 PM
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Swap the batteries with planes that do not pulsate.

Simple enough to test ?
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Old Nov 21, 2012, 07:09 AM
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Thanks for the response.

I put the battery from my EP Falcon into the SE5 and it pulsed in the same way. Then I put all the batteries in the Falcon and they sort of pulsed. I built the Falcon last winter and got the battery about the same time. All are 2 cell. The 3 cell batteries I have been using for a few years in my Magpie have never behaved this way. Maybe this is a characteristic of the smaller 2 cell batteries?

Batteries are supposed to be stored “for long periods” in the storage mode, but “for long periods” is not defined. Weeks? Months? I am probably guilty of not using the “storage” mode.

Maybe my previous post “Cold Weather??? http://www.rcgroups.com/forums/showthread.php?t=1766032 is not all about temperature, because the 3 cell Magpie seems to do fine in the cold.

The flying season is about over here in central New York State, so if it’s new batteries I need I’ll wait until Spring to get them, because the Falcon battery seems to be shot in less than a year.

Do the small LiPo’s wear out in a year or so?
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Old Nov 21, 2012, 07:32 AM
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I am with PGR on your ...........LVC starting to just cut off.
ESCs DO NOT really like 2 cells...........LVC setpoints can be touchy at 2 cells Try a different brand of .......2 cell RATED esc.

Post that question in the ESC electrical sections

Can you reprogram the LVC points in your E$SC ?
My little 6 & 10 amp ones have several LVC cutoff points. Not cheap tho.
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Old Nov 21, 2012, 07:46 AM
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My Feigao 2 cell 6amp & 10 amp ARE TRUE 2 cell ESCs.

LVC is 2.6.......... 2.85.............. 3.1 volts.
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Old Nov 21, 2012, 04:10 PM
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My Electrifly ESC says cutoff occurs at .67v. If you assume the charge was 4.2 volts, that makes .67x4.2=2.8v. According to Wickipedia anything below 3.0 is supposed to damage the cell.

I guess the only way to really know is to monitor the voltage while the motor is running, but I doubt that voltmeters could follow the pulses.

I just went out with the 3 cell batteries and they flew great. Guess I'll wait til spring to get some new 2 cells. I don't know how long the local hobby shop had them on the shelf, so I'll get the new ones online.
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Old Nov 22, 2012, 06:29 PM
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Does the ESC recognize the battery as a 2 cell?

Does it beep twice, or 3 times?
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Old Nov 23, 2012, 04:46 AM
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Yes, time for new batteries.
Storing batteries fully charged shortens their life but over discharging is probably the worst thing. Use a timer with flight time adjusted by trial and error so that when you measure voltage shortly after a flight you have about 3.7v per cell minimum. Try to avoid ever running all the way down to LVC.

Steve
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Old Nov 25, 2012, 03:54 PM
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ESC beeps twice. There is no cutoff adjustment, but I never fly that long, because the planes donít have enough power to fly long before that.

Although the 3 cell batteries still give good, everyday performance, I realize that all my batteries are getting a little tired. I decided to take a close look and hook up the USB to the charger and computer. The attached pictures tell the story. Storage voltage and current 1 refer to the 3 cell and Storage voltage and current 2 refer to the 2 cell. I donít have any new batteries for comparison (Iím waiting Ďtil Spring).

First, note that the voltage curves should remain flat until nearly discharged. Not so here.

In the case of the 3 cell, note that the voltage drops from 12.6 to 12.34 volts immediately upon application of the 0.4 amp discharge current. A little oversimplification of the equations says that R=(12.6-12.34)/0.4=0.26 ohms. The most current you could pull, instantaneously, without hitting the cutoff voltage is I=(12.6-11.4)/0.26=4.6 amps. This is enough to keep the larger plane happy, although not enough for full power activity.

The two cell battery is a different story. The voltage drops from 8.4 to 8.23 immediately with the 0.4 amp storage current. In this case R=(8.4-8.23)/0.4=0.425 ohms. The most current you could pull without hitting the cutoff voltage in this case is I=(8.4-7.6)=1.88 amps. Iím sure this is why the little motors are pulsing.

The motors are not purely resistive and the battery voltages are not constant with time, so a more thorough graphical analysis would have to be done to get the complete story. Also, the resistance of the battery leads enter into the picture, although I wouldnít expect it to be that much at these low currents. This is all an approximation, but it does show that the battery voltages donít remain flat, and full battery voltage is not available to the motor, initially. The milliamp-hours are way low.
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