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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> RE: RX voltage display
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RE: RX voltage display - 10/28/2004 3:48:48 AM   
Hangtime



Posts: 346
Joined: 6/5/2002
From: Babylon, NY, USA
Status: offline 		Hi Mike..

Just a quick question... do you check your pack voltage with a DVM alone, or do you use a device that applies a load (250ma minimum) and then observe the voltage while it's loaded for 10 seconds?

The reason I ask as the 'load' part of checking the pack seems to be missing from your previous posts.. and we all know that unloaded pack voltage is pretty much useless information.

Cheers!

(in reply to Mike01)
       Post #: 76

RE: RX voltage display - 10/28/2004 4:04:19 AM   
BillS


 

Posts: 2994
Joined: 9/6/2004
From: Greensboro, NC, USA
Status: offline 		Oh my goodness a post that illustrates the issue under discussion.

quote:

I am flying a U-Can-Do-3D with 6 servos. My problem is I have a 600Mah rx battery and during the 3rd flight of the day, I get the throttle going to ldle while the stick is over half throttle. The airplane is still flyable with all the other controls, just throttle goes to idle. All the other controls work fine. I have to move the throttle to idle and back up to get power back. Then it happens again after a minute or two. Every flight beyond the second flight has been plagued with this problem this year. Last year everything was fine. I could fly many flights without problems.

The T6xas has a fail safe feature that reduces the throttle to idle if the voltage is below 3.8 volts. But, when I take the rx battery home and discharge to check remaining voltage, I receive 4.9 volts and 250 Mamps remaining. I can hook up all servos and move all rapidly while on a VOM and still get 4.8 - 4.9 volts continuously. Fully charged I get 5.6 volts.

Is it the fail safe feature activating prematurely? All connections are secure and I never get a glitch at the field. Will a 6 volt battery at 1200 Mah cure this? Any body else have this same problem? Should I send in the receiver for repair? Can I disable the fail safe feature?

Any response will be greatly appreciated.


quote:

... happens again after a minute or two ... Can I disable the fail safe feature?


Scary!

(in reply to Mike01)
       Post #: 77

RE: RX voltage display - 10/28/2004 4:40:34 AM   
Flying Geezer



Posts: 1009
Joined: 4/12/2003
From: Bowling Green, KY, USA
Status: offline
quote:

btw...I just wanted to clarify that I think BillS had a great idea in his original post on this topic...a voltmeter in the plane that sends telemetry to your radio. That would work...because you get to monitor the voltage under load and you see it steadily drop, thus getting a pretty good idea as to the state of the battery. Mike01



Mike, if you insist that battery voltage has no corelation to state of charge, whey monitor battery voltage in flight?

I'm confused with your position.

_____________________________

Flying Geezer
Hughes RC

(in reply to BillS)
       Post #: 78

RE: RX voltage display - 10/28/2004 5:12:25 AM   
Mike01


 

Posts: 643
Joined: 12/29/2003
From: Brooklyn, NY, USA
Status: offline 		Geezer,

Because monitoring voltage as a curve....seeing what it is at rest, then when you apply a load, and watching it change over time can indeed be used to approximate remaining capacity, if you know what to look for. Just measuring voltage when your plane lands, even under load, doesn't tell you squat. It's like the voltage display in your radio...when you first turn it on, it usually gives you a high number, regardless of state of charge...then over time, you watch voltage go down...if it goes down slowly, good, if it drops rapidly, bad....but the point is...you are watching it all the time.

Hangtime,

Short answer...I don't check voltage. As I said, I'm pretty good at knowing the state of charge. If I'm uncertain, I swap batteries and discharge to verify what I thought...whcih in turn teaches me to guess the state of charge all the better.

But remember that in my post where I asked BillS to tell me the capacity of my RX pack, I gave him two figures, one for voltage at rest, and one for voltage under load.

Voltage under load is fairly useless too, if it's a small load applied for a very small amount of time.

(in reply to Flying Geezer)
       Post #: 79

RE: RX voltage display - 10/28/2004 6:59:04 AM   
Hangtime



Posts: 346
Joined: 6/5/2002
From: Babylon, NY, USA
Status: offline
quote:

Voltage under load is fairly useless too, if it's a small load applied for a very small amount of time.


Whelp, allow me to respectfully beg to differ.. a loaded ESV is the best device we currently have to determine not how much capacity remains, but it does certainly answer the question "do I have enuff juice for another flight".. Tho I'm sure some folks use different variations on the theme, the routine I use is a 500ma load fer 10 full seconds and I observe voltage closely while the loads applied before every flight.. expecially the first one. If I'm in the least doubt about the state of charge, out comes the fast charger and I pay attention to what that thing does and then I check the pack again as outlined above before I start crankin the starter.

Works great fer me. Ain't lost a plane to a pack yet.

Cheers!

(in reply to Mike01)
       Post #: 80

RE: RX voltage display - 10/28/2004 7:41:40 AM   
Mike01


 

Posts: 643
Joined: 12/29/2003
From: Brooklyn, NY, USA
Status: offline 		Whelp?!? I would say something nasty, grandpa, but I'll pass in the name of civil behavior.

That aside...

I ran a 500ma load on my discharged RX pack for well over ten seconds, with the results being above 4.7 volts...remember, gramps, this was a fully discharged small capacity pack that had been resting a while. So why didn't you harp up and say "Aha! Whelp! That pack is dead! What trickery are you trying to pull on us?" Was it because you had no clue?

Now you may choose to not fly at 4.7 volts (that would have been a great choice with this particular pack), but what if it read 4.9 or 5.1? Would you fly then? I bet you if that pack had 50mah left in it, it would have given you numbers your would have been proud to lose your plane to.

You know, grandpa, I wish you were right. I wish I could tell something about a battery's capacity from voltage...it would save me a lot of time, with not having to discharge packs to see how much they had. If there's some magic trick to it that I'm missing, please share the benefit of your jurassic wisdom with a simple whelp who wasn't even alive when the war of Northern Aggression raged accross our land.

(in reply to Hangtime)
       Post #: 81

RE: RX voltage display - 10/28/2004 2:46:12 PM   
Red Scholefield



Posts: 4779
Joined: 12/8/2001
From: Newberry, FL, USA
Status: offline
quote:

ORIGINAL: Mike01

quote:

It's not perfect, but the corelation of loaded battery voltage, and remaing charge is NOT a myth. I don't care who says so.


Anyone care to play? I have a bunch of packs in various states of charge (mostly rx and tx packs...but we can play with GP3300s if you like as well) and I dare anyone to try to predict their capacity based on voltage.


I'll play. If it is a four cell pack and reads less than 4 volts the pack has zero charge left. It it reads over 5.8 volts it has 100 % of the charge left. I've taken the hard ones, I'll leave those that believe there is a corrolation between loaded voltage and remaining charge to guess how much charge is left for the range between 4.8 and 5.2. There is no substitute for knowing what your particular plane draws in the way of mAh/minute and using that as a guide to flight time allowable. Periodic capacity check is mandatory as you will find when you discover 50% of nothing is still nothing.

_____________________________

Red S.
AMA 951 Leader Member

(in reply to Mike01)
       Post #: 82

RE: RX voltage display - 10/28/2004 3:26:02 PM   
Hangtime



Posts: 346
Joined: 6/5/2002
From: Babylon, NY, USA
Status: offline
quote:

ORIGINAL: Mike01

Whelp?!? I would say something nasty, grandpa, but I'll pass in the name of civil behavior.

That aside...

I ran a 500ma load on my discharged RX pack for well over ten seconds, with the results being above 4.7 volts...remember, gramps, this was a fully discharged small capacity pack that had been resting a while. So why didn't you harp up and say "Aha! Whelp! That pack is dead! What trickery are you trying to pull on us?" Was it because you had no clue?

Now you may choose to not fly at 4.7 volts (that would have been a great choice with this particular pack), but what if it read 4.9 or 5.1? Would you fly then? I bet you if that pack had 50mah left in it, it would have given you numbers your would have been proud to lose your plane to.

You know, grandpa, I wish you were right. I wish I could tell something about a battery's capacity from voltage...it would save me a lot of time, with not having to discharge packs to see how much they had. If there's some magic trick to it that I'm missing, please share the benefit of your jurassic wisdom with a simple whelp who wasn't even alive when the war of Northern Aggression raged accross our land.


Never claimed you could tell capacity from voltage, Mike. I explained how to determine if there's enuff voltage to fly. There's no magic tricks, just homework. Now, since it's apparent I'm wasting my time coversing with a kid that seems more intent on gaining bad attention and making noise than learning anything, and as you have so kindly reminded me of my why I hate posting on these boards in the first place and of course, since as you point out I have little time left of to begin with..

*poof*

(in reply to Mike01)
       Post #: 83

RE: RX voltage display - 10/28/2004 3:29:52 PM   
Mike01


 

Posts: 643
Joined: 12/29/2003
From: Brooklyn, NY, USA
Status: offline 		Ok Red, let's play.

I have a NiCD transmitter pack, 8 cells. Sanyo 600mah.

Resting voltage...10.284

momentary 500ma load...9.843 volts

What can you tell from that?

(in reply to Hangtime)
       Post #: 84

RE: RX voltage display - 10/28/2004 3:33:40 PM   
Mike01


 

Posts: 643
Joined: 12/29/2003
From: Brooklyn, NY, USA
Status: offline
quote:

Never claimed you could tell capacity from voltage, Mike. I explained how to determine if there's enuff voltage to fly.


If that's true, what were we arguing about? I know there's a way to determine capacity...and voltage checking has little to do with it. If you agree...what are we doing here?

quote:

Now, since it's apparent I'm wasting my time coversing with a kid that seems more intent on gaining bad attention and making noise than learning anything, and as you have so kindly reminded me of my why I hate posting on these boards in the first place and of course, since as you point out I have little time left of to begin with..


So while it's perfectly fine for you to call me "whelp", if I snap back and call you grandpa, then I am a terrible person that is making the Internet a bad place? That reminds me of the old saying about driving on the highway, how everyone who is driving slower than you are is an a*shole, while everyone who is driving faster is a maniac. It's never you, is it, Hangtime?

(in reply to Mike01)
       Post #: 85

RE: RX voltage display - 10/28/2004 3:48:28 PM   
BillS


 

Posts: 2994
Joined: 9/6/2004
From: Greensboro, NC, USA
Status: offline 		A simpler first approach.

Maybe there is a simpler method that avoids down linking.

Transmitters have built in timers.
Transmitters have built in voltmeters.

If the RX voltage was checked under load with the built in transmitter volt meter all the information necessary could be available to calculate battery time. Airplane set up would include type of battery and capacity and resistance load used. Capacity would be either rated or measured. Measured capacity would be more accurate but many would not know the capacity.

The transmitter voltmeter would be used to measure RX voltage before the first flight of the day and between each flight. Enough information would then exist to roughly calculate the battery use profile and determine battery time remaining.

There are a number of ways for people to distort the accuracy of the calculations. With a disciplined approach the calculations could be quite accurate.

A first step.

Bill

(in reply to Red Scholefield)
       Post #: 86

RE: RX voltage display - 10/28/2004 3:54:58 PM   
Mike01


 

Posts: 643
Joined: 12/29/2003
From: Brooklyn, NY, USA
Status: offline 		Here's a much more interesting game to play...

600mah NiCD receiver pack, 4 cells.

Resting voltage: 5.447

Voltage under momentary 500ma load: holding steady above 5.2

Pretend I am a member of your club and I tell you "I just checked this pack's voltage...is it safe to fly?"

(in reply to Mike01)
       Post #: 87

RE: RX voltage display - 10/28/2004 4:45:03 PM   
BillS


 

Posts: 2994
Joined: 9/6/2004
From: Greensboro, NC, USA
Status: offline 		Couple of thoughts.
1. I believe you understand batteries.
2. Sucker questions with insufficient data are for the foolish.
3. Arguments are often counterproductive.
4. We should all be searching for solutions.
5. The battery is sort of small for the load applied or maybe weak and questionable.
6. Almost 100% of ‘Battery Reckless’ and 'battery clueless' would fly.
7. Flying might not be smart depending on the pack size, in flight loading, and total time on the pack since full charge.
8. An interest in games does not exist.
9. However an interest in solutions is important.

Don’t forget that the person checking the battery has an intuitive feel for the airplane, knows the number of servos, knows the flight pack capacity, and probably knows when it was last charged. He also has an intuitive feel for the flight time since recharge. The human mind is intuitively good at integral calculus even if the words have no meaning.

(in reply to Mike01)
       Post #: 88