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TX battery question - 5/27/2002 7:27:23 PM   
kevin mcgrath


 

Posts: 739
Joined: 1/24/2002
From: Sault Ste Marie, ON, CANADA
Status: offline 		Keeping in mind that Im an electronic nincompoop,would any of you educate me on the following please.
I have6 and 8 chnl Futaba puter radios.Both TXs use 9.6 volt 600mah batteries (I beleive).When I cycle these batteries (I have bridged the diodes on both) they each test out over 600 mah,using both Hobbico and Ace cyclers.However at full charge the 6 chnl shows about 10 volts max on its little screen,and the 8 chnl about 11.4.
Why the difference ,what is this telling me if anything,and is there anything to worry about?
I watched a friend totally destroy his Top flite Stinson,and its Saito radial (he came back from the crash scene with a handful of pistons,not cylinders,pistons!)on Saturday,due apparently to battery failure, and it got me to thinking!

Thanks.....


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Kevin
MAAC 6401L,CD.
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TX battery question - 5/27/2002 8:51:03 PM   
Jazzy



Posts: 1106
Joined: 1/8/2002
From: Erie, PA, USA
Status: offline 		Try switching the packs in the TXs. It may be that the 6 chnl radio's display is slightly off.
Wait a few days after full charge and then discharge the pack in question. If the capacity has decreased significantly, you've got a bad pack.

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Aww $#!^.... I left the )@#& transmitter at home!

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TX battery question - 5/27/2002 9:13:40 PM   
mglavin



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Joined: 11/29/2001
From: Elverta, CA, USA
Status: offline 		Kevin

You can safely fly your models down to and below 9.6 volts, If I recall the cutoff alarm on the 8U series sounds off at 7.6 volts.

The discrepancy with one TX voltage display is negligible. There are many considerations; voltage at completion of charge, battery age and condition, required MA to run the specific TX and the calibration of each TX's voltage display.

I would not let this effect my flying time. I would simply stop flying at 8.4 volts or use the a cut-off voltage of .95 per cell multiplied by eight which equals 7.6 volts and then recharge my TX battery, admittedly I find this voltage a little low. But the NiCad's will provide power down to this number safely. The question is will the lower voltage sustain a consistent full power RF signal.

You should consider this, a TX battery pack consists of eight 1.2 volt NiCad cells, this equals at best 9.6 volts. Typically the battery comes off the charger at a higher voltage reading, in your case 10 and 11.4 volts loaded with your TX's. NiCad's are well known for averaging and maintaining approximately 1.0 volts under sustained use. If you were able to view a graph showing the discharge capacity and voltage you'd find it very flat for a long time and then falling off near the rated capacity at depletion of the MAH rating.

< Message edited by mglavin -- May 28 2002 1:56AM >

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TX battery question - 5/28/2002 1:19:39 AM   
lynngordon


 

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Joined: 5/19/2002
From: Orlando, FL, USA
Status: offline 		Just a quick note: My Futaba 8U sounds the battery warning at 8.5 volts. The manual says anything below 8.5 volts will trigger the warning, but my warning goes off as soon as it hits 8.5 volts.

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TX battery question - 5/28/2002 6:55:18 AM   
mglavin



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From: Elverta, CA, USA
Status: offline 		Lynn

Your number of 8.5 volts makes sense to me. Sounds like Futaba has decided anything below 8.5 volts starts to impede TX power/ RF output... I stand corrected on my recollection of 7.6 volts...

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TX battery question - 5/28/2002 5:28:03 PM   
kevin mcgrath


 

Posts: 739
Joined: 1/24/2002
From: Sault Ste Marie, ON, CANADA
Status: offline 		Thanks to all who replied......you have furthered my education by responding in language even I could understand,and given me a few things to try.
For interest the manuals for both the 8U and 6X Futabas say the alarm goes off at 8.5 volts.I have never run a TX this low so I have never heard the alarm.I fly a lot in season,mostly every day,but I have the luxury of being about 10 min from our club field,so I often fly in the am,go home for lunch and mebbe a siesta and put the TXs on charge before going back in the evening for some magic summer dusk flying.......Aint life grand?


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Kevin
MAAC 6401L,CD.

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TX battery question - 5/28/2002 9:56:08 PM   
mglavin



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Joined: 11/29/2001
From: Elverta, CA, USA
Status: offline 		On a side note the actual available MAH capacity that is l available in the battery pack is a more accurate method of distinguishing an appropriate and safe time to stop using the TX.

One could simply cycle the battery with a load tester/cycler that records the MAH capacity depleted. Attention to the voltage supplied and time required to burn the battery down to 8.5 volts would yeild a projected use time based on actual numbers from your system. However as mentioned previously the voltage required to maintain the RF signal at full strength is more important than the capacity left in the battery pack, at least in this circumstance.

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TX battery question - 5/29/2002 8:29:26 PM   
hebertjj


 

Posts: 323
Joined: 1/18/2002
From: Knoxville, TN, USA
Status: offline 		Kevin,

I would be a little concerned about the low reading on the 6 ch Tx if I were you. I would have expected the 8ch to read lower than the 6ch because I'd assume the 8ch computer had a greater load on the battery (I might be wrong about this, it's just an assumption.) The advice to switch the packs and compare (if possible) sounds like a good idea. When you say you cycled them and they both showed over 600 mah, are we talking about input or output? If capacities (output) match, maybe it is just a bum meter, but that would bother me; maybe it's a bum Tx that's overloading the battery pack; I might want to send it in for a checkup. Ignoring warning signs from your equipment instrumentation is not a trait conducive to long life in the aviation business.

As to the numbers and terms being bandied about here; be careful. You can't say voltage is more important than capacity or vice versa. They are both related and if you run out of either, you're in trouble. Nicads are normally considered discharged at 1.1 volts per cell under load, so an 8.5 V alarm for an 8 cell Tx pack means, "Get down NOW!" Voltage drops off VERY quickly after the 1.1 volt/cell level is reached.

Joel

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TX battery question - 5/30/2002 5:42:17 AM   
mglavin



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From: Elverta, CA, USA
Status: offline 		Below are some notes liberated from Red's Battery Clinic. You'll find that as mentioned by myself and others the usable capacity is generally depleted between 1.0 - 1.1 volts for our purposes, what this really means is we can expect our Ni Cad battery packs to deliver approximately 95% of there rated capacity while supplying the required voltage, all within the numbers previously mentioned.

[COLOR=blue]Most manufacturers rate cell capacity by stating a conservative estimate of the amount of capacity that can be discharged from a relatively new, fully charged cell. The accepted rating practice is to state a cell rating in ampere-hours (or milliampere-hours) to a cutoff voltage of 0.9 volts at 5 hour discharge rate.

The key points to remember about discharge characteristics are that nickel-cadmium cells are rated at 1C or C/5 discharge to 0.9 volts at 23 degrees C and have a nominal voltage of 1.2 volts. Cell ratings are conservative design minimums and actual performance is affected by the conditions under which the cell is charged and discharged. The voltage profile of a Ni-Cd cell is very flat during most of its usable capacity and it drops off very rapidly when the cell approaches the end of its usable capacity.

The recommended voltage cutoff depends upon the discharge rate and whether the battery is used in "float" applications or cyclic applications. Choosing the right voltage cutoff provides the maximum capacity utilization and the maximum reliability.[/COLOR]

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TX battery question - 5/30/2002 8:34:41 AM   
hebertjj


 

Posts: 323
Joined: 1/18/2002
From: Knoxville, TN, USA
Status: offline 		Cutoff for capacity rating and cutoff for "If you fly any longer your going to crash" warning may be two different things. Admittedly, I haven't kept up to date on the latest battery industry specs, but I thought the cap rating cutoff voltage was 1.1 V; maybe our admin, Red, can weigh in on this.

This is irrelevant to the question of Tx warning voltage level. The discharge voltage curve of Nicads between 1.1 volts and 0.9 volts is definitely NOT FLAT !!! A Tx will quickly go from 1.1 volts to .9 volts per cell and go even quicker from .9 to .8 or whatever the minimum working voltage for the Tx is.

Getting back to Kevin's question; I have a Futaba T6XA Tx that hasn't been charged in two weeks or more and I just turned it on and it shows 9.9 volts. I don't like the fact that his barely shows 10 when fully charged. As Tim the wizard said:" I'm warnin' ya; don't go in there; it'll rip your throat out!" This is a trouble sign and I'd check it out before I trusted one of my planes to it Maybe ask Ann-Marie on the factory rep site and see what she says.

Joel

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TX battery question - 5/30/2002 9:35:18 AM   
mglavin



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From: Elverta, CA, USA
Status: offline 		Joel

I was not disagreeing with your statements as such, on the contrary you made some very valid points. I provided some additional data for those that have been overwelmed. I also was including you in the statement [COLOR=darkblue]"by myself and others".[/COLOR]

I assert that Ni Cad's exhibit a steep dive in the discharge curve and voltage after 95% MAH capacity has been depleted to approximately .095-1.0 volts. Until this figure is reached the Ni Cad's exhibit a fairly flat [steady voltage] discharge curve. The voltage then begins to decay rapidly, as you suggested.

The notes from Red's Battery Clinic offers essentially the same spec's/data and conclusions that we have been discussing.

You are right about Kevin's TX meter showing 10.0 volts off charge raising question, that's were all this started. I referenced it in my original post, seen below. I also read the Kevin cycled the battery pack and it delivered rated capacity plus!!! If there was a problem with the battery pack it would not cycle at rated capacity, IMO. I don't recall does the T6XA TX utilize an analog or a digital voltage display? Is it a voltage display or a power output meter or both, applies if its analog... You made good point regarding the power consumption of the 8U verses the T6XA.

Kevin did you read the voltage display of the cycler's at the termination of charging or there after? Did it differ from the TX's display?

Michael

[COLOR=orangered]The discrepancy with one TX voltage display is negligible. There are many considerations; voltage at completion of charge, battery age and condition, required MA to run the specific TX and the calibration of each TX's voltage display. [/COLOR]

< Message edited by mglavin -- May 30 2002 4:46AM >

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TX battery question - 5/30/2002 6:45:07 PM   
mulligan



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Joined: 4/14/2002
From: Sanford, FL, USA
Status: offline 		I am no expert either, but I have never kept a pack with a max voltage of 10.0V. I would immediately suspect either the pack has been overcharged at some point in its life and has vented or it is a very old pack and dentrites have formed in one or more of the cells. The latter can be solved by a quick charge (e.g., C/1).

I am also wary of the original statement that the pack in question tested to rated capacity plus. What exactly did you do to measure the capacity with the Hobbico and Ace chargers? Which chargers exactly are these?

If you put this pack in your 8 channel and you get an hour of transmit time or so (with a 600 mAh pack), you may think you are all right. However, the low peak voltage might indicate a more serious short around the corner. This would be beyond me, but hopefully Red will jump in and tell you to throw the pack away or don't worry at all.

In any case, my philosophy is ANYTHING abnormal about a $15 part that could directly result in the loss of $300 or more should be replaced! BTW, with these computer radios, most people go ahead and spend $25 for 1100-1600 mAh NiMH packs, especially since you can use it with more than one plane. They really should come with higher capacity batteries these days, IMO.

- George

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TX battery question - 5/30/2002 7:04:59 PM   
hebertjj


 

Posts: 323
Joined: 1/18/2002
From: Knoxville, TN, USA
Status: offline 		I'm assuming Kevin has a T6XA series Tx, as he said he had a 6 ch Futaba computer Tx. Maybe there's an older version of Futaba computer 6ch Txs, but the T6XA series has a digital voltage display; that reads XX.X V . The difference between Keven's 10V reading and the expected 11.1 or there abouts is a suspicious (and not insignificant) 1.1 volts. Get this checked out! You've been given a warning by your equipment (and me and Tim); fly at your own risk!

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