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Do I need a larger capacity battery for my Rx.

Old 07-02-2011, 06:26 PM
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karolh
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Default Do I need a larger capacity battery for my Rx.

I recently switched my Futaba 8UAF system from 72Mh to 2.4Gh by a module change, but still use a 4.8 volt 700Ma nicad pack to power the Rx and 5 std. analog servos in the model. I seldom fly more than five, 10-12 minutes flights per flying session and need to know if I should increase the battery capacity to say 1000Ma to guard against the possibility of the system suffering a brown out.

KaroL
Old 07-02-2011, 06:43 PM
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Default RE: Do I need a larger capacity battery for my Rx.


ORIGINAL: karolh

I recently switched my Futaba 8UAF system from 72Mh to 2.4Gh by a module change, but still use a 4.8 volt 700Ma nicad pack to power the Rx and 5 std. analog servos in the model. I seldom fly more than five, 10-12 minutes flights per flying session and need to know if I should increase the battery capacity to say 1000Ma to guard against the possibility of the system suffering a brown out.

KaroL
How long you can fly depends upon the Capacity of your Rx batteries. Brownout issues result from large, sudden, current draws that cause the Rx battery voltage to drop to levels that force the Rx to reboot. With 2.4 radios, it is much safer to use 6v or higher Rx batteries. If your servos do not run well at 6v, or you plan on using LiPos or LithIons as Rx batteries, you can use a voltage regulator. This will reduce the chance that your Rx will suffer from a dramatic voltage drop.

You can also use a Wattmeter or H9 Current Meter to measure how much current your servos will draw in the worst case scenario, when they are all Stalled. This will not only help you determine what capacity batteries you should be using, but it can determine whether you could experience a Brownout.
Old 07-02-2011, 08:32 PM
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Default RE: Do I need a larger capacity battery for my Rx.

In my opinion Yes you Do.

I have equiped all thirtyseven of my 2.4 equiped aircraft with five cell batteries and with capacitys that is roughly three times what we formerly used with similar aircraft that was equiped with 72 systems.

In other words for your airplanes that you did use 600Mah capacity Nicd batteries I now use about 1800 mahNimh batteries. I do not even consider 1000 mah enough.

Changing to five cell Nimh easily will provide this capacity in about the same weight as the old four cell Nicd's.

I also recommend this to all my students as well and currently only fly with those using five cell packs.

I have never occured anything close to a brown out nor has any of my students but yet agine I did withness just this morning what I beleve was a brown out off a brand new trainer being flown by another instructor and student that insisted on four cell packs of low capacity and there may have been charging issues.

I did not mention any brands simply because I think these issues applies to all 2.4 systems.

Do yourself a favor and change over to higher capacitys and five cell packs where you also enjoy the benefits of faster servos. Faster servos will help even students fly and learn better although they may not even realize this. Thats a fact and I have withnessed this improved performance by pilots accross the entire experiance spectrum in every case.

John
Old 07-03-2011, 02:30 AM
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Default RE: Do I need a larger capacity battery for my Rx.

JohnBuckner, you wrote above that "I have equiped all thirtyseven of my 2.4 equiped aircraft with five cell batteries." With that many batteries, you must share where/what is the best source for 5-cell receiver packs. Hopefully at at good price
Old 07-03-2011, 05:02 AM
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Default RE: Do I need a larger capacity battery for my Rx.


ORIGINAL: JohnBuckner

In my opinion Yes you Do.

I have equiped all thirtyseven of my 2.4 equiped aircraft with five cell batteries and with capacitys that is roughly three times what we formerly used with similar aircraft that was equiped with 72 systems.

In other words for your airplanes that you did use 600Mah capacity Nicd batteries I now use about 1800 mahNimh batteries. I do not even consider 1000 mah enough.

Changing to five cell Nimh easily will provide this capacity in about the same weight as the old four cell Nicd's.

I also recommend this to all my students as well and currently only fly with those using five cell packs.

I have never occured anything close to a brown out nor has any of my students but yet agine I did withness just this morning what I beleve was a brown out off a brand new trainer being flown by another instructor and student that insisted on four cell packs of low capacity and there may have been charging issues.

I did not mention any brands simply because I think these issues applies to all 2.4 systems.

Do yourself a favor and change over to higher capacitys and five cell packs where you also enjoy the benefits of faster servos. Faster servos will help even students fly and learn better although they may not even realize this. Thats a fact and I have withnessed this improved performance by pilots accross the entire experiance spectrum in every case.

John
With 37 5cell batteries, it must be a full time job just keeping all the batteries charged. Most 5cell NiCad and NiMh self discharge while sitting around not connected to an Rx. Do you have them all on some kind of Trickle Charge? I have seen some people who store their multitude of aircraft on racks and connect each charging jack to a separate "Little Trickler" device, to keep them ready for use.

I have abandoned NiCad and NiMh batteries. I use LiPo, LithIon, or LiFe batteries for Rx packs. They are Light, they Hold their Charge forever, and they are fast to charge (30min at most) without the batteries heating up. After 33 years of flying RC, I no longer get caught with a battery that is not ready to use. No Brownouts, as well.
Old 07-03-2011, 07:22 AM
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karolh
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Default RE: Do I need a larger capacity battery for my Rx.

Rich & John,

Thanks for that insight regarding 2.4GHz Rx battery requirements, as I WILL be changing to a 5 cell 6.0volt 1650 mAh NiMh battery for onboard power. Sure hope my indirect drive S148's can handle the increased voltage.

Karol
Old 07-03-2011, 08:28 AM
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Default RE: Do I need a larger capacity battery for my Rx.


ORIGINAL: karolh

Rich & John,

Thanks for that insight regarding 2.4GHz Rx battery requirements, as I WILL be changing to a 5 cell 6.0volt 1650 mAh NiMh battery for onboard power. Sure hope my indirect drive S148's can handle the increased voltage.

Karol
I don't think 148's are 6v compatible.
Old 07-03-2011, 08:34 AM
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karolh
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Default RE: Do I need a larger capacity battery for my Rx.

I checked the Tower Hobbies site on the S148 specs and they are rated for 6.0 volts.

Karol
Old 07-03-2011, 08:40 AM
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Default RE: Do I need a larger capacity battery for my Rx.


ORIGINAL: karolh

I checked the Tower Hobbies site on the S148 specs and they are rated for 6.0 volts.

Karol
Excellent
Old 07-03-2011, 08:56 AM
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Default RE: Do I need a larger capacity battery for my Rx.

Just a small program note regarding low voltage and FASST radios. The FASST receivers will operate down to about 2.8 volts or so. Regardless of what packs you are using, if you get voltage that low, even under a load, you have a problem. In addition, all current FASST receivers will simply shut of at that voltage and turn back on virtually instantly once the voltage recovers above 2.8 volts. Your servos will work until they reach their limit voltage, albeit running very slowly.

Having said that, I have not used a 4.8 volt pack in I cannot remember how long. I started using 5 cell NiMH and for the last 2 years run all 2S (6.6 volt) LiFePO4 packs.
Old 07-03-2011, 09:13 AM
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Default RE: Do I need a larger capacity battery for my Rx.

Airbusdrvr - I actually buy most of my batteries through my LHS and the brands I use a lot of are Venoms from Great Planes in both stick and hump pack style (I actully prefer the hump pack in some aircraft so keep both on hand) these being mostly 1600 Mah five cell Nimh.

The other brand I use a lot of and buy through my LHS are Tenergy not Turnigy. The Tenergys are wholesaled through a Warehouse in california and the have served quite well. I attended the dealer show several years ago in Las Vegas and got my dealer connected up with this wholesaler. The Tenergys that I use most are 16oo to 2500 mah five cells as well as a few LiPo's of various capacitys for my just three electric airplanes.

Buschbarber - Yes you are correct some airplanes naturally do not get flown as much as some others and I am slowing considerably as I become more disabled but still manage to add perhaps five or six completions a year some complex and some very simple Jobs.

I do still fly almost every day. The Nimh's have never been a problem and I do date them when installed and never bury them in the airplane. Always making sure that a change out is easy with access doors or othewise mount on velcro and a simple replacement . My preference is change out the Nimh's after perhaps about three years regardless. Fourteen or fifteen dollars is the typical price I pay for these batteries.

Except for my few electric I choose not to us lipo's as this I beleve will increase my costs considering the likely service I would get from them. Also I particularly will not use Lipo's in Tx's or my starters that is only asking for trouble for me. In my starter I am estatic over the Harbour Freight 18 volt Nicd drill pack I am now using on all my starters from the Sullivan half A throuh my mondo starter. This is a ten dollar pack that is perfect for the job. This enables me to be completely portable and I do not use power panels or carry heavy flight box batterys, using only single cell glow ignitors or portable ignitor box's and geared manual fuel pumps mounted to my one gallon or one quart metal fuel cans.

Karolh - Excellent decision and that set up will work just fine for you with no worries of brownout if you use good charging teckniques and the 148 are no issue either. I have many 148's running in various airplanes although I could not tell you which off the top of my head. I am also a heavy Hitec user and acturally I use a lot of the delight full little HS 225.


John

This is my most recent completion a simple arf which I maidened yesterday and bought a week ago at the club auction and night fly which I promoted for the club. This delightfull litte ship I bought for thirty seven dollars without engine or electronics of course but I am mentioning this as its one I also mounted the battery forward which makes no lead neccessary and I beleve allows the battery run cooler but also in keeping with the question of accessability makes battery changout very simple:


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Old 07-03-2011, 12:32 PM
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Default RE: Do I need a larger capacity battery for my Rx.

karolh, all Futaba receivers are specified to work on 4.8 volts. That's four healthy NiCads. In fact, they will even work down to 3.3 volts. That is why the battery fail safe activates at 3.8 volts. The rumors you have heard about brown outs, lock outs and any other kind of "outs" do not apply to Futaba receivers on 2.4Gig, 72Meg, 50Meg and the other frequencies they use for world wide sales. If you stick with Futaba receivers, the best thing you can do is use a four cell pack of NiCads. Dan.
Old 07-03-2011, 12:34 PM
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Default RE: Do I need a larger capacity battery for my Rx.


ORIGINAL: airbusdrvr

JohnBuckner, you wrote above that "I have equiped all thirtyseven of my 2.4 equiped aircraft with five cell batteries." With that many batteries, you must share where/what is the best source for 5-cell receiver packs. Hopefully at at good price
I got two at flee bay for $13
Old 07-03-2011, 02:02 PM
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Default RE: Do I need a larger capacity battery for my Rx.


ORIGINAL: DAN REISS

karolh, all Futaba receivers are specified to work on 4.8 volts. That's four healthy NiCads. In fact, they will even work down to 3.3 volts. That is why the battery fail safe activates at 3.8 volts. The rumors you have heard about brown outs, lock outs and any other kind of ''outs'' do not apply to Futaba receivers on 2.4Gig, 72Meg, 50Meg and the other frequencies they use for world wide sales. If you stick with Futaba receivers, the best thing you can do is use a four cell pack of NiCads. Dan.

Thanks for your concern Dan, but one of the reasons for my cautious approach here is that I am NOT using a Futaba 2.4 Ghz system, but the Futaba compatable FrSky 2.4 module/Rx combo, which so far has been rock solid. Plus one of the benefits of using 6.0volts is a little faster servo response time.

Karol
Old 07-03-2011, 03:02 PM
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Default RE: Do I need a larger capacity battery for my Rx.


ORIGINAL: DAN REISS

karolh, all Futaba receivers are specified to work on 4.8 volts. That's four healthy NiCads. In fact, they will even work down to 3.3 volts.
It is actually a bit lower than that. They will simply shut off at 2.8 volts. At 3.3 you will still have a nice solid green LED. Your servos may not move, but the RX is still working.



That is why the battery fail safe activates at 3.8 volts. The rumors you have heard about brown outs, lock outs and any other kind of ''outs'' do not apply to Futaba receivers on 2.4Gig, 72Meg, 50Meg and the other frequencies they use for world wide sales. If you stick with Futaba receivers, the best thing you can do is use a four cell pack of NiCads. Dan.

I agree with all of this except the very last sentence. While a 4-cell NiXX pack is certainly adequate I would not say it is "the best".
Old 07-03-2011, 05:12 PM
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Default RE: Do I need a larger capacity battery for my Rx.

Thanks to all who responded to my post. I have heard both the for and the against arguments on this issue, and I think that in this case there are simply to many advantages in going to 6.0 volts than continuing with 4.8 volts.

Karol

Old 07-04-2011, 03:51 AM
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Default RE: Do I need a larger capacity battery for my Rx.


ORIGINAL: Silent-AV8R


ORIGINAL: DAN REISS

karolh, all Futaba receivers are specified to work on 4.8 volts. That's four healthy NiCads. In fact, they will even work down to 3.3 volts.
It is actually a bit lower than that. They will simply shut off at 2.8 volts. At 3.3 you will still have a nice solid green LED. Your servos may not move, but the RX is still working.



That is why the battery fail safe activates at 3.8 volts. The rumors you have heard about brown outs, lock outs and any other kind of ''outs'' do not apply to Futaba receivers on 2.4Gig, 72Meg, 50Meg and the other frequencies they use for world wide sales. If you stick with Futaba receivers, the best thing you can do is use a four cell pack of NiCads. Dan.

I agree with all of this except the very last sentence. While a 4-cell NiXX pack is certainly adequate I would not say it is ''the best''.
Just before I put this topic to rest, is there any disadvantage or down side from using 6.0 volts.

Karol
Old 07-04-2011, 04:38 AM
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Default RE: Do I need a larger capacity battery for my Rx.

None that I have ever run into except I suppose a very few servos that may jitter when first turning on only I have not managaed to own any like that.


However going beyond the simple obvious safety factors with all the 2.4 systems useing five cell packs of capacitys roughly three times what we formerly used with 72 systems, this at about the same weight there is the hugh advantage of the faster servos.

Indeed it is a hugh advantage to all pilot skill levels even down to the lowly trainer plane with a brand new student.

I have been thourghly chastized for even suggesting this on the forums and even received hate mail because of this but one only need to spend day in and day out every day training folks to realize the hugh advantage and its accross the board for all skill levels.

Its also true that the advantage may not even be self evident to the individual however it will show over time.

I Did not take the complete changeover to 6 volts lightly as it was a major commitment and it was well before 2.4. 2.4 had nothing to do with that decision even though there are obviously advantages for 2.4 operations now that I made that changover also.

John
Old 07-04-2011, 05:38 AM
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Default RE: Do I need a larger capacity battery for my Rx.


ORIGINAL: karolh

ORIGINAL: Silent-AV8R


ORIGINAL: DAN REISS

karolh, all Futaba receivers are specified to work on 4.8 volts. That's four healthy NiCads. In fact, they will even work down to 3.3 volts.
It is actually a bit lower than that. They will simply shut off at 2.8 volts. At 3.3 you will still have a nice solid green LED. Your servos may not move, but the RX is still working.



That is why the battery fail safe activates at 3.8 volts. The rumors you have heard about brown outs, lock outs and any other kind of ''outs'' do not apply to Futaba receivers on 2.4Gig, 72Meg, 50Meg and the other frequencies they use for world wide sales. If you stick with Futaba receivers, the best thing you can do is use a four cell pack of NiCads. Dan.

I agree with all of this except the very last sentence. While a 4-cell NiXX pack is certainly adequate I would not say it is ''the best''.
Just before I put this topic to rest, is there any disadvantage or down side from using 6.0 volts.

Karol
Yes, higher operating temp for servo and rx, higher servo speed and higher power draw. A fully charge NiXx is higher than rated voltage. It's only when battery is at full charge. For regulated 6V, it's fine...
Old 07-04-2011, 06:18 AM
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Default RE: Do I need a larger capacity battery for my Rx.

When we talk about increased operating temps on servos and Rx's or increased power draw, isn't all these just marginal technicalities at best, plus if the units are rated by the manufacturer for 6.0 volts there should be no problem. Has it been documented anywhere that systems run at 4.8 volts last longer or perform better than those run at 6.0 volts. It seems to me to be almost a case of dammed if you do and dammed if you don't, so I guess it's left up to the end user to decide. Whichever of the two is used, it's quite obvious that good judgement and common sense should prevail.

Karol
Old 07-04-2011, 08:13 AM
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Default RE: Do I need a larger capacity battery for my Rx.

I got your point... the author has a wise decision of asking downside between alternatives.

Although it's not a big issue but it's also a point to consider when selecting. For me thermal increase is a disadvantage due to losses or power efficiency and wear and tear of devices when vent is insuficient for a long time. The devices are specified for 5 to 6V and power supply of 4S is between 5 and 6V while 5S is close to 7V when fully charge considering normal load. For the Rx since it's a digital electronics circuit 5V is the best.

The reason also why current draw is a disadvantage eventhough this can use as an advantage for output power, because it can cause power surge at high speed as the internal resistance of battery increases as it closes to the curve.
Old 07-04-2011, 08:37 AM
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Default RE: Do I need a larger capacity battery for my Rx.

Here's an example of how to estimate for power requirements





Disregard the title...
Data were gathered thru actual reading under approx full mechanical load and used 100% demand factor.
Use only as illustration.
Old 07-04-2011, 09:10 AM
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Default RE: Do I need a larger capacity battery for my Rx.

I can't see the second one, here's a simple calculation how to get the duration or reverse it if you want to get the battery size using time and current.



SF is safety factor, although there might be losses in voltage regulator but I use ratio of transformation instead.

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