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Old Oct 01, 2012, 07:12 AM
Registered User
jsf135pal1's Avatar
United States, CT, Plainville
Joined Aug 2012
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Question
4.8v or 6v Rx battery?

Hello. I hope this is the right forum to ask this but I am ready to pull the trigger on my first 2.4ghz Tx sytem. It's the 7c 7ch Futaba for airplanes.
My question is the battery for the Rx? I know I have seen discussions on this topic but I can't seem to find it when I search the forums.
Do I go with the 4.8v or 6v? Do I use a LIPO? I'm pretty much a weekend warrior flyer but will go any chance there is calm winds and being that I live in New Engalnd those days are few and far between. So on those rare calm days I would like to get at least 6 or more flights so will the recommended 4.8 v 600mAh be good enough?
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Old Oct 01, 2012, 07:24 AM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
34,833 Posts
Simple answer 4 cell NiMH .

This is really a Radio question and belongs in the Radio Forum

http://www.rcgroups.com/radios-135/

Capacity determins how many flights . There are 600 , 800, 1500 and larger receiver batteries.



Charles
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Old Oct 01, 2012, 08:09 AM
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ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
5,807 Posts
Is this for a gas powered or electric powered plane? If electric you shouldn't need an Rx battery. The ESC will provide power to the Rx.

Glen
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Old Oct 01, 2012, 09:24 AM
FPV'r
ror1's Avatar
Canada, ON, Carleton Place
Joined May 2011
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Quote:
Originally Posted by jsf135pal1 View Post
Hello. I hope this is the right forum to ask this but I am ready to pull the trigger on my first 2.4ghz Tx sytem. It's the 7c 7ch Futaba for airplanes.
My question is the battery for the Rx? I know I have seen discussions on this topic but I can't seem to find it when I search the forums.
Do I go with the 4.8v or 6v? Do I use a LIPO? I'm pretty much a weekend warrior flyer but will go any chance there is calm winds and being that I live in New Engalnd those days are few and far between. So on those rare calm days I would like to get at least 6 or more flights so will the recommended 4.8 v 600mAh be good enough?
http://www.hobbyking.com/hobbyking/s...iver_Pack.html

charger:
http://www.amainhobbies.com/product_...rger-6S-6A-50W

NiMh are not much better than NiCD and NiCd are way too old technology.
The LiFe are best for Rx or Tx, no memory,can leave it at any charge state, pretty much can not damage it by misuse.
Each cell is 3.3V so a 2S is 6.6V which is close enough to 6V . If Rx and servos work at 6V then 6.6v is ok as well..
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Old Oct 01, 2012, 12:22 PM
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jsf135pal1's Avatar
United States, CT, Plainville
Joined Aug 2012
137 Posts
Quote:
Originally Posted by ggcrandall1 View Post
Is this for a gas powered or electric powered plane? If electric you shouldn't need an Rx battery. The ESC will provide power to the Rx.

Glen
Gas powered.
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Old Oct 01, 2012, 12:31 PM
FPV'r
ror1's Avatar
Canada, ON, Carleton Place
Joined May 2011
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Quote:
Originally Posted by jsf135pal1 View Post
Gas powered.
If gas, must be a big plane so you need Life batteries for sure to power those large servos.
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Old Oct 01, 2012, 01:01 PM
Pompano Hill Flyers
Miami Mike's Avatar
Miami Lakes, Florida, USA
Joined Mar 2003
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Quote:
Originally Posted by ror1 View Post
NiMh are not much better than NiCD and NiCd are way too old technology. The LiFe are best for Rx or Tx, no memory,can leave it at any charge state, pretty much can not damage it by misuse. Each cell is 3.3V so a 2S is 6.6V which is close enough to 6V . If Rx and servos work at 6V then 6.6v is ok as well..
Sorry, but this is not good advice, especially since you don't know what kind of receiver and servos "jsf135pal1" is using.

First of all, NiMh cells are a lot better than NiCd cells, with over three times the capacity of NiCd cells at the same weight, and unless he's using a receiver and the newer high-voltage servos that are made for two LiFe cells, a four- or five-cell NiMh pack (preferably Eneloops or similar low-self-discharge cells) would be his best choice for several reasons. For a start, they don't have the "memory" that you implied they did, and they can be recharged with the ordinary wall charger that comes with most radios.

Please don't be so careless with your advice, because if he's not using high-voltage servos, there's a fair chance that a two-cell LiFe pack will burn them out, and you'll be responsible for a crash.
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Old Oct 01, 2012, 06:10 PM
FPV'r
ror1's Avatar
Canada, ON, Carleton Place
Joined May 2011
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well excuse me for breathing, but I said to check the specs of his gear or did you miss that part..
" If Rx and servos work at 6V then 6.6v is ok as well.."

I will not use NiMh, I am using the Life with no problems.
It is in my opinion and you have to make up your own mind.
I believe the term "high voltage servo" is referring to operating on 2S LiPo where the voltage is 8.4
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Old Oct 01, 2012, 09:17 PM
Pompano Hill Flyers
Miami Mike's Avatar
Miami Lakes, Florida, USA
Joined Mar 2003
8,486 Posts
Quote:
Originally Posted by ror1 View Post
well excuse me for breathing, but I said to check the specs of his gear or did you miss that part..
Oh, really? You do know that anyone can scroll back, re-read your posts in this thread, and clearly see that you didn't say anything of the kind, right?

But the important thing is that "jsf135pal1" understands that if servos and receivers that are rated at 6 volts maximum are powered by more than 6 volts, such as with two LiFe cells, then the manufacturer's ratings are being exceeded.
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Old Oct 01, 2012, 11:22 PM
FPV'r
ror1's Avatar
Canada, ON, Carleton Place
Joined May 2011
1,219 Posts
why repeat what was already said.
read this thread and make up your own mind.
http://www.rcgroups.com/forums/showthread.php?t=1596246

I know I sleep well at night.
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Old Oct 02, 2012, 06:08 AM
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jsf135pal1's Avatar
United States, CT, Plainville
Joined Aug 2012
137 Posts
Thanks for the input everyone. I will do a little more research.
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Old Oct 02, 2012, 07:46 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
8,574 Posts
Quote:
Originally Posted by ror1 View Post
If gas, must be a big plane so you need Life batteries for sure to power those large servos.
I run a gas plane ...... and I use 2 NiMH packs ... one for ignition and other for Rx.

My NiMH are 2300mAh AA's ... and both are 4 cell .............

If I was really pushed on power required ... I would go for a LiPo via a high amp rated UBEC without any ESC etc. The fact is I have loads of smallish LiPo's that I no longer need for flight ... so could be ideal for Rx power.

But anyway for original question .........

4.8 or 6 .... all depends on the model, servos and what use you want from it. 6v gives you faster servo response and increased torque. But generally the right servo for the job will be OK on 4.8v. Not all servos can take 6v ... and the previous post about 6.6v - I would personally not use. I'm not saying it will not work ... I just don't like putting 6.6v into a servo that is rated to 6v max.
Final comment ... a 4.8v pack is actually not 4.8v ... but over 5v in fact.... it will dip under load to 4.4 - 4.9v depending on load ... and that shows you the 6v is actually higher .. and the 6.6v even more so ...

My answer ? Go for a decent capacity 6v pack .....

Nigel
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Old Oct 02, 2012, 08:00 AM
Registered User
So. Cal.
Joined Oct 2004
8,363 Posts
For those who prefer to make decisions based on facts and data rather than hearsay and speculation....

A fully charged Nixx cell is ~1.45 volts off charger.

A 6V (5 cell) receiver pack when fully charged is 5 x 1.45 = 7.25 volts.

A 2 cell LiFe receiver pack when fully charged is 2 x 3.6 = 7.2 volts.

7.2 < 7.25.

The net result is that if a 6 volt (5 cell) receiver pack is acceptable in your application, a 2 cell LiFe pack will likewise be perfectly acceptable (and even preferred for other reasons).

But do not take my word for it. Do a search on the following terms: LiFe receiver, A123 receiver, LiFePO4 receiver, etc., and you will find many stories of success.

Mark
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Old Oct 02, 2012, 08:01 AM
Registered User
Dallas, TX
Joined Jan 2005
2,169 Posts
If a servo is rated for 6v than it is meant to be used with a 5 cell NiCd or NiMh, correct? A full charged 5 cell can be more than 7 volts and a fully charged LiFe 2s is 7.2 volts. The problem with NiMh is that they are typically not a high discharge cell and the voltage drops a good bit under load. These problems are lessened with a good LiFe battery like the A123 2300s. Also another area that causes rx voltage problems are the switches as they can become a large voltage drop as they age. The eneloops are great tx batteries but I would not recommend them for a rx pack. If the choice is to stick with NiMh then just be sure to get a good 5 cell pack. In NiMh for a given physical cell size, as the capacity goes up the max discharge rate goes down so it is not always the best thing to go for the high capacity pack. I do not use NiMh packs but my understanding is that the packs made using Elite cells are very good.

Alan
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Old Oct 02, 2012, 12:19 PM
Registered User
Joined Jan 2009
130 Posts
This is a subject that interest me due to the fact I just ordered three 4.8 volt 650 NiMH AAA rec. packs and one 6Volt 1000 NiMH AAA rec. packs. I actually made a mistake and really meant to order AA packs. Question, has anyone had experience using these AAA pack as rec. batteries in a 60 size airplane. Logair
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