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4.8 or 6 volt battery ?

Which one for use on 2.4 GHZ

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blackninja16/01/2015 20:53:01
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21 forum posts

Is a 4.8v NIMH battery ok to use with 2.4 GHZ system or should it be 6 volt.This is for the receiver and controls only as the plane has an IC engine.

I've heard 4.8v can cause brown outs after buying the battery and I should have got 6v so just want to be sure.

Pete B - Moderator16/01/2015 21:10:23
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If you put '4.8v' in the search box, there are a number of threads that discuss the issuethumbs up

Pete

blackninja16/01/2015 21:20:54
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Posted by Pete B - Moderator on 16/01/2015 21:10:23:

If you put '4.8v' in the search box, there are a number of threads that discuss the issuethumbs up

Pete

Thanks Pete.

Mark a16/01/2015 21:27:13
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I only use 6 volt packs on my rx.

John Privett16/01/2015 21:52:22
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On the other hand, I've never used a 6v battery on any rx, either 2.4GHz or 35MHz.

A 4.8v battery won't cause a brown-out. It may make a brown-out more likely, if you've got a bad installation or a bad battery.

Bill_B16/01/2015 22:20:02
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I on the other hand use a 2s LiPo in some of my airframes. It all depends on which make of radio gear you're using. Multiplex receivers can operate on voltages from 3.4 - 9 volts. wink

Pete B - Moderator16/01/2015 23:25:08
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I think the general consensus would be that, provided you have a reliable installation using good quality cells and, most importantly, make sure they are looked after and charged before flight, there's no reason why a 4.8v setup shouldn't be suitable for all radio systems....

Pete

Phil Green16/01/2015 23:33:46
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All 2.4ghz receivers are 3.3 volt devices. The internal 3.3v voltage regulator needs a small overhead above 3.3v to function properly (confusingly this is called the regulator's 'drop out voltage' - when they don't 'drop out' at all) .

So a 4.8v supply to the receiver is plenty, assuming a flat battery at 1.1v per cell that's 4.4v which still gives 1.1v of dropout voltage - this should be ample.

But it has to be said that some are better than others - taking two extreme examples Frsky is particularly good and still functions well below 3.3volts. Spektrum is demonstrably less tolerant, to the extent that 5 cell packs are often used to sidestep the higher dropout problem, particularly where there is a heavy servo load and the power system hasn't been specced adequately.

Many current receivers are specced to 16v or more, whereas most servos are not and therefore become the most stressed airborne component in an HV setup. High voltage isn't necessarily the 'Good Thing' that some would have you believe.
Internally the receiver is still a 3.3v device and a 16v supply will leave 12.7v across the regulator where it simply creates heat. The servo signals from the 16v receiver are still only 3.3v peak, so as a proportion of the supply voltage the servo signals diminish with higher supply voltages. Conventional digital wisdom is that pulses should be rail to rail - a 3.3v signal on a 16v supply is only 20% rail. Taking an extreme example, in a 100v system it would be 3.3% and very likely below the digital noise threshold.

I would suggest that a good 4.8v battery via a switch harness that is up to the job, should be just fine  but as with everything, its down to personal choice - whatever gives you confidence in your setup.

Cheers
Phil

 

 

 

Edited By Phil Green on 16/01/2015 23:37:35

Frank Skilbeck17/01/2015 09:40:38
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The warning I would give is to be wary of some of the very high capacity AA cells, while they have lots of mah, some of them have a high internal resistance which means the terminal volts drop dramatically if asked to power a heavy load. I had one new 2600 mah 4 cell Nimh AA pack and setting up a 7 servo model on the bench the telemetry low volts alarm kept going off as I cycled the servos, I changed to a 4 cell sub C pack and the problem went away.

GrahamWh17/01/2015 10:31:48
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I too fell for the more is best idea with AA cell capacity, but I think my 2000 mAh 4 cell packs are only really good for 400 to 500mAh before they suffer bad voltage drops when servos are highly loaded. I think your idea of using sub C cells for 4 cell packs is very sensible and will avoid this Frank. (I'm experimenting with 2S LiFes and regulated lipos now though).

Edited By GrahamWh on 17/01/2015 10:32:57

Cuban817/01/2015 10:55:28
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As has been said, a decent 4.8V setup is perfectly fine provided it can supply adequate current for a particular installation. The only reason I tend to use five cell packs these days is that in the past I've discovered some of my older four cell RX packs with a weak cell after one of my regular capacity checks. A five cell pack will still work the RX with one of its cells dead (not open circuit obviously).

Regular capacity/load tests are vital on RX packs and I'm amazed that many modellers make no attempt to check the performance of their batteries at all other than a quick test with a cheap led tester from time to time - which really tells you next to nothing.

Echo the comments about some of the high capacity AA cells as well. I tested a 4.8V 2200mA pack, and from fully charged could only sustain 2 A before collapsing to below 4V. Just one other point that is often forgotten is the voltage drop across battery leads, switch harness and extension leads before even getting to the RX can be significant, and may just push a struggling system over the edge into failure.

blackninja17/01/2015 11:10:38
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21 forum posts
Thanks for the replies and to be safe I think I'll get a 6v l. Can anyone recommend a nimh one. Ie. Size and brand.
Cuban817/01/2015 11:38:35
2961 forum posts
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I like these. Unfortunately only in the Global warehouse, but if you choose UK direct channel they usually come through within 10 -15 days.

**LINK**

Phil Green17/01/2015 12:05:53
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1598 forum posts
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What system is this for?, I dont think you said...

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