6 volt application

6 volt application
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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> 6 volt application

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6 volt application - 1/24/2004 10:34:08 PM

huggins

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From: Greentown, IN, USA
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I have an application with 5 digitals and one standard servo. The digitals are oversized a bit and provide all of the speed and the torque that I think that I will need on 4.8 volts, so any gain with 6 volts is not really needed. I will also be using two packs for redundancy, so if a cell goes bad the voltage drop will not be an issue since the other pack will still be there to keep the rx and servos alive until the end of the flight. So the question is, what would I gain by going 6 volts in this case since I have redundancy and don't need the extra speed or torque? It seems like all I would be getting it reduced flight time and extra weight. Am I missing something?

Thanks,
Mike

Post #: 1

RE: 6 volt application - 1/25/2004 1:47:30 AM

Geistware

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If you have two 4 cell packs and on cell opens, then you are OK. If one sell shorts, you will only have 3.6 volts. Remember this. If you have a 5 cell pack, you will have 4.8 volts if one cell shorts.

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RE: 6 volt application - 1/25/2004 3:56:44 AM

sfaust

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quote:

ORIGINAL: Geistware
If you have two 4 cell packs and on cell opens, then you are OK. If one sell shorts, you will only have 3.6 volts. Remember this. If you have a 5 cell pack, you will have 4.8 volts if one cell shorts.

Eggxactly! 3.6v is the cutoff point for Futaba receivers (or maybe its 3.3v). Either way, put any load on the batteries from servo movement and you will also get another drop in voltage. Further, by using 6V to start rather than 4.8V, you have a head start of 1.2v to compensate for voltage loss over long servo leads, more connectors, etc. This is more of an issue when the planes start reaching 33% or larger. Its nice to have that 1.2v buffer.

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RE: 6 volt application - 1/25/2004 4:19:16 AM

huggins

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From: Greentown, IN, USA
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First off, I appreciate you comments. If one cell shorts on a 4 cell pack, I understand that the voltage of that pack will be 3.6 volts. But won't the reciever still be seeing 4.8 volts due to the second pack?

I am just trying to justify the weight in a 27% Extra. Two rx packs and and an ignition pack, all 5 cells, would be full pound of batteries. I realize that I can go Lithium-Ion and save a bunch of weight, but cost becomes a much bigger factor.

Thanks again,
Mike

(in reply to sfaust)

Post #: 4

RE: 6 volt application - 1/25/2004 5:10:59 AM

RDespins

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I would say that you are plenty safe with 2 4 cell packs if you feel that the 4.8V is enough for the digital servos. I do prefer 6V with my digitals, but weight is the real issue here. Ultimately the choice is yours, a Single 5cell would be another option, it just depends on how much you trust your Batt/charger/flight pack.

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RE: 6 volt application - 1/25/2004 11:24:26 AM

Geistware

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NO, if the packs are in parrellel then you will see the voltage of the lower pack. Think of it this way, how are you going to raise a 3.6 volt pack to 4.8 volts? There will be some increase, but more on the order of 4 volts but you will be greatly loading the 4.8 volt pack. I think your bigger failure mode would be an open pack so two packs is advisable if you use 4 or 5 cells.

I have a PW Extra which is 16lbs and I fly with 3 packs that weigh 19oz. I could get the weight down to 12 oz but I don't see they 1/2 lb savings in the air.

quote:

ORIGINAL: huggins

First off, I appreciate you comments. If one cell shorts on a 4 cell pack, I understand that the voltage of that pack will be 3.6 volts. But won't the reciever still be seeing 4.8 volts due to the second pack?

I am just trying to justify the weight in a 27% Extra. Two rx packs and and an ignition pack, all 5 cells, would be full pound of batteries. I realize that I can go Lithium-Ion and save a bunch of weight, but cost becomes a much bigger factor.

Thanks again,
Mike

_____________________________

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http://www.rcaircraft.net/
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Site for hobbyist in the R.C. Aircraft modeling world.

(in reply to huggins)

Post #: 6

RE: 6 volt application - 1/25/2004 2:45:13 PM

sfaust

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quote:

ORIGINAL: Geistware
NO, if the packs are in parrellel then you will see the voltage of the lower pack. Think of it this way, how are you going to raise a 3.6 volt pack to 4.8 volts? There will be some increase, but more on the order of 4 volts but you will be greatly loading the 4.8 volt pack. I think your bigger failure mode would be an open pack so two packs is advisable if you use 4 or 5 cells.

Geistware is correct. You won't be seeing 4.8v from the higher pack, but something much lower. There will also be some cross charging from the 4.8v pack to the 3.6v pack, and that will lower the voltage slightly as well. So with 4.8v packs, you will see something in the low 4.Xv or high 3.Xv range. Add in the current drain from flying, and you will definitely be in the 3.Xv range. Not good. With the 6.0v packs, you will end up somewhere in the mid to low 5.Xv range before the servo load, which is a healthy margin to complete your flight and land normally if you weren't aware of the problem.

I would always recommend 6V in a dual pack setup for the above reasons, unless the receiver and servos/aux equipment can't handle the 6v. Most current equipment is designed with 4.8v and 6v operation in mind, and Futaba and JR spec their servos at both 4.8v and 6v.

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Post #: 7

RE: 6 volt application - 1/25/2004 7:12:18 PM

huggins

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Well, I guess I will go 6 volts. I guess we are only talking about 2-3 ounze difference between 2 - 4.8's and 2 - 6's anyway. Probably not enough to worry about. Once again, thanks for the input.

Mike

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Post #: 8

RE: 6 volt application - 1/25/2004 10:04:34 PM

Geistware

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Actually, it will about 2-3 oz per pack.
I save all my 4 cell packs for ignition.

quote:

ORIGINAL: huggins

Well, I guess I will go 6 volts. I guess we are only talking about 2-3 ounze difference between 2 - 4.8's and 2 - 6's anyway. Probably not enough to worry about. Once again, thanks for the input.

Mike

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Site for hobbyist in the R.C. Aircraft modeling world.

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Post #: 9

RE: 6 volt application - 2/9/2004 1:11:05 AM

Nogyro

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Check out Radical RC on his 1100 mah Nicad AA Sanyo cells. That's what I'm running in my new Wild Hare Edge. 4.8 volt for the ignition, and two 6 volts for the receiver. They cycled at 1150 mah.

Should give me 2 hrs worth of flying easy I would think. I was running 2-4.8 volt 700 mah packs on my Giant Stinger that gave 2 hrs flight time. The servo speed really does pick up when you switch to the 5 cell battery.

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Frank

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Post #: 10

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