How many Batteries are NEEDED? - RCCanada - Canada Radio Controlled Hobby Forum
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Old 08-24-2016, 06:24 PM   #1
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How many Batteries are NEEDED?


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OK Guys;

Here is an ‘Interesting’ Question come Situation – completely open for discussion…

In the giant scale world it is common to employ a pair of batteries (on the receiver) with a battery sharing device to ensure that the plane does not fail. PLUS a separate battery for the ignition system.

SUPER! I Subscribe to the safety logic!

BUT!

As of late I have been buying 2300 ma batteries and have noted that after a FULL day of flying (2-4 flights) the maximum recharge is around 400 ma per battery (2 x 400 = 800 ma)… which is WAY LESS than the rating of a single battery pack… (2300ma)

So!


The question is – WHY have the Second Receiver pack??!

I can save weight, expense, a battery share device as well as the extra switch etc…

I do realize the safety concept of a spare battery. BUT! How often do they REALLY fail?

The average flier has (as I said) 2-4 flights and then they go home, this consumes 4-800 ma of power leaving a mere 1500ma of reserve PER BATTERY Pack! (yes I have analogue servos)

What am I to do with such a shortage of safety??

I am considering launching my next project with a single battery pack for the receiver and a single battery pack for the ignition!

… I’m just such a radical!

Comments?
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Old 08-24-2016, 06:34 PM   #2
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Re: How many Batteries are NEEDED?

Murphy's law dictates that if you remove the redundant battery, on the very next flight the main one will experience a glitch.

Rather than eliminating one battery, why not use two smaller packs?
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Old 08-24-2016, 06:43 PM   #3
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Re: How many Batteries are NEEDED?

yes use 1 battery for the RX and 1 for the motor - I fly a simple plane GP Escapade 33cc
just replace them after 2-3 seasons - Lots are using Life style batteries vice lipo's these days

unless your got retracts or other high voltage devices draining your system

If your model is worth thousands yes go for the extra battery
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Old 08-24-2016, 06:48 PM   #4
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Re: How many Batteries are NEEDED?

I run 2x1800mah which is good for 4 flights 450mah per flight

and an ibec for the ignition
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Old 08-24-2016, 07:18 PM   #5
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Re: How many Batteries are NEEDED?

Couple reasons I suppose. Batteries have become cheap and very reliable so the question is why not. Also we have room for bigger batteries and I would rather use a 2nd battery pack to adjust my C of G and then lead.

Standard practice for me is to run 2 or 3 batteries in all my airplanes. Just makes good sense to have a backup. And Once that saved a airplane of mine.
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Old 08-24-2016, 07:34 PM   #6
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Re: How many Batteries are NEEDED?

What type of batteries? Asking since even though NiMH may have lots of storage they cannot supply high surge current demands. If your demand exceeds the supply the voltage will fall off, perhaps to the point the Rx will reset.

Two packs would obviously supply twice the current.

There are other factors to concern yourself with. What power path feeds the system. Standard servo connectors and those slider switches that used to come with Radio systems are not rated for much more than 4A. Same with extensions. Anything long should have at least 22Ga conductors to reduce loss.

Reason I bring all this up is high servo counts, long extensions and especially digital servos can demand more than the source can supply. I have seen some digital servos draw in excess of 1.5A each under load or stalled. Same with servoless retracts.

Seems some receivers are more vulnerable to the voltage drops under those conditions.

ps. I think you should tie the negatives together between the system and separate ignition battery if you see any interference problems.
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Old 08-24-2016, 07:58 PM   #7
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Re: How many Batteries are NEEDED?

Quote:
Originally Posted by Cougar429 View Post
Two packs would obviously supply twice the current.
Nope they supply the capacity of Bat #1 + capacity of Bat#2. so two 1200 mah will give you a total of 2400 mah capacity if they are connected in parallel and in a perfect world.

If they were connected in series then they would supply twice the current.


Never, Never hook your batteries up in series as you will smoke your system
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Old 08-24-2016, 08:25 PM   #8
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Re: How many Batteries are NEEDED?

2 batteries or an optical isolator.

If my old school memory serves me correctly... The separate battery for ignition was simply to reduce the Radio interference coming from the motor/ignition. Even with 2.4 radio systems I personally feel it is a good practice to separate the ignition from the receiver as much as possible. Super important if using 72Mh

If I have only one battery for the receiver with full size servos installed, I will always use 2 power plugs into the receiver. This I feel is insurance should a spike in current draw try to take me down.

Last edited by Cougar429; 08-24-2016 at 10:25 PM.
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Old 08-24-2016, 10:24 PM   #9
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Re: How many Batteries are NEEDED?

Quote:
Originally Posted by Mike Sebastien View Post
Nope they supply the capacity of Bat #1 + capacity of Bat#2. so two 1200 mah will give you a total of 2400 mah capacity if they are connected in parallel and in a perfect world.

If they were connected in series then they would supply twice the current.


Never, Never hook your batteries up in series as you will smoke your system

First sentence basically correct but then...........I think you should go read about volts and amps and current. Or stop smoking whatever!
Series increases voltage 1s lipo 3.7 2s 7.4 3s 11.1
Parallel leaves voltage and increases capacity/ability to provide current.
I know what I just wrote isn't in scientifc terms but there's enough info out there that can be found and explained to the n'th degree.
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Old 08-24-2016, 10:25 PM   #10
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Re: How many Batteries are NEEDED?

Mike, basic electrical rules contradict your statement. Two equal sources hooked in parallel will supply the same voltage, but twice the current, (if there is no hindering resistance in the circuit). Those same sources connected in series will double the voltage, but the same current.

Here are some extra notes:

Connecting in Series
When connecting your batteries in Series you are doubling the voltage while maintaining the same capacity rating (amp hours). Series adds the voltage of the two batteries, but keeps the same amperage rating (also known as Amp Hours).

Connecting in Parallel
When connecting in Parallel you are doubling the capacity (amp hours) of the battery while maintaining the voltage of one of the individual batteries. Parallel connections will increase your current rating, but the voltage will stay the same.

Nick, to be honest I have not had experience with powered ignition systems, only self-contained mag setup, but from my own uses, (mostly helis with some hefty ESC rigs) by tying the negatives together you provide a path to dump the interference to ground.

Also, it seems our 2.4 are not as vulnerable to RF as legacy 72MHz. Still, it's likely an onboard ignition is a pretty strong source for RF.

Would like someone with experience with these ignition types to jump in and perhaps correct my thinking. Never know what might be in my future.
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Last edited by Cougar429; 08-24-2016 at 10:59 PM.
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