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14V from 28V system

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n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Tue Apr 18, 2006 3:54 am Post subject: 14V from 28V system

I am building a 28V system and have some items that will be 14v others that can go 28 or 14V.



Is it better to use a 28-14v converter or use 2 14 V batteries in series and tap off the center?

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Milt

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Tue Apr 18, 2006 5:49 am Post subject: 14V from 28V system

N395V wrote:

 	  Quote: 	
		   

 

 I am building a 28V system and have some items that will be 14v others that can go 28 or 14V.

 

 Is it better to use a 28-14v converter or use 2 14 V batteries in series and tap off the center?


	


It is much better to use a converter or, better still, an equalizer.



The problem with center tapping the batteries is that you will force the 

lower battery into an undercharged state and the upper battery into an 

overcharged state. You will quickly destroy the upper battery and the 

lower battery will permanently suffer a loss of capacity leading to its 

early failure. And when I say "early" I am talking on the order of 40 

hours or less.



There are a number of companies making switching-type DC-DC converters 

that are very efficient. The only problem is that they become a single 

point of failure in your system. If that converter fails you have no 14V 

for anything that needs it.



Better still is a battery equalizer. This device connects across your 

pair of batteries and to the center tap between them, i.e. to ground, to 

the center tap, and to the 28V bus. It is a converter but it maintains 

the center tap at exactly 1/2 the voltage of the hot lead. The equalizer 

serves three purposes:



1. it ensures that both batteries charge equally and neither overcharges 

at the expense of the other;



2. it carries the load for your 14V devices ensuring that you don't 

damage either battery;



3. if you lose the charging system it makes the energy from both 

batteries available for your 14V loads.



And if the equalizer fails you still have the lower battery available to 

provide power to your 14V loads. Sure it is hard on the batteries but it 

will allow you to finish your flight without losing your 14V loads.



I have used equalizers from Sure Power Industries. Their equalizers 

range from 30A to 100A. See: http://www.surepower.com/conv.html.



-- 

Brian Lloyd                         361 Catterline Way

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

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Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Tue Apr 18, 2006 6:46 am Post subject: Re: 14V from 28V system

Brian,

Thanks the equalizer looks just like what the Dr ordered.



Do not Archive

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Milt

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