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Batteries and step down converters

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donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Tue Feb 04, 2014 8:34 am Post subject: Batteries and step down converters

Two totally unrelated questions...



1) To keep my primary EFIS up during engine start, I'm thinking of using a small battery (I will need two since I've got a 24v system). I've seen mention of people using 7ah batteries for this. What manufacture/model battery people are using?  



2) I've got one device that is only available in a 12v version. I was going to get this step down converter from Lone Star.

http://www.lonestaraviation.com/Step-Down-Conveter-24V-to-13.8-Volts.html



Then I ran across this one at 1/5th the cost.  

http://www.pyleaudio.com/sku/PSWNV480/24V-DC-to-12V-DC-Power-Step-Down-480-Watt--Converter-W-PMW-Technology



I'm wondering if it's likely that there is a fundamental difference between the two beyond one of them being for the aviation market.

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tim2542(at)sbcglobal.net
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Posted: Tue Feb 04, 2014 9:14 am Post subject: Batteries and step down converters

I think most any of them will run on 12 volts just fine. If so no need to convert it.  Here's what I use:

http://www.batteriesplus.com/product/46043-WKA12--7F-12V-7Ah-AGM-Battery/566-0/8183-Emergency-Light-Security-Battery/655122-Moose/Z1100-Security-Alarm.aspx

Tim



 	  Quote: 	
		   On Feb 4, 2014, at 8:34 AM, "donjohnston" <don(at)velocity-xl.com> wrote:

 

 

 

 Two totally unrelated questions...

 

 1) To keep my primary EFIS up during engine start, I'm thinking of using a small battery (I will need two since I've got a 24v system). I've seen mention of people using 7ah batteries for this. What manufacture/model battery people are using?  

 

 2) I've got one device that is only available in a 12v version. I was going to get this step down converter from Lone Star.

 http://www.lonestaraviation.com/Step-Down-Conveter-24V-to-13.8-Volts.html

 

 Then I ran across this one at 1/5th the cost.  

 http://www.pyleaudio.com/sku/PSWNV480/24V-DC-to-12V-DC-Power-Step-Down-480-Watt--Converter-W-PMW-Technology

 

 I'm wondering if it's likely that there is a fundamental difference between the two beyond one of them being for the aviation market.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=418075#418075

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edpav8r(at)yahoo.com
Guest

Posted: Tue Feb 04, 2014 9:59 am Post subject: Batteries and step down converters

What device are you planning to power from such a DC/DC converter that needs a supply capable of 10-20 amps?



Lone Star's prices reflect the high cost of TSO compliance testing and, as you suggested, application of the word "aviation" to their products.  That said, I'll bet they're high quality.  The Pyle... who knows?



As long as in-flight failure of the connected device would have no safety implications, I wouldn't hesitate to use the Pyle converter, or indeed any you might find on eBay for even less $, smaller size and lower weight.



Perhaps this:  http://bit.ly/1frGS3M  -or this-  http://bit.ly/1eQFmXj  -or this-  http://bit.ly/LM7x2A



Or, if 5A current capacity is enough, this:  http://bit.ly/1n8N17Y



Search eBay for "DC buck" and you'll get endless hits.



I would figure out the peak current draw of your device, double it, and buy a converter with that capability to assure adequate supply without high operating temps.  I wouldn't lose much sleep about reliability; if a converter functions out of the box, it's probably unlikely to fail later, assuming it's not driven to absurd temperatures or subjected to mechanical abuse.



Eric

On Feb 4, 2014, at 9:34 AM, "donjohnston" <don(at)velocity-xl.com> wrote:

 	  Quote: 	
		   

 

 Two totally unrelated questions...

 

 1) To keep my primary EFIS up during engine start, I'm thinking of using a small battery (I will need two since I've got a 24v system). I've seen mention of people using 7ah batteries for this. What manufacture/model battery people are using?  

 

 2) I've got one device that is only available in a 12v version. I was going to get this step down converter from Lone Star.

 http://www.lonestaraviation.com/Step-Down-Conveter-24V-to-13.8-Volts.html

 

 Then I ran across this one at 1/5th the cost.  

 http://www.pyleaudio.com/sku/PSWNV480/24V-DC-to-12V-DC-Power-Step-Down-480-Watt--Converter-W-PMW-Technology

 

 I'm wondering if it's likely that there is a fundamental difference between the two beyond one of them being for the aviation market.

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 04, 2014 10:59 am Post subject: Batteries and step down converters

At 10:34 AM 2/4/2014, you wrote:




Two totally unrelated questions...



1) To keep my primary EFIS up during engine start, I'm thinking of 

using a small battery (I will need two since I've got a 24v system). 

I've seen mention of people using 7ah batteries for this. What 

manufacture/model battery people are using?



   What is the input voltage requirement for your

   electro-whizzies. Many contemporary products now

   use switch-mode power supplies with a wide range

   of acceptable inputs . . . typically 0-32 volts.



   If your devices are of this generation, then you

   don't need brownout protection in a 28v system . . .

   starter inrush drain won't pull your bus below

   10 volts and the glass will stay powered up.



   The problem arises when a device with a 10v minimum

   input voltage sees a drop to 7-8 volts during starter

   inrush events.

2) I've got one device that is only available in a 12v version. I was 

going to get this step down converter from Lone Star.

http://www.lonestaraviation.com/Step-Down-Conveter-24V-to-13.8-Volts.html



Then I ran across this one at 1/5th the cost.

http://www.pyleaudio.com/sku/PSWNV480/24V-DC-to-12V-DC-Power-Step-Down-480-Watt--Converter-W-PMW-Technology



I'm wondering if it's likely that there is a fundamental difference 

between the two beyond one of them being for the aviation market.

    What is the device you're fitting with the down-converter

    and what are its input demands?

   Bob . . .

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