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CB Size requirements?

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FLYaDIVE(at)aol.com
Guest

Posted: Fri Jun 23, 2006 8:50 pm Post subject: CB Size requirements?

Hello Group:

  

 I have searched the web without any luck ... I'm looking for the CB requirements for a King KX 125, would anyone have info on this?

  

 Thank you for your assistance,

 Barry

khorton01(at)rogers.com
Guest

Posted: Sat Jun 24, 2006 1:34 am Post subject: CB Size requirements?

On 24 Jun 2006, at 24:43, FLYaDIVE(at)aol.com wrote:



 	  Quote: 	
		   Hello Group:



 I have searched the web without any luck ... I'm looking for the CB  

 requirements for a King KX 125, would anyone have info on this?




	


The purpose of the CB is to protect the wire from overheating if  

there is a short.  The purpose is not to protect the radio.  The only  

thing the wiring can do that can hurt the radio is provide high  

voltage if the alternator's voltage regulator fails.  You need an  

overvoltage protection system to prevent this.  A CB cannot stop high  

voltage, as a CB is triggered based on excessive current, not  

excessive voltage.



The size of CB depends you need depends on the size of the wire.   

What size wire provides power to the radio?



Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

wjoke(at)shaw.ca
Guest

Posted: Sat Jun 24, 2006 8:37 am Post subject: CB Size requirements?

Kevin has described the rationale for the "maximum size" circuit breaker 

in a circuit powering a radio (or other electrical device) which is to 

protect the power feed wire in the event of a short. There is also a 

"minimum size" CB required to pass enough electrical power to the device 

(avionics engineers that I know like the term "appliance").  Since 

voltage is generally fixed at close to 12 -14 volts, this really means 

getting enough current to power the device. Typically a VHF radio will 

use something like 200-400 milliamps on receive (depending on the audio 

volume and squelch settings) and 3-5 amps on transmit. Too small a CB 

means a nuisance trip of the CB every time you attempt to transmit - 

nothing is wrong just the CB is too small to pass enough power to the 

radio when it is transmitting. Typically a 50% extra capacity is added 

to deal with power surges as the transmit cycle begins so if 5 amps 

needed - use 7.5 amps, etc.

The manufacturers are reluctant to widely advertise the installation 

details of their equipment perhaps to encourage buyers to hire the 

dealers who sell the stuff to do the installation as well thus sending a 

bit of business their way. So that's why the power supply specs are less 

than readily available. The KX-125 specs seem to suggest a 5 watt 

transmitter (RF) power output. Most radios in this range will do fine 

with a 10 amp CB so, failing anything else, try that size of CB. This 

means sizing the wiring so that it is big enough to pass that amount of 

current continuously without harm in the event of a short. A bit of 

oversize on the wiring does no harm and helps reduce voltage drop at the 

radio which is a separate issue but related issue when powering a 

device. No harm is done if the wiring will take more current than the CB 

will pass as the wire is quite adequately protected by the CB.

Jim Oke

Wpg., MB

RV-6A C-GKGZ

Kevin Horton wrote:

 	  Quote: 	

 <khorton01(at)rogers.com>

 On 24 Jun 2006, at 24:43, FLYaDIVE(at)aol.com wrote:

> Hello Group:

>

> I have searched the web without any luck ... I'm looking for the CB  

> requirements for a King KX 125, would anyone have info on this?

>

 The purpose of the CB is to protect the wire from overheating if  

 there is a short.  The purpose is not to protect the radio.  The only  

 thing the wiring can do that can hurt the radio is provide high  

 voltage if the alternator's voltage regulator fails.  You need an  

 overvoltage protection system to prevent this.  A CB cannot stop high  

 voltage, as a CB is triggered based on excessive current, not  

 excessive voltage.

 The size of CB depends you need depends on the size of the wire.   

 What size wire provides power to the radio?

 Kevin Horton         RV-8 (finishing kit)

 Ottawa, Canada

 http://www.kilohotel.com/rv8

 http://www.matronics.com/Navigator?AeroElectric-List

 http://wiki.matronics.com

FLYaDIVE(at)aol.com
Guest

Posted: Sat Jun 24, 2006 12:08 pm Post subject: CB Size requirements?

In a message dated 6/24/06 12:42:13 PM Eastern Daylight Time, wjoke(at)shaw.ca 

writes:



 	  Quote: 	
		   Typically a 50% extra capacity is added 

  to deal with power surges as the transmit cycle begins so if 5 amps 

  needed - use 7.5 amps, etc.

  

  The manufacturers are reluctant to widely advertise the installation 

  details of their equipment perhaps to encourage buyers to hire the 

  dealers who sell the stuff to do the installation as well thus sending a 

  bit of business their way. So that's why the power supply specs are less 

  than readily available. The KX-125 specs seem to suggest a 5 watt 

  transmitter (RF) power output. Most radios in this range will do fine 

  with a 10 amp CB so, failing anything else, try that size of CB. This 

  means sizing the wiring so that it is big enough to pass that amount of 

  current continuously without harm in the event of a short. A bit of 

  oversize on the wiring does no harm and helps reduce voltage drop at the 

  radio which is a separate issue but related issue when powering a 

  device. No harm is done if the wiring will take more current than the CB 

  will pass as the wire is quite adequately protected by the CB.

  

  Jim Oke

  Wpg., MB

  RV-6A C-GKGZ

=================================
	


Jim:



Thank you for a very realistic answer.  I should have phrased my question 

better ... "What is the current draw of a King KX 125?"



I found that the current draw on a Garmin GNC 250 XL is rated at 5.5 Amps 

during transmit.  Of course that also has a moving map and its additional current 

draw.  If I subtract 0.5 Amps for the GPS and moving map that leaves me with 

5.0 Amps. Taking that with a 50% safety margin that puts me right at 7.5 Amps 

..   Good size for a CB.

GOOD SUGGESTION Jim.  



I wired the feed to the Radio Buss with 12 AWG and the Buss itself with 14 

AWG so I have ample capacity. 



Now here is a follow up question.  I don't have much experience with radar, 

but the Xponder only requires a 5 AMP CB; yet the power output of the unit is 

250 Watts.  How come such a low CB?

I'm taking a WAG here, does it have to do with the Duty Cycle of the 

transmission?  



Thanks again Jim,



Barry

"Chop'd Liver"

jcorner(at)shaw.ca
Guest

Posted: Sat Jun 24, 2006 3:19 pm Post subject: CB Size requirements?

I too will soon be installing a KX 125 and was able to purchase an  

installation manual

from AC Spruce.



The manual recommends a 10 amp fuse as deduced below, and shows a max  

transmit

power consumption of 6 amps.



It also recommends power wiring to be 2 #18 AWG wires to the circuit  

breaker

and also 2 #18 wires to ground.  What would be the advantage of this  

over the 12 and 14 AWG

being installed by Barry?  More resistance to breakage or is there  

another reason?



Jim Corner



Kitfox 5 under construction.

Kitfox 2 flying



On Jun 24, 2006, at 2:04 PM, FLYaDIVE(at)aol.com wrote:



 	  Quote: 	
		   



 In a message dated 6/24/06 12:42:13 PM Eastern Daylight Time,  

 wjoke(at)shaw.ca

 writes:



> Typically a 50% extra capacity is added

>  to deal with power surges as the transmit cycle begins so if 5 amps

>  needed - use 7.5 amps, etc.

>

>  The manufacturers are reluctant to widely advertise the installation

>  details of their equipment perhaps to encourage buyers to hire the

>  dealers who sell the stuff to do the installation as well thus  

> sending a

>  bit of business their way. So that's why the power supply specs  

> are less

>  than readily available. The KX-125 specs seem to suggest a 5 watt

>  transmitter (RF) power output. Most radios in this range will do  

> fine

>  with a 10 amp CB so, failing anything else, try that size of CB.  

> This

>  means sizing the wiring so that it is big enough to pass that  

> amount of

>  current continuously without harm in the event of a short. A bit of

>  oversize on the wiring does no harm and helps reduce voltage drop  

> at the

>  radio which is a separate issue but related issue when powering a

>  device. No harm is done if the wiring will take more current than  

> the CB

>  will pass as the wire is quite adequately protected by the CB.

>

>  Jim Oke

>  Wpg., MB

>  RV-6A C-GKGZ

 =================================

 Jim:



 Thank you for a very realistic answer.  I should have phrased my  

 question

 better ... "What is the current draw of a King KX 125?"



 I found that the current draw on a Garmin GNC 250 XL is rated at  

 5.5 Amps

 during transmit.  Of course that also has a moving map and its  

 additional current

 draw.  If I subtract 0.5 Amps for the GPS and moving map that  

 leaves me with

 5.0 Amps. Taking that with a 50% safety margin that puts me right  

 at 7.5 Amps

 ...   Good size for a CB.

 GOOD SUGGESTION Jim.



 I wired the feed to the Radio Buss with 12 AWG and the Buss itself  

 with 14

 AWG so I have ample capacity.



 Now here is a follow up question.  I don't have much experience  

 with radar,

 but the Xponder only requires a 5 AMP CB; yet the power output of  

 the unit is

 250 Watts.  How come such a low CB?

 I'm taking a WAG here, does it have to do with the Duty Cycle of the

 transmission?



 Thanks again Jim,



 Barry

 "Chop'd Liver"

FLYaDIVE(at)aol.com
Guest

Posted: Sun Jun 25, 2006 3:52 am Post subject: CB Size requirements?

In a message dated 6/24/06 7:21:48 PM Eastern Daylight Time, jcorner(at)shaw.ca 

writes:



 	  Quote: 	
		   I too will soon be installing a KX 125 and was able to purchase an  

  installation manual from AC Spruce.

  

  The manual recommends a 10 amp fuse as deduced below, and shows a max  

  transmit power consumption of 6 amps.

  

  It also recommends power wiring to be 2 #18 AWG wires to the circuit  

  breaker  and also 2 #18 wires to ground.  What would be the advantage of 

this  
	


 	  Quote: 	
		    over the 12 and 14 AWG being installed by Barry?  More resistance to 

breakage or is there another reason?
	


 	  Quote: 	
		    

  Jim Corner

===================================
	


JIm:



Thanks for the post.  



This install manual, is it by King or ACS?  I would have to really question 

that manual.  I do not see ANY advantage of using two 18 AWG wires running in 

parallel.  Maybe it was done for ease of routing and soldering to connectors?  

Yes, there is the current carrying capacity but there is also the extra work, 

extra weight, extra points to fail ... Now when talking failure points, what 

are the possibilities of wire harness failure?  Pretty low even on GA aircraft. 

 Maybe the double runs are for future use?  I tend to do double runs for 

further expansion.  I also will go up one size for expansion or where a voltage 

drop might be a problem; such as in alternator and ACU systems.



18 AWG = 10 Amps

16 AWG = 15 Amps

14 AWG = 20 Amps

12 AWG = 30 Amps



This circuit/PROBLEM I'm working on was built by someone else.  They used 

POP-RIVITS to attach wires to CB'ers.  They also tied ALL radios [Xponder, 2 Coms 

and Audio Panel] to one 10 AMP CB-Switch.  I'm just breaking each item out 

with their own wiring and CB. 



Barry

"Chop'd Liver"

klehman(at)albedo.net
Guest

Posted: Sun Jun 25, 2006 6:03 am Post subject: CB Size requirements?

My icomm also has two pins for power (and two for ground) and calls for 

those two #18 wires. I assume  it is for two reasons. An attempt to 

provide some tolerance for bad pins or dirty connections with a separate 

wire for each pin... Not more failure points but rather a bit of 

redundancy since either wire will carry the load. The first thing that 

an avionics tech seems to do is to remove and then reseat the unit to 

see if anything changes. So why aren't all pins doubled - my guess is 

that the dual power wires help distribute the current between the pins 

also for an increase in reliability. With one wire to two pins, the 

current would tend to mostly go through the pin with the lowest resistance.

Ken

FLYaDIVE(at)aol.com wrote:

 	  Quote: 	

In a message dated 6/24/06 7:21:48 PM Eastern Daylight Time, jcorner(at)shaw.ca 

writes:

>I too will soon be installing a KX 125 and was able to purchase an  

> installation manual from AC Spruce.

> 

> The manual recommends a 10 amp fuse as deduced below, and shows a max  

> transmit power consumption of 6 amps.

> 

> It also recommends power wiring to be 2 #18 AWG wires to the circuit  

> breaker  and also 2 #18 wires to ground.  What would be the advantage of 

>    

>

this  

> over the 12 and 14 AWG being installed by Barry?  More resistance to 

>    

>

breakage or is there another reason?

> 

> Jim Corner

>    

>

===================================

JIm:

Thanks for the post.  

This install manual, is it by King or ACS?  I would have to really question 

that manual.  I do not see ANY advantage of using two 18 AWG wires running in 

parallel.  Maybe it was done for ease of routing and soldering to connectors?  

Yes, there is the current carrying capacity but there is also the extra work, 

extra weight, extra points to fail ... Now when talking failure points, what 

are the possibilities of wire harness failure?  Pretty low even on GA aircraft. 

 Maybe the double runs are for future use?  I tend to do double runs for 

further expansion.  I also will go up one size for expansion or where a voltage 

drop might be a problem; such as in alternator and ACU systems.

18 AWG = 10 Amps

16 AWG = 15 Amps

14 AWG = 20 Amps

12 AWG = 30 Amps

This circuit/PROBLEM I'm working on was built by someone else.  They used 

POP-RIVITS to attach wires to CB'ers.  They also tied ALL radios [Xponder, 2 Coms 

and Audio Panel] to one 10 AMP CB-Switch.  I'm just breaking each item out 

with their own wiring and CB. 

Barry

"Chop'd Liver"

jcorner(at)shaw.ca
Guest

Posted: Sun Jun 25, 2006 7:23 am Post subject: CB Size requirements?

The manual is by Allied Signal  Bendix/King

The drawing shows 13.75 volts to pin 1 and pin A which are tied  

together.

Also ground pins 4,5,19 and Z are tied together.

Jim

On Jun 25, 2006, at 5:44 AM, FLYaDIVE(at)aol.com wrote:

 	  Quote: 	

 In a message dated 6/24/06 7:21:48 PM Eastern Daylight Time,  

 jcorner(at)shaw.ca

 writes:

> I too will soon be installing a KX 125 and was able to purchase an

>  installation manual from AC Spruce.

>

>  The manual recommends a 10 amp fuse as deduced below, and shows a  

> max

>  transmit power consumption of 6 amps.

>

>  It also recommends power wiring to be 2 #18 AWG wires to the circuit

>  breaker  and also 2 #18 wires to ground.  What would be the  

> advantage of

 this

>  over the 12 and 14 AWG being installed by Barry?  More resistance to

 breakage or is there another reason?

>

>  Jim Corner

 ===================================

 JIm:

 Thanks for the post.

 This install manual, is it by King or ACS?  I would have to really  

 question

 that manual.  I do not see ANY advantage of using two 18 AWG wires  

 running in

 parallel.  Maybe it was done for ease of routing and soldering to  

 connectors?

 Yes, there is the current carrying capacity but there is also the  

 extra work,

 extra weight, extra points to fail ... Now when talking failure  

 points, what

 are the possibilities of wire harness failure?  Pretty low even on  

 GA aircraft.

  Maybe the double runs are for future use?  I tend to do double  

 runs for

 further expansion.  I also will go up one size for expansion or  

 where a voltage

 drop might be a problem; such as in alternator and ACU systems.

 18 AWG = 10 Amps

 16 AWG = 15 Amps

 14 AWG = 20 Amps

 12 AWG = 30 Amps

 This circuit/PROBLEM I'm working on was built by someone else.   

 They used

 POP-RIVITS to attach wires to CB'ers.  They also tied ALL radios  

 [Xponder, 2 Coms

 and Audio Panel] to one 10 AMP CB-Switch.  I'm just breaking each  

 item out

 with their own wiring and CB.

 Barry

 "Chop'd Liver"

FLYaDIVE(at)aol.com
Guest

Posted: Sun Jun 25, 2006 7:38 am Post subject: CB Size requirements?

In a message dated 6/25/06 10:07:48 AM Eastern Daylight Time, 

klehman(at)albedo.net writes:



 	  Quote: 	
		   My icomm also has two pins for power (and two for ground) and calls for 

  those two #18 wires.

=====================
	


One of the questions that has to be addressed is: What kind of connector does 

the radio have?  Many of the OLD NARCO style radios used edge-card 

connectors.  The pin size was quite large compared to the size of the pins on the DB-9, 

DB-25, DB-26 or larger computer type connectors of today. So, it does make 

better sense to run two wires to two pins sets.



Barry

"Chop'd Liver"

wjoke(at)shaw.ca
Guest

Posted: Sun Jun 25, 2006 1:55 pm Post subject: CB Size requirements?

I cannot say for sure for a KX125, but some members of the King 

equipment line use an edge connector which slides onto a  main circuit 

board. I have been told the thin copper foil on a typical circuit board 

is marginal to take the full supply current at a single point of contact 

and so provision is made to transfer the power through two pins of the 

edge connector. This is to enhance reliability over the long term by 

avoiding "burning" the PC land.



The circuit diagrams will show two pins "bridged" together for this 

purpose. Same thing applies for the ground as the same amount of current 

has to "return" though the ground eventually. Whether a single large 

conductor (connected to two pins) or a pair of small wires (each going 

to one pin) is used is as much a matter of manufacturing and 

installation convenience as anything else.



Jim Oke

Wpg., MB

RV-6A C-GKGZ



Jim Corner wrote:



 	  Quote: 	
		   



 I too will soon be installing a KX 125 and was able to purchase an  

 installation manual

 from AC Spruce.



 The manual recommends a 10 amp fuse as deduced below, and shows a max  

 transmit

 power consumption of 6 amps.



 It also recommends power wiring to be 2 #18 AWG wires to the circuit  

 breaker

 and also 2 #18 wires to ground.  What would be the advantage of this  

 over the 12 and 14 AWG

 being installed by Barry?  More resistance to breakage or is there  

 another reason?



 Jim Corner



 Kitfox 5 under construction.

 Kitfox 2 flying

europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Sun Jun 25, 2006 5:29 pm Post subject: Re: CB Size requirements?

 	  FLYaDIVE(at)aol.com wrote: 	
		  Now here is a follow up question.  I don't have much experience with radar, but the Xponder only requires a 5 AMP CB; yet the power output of the unit is 250 Watts.  How come such a low CB?

I'm taking a WAG here, does it have to do with the Duty Cycle of the transmission? 	


Yes, the duty cycle of the 21 microsecond pulse train, which depends upon the number of on bits sent.  And then figure the number of pulse trains in our reply, a function of distance and parameters of ATC's ATCRBS interrogator, like sweep speed, interrogation rate, and antenna design.  Finally, the average number of interrogations we reply to, so the number of ATC sites within range, and volume of TCAS planes lately talking to us.  I reckon a mere 100mA worst case might come out of all the math.  Can't be much, as the capacitor which stores the typical 1500V so we can put out peak power of 250W+ when an on bit is sent isn't very big.  The do have a warning sticker saying don't touch the wire part of that puppy so you don't have a Homer Simpson moment.



Fred F.

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