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Recommended wire gauge for battery

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alec(at)alecmyers.com
Guest

Posted: Tue Jan 15, 2019 5:17 am Post subject: Recommended wire gauge for battery

Here is a question about what gauge of wire the list would recommend for extending a battery installation on an aircraft.



Parameters are that a 24V battery needs to move from behind the baggage compartment to the firewall, for balance purposes.

The aircraft has a Lycoming O320 engine. The battery is 24V 11AH and rated at cold cranking amperage 200A. It needs to move about 5’ from its present position.



I can re-site the ground terminal (to the airframe) to the new location, but I’m unwilling to move the battery and starter contactors, as an alternative I’d prefer to run a heavy 24V wire back to the original battery position where the contactors are.



My certification engineer says he’s willing to sign off the extended unswitched and unfused power line as long as it’s properly grometted through the firewall etc. 



What gauge of wire should I be considering?



Anything other considerations I’m missing?

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art(at)zemon.name
Guest

Posted: Tue Jan 15, 2019 6:11 am Post subject: Recommended wire gauge for battery

Alec,

I do understand wanting to keep the contactors in their existing positions, aft of the baggage compartment. It is a paperwork hassle to move them. Even still, I would reconsider that decision. You need BIG wire to carry the current for the starter. In my airplane with an IO-360 and the battery on the firewall, I used 4 and 6 gauge wire in the circuit from the battery through the contactors to the starter. I'll bet that you already have something BIG running from the contactor to the starter and you would want something at least that large to run from the battery's new location back to the contactor.

    -- Art Z.

On Tue, Jan 15, 2019 at 7:33 AM Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>

 

 Here is a question about what gauge of wire the list would recommend for extending a battery installation on an aircraft.

 

 Parameters are that a 24V battery needs to move from behind the baggage compartment to the firewall, for balance purposes.

 The aircraft has a Lycoming O320 engine. The battery is 24V 11AH and rated at cold cranking amperage 200A. It needs to move about 5’ from its present position.

 

 I can re-site the ground terminal (to the airframe) to the new location, but I’m unwilling to move the battery and starter contactors, as an alternative I’d prefer to run a heavy 24V wire back to the original battery position where the contactors are.

 

 My certification engineer says he’s willing to sign off the extended unswitched and unfused power line as long as it’s properly grometted through the firewall etc. 

 

 What gauge of wire should I be considering?

 

 Anything other considerations I’m missing? 	


-- 

https://CheerfulCurmudgeon.com/"Be kind, for everyone you meet is fighting a hard battle."

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Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Tue Jan 15, 2019 6:43 am Post subject: Recommended wire gauge for battery

If I understand correctly, you currently have battery box with master 

contactor and the starter contactor both behind the baggage compartment.

That implies you are running a heavy cable for the starter and a 

somewhat smaller cable for the main aircraft bus, both from behind the 

baggage compartment. I don't understand why the starter contactor wasn't 

placed on the firewall to begin with, but okay.

Presumably anything in the tail cone that is powered is getting power 

from bus on the instrument panel. I don't see any advantage of keeping 

the contactors in their current location. You can use existing wire, 

just shortening the cable to what is needed from the battery box on the 

firewall. No new cable needed, just cutting and crimping new connectors 

on existing cable. Only other wires to move are the master switch wire 

and the ignition switch wire, again just making them shorter.

While you could do the calculations to the W&B for the battery move, you 

would be better off just re-weighing the plane.



O

 	  Quote: 	
		   On Tue, Jan 15, 2019 at 7:33 AM Alec Myers <alec(at)alecmyers.com 

 <mailto:alec(at)alecmyers.com>> wrote:

 

     

     <alec(at)alecmyers.com <mailto:alec(at)alecmyers.com>>

 

     Here is a question about what gauge of wire the list would recommend

     for extending a battery installation on an aircraft.

 

     Parameters are that a 24V battery needs to move from behind the

     baggage compartment to the firewall, for balance purposes.

     The aircraft has a Lycoming O320 engine. The battery is 24V 11AH and

     rated at cold cranking amperage 200A. It needs to move about 5’ from

     its present position.

 

     I can re-site the ground terminal (to the airframe) to the new

     location, but I’m unwilling to move the battery and starter

     contactors, as an alternative I’d prefer to run a heavy 24V wire

     back to the original battery position where the contactors are.

 

     My certification engineer says he’s willing to sign off the extended

     unswitched and unfused power line as long as it’s properly grometted

     through the firewall etc.

 

     What gauge of wire should I be considering?

 

     Anything other considerations I’m missing?

 

 

 -- 

 https://CheerfulCurmudgeon.com/

 

 /"Be kind, for everyone you meet is fighting a hard battle."/

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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

user9253

Joined: 28 Mar 2008
Posts: 1923
Location: Riley TWP Michigan

Posted: Tue Jan 15, 2019 7:26 am Post subject: Re: Recommended wire gauge for battery

The engine is on the front of the airplane, correct?  As others have said, it is

best to move the contactors forward near the battery.  Weight will be less and 

safety will be increased.  What is the reason for not moving the contactors, no 

room, more work, regulator?

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_________________
Joe Gores

alec(at)alecmyers.com
Guest

Posted: Tue Jan 15, 2019 2:30 pm Post subject: Recommended wire gauge for battery

I miswrote, and in fact the starter contactor is already on the firewall. 



So I would have to move the battery contactor only, but that’s not trivial in this airplane. Also I would have to keep or install a heavy cable from the external power relay back to the battery - the external power relay, connector (through the fuselage side) and external power control relay are all colocated behind the baggage compartment.



I was really wondering what gauge of wire people use for a 24v starter...

On Jan 15, 2019, at 10:26, user9253 <fransew(at)gmail.com> wrote:






The engine is on the front of the airplane, correct?  As others have said, it is

best to move the contactors forward near the battery.  Weight will be less and 

safety will be increased.  What is the reason for not moving the contactors, no 

room, more work, regulator?



--------

Joe Gores





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=486988#486988

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Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Wed Jan 16, 2019 6:38 am Post subject: Recommended wire gauge for battery

OK, nothing wrong with having a single heavy lead back to your remote 

power. The Master solenoid/contactor still should be as close as 

possible to the battery. Your starter wire is not going to change. The 

only wire you need to add is from the battery to the starter relay. You 

can leave the existing wire from the battery and connect it to the 

external power relay.

Typically 24/28V wire can be one or two number sizes smaller than 14V 

wire for same current. That would likely put you at #4 or #6.



On 1/15/2019 3:29 PM, Alec Myers wrote:

 	  Quote: 	
		   

 

 I miswrote, and in fact the starter contactor is already on the firewall.

 

 So I would have to move the battery contactor only, but that’s not trivial in this airplane. Also I would have to keep or install a heavy cable from the external power relay back to the battery - the external power relay, connector (through the fuselage side) and external power control relay are all colocated behind the baggage compartment.

 

 I was really wondering what gauge of wire people use for a 24v starter...

 

 

 On Jan 15, 2019, at 10:26, user9253 <fransew(at)gmail.com> wrote:

 

 

 

 The engine is on the front of the airplane, correct?  As others have said, it is

 best to move the contactors forward near the battery.  Weight will be less and

 safety will be increased.  What is the reason for not moving the contactors, no

 room, more work, regulator?

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=486988#486988

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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

ceengland7(at)gmail.com
Guest

Posted: Wed Jan 16, 2019 8:18 am Post subject: Recommended wire gauge for battery

Kelly said something important: The Master solenoid/contactor still 

should be as close as possible to the battery.



Is your inspector ok with having the battery's 'fat' wire running 

unprotected all the way from firewall to the back of the a/c?



I know it's frustrating to get answers that aren't answers to your 

question, but sometimes that's needed.



Charlie



On 1/16/2019 8:36 AM, Kelly McMullen wrote:

 	  Quote: 	
		   

 <kellym(at)aviating.com>



 OK, nothing wrong with having a single heavy lead back to your remote 

 power. The Master solenoid/contactor still should be as close as 

 possible to the battery. Your starter wire is not going to change. The 

 only wire you need to add is from the battery to the starter relay. 

 You can leave the existing wire from the battery and connect it to the 

 external power relay.

 Typically 24/28V wire can be one or two number sizes smaller than 14V 

 wire for same current. That would likely put you at #4 or #6.



 On 1/15/2019 3:29 PM, Alec Myers wrote:

> 

>

> I miswrote, and in fact the starter contactor is already on the 

> firewall.

>

> So I would have to move the battery contactor only, but that’s not 

> trivial in this airplane. Also I would have to keep or install a 

> heavy cable from the external power relay back to the battery - the 

> external power relay, connector (through the fuselage side) and 

> external power control relay are all colocated behind the baggage 

> compartment.

>

> I was really wondering what gauge of wire people use for a 24v 

> starter...

> On Jan 15, 2019, at 10:26, user9253 <fransew(at)gmail.com> wrote:

>

> 

>

> The engine is on the front of the airplane, correct?  As others have 

> said, it is

> best to move the contactors forward near the battery.  Weight will be 

> less and

> safety will be increased.  What is the reason for not moving the 

> contactors, no

> room, more work, regulator?

>

> --------

> Joe Gores


	




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alec(at)alecmyers.com
Guest

Posted: Thu Jan 17, 2019 7:06 am Post subject: Recommended wire gauge for battery

On closer examination, I don’t have to add any fat wires if I do move the battery contactor along with the battery. The heavy cable that currently (no pun intended) provides power forward to the engine compartment (and starter) will now be the heavy cable that feeds power from the external power connector. So it’s less work.

There are just two wires I need to add through the firewall:

1. The battery contactor coil current, which goes from the contactor coil low side in series through the external power control relay (at the old battery location), a diode and then forward to the battery master switch. 

2. Permanent power to the hour meter

On Jan 16, 2019, at 11:20 AM, Charlie England <ceengland7(at)gmail.com> wrote:

Kelly said something important: The Master solenoid/contactor still should be as close as possible to the battery.

Is your inspector ok with having the battery's 'fat' wire running unprotected all the way from firewall to the back of the a/c?

I know it's frustrating to get answers that aren't answers to your question, but sometimes that's needed.

Charlie

On 1/16/2019 8:36 AM, Kelly McMullen wrote:

 	  Quote: 	

 OK, nothing wrong with having a single heavy lead back to your remote power. The Master solenoid/contactor still should be as close as possible to the battery. Your starter wire is not going to change. The only wire you need to add is from the battery to the starter relay. You can leave the existing wire from the battery and connect it to the external power relay.

 Typically 24/28V wire can be one or two number sizes smaller than 14V wire for same current. That would likely put you at #4 or #6.

 On 1/15/2019 3:29 PM, Alec Myers wrote:

> 

> 

> I miswrote, and in fact the starter contactor is already on the firewall.

> 

> So I would have to move the battery contactor only, but that’s not trivial in this airplane. Also I would have to keep or install a heavy cable from the external power relay back to the battery - the external power relay, connector (through the fuselage side) and external power control relay are all colocated behind the baggage compartment.

> 

> I was really wondering what gauge of wire people use for a 24v starter...

> 

> 

> On Jan 15, 2019, at 10:26, user9253 <fransew(at)gmail.com> wrote:

> 

> 

> 

> The engine is on the front of the airplane, correct?  As others have said, it is

> best to move the contactors forward near the battery.  Weight will be less and

> safety will be increased.  What is the reason for not moving the contactors, no

> room, more work, regulator?

> 

> --------

> Joe Gores

---

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