confused about wires....

blueflyer · #1 06-29-2012, 05:04 AM

My question here only concerns the alternator and associated wiring of it and the switch. I understand the 12GA shielded wire is being protected by the 35A circuit breaker. But then, another 5A circuit breaker is used to run the wire from the power bar to the alternator switch. So, should I have 2 alternator related breakers on my panel?? No doubt, I'm confused.

Walt · #2 06-29-2012, 05:57 AM

I would suggest you obtain/read some of the Aeroelectric articles/manual, and use one of their diagrams as a basis for wiring your aircraft.

But to answer your question, the 35a bkr protects the alt 'B' lead and the 5a bkr is to protect/control the alt field circuit. (BTW I've never seen a shielded 'B' lead).

Captain_John · #3 06-29-2012, 05:58 AM

BF, That is the first time I have seen that diagram.I would say that it is good. Where did you find it?

Anyways, in answer to your question... yes. You may locate another overcurrent protection device on your panel for each circuit. I think the diagram is hinting towards a combined "Cessna style" Master/Alt Field type switch and for the 35amp "Bat" (12ga) wire I would use a B and C Specialties current limiter mounted on the front of the firewall.

While you are on the B and C site, click on the resources tab on the left hand side and review the Z13 diagram. It is quite similar to your diagram but more detailed.

In addition, PERSONALLY, I would make the 12 gauge wire larger. 35 amps is a fair amount of juice for a #12 conductor.

My 2!

CJ

Captain_John · #4 06-29-2012, 06:02 AM

Quote:

Originally Posted by Walt

I would suggest you obtain/read some of the Aeroelectric articles/manual, and use one of their diagrams as a basis for wiring your aircraft.

But to answer your question, the 35a bkr protects the alt 'B' lead and the 5a bkr is to protect/control the alt field circuit. (BTW I've never seen a shielded 'B' lead).

...and Walt, YES! I was going to say that too.

A) Get Aerolectric and,

B) The shield can't hurt, but why? You really don't need it.

CJ

jdeas · #5 06-29-2012, 07:44 AM

I have never seen shielded wires on a modern Alt. Check out Chapter 11 of AC43.13 to gauge your wire. I see a max of around 6ft for 12v 35amp circuit.

az_gila · #6 06-29-2012, 07:59 AM

I'm guessing that picture is from one of the very early Bingelis books, and is now somewhat obsolete.

As other have mentioned, use the AeroElectric schematics as a baseline. Here is the equivalent to the one in post #1, use this to start your design with -

http://www.aeroelectric.com/PPS/Adob..._Pdfs/Z11M.pdf

SteinAir · #7 06-29-2012, 08:33 AM

I think Gil and others are right here in the fact that it appears to be a relatively outdated drawing (looks very much like a basic 60's/70's era 172 diagram)...the last shielded wire on alternator leads that I've seen is in 70's era planes - and we end up replacing them a lot. In fact, it's pretty difficult to get shielded wire in that size, most of us don't even stock it. I'd also probably suggest moving the wire size from AWG12 up to AWG10 or AWG8 in case you ever want to upgrade the alternator, you already have a larger wire (and price/weight differences are negligible). As mentioned, AWG12 is on the edge for carrying capacity. You'll also notice that the wire sizing is pretty much outdated as well if you're using modern equipment, modern LED lights, etc..

Also, we don't normally advocate running the fat wire all the way back to the panel anymore (no need). It's a noisy and heavy wire. Typically, run that big fat noisy wire from the Alt to the downstream side of the master relay, or the upstream side of the starter relay, then run a short (and usually smaller wire) from there to your main buss. It keeps the fat wire runs shorter, makes wiring simpler, and there is no need for that fat braker or ANL current limiter/fuse to be inside the cockpit. Also note that as shown in the diagram, that's an inefficient way to charge the battery (have the wire go all the way into the cockpit, across the main buss, through a jumper, then back out the firewall to the relay).

Just my 2 cents as usual.

Cheers,
Stein

aerhed · #8 06-29-2012, 08:58 AM

Quote:

Also, we don't normally advocate running the fat wire all the way back to the panel anymore (no need). It's a noisy and heavy wire.

Ah ha moment. Thanks.

blueflyer · #9 06-29-2012, 11:59 AM

yes, its an old Bingelis drawing off the EAA website. For discussions sake, you may need to know that I plan to have a 60A alternator breaker on the one and only buss bar in my panel. I (now) plan to have a 5A fuse between the alternator switch and the over voltage regultor (like in Gils linkable drawing). I plan to use one SPST switch each for master and alternator. I realize I'm way behind the power curve here, so please forgive the questions, but I think it will help me grasp this whole electric thing if I ask these questions:

1)is the sole purpose of that 35A breaker (in post #1) to protect the 12GA wire if the alternator itself malfunctions in some way that would cause this 12GA wire to overheat? what kind of alternator failure would cause this wire to overheat?

2) Is the 5A fuse protecting the wire in case the overvoltage regulator fails? if so, could I safely think of this CB as an overvoltage regulator breaker?

3) Why does Gil's drawing not have the 5A fuse located with the all the other fuses up on the panel?

4) How do people secure this 5A fuse if its in that location?

SteinAir · #10 06-29-2012, 12:22 PM

Quote:

Originally Posted by blueflyer

For discussions sake, you may need to know that I plan to have a 60A alternator breaker on the one and only buss bar in my panel.....

I'll try to answer your other questions when I get a chance, but let me re-iterate. DON'T put that big breaker on the end of the buss bar in the panel...no benefits but lots of negatives. Leave it forward of the firewall and make the battery charging circuit properly, NOT like that original drawing (which sounds like you still intend to follow as far as the main circuitry goes).

Please listen to what everyone has been telling you and IGNORE that charging circuitry in that old drawing and set it up similar to the drawing that Gil linked to and Walt referred to. You don't have to follow it exactly, but at least do the basics that way. The best way to at least get a starting grasp on this is to heed the well placed advice and pick up a copy of the aeroelectric connection book. It'd answer lots of questions and would be a good place to start, even if you don't eventually wire the plane up exactly like it. Walt knows a thing or two about 'lectrics, and we work with them regularly. Not saying our advice is law, but it's at least up to date and industry best practices.

Cheers,
Stein