SHORTRV7

SHORTRV7

Well Known Member
I am studing Bob Nuckolls AeroElectric Connection and I do not understand why he wants the wire to be 6 inchs or less to the Main Battery Buss in Figure z-11. My problem here is that I am installing circuit breakers in my panel instead of Muti-Slot auto fuse blocks and the distance is about 24 inches to where I need to build a Battery Buss (Always Hot) with circuit breakers. Do I up the wire size for the length and Amps or what? I just need some help here to proceed with my wiring.
Thanks now for all the help.
Don Short
 
6 inches

I believe this rule of thumb is to minimize the risk of sparks if something bad happens, like an off field landing.

The size of the wire should be enough to carry all the expected loads on the battery buss. There is a formula in Bob's book, and nice little table in the Van's manual that gives a good indication of the wire size to use depending on the current expected and the length of the wire.
 
SHORTRV7 said:
I am studing Bob Nuckolls AeroElectric Connection and I do not understand why he wants the wire to be 6 inchs or less to the Main Battery Buss in Figure z-11. My problem here is that I am installing circuit breakers in my panel instead of Muti-Slot auto fuse blocks and the distance is about 24 inches to where I need to build a Battery Buss (Always Hot) with circuit breakers. Do I up the wire size for the length and Amps or what? I just need some help here to proceed with my wiring.
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The reason for the recommended length is because this wire is FULLY unprotected and the longer you make it, the greater your potentially risk. You have to remember that the PRIMARY purpose of circuit protection devices (fuse or circuit breakers) is to protect the WIRE. The secondary purpose is to protect the attached device(s). Battery buss circuit protection devices are usually not on the panel but right by the battery. If you are going to bring an always hot wire back to the panel (no matter what size) and "then" put circuit protection devices after it, you might as well forgo those circuity protection devices since they are mostly useless for their primary purpose anyway. This may be stating it a little over dramatic but is still true. A short circuit of that 24" wire will just burn the wire and surrounding material with nothing to stop it.

Go ahead and install you circuit breakers, but install them *by the battery*. Ask yourself "why do these need to be on the panel" --always on devices are the last thing you want to reset or troubleshoot in the air.
 
Confused

Don,
I am not clear on what you are trying to do or maybe we are talking about different things.

Hot Battery Bus.
The ONLY thing on the HOT Battery Bus (on the airliners I flew) was the FIRE BOTTLES, because you never want to switch them off or have them inoperative because they were down stream of a failed switch or solenoid.

Everything else should be the other side of the MASTER SWITCH SOLENOID.

As we don?t normally have Fire Bottles on Rvs, the only thing that will always be live is the cable between the Battery and the MASTER SWITCH SOLENOID. (I suppose you could call that cable, the Hot Battery Bus, but there should be nothing on it, except the Master Switch Solenoid.)
That cable should be short for that reason, as stated by others.

In the event of a fire, selecting the Master Switch OFF, turns off EVERTHING in the aircraft, EXCEPT the cable between the Battery and the Master Switch Solenoid.

So on an RV I don't see why you would have a HOT Battery Bus.
(The above is an Airline Pilots perspective, not and electrical engineers.)

I can't give you an engineer?s perspective as I did not wire my RV, but paid a Pro. to do it. But I can tell you what he did; and he is a disciple of Nuckholls.
It is wired such that with the Master switch OFF, no live wires pass through the Firewall. The wire to the Master Switch is the Solenoid Earth; not the positive.

This is not my forte, so I stand ready to be shot down.

Pete.
PS. Don, ironic surname. Oop! Sorry.
hotbatterybusgd8.jpg
 
That's the way I did it, Peter. It is the way Van's shows on the electrical plans using a Continuous Duty Solenoid to power the bus and starter solenoid.

Roberta
 
fodrv7 said:
Hot Battery Bus.
The ONLY thing on the HOT Battery Bus (on the airliners I flew) was the FIRE BOTTLES, because you never want to switch them off or have them inoperative because they were down stream of a failed switch or solenoid.

Everything else should be the other side of the MASTER SWITCH SOLENOID.

In the event of a fire, selecting the Master Switch OFF, turns off EVERTHING in the aircraft, EXCEPT the cable between the Battery and the Master Switch Solenoid.
Click to expand...

It's normal to have a clock on the hot side of the master solenoid. But it needs it's own fuse, very close to it's connection.
 
Peter/Roberta,

The purpose of an "always hot" battery buss is for devices that need to be independent of the Master switch. Things such as the clock, electronic ignition, computer, etc. I'm sure even airlines have something similar as there are devices you DO NOT want to be powered off with the main *master* switch. You still want them the wires protected by a fuse or circuit breaker however.
 
Still Confused

Most drawings I have seen show a Battery Bus that in my case will provide power to P-Mags, Clock, Alternate Feed for the E-Bus, and Accessory Port. I would prefer to build a bus bar with fusses that I can get to while flying. but it looks like I should just use an Automotive fuse block with a 6 inch wire. Using it would provide me with fuses for the Clock, Alternate E-Bus feed, and the Accessory Port. But ----- The P-Mag requires a 3 amp pullable circuit breaker to test the internal support to keep the Mag working. So from the Automotive Fuse Block HOW do I install such a fuse that I can test the P-Mag preformance???
I really appriciate your resposes to this.
Don Short
 
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Hot Battery Bus

I can understand the need to have a wire for a clock, which you wish to keep running when the aircraft is hangared.
If so, I would have thought it best to have a SMALL wire- separate to the main power supply- that was ONLY large enough to carry the power for the clock. That way, if it shorted it is less likely to be drawing enough amperage to do any serious damage.
What you should be avoiding is having a LARGE wire penetrating the firewall that you can not take the power off. Otherwise you have negated your 'Firewall'.
You could also fuse it forward of the firewall to protect your clock. If the fuse blew because of a short, I am sure you could live without the clock.

I have Lightspeed igntion, which has it it's own wire, but it still comes of the Master Solenoid so I can isolate it with the Master Switch. I accept the extremely remote possibility that I could have a fire and turn off the master, loose the Lightspeed ignition and have a Magneto failure shortly after. I am willing to risk that.
As I said, I am not an Engineer, but I can't see why your power to this Fuse bus cannot come through the Master Solenoid so that you can isolate it.

The other option 9the one that I used) is to install a small drycell in the cockpit for those itemswith a switch (Avionics Master in my case) to isolate the battery.
If you are planning to install and EFIS (such as GRT) you can use it to power the EFIS during start up- as it should not be on the battery being used to start the engine.

Pete.

avionicsbatterypt9.jpg
 
robertahegy said:
That's the way I did it, Peter. It is the way Van's shows on the electrical plans using a Continuous Duty Solenoid to power the bus and starter solenoid.

Roberta
Click to expand...

Roberta,
Glad I did it the same as you; you being in the trade.
Pete.
 
How about Fuse block and circuit breaker?

Why don't you locate a fuse block next to the battery, and use it to feed a circuit breaker or plain old switch? If you're worried about the fuse blowing and taking out your p-mag, you can find automatic resetting circuit breakers that will just plug into an automotive ATC fuse block. To reset them, all you need to do is remove the load (or fault). You could probably use a 10A auto-reset circuit breaker to feed the 3A breaker in the cockpit.

I suppose another option would be one of 'lectric Bob's fusible links located near the battery feeding a circuit breaker.

I've seen hot battery busses in Boeing products, but they are usually limited to things you really need like emergency instruments, airbrake control, and antiskid protection. Even Boeing puts the battery busses right next to the battery (aka, circuit breaker panel in the wheel well).

Paige Hoffart
RV-8A (finish kit)
 
SHORTRV7 said:
...I would prefer to build a bus bar with fusses that I can get to while flying.
Click to expand...
Don,

Again I ask the question why?

It does not matter if you use fuse or circuit breaker with a buss bar, just place them "by the battery" and then insert a switch on the panel for this device so that you "can test the P-Mag performance."

fodrv7 said:
..If so, I would have thought it best to have a SMALL wire- separate to the main power supply- that was ONLY large enough to carry the power for the clock.
Click to expand...
Peter,

Try this: Take a very SMALL 24 gauge wire and connect it to both terminals of your aircraft battery and watch it glow red hot and BURN itself and the surrounding material. A bigger wire will take a little more time and current but will still BURN if left unprotected by a fuse or circuit breaker.

Again, standard practice for the battery buss is to place the circuit protection devices BY THE BATTERY -which means on the engine side of the firewall or behind the rear bulkhead- and then install whatever switches on the panel or wherever to control such devices if necessary.

fodrv7 said:
I have Lightspeed igntion, which has it it's own wire, but it still comes of the Master Solenoid so I can isolate it with the Master Switch. I accept the extremely remote possibility that I could have a fire and turn off the master, loose the Lightspeed ignition and have a Magneto failure shortly after. I am willing to risk that.
Click to expand...
It is good that you recognize the limitation of this configuration. Wouldn't fly in the certified FAR 23 world as you have now placed reliance of your engine ignition on your single electrical system.

http://wcurtis.nerv10.com/90Electrical/RV10Electrical_v3a.pdf
 
w1curtis said:
Don,
Peter,

Try this: Take a very SMALL 24 gauge wire and connect it to both terminals of your aircraft battery and watch it glow red hot and BURN itself and the surrounding material. A bigger wire will take a little more time and current but will still BURN if left unprotected by a fuse or circuit breaker.

QUOTE]
William,
As I said I stand to be corrected. I realise they will both burn. I have seen it and was observing how much heat is generated by a melting #1.
But I stand corrected, for I should have stuck with warning against any unprotected wire through the firewall.

Pete
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This thread has got me thinking, since I have been planning on an always-hot battery bus with the fuse block on the cabin side of the firewall. I don't think simply moving the fuse block to the other side will do, as those plastic fuse blocks don't seem like they would tolerate being inside the engine compartment. So, how about an ANL current limiter in the always hot bus feed line, as close to the battery as possible? Obviously you'd still have individual (smaller) fuses on each circuit, but the big ANL limiter would help protect against fire in the event of a massive short circuit. Of course the tradeoff would be added complexity, and another potential failure point.

mcb
 
How to wire

w1curtis said:
Don,

It is good that you recognize the limitation of this configuration. Wouldn't fly in the certified FAR 23 world as you have now placed reliance of your engine ignition on your single electrical system.

http://wcurtis.nerv10.com/90Electrical/RV10Electrical_v3a.pdf
Click to expand...
Willaim,
The way Jake wired my System is , I believe, how Lightspeed required it to be done. That is a separate power supply from the Master Solenoid via it's own Switch (which is a CB S/w).
Day VFR acceptable risk to me.
Pete.
 
I'm just a machine operator.

w1curtis said:
Please don't take this the wrong way but, just curious; what trade is that?
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Roberta lists herself as Transformer and Bushing Tester. That makes her a lot more informed than I.
I have only ever been a machine operator trying to understand how the machine works.

And she built a superb RV.

Pete.
 
My background is 17 years in the automotive and heavy equipment repair and testing for We Energies (SE WI Electric Utility), 11 years Nuclear QA Technician, 9 years Substation Electrician Transformer, Bushing and Breaker Tester. I work with everything from flashlight batteries, DC systems to 125 V and AC to 345KV. I have an Associates Degree in Electronics and Fluid Power. I was a Certified Welder and Welding Inspector (AWS), Certified Lead Auditor in ASME, ISO 9000, and 10 CFR 50 Append. "B" (Nuclear QA). I was Certified Level II in MT PT UT and Level I Radiographic Interpretation.

I've been around and I know there are more ways to kill a cat than kiss it to death. :)

Thanks for the compliment, Pete. Your Plane is also Superb!

Roberta
 
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