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05-04-2008, 08:16 AM
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Join Date: Oct 2006
Location: Gilbertville, Iowa
Posts: 8
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Lightspeed Ignition Wiring
I am building a 9A and trying to wire the power to the dual Lightspeeds for my O-320. The manual says to connect the supplied power cable to a breaker and directly to the battery. The power cable is a shielded cable with the center conductor going to the positive side and the shield going to the negative side of the battery. My question is about the length of unprotected cable from the battery through the firewall to the breaker. After the breaker is protected. Before the breaker is not. How have others done this?
mdud
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05-04-2008, 12:29 PM
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Join Date: Jan 2005
Posts: 4,285
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Don't worry its pretty easy
Quote:
Originally Posted by mdud
wire the power to the dual Lightspeeds. The manual says to connect the supplied power cable to a breaker and directly to the battery.
The power cable is a shielded cable with the center conductor going to the positive side and the shield going to the negative side of the battery. My question is about the length of unprotected cable from the battery through the firewall to the breaker. After the breaker is protected. Before the breaker is not. How have others done this?  mdud
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The short answer is you don't have to leave the center conductor (POS) unshielded except for an inch at the very end. Don't worry.
This is how to do it. Peal back the insulation and shield only an inch and than splice in a wire to run the ground to where you need. This way you have max shield.
=====================---(+)
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...................................(-)
Here is what it will look like.
http://www.aeroelectric.com/articles...l/pigtail.html
You will solder and wire wrap a pigtail onto the shield for the ground. Of course heat shrink it all. This will minimize the center conductor from being unshielded, BUT it probably is worry for nothing. The ground does not need to be shielded of course. This is a good clean way to do it from a wiring / installation standpoint.
Also be sure to support and strain relief the POS wire. It will not do any good to have a fancy shield if the POS wire breaks off at the battery lug. Those two wires are as important as your wing spar and crankshaft to staying in the air. Of course you'll route two separate independant power lines in parallel. However having physical separation is key idea. I'd power one from the battery side of the master relay and one on the battery, again two physically separate positions. To run one power feed from the battery to power dual LS ignitions is a bad idea. Frankly, one FEED from the battery BUSS is OK, as long as ONE is direct to the battery. Make all connections as high quality as possible, stout, robust and protected. Done right you'll have a lifetime worry free installation.
Also consider a SMALL AUX BATTERY to drive one ignition as Klaus shows. I have plans for dual LS and will use a small Aux battery. It will add an independant power supply and isolation.
************************************************** *****
It might help to know why your are doing this?
The reason for direct connection to the battery is its simple , bypasses the master relay and main buss. Also a direct battery feed to the LS is a safety thing. If you ever have an electrical fire, God forbid, you will turn the master off first thing. You don't want to turn the ignition off. Therefore the independent power feed direct to battery. The down side of the battery feed is you MUST turn the ignition's off along with the master after shut down.
BUT WHY SHEILD? Well it may be overkill but here are the usual reasons for a shielded wire. BTW power wires are not often shielded.
Usually shield wire is used for:
Coaxial cable for radio antenna - Radio Freq transmission is different and works at 100 Mhz for example. Your strobe and LS ignition are no where near this freq. Radios need coaxial to minimize loss and not make the FEED LINE an antenna itself.
Audio wires (mic, phone & radio) - These work on small milli volts and than go to an amplifier. It's easy to pick up RFI or EMF** in the wire and than amplify it and make audio noise. Noise does not exist unless you hear it through audio so the audio systems get shielded wires.
Light Speed Coil Feed - This is more likely to make RFI noise, so it makes sense to have a coaxial or shielded wire. If you figure the engine is at 2,700 rpm. Each cyl fires once every two rotations. Each coil double fires so the "pulse" is about 2,700 or 2.7 Khz. That is like a radio station but at a very low freq. Is it a problem, it could be so shield it. But what about the power line.
Why did Klaus spec the battery power wires to be shielded? Well you have to ask Klaus, but my opinion is the Light Speed power line MIGHT make RFI (radio freq interference) and cause noise in your radio or intercom (may be). The other reason for shield power cable is a shielded wire is more stout. You could run separate single wires for each, Pos power and negative and not have a "noise problem". The LIGHTSPEED will not care.
**RFI Noise - Radio transmission involves a form of non ionizing ElectroMagnetic Radiation (EMF). The radio spectrum is say from 100Khz to 1Ghz. Below is the sonic range and above its into the microwave, radar, infrared, visible light, UV, x-ray, gama & cosmic range. When ever some device sets up alternating current (freq) in the radio range, in a wire of proper length to resonate at that "wave length" (antenna), nearby wires also of the right length or proximity can also resonate and can pick up that RFI. Many ways to keep these accidental radio transmitters from transmitting and accidental radio receivers from receiving. One way to avoid receiving or RFI is shielding, to drain off that external EMF. Transmitting is different but the idea of EMF is the same, shielding works both ways. However weight & cost makes shielding impractical for all wires. Also not all wires or devices make or are affected by EMF.
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767
2020 Dues Paid
Last edited by gmcjetpilot : 05-04-2008 at 12:59 PM.
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05-04-2008, 12:34 PM
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Join Date: Jan 2005
Location: SoCal
Posts: 2,061
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George,
Great info, but I think the concern was about the lack of circuit protection. For what it's worth, I put an inline fuse on mine a couple of inches back from the battery connection.
__________________
Steve Zicree
Fullerton, Ca. w/beautiful 2.5 year old son 
RV-4 99% built  and sold 
Rag and tube project well under way
paid =VAF= dues through June 2013
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05-04-2008, 12:50 PM
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Join Date: Jan 2005
Posts: 4,285
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Great Idea
Quote:
Originally Posted by szicree
George,
Great info, but I think the concern was about the lack of circuit protection. For what it's worth, I put an inline fuse on mine a couple of inches back from the battery connection.
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Oh yea great idea. I struggled with that.
I mean its a hard choice. Running a HOT battery wire a good distance to a CB with out a fuse could be ugly.
On the other hand may be a fusible link might be better? Something that will not FAST blow but on the other hand will not make the wire turn into 4 feet of a glowing RED smoking snake, burning anything nearby.
They do make nice inline fuses. If going fuse I'd size as big as possible for the wire not the load. For example a 18 awg wire will "fuse" at about 83 amps, so a 20 amp fuse would work, even a little more. It would be just for a hard short. A 30 or 40 amp fuse would work. If the wire shorts dead to the battery, it will go to +1000 amps in short order and fuse will blow within a fraction of a second (before the wire got red smoaking hot).
(As a kid I did that on an old Ford car, running an unprotected hot battery wire to a car stereo. Yep, I grounded it and it was spectacular. Fortinitly the wire melted before too much damage was done or burned the car down. Look at all new cars they have a power fuse box right there next to the battery. In the old days they used fusible links. So on second thought fuses should be fine.)
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767
2020 Dues Paid
Last edited by gmcjetpilot : 05-04-2008 at 09:50 PM.
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05-04-2008, 09:16 PM
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Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,333
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Quote:
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Why did Klaus spec the battery power wires to be shielded?
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It might be as simple as mechanical protection for the conductor.
__________________
Alex Peterson
RV6A N66AP 1700+ hours
KADC, Wadena, MN
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05-05-2008, 10:24 AM
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Join Date: Jul 2005
Posts: 1,346
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Quote:
Originally Posted by szicree
George,
Great info, but I think the concern was about the lack of circuit protection. For what it's worth, I put an inline fuse on mine a couple of inches back from the battery connection.
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Steve,
What kind of inline fuse / holder did you use? Some are very unreliable.
__________________
Mike W
Venice, FL
RV-6A. Mattituck TMX O-360, FP, GRT Sport EFIS, L3 Lynx NGT-9000
N164WM
N184WM reserved (RV-8)....finishing kit in progress. Titan IOX-370
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05-05-2008, 01:06 PM
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Join Date: Jan 2005
Posts: 4,285
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Bussman
Quote:
Originally Posted by fl-mike
Steve,
What kind of inline fuse / holder did you use? Some are very unreliable.
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Mike I am not Steve nor did I play Steve on TV or stay at Holiday Inn. The BussMan brand makes very nice in-line fuse with that use a STC type blade fuse. They have Mini, Std and Maxi that goes up to almost like 50 amps. Just do the Google. The ones I am thinking have two short pig tails you splice in and the holder is heavy duty rubber/plastic with a cool cap attached. I am NOT talking about the big ANL fuse and fuse holders some people attach to their firewall, also made by Bussman (and others). You could go that way as well.
This is what I am talking about, take your pick.
http://www.bussmann.com/6/BladeFusesandAccessories.html
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767
2020 Dues Paid
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05-05-2008, 08:37 PM
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Join Date: Feb 2006
Posts: 81
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Fusible link data point
A fusible link has worked good so far for my single lightspeed ignition (flying 200 hrs and 2 1/2 years). It's located right at the hot side of the master relay. I emailed Bob Knuckles a few years ago on this issue and this was his advice. Fusible links are supposed to be very reliable.
Greg
__________________
Greg Grigson
Yellow Peril / RV-6A SOLD
Albuquerque, New Mexico
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05-05-2008, 10:10 PM
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Join Date: Oct 2006
Location: Gilbertville, Iowa
Posts: 8
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Fusible Links
Quote:
Originally Posted by Grigson
A fusible link has worked good so far for my single lightspeed ignition (flying 200 hrs and 2 1/2 years). It's located right at the hot side of the master relay. I emailed Bob Knuckles a few years ago on this issue and this was his advice. Fusible links are supposed to be very reliable.
Greg
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Thanks for all the good suggestions. Many good points made and I will get some type of fusing for the power leads just for my peace of mind. With the ground shield protecting the inner conductor it may not be necessary but I can't see any problem with being extra careful. I am thinking that the fusable links are the most likely choice for me. Thanks again.
mdud
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05-06-2008, 05:44 PM
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Join Date: Jan 2005
Posts: 4,285
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Fusible links
I like a fusible link but what is it. (For those that don't know.)
Fusible link is like a fuse but non-replaceable easily. You can buy them ready made and compact in auto stores. They are basically a sacrificial part of a wire the melts, one time. If it does melt down you need to splice in a new fusible link. These where common on cars in the 70's. You can tell by looking at wires off the battery, there is a thick barrel part an inch or two long. Now most cars use fuse boxes adjacent to the battery, no fusible links.
Bob has a home grown DIY fusible link, which is really a sacrificial length of smaller gage wire that will melt and burn if overloaded. To protect that RED HOT GLOW WIRE in the event of a short, you wrap it in fiberglass sleeve. Seems like a lot of effort when commercial fusible links are still around. Most car part stores have them.
In line fuse holder are very common now and the ATC blade fuse reliable. In the class tube says the fuse was may be a little more delicate. To recommend a fusible link is it doesn't rely on two contacts to hold the fuse in place.
The choice is yours. A fusible link application is a "OH NO", don't think it will ever fuse and don't want it to deal. Of course replacing a fusible link is harder but than again its something that should never fuse. Fusible links come in all shapes and sizes and types, but like a fuse its something made to melt and OPEN the circuit. Personally most fusible links have gone to what is really a fuse or slow blow fuse. My idea is just oversize the fuse greatly, 50%-75% more of the wires max capacity. (Max is well over its max continuous.)
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767
2020 Dues Paid
Last edited by gmcjetpilot : 05-06-2008 at 05:51 PM.
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