Electrical Questions

Romeo Tango · Post by **Romeo Tango** » Mon Feb 16, 2004 7:32 am

Well, this weekend was under the panel with the voltmeter to finally put together a schematic for the airplane. It was pretty straightforward, with a few interesting twists.

A few questions remain, answers welcomed -

1) I could not find an obvious fuse for the cigarette lighter. Perhaps there was a fusible link in the wiring, but nothing jumped out. It's on with the master switch, but that's not protected per se.

2) Is there a replacement panel light dimmer rheostat that has an "off" position? Mine has a very low voltage at the "off end", but the lamps are still on just a bit. I'd prefer a specific "off" position to preserve lamp life. I can put in a dedicated panel switch, but a potentiometer with an "off bump" would be ideal.

3) One of my panel lights was not working, and on closer inspection I found that the grounding frame was not very secure. The other sockets were quite sturdy and provided a good ground. This balky one wobbles around a bit. It is kosher to solder the grounding portion to increase the strength? Or are there are replacements available?

4) How does the hourmeter on the tachometer get power to run the meter? A cable bundle goes into a firewall position but it was not clear which wire was what. There is an impulse coupling to get the meter to register, but the hourmeter needs some standard voltage to do it's work. Is this on the avionics bus? And should there be an inline fuse for it, too?

5) I'm thinking of replacing the fuses with circuitbreakers. Unfortunately the Klixon CBs stop at 20A and the system has two 25A fuses (the starter and the avionics). I am pretty sure the avionics would not complain (new Garmin boxes and a new TC < 15A). But the starter is unknown to me and could spike up over 20A. Any experience here is appreciated.

Thanks in advance for the assistance. I found it quite illuminating to suss out how the wiring is all set up. Especially some of the inline fuses that are under the dash and not easily replaced. Now I have a spare 3A fuse in my kit(!)

Richard

Post by **Bruce Fenstermacher** » Mon Feb 16, 2004 4:29 pm

Answer to #1 The cigar lighter was unfused from the factory and is the subject of an AD that your aircraft might not be in compliance with. Basicly you need to disable or fuse the cigar lighter. See the AD for details.

Answer to #2 Not sure if there is a reostate with an off position put you could easliy modify yours with a little dab of non-conducting paint. Haven't done this myself but if I was to do it I'd try something like nail polish. It may wear eventually but you could also remove it if you wanted.

Answer to #3 Not sure exactly what light you have by your description but you seem to think you can solder it so you must know how to solder. If so and you can, go for it.

Answer to #4 The hour meter in a tach generally runs of the tach drive itself. It will not be accurate except at one rpm which is somewhere around 2500 rpm I think.

Answer #5 Use POTTER & BRUMFIELD W31 series of circuit-breaker/switches. If you want to stick to button type breakers use POTTER & BRUMFIELD w23 series. They are cheaper and come in the sizes you need.
Klixon breakers are available in larger sizes but maybe not in the series you looked at. They are also very very expensive.

I used the W31 series myself. They are mounted in the original postions with out any modification to the A/C. I made adapter plates out of aluminum sheet mounted in front and behind the original mount plate. The adapters have the correct size hole which is smaller than the original fuse holder and I made it a little taller to cover the larger circuit breaker. For the buse bar across the top of the breakers I did as my avionics shop does and used a piece of heavy copper water pipe flattened with holes drilled as needed. I could send you a drawings and maybe dimensions of my adapter plates in a few days if you'd like.

zero.one.victor · Post by **zero.one.victor** » Mon Feb 16, 2004 5:52 pm

Looking thru my records,I believe the cigar lighter AD is AD79-08-03,but I don't have a copy of the text. It called for disconnecting the unfused cigar lighter. Mine has the cigar lighter connected with an inline fuse,don't recall the fuse amp rating,and don't know if that is really in compliance with the AD. Complies with the spirit of the law,but maybe not the letter.
As I recall,there was some discussion regarding replacement rheostats here a while ago. Maybe use the search feature to find them? When you do,please refresh our memories with what you discover.

Eric

dacker · Post by **dacker** » Mon Feb 16, 2004 7:51 pm

The thread you are talking about is under "INSTRUMENT LIGHTING" in the hangar. We discussed rheostats amongst other stuff. I soldered a continuous ground wire along my light harness per my mechanic's suggestion in order to cut out on the flicker that sometimes happens as a result of the vibration. Since my airplane is still in pieces due to all the work I have had done ($$$), I have not been able to test it out yet. I also wound up having my panel completely rewired with CBs installed, the mechanic did a much nicer job than I could have done. I was going to rewire myself using the same fuse sizes, but after really going through and looking at the circuits found that I was going to have to basically start from scratch in order to do it right (per AC 43.13). At least now I will have the peace of mind of knowing that I don't have an electrical fire hazard behind my instrument panel. Good luck!
David

doug8082a · Post by **doug8082a** » Tue Feb 17, 2004 2:05 am

Eric's got the right AD. The pertinent text is as follows:

"To prevent an inflight electrical system failure, smoke in the cockpit, and/or fire in the wire bundle behind the instrument panel, accomplish the following:

A) Disconnect the wire, at the ammeter or at the electrical system bus as applicable, that connects the bus to the cigar lighter receptacle. (The wire is connected to either the bus side or equipment side of a circuit breaker or to the ammeter.) Following the disconnection of this wire either:

1) Reconnect the wire to the electrical bus by using an existing or newly installed circuit protection device that is properly rated to protect the wire gauge used for this circuit, or

2) Disconnect the wire from the lighter receptacle at the opposite end and remove it from the airplane, or

3) Protect the wire by insulating its disconnected end, fold this wire end back against the wire bundle in which it is routed and secure it to that bundle. "

doug8082a · Post by **doug8082a** » Tue Feb 17, 2004 2:03 pm

BTW, here's the link to the AD online:

http://www.airweb.faa.gov/Regulatory_an ... t=79-08-03

Post by **GAHorn** » Thu Feb 19, 2004 1:25 am

I suggest using a small "blob" of epoxy to insulate the moveable brush from the wire-wound resistance wire on the rheostat, in order to achieve an open circuit in the lighting.

zero.one.victor · Post by **zero.one.victor** » Thu Feb 19, 2004 6:22 pm

gahorn wrote:I suggest using a small "blob" of epoxy to insulate the moveable brush from the wire-wound resistance wire on the rheostat, in order to achieve an open circuit in the lighting.

I think Bruce suggested this in the first response on this topic.
This topic comes up as more than one screen wide--I have to scroll back forth to read it. Anyone else have this trouble? What causes this? Same thin occasionally happens on other posts.
And whoever is causing it,knock it off! It's a big pain in the ###!

Eric

Dave Clark · Post by **Dave Clark** » Fri Feb 20, 2004 1:02 am

Hey Eric, it's a computer. Waddaya expect, perfection?

doug8082a · Post by **doug8082a** » Fri Feb 20, 2004 1:18 am

Sorry dude. It was probably me posting that link to the AD. Oops. Oh well, as the saying goes... "Computers do what you tell them to do, not what you want them to do".

Post by **GAHorn** » Fri Feb 20, 2004 11:02 pm

zero.one.victor wrote:
gahorn wrote:I suggest using a small "blob" of epoxy to insulate the moveable brush from the wire-wound resistance wire on the rheostat, in order to achieve an open circuit in the lighting.
I think Bruce suggested this in the first response on this topic.
This topic comes up as more than one screen wide--I have to scroll back forth to read it. Anyone else have this trouble? What causes this? Same thin occasionally happens on other posts.
And whoever is causing it,knock it off! It's a big pain in the ###!

Eric

Bruce suggested nail polish and that prompted me to recommend what I recommended last year when this subject was discussed. (See the topic "Instrument Lighting".)
I was concerned that many nail polishes are flammable and the rheostat generates heat.