Generator fuse blowing

[Bruce Fenstermacher]

(Notice that the 20 Amp generator, found on some 170's I've seen are not approved by the Type certificate. There must be some other basis of approval.)

Thanks George, you have just found yet another undocumented and apparently unapproved mod to my plane I'm sure you recall the rest which I will not elaborate here.

Joe are you sure you only have a 12 amp generator. As I recall the landing lights are 100w a piece which at 12 volt would be pulling 8.3 amp a piece or 16.6 for both. OK you don't fly around with them on all the time but I'll bet if you do a load analysis of you radios and lights at night, you are pulling more than 80% of the rated output (12amps in your case) which would be 9.6 amps. 43.13-1B para 11-33 (your IA does use this as part of his annual inspections doesn't he) says that "When electrical load calculations show that the total continuous electrical load can exceed 80% output load limits of the generator or alternator, steps must be taken to reduce the electrical load or increase the generating capacity of the charging system." Of course if you are exceeding 80% of rated capacity, according to 43.13-1b para 11-36(a), you could just placard your instrument panel to just not turn on all your equipment at the same time so you don't exceed the limit.

[N1478D]

Hi Bruce, yes, very sure that I have the 12 amp generator. Would believe that the words "total continuous" keep me out of trouble. Total continuous is near nothing. Unless I am in a high traffic environment, I usually wait till final to turn the landing lights on because the RPM is down and the battery is supplying most of the electrical power. A lot of times flying to work is before sunrise and lights, lots of class B radio talk, etc have never been a problem. The system works fine, at cruise speed the generator replaces whatever was used at low RPM. I like my 12 amp generator and regulator. If I want to fly with the landing lights on I do, but I try to be as easy on all systems as I can. Our batteries are small and low power to save weight and I think the 12 amp system matches up very well with our size battery. It might be why my batteries last so long. The plane is an easy starter, a blade or two is all it takes, so that is probably part of the formula. I have had to replace one regulator, and a 51 year old wire gave it up last year, and I have a static sound now like another is maybe shorting - but there have been well over 500 hours of trouble free flying day and night with the system. It worked well up in cold Colorado a couple of years ago too.

George, YOU calling my plane a turtle is pretty funny. How come you didn't make it to the pancake breakfast flyin this morning? Are you wanting to race? You still trying to outrun the sun with your elbow and flaps out?

We flew on over to Clark Field and had that fantastic BBQ for lunch. A couple of guys picked us up in a golf cart on our walk back to the airport. Turns out they are the BBQ judges for Texas and were flying to different places judging. Claimed as in years past, Lockhart still is ranked #1 and there at Clark is rated #7. Robert and I are not sure we could handle #1 BBQ as much as we liked #7. ha ha Anyway, those guys jumped in a low wing nosedragger - how smart could they be?

[rudymantel]

Since a larger generator places more strain on the crankshaft it of course follows that there would be a loss of power. I remember when being checked out on the Islander, the instructor pilot's engine out procedure included turning off the generator in the good engine. Not a great idea at night of course. But the engine out performance was so marginal every little bit helped...
Maybe on a 170 when taking off from those short airstrips on a hot day, turn off the electrical system ?
What is the comparable power drag for an alternator ?
Rudy

[Bruce Fenstermacher]

I'm surprised Eric. My plane has about the same equipment with one extra Collins nav com and glide slope, I have strobes and and a few extra psot lights and such on the panel. Using the manufacterers load data and a fudge factor cause I'm not keying the mic on both radios continuous. We are not including the landing lights either. My load analysis was 19.5 amps which was magically 80% of the 25 amg generator I thought I had. Of course I suspect the load is less than that but I haven,t measured it yet.

Update. Just checked a friends 170 today. Fuse and panel marking is 15 amps yet he has a 35 amp gen installed. Wiring was probably not updated hence the small fuse. Go figure. He hardly uses any electrical power and yet could have it, I need the power and don't have it.

[GAHorn]

Rudy, that's an interesting question. Perhaps (with a few mechanical losses) the answer can be found by recognizing that the 145 hp engine can also be rated in kW, which is 108 kw. So how much is a 35 or 60 amp gen/alt? Less than 1/10th of 1% of total hp?

[uturn]

Het guys I have been reading all your posts about generator issues. So I have a 170B with a 35 amp generator and a 35 amp regulator. The total draw on the system is right at that 80% drawing 28 amps with everything on. The wiring between the generator and the regulator Has been increased to 8 gauge to handle the amperage draw. Also the wire between the regulator and the buss has been increased to the same size wire. The problem I am having before the wire increase and after is excessive heat at the back of the generator fuse holder at the connection point. There is a 35 amp fuse in the holder at some point got hot enough to began to melt the solder that holds the fuse together. I have verified that the generator and the regulator are both 35 amp and with everything on the system is drawing 28 amp. Any ideas as to what can causing the heat problem.

[Bruce Fenstermacher]

A cracked solder joint. It happens.

Flying to work one day I suddenly had a stinging burning sensation on my ankle. I first thought something was stinging me and I swatted it. That's whe my hand started to burn and I realized solder had dripped on my ankle. HOLY S--- something is getting hot enough to melt solder I though and immediately shut down all electrical power til I landed.

Once on the ground inspection of the fuse connection showed the solder in the joint had all but melted away. I borrowed a large enough solder iron and resoldered the joint. For the next several flight hours I continually reached under the panel feeling for any heat. Never had another issue. My generator was a 20 amp generator putting out less than 20 amps.

28 amps continuous seems like a lot. Have you done an analysis why so much?

[GAHorn]

If your generator system was upgraded from a lower-rated system...you are correct to also change out all the wiring to 8 AWG wire. But the wire between the gen armature and regulator is only part of the wiring in that circuit.
The wire between the regulator Bat terminal to the aircraft buss must also be changed to 8 ga, as well as that which serves the fuse (which is what connects the reg to the buss, via the ammeter) which must also be changed. In other words, all the wire in the generator circuit must be of the appropriate gage for 35 amps.

Also, it's important to use the correct PHYSICAL SIZE fuses. The original holders were intended for AGS fuses and they are getting difficult to find. (Cessna dealers such as Hill Aircraft in Atlanta, Ga still has them cessnaparts.com ) The commonly-found automotive glass fuses are AGC and are too small physically for the holder, so they generate heat due to poor contact surface area.

Edit> I had a bran-phartt and forgot that McFarlane has them cheaper. See the next post.
Tribal-Knowledge is a good thing! Thanks Karl! (You can add two more eagle-feathers to your headdress!)

[lowNslow]

Mcfarlane also carries these fuses.
http://www.mcfarlane-aviation.com/Produ ... ber=4AG-10&