Another generator question

[jetguy]

In the process of "upgrading" the '55 to a 35A generator (note to alternator guys: please, no boos or hisses.....my airplane's just not sexy enough to be sporting anything that fancy). Somewhere on the forum, I've found reference to the addition of a blast tube but can't locate any 'official' documentation in any of the Cessna publications. Should be easy enough though to fabricate something (George?), but why go to the trouble of inventing a retrofit if there's already an acceptable way of doing it in the first place. Suggestions? Also, at the risk of opening a can of worms, I gotta ask about wiring. AC 43.13-1B and other publications notwithstanding, the IPC itself only references #10AWG (vs. #8) for the main feeds....does that mean Cessna was comfortable using the smaller gauge wire with the 'optional' 35A generator? And speaking of which, I also see a reference in the IPC for a "25A generator kit", but no mention of a "35A gen. kit" even though listed, along with I believe a 12A gen., in the TCDS. ?????
Lastly, amongst other reasons, I yanked the 20A generator mainly because there's no 20A option listed in the TCDS. Overall, I'm good with that decision, but I'd feel a little silly if there actually exists some sort of approval for a 20A installation and I somehow missed it.
Let the comments begin!

P.S. George, my condolences on your family's loss...

[n2582d]

Hi Greg,
I've added AK 172-6A to the Maintenance Library. Hope it helps!

[pdb]

No need to apologize for the generator. Alternators have a lot going for them, not the least of which are weight and reliability but the first time you leave your master on and come back to find a totally dead battery, you may appreciate your decision.

My O-300 is easy and safe to hand prop and once it's going and revved up a bit, the generator comes right on line providing current. That won't be happening with an alternator unless and until you can figure out how to energize the alternator's field after you have the engine started.

This may not be a big problem at many airports but in remote locations, you know you can get things up and running and have the juice to run the radio and transponder for getting home.

[GAHorn]

Thank you, Greg.

The guidance for the 35 Amp generator is sometimes confusing, but the requirements of AC43 are specific. An 8 ga wire is necessary to accommodate the maximum amperage possible, even tho' in some cases Cessna did things on the "cheap" to save weight. (There is some allowance for OEMs to depart from the rules with proper engineering support...and a perfect example is the battery cables which are invariably too small for the expected starting current. The exceptions are allowed due to the short-term use expected of them.

The problem with wiring is heat, and it's always better to plan for the worst-case scenario. I suggest you install 8 ga wire in the generator ARmature-to-regulator and regulator to main buss circuits of your airplane if you upgrade to a 35 A gen. Also, be certain to install a 35 A regulator or you're wasting your time. Of course, you will also now require a 35-40A fuse or C.B. for the generator.

Hope that helps. (See the TIC170A Electrical Systems Service Manual.)

[blueldr]

It has been mentioned on this thread about the neccessity to somehow energise the field of an alternator in the event of a completely dead battery. On my
C-170B I had installed a couple of cigarette lighter receptacles for use with my hand held GPSs. I had a small 9v dry cell battery connected to a Gig Lighter plug to excite the alternator field in an emergency.
Remember that the battery solenoid is required to be energised from the battery side to close it enabling connection to the buss. Unless that solenoid is closed, the battery will not be electrically attached to the buss and will be unable to be charged.
I believe I remember about a method of installing a jumper wire, containing a diode, around the battery solenoid ot solve this possible problem.

Gahorn,
Perhaps you can better explain what I'm talking about. I used to hand prop my old Stinson L-5, which always had a dead battery after about three days. It had a self exciting generator, but I had to jumper across the battery solenoid to get power to recharge the battery. I finally installed a posh button switch on a jumper circuit.

[pdb]

If any one knows how to energize both the alternator and generator (if required) after hand starting a plane with a dead battery so that the battery can then be recharged and power restored in the system to radios, etc, I would very much appreciate a detailed explanation.

I have hand propped my plane with a very low battery and restored power but not one that was completely dead and it would be nice to know how to do this properly.

Pete

[GAHorn]

BluEldr, I believe it to be possible if... after the engine/generator is up and running, with generator output... to power the batt-side of the relay while simultaneously grounding the relay terminal. This would require an added circuit to manually connect the gen armature output to the positive side of the batt for momentary use.

Generators are heavy but robust. Alternators are light and put out voltage at low rpm...but are not tolerant of abuse. Like all things aviation and female..... it's all a compromise.

[blueldr]

Pete Brown,
See my above comment on how to use a 9v dry cell for emergengy exciting of an alternator when the battery is completely dead. In my former C-170, the cigarette lighter receptacles were wired to the main buss. One must remember that a completely dead battery that cannot close the battery solenoid will have to be closed by some alternate means in order to charge the battery.

[jatkins]

I thought that a "dampened Crankshaft " was required for the 35 amp Gen ?
I am not certain if it is required for an alternator or not ?


John

[pdb]

BL

One must remember that a completely dead battery that cannot close the battery solenoid will have to be closed by some alternate means in order to charge the battery.

Is there some nifty field trick to do this once the engine is started, like using some "safety" wire as a jumper somewhere?

[blueldr]

Pete,

If the battery is completely dead and will not close the battery solenoid, after the engine has been sterted and the generating system is active, an electrical jump across the main terminals of the battery solenoid will do it.
When I was up in Alaska ( This was 67 yeqrs ago.) on my Stinson L-5G I installed a permanent jumper that was energized by a push button switch. The 24v battery was always dead after the third idle day and I was unable, or unwilling, to afford a new one on my master sergeants pay. (I was in the Air Force at Ladd AFB in Fauirbanks)
That airplane had a generator on the Lycoming O-435-11 engine. Because generators have residual magnetism, they are self exciting and will come on the line without external power to the field.
If the battery has enough poop left in it to hold the battery solenoid closed, there will be enough to excite the alternator field and charge the battery.

[pdb]

Thanks BL...

I think I have to talk one of my friends into trying this first to figure out how thick the wire and gloves have to be for a hand held portable jumper....

I will call FSDO tomorrow to see if they can give me any additional advice on glove material or wire gauge. . On second thought, I may go the temp mod route to avoid unnecessary paperwork and perhaps customize a bit of coat hanger instead of safety wire.

I will keep you posted.

Pete

[blueldr]

Whatinell! Almost any size or kind of wire will work for a temporary jumper. It only takes a split second for the solenoid to close the contactor points. Before I installed the permanent switched jumper, I used to use a short "U" shaped piece of #12 insulated solid copper that I kept in my flying tool kit.

[pdb]

BL....

This is great information and precisely that kind which will be lost if we (you) don't pass it on. Young guys don't have a clue.

I am out to buy some suitable 12 ga. copper wire tomorrow and will slip a suitable length in my glove compartment. If I ever make the mistake of leaving my master on and draining the battery in Kwethluk (in the middle of nowhere on the lower Kuskokwim), I will be prepared to solve the problem.

Thanks

Pete

PS: I will not be consulting with FSDO before I try this if I get stuck.

[blueldr]

Pete,

If your battery solenoid is up on the front side of your firewall, all bets are off!