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#91662 - 09/05/12 05:55 PM APU plug doesnt' work
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
I had a dead battery. Yesterday I thought I would jump off using the APU plug to just check out the charging system. I Put the yellow apu adator plug in connected a 2000 ahr cranking battery and got no power with the master on. (polarity was correct) I checked the plug and apparently no power is getting through the apu connection/port. Any thoughts where to look on this?

I did pull the battery and it was down to 8 volts under load so the plane battery had given up the ghost even if it isn't Haloween yet.


Edited by vettdvr (09/05/12 05:56 PM)
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Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#91675 - 09/05/12 07:42 PM Re: APU plug doesnt' work [Re: vettdvr]
Don Tedrow Offline
Gold Pilot

Registered: 07/16/10
Posts: 1996
Loc: Bastrop, TX
I don't have an APU plug, but dimly recall seeing in parts manual I think there is a fuse for the APU contactor on the firewall port side of Battery box, next to the clock fuse. Might check that.
_________________________
1972 C172L



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#91713 - 09/05/12 11:28 PM Re: APU plug doesnt' work [Re: Don Tedrow]
EdW Offline
Club Sponsor
Gold Pilot

Registered: 11/21/10
Posts: 1186
Loc: Just east of Graceland
There should be a plastic (bakelite) piece behind the plug that holds two diodes. The purpose for the diodes is to make sure you can't get a reverse polarity condition to your electrical system from the jumper system. If the diode goes bad (they will, if repeatedly exposed to polarity problems or the small piese vibrates and breaks either the diode or the connection) then no amount of power from the jumper will get to the airplane.

Have your mechanic check the diodes with a VOM.

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#91725 - 09/06/12 01:24 AM Re: APU plug doesnt' work [Re: EdW]
wrecksum Offline
SVP Public Relations
Platinum Pilot

Registered: 09/26/10
Posts: 2704
Loc: Dominican Republic
Like Ed says,

But you should first find out why the battery was discharged in the first place.
That should not happen normally anyway.
_________________________
A person without a sense of humour is like a wagon without springs.It's jolted by every pebble in the road.

Cessna 172, C172, C-172, Cessna Skyhawk fan.
www.cessna172club.com

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#91775 - 09/06/12 12:02 PM Re: APU plug doesnt' work [Re: wrecksum]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
The battery was in the plane when I bought it and wont take a bench charge. Don't know how old but white casing is faded to a yellow and looks very old. I plan to pull the cowl to install the new battery I'll take a look for fuses and take some photos. It will need oil change in another 5 or so hrs hopefully I'll have a cool apell for that and parts in hand if needed for apu. fuse??
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Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#91880 - 09/07/12 02:07 AM Re: APU plug doesnt' work [Re: vettdvr]
Nightowl Offline
Club Sponsor/Speed Demon
Gold Pilot

Registered: 02/14/10
Posts: 1826
Loc: Northwest lower Michigan
No APU plug here either, but do check at least the clock fuse, as it's also the fuse that feeds the Hobbs.

What battery are you replacing the old Gill with? DO NOT USE A SEALED GILL (imho). BTDT, and it did not go well.

John
_________________________
CP-ASEL-IA
'77 C172N, AirPlains 180 hp conversion

Our sigmap has been flown entirely using aircraft with capabilities at or below those of the C-172.


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#91884 - 09/07/12 07:03 AM Re: APU plug doesnt' work [Re: Nightowl]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
Originally Posted By: Nightowl
No APU plug here either, but do check at least the clock fuse, as it's also the fuse that feeds the Hobbs.

What battery are you replacing the old Gill with? DO NOT USE A SEALED GILL (imho). BTDT, and it did not go well.

John




How does the clock fuse affect APU? This plane has a power point for solar charger that was installed on the clock circuit. It was signed off and blessed in the records. Wonder if that has anything to do with the apu?
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#91889 - 09/07/12 08:41 AM Re: APU plug doesnt' work [Re: vettdvr]
Don Tedrow Offline
Gold Pilot

Registered: 07/16/10
Posts: 1996
Loc: Bastrop, TX
Just re-checked my parts manual. There should (I think) be two fuses on a little bracket just left of the battery box. One for clock, the other for Ground Power. There's also a separate solenoid for the APU plug on the battery box. Could be either of those two items I'd guess.
_________________________
1972 C172L



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#92003 - 09/08/12 07:38 AM Re: APU plug doesnt' work [Re: Don Tedrow]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
What does the solenoid for the apu do? make the connection to the plane buss to external power? What energizes it? Power from the fuse? Any place I can find an electrical drawing on this circuit?
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#92040 - 09/08/12 10:54 AM Re: APU plug doesnt' work [Re: vettdvr]
EdW Offline
Club Sponsor
Gold Pilot

Registered: 11/21/10
Posts: 1186
Loc: Just east of Graceland
When you look at your battery box you should see two solenoids...one on the front and one on the outboard side. The side one should have two heavy wires connected. One goes up to the external power plug and the other goes to the front solenoid. There should also be a small (18 ga) wire from a side terminal up to the power plug.

When the aircraft is in 'normal' mode, the side solenoid is relaxed and there is no voltage at the external power plug pins. Once you plug in the external battery there is voltage to the small wire, which energises the solenoid, allowing voltage through it from the external power to the main solenoid. And, hopefully, you can start that puppy up. That small wire goes from the small pin in the external power socket through a diode pack and down to the solenoid to protect against reverse polarity.

Let me have the serial number on your plane and I'll PM you a copy of the wiring diagram if I have it.

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#92064 - 09/08/12 01:22 PM Re: APU plug doesnt' work [Re: EdW]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
I put the new battery in this morning before it got way hot. I saw the two fuses on the pilot side of the battery. Ohe had a 5 amp fuse and it was blown. The other was 1A. I believe from previous post 1A is clock and 5A is the solenoid to the apu. Didn't have more time had to close up before rains. I did get the new battery all buttoned up cowl fastners repaired and test ran the engine to check the charging system. All is well and the bird ready to fly minus two broken fastners on the cowl. Parts on order.

I still want to work through the APU plug. I will be needing an oil change soon and will be installing all new plugs, change oil/filter and replacing any damaged bend/stripped cowl fastners. This will also be a great time to work the APU.

Who sells these old style glass 5 amp slow blow fuse. ??
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#92066 - 09/08/12 02:12 PM Re: APU plug doesnt' work [Re: vettdvr]
Lee T. Hargic Offline
Gold Pilot

Registered: 08/13/10
Posts: 1629
Loc: Louisville, KY
My Illustrated Parts Manual shows the as Cessna S1091-5

"The Google" leads me to these websites:

http://www.broadiesaircraft.com/shop/search.asp?lookup=S1091-5

http://www.ebay.com/itm/FUSE-CESSNA-P-N-S1091-5-QTY-3-AIRCRAFT-/180927112224

http://www.airpowerinc.com/productcart/p...p;prodid=425589

I am sure someone with more experience than I may have a better source and price.
_________________________
"A smart man learns from his mistakes. A wise man learns from the mistakes of others" -Anonymous

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#92082 - 09/08/12 03:32 PM Re: APU plug doesnt' work [Re: Lee T. Hargic]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
Thanks Kevin, I can't help but wonder. Why is the aircraft part different from normal fuse? If it is the same length? I suppose the glass could be thicker but a fuse looks like a fuse to me if it fits and correct amperage.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#92083 - 09/08/12 03:42 PM Re: APU plug doesnt' work [Re: Lee T. Hargic]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
Thanks Kevin, I can't help but wonder. Why is the aircraft part different from normal fuse? If it is the same length? I suppose the glass could be thicker but a fuse looks like a fuse to me if it fits and correct amperage.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#92087 - 09/08/12 05:06 PM Re: APU plug doesnt' work [Re: vettdvr]
Lee T. Hargic Offline
Gold Pilot

Registered: 08/13/10
Posts: 1629
Loc: Louisville, KY
Perhaps it has something to do with the PMA number and the litigious society in which we all live.
_________________________
"A smart man learns from his mistakes. A wise man learns from the mistakes of others" -Anonymous

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#92102 - 09/08/12 06:58 PM Re: APU plug doesnt' work [Re: vettdvr]
Don Tedrow Offline
Gold Pilot

Registered: 07/16/10
Posts: 1996
Loc: Bastrop, TX
Heck, the last fuses I bought at Oreilly's or NAPA, can't remember which. Surely they still stock them? There's still a few '60's muscle cars out there.
_________________________
1972 C172L



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#92128 - 09/08/12 09:58 PM Re: APU plug doesnt' work [Re: Don Tedrow]
Lee T. Hargic Offline
Gold Pilot

Registered: 08/13/10
Posts: 1629
Loc: Louisville, KY
You know it is tough for a simple minded man that uses what the IPC calls for.

"The Google" showed me this from the C-170 site:

The fuse series is AGS as apposed the automotive AGC series. Several of the local hardware stores that use to carry AGS fuses now do not. After several trips to local aircraft outlets I was able to get a few of each AGS 25, AGS 20, AGS 15, and AGS 5.
I eventually called Buss Fuse Company directly and found that many of these fuses were not in current manufacture. They are not listed in their catalog. They did however have some stock, which I ordered a minimum order of 10. None of the local dealers that are listed on their web site had any product at all or were they familiar with the AGS series of fuses.

I found that many people are using the AGC series fuses in the fuse housings requiring AGS series fuses. This does not work well. I found that sometimes the circuit goes open because the AGC's do not always make good contact inside the fuse holders.

I am sorry I do not have their web address. But little fuse is another product name for the company. I would try to contact them directly and see what you can get from them or change to circuit breakers. I also called aircraft spruce thay did not carry AGS series fuses.

Good Luck,
Jim

------------------
And then some one suggested modifying the fuse holder. The response is great, although he might get flamed here for his lack of open mindedness. After all, our members know what they are doing! wink
-------------------

from the c-170 site:

The associated illegal labor and lack of documentation this implies is a bit more than I'd be comfortable with. I realize you're a practical kind of guy and willing to take short cuts with your own airplane, Eric, but ... If one believes such a mod is a good one, then it deserves the simple matter of gaining proper approval. IMHO.
How many times has someone taken interest in an airplane offered for sale and then found that kind of garbage during a pre-buy inspection? I'm tired of seeing that kind of junk airplane.
(It would be more cost effective to simply buy the correct AGS fuses from Cessna, and would certainly be less labor.)
Fuses are: 1. Safety-of-flight items, 2. Relatively inexpensive, and 3. Available from the places many folks shop for Cessna parts.....Cessna distributors.


I love "the Google."
_________________________
"A smart man learns from his mistakes. A wise man learns from the mistakes of others" -Anonymous

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#92141 - 09/09/12 05:39 AM Re: APU plug doesnt' work [Re: Lee T. Hargic]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
Thanks for the info on the fuses. Looks like I'll be shopping for one. From my limited understanding of the circuit this fuse only has power when the external power is connected. In flight and disconnected from external power the fuse is there for the ride. This might be short sighted but $7 to $15 for ONE fuse doesn't seem to be cheap for a part that is only along for the ride. I am still looking for a fuse locally. I hate paying $7 for a part and $10 to ship.

I don't mind open discussions. All work done is properly signed off on my plane. When it is a mod the proper forms are completed.

(now where is that copper tubing?) grin
I really don't need any input on telling me to use AP for all work. Just takes up band width. My last FAA ramp check on all paperwork was 6 weeks ago all is well down to the smallest fuse on paperwork and inspection. Doesn't mean we / they didn't miss something but we all do our best.


Edited by vettdvr (09/09/12 05:44 AM)
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#92167 - 09/09/12 09:07 AM Re: APU plug doesnt' work [Re: vettdvr]
Lee T. Hargic Offline
Gold Pilot

Registered: 08/13/10
Posts: 1629
Loc: Louisville, KY
Originally Posted By: vettdvr

I really don't need any input on telling me to use AP for all work. Just takes up band width.




You are welcome. I have the IPC handy so looking up the part number is easy. Any of the Cessna parts sites are around $5 a piece.

The "input" is as cheap as the "band width." My opinion is worth what is generally paid for it. Price I charge for doing the research. Looking around the Internet, I'd say it is something that needs to be repeated often. Like the guy in the other post said, I'd hate to get to pre-buy inspection and find a tiny bunch of modifications or unapproved parts.
_________________________
"A smart man learns from his mistakes. A wise man learns from the mistakes of others" -Anonymous

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#92219 - 09/09/12 05:32 PM Re: APU plug doesnt' work [Re: Lee T. Hargic]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
Originally Posted By: KevinMcP
Originally Posted By: vettdvr

I really don't need any input on telling me to use AP for all work. Just takes up band width.




You are welcome. I have the IPC handy so looking up the part number is easy. Any of the Cessna parts sites are around $5 a piece.

The "input" is as cheap as the "band width." My opinion is worth what is generally paid for it. Price I charge for doing the research. Looking around the Internet, I'd say it is something that needs to be repeated often. Like the guy in the other post said, I'd hate to get to pre-buy inspection and find a tiny bunch of modifications or unapproved parts.


As a retired professional engineer one thing I learned early on. Get ALL the input unfiltered. Learn as much as you can then evaluate with the pros/cons gains/risk then decide. If I were stuck and had to get home as I have been many times in the past I could make it work.

Since we have gotten a tad off fuses.

In SEA we blew an engine starter on #2 engine. Could not take off on 3 due to short field. Pulled starter off engine, removed broken starter drive and then put sheet metal cover over hole. Next Herk in landed backed up to tail to our nose and went to full take off power on #2 engine. Our engine began to windmill and finally at 16% we pushed the CB in for the ignition ignitors, then at 35% throttle went from cutoff to ground idle and we had light off in the turbine. Hot day high density the blowning bird held full power and our rpm reached 50% and sorta hung. We "milked" the throttle back and forth and it began to work up in rpm. The bleed balves were open on the turbine section and around 60% or so the bleed valves closed and the engine ramped up to 100% rpm. We then took off and went home. Was that an ok FAA procedure, probably not didn't even have a ferry permit but IMO it was save and we got the plane and crew home. So for the 5A fuse I know I will find one and have lots of time to find a correct one. But I know that a 5 AM fuse will work no matter the type but to stay 'by the book' I am looking for the right one and my AP told me today where to go to find one.

The real question is" Why did the origional fuse blow?"


Edited by vettdvr (09/09/12 05:34 PM)
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#92247 - 09/09/12 09:54 PM Re: APU plug doesnt' work [Re: Lee T. Hargic]
Don Tedrow Offline
Gold Pilot

Registered: 07/16/10
Posts: 1996
Loc: Bastrop, TX
Interesting, I did not know that Cessna only used AGS fuses vs the standard automotive AGC. Also interesting that 'Spruce only sells AGC fuses and holders, and makes no mention of AGS that I found. Aircraft Supply lists a few, but not in 5 amp.

The only fuse mine has that I recall off hand is the 1 amp clock fuse. There may be one or two hiding behind the panel I haven't found yet.
_________________________
1972 C172L



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#92273 - 09/10/12 12:23 AM Re: APU plug doesnt' work [Re: Don Tedrow]
Ed M Offline
Second in Command

Registered: 08/31/10
Posts: 134
Loc: Oregon, USA
If I remember right the difference between the fuses is 1/32" bigger diameter on the Cessna fuse (9/32" vs 1/4") which lets the AGC fuse fall out of the AGS holder. Not something you want to have happen when you are inverted at night in the clouds. I changed my 150 to all circuit breakers back when field approvals were more reasonable. You might even find a mechanic who would determine that replacing a fuse with a circuit breaker is not a change to the "basic electrical system" and therefore a minor alteration.

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#92329 - 09/10/12 03:20 PM Re: APU plug doesnt' work [Re: Ed M]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
I found fuses that appear correct at Napa and radio shack. Both are slow blow varity not the fast blow versions. They look very much like the one I pulled out. I'll pull out the verniers and measure later.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#92346 - 09/10/12 05:42 PM Re: APU plug doesnt' work [Re: vettdvr]
November X-ray Offline
Club Sponsor
Gold Pilot

Registered: 08/15/10
Posts: 1589
Loc: Brookshire, Texas, USA
This is sort of like only use the right tool for the job. Of course in some circumstances, any tool that gets the job done IS the right tool!

Thanks for the info on fuses, it's good to learn!
_________________________
N. X.




www.cessna172club.com

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#92348 - 09/10/12 05:55 PM Re: APU plug doesnt' work [Re: November X-ray]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 5586
Loc: Slidell La
The real question is why did the fuse fail, is there another problem? Guess I'll install the fuse and check it out and if it blows will have to look further.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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