Reasons for weak generator

How to keep the Cessna 170 flying and airworthy.

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Jim Collins
Posts: 68
Joined: Tue Oct 17, 2017 1:34 pm

Reasons for weak generator

Post by Jim Collins »

Hi All,

Question for the group. My generator seams to have always been weak as noted by my amp meter. The other night it went out completely when under the load of the lights and stuff. In trouble shooting, I found the regulator had burned out and I think I might know why it burned out. I replaced the regulator and noted the generator is now working but only at a few amps (instead of the 35 amps it should be at higher RPMs). I looked up what I could on this message board and learned to re-magnetize the generator magnets which I did but no help. I then learned to jump the generator by grounding the field line to force the generator into full power, this was also no help as the generator would still only put out a few amps So I think the reason the regulator burned out might be because it was forced to operate at full field current for who knows how long and it just could not take it ( the PCB inside the regulator is burned up and I tried to contact the vendor and get a schematic but they will not talk to me).

Anyway, does anybody have a theory as to why the generator is now weak?? I'll be looking for possible resistance someplace it is not supposed to be (like power and field line cables) but otherwise I am looking for ideas.

Thanks
Jim Collins C170B N2488D
Hineywheel Bill
Posts: 93
Joined: Fri Feb 17, 2006 8:55 pm

Re: Reasons for weak generator

Post by Hineywheel Bill »

Have you checked the brushes?
Owner of:
1954 C170B N1921C S/N 26066
Former owner of:
1948 C170 N3815V
1951 C170A N1490D
1946 C140 N76447
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Jim Collins
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Re: Reasons for weak generator

Post by Jim Collins »

Not yet, that is a good suspect
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Joe Moilanen
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Joined: Sun Dec 28, 2003 5:45 am

Re: Reasons for weak generator

Post by Joe Moilanen »

Generator brushes.... if you are handy you can replace them without even taking the cowling off. There is a band clamp on the rear of the generator and with some ingenuity you can replace the brushes by laying on your back with your head on a stool and using all of the patience that you can muster.... happens about every 1000 hours...

Joe
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daedaluscan
Posts: 497
Joined: Fri Apr 20, 2012 7:03 pm

Re: Reasons for weak generator

Post by daedaluscan »

I was going through a lot of brushes - about every 75 hours or so. I think my commutator was out of true or rough and eating them. When I had the motor off last year I took it to a local generator shop and he told me that only two of the armature coils were working. I got a rebuilt generator and was amazed at the increase in output. I also have a Zeftronics regulator which gives me charge at a lower RPM.
Charlie

1956 170B C-GDRG #27019
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GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Reasons for weak generator

Post by GAHorn »

Jim Collins wrote:Hi All,

Question for the group. My generator seams to have always been weak as noted by my amp meter. The other night it went out completely when under the load of the lights and stuff. In trouble shooting, I found the regulator had burned out and I think I might know why it burned out. I replaced the regulator and noted the generator is now working but only at a few amps (instead of the 35 amps it should be at higher RPMs). I looked up what I could on this message board and learned to re-magnetize the generator magnets which I did but no help. I then learned to jump the generator by grounding the field line to force the generator into full power, this was also no help as the generator would still only put out a few amps So I think the reason the regulator burned out might be because it was forced to operate at full field current for who knows how long and it just could not take it ( the PCB inside the regulator is burned up and I tried to contact the vendor and get a schematic but they will not talk to me).

Anyway, does anybody have a theory as to why the generator is now weak?? I'll be looking for possible resistance someplace it is not supposed to be (like power and field line cables) but otherwise I am looking for ideas.

Thanks
Jim Collins C170B N2488D
Jim, have you read the generator/regulator section of the Electrical System Service Manual? You can download it as a Member from this website.

The generator does not have "magnets" that need re-magnetising. Perhaps you meant "polarizing"? But if it was putting out any at all... then that's not the problem. Brushes wear out between 700-1000 hours under normal conditions, IMO. Half-life (length) of brushes is 500 hours in my personal ACTUAL observation and that's when I replace them, but it's a good idea to send your generator in for complete service at/before 1K hours. Aero Tech of Louisville will do it for you for $100 (for operating gens that have not completely failed) was their offer to Members at the Bardstown convention. That's a bargain.

But, if you grounded your gen field terminal and the gen did not provide full output... that test tells you exactly what your problem is... the generator...

Exactly WHICH MODEL generator do you have according to it's DATAPLATE? And also, WHICH regulator according to it's PN?
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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MoonlightVFR
Posts: 624
Joined: Sun Jan 02, 2005 5:55 pm

Re: Reasons for weak generator

Post by MoonlightVFR »

We are contending with circuitry of a 65 year old machine.
As you are experiencing you may end up throwing money at supposed "solution" and you don't really receive the fix you want.

Try this five dollar solution. 1950's ground was one simple ground strap.
First test - R Front of engine there is a really small mealy tiny ground strap Jumps over rubber motor mount.

Put a short good small 10 gage jumper - test all your electrical - Do you like results? Yes ,well it is about to get better.
Do not replace tiny measly cable. You may want to soak it with cleaning solution of baking soda. Your big Starter motor is dependent on the tiny ground strap 3 Feet away.

Go to NAPCO aviation parts store. Purchase an 18 inch long (measure your install] braided ground strap (3/4" wide). Leave all original grounding straps in place. Add the new strap to Firewall right over the original. other end of new strap to rear left side engine mount. True grounding is about to change everything

Greatest benefit is faster engine start - do not accept less than 1/2 to 1 blade rotation before engine roars into power. Your heart will jump - May the Power be with you.

$5.00 Solution
gradyb, '54 B N2890C
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Jim Collins
Posts: 68
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Re: Reasons for weak generator

Post by Jim Collins »

Thanks all for the input. I am attaching phots of the field coil inside the generator. As you can see one side is all burned up. I don't know how this happend as the regulator (as I understand it) is limited to 3 amps of field current but it did happen and I suspect it has been this way the whole time since I bought the airplane (most likely a short to ground in the upper part of the coil). I am also including a photo of the inside of the regulator that also burned up. I suspect the generator fault slowly took the regulator with it. Anyway the generator is being rebuilt by a overhaul house in northern Illinois that was highly recommended.

P.S. I am not sure how this attaching photos stuff works on this site, so I may have done it wrong
Attachments
Regulator.JPG
Generator2.jpeg
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GAHorn
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Re: Reasons for weak generator

Post by GAHorn »

Field coils are insulated from the generator case with fiber sheet and sprayed with an electrically-insulating coating, but vibration can wear through those insulators and short out a field coil. The individual wires within the coil are painted with shellac and baked before insulation to discourage electrons from taking "short-cuts" across the coils, and that too can fail, leading to localized overheating, warping of the coils, and shorts. It's a forensic study to try to determine what caused the failure pictured, but it's also rare, but possible, a foreign object was sucked into the generator and impinged upon the coil damaging it. This is why brush covers should be installed, and blast-tubes should be protected by screen.

Thanks for the pics, I know everyone will enjoy seeing them, even if none of us like seeing it happen to anyone. :wink:
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Jim Collins
Posts: 68
Joined: Tue Oct 17, 2017 1:34 pm

Re: Reasons for weak generator

Post by Jim Collins »

George,
I work with electronics and have seen winding's fail but your right, it is rare. I like the particle getting in and damaging things theory. Putting a screen on the breather pipe is a good idea
Thanks
Jim Collins N2488D
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