Generator intermittent

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Generator intermittent

Postby Jtramo » Mon Feb 04, 2019 8:33 pm

Replaced my generator last month. It worked out of the box but the amps were swinging wildly occasionally. I replaced the regulator and it now seems to work perfectly until about 1 minute after takeoff. I got it back online momentarily by reducing power to idle. Then it died off again. It’s either at 0 or with a negative 5 or so reading with a load on it.

This condition doesn’t seem be listed in the electoral guide. It’s the fact that it works on the ground perfectly that’s got me. Thought maybe at high RPM it’s spiking or physically overheating and dropping off as a result. Or a wire is arching or grounding at high RPM.

It’s a 25 amp unit with the proper regulator for its amperage.
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Re: Generator intermittent

Postby gahorn » Mon Feb 04, 2019 8:38 pm

Jtramo wrote:Replaced my generator last month. It worked out of the box but the amps were swinging wildly occasionally. I replaced the regulator and it now seems to work perfectly until about 1 minute after takeoff. I got it back online momentarily by reducing power to idle. Then it died off again. It’s either at 0 or with a negative 5 or so reading with a load on it.

This condition doesn’t seem be listed in the electoral guide. It’s the fact that it works on the ground perfectly that’s got me. Thought maybe at high RPM it’s spiking or physically overheating and dropping off as a result. Or a wire is arching or grounding at high RPM.

It’s a 25 amp unit with the proper regulator for its amperage.


If it had wildly-swinging Amps right out of the box... it already had a problem. Sounds like an internal short or intermittent terminal connection or commutator issue (bouncing brushes). Who/What/Where did you obtain it? Does it have a warranty? Is it new/rebuilt or used/as-is? What was the reason you replaced the generator to begin with? Were the amps crazy/swinging previously?
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Re: Generator intermittent

Postby Jtramo » Mon Feb 04, 2019 9:18 pm

Came from Aerotec and I’m assuming it has a warranty. My log shows the old one was replaced under warranty as well (years ago) so I guess aerotech is potentially a “second times the charm” rebuilder. I replaced the old one because it was not functioning and there were pieces of it strewn about inside. To say it “Grenaded” inside would be accurate.
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Re: Generator intermittent

Postby Hineywheel Bill » Mon Feb 04, 2019 9:53 pm

It would be worth checking the Master Switch. It is a double pole single throw switch, one set of contacts is for the master (battery) relay and the other set is for the generator. If you have intermittent contact or high resistance through the contacts it will definitely cause problems.
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Re: Generator intermittent

Postby Jtramo » Mon Feb 04, 2019 10:00 pm

I’ll check that as well Bill thanks!
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Re: Generator intermittent

Postby Bruce Fenstermacher » Tue Feb 05, 2019 3:03 am

I was going to say, check your master switch. It is probably bad. You could for testing purpose, bypass or Jump the switch taking it out of the equation Be careful if you do.
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Re: Generator intermittent

Postby hilltop170 » Tue Feb 05, 2019 3:42 am

My C180 electrical system was doing strange things for months and it finally boiled down to the 50amp generator breaker. Replaced the breaker, all is good again.

Took old breaker apart and there is no obvious defect and it operates as-designed, just doesn’t work like it should. My guess is it was not set-up correctly causing malfunction during service. But then again, I’m no electrician so who knows?

A7F30595-B7E6-45EC-848B-77F0C6C33FB4.jpeg
Breaker closed


E71886A8-636F-4B5E-86E3-27E38F78FA69.jpeg
Breaker open
Last edited by hilltop170 on Sun Feb 10, 2019 4:48 am, edited 1 time in total.
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Re: Generator intermittent

Postby gahorn » Wed Feb 06, 2019 2:41 pm

Jtramo wrote:Came from Aerotec and I’m assuming it has a warranty. My log shows the old one was replaced under warranty as well (years ago) so I guess aerotech is potentially a “second times the charm” rebuilder. I replaced the old one because it was not functioning and there were pieces of it strewn about inside. To say it “Grenaded” inside would be accurate.


Can we be more specific please? There are at least three companies in aviation parts/repair that use similar names and I've had varying results from callers searching for help.
The company which supports us best in this area IMO is Aerotech of Louisville http://www.aerotechlou.com/ (This is not "Aerotek" "Aero-Tech" "Aerotec" or "Aero-tech".
The owner visited us at our Bardstown convention and made an excellent presentation on starters, generators, alternators and such and also offered generous rebuilding discounts to our Members. (John may have retired since, and there are rumors the company is joining-hands with certain other suppliers/CRS outfits, but their reputation has always been excellent when it comes to the original generators.)
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Re: Generator intermittent

Postby Jtramo » Wed Feb 06, 2019 11:32 pm

Well I didn’t get it from an aviation staffing company in New Jersey, a motion control device company for the military nor did my 1940s tractor generator come from a big jet winglet/major mod shop. I’m pretty sure you know exactly where I got it even with my autocorrect typo hahaha!!

It came from the land of Looey and they think it got hot and “threw a lead” for unknown reasons pretty much right outta the box. I’ve got to pull it again and send it back. This is starting to add up in labor and oil (not covered by the warranty) so maybe they can offer the association discount if it turns out it needs repairs not covered by warranty due to it being a regulator issue or some other odd reason. I didn’t know about it prior to today!
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Re: Generator intermittent

Postby MoonlightVFR » Fri Feb 08, 2019 10:53 pm

I went through YEARS of an intermittent electrical anomaly in 54 C170B s.n. 26433

It was the Master Switch.

The switch can be simply repaired.

Orig mfg of MS is gone, the problem is a few of the riveted studs are slightly loose. When new they were tight enough, however through the years when some A/P was under the dash the Nest of wires gets shoved around and loosens a riveted stud. Vibration in flight brings on the problem not while on ground.

How TO: remove M S after flagging each connection. Set MS in big vise. individually check each stud for loosened.

Carefully bend up tangs that hold aluminum switch body to bakelite board. Set riveted contact on steel anvil and using a punch and small ball peen . Gently re tighten Each electric stud. Small series of gently taps.
I have purchased Cessna Master Switch off Ebay it had same defect in same stud!

Factory riveting equipment can get out of adjustment and poor parts get installed in new equipment.

Suggest buying used M.S. practice on it.
gradyb, '54 B N2890C
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Re: Generator intermittent

Postby gahorn » Sat Feb 09, 2019 3:17 pm

Grady is giving good guidance on this. My gen was not charging one flight and I wiggled the master and it came online. Returning home, I disassembled it per Grady and cleaned the contacts, lubed it with a touch of grease, and 15 years later is still working fine.

Here is only one example of how automotive switches can substitute. (It's true that automotive quality items were used on our airplanes in many areas.) These switches have been used to replace faulty landing/taxi light switches and others in members airplanes. It controls two circuits of course.
While it is not original, it is an example of how things can be "made to work". NAPA and some electronics suppliers can be suppliers of these types of switches.

https://www.napaonline.com/en/search?te ... rm-allprod
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Re: Generator intermittent

Postby ghostflyer » Sun Feb 10, 2019 1:50 am

We just ordered and received a switch from Cessna for a client exactly the same as the 6390 part no.from Napa BUT just put a one in front of the Napa price . I am blown away. Plus the cost of shipping another $70.
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Re: Generator intermittent

Postby Jtramo » Sun Feb 10, 2019 3:16 am

Awesome guys thanks. I think I’ll try this before I go pulling and sending generators back. The symptoms and the visible overheating (albeit mild at first glance) evidence from spiking are there though so I’m not sure that this is the case with mine. I think the old regulator was arching or something along those lines. The new regulator seems to hold steady amps better but only until about a minute after takeoff. This makes sense for some form of heat damage and subsequent arching only at WOT. I’m thinking about setting up a go pro inside the engine bay for a WOT run with the generator inspection cover band removed to watch for arching/sparking from the commutator area.
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Push-Pull Master Switch

Postby n2582d » Mon Feb 11, 2019 6:10 am

gahorn wrote:... Here is only one example of how automotive switches can substitute. (It's true that automotive quality items were used on our airplanes in many areas.) These switches have been used to replace faulty landing/taxi light switches and others in members airplanes. It controls two circuits of course.
While it is not original, it is an example of how things can be "made to work". NAPA and some electronics suppliers can be suppliers of these types of switches.

https://www.napaonline.com/en/search?te ... rm-allprod
George, Not sure if you had a specific push/pull switch from the NAPA website that you were recommending? I can only find one that had four terminals: ECH SW83. But it is a three position—OFF-ON-ON—switch designed to select running or anchor lights for boats. What we need to replace the master switch is a double pole, single throw (DPST) switch.

The push-pull master switch on the later 170B’s is p/n 0713026-5 (fig. 42a-28 & fig. 42b-24). Google the part number and you’ll see on the image that it was manufactured by Cole. (You’ll also find NOS switches readably available,but pricey). The Association of Fleet Maintenance Supervisors, Inc. gives this brief history of Cole:
The Henry Cole Company of Boston was founded in 1914, as a manufacturer of lamp sockets and other equipment. The F.C. Her- see Company was an old-established machine shop. Leo Mayer purchased the Henry Cole Company in 1924 and the F.C. Her- see Company in 1935, the name of these two old Boston busi- nesses was changed to Cole Hersee Company in 1941 and has been synonymous with high quality automotive electrical products.

Don and Steve Mayer are the third generation of the Mayer family to manage this privately-held, family-owned business. Don started working for the family business during the summers and vacations, holding every position, from the mail room, shipping and receiving to accounting and engineering. He started full time in 1987 and became the Vice President, responsible for sales, finance, marketing, communications and corporate strategy.

Chicago based, Littelfuse, purchased Cole Hersee Company in December, 2010.
Don continues today as a Business Consultant for Littelfuse, he is based in South Boston.
Now knowing that Littelfuse is the company that purchased Cole Hersee it’s a matter of looking in their catalog for a 4 terminal double pole single throw (DPST) switch. The result is Cole Hersee p/n 50047-01. It’s available online for under $30. Unfortunately, the chrome knob is part of the shaft rather than screwed on. So, digging a little deeper, I find that by dropping the “-01” from the part number, I.e. p/n 50047, you get the same switch with a plastic ivory colored knob which screws on a 10-32 shaft.
56713D46-F2B7-442B-B8E8-52E2A43DBF0B.jpeg
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Re: Generator intermittent

Postby lowNslow » Mon Feb 11, 2019 4:01 pm

Gary, I found this same info a while back but could never find a new 50047 switch for sale anywhere, there were several places to buy the 50047-1. Have you found these for sale anywhere other then the used ones on eBay?
Last edited by lowNslow on Mon Feb 11, 2019 6:52 pm, edited 1 time in total.
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