Generator Problems Again

Bryce · Post by **Bryce** » Tue Jul 11, 2006 4:59 pm

George
Here I am down at the airfield and it is a really lovely afternoon but I have to get this generator system working before I can enjoy.
I have just carried out the tests you wrote down in an earlier post Monday 13th June 2006

"If still no charge, then hook up a small jumper wire between your Generator field terminal [/b]and clip the other end directly to a good airframe ground. If the generator now charges, the problem lies with the regulator or ships wiring. If it doesn't charge the generator is at fault.
The Gen Field Post (this is the small one on the Gen) can remain hooked up just exactly like normal. All you should do is clip a jumper wire onto it and clip the other end of the jumper to a good airframe ground, and start the engine and see if it charges. If it does produce a charge...then your Generator is fine and healthy. This jumper wire has bypassed the master switch and regulator completely. The problem lies either in the regulator or in the aircraft wiring or cockpit master switch. Remove the jumper from aircraft ground (leaving it hooked up to the Gen FieLD terminal, and hook the other end up directly to the regulator FieLD terminal. If the system now charges...the problem lies in the ships wiring or in the cockpit master switch itself.

If it doesn't, ...If it still doesn't produce a charge, then leave one end clipped your regulator FieLD terminal and the other end of the wire to a good airframe GROUND. Run the engine at 1800 to see if the generator charges. If so, then the regulator is bad. If it doesn't then your generator is bad. "

The first test with jumper between gen field and airframe ground made the gen light extinguish at 1500 RPM.
The second test with jumper between gen field and regulator field did not get the gen light to extinguish up to 1700 RPM.
The third test with jumper between regulator field and airframe ground made the generator lamp extinguish at 1500RPM.
I have carried out a fourth test of ensuring the regulator chassis is grounded with a jumper between chassis and airframe ground but again the generator lamp would not extinguish.
I know it points to a faulty regulator but this one was only replaced two months and 20 hours previous.
If it is the regulator again can there be any thing that can cause such early failure ?
Finally is there any further test I can carry out myself on the regulator or must it be sent away to be checked.
Thanks
Bryce
[/b]

Post by **GAHorn** » Fri Jul 14, 2006 7:53 pm

This does indicate a defective regulator. There are several tests which may be made "in the field/under the shade-tree" to the regulator. Those tests are delineated in the Electrical Systems manual I wrote for the Assoc'n, and if you have a copy you might attempt them. The manual can be obtained from headquarters@cessna170.org in either hardcopy or CD format.

The reverse-current relay is adjustable and will determine when/what rpm your generator comes online, and that process is described in the manual. A simple thing to do is remove your regulator cover and examine the points of the regulator coils to see if any of them are burned/pitted. They can be cleaned/filed just like ignition points if pitted, but unless the cause of pitting/burning is corrected the defect will likely reappear. A possible fix for burning points on the middle (armature) coil is a condenser installed between the ARMature terminal and aircraft ground. Those Armature points are the most commonly found to be burned when regulators fail for that reason. This "filter" is sold at NAPA autoparts stores as a generator/ignition "noise" condenser, and is very inexpensive (a couple of dollars). Again, on the road, so my notes are not available to me, or I'd provide a part number.
You might research these forums to find an inexpensive AutoZone part number for a "ground test" only replacement regulator. They typically cost less than $35, and are virtual copies of the Delco reg. They are not "blessed" by the FAA. The part number determines the amperage of the regulator. (Never install a regulator of greater capacity/amperage than the generator. A small regulator on a large gen is OK, but never the reverse.)

wa4jr · Post by **wa4jr** » Sat Jul 15, 2006 1:52 am

Seeing the numerous references to "generator light" I just have to ask about it. I have no such light in my 1954 170B, nor any location that I can see where one was put. Is the gen warning light a modification to bring your eyes over to the amp meter

Bryce · Post by **Bryce** » Sat Jul 15, 2006 7:56 am

George
Thanks for further advice.I have managed to obtain automobile voltage regulator VR-699 from Autozone and a friend in Andover Kansas is sending it to me in the post so that we can carryout some ground tests.
I will inspect the voltage regulator today and check the contacts.
I will also contact your HQ to purchase copy of your manual.
Many Thanks
Bryce

Post by **GAHorn** » Sat Jul 15, 2006 10:24 pm

wa4jr wrote:Seeing the numerous references to "generator light" I just have to ask about it. I have no such light in my 1954 170B, nor any location that I can see where one was put. Is the gen warning light a modification to bring your eyes over to the amp meter

Some aircraft with gens did not have an ammeter and used a gen-warn lite instead....usually the early 172/175 types. It's a simple "idiot" lite that senses reverse-current relay position on the regulator..... almost useless because it's normally extinguished....which does NOT really indicate a healthy system. (If the lamp is burned out... what does that tell you?)

wa4jr · Post by **wa4jr** » Sun May 13, 2007 12:49 am

I am the most recent victim of a generator failure. Grounding the FLD does not produce a charge, nor does reflashing the ARM. I've got a unit coming from AeroTech of Louisville, but I have a question. My present generator has not held up very long, lasting less than 400 hours, and I am wondering if I should install another blast tube fitting in the rear baffle and run scat tube to the cooling air shroud on the rear of the generator. Any comments from the peanut gallery

jrenwick · Post by **jrenwick** » Sun May 13, 2007 1:45 am

Whether or not your generator needs a scat tube for cooling help depends on the amperage it's producing. If your generator and voltage regulator are both rated at 35 amps, and you have enough equipment turned on normally to use close to that much (landing lights are a big draw) then you probably need to give it cool air through a tube. 25 amps, maybe. Smaller than that, probably not, but it couldn't hurt anything to add it.

Post by **GAHorn** » Sun May 13, 2007 4:53 am

Generator brushes should be inspected annually and replaced regularly (about 300 hours is about all they're good for...but at least they're cheap and easy to do.)
I'd route cooling air to the blast tube on any size generator.

wa4jr · Post by **wa4jr** » Wed May 16, 2007 6:57 pm

Made it as far as Olive Branch MS from WV without a generator, but ran the battery down pretty low. Took my battery box cover off to once again find that my Concord RG25XC battery (that everybody says can't puke in the box) puked in my box for the third time

My next battery will be a standard flooded cell battery....that doesn't puke. Anyway I got the shop to install a new generator...at a cost of $430 plus labor

and when I got home oil was bathing the belly though a severe mounting flange leak

Regarding the SCAT tube run, I need to do that. When the mechanic opened my old generator, the brushes were in horrible shape and the commutator segments were smeared all over the mica insulation material. Victim of overheating. Problem now is finding an aluminum baffle flange to mount 7/8" SCAT tube in order to feed the cooling shroud on the generator. Everyone I call wants a part number, but I tell them that there is NO part number as this is a new installation. I guess nobody knows what a simple baffle SCAT flange is

There was never any provision for a 7/8" SCAT tube generator line on my plane...both factory blast tubes are directed to the oil filter adapter head. Does anyone have a 7/8" flange they would like to part with??? Spruce has what I need, but they only go down to 1".

Post by **GAHorn** » Wed May 16, 2007 8:10 pm

The 1" Spruce flange is what you need. And use 1" SCEET not SCAT hose. (You don't want exposed wire coils rusting and later being blown into your generator.)
I mounted the 1" flange beside my port-side blast-tube and used the blast tube and adel clamps to hold the SCEET next to it all the way down to the generator.

wa4jr · Post by **wa4jr** » Thu May 17, 2007 1:43 am

Great idea George. I've already ordered the 1" flange from Spruce as trying to find a 7/8" unit is going to be next to impossible. Never thought about SCEET tube though. Good idea. I know I always have a problem with the hoses up front feeding the heater muff and carb box rusting and then caving in. Do you use SCEET in the forward part of the cowl as well?

Post by **GAHorn** » Thu May 17, 2007 2:25 am

I use sceet whereever/whenever I need to replace scat.

Post by **GAHorn** » Thu May 17, 2007 5:16 pm

John,... if your battery is boiling over into your battery box ... (and any battery will do that if it's overcharged... Recombinant Gas/SLA or not....) then you've got voltage regulation problems. The most likely culprit is your voltage regulator, but remember... the way an aircraft voltage regulator works is by controlling the FIELD of your generator.

This brings in a few other possibilities....

1- Your regulator is failed. (Probable short to ground in the Field circuit or stuck/burned ponts ...if you have an original vibrating-points type regulator.)

2- Your generator FIELD is shorted to ground. (This can happen in several ways, but the most common is due to vibration and a short developing within the generator case....or the Field terminal insulation has failed where it exits the generator case.)

3- The wire from your Gen Field to your regulator Field terminal ... passes through one circuit of your cockpit MASTER switch. Somewhere...anywhere...along that line/circuit...there could be a short-to-ground. (Remove the terminal ends of that wire from your generator Field terminal and remove the wire terminal at your regulator Field terminal. Then with your cockpit MASTER switch ON.... check for continuty between EACH terminal to Airframe-Ground. If you observe such a short-to-ground you'll need to find and repair that.)

wa4jr · Post by **wa4jr** » Sun May 20, 2007 1:11 am

I've made a check of all those points in recent months, and seem to remember something about the AGM batteries not being recommended on generator equipped aircraft as they would tend to encourage overcharging. At any rate, I've got "pink power" installed once again in the form of a Gill G25, and also put an acid neutralizing mat at the bottom of the battery box just in case. Ran the engine today and get a regulated charge of 13.9 volts from my Zeftronics regulator.

In other news, I found out taking a short cut doesn't always get you into the air faster. When I took the new generator off to replace and reseal the mounting flange gasket...I saw no reason to take the tach drive off as well...so you guessed, I cut the gasket in two, left the tach drive in place and just replaced the generator portion of the gasket, making sure there were no overlaps up top. Bad,Bad,Bad. Somebody got the cute idea of putting a rather large hole at the top of the gen flange on the case going nowhere. I thought I could get it to seal up, but a five minute engine run proved me wrong. Moral of the story is to bite the bullet and take the tach drive housing off as well, and use the combined gasket so the "mystery hole" will seal up

Two more gasket on order. Three more days on the ground.

Post by **Bruce Fenstermacher** » Sun May 20, 2007 2:18 am

Hey John

Sorry to hear of your generator seal problems.

I wanted to point out that you have found out what George told us here on the forum probably 4 years or more ago. Your know a believer.

Don't cut the gasket.