Generator activation RPM?

[Bruce Fenstermacher]

After a long engine rebuild I've finally run up my engine. Among several problems I need to address is that the generator doesn't come on line tile the engine reaches about 1600 rpm. This is probably the way it alway was I just doen't remember.

Is this the right rpm range or can and should I adjust it lower in the voltage regulator (old style regulator).

[C170BDan]

That is about where mine kicks in (1500/1600). So taxing out for take-off with all my radios and lights on is not good. When I get to the runup area I useally turn it all on and run the rpm up to that range.

Blue Skies,

[N1277D]

I would adjust the regulator so that the the generator cut in voltage is equilivant to the static battery voltage.

[n3833v]

After I start, I run up to start generator and after that I am fine as long as I don't idle.
John

[GAHorn]

While the Service Manual does not specify a cut-in rpm, my own 1101878 35A generator (Delco-Remy/Electrodelta regulator) cuts-in at 1200 rpm and by 1400 rpm will support 25 AMPs. By 1600 it supports 30 AMPs. Electronic voltage regulators by Zeftronics claim cut in rpms around 900-1000.
A weak field (or damaged field circuit wiring) can cause increased rpm requirements. Check all connections and grounds, including master switch connections/resistance.

[Doug Echelberger]

I concur, just installed the Zeftronics regulator and it “cuts in” at about 1000 rpm. The old regulator “cut in” was 1200+.

Doug

[Bruce Fenstermacher]

Well the generator is out for a closer inspection. Seems it won't produce any appreciable energy till nearly 2000 eng. RPM. We disassembled the generator and inspected it. Armature was checked with a grawler and also the commutator was checked for continuity and found OK. We then turned the commutator and under cut the mica just to make things really nice. The brushes are very healthy as well as the brush spring pressure.
The field windings don't have a short to ground and since we don't have any info what the ohms of each winding should be we checked it against another auto Delco Remy generator an athoughno the same it was close. Put it all back together and tested it on a test bench and still no juice till we reached about 3600 RPM which would be the equivalent of about 1800 engine RPM. Way to high.
We are going to talk to a local auto electronics shop oner (an old timer sort of) to see what he thinks. (he also happens to be an A&P). As George pointed out we probably have a weak field. Does any body have any more informatin about the Delco Remy 25 amp generator other than what is found in the Continental 0-300 overhaul manual for the 12 amp. unit.

[GAHorn]

Try grounding the field terminal to the case and run it up to see if it's the generator and not the regulator. (Grounding the Field terminal...the small one on the gen...takes the regulator out of the circuit. A healthy generator should charge up a storm by 1600 engine rpm and be full output by 2000 rpm.)

[Bruce Fenstermacher]

Yes thats the way they are supposed to act George. Not so in this case which is why we removed it from the aircraft.

We have grounded the field and polarized this generator so many times in the past few days I've lost count

At less than 3000 generator RPM (about 1500 eng RPM) the generator does nothing even full fielded (grounded).

I'll let you al know what the local auto electric shop says.

[Bruce Fenstermacher]

An update

A further check on the bench shows this 25 amp generator starts to produce electricity between 1400 and 1600 engine rpm(erpm) or 2850 and 3250 generator rpm(grpm). Slower than that it is dead. These readings with the field grounded.
Over 3250 grpm it starts to produce over 12 volts and by 3660 grpm (1800 erpm) its abotu 13.5 volts at about 25 amps with a load on and from tests in the plane I know that at about 5300 grpm (2600 erpm) it will do about 14.5 volts.

We took it to a local auto generator expert thinking that it should produce some electricity or more thain it is at a lower rpm. He put it on his test bench and took some readings and said that it was working fine and that all of the readings where within the level he'd expect from a car generator of similiar make and design. He also said he new of no way other than modifying the generator to get it to produce more electricity at a lower rpm.

We went back to our test bench and confirmed our earliar readings. We then installed the 20 amp generator I'd removed to see how that compared. Sure enough the 20 amp generator made 13.5 volts at 2850grmp (1400erpm). My 25 amp generator is just along for the ride at this rpm.

So here is the question for anyone who is flying a 25 amp generator. How does your generator act. Similiar to mine rmp/power output wise or is it better in that it will produce electricity at a lower rpm.

[GAHorn]

Bruce, I'm suspicious that your 25A generator has had some parts substitutions at some point in it's life. Has this gen always behaved as you've described?
As you know, this is not correct and your substitution of a different gen proves the problem lies within the 25A gen, not your reg or aircraft.
It make me believe that either there's been a substitution of parts with non-specified parts, or an internal break in the armature windings (no or low continuity until high rpm and centrifugal force makes the windings contact each other and provide continuity) or your field windings are shorting internally...not to the case necessarily...but across their loops and providing a weak field.
I suggest you send it to AeroTech in Louisville and ask them to bench-check and correct it. (Or simply exhange it. This is a time you might consider the 35A version if you don't mind buying a regulator and have a dampened (not dampered) crank.)

[Bruce Fenstermacher]

Well George after trying unsuccessfully to find a 25 amp generator through the association and then all the vendors who deal in generators in trade-a-plane I bought this one from your favorate online auction E**** (dare I type the word). I was told 25 amp generators are hard to come by and was assured by at least one of the vendors I called that a 25 amp core was worth more than I eventually paid for the generator and the regulator. I figured I couldn't loose.

I have an undampened crank so the 25 amp generator is all I can do and I must install at least 25 amps to clear up some dark areas of previously installed equipment paperwork(i don't have enough rated capacity with my good 20 amp for the equipment thats installed)

As we don't have another 25 amp generator to compare to this one so we don't know if it has the right parts. We also don't have the data sheets to check the fields to see if they are correct and unshorted. We only know that the local car expert thought they where right. The armature has continueity on all of the commutator poles when it is static and has been checked with a grawler. I may end up sending the unit out but I'm trying to save some bucks. . Besides the expertise/knowledge to identify the parts as being right for this generator I do have access to all the tools to repair the generator myself.

If I could find out what the resistance of the fields should be and the rated voltage and amperage at a specific rpm for the 25 amp generator that would be a big help.

BTW as I said in one of my posts the generator does eventually produce enough voltage and amperage.

George, off the top of your head do you know if the alternator STCs require the dampened crank? I'm not anyhere near able to afford that conversion but if I have to back up ten and punt, it be nice to know there is a touch down play.

[GAHorn]

That's a good question, Bruce! By the time alternators came out ALL the aircraft already had counterweighted (dampened) cranks so I'm not aware of that issue being addressed.
The problem with undampened cranks is a 4th order vibration that causes stess cracks and leads to crank failure when those cranks are loaded up on their aft ends (like with a 35A gen load). My guess is that although the STC's don't address the issue and it may be legal due to paperwork oversight in some cases...it may not be prudent. But that's only my guess.
Here's an idea: Call Aerotech and ask them the specific data for the Generator in question. Also call over to Hazotronics (Zeftronics) in Longview, TX. The electrical engineer there is pretty sharp (but be prepared....he's got a difficult accent being from Nigeria. He's a grad of Le Tourneau Univ. and a devoted Christian who set up business in aircraft voltage regulators and uses the profits to support/loan Christian businesses in Nigeria and West Africa to help them fight off the Muslim attacks against Christian enterprises and families there. Very talented engineer and a devoted Christian who puts his money where his mouth is.)

[Bruce Fenstermacher]

A followup. I replaced my 25amp gen. with an overhauled unit from Aeroelectric as George had suggested. My airplane is finally making electrical power. Know I have to readjust the regulator after tweeking it to try to make the faulty generator work.

As of right now I have the regulator adjusted as follows. The low voltage warning light, which indicates when the cut-out relay is activated, goes out between 900 and 1000rpm. This is good I think. The generator doesn't make voltage over 12volts til about 1200 rpm and at full rpm (2600) it will go to about 13.8 and climb slowly to about 14.2. I think this is good and i can live with it.
Know for the amperage. First my amp gage has a -60 to +60 range. I know this is to broad for my 25amp system but it's what I have. My guestion is this. My amp gage seems to be read total amps available because with nothing turned on it goes to +15amps with the engine running and the generator producing power. The battery may be charging I'm not sure. If I turn the master off the gauge goes to center or 0. As I add a load like my radios the amp meter moves from the plus side towards zero. More load moves it closer to zero. It seems to be indicating the correct load that I add. If I put on my landing lights it will go negative which I expect.

OK here is the problem. First I didn't think the indicator worked this way. I thought no load was 0 then as load was added with the generator working you would see a +load indication equaling the load added. if the generator was not working or over loaded it would go negative.

Second. If my amp gage is working correctly then it should read 25amps (generator rating)at higher rpm not 15 to start. Should I adjust the amperage relay to achieve this? If not how wold I tell if the amp relay is adjusted to allow max output from the generator.

BTY don't ask how it used to work as this is a completely different generator and regular the old ones being a 20 amp unit. The amp gauge barely moved one way or another but the battery was always charged.

Gee wiz by the time George gives his electrical seminar at Tehachapi, I'll aready be an expert.

[zero.one.victor]

Did you start out your test-running the new generator with a fully charged battery? If you did,seems like the amp-meter should spike right after starting then start back down toward zero immediately,since you're only recharging what the start-up drained down. Your engine starts after just a blade or two,doesn't it?
As long as you're doing all the other electrical stuff,be sure your battery is good. IMHO a hundred bucks for a new battery is cheap insurance,especially since you've been having electrical troubles anyway.
I buy the Gill G-25,it seems like they're good for 3 or maybe 4 years (500-600 hours) then they start getting a little tired.

Eric