The Cessna 120-140 Association Forum

Hello,
I am trying to figure out why the delco remy 20 amp generator with a voltage regulator isn't charging the battery.
It wasn't a problem for the first 100 hours or so, then when it started to get warmer outside and it is having problems (maybe related).
A generator won't start charging until about 1300 rpm, When I am at idle and I take off the plane will either start charging or not. If it charges it will charge all flight. Then when I pull the power back and land the process repeats itself. If I add full power and it doesn't charge it won't charge the whole flight. Everytime I go from full power to idle it will either charge or not charge. It will normally either work for a whole flight or not work at all for a whole flight. To note, it seems to do a better time charging for the first hour or so of flying and when the plane is hotter it will stop charging.

I am wondering if the heat had something to do with it. The bushing look fine, another voltage regulator was tested. The generator did fail a bench test and did not spin when it was connected to a 12 volt battery. It did spin when you touched one the positive to the front of the generator case. Indicating it was grounding. It was then pulled apart and noted that two wires to one of the bushing had melted the insulation off. It was taped but it wasn't cleaned (Wondering if all the grease might be still causing the problem and it needs to be cleaned before taped).

Yes I have flashed the field and I have also tested the generator on the plane.

With the generator on the plane if you disconnect the A and F terminal and run it to 1500 rpm it reads about 1.6 voltage. Then if you connect the F terminal to the ground and check the voltage from the A terminal to ground, it reads about 17-18 volts.
The generator wasn't field tested before being put back in, but with the above results, is it fair to say it isn't the generator?

I am still confused about what all the wires coming to and from the voltage regulator go to. If someone has a diagram or can explain them all it would be very helpful. The only other thing I can think to try checking the continuity of all the wires or just start running new wires. I believe ordering another generator or getting a solid state relay may help too.

Please help!

The failure to come back in after going to idle and back to power would point to the brushes or an internal fault with the generator, especially since you tried a different voltage regulator.

All the grease? What grease? I assume bushes are brushes. Melted wires is always a bad sign...

It is possible you have a problem with a break in the wiring. Try checking continuity with an Ohm meter while wiggling the wiring. There is a set of contacts in the master switch that carries the field current for the generator. Be sure to check them, as well. Also make sure you have a good ground between the engine case and the engine mount and between the regulator case and the firewall.

Alan,

I sent you a private message. I have a publication that may help you, Send me your email via the private message.

Mike

Thank you for the help! It turns out it is the voltage regulator! It seems like they both were bad, or perhaps something is causing them to go bad? I'll look into it. It is a 20 amp system. I am seriously considering if it would be worth it to go to an alternator instead of pay 400 bucks for a voltage regulator... perhaps I could find a used one from someone.
I will look into the most affordable alternator upgrade. I see some people suggest the ford/cessna alternator but not exactly sure what they mean by that.

Can you post a picture of the regulator? How many relays are inside? (The correct answer is 3.) If the three terminals are equally spaced it probably isn't the right part...

I think that's what it is. What is suppose to be in there?

alan wrote: ↑Sun Jul 21, 2024 12:35 pm I think that's what it is. What is suppose to be in there?

You need a voltage regulator and a reverse current cutout. The third one is an over current regulator. Cars are not required to have that one.

Alan:

For the Ford/Cessna alternator info, see the thread below, "Plane Power conversion xxxx" below, the two entries
6-6-24, jOHN c and David S. It;s not just a Ford auto alternator, it is more robust insides. IIRC one can look thru the case openings and see the diodes plate with the marking "aviation". The weight comment may not concern you because the DR generator "ain't" light. If you elect to go this way now or in the future, possibly, John and David would give you complete copies of their field approvals, which in most FSDOs, yours would be be readily approved.

I did the same type conversion on a Bonanza about 30 years ago using a modern Zefftronics controller. When I discusssed with my FSDO contact he said "make it (field approval) look good"! I had about 11 pages incuding a drawing for the new mounting bracket. DR 50a generator to 60a Cessna/Ford alternator. IIRC didn't have to change W@B. That egine had a belt driven alterntor, same Cessna/Ford alternator.

Edd

Some years back.........(6?) my generator started acting up similar to yours. I had the "electronic" (Zeftronics) regulator, and I knew the generator was ancient. Rather than put the money into the generator I just opted to install the Plane Power STC unit. I've been very happy. Straightforward install, positive electrical power at idle(well....900-1000rpm) so no dead battery operating lights in the pattern at night.

There are a few "tricks" to installing the Plane power, so if you do, contact me.

Another vote for Plane Power STC. Three years and 250 hours in and works great.