The Cessna 120-140 Association Forum

I replaced the old regulator for a Zeftronics 20A unit a while ago... Usual Delco 20A generator etc...

Recently I had my radio quit in the air. Returning the unit to FUNKE they diagnosed a fauty headphone amp.. All repaired and refitted.

For piece of mind I decided today to check the bus voltage when at cruise and take off power... I have no reason to think that ovevolts killed the radio, but when I measured the bus it was higher than I expected... About 16v in the criuse and 17.5 in the climb.

I had expected 13.8-14ish in order to charge the batt, but nothing higher.

Radio has an operating range of 11-18v.

Regulator fault? or just normal for this type of set up?

I do have a problem with the generator as it runs fine for a while but then needs the comutator cleaning as it seems to pick up brush matter... Clean it and all is good for another 10 hours or so. I thought that initially the gen might be running hot as there was no blast tube fitted, but Ive added that but still need to clean regularly etc.

I’d say anything over 14 volts is too high.

I'd suspect regulator -- maybe check with Zeftronics for troubleshooting. Their product is known to be almost bullet proof and they tend to back them up energetically if a rare issue "pops up". John may have thoughts on the generator issue and it may be related...but, it seems that the regulator should stop the voltage well before 17+...as Randy sez, 14 should be about tops. Mac

Sometimes the problem is a difference between the ground the regulator sees and the ground the generator sees.

You shouldn't have to clean the commutator every 10 hours. I don't have any ideas, though, unless maybe the brushes are not correctly positioned, causing them to arc excessively. Is there any chance the plate holding the brushes came from a different generator?

Oh, I'm not surprised you're having radio issues with that voltage. I'd avoid using any electrical gear until you figure it out. Even light bulbs will fail under those conditions.

Thanks for the replies...

I'll look at Zeftronics site and also check the ground points and do some run up tests..

Taken a while but finally managed to get to the airfield and ran some checks...

The wx hasn't allowed any run up checks but I ran through the resistance checks in the Zef guide... Taking into account the resistance of the test leads all appears to be in spec.

When switched on with engine off the lights on the Zef are all green with the exception of CL.

Thinking it could be breakdown of gen coils under load??

Your system is overcharging. A breakdown inside the generator would not cause this, unless the field wire is shorted to ground. (This can happen where it exits the generator case).

Your generator output should never exceed 15 volts. I suggest these tests:

(Keep all your electrical equipment, especially any electronics, off during the tests.)

Remove the field wire at the generator. Connect a volt meter between the "A" terminal on the generator and ground. Run the engine at 1500 RPM. You should see about 2 volts output. If it is a lot higher, the field circuit must be grounded internally and the generator is unregulated.

If you get the ~2 volts, then reconnect the field wire to the generator and remove it from the regulator. Insulate the free end from ground and repeat the test. Expect the same results. If the generator output follows RPM and exceeds about 2 volts the field wire is shorted to ground somewhere.

If you got this far and didn't find a problem, reconnect the field wire to the regulator. Connect the + of the volt meter to the ground of the regulator and the (-) to the case of the generator. Run the engine again. Expect very close to 0 volts. If you get 0, I gotta think the regulator is bad.

Your generator should be an "Type A" and the regulator needs to match. The regulator grounds the field wire. Inside the generator, the other end of the field coils is connected to the "A" (insulated) terminal of the generator. If there is any question, confirm you have an "A" type generator and an "A" type regulator.

John, that's great info, thanks for taking the time to provide it... It's much appreciated.

I'll run the tests and see what happens.

The gen is Delco 1101890

7698 wrote: ↑Tue Dec 17, 2019 11:10 amThe gen is Delco 1101890

If it's assembled correctly, that is Type A. If it's suspect (can you confirm it ever regulated correctly?) then the only recourse is to actually check the internal connections.

Difficult to confirm that it has worked as I don't have a v guage in aircraft... Only checked with MM after fault with radio... Prior to that with older 25khz radio, never seen a problem...

That said, for as long as I have had VM the charge current has always fluctuated and has never been a steady indication... In the cruise etc...

This led me to replace reg with Zef unit, which seemed to resolve that issue... But in time the fluctuations came back and cleaning the commutator seemed to resolve... However during this time I never checked for a rising voltage..

So I guess gen could always been at fault?

The charge current is always towards the high end... So perhaps the F isn't regulated as you say and is just on... Shorted somewhere?