The Cessna 120-140 Association Forum

I think my VR is bad. With a voltmeter attached to the bus and ground when flying, I was getting voltage readings in the range of 15.38v to 12.6v.

I have a VR300-14-50 installed off a Delco 110189020, 20 amp generator. I'm thinking about replacing the Electrodelta with the Zeftronics G1200N rated for 20 amps. I don't know why I have a 50 amp VR installed with a 20 amp generator....do I need a 50 amp?

Any thought appreciated. Thanks!

Hey, Mike -- I can't answer the ? regarding your "current" VR, but can't say enough about the quality of the Zeftronics unit. My experience with it was trouble free operation, the generator came "online" earlier than with the old tractor VR and the voltage level was much smoother (In fact, I penned a NL article a "few" years back with heading: "The next best thing to an alternator".). Mac

Generator controllers are rated for a particular amperage because they incorporate an over current cutout. Since a generator generates its own exciter (field) current, having just a voltage regulator could result in the generator being commanded to generate more current than it can safely produce, resulting in burnt armature coils. For this reason, a 20 amp generator should have a regulator with a 20 amp over current cutout.

Thanks John & Mac,

I am pretty sure I am going to install the Zeftronics unit like you recommended, Mac. John - I talked to Lamar and they basically said what you said...an oversized regulator will not provide proper overcurrent protection. I still can't figure out why the airplane has a 50 amp unit in it. Maybe replaced at some point in the past with an incorrect regulator?

I did have another question...the generator is rated for 12V but the regulator for 14V. Is there something about this that I need to pay attention to?

Thanks again!

6930 wrote: ↑Tue Nov 23, 2021 11:35 amI did have another question...the generator is rated for 12V but the regulator for 14V. Is there something about this that I need to pay attention to?

No, that's just semantics. If the regulator is regulating at 15+ volts, and is consistent, you can probably adjust it to get it down around 14.8. Very cost effective fix... When you're seeing 12.6 you're seeing battery voltage and the generator is not producing enough voltage to charge the battery. There is a reverse current cutout that disconnects the generator to prevent the battery from discharging through the generator.

+1 on the Zeftronics.
Put one in about 10 years ago and no issues.

Oh, I suppose it's possible someone adjusted the overcurrent relay down, too.

I had a conversation with someone at AeroTech a few years back. Some planes use a 12 amp generator and there aren't any new 12 amp regulators. He said it was OK to use a 20 amp version as the Delco generators cannot generate enough current to damage themselves regardless of field current. Maybe that's true of the 20 amp version, too.

Thanks again, everyone for the great input. I'm kind of in a late developing quandary right now. It seems a number of pilots have been experiencing GPS loss of integrity over the past few days here in Northern Illinois (I'll do a separate post on that). Including me...which led me to think I had voltage regulator issues. Now, I'm wondering if I need to change the VR at all. I have a Zeftronics VR on order, coming Friday. I may not install it...still thinking about what to do.

Did someone just turn up a 5G wireless system?.

[Edit] Oh, I see you already thought of that. Aren't you sort of in the birthplace of wireless, anyhow?

John,

Don’t know how this 5G thing is going to sort out. May turn out to be a non issue….but then, may turn out to be an interesting ride!