Field adjustment of Mooney Voltage Regulators

[squeaky.stow]

Reviving an old thread probably wasn’t the best way to post this question so I will start a new thread.

A couple of questions for @kortopates and anyone else with experience in this. I have two of the Mooney 800270-501 28v voltage regulators in my 252. My JPI typically indicates about 28.9V with either or both alternators on at 2000 RPM. When I put a meter on the cigarette lighter I get 29.2V. 

For my serial number, the aircraft may have either Electrodelta or Mooney VRs. The Service and Maintenance Manual says that for aircraft with Electrodelta VRs they should be field adjusted to 28.6 - 28.8V while the Mooney regulators should be putting out 28.3 +.2/-0 but “No field adjustment authorized” 

So the Electrodelta VR should be putting out a minimum of 28.6V but the Mooney VR has a maximum of 28.5V? 

So I am running a little high. My questions are:

1) Why the difference in output voltage for two different manufacturers VRs that would both be running the same 28V equipment  and charging the same 28V battery? 
2) Should I be concerned about a level of 28.9 - 29.2V?
2) Can the Mooney VRs actually be field adjusted? I see a couple of tiny adjustment screws in the photo posted by the OP. 

I am reluctant to mess with stuff that is working well, but I also don’t want to be overcharging my battery.

[Guest]

I would not trust the JPI volt meter or the ship volt meter.  The maintenance manual says to connect an accurate volt meter to the buss to take the readings.  I would verify buss voltage, then connect it directly to the battery and read what they are getting from the system.  Variations at different points in the system are quite common.

Clarence

[squeaky.stow]

Thanks Clarance,

Is there an easy place to put a meter clip on the bus? I could find anything obvious so I used the cigarette lighter because it comes right off the battery bus I believe. I suspected the JPI might be a little unreliable but I was surprised to see it off by .3V

[ArtVandelay]

Thanks Clarance,
Is there an easy place to put a meter clip on the bus? I could find anything obvious so I used the cigarette lighter because it comes right off the battery bus I believe. I suspected the JPI might be a little unreliable but I was surprised to see it off by .3V

That’s a large drop, I would check if it’s the circuit breaker, might be time to replace it.

[Guest]

9 hours ago, squeaky.stow said:

Thanks Clarance,

Is there an easy place to put a meter clip on the bus? I could find anything obvious so I used the cigarette lighter because it comes right off the battery bus I believe. I suspected the JPI might be a little unreliable but I was surprised to see it off by .3V

Anywhere on the copper buss bar in the circuit breaker rows, I wouldn’t use the avionics buss either.

Clarence

[squeaky.stow]

Meter clip attached to main battery bus as per the SMM.

2000 rpm, no electrical load. 
 

Both on 29.15V

Shaft drive only 29.17V

Belt drive only 29.14V

 

 

 

[Guest]

It’s still a bit higher than Mooney suggests.

Have you checked the voltage at the battery terminals?

Clarence

Edited August 30, 2020 by M20Doc

[PT20J]

Here's the Concord recommendation. As you can see, the recommended voltage varies from 27.5 to 29 depending on temperature. Mine runs about 28.8. Don Maxwell told me he has adjusted the Mooney regulator, so he must know which pot does what. You might give him a call. It would be a cut and try sort of thing. On the other hand, if you are getting good life from your batteries, maybe it doesn't matter that much. All we have to go on is what the recommended voltage is, but what we don't know is how broad the optimum range is. In other words, what's the effect on battery life by by being 0.1 volt high? Or 0.5 or 1.0 or 1.5? The curve  might be fairly flat. Obviously at some high voltage overcharging will cause out-gassing and the battery life will be affected. But these charging systems are pretty basic and my guess is that the optimum is fairly broad.

 

[squeaky.stow]

15 hours ago, M20Doc said:

Have you checked the voltage at the battery terminals?

Not yet, due to the requirement to have two people to do that check, one of whom will have to trust the other one a lot. ;-)

If I do this test and see lower voltage at the battery, isn’t that telling me that I have a wiring or grounding problem? I can see it being either the same or lower than the battery bus but in either case it seems to me that I will still need to get the VRs adjusted.

[glenn reynolds]

I just had both batteries conditioned by a batteryshop and the owner explained that I needed to look at the voltage at the battery terminals not the bus. My ovation trickle charges the standby battery so it uses a diode which causes a voltage drop. I ran wires into the baggage compartment so I can test and then  I’ll know the difference between the bus and the batteries. 

[LANCECASPER]

7 hours ago, glenn reynolds said:

I just had both batteries conditioned by a batteryshop and the owner explained that I needed to look at the voltage at the battery terminals not the bus. My ovation trickle charges the standby battery so it uses a diode which causes a voltage drop. I ran wires into the baggage compartment so I can test and then  I’ll know the difference between the bus and the batteries. 

To get max life out of your batteries I wouldn't view one battery as the standby battery. You are supposed to alternate. Each of them has a trickle charge circuit when the opposite is being used. When I fly on odd days I start on battery one and if its an even day I use battery two.