InterAv Alternator conversion troubleshooting

[danb35]

I've seen several references to a troubleshooting guide that InterAv is said to have had available.  Unfortunately, they're out of business, and although QAA has picked up the product line, I don't see that guide on their web site anywhere.  Would anyone happen to have a copy they could share?

 

Here's the issue I'm trying to resolve.  Last week when preparing to take the runway for takeoff, I turned on the landing

light, whereupon my low voltage warning came on. I pulled and reset the field breaker, and voltage returned to normal (~14.1 volts).

    Once airborne, the low voltage light came on again. Intending to reset the field breaker again, I pulled it. When I did so, the voltage rose to ~14.5 volts. When I reset the breaker, the voltage dropped slowly, eventually dropping below 13 volts. When I pulled the breaker again, the voltage immediately rose to above 14 volts (but under 15).

    Given the fact that the alternator is clearly charging while the breaker is pulled, it doesn't seem likely that what I'm calling the
field breaker is, in fact, the field breaker. It's a 5-amp pullable breaker in the RH panel, placarded with instructions to pull and restore
it in the event of a overvoltage trip.

 

I've since located InterAv's installation instructions, and from the wiring diagram in those instructions, the 5-amp breaker in the panel isn't for the field at all--it's for their overvoltage protection relay.  The fact that pulling the breaker lets the alternator charge as normal suggests to me that the relay is defective, but I'd like to be more certain before replacing $200 parts (in which case I'd likely replace it and the regulator with a PlanePower unit).

[orionflt]

your trouble shooting is taking you in the correct direction and your solution is the one i would recommend. the interav regulators are a piece of junk and i'm surprised that it hasn't already been replaced. when i did my conversion i used a plane power alt with a a standard mooney regulator and had a field approval done, now that plane power has a regulator you just have to do the change over, nothing special is needed beyond the log book sign off and some wire identification when installing it.. 

 

i know it will add to the expense but i would get rid of the interav alt and throw a plane power on, mines been on for 7 yr and i couldn't be happier. infact when i redid my engine, panel and wiring i replaced my VR-415 reg with the plane power reg because my old one was was fluctuating more then i liked. now i'm 13.9-14.1 depending on my load.

 

Brian

[N601RX]

I have an interav conversion also.  I had problems with he regulator last year and replaced the regulator and overvoltage relay with a plane power regulator.  Since you already have the interav alternator the plane power regulator is an approved replacement. The plane power regulator has never moved off 14.1 volts, even with lots of stuff turned on.

 

I don't have the internav drawings with me at work, but if I remember correctly there was 3 CB for it.  One that provided the Sense voltage to the overvoltage relay coil, One that provided the Field voltage to the regulator/alternator, and it was also connected to the overvoltage relay contacts. The 3rd breaker was then the output for the alternator. I may still have the ov relay if you need it, it was ok my regulator was bad.

 

It sounds like your ov relay thinks the voltage is too high and shuts the field voltage off.  When you pull the sense voltage breaker to the ov relay coil it then turns the field voltage back on.

[Andy95W]

+1 for Plane Power voltage regulator.

Works great, easy install.

[robert7467]

Just switch from Interav to Plane Power and its a difference between night and day. Plane Power's bracketing system is far superior to Interav.

[Skybrd]

I recently had intermittent alternator problems and it turned out to be brushes worn out. The brushes slowly wear down and when they or one of them gets too short it  causes intermittent operations. If your alternator has some age since since new or overhaul it might be good to check this and also it would be good to change bearings and check the diodes.

[cliffy]

Skybrd makes sense How many hours on your alt? Mine had worn brushes and the slip rings were worn out. I'd probably look at the brushes first if I had lots of hours on it. Why spend bucks if the reg is not the problem. If the brushes are gone, my bet is that the rings are also worn out. Maybe time for another alt.

[danb35]

Thanks for all the suggestions.  I recognize that the Plane Power alternator is a better unit, and when my current alternator is beyond economic repair I intend to install one.  I had the current unit IRAN'd about 18 months ago, less than 100 hours ago.  The brushes and bearings were replaced.

 

Does anybody have a copy of the InterAv troubleshooting guide, or a suggestion as to how to either confirm or rule out the OV relay as the problem?

[N601RX]

You can remove it and connect the sense leads up to a variable power supply. Connect an ohm meter across the contact side of it. Slowly bring the voltage up until the ohm meter shows the contact have switched. It should happen around 16 volts.

[danb35]

N601RX, that makes perfect sense, and I have a bench power supply that should do the job just fine.  Might even try heating it a bit with a hair dryer to see if that makes a difference.

[N201MKTurbo]

It sounds like pulling the breaker defeats the over voltage sense circuit. Just leave it out and fly happily ever after. My 201 doesn't have an over or under voltage sense circuit and my plane flies just fine!

[N601RX]

Sometimes these are wired up in a "crowbar configuration". When the voltage goes too high the relay closes and shorts the field voltage to Ground. This overloads the field breaker and trips it immediately.

[danb35]

If wired per the InterAv instructions (which my plane seems to be), there wouldn't be any way to do a crowbar, since there's no field breaker.  The 5-amp pullable breaker that's mounted in my panel goes to the input of the OV relay; it isn't in the field line.

 

Tested the OV relay on the bench today, and it seems to be fine.  The resistance between field in and field out sits at 0.2 ohms until the input voltage reaches 16.5 V DC, whereupon the field terminals open.  To restore the field circuit, I need to remove power entirely from the device.  I haven't yet tried heating it, but I have left it at 15.5V for about an hour with no change.  This seems to rule out the OV relay as the culprit.

 

My new hypothesis is that the voltage regulator is allowing a voltage overshoot which is being caught by the OV relay.  I have an idea of how to test this as well, but it involves running the engine, which is missing a cylinder at the moment.

[N601RX]

You can test the regulator on the bench similar to the way you tested the ov relay. Monitor the regulator output while slowly increasing the sense voltage to the regulator. Whether the problem is the ov relay or regulator the plane power regulator is the cheapest fix. It has both functions combined into it and is cheaper than either of the other interav components. Then the pp alternator can be added at a later date if the interav alternator ever fails.

[Alan Fox]

I have had multiple interav setups on different aircraft trouble free.....Instead of "replacing it with a plane power" why not fix it........I think it is boneheaded logic to replace it , fix it and get a nother 15 years out of it......

[danb35]

N74795, as N601RX (how about some names?) points out, the Plane Power regulator (which includes OV protection) is about the same price as either the InterAv regulator or the OV relay (one is $160, the other is $200, while the Plane Power unit is $185).  The OV relay is not user- or field-serviceable--it's completely potted in epoxy.  I haven't checked out the regulator yet, but I wouldn't be surprised if it's the same.  Therefore, neither of those parts can be fixed; the defective part must be replaced.

 

I'm not interested in proactively replacing parts that haven't failed and don't give any indication of failing, simply because there's something "better" available--this is why I don't intend to replace the entire setup with the PlanePower alternator conversion at this time.  However, it seems very likely that either the regulator or the OV relay (currently the regulator seems like the more likely culprit) is defective and must be replaced.  If I have to replace it, is it better to replace with the same InterAv unit, or to use PlanePower instead?  I don't have personal experience with PlanePower, but everything I've read about their products is good.  I like that they integrate OV protection into their regulator.  I'm not committed to PP, but I'm leaning strongly that way.

[N601RX]

Dan,

One other thing you might want to look at is the large cap that goes with the interav setup. If this is bad it could be allowing some of the peaks of the rectified sine waves from the alternator to present a brief peak that goes above the threshold of the ov relay. I have no idea if the ov relay even be able to respond to a peak pulse or not.

My interav alternator was installed in 93 and is still working fine and I'll keep it as long as it working or makes sense to repair it. I had to replace the regulator and ov relay about 2 years ago. I went with the pp regulator and it's worked well the interav alternator.

Mike

[Andy95W]

Totally agree with Mike, and I have the exact same experience. Love my Interav alternator, when my regulator went bad I replaced it with the Plane Power and have loved that even more. I will continue to overhaul my Interav alternator until it dies completely.

[danb35]

Well, the annual took quite a bit longer than I'd expected.  I decided to replace the InterAv regulator and overvoltage relay with the PlanePower regulator, following PlanePower's installation instructions.  On the test/break-in flight last week, voltage was rock steady irrespective of system load.  I'm going to call this one fixed.

[DrBill]

Dan,

 I just went thru this with my A&P on a Cessna he had in annual.  Same symptoms as you.  He asked me to assist in diagnosis (EE my speciality).  I showed him how it was SUPPOSED to work and why it failed.  We replaced the regulator with Plane Power.  END OF PROBLEM.  

As a professional engineer I find it apalling that they would misuse the purpose of a circuit breaker. The field wire is not protected.  No surprise they are out of business.

BILL

[drbob]

InteAv:

   Appears to be Motorola (12V) # A12N-600  55A N  grd. alternator

these are/were ubiquitous in marine and farm tractors in years past--parts available! 

Common V regulator was Motorola PN R2CM1 12V controller.

InterAv  regulator appears to be   Motorola 8RD 2023 12V 

     three wires Gnd (-)Blk, Fld Grn and Reg red (+).

 

   My notes say when the 0-500 ohm  trim pot fails  voltage then goes out of spec. (the red&blue wires go to it)

       Before PlanePower or any others this was- I think -the  STC'd alt conversion.

  Heavy & needs a reverse cooling fan, but robust and long lived.

The trim pot can be seen in the potting medium just above the lower single mounting hole, the overvolt relay prob. proprietary.

       Just my 2C's worth,  not bad alts, just older rugged units! 

                                                    drbob

[dmevans]

I have a quick question. I just bought a plane power r1224 regulator to replace my InterAv one that just took a dive. 

On the back of my InterAv alternator, I have 4 terminals. POS, GND, Field, and REG. The plane power instructions do not address what I should do with the REG wire? Do I get rid of it? Does it run to Aux on the new regulator. Any information would be appreciated.

Thanks in advance!

[Andy95W]

I am nearly positive that is how I did it when I installed my PlanePower regulator 7 years ago- but your best bet is just call PlanePower.  5 minute phone call and you'll have the exact right answer.

[cliffy]

Talked to InterAv years ago when they were in business about the backwards fan and they said they knew it but that's the way they certified it.