revmaster help

[tx_swordguy]

Hey Guys, I am helping a friend that has a revmaster sonex that crapped out coming back from Oshkosh. The last fuel stop 200 miles from home it was exceedingly hard to start ( much more so than normal). It would turn over and pop on maybe one or two cylinders and die. Then it would flood. This went on for 1/2 hr and really working the starter. The plane finally started and ran rough but seemed to be running ok after several min of higher rpm ground running. He took off and made the radio call and I heard whining static in the radio call and said so to him. With in about 10 miles he started smelling a burning odor and I followed him back to the air port where he shut down and we could smell an electrical burning smell but luckily no smoke or fire. During his ten mile run his tach crapped out on his efis. We trailered the plane home from there. The preface to this is his starter didn't work prior to going to Oshkosh and after trying everything else I rapped on it with a hammer to knock any dust etc off the brushes etc and it cranked up and never quit cranking it for the next 4 days. He installed a usb power source 2.1 amp that over the course of the flight did not keep up with his Ipad amp draw however did keep his other stuff going . ---- Ok back in Gainesville (after trailering home) I pulled the back panel off of the fly wheel plate and you can smell the burnt odor behind it but no exerior wiring is burned. I am thinking his stator is burned up. He did have both blown fuses on this starter solenoid wiring. The revmaster is a "2" alternator system. basically the stator has two completely seperated sides and has two seperated regulators to give 2-18 amp outputs. I am thinking that one side of the stator was going bad (lack of charging his ipad) and the exceedingly hard starting caused such a draw that it finished off the stator once it got running (and blowing his starter fuses on the last startup) does this sound logical? I am pulling the engine tomorrow to get the stator out and pulling the plugs to take a look (betting they were fouled and thus the hard starting) He has no shut off between the two alternator sides. Would a simple on/off switch at one of the ac output sides work? or would I have to shunt it to ground or something? I am wondering if the good side was back flowing to the bad side causing it to overheat and burn up. Would a simple replacement of parts be ok or are we looking at trying to fix a problem that may creep up again? He has put 75 hrs on the plane since last summer with a TT of 160ish so not much to be loosing a stator. Sorry for the long post
Mark

[WesRagle]

Hi Mark,

I can't be of help. But ..., I occasionally visit the CX4 Yahoo group just to lurk and see what those guys are up to. The accessory problems you describe sound a lot like the problems experienced by GLEN BRADLEY. Glen hangs out on the CX4 group. If you can figure out how to reach out to him it's possible he could help.

Edit: Ref. https://groups.yahoo.com/neo/groups/CX4/conversations/topics/34039
https://groups.yahoo.com/neo/groups/CX4/conversations/topics/34002
Wes

[pilotyoung]

I was at the Revmaster facility on Tuesday. I was talking with Joe about the engines as I may put one in my Onex. We talked about the 2 alternators. He said he recommends putting two switches on the panel, one for each alternator. You only use one at a time, but if one fails you can turn it off and use the other one. You can also alternate between flights if you want to.

So he says on a Onex you don't need both connected at the same time so two switches is their suggestion.

[tx_swordguy]

Update. Pulled the engine and the stator is badly fried. My friend talked to the revmaster shop and they told him to just send the whole housing in and they would rebuild it for him. Before he talked to the revmaster shop I suggested he replace both voltage regulators along with the stator. The shop is undecided about that (vr replacement) at this point but will get back with him about it. They also state that the battery is what ate the stator up. He uses an odyssey 680 battery I believe . Not sure how a battery can do that but they know the engine better than I do. Is there a battery the revmaster guys are using without problems? At first they suggested just a regular lead /acid battery. I am not sure I like the idea of a leaky, off gassing battery in an airframe. Any suggestions for revmaster specific applications would be appreciated. I believe the issue is the two sided stator and the power output there in. We will be wiring a set of switches for each side at some point.
Mark

[DJ_Theis]

Hi Mark,
My partner and I are building a Sonex with the Revmaster 2300 and I’ve studied the charging system (but not run our engine yet). I’ll offer my opinion and am willing to take whatever feedback or questions on the subject.
First, Joe (at Revmaster) recommends running one alternator at a time (as you pointed out). I think there might be a couple reasons for this. Two parallel charging systems will (almost) always run off of the slightly higher output (voltage wise) system. The second charging system (with a second regulator) will pretty much coast. In fact, if you follow the Aeroelectric Forum (Matronics), running dual alternators (a primary and a secondary as backup) is typically done with the secondary offline or (in effect) offline by having its VR set (intentionally) to a slightly lower voltage. So, system 1 is set to 14.5 volts and system 2 is set to 14.1. System 2 is always standing by (coasting) until system 1 fails or is turned off.

So, while the plane in question was running the last 160 hours with both systems “on,” it’s possible (likely) that only one charging system was ever generating current to top the battery off and run the avionics.

The other thing to consider is the VR that Joe uses. These are functionally the same as what the Aerovee uses (I believe) and to me (as an electrical engineer), they are a bit confusing, or at a minimum, their operation is not obvious. Without the advantage of an internal circuit diagram of the regulator, I am guessing how they will act when under duress and how they are designed to operate “normally.” Note, these are 2 wire (plus case ground) regulators where-as the majority of PM regulators are 3 wire + ground devices, with two wires dedicated to the AC side. The DC side typically (often) uses the case of the VR as a ground path but provides a separate DC+ terminal. I’m guessing here but I suspect that neither Sonex nor Joe really understand how they operate. They likely (both) outsourced the electrical design to others or if they do understand it, are pretty tight lipped about the details.

The workings of the VR is to “Open” the AC circuit path (the stator) at the regulator, when the voltage of the bus exceeds the (fixed) setpoint. A PM alternator does no work when the stator windings are not allowed a complete circuit. So, a PM alternator that has it’s stator wires “open” by the regulator (or by ay means) does no “work,” runs no current and should not contribute to any heating of nearby engine parts.

Ok, now I’m really going out on a limb with a little too much supposition but here’s where I think the questions lie.
1) If we run both of these (funky) two wire regulators at the same time, it is pretty likely, under normal conditions, that only one regulator is active while the second one is pretty much off.
2) If the VRs are very closely matched (and I believe the two stators generate a waveform that is “in phase,” I’ve checked this) then in certain conditions (like when the battery is severely discharged after extended cranking) and/or you are pulling a lot of current (like running lights or chargers or whatever) then both charging systems could be active and trying to charge the battery. This occurs if the battery bus voltage stays below the lowest VR setpoint. I’m not sure how long this would be likely but let’s say it occurs for only a few minutes.
3) If both charging systems happen to be active (charging) at the same time, then it may be that the stator could overheat. I do not know what the complete design criteria of the charging system is. I’ve had a few discussions with Joe, at Revmaster, on the point but really, did not get a feel for what the design strategy is or was. Is it designed for both systems to be outputting 18 amps at the same time? I’ve come to guess the answer to this in “no.” It is only an educate guess, at this point. It could be that drawing current from both alternators could overheat the stator windings of one or both alternators.
4) Finally, my partner had a long conversation with Glen Bradley (coincidentally, just last week) and Glen indicated he has 800 hours on the Revmaster with “very” few problems. He always runs one alternator at a time. He ran the first 600 hours with the PC680 battery and reported zero problems with the battery or the charging sytsem. I think blaming any part of this issue on the RVLA (Regulated Valve Lead Acid) battery, which I believe the PC680 is, is a red herring. I don’t believe the charging or load characteristics of this type of battery is substantially different than a standard, flooded cell lead acid battery. I will take a moment to ping Bob Nuckolls /the AeroElectric-list forum but I would predict agreement on this point.
One final note. If the electrical wiring is modified to run one alternator at a time, there is a relatively standard approach for a PM alternator, which is to disconnect the AC circuit on the alternator from the regulator, with a pilot controlled relay. I can forward a portion of our wiring diagram, as an example, if anyone is interested. This circuit layout follows one of several offered by the Aerolectric Connection and accessible on Bob’s web site.

http://www.aeroelectric.com/articles.html

Just before sending this note (sorry for the long-worded comments) I re-read the original post. Not sure if I understand the comment, “He did have both blown fuses on this starter solenoid wiring.” Did you mean “stator wiring?” The fuses that Revmaster (Joe) provides with the stator windings are 20 amp. If I recall (please correct me if I’m wrong, I’m not in front of my engine) there is a 20 amp fuse for one leg of the AC winding (stator) and one fuse for the DC + terminal. Did both of these go out on one alternator or did fuses on both alternators go out?

You made mention of the tachometer of the EFIS dropping out, I would expect this if the stator wiring fuse blew, (the standard Revmaster drawing is to use one of the stators as an input for a tach signal). I suspect that is obvious to you as well.

Also you mention the method to select one or the other charging system. I may have answered that above but just to be clear, DO NOT SHUNT THE STATOR TO GROUND. You will want to use a relays to open one of the stator wires from the regulator and, of course, you can use a simple low current toggle switch to energize the relays (one relay for each charging circuit).

Respectfully,
Dan Theis
Sonex 1362R

[WesRagle]

Hi Mark,

4) Finally, my partner had a long conversation with Glen Bradley (coincidentally, just last week) and Glen indicated he has 800 hours on the Revmaster with “very” few problems. He always runs one alternator at a time.

Hi Mark,

Just so there is no confusion, Glen always runs one alternator at a time *now*. He added the switch at approximately 450 hours after his stator burned up.

Here is a snip from Glen's "Revmaster 2300 800 hour report" :

"Approx 450 hours --A strong electrical smell developed during flight and continued for until I landed/about 7 min. I had had an ignition coil burn out long ago - super easy fix...but this smell was different. After some searching I took the CDI cover off and ohmed out the STATOR. It was bad- burnt to a crisp. Joe did not have any in stock so a month or more went by and I finally got a new one. Installing it meant removing the engine---not fun. The install of the stator was quite easy once the engine was removed.
In the process I learned a lot about the charging system. Revmaster wasn't sure what had caused this issue but they decided that it may have resulted from running BOTH alternators at the same time, thus overloading the battery with the excess current. They also decided to recommend a wet cell battery....I had just bought a new Odyssey battery a few days before even thought the 5 year old battery worked fine. Anyway, I set up a three way switch ALT 1 OFF ALT 2 and have had no problems since."

Glen's entire report can be read here" https://groups.yahoo.com/neo/groups/CX4/conversations/topics/36336

EDIT: The entire report can be read here: http://sonexbuilders.net/viewtopic.php?f=9&t=5095

Wes

[DJ_Theis]

Thanks Wes,

I appreciate the correction. My retelling of my partner's conversation was probably not in the best form. Second hand information is easily distorted this way. My mistake.

I would say that Glen's experience, perhaps, is not that different from what Mark described. Obviously there is more to learn, regarding the Revmaster PM alternators.

I would still not be inclined to suspect the battery had anything to do with it but again, that is my best guess and in no way tested. The Aerovee uses (or at least Sonex promotes) using the Earthx batteries. The two charging systems are not that different...but they are not the same. And Revmaster (Joe) does not recommend using the Lithium batteries either, (apparently in addition to the RVLA technology).

Thanks again,

Dan Theis
Sonex 1362R

[WesRagle]

HI Dan,

I have not studied the charging systems used with any of the VW conversions. However, it seems to me that blaming a long standing aircraft battery on a charging system melt down is equivalent to admitting a design flaw with the charging system. Regardless of whether Joe fully understands the failure mechanism or not, I do hope isolating the two charging circuits solves the problem.

For anyone considering the Revmaster I would suggest you read Glen's entire 800 Hour Report. It might save you some heart ache.

All the Best,

Wes

P.S. Dan, I intended to address my previous post to you. I didn't mean to talk around you.

[tx_swordguy]

THanks guys for the input. Dan, yes it was the starter not the stator fuses blown. The starter solenoid is tied into the bus bar . I assume it was the masive draw trying to get the plane started that did this on the last engine start when it finally took. The stator fuses were all good (strange I thought for a burned stator) Now to just make sure I understand this correctly. Electrical is my weakness so bear with me. Can I just tie a simple on off switch between the VR and the stator on the AC line to be able to choose which side of the stator (alternator) I draw power from? I would assume I splice the same size wire to/from the switch to the stator ac line.
Mark

[DJ_Theis]

Hi Mark,

Can I just tie a simple on off switch between the VR and the stator on the AC line to be able to choose which side of the stator (alternator) I draw power from?

Technically yes but few would run the wires from the alternator to the panel. I would not advocate this, regardless of how appealing (straight forward) this might appear. The reasons are 1) the switch needs to be rated for the AC current and voltage of the alternator at full rpm and 2) it's not common practice for higher power circuits to be run through the panel and running those AC wires further than necessary is not a good plan. Sorry.

The best way (and most common) is to insert a relay into the line from one leg of the alternator to the VR and use a low power control signal (from the panel switch) to energize the relay. If this sounds too vague, my apologies.

This is the same approach that is taken for other high energy connections on the plane. Examples would be the landing light, or even the master contactor. The alternator relay (or contactor) needs to be "continuous duty." Finding a relay capable of handling the 18 amps from the alternator should not be difficult to achieve.

Another reason a relay is advisable is that the AC voltage from the stator will rise with engine RPM. So if you want to push the issue and add a full voltage and current rated switch to the pane (without a relay) you'll want to fully understand WHAT that voltage is. I've not seen any specifications on the Revmaster (nor spun my engine to test the alternator output,... yet) but it could easily exceed 50 volts on the AC side.

So again, plan on adding a separate relay for each of the alternators.

One other thing that occurs to me, the VR is actually a "Rectifier / Regulator." That's not a big surprise to most but I bring it up because I am suspicious that this particular regulator might be a "half wave rectifier." I've not completely confirmed this but if this is true, replacing the Revmaster regulator with a full wave rectifier/regulator could add additional stress (heat) on the stator windings. Something to keep in mind.

I wanted to get this out to answer your question and will follow up with an example part number for the relay and a circuit drawing.

Best regards,

Dan Theis
Sonex 1362R