wabower
Touchdown! Greaser!
- Joined
- Sep 1, 2008
- Messages
- 12,013
- Display Name
Display name:
Wayne
First failure
- Thread starter azure
- Start date
gismo
Touchdown! Greaser!
I'll bet he's done it more than once
.
azure
Final Approach
Thanks, that's the most helpful info anyone has given so far in this thread.
And yes, it's a DOFF10300JR Ford alternator. I redid the FLD-GND resistance measurement today with better test leads. I still get some variation in readings from just turning the whole alternator (possible crappy contact with the test leads), but the range of variation from turning the pulley is a lot greater -- it's definitely from around 5 ohms to at least 15. The variations are very abrupt with large changes in only 4-5 degrees. Also, the resistance ALWAYS goes up while the pulley is being turned and then settles down when it stops. I don't know whether that's normal.
Lance, I located the service manual last week -- Tom did bring it with the plane and that's where it was, in the back seat.
And yes, I'll keep in mind that low output current can be a common symptom with a number of possible causes internally. That is important to know, but I also need to know if my mechanic's measurements were done correctly. If they were, it's pretty clear I have two weak alternators... but I need to be sure about that.
What is driving me crazy is that this certified alternator rebuild shop (T&W) passed an alternator that an auto parts place said was bad, and my own measurements support that as well (though not sure about the bad stator). So at this point I'm really not sure who or what to believe.
Dan Thomas
Touchdown! Greaser!
- Joined
- Jun 16, 2008
- Messages
- 10,750
- Display Name
Display name:
Dan Thomas
What does the ohmmeter say when you pull the prop forward a tiny bit? Sounds like the brushes might be short and worn at an angle (because they're cocking in their holder) and lifting off the slip rings when it's turned backward. In any case, it sure needs checking out.
Dan
gismo
Touchdown! Greaser!
I'm pretty sure that bit about intermittent high field resistance was about the alternator that's not on the airplane at this time. You just posted the connector pinnout for the regulator where such a measurement could be made on the airplane and I don't think that's been put to use yet.
azure
Final Approach
That's a good idea, thanks -- I'll see if my mechanic can put me in touch with him. I'd also like to know what kind of testing they do on their rebuilds before they're deployed.
azure
Final Approach
Yes -- I wasn't even at the airport today. I've been playing with the original alternator at home. I have a full day at work tomorrow but I'll try to get out there Tuesday and see what I can do.
azure
Final Approach
Well I just made a quick decision that I hope I don't come to regret later -- but I spoke with my airplane's former mechanic in New York and described the symptoms and all of the tests we had run, and he had absolutely no doubt that the alternator is bad. Then I spoke with the tech my mechanic referred me to at T&W, who would not offer any helpful diagnostic hints over the phone and only offered to bench test this alternator as he had the previous one. Given that I'm skeptical of their bench testing, for me that was the final straw. I ordered a Plane Power alternator from Aircraft Spruce. When it arrives we will yank the T&W out and send it back for a full refund (less restocking fee) and hopefully, the problem will be solved.
Before installing the Plane Power I might take it to a local auto electric shop I just located (formerly owned by a friend of a friend) and have them check it out, and also measure its field resistance myself.
BTW the T&W tech said the varying field resistance as the pulley is turned is NORMAL. Since I have read in several places that this kind of variation is a red flag, I have even less confidence now in T&W.
Before installing the Plane Power I might take it to a local auto electric shop I just located (formerly owned by a friend of a friend) and have them check it out, and also measure its field resistance myself.
BTW the T&W tech said the varying field resistance as the pulley is turned is NORMAL. Since I have read in several places that this kind of variation is a red flag, I have even less confidence now in T&W.
Last edited:
gismo
Touchdown! Greaser!
Some variation is normal, but by that I mean something like 20-30% of nominal. But I do believe it's possible that one with significantly more could operate just fine. The best test of slip ring function would be to measure the average field current with the alternator spinning at the speed it would see if the engine was running 1000-1200 RPM and the field powered from a 12v regulated source.
And if the stator became magnetized (might happen if the field was powered with the rotor stopped) the rotor will produce a small AC voltage when spun and this will affect a resistance reading if the rotor is turned slowly. I would expect the resistance to vary up and down (i.e. below nominal as much/often as above) in that case though and I didn't see you write that. The resistance would return to normal as soon as the rotor was stopped and wouldn't vary significantly regardless of the position when stopped (it's the motion of the rotor within a constant magnetic field that produces the AC voltage),
Last edited:
azure
Final Approach
And that's the one test we can't run, unless my mechanic can figure out a way to stick a meter in series with the field wire. His inductive ammeter is calibrated in 10s of amperes so it's useless for this purpose.
It's very possible that the meter fluctuations as the pulley was being turned were due to residual magnetism -- it behaved exactly as you would expect. But stop turning, and you notice a position dependence that is quite dramatic. I never saw a resistance less than about 5-6 ohms, and in places it was as high as 15 or more, with abrupt changes of 20-30% over a range of a few degrees. I didn't describe this in detail to the T&W tech, so it's possible he would have agreed with what you're saying. However, they recently bench tested this alternator and were decidedly, shall we say, skeptical of anything my mechanic or I had to say, so I'd expect some reluctance to consider new information from our quarter.
Dan Thomas
Touchdown! Greaser!
- Joined
- Jun 16, 2008
- Messages
- 10,750
- Display Name
Display name:
Dan Thomas
Residual magnetism in an alternator is so weak that it will not bootstrap the aircraft's system like a generator will. It can't even overcome the one-volt voltage drop across the stator diodes. I've never seen any evidence of meter swing due to a magnetized rotor being turned slowly.
In an older car a generator, or in an old airplane for that matter, you could wake up a totally dead system just by push-starting (or hand-propping). The residual magnetism in the field shoes was enough to generate a little current in the armature, and that was used to raise the field current to get more out of the armature, and so on. Bootstrapping. An alternator won't do that. You can push a dead alternator-equipped car but if there isn't enough juice in the battery to fire the ignition, it won't go no matter how fast it's towed or pushed.
Dan
In an older car a generator, or in an old airplane for that matter, you could wake up a totally dead system just by push-starting (or hand-propping). The residual magnetism in the field shoes was enough to generate a little current in the armature, and that was used to raise the field current to get more out of the armature, and so on. Bootstrapping. An alternator won't do that. You can push a dead alternator-equipped car but if there isn't enough juice in the battery to fire the ignition, it won't go no matter how fast it's towed or pushed.
Dan
gismo
Touchdown! Greaser!
Agreed (with the exception of a few alternators that are designed to self excite and have PMs in the rotor, none of which are on certified airplanes AFaIK).
And in this case I was talking about residual magnetism of the stator, which wouldn't improve the ability to self excite like a magnetized rotor would. The thing is, with most digital multimeters, the resistance function uses less than one ma of current so it doesn't take more than a couple millivolts to affect a resistance reading of 5 ohms.
azure
Final Approach
The meter I am using is an old needle-type B&K -- my digital Fluke seems to have some corrosion in the leads or contacts and gives erratic readings. I'll trace it down sometime. I have no idea how much current the B&K ohmmeter function uses though.
But my Plane Power alternator arrived today and the first thing I did was measure its field resistance. First, it has two field terminals F1 and F2, but F2 is shorted to an unmarked terminal that I assume is ground (it is the only terminal that's unmarked; the others are B (for BAT I assume) and AUX). So I measured from F1 to ground and got 2-3 ohms pretty consistently regardless of pulley position -- it rises to 5 ohms at one point but no higher.
I hope to have it installed later today or tomorrow.
KOOL.
Sounds like the patient is out of intensive care, IV needles are withdrawn and on the road to a full recovery. I hope this cures the problem and I am betting the rest out there are right with me.
Ben
www.haaspowerair.com
Sounds like the patient is out of intensive care, IV needles are withdrawn and on the road to a full recovery. I hope this cures the problem and I am betting the rest out there are right with me.
Ben
www.haaspowerair.com
azure
Final Approach
My mechanic has finished installing the alternator and ground tested it. He just got off the phone with me with good news and bad news. The good news is that now, with everything on except landing lights (lower cowl is still off), the bus voltage under load is 13.6V. Without the pitot heat, it sits at 13.8. That's a little lower than I'd like, and the bad news is that the alternator geometry is different enough that he couldn't attach his test leads and read off the output voltage. There is no way to get at the back of the alternator to do those measurements while the engine is running.
But we already know from previous measurements that there is about a 0.3v drop through the wiring with that much current being drawn. That means I'll be redoing the wiring at some point, but it's not an immediate concern. Based on those (previous) measurements, the alternator output voltage should be about 13.9v fully loaded and 14.0 or so with everything except pitot heat. So I'm going to test it and test fly it tomorrow, but (fingers crossed) it sounds like two bad alternators were the major part of the problem.
BTW I asked him to measure the field resistance of the one he took off and he reported that it varied between 15 and 24 ohms. MUCH worse even than the Kelly. He expects that T&W will agree that it's bad and not even charge a restocking fee. I think pigs are likelier to fly, but I'll defer to my mechanic's powers of persuasion. B)
But we already know from previous measurements that there is about a 0.3v drop through the wiring with that much current being drawn. That means I'll be redoing the wiring at some point, but it's not an immediate concern. Based on those (previous) measurements, the alternator output voltage should be about 13.9v fully loaded and 14.0 or so with everything except pitot heat. So I'm going to test it and test fly it tomorrow, but (fingers crossed) it sounds like two bad alternators were the major part of the problem.
BTW I asked him to measure the field resistance of the one he took off and he reported that it varied between 15 and 24 ohms. MUCH worse even than the Kelly. He expects that T&W will agree that it's bad and not even charge a restocking fee. I think pigs are likelier to fly, but I'll defer to my mechanic's powers of persuasion. B)
gismo
Touchdown! Greaser!
It's quite possible that the landing light either by itself or more likely in addition to other loads draws more current than a good alternator can deliver, especially at less than cruise RPM. The requirements of the charging system are that it be able to provide 125% of the "continuous load". The continuous load includes everything you might have on at the same time for an indefinite period including all receivers, lamps, instruments, displays, etc. but it specifically excludes "temporary loads" such as landing/taxi lights, transmitters, gear and flap motors, and so on.My mechanic has finished installing the alternator and ground tested it. He just got off the phone with me with good news and bad news. The good news is that now, with everything on except landing lights (lower cowl is still off), the bus voltage under load is 13.6V. Without the pitot heat, it sits at 13.8. That's a little lower than I'd like, and the bad news is that the alternator geometry is different enough that he couldn't attach his test leads and read off the output voltage. There is no way to get at the back of the alternator to do those measurements while the engine is running.
But we already know from previous measurements that there is about a 0.3v drop through the wiring with that much current being drawn. That means I'll be redoing the wiring at some point, but it's not an immediate concern. Based on those (previous) measurements, the alternator output voltage should be about 13.9v fully loaded and 14.0 or so with everything except pitot heat. So I'm going to test it and test fly it tomorrow, but (fingers crossed) it sounds like two bad alternators were the major part of the problem.
BTW I asked him to measure the field resistance of the one he took off and he reported that it varied between 15 and 24 ohms. MUCH worse even than the Kelly. He expects that T&W will agree that it's bad and not even charge a restocking fee. I think pigs are likelier to fly, but I'll defer to my mechanic's powers of persuasion. B)
I suspect the landing light in your airplane is 100W or 150W but it could be as much as 250W and double if there are two (IIRC there's only one landing and one taxi lamp).
If you really have a .3V drop from the alternator to the bus you likely do have a terminal corrosion problem (likely somewhere other than at the alternator since that one's been moved several times now). It could be a bad crimp on any terminal but IME that's very rare as a proper crimp is a gas tight connection very similar to welding. The alternator output CB is one potential source of that drop, if yours can be operated manually, cycling it a few times might improve things.
Finally, assuming the voltage regulator senses the bus voltage (typical in airplanes) rather than the alternator's BAT or AUX terminal, it should compensate for the voltage drop you have and maintain a constant bus voltage. It should be possible to adjust the regulator and bring the nominal voltage up to at least 14.0, 13.8 may lead to an accelerated loss of battery capacity with time. This is even more true with an AGM battery like Concord RG or RGXC (some of the best aircraft batteries available IMO) which do better with a bus voltage in the 14.2- 14.4 range.
BTW the optimum battery charging voltage varies with temperature and some regulators include temperature sensing to compensate for this. The ideal voltage goes up as the temp goes down, for an AGM type the ideal charging voltage is around 15 volts at or below freezing temps but I wouldn't set the regulator that high, 14.5 (in really cold temps) is about as high as you should go.
Last edited:
azure
Final Approach
No chance of that, I don't think. The specs on the Whelen Parmetheus say 1.2A @ 14V, so they should be about 17W each, total current draw no more than 3.5A.
Thanks for that information Lance. BTW I flew it today and found that my mechanic had exaggerated a little. The bus voltage in flight with beacon, strobes, and avionics varies between 13.5 and 13.7. Adding navs brings it down to a solid 13.4, the pitot heat along with everything else puts it at 13.3. Similarly, the bus voltage goes down to about 13.3 when the gear are cycling. No drop into 12v territory like before, so I doubt if the alternator is having trouble putting out the current. I also noticed that the bus voltages under load were higher on the ground soon after the engine was first started, so maybe the regulator does do temperature sensing and is holding a lower voltage once everything warms up. I don't know if it's adjustable; according my mechanic's invoice it's a DRG6. Does that mean anything to you? How does one adjust a voltage regulator?
gismo
Touchdown! Greaser!
Ah, didn't realize (or remember) you had LEDs already.
The readings you posted indicate you still have a serious problem with the charging system assuming those voltages are accurate and occurred at cruise RPM. Chance are the reason the voltages were higher on the ground after running a short while is that the battery itself loads the bus after starting while it's recharging for the energy drained during cranking.
I don't recognize the regulator part number but I'm not all that familiar with aircraft regulator PNs especially Cessna ones.
One thing I'd try if this were my airplane is connecting a lab supply to the alternator's BAT terminal and the case. Then you can make all sorts of measurements without running the engine with the lab supply powering the bus. Ideally you need something capable of providing 12-15 volts at up to 20 amps. The one I have will only go to 4 amps but even that would allow you to assess any drops between the alternator and the main bus. You can also do things like dial the voltage up and down while watching the regulator output (field voltage and current) as long as the loads switched on are less than the supply can produce.
I wish you were a bit closer, I'll bet I could find your problem in a couple hours if I were there.
Last edited:
azure
Final Approach
So the regulator senses the lower battery voltage and compensates by increasing the output until the battery is recharged? In that case wouldn't it be possible to compensate for whatever normally keeps the bus voltage low by adjusting the regulator? Again, assuming it is adjustable... and I have no idea how to adjust it if it is.
Edit: this doesn't make sense to me. I don't see how a regulator could be designed to hold the voltage higher than it normally would in response to a depleted battery. The other way I read you is that the battery acts as a load on the alternator, which would lead to lower bus voltage because of resistive losses. But that's not what I see, instead the bus voltage is higher at first even with substantial loads, then gradually creeps lower.
The supplies I have access to only go to about 1 amp. I might be able to find a better one from one of the research groups at work but the real problem is that you have to take the alternator off just to attach anything to the terminals. It takes about an hour each way for that and I'm not qualified to do that. So I really need to find someone who can troubleshoot this efficiently, and there doesn't seem to be anyone locally. I am very tempted to make the pilgrimage to Kenosha to see Cardinal expert Bob Russell.
Unfortunately the Branded Bird is grounded indefinitely again because of another problem that just showed up today, exhaust getting into the cabin in the pattern after the gear are lowered. My mechanic promises to see if it's something easily fixed tomorrow, but I'm starting to think this airplane is just falling apart at the seams.
You probably could!
Last edited:
Dan Thomas
Touchdown! Greaser!
- Joined
- Jun 16, 2008
- Messages
- 10,750
- Display Name
Display name:
Dan Thomas
So the regulator senses the lower battery voltage and compensates by increasing the output until the battery is recharged? In that case wouldn't it be possible to compensate for whatever normally keeps the bus voltage low by adjusting the regulator? Again, assuming it is adjustable... and I have no idea how to adjust it if it is.
Edit: this doesn't make sense to me. I don't see how a regulator could be designed to hold the voltage higher than it normally would in response to a depleted battery. The other way I read you is that the battery acts as a load on the alternator, which would lead to lower bus voltage because of resistive losses. But that's not what I see, instead the bus voltage is higher at first even with substantial loads, then gradually creeps lower.
The supplies I have access to only go to about 1 amp. I might be able to find a better one from one of the research groups at work but the real problem is that you have to take the alternator off just to attach anything to the terminals. It takes about an hour each way for that and I'm not qualified to do that. So I really need to find someone who can troubleshoot this efficiently, and there doesn't seem to be anyone locally. I am very tempted to make the pilgrimage to Kenosha to see Cardinal expert Bob Russell.
Unfortunately the Branded Bird is grounded indefinitely again because of another problem that just showed up today, exhaust getting into the cabin in the pattern after the gear are lowered. My mechanic promises to see if it's something easily fixed tomorrow, but I'm starting to think this airplane is just falling apart at the seams.
You probably could!
The voltage regulator senses the voltage right at the alternator output stud and adjusts the field current to keep the output voltage where it wants it. The bus voltage shouldn't vary much at all with load until the alternator is maxed out. If the voltage is dropping at the bus as you add load, it sounds like poor conductivity between the alternator output and the bus. The regulator might be keeping the alternator's output exactly at 13.6 or whatever but any significant resistance in that output line, between the alternator and bus, will drop the bus voltage as current increases. Ohm's law at work. Replacing or adjusting the regulator won't fix that.
Dan
gismo
Touchdown! Greaser!
That's close. The regulator would increase the alternator field current until it reached the maximum or the bus voltage raised to very near the setpoint. As an indirect result the current flowing into the battery would increase, then taper off as the battery became charged.
I've never seen an alternator regulator that wasn't adjustable (but that doesn't mean they don't exist). If yours is a solid state type there should be a screwdriver adjustment accessible from the exterior, often it's even marked with "increase" and "decrease" labels with arrows. If it's a mechanical regulator you probably have to remove the stamped cover to get at the adjustment (which could be a screw or maybe just a tab you bend). If the regulator is a match to the original equipment the adjustment procedure should be in the shop manual, if it's an aftermarket replacement (e.g. Zeftronics) there should be an STC with the adjustment procedure.
OK, I misinterpreted your comment about that to mean that the voltage was low right after start and then gradually increased to "normal", not the other way around. With the voltage starting out higher then falling off as the engine warms up (what's the timeframe here?) I'd be thinking of something else warming up such as the regulator or a load that increases a short time after starting. This is assuming the RPM was constant during this period, any decrease in RPM is likely to result in a reduction in bus voltage if the charging system isn't able to produce enough current to maintain the regulator setpoint.
I don't know anything about Bob Russell, but there's little about your charging system that's Cessna Cardinal specific. I'd be looking for someone with a good track record on electrical gremlins, especially charging systems. I'm not saying that Bob isn't the right person, just that his status as a Cardinal guru doesn't say much about his electrical expertise. I'll bet he'd be willing to give you an honest opinion of his skills in that area. He might even know someone closer to you with the talents you need.
A real "Morton Salt" experience (when it rains it pours), eh? I wouldn't fly it til that's fixed either, CO is nothing to mess around with. Do you have a decent CO detector (hopefully better than the "Dark Spot" type)?Unfortunately the Branded Bird is grounded indefinitely again because of another problem that just showed up today, exhaust getting into the cabin in the pattern after the gear are lowered. My mechanic promises to see if it's something easily fixed tomorrow, but I'm starting to think this airplane is just falling apart at the seams.
azure
Final Approach
Okay, that's how I thought it worked. I misinterpreted what you wrote and got confused.
Thanks. I'm not sure what kind my mechanic put in (DRG-6 doesn't mean anything to me either). It's not a commercial aftermarket replacement I don't think. Are Cessna regulators pretty generic across the 14v systems? I think he originally bought it to put in someone else's plane and was waiting for someone to sell it to.
The RPM is actually greater since I'm noticing the slightly lower voltages during run-up and at cruise -- starting 5-10 minutes after engine start. There shouldn't be any increased load that I know of that comes on in that time frame. You mentioned that some regulators sense temperature and that's why I wondered if it could be that the regulator is set a little low and at warmer temps, slacks off even more. The dependence of the voltage difference on load I would bet is some kind of resistive loss, as Dan says.
Also, someone on a different board said that a charging voltage of even 13.7 will lead to an undercharged battery "very quickly". Is that true?? I thought anything above 12.6 or so would charge the battery, and 13.7 sounds well above that.
He might. Unfortunately, Bill McKelvey @ PHN (Huron Avionics) who hears a lot of tales of electric woe and who would know better than anyone if there was a good charging system troubleshooter in the area drew a complete blank when I asked him. Everyone around here seems to just use the "swap this out, if that doesn't work, swap that out, if that doesn't work, replace all the wiring" approach. Very expensive.
There isn't one installed, no. Aren't there portable battery-powered models that you can carry with you?
Last edited:
gismo
Touchdown! Greaser!
I doubt that Cessna had any regulators made for their exclusive use on the piston singles, chances are they simply adopted something off the shelf and changed that only when the original was no longer available or something much better/cheaper came along. There are functional differences between brands and models of regulators but as long as it was designed for the configuration you have (control the positive side of the field, sensing the bus, 14v) it would work if it could be physically connected. Most electronic ones have a built in overvoltage protection function, something that required a separate "overvoltage relay" with the old mechanical type. And unlike automotive types, the ones used in certified aircraft must have a way to shut the field current off manually (your "alternator" switch).
With a solid state regulator, the setpoint does change with temperature whether it's designed to or not so it's quite plausible that the change you saw was due to the "warming up" of the regulator's electronics.
There's a range of voltage (about 12.5 to 13.5 @70F) where little if any charging or discharging occurs. Above that, the charging current increases with voltage. Fully charging a lead acid battery isn't a simple task but 13.8 volts is considered the absolute minimum for a cyclic (non-continuous) charge on a flooded or gel cell battery and 14.0 is supposed to be the min for an AGM type. For the ideal voltage add a couple tenths to those numbers in the summer and twice that in the winter (most folks including myself don't bother to adjust the regulators for winter and just live with the resulting shorter battery life). You would also be OK with the voltage running a little low (but high enough to prevent discharge) if you occasionally charged the battery fully with an external charger, or better yet with a charger/conditioner. I have the latter and connect it for a few days occasionally and my latest set of batteries is going on 6 years with no unacceptable drop in capacity. BTW, unlike what many owners believe, a battery is "unairworthy" if its capacity is significantly degraded but still able to start the engine. If you fly IFR in a single without a standby alternator your battery is your only backup to the alternator WRT supplying enough power to safely exit the clouds so it's best to replace it when it's no longer up to that task. A voltage sensor that gives an obvious warning if the bus drops below 13 volts is also a must in my book, otherwise the first indication that the charging system is out is likely to occur at the point when there's almost no energy left in the battery.
This is probably one of the best options for $140. I have a larger product that Aeromedix used to sell that's no longer on the market. The ones sold in department and hardware stores for home use are designed to prevent any indication of a problem until the level gets pretty high.
http://tinyurl.com/COmon300
rpadula
En-Route
Speaking of Zeftronics, they have some pretty good troubleshooting documents on their site (although the site itself is a haphazard mess of frames - UGH!). Is the Cardinal in question a Type A or Type B system?
http://www.zeftronics.com/faq.html
azure
Final Approach
I'm pretty sure there's a separate OV sensor in the Cardinal system. Does that mean that the regulator is the mechanical kind? Would a mechanical VR be insensitive to temperature?
The other thought I had was that maybe the resistance of some corroded junction is increasing with temperature, but it would have to be a ~50% increase to cause the downward creep I observed (about 0.1-0.2v lower in cruise vs immediately after engine start).
It sounds like I really need to get that bus voltage higher then, or use a Battery Minder or such. I'm pretty sure the JPI low voltage warning is user-settable and it seems to be set now at 12v. The Sandel seems to be a good canary though, as it was acting up as soon as the charging system started failing, even before the bus voltage had dropped below 12v.
Thanks! I'm going to order one of those...
Last edited:
azure
Final Approach
Thanks. I've been to the Zeftronics site and yeah the links are a mess. I had to use Safari to access those documents as Firefox doesn't do anything when I click the links. Anyway the Cardinal system is a Type B (the OEM alternator is a Ford).
azure
Final Approach
Dan Thomas
Touchdown! Greaser!
- Joined
- Jun 16, 2008
- Messages
- 10,750
- Display Name
Display name:
Dan Thomas
Solid state. I notice that the cover is held on by screw to enable access; many are riveted shut. There will be a potentiometer inside for adjustment.
Could be that whatever voltmeter you're getting that voltage indication from is out of whack a little. A guy needs a calibrated voltmeter to make adjustments to regulators and such. With so much stuff coming from Asia these days, accuracy is always suspect until calibrated by a certified lab.
Dan
bbchien
Touchdown! Greaser!
Liz, what battery do you have..... a gill, a concorde AXC....they have different specs. You want to set the Voltage Regulator to whatever the battery manufacturer wants it at.....minus 0.1 V IMO, and use the battery minder, whose fused harness you just attach at the battery terminals and strap tie just inside the oil filler door.....
azure
Final Approach
Great, that should be an easy fix then -- err, workaround.
Eventually I'll have to redo the wiring though. True, but we've checked my mechanic's meter against my own Fluke and the JPI's bus voltage reading. They agree to within a tenth of a volt (meter precision).
gismo
Touchdown! Greaser!
Looks solid state to me. Also I'm pretty sure it does not have internal overvoltage protection so it's important to confirm you have a separate device connected for that. If the an Electrosystems (Zeftronics) regulator was installed at some point in the past, the overvoltage device would have been disconnected and/or removed. Of course that should be in the logs.
azure
Final Approach
That's a good point, I'll have to go through the logs to make sure. The previous VR was not aftermarket either though, so if Tom ever had one installed, he should have reinstalled the overvoltage switch when he went back to the OEM type. I'm not sure what it looks like, so I'll ask my guy if it's physically there.
azure
Final Approach
Morton salt for sure... my mechanic reported yesterday that he found an induction leak in cylinder #2 while he was looking for my exhaust leak (which he didn't find). He thinks he can seal the induction leak, but has no idea when... he's going up north tomorrow to try to get a deer.
azure
Final Approach
I agreed too fast. I took another look at mine tonight. This one is riveted.
Apparently the one in the picture is used (it's a salvage outfit, after all) and someone had taken the rivets out and replaced them with screws.What are the chances that there is an adjustment inside, given this new information?
Dan Thomas
Touchdown! Greaser!
- Joined
- Jun 16, 2008
- Messages
- 10,750
- Display Name
Display name:
Dan Thomas
I agreed too fast. I took another look at mine tonight. This one is riveted.
What are the chances that there is an adjustment inside, given this new information?
Is there a small hole in the back? Or in the front but hidden by the sticker?
I'd still be interested to know the voltage at the "A" terminal on the regulator (with the engine running) as compared to the bus voltage. (That "A" terminal connects via a small wire to the alternator's output stud and might be easier to get at than the alternator's stud.) If there's resistance between the alternator and bus that shouldn't be there (and which will cause an increasing voltage drop as load rises) it'll only get worse as heat is created, and adjusting the regulator upward to get the bus voltage to rise is only a patch on the problem.
Glad you found that the previous alternators were at fault. Not that it cost you money, mind you, but that no further money was wasted on "repairing" those units or in buying more of the same trash.
Dan
azure
Final Approach
I'm not sure -- I'll check the back next time I'm out there, but to know if there's one under the sticker I'd have to take it off. Is it likely they would cover an adjustment control with a sticker?
We already know that there is a voltage difference between the alternator's BAT terminal and the bus that we measured with the previous alternator under full load. So yes, there is definitely resistance and I realise that the only way to get rid of it is to replace that output wire. But I don't want my current mechanic doing that, or any other detailed electrical work on my airplane. I will see about having it done at next annual time if I can get that bus voltage up into the safe range (13.8-14.0v) for now with full continuous load without pushing it too high unloaded.
Yep, but what bites is that I paid my mechanic several tenths of an AMU to troubleshoot the problem in a very inefficient and unsystematic way that actually made it harder to figure out what was wrong (because he swapped out the first alternator and voltage regulator without measuring anything but the bus voltage and the voltages across switches and breakers). I guess it's another case of live and learn.
gismo
Touchdown! Greaser!
If there's a sticker on the front, rub your finger across it while pressing hard, then look for a round depression imprint on the sticker. If there's a hole under the sticker it will usually show up that way and chances are pretty good the adjustment is accessed through that hole. And yes, it's common to cover adjustments with a self adhesive "sticker" to keep contaminates out.
Dan's suggestion is a good one. Even though you already "know" there's a drop between the alternator and the main bus, it would be good to confirm that this isn't the remaining problem. If you can get at the 'A' terminal on the regulator with a meter probe you can check two things. One would be the voltage at the alternator BAT terminal, if that's up at 14 volts or higher when the bus voltage is low, your regulator and alternator are doing what they're supposed to. If it's below 14 when the bus voltage is down but holds 14 or more when the load is light the field voltage and current need to be checked. If it's always low you can probably adjust the regulator to bring it up. OTOH, if the problem is resistance in the feed from the alternator to the main bus, you'd have to live with a higher voltage when the load is light or lower when it's heavy if the regulator senses directly from the alternator's BAT terminal as Dan stated.
The other check you can do is measure the voltage drop from the alternator to the bus directly by putting one lead on the bus and the other on the 'A' terminal (again this is assuming Dan is correct that this terminal connects via a separate wire to the alternator BAT terminal). This is a much more reliable method of measuring voltage drops than just comparing readings taken at two points.
azure
Final Approach
The diagram Dan or someone else supplied of the Type B charging system does show the A terminal connected directly to the alternator, so that would be a good measurement to do -- I'm just not sure how to do it, practically, without disconnecting the regulator which would kinda defeat the purpose. The I-A-S-F regulator terminals connect externally via a wide insulated plug. Unless the terminals can be exposed by pulling the plug out halfway -- but it's very snug and I can't budge it. I'll discuss this with my mechanic when he gets back. This will be something to look into after he fixes the induction leak (crossing my fingers that he can) AND the exhaust leak which he hasn't been able to find so far...
gismo
Touchdown! Greaser!
If the plug isn't hermetically sealed (be nice for corrosion protection if it was) you can probably stick a small diameter single strand wire (e.g. 010 safety wire) into the plug from the wire side. If it is sealed you might be able to jury rig a set of jumpers from the plug to the regulator (one for each connected wire). Just make sure it won't short out.
BTW, where in SE Mich. is the plane located?