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Alternator overvoltage

T

trackdom

Well Known Member
Hi,
Today I experienced an alternator trouble. During flight GRT Efis sent an alert message , alternator overvoltage . On engine page I read 15 to 16V . 15 mn later total electric failure , all switches are off. 5 mn before landing I switch master switch on, radio on and Efis on to get IAS.
2 hours later I start the engine and get back to home base but without radio, transponder, And Efis.
My question is, can I decrease alternator voltage ? It's a plane power, 40 flight hours , internally regulated.
In the same time I noticed that master switch needs a few minutes before being operative , I am not sure there is a link between both issues.
Before buying a new alternator I would like to know If I am able to fix it by myself...
Thanks
 
The Plane Power unit uses the alternator field line for the sense voltage. If there is high resistance in that line you'll see higher voltages. Start at the main buss, and look for any voltage drops across the switch, any connections, and at the alternator plug itself (this last one being most likely IMHO).
 
What Type of Master Switch?

What type of master switch do you have? Main reason I ask is to verify if you have the old style "Split" switch that had a Batt/ALTernator side.

Many years ago I had an overvoltage/charge condition because someone had removed the one piece Master Switch, replacing it with the old style "Split" switch.

On short flights it wasn't a problem, but on a really long cross-country (Alaska to Idaho) it was a problem. Switch was dropping 8-watts between the contacts, regulator saw this as under voltage and overcharged the battery-destroying it.

Hot electrical smell in the cockpit, lights, nav equipment problems, etc.. Including Hydrogen gas inside the cockpit, from the over charging of the battery.

Was very lucky to find an airport that night!
 
There is no way a good switch will take a few minutes to become operational. There are two possible options: 1) the switch is bad, 2) you just think the switch is taking a while to become operational and it's actually something else.

What type of switch do you have? Is it rated for the current you are drawing through it? Normally there is a contactor (relay) that is controlled by the master versus switching your loads directly with the master.
 
Alternator

Salut Dominique,

I have a spare PP alternator if you want to use that. I'm up near Geneva. I can mail it to you by post or you can fly into Bellegarde (LFHN) and I can meet you there.

Mickey
 
Hi Mickey,
Thanks for your proposition , Bellegarde is not far from my base. But before changing alternator I'll change master switch which is the beginning of the trouble I suppose .
Rapid ascent,
I bought the master switch from vans catalog , I have no part number.
Today I put away cowlings And look carefully at all connections . I am ordering a new master switch, from vans or stein air or other , what could be the most reliable?
Thanks for your help
 
Coming back from the hangar, I noticed nothing special . When switching Master switch it took 6 mn to get a contact . I suppose alternator overvoltage is due to the master relay malfunction .
 
As for the master switch, I have the split rocker Cessna style switch but was suggested by B&C to switch it out for a 3 way toggle. They said they have seen lots of failures with the split rockers, and the 3 way toggle holds up better. For what it's worth.

Have not switched mine out yet. Still AOG from my over voltage incident.
 
If you're looking for the best switch the Honeywell 2TL series is most reliable switch I know of.
Z-s2q0mcpEx_.JPG
 
I'm with Walt. Those Honeywell TL switches are the best. They even look higher quality. I bought most of mine at Onlinecomponents.com for the best price.

The switch will have the rating stamped on the body of the switch. The rating is something you should know. A switch is not a switch. Do you have a contactor? If so do you have a protection diode on the coil?
 
climberrn said:
As for the master switch, I have the split rocker Cessna style switch but was suggested by B&C to switch it out for a 3 way toggle. They said they have seen lots of failures with the split rockers, and the 3 way toggle holds up better. For what it's worth.

Have not switched mine out yet. Still AOG from my over voltage incident.
Click to expand...

This is the style that caused my problems. I would replace as soon as possible!

Not any fun when the instrument lights are going from really bright to completely dim, hot smell of electrical, all radios including NAV won't work and it is night/dark above some broken white fluffy clouds. Only option is turn off the Master completely to stop all the above.

ADF and Loran were the first to go. That's when I started to realize something was amiss.

Moonlight, a flashlight and compass are not the best way to fly!
 
I am not sure the switch is not good, but rather the master relay from vans catalog. I'll order the White and Roger from aircraft spruce, but that will take 2 weeks to be shipped....
 
Walt said:
If you're looking for the best switch the Honeywell 2TL series is most reliable switch I know of.
Z-s2q0mcpEx_.JPG
Click to expand...

Hi,
Today I removed the master relay, came back to my garage. I checked it with a battery and direct contact, and no problem that works on every attempt. So the switch could be the issue. I order soon a new one, as Walt told me.
I'll tell you the final story , and happy ending I hope.
 
High voltage

Had the same high voltage issue with my internally regulated ND 60 Amp alternator (87 Suzuki Samari). Noticed that wiggling the 5 amp breaker switch for the field circuit would bring the voltage back in to range. Replaced the 5 amp breaker switch and had no more problems.
YMMV.
 
You could take some measurements in circuit to see where the problem is. If you turn on the master and then measure the voltage across the coil on the relay that should tell you if you have sufficient voltage on the relay. If you don't then try to measure right on the master switch. If those voltages look OK then you can measure the voltage on the switched relay contacts to see that voltage.

It sounds like from your bench testing of the relay it is operating properly but its always best to test these things in the actual circuit. The method that you used to energize the relay coil in your garage is different from being switched from the master switch. You could have a bad switch or even an intermittent broken wire. If you find a low voltage work toward the source to track down the problem.
 
Today I checked the master switch , it's ok ... master relay was ok in the garage, but not in the plane. When switching on the master switch I had a short circuit and some smell, I don't know exactly where. I don't understand ... master switch is ok, master relay is ok apart from the plane . I suppose there is a short circuit somewhere...I don't understand why the switch wich is a ground wire can induce a short circuit.
I tried to connect the relay ground connection to the battery negative pole, I felt high temperature in the wire ,??
I am speaking with Marc Ausman, from vertical power to fix that issue.
 
Next step, I remove the master relay, waiting for a brand new one. Then I check all the ground connections, probably remove a burned wire
I'll open the old relay to see inside just for information.
 
master relay

trackdom said:
Next step, I remove the master relay, waiting for a brand new one. Then I check all the ground connections, probably remove a burned wire
I'll open the old relay to see inside just for information.
Click to expand...
I have spares if you like - happy to mail them to you when I get back home tomorrow. They look like this:

S701-1.jpg
 
rv8ch said:
I have spares if you like - happy to mail them to you when I get back home tomorrow. They look like this:

S701-1.jpg
Click to expand...

That's very nice, but I have just ordered one today, don't how long it will take...
I really hope a new master relay will solve the problem!
 
From your descriptions it's hard to help. At one point you thought you had low voltage. Now it seems you have a burned wire. You need to provide more specifics so that folks on here can help.

Did you start at the master switch and measure the voltage, then move to the relay and measure those voltages?

If you suspect the relay is shorted then disconnect it and use your meter to measure the resistances. The measured resistance between the relay coil terminals should be a low resistance. Then measure across the switch terminals it should be normally open so a high resistance. Then measure between the coil terminals and the switch terminals it should be a high resistance. There should never be a low resistance between the coil and switch terminals.

Not sure where your burned wire is. Please elaborate.

You can cause a short with a ground wire because the ground is creating the short. It could be the grounded master switch wire itself or it could be that ground wire is energizing the master relay and that intern is turning on and indirectly causing the short.

I wouldn't suggest just randomly replacing parts. It sounds like you may need to get some help on this.
 
I think I found the origin of my electric short circuit.
In my garage I first tried a connection with a wire and saw that wire was warming up. At the second attempt I removed the yellow diode and it was absolutely different, normal in fact . I suppose this diode is the problem . I am looking for a new one and go back to the plane to connect everything, hoping I found the solution....
 
Master relay is back in the plane. All works fine, but without diode I am waiting for . When diode is on , and in the correct direction , I start the engine and check the voltage .
It seems the short circuit was due to the diode. It should protect and indeed was able to set on fire the wire from the master switch to the ground!
I told you the end of the story after the next flight.
Thanks for your help
 
Just make sure you really know what the correct direction is because your explanation sounds like you have it in backwards.

You can check the diode out if circuut. Most multimeters have a diode check selection. If yours does you should read about 0.7 volts in the forward direction and open or high resistance in the reverse direction. If your meter only has ohms then take the same 2 measurements. Forward will be low resistance and reversed will be high resistance. If this is not the case then the diode is bad. Sometimes a bad diode will not show the difference in resistance based upon the direction.
 
Ray, recheck your terms. I'm afraid you're mixing voltage & resistance terms and numbers.

A 'normal' diode will drop ~0.7 volts when under load. It won't matter which way the leads are oriented; it'll just change the sign (+/-) in the display.

The same diode *out of circuit* will typically check somewhere between 400 & 1K ohms in one direction and open circuit in the other when using the diode check function of a digital ohm meter

To the OP:
If the diode was indeed your problem, and it's wired across the terminals of the contactor, it's there to suppress inductive spikes as power is being removed from the coil of the contactor. It's not doing anything when the contactor is either on or off. If the diode goes bad and is shorted internally, *then* it can smoke a wire.
 
Nope not mixing. Some meters display different things when in the diode test position. In circuit yes it will be 0.7 volts if forward biased. When reversed biased it be whatever the applied voltage is. In this application you should never be able to measure it as 0.7 since it is only acting to surprise spikes.

Just make sure the cathode (-) , end with the stripe is connected to your positive voltage on the coil, not the ground switched end.

Sorry I'm blind and on my phone today. :D
 
"If yours does you should read about 0.7 volts in the forward direction and open or high resistance in the reverse direction"
 
I checked the cathode connected to the BAT of relay. The vans diode has a red strip showing the cathode.
As I am waiting for diode ( 1N5407 ) I flew today without anyone .I know solenoid is not protected by the diode when switching of the master witch , but it was for one flight , taking care to switch off Efis , strobe and alternator prior to master switch.
Nothing to declare during the flight, voltage was between 14,4 and 14,6 .
So this single diode was able to set on fire wires , and incidently to induce overvoltage...
 
Critical diodes

For these critical diodes, I normally use 2 in series. I had millions of dollars of commercial hardware go bad because of a similar diode failure; never again.
 
Is it really as simple as it sounds?

PilotjohnS said:
For these critical diodes, I normally use 2 in series. I had millions of dollars of commercial hardware go bad because of a similar diode failure; never again.
Click to expand...

Can you say a little more about this. Is it as simple as indicated, just take two, solder in series, add terminals and cover with shrink wrap?

Any additional operational negatives to be aware of?

Thanks for posting - been reading VAF posts for many years, don't remember this failure mode or solution.
 
trackdom said:
I checked the cathode connected to the BAT of relay. The vans diode has a red strip showing the cathode.
As I am waiting for diode ( 1N5407 ) I flew today without anyone .I know solenoid is not protected by the diode when switching of the master witch , but it was for one flight , taking care to switch off Efis , strobe and alternator prior to master switch.
Nothing to declare during the flight, voltage was between 14,4 and 14,6 .
So this single diode was able to set on fire wires , and incidently to induce overvoltage...
Click to expand...

It would be useful to 'show your work' (wiring diagram of the system). If the diode you're talking about is indeed a spike suppression diode on a contactor, it's very difficult to see how it could cause an overvoltage event. Burn a wire (due to a short to ground), yes, if that wire isn't properly protected for overload. (This implies a need to re-evaluate your system design, though.)

Overvoltage? Not so much. Sounds more like indicator error, or possibly multiple problems at once, and the actual OV problem got fixed inadvertently during troubleshooting.
 
yes

BillL said:
Can you say a little more about this. Is it as simple as indicated, just take two, solder in series, add terminals and cover with shrink wrap?

Any additional operational negatives to be aware of?

Thanks for posting - been reading VAF posts for many years, don't remember this failure mode or solution.
Click to expand...

Yes that simple. Most people figure a diode drop is 0.7 v but in reality they are closer to.3 when under heavy load, so the droo from the two diodes in series is still about .7v
 
14bkg06.png
[/IMG]
Here is how I made connections , according to excellent Vertical Power documentation.
The diode and master relay , from Vans can't be badly connected as there is a little ring for master switch contact and large one far BAT contact,
 
Never do this

trackdom said:
14bkg06.png
[/IMG]
Here is how I made connections , according to excellent Vertical Power documentation.
The diode and master relay , from Vans can't be badly connected as there is a little ring for master switch contact and large one far BAT contact,
Click to expand...

I would Never do this with unfused power. Fuses are there to prevent fires. This circuit should have a fuse or circuit breaker in line somewhere. If the diode or contactor shorts, or if something gets across the contactor terminals, you not only lose the circuit fed by the contactor, you also probably have a fire to deal with.

6/21/17 Update:
I would rather see two diodes in series as a minimum. If you are a high flier and wish to protect further, then one could add a resettable a circuit breaker, or two fuses in parallel to protect against one going bad and opening contactor. JMO
 
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You are probably right, it is strange this is not mentioned in the documentation ...What type of fuse? And value?
Thanks
 
Fuse sizing

trackdom said:
You are probably right, it is strange this is not mentioned in the documentation ...What type of fuse? And value?
Thanks
Click to expand...

I am just getting involved with experimental aircraft, so dont know what formulas the aircraft industry uses for fuse sizing. In my day job, i would normally pick a fuse rated for twice the nominal current. Alternately the size can be slightly below the wire current rating. If you are a high flyer, i would use the high altitude wire derating current.
 
no fuses on grounds needed

I'm not an expert, but I did read the aeroelectic connection book, and they say that you don't need fuses on grounds, and don't show them in their excellent wiring diagrams.

HuKOO1z.png
 
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I asked the question to Vertical power , and they say to act as plans say. I prefer to do as they tell , I am not an expert, they are !
 
It would be safer to have a fuse

If the internal coil develops a short it's possible to pass a large enough current through the ground wire going to the master to cause the wire to overheat. Most of the time the coil just opens on a short but I'm not sure that is always the case.
 
jj13 said:
If the internal coil develops a short it's possible to pass a large enough current through the ground wire going to the master to cause the wire to overheat. Most of the time the coil just opens on a short but I'm not sure that is always the case.
Click to expand...

It would seem quite unlikely that a short in solenoid could pass high current down the activation circuit (i.e. the ground that is referenced above). That would be a really bad design. I doubt this circuit is fused in the certified world either and that is likely the case because the risk off high current here is not significant. Further, if it shorted, opening the master switch would open the circuit to ground, ending the event.

Larry
 
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lr172 said:
It would seem quite unlikely that a short in solenoid could pass high current down the activation circuit (i.e. the ground that is referenced above). That would be a really bad design. I doubt this circuit is fused in the certified world either and that is likely the case because the risk off high current here is not significant. Further, if it shorted, opening the master switch would open the circuit to ground, ending the event.

Larry
Click to expand...

The solenoid is a device similar to other electrical devices in the plane that draw power from the electrical system. What makes a solenoid different from lets say a radio? A radio can have an internal short that if unprotected could induce an electrical overload, are you saying that is not possible with a solenoid? As some of us replace components with new technology, sold-state relays for example failure modes my even be more pronounced.
 
Well actually a short in the diode may not be that inconceivable and it appears to be the case here. While we don't have very complete information in this case but it appears to have resulted in the damage to the master control wire.

If you have a 4 terminal contactor then the positive supply to the coil may be fused instead but for a 3 terminal version it probably is advisable to fuse the ground connection since the positive supply is a high current path. An alternative may be a fusible link that B&C sells.

If in this case if the diode shorted and the wire burned. I would suggest replacement of the wire and the switch since it may still be operating, but may have also been damaged.
 
rapid_ascent said:
Well actually a short in the diode may not be that inconceivable and it appears to be the case here. While we don't have very complete information in this case but it appears to have resulted in the damage to the master control wire.

If you have a 4 terminal contactor then the positive supply to the coil may be fused instead but for a 3 terminal version it probably is advisable to fuse the ground connection since the positive supply is a high current path. An alternative may be a fusible link that B&C sells.

If in this case if the diode shorted and the wire burned. I would suggest replacement of the wire and the switch since it may still be operating, but may have also been damaged.
Click to expand...

I suppose this depends upon the diode used. a typical 1N400X diode is rated for 1 amp and has leads that are a thinner gauge than 20 AWG wire. I don't believe the leads on those diodes can pass enough current to create problems on a 20 AWG wire. Under heavy cuurent loads, the diode leads will separate and act as a fusible link, protecting the 20 AWG wire and the switch. Even a 3A diode will provide adequate protection for 20 AWG wire.

Larry
 
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jj13 said:
The solenoid is a device similar to other electrical devices in the plane that draw power from the electrical system. What makes a solenoid different from lets say a radio? A radio can have an internal short that if unprotected could induce an electrical overload, are you saying that is not possible with a solenoid? As some of us replace components with new technology, sold-state relays for example failure modes my even be more pronounced.
Click to expand...

Actually it is not that similar to other electrical devices. It is a simple relay, with a plunger approach vs an arm. If you examine a sectional view of the device, you will see the that coil circuitry (used to create the magentic field that pulls the contactors together) is physically and electrically separated from the contacts and their circuitry. I cannot see how any portion of the contacted path can come in contact with coil path, short of molten and running metal inside the device. I suppose anything is possible and the wire feed from the main input to the coil could short inside the case. That coil draws about an amp. Good design practice would mean using a 24 AWG or 26 AWG wire to feed it, possibly thinner. This allows that wire to act as a fusible link if a upstream short occurs. You are assuming you can get 10's or 100's of amps from the batt input to the activation lug and I'm suggesting that is not likely possible.

My experience is that Bob Knuckles is a pretty knowledgeable guy. If this were really a risk, I have all confidence that he would be recommending a fuse in this circuit.

This applies to mechanical solenoids. I know little about the makeup of solid state relays/contactors and their potential failure modes. However, I believe that any properly designed relay or contactor has protections to keep coil current in the neighborhood of the coils rated current and prevent contacted currrent from reaching the coil circuit. the whole point of a relay is to let low current control circuits activate and deactivate a higher current circuit. Interna protection must be in place to protect the low amperage circuit. That protection is properly sizing the internal wiring or traces to act as fusible links at reasonable current levels.

Larry
 
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Larry, you might need to clarify that a bit. You can use a fusible link (~4-6", protected with a fire proof sleeve), but certainly not use that size wire for the entire run, allowing the entire wire to be the fuse.
 
rv7charlie said:
Larry, you might need to clarify that a bit. You can use a fusible link (~4-6", protected with a fire proof sleeve), but certainly not use that size wire for the entire run, allowing the entire wire to be the fuse.
Click to expand...

I wasn't suggesting the use of a fusible link. Only suggesting that the smaller size of the diode leads would ACT as a fusible link if the diode body shorted across the leads, as suggested by another poster. However, I believe it is quite uncommon for a diode to short. It typically fails open, also preventing current flow. Either way I don't see how the diode can allow enough current to cause an issue for either the 20 AWG wire or the the switch unless you installed too large of a diode. The diode leads will melt and create an open (just like a fuse) long before the 20 AWG is in risk of danger. A fuse is nothing more than a short strand of wire that is sized to melt and open at a designed amperage level.

Further, within the interior of the solenoid will be a thin wire that bridges the Batt contact to one side of the coil. The other side of the coil goes to the small post. If designed properly, these internal wires will be in the 26 AWG range or thinner (designed to melt and open around 3-4 amps). These will also act as a fusible link in the event of an internal short, preventing dangerous current levels from harming the 20 AWG chasis wiring attached to it.

It is not a standard practice to fuse this lead from the solenoid to the mater switch because there is not a meaningful risk of current beyond the chasis wiring's rated capacity.

Larry
 
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