Van's Air Force
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what is this ?
- Thread starter lawrence
- Start date
Diode
If you replace it pleae NOTE the ORIENTATION.
See the BAND on one end.
James
my old alternator had this device between 2 terminals on the backside.
any one know what it is? or if it is needed? i have a two wire external voltage regulator.
thanks for any and all replys.
If you replace it pleae NOTE the ORIENTATION.
See the BAND on one end.
James
Yes, it is a high current diode. Polarity is important, as mentioned.
vlittle
Well Known Member
I can't see the part number, but my guess is that it is zener diode installed as part of an overvoltage clamp. Clearly, it has been 'tripped' and is no longer functioning.
Neverless, if it it an OVP clamp, it may be the wrong place. Time to find a local guy with the nickname 'Sparky' or similar to help you work through this one.
If you can post the part number, I can confirm my hypothesis.
Neverless, if it it an OVP clamp, it may be the wrong place. Time to find a local guy with the nickname 'Sparky' or similar to help you work through this one.
If you can post the part number, I can confirm my hypothesis.
what is it
thank you for reply. the diode fell apart into about 3-4 pieces .
could not determine which end was connected ti the "b" terminal.
the other end is connected to an unmarked terminal adjacent .
the banded end goes to the "b" terminal ?
where to buy a new one?
thank you for reply. the diode fell apart into about 3-4 pieces .
could not determine which end was connected ti the "b" terminal.
the other end is connected to an unmarked terminal adjacent .
the banded end goes to the "b" terminal ?
where to buy a new one?
Diodes of that size are commonly used for arc suppression on relays and contactor coils. The banded end connects to the positive side of the coil. I do not know why an arc suppression diode would be connected to an alternator unless the field circuit is routinely shut off while the engine is running. The diode could have been intended for some other purpose, but only the installer knows.
DaleB
Well Known Member
No way to read the two digits that were below "53"? That would tell us exactly what it was. Could be a rectifier like a 1N5391, which seems not to make much sense where you found it, or a Zener like a 1N5353. Which would also leave me scratching my head a little, but it's hard to say.
what is it
my original problem was an overvoltage of 16 volts on the engine monitor.
i found alternator bearings very noisy. and this diode separated,nonfunctioing.
rebuilt alternator is ordered. and if i can obtain a new diode like this one. hoping that will fix my overvoltage.
i have replaced the cessna master switch, (no change). and checked numerous conections,(no change). and tightened the loose alternator belt, (no change).and replaced the 2 wire external voltage regulator,(no change).
i plan to replace the field switch at the panel next. as i suspect the new alternator and new diode will not cure the overvoltage.
any other checks recomended?
my original problem was an overvoltage of 16 volts on the engine monitor.
i found alternator bearings very noisy. and this diode separated,nonfunctioing.
rebuilt alternator is ordered. and if i can obtain a new diode like this one. hoping that will fix my overvoltage.
i have replaced the cessna master switch, (no change). and checked numerous conections,(no change). and tightened the loose alternator belt, (no change).and replaced the 2 wire external voltage regulator,(no change).
i plan to replace the field switch at the panel next. as i suspect the new alternator and new diode will not cure the overvoltage.
any other checks recomended?
Last edited:
vlittle
Well Known Member
A bad field switch will result in over voltages. There is an architectural issue with common aircraft regulators and alternators in that they are powered by the same circuit that senses the input voltage. A bad or resistive switch will lead to a voltage run-away.
Even the expen$ive 'built for airplane' alternators have this problem.
There is a simple design solution that I posted on this site several years ago... You may have to search.
wjb
Well Known Member
Does it have any evidence of burning or blistering? I can't tell in the photo. One thing to consider is that it failed due to vibration stresses, not necessarily due to over voltage. Zeners don't "trip" like a fuse; the reverse biased junction breaks down a certain design voltage (there is a wide range .. device dependent), and does not cause damage unless the reverse current is over the design limit (the damage due to heating). When operating normally, it acts as a poor man's voltage regulator, not allowing the terminal voltage to rise above the zener voltage.
This package is not designed for a high vibration environment.
PaigeHoffart
Well Known Member
A high current transient overload will cause an explosive case separation well before the heat from the die has time to propagate to the outside case. You might be able to smell it, but that's probably the only evidence you will find without a microscope.
In my experience, vibration failure normally manifests as metal fatigue right where the lead enters the case.
It is surprising that the system voltage was able to get that high. With under-cowl heating effects on the Zener, the avalanche voltage might have been in the 45V range. The other possibility is a forward bias event, perhaps from a reversed battery connection, or improper installation of the diode.
It's pretty safe to say the diode won't prevent most over voltage events. If you want that protection, I'd suggest a crowbar module from B&C.
Paige
