Bridge rectifier replacement

C

[email protected]

Jan 1, 1970
0
I have to replace a KBPC602 bridge rectifier. It is rated 200VRMS at
6.0 A. It is wired into the circuit using only the + and - terminals.
The AC connections are not used. If I were to build a bridge out of
four 6.0 amp 100V diodes, would I be able to directly replace this
device? Does the circuit basically require a 12.0A 200V device?
Conversely if I were to place four 3.0 amp 200V diodes in parallel
would that arrangement work also? Thanks. Lenny Stein, Barlen
Electronics.

G

GregS

Jan 1, 1970
0
I have to replace a KBPC602 bridge rectifier. It is rated 200VRMS at
6.0 A. It is wired into the circuit using only the + and - terminals.
The AC connections are not used. If I were to build a bridge out of
four 6.0 amp 100V diodes, would I be able to directly replace this
device? Does the circuit basically require a 12.0A 200V device?
Conversely if I were to place four 3.0 amp 200V diodes in parallel
would that arrangement work also? Thanks. Lenny Stein, Barlen
Electronics.

Probably just fine. You loose the sinking unless you use tab diodes.

greg

E

Eeyore

Jan 1, 1970
0
I have to replace a KBPC602 bridge rectifier. It is rated 200VRMS at
6.0 A. It is wired into the circuit using only the + and - terminals.
The AC connections are not used.

In which case it's not being used as a bridge rectifier !

What's the application ?

Graham

A

Arfa Daily

Jan 1, 1970
0
I have to replace a KBPC602 bridge rectifier. It is rated 200VRMS at
6.0 A. It is wired into the circuit using only the + and - terminals.
The AC connections are not used. If I were to build a bridge out of
four 6.0 amp 100V diodes, would I be able to directly replace this
device? Does the circuit basically require a 12.0A 200V device?
Conversely if I were to place four 3.0 amp 200V diodes in parallel
would that arrangement work also? Thanks. Lenny Stein, Barlen
Electronics.

That's a strange use of a bridge. You've effectively got two diodes in
series plus two diodes in series, with the two strings formed, in parallel.

Arfa

H

Homer J Simpson

Jan 1, 1970
0
Does the circuit basically require a 12.0A 200V device?

S

Sofie

Jan 1, 1970
0
Lenny:
How is the bridge wired into the circuit? ..... as a half wave rectifier?
.... or ??
Might I suggest that hooking up diodes in parallel without low ohm
(equalizing) series resistors is not a good practice.... in fact, it is not
a good practice to hook up diodes in parallel even with series resistors.
Also if diodes are hooked up in series to increase voltage rating... fairly
high ohm parallel equalizing resistors should be used.
All of this is needed because no two semiconductor junctions are the same
and one or the other diode will hog the current or voltage. Most good
designs AVOID these kind of hook ups altogether and go with a single diode
device.
You should look at the circuit and determine what the rough current draw is
and what voltage it should handle...... if the circuit current permits a
single 6 amp "barrel" diode may suffice or a heat sinkable diode in a To-220
or Stud-mount case with a higher current rating could be used.
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - -

E

[email protected]

Jan 1, 1970
0
Captain Video,
This is a strange way to connect a rectifier diode, unless the design
called for a high current diode and only a bridge was handy.
Is this a "commercial" piece of equipment or is is someone's homebrew
design. .
Take a close look at the circuitry and components and fairly easily
you should be able to determine the approximate voltage and current
needed for the replacement (single) diode if in fact it is used as a
rectifier in a half wave configuration.

If there is something else going on here with the circuitry and it is
a commericial design and it has worked that way for years then why not
just replace it with an "original" 6A, 200V bridge or even a higher
voltage and current rating as these bridges are commonly available,
even from scrapped televisions and other devices.

In either case, you should consider Sofie's textbook argument
regarding parallel and series diode connections, he is absolutely
correct with what he stated.

electricitym

A

Arfa Daily

Jan 1, 1970
0
Homer J Simpson said:
Yeah, I was thinking that too, but couldn't quite get my head around it. I'm
not sure how they rate bridges. When it's being used normally, two diodes
are in conduction at any one time, in what amounts to a series circuit, so
the quoted current rating must only be the rating of any one diode. However,
as there are two diodes series'd into the circuit, the voltage rating should
be twice that of any one diode, so when a bridge is quoted at 200v, is each
individual diode 100v ? That would make the arrangement that's being
enquired about, still 200v, but at twice the current, as all four diodes
will be in conduction. Either way, should be easy enough to pick up either a
direct replacement bridge, or 200v 3A diodes, which should be plenty enough.

Arfa

H

Homer J Simpson

Jan 1, 1970
0
Yeah, I was thinking that too, but couldn't quite get my head around it.
I'm not sure how they rate bridges. When it's being used normally, two
diodes are in conduction at any one time, in what amounts to a series
circuit, so the quoted current rating must only be the rating of any one
diode. However, as there are two diodes series'd into the circuit, the
voltage rating should be twice that of any one diode, so when a bridge is
quoted at 200v, is each individual diode 100v ? That would make the
arrangement that's being enquired about, still 200v, but at twice the
current, as all four diodes will be in conduction. Either way, should be
easy enough to pick up either a direct replacement bridge, or 200v 3A
diodes, which should be plenty enough.

I imagine it's all about dissipation so the amps should be the same.

C

[email protected]

Jan 1, 1970
0
I imagine it's all about dissipation so the amps should be the same.

The application is an Elmo school overhead projector. The unit uses an
82v 360W bulb. It looks like the bridge, that is, two sets of diodes
in series with those two sets then in parallel, is in series with the
lamp. When these bridges short, (usually just one diode in the bridge
shorts) the bulbs burn out. In this application it is used as a half
wave rectifier. I thought that perhaps by using a bridge in this
manner they were attempting to get a higher voltage drop across the
unit and less voltage to the bulb as there would be two junction
drops instead of one. However with those junctions then paralleled
with the other diodes maybe it would be a wash. Lenny.

A

Arfa Daily

Jan 1, 1970
0
The application is an Elmo school overhead projector. The unit uses an
82v 360W bulb. It looks like the bridge, that is, two sets of diodes
in series with those two sets then in parallel, is in series with the
lamp. When these bridges short, (usually just one diode in the bridge
shorts) the bulbs burn out. In this application it is used as a half
wave rectifier. I thought that perhaps by using a bridge in this
manner they were attempting to get a higher voltage drop across the
unit and less voltage to the bulb as there would be two junction
drops instead of one. However with those junctions then paralleled
with the other diodes maybe it would be a wash. Lenny.
So is this arrangement hooked directly to the incoming line voltage ( I
guess 110v in your neck of the woods ? ) The drops across the diodes will be
insignificant in this application, I feel, and it will be all about 'area
under the curve' from the half wave rectification that the diode is
performing. A bulb rated at 82v ( RMS ?? ) 360W will pull about four and a
half amps RMS when hot, more when it's cold. I guess that this is what this
is all about. The designer figured that it was a good way to get a high
voltage high current diode in a compact package with enough surface area to
self-cool. As it's a schools unit and probably subject to all sorts of
health and safety regulations, I think that I would feel inclined to stick
with the way it was designed originally, possibly uprating the specs of the
bridge, if they are a regular failing point.

Arfa

J

Jitt

Jan 1, 1970
0
The application is an Elmo school overhead projector. The unit uses an
82v 360W bulb. It looks like the bridge, that is, two sets of diodes
in series with those two sets then in parallel, is in series with the
lamp. When these bridges short, (usually just one diode in the bridge
shorts) the bulbs burn out. In this application it is used as a half
wave rectifier. I thought that perhaps by using a bridge in this
manner they were attempting to get a higher voltage drop across the
unit and less voltage to the bulb as there would be two junction
drops instead of one. However with those junctions then paralleled
with the other diodes maybe it would be a wash. Lenny.

It may be the other way around. I have seen a small bridge used as
protecion. When the big projector bulb fails, there's a big current
spike, blowing the diode.

FWIW on ESP website (Rod Elliot), the 100W guitar amp
project, power supply schematic shows a "protector" bridge.

T

**THE-RFI-EMI-GUY**

Jan 1, 1970
0
Why do I get the idea that the designer was seeking a proprietary lamp
voltage so that they could soak the school boards for $200 replacement bulbs? Arfa said: So is this arrangement hooked directly to the incoming line voltage ( I guess 110v in your neck of the woods ? ) The drops across the diodes will be insignificant in this application, I feel, and it will be all about 'area under the curve' from the half wave rectification that the diode is performing. A bulb rated at 82v ( RMS ?? ) 360W will pull about four and a half amps RMS when hot, more when it's cold. I guess that this is what this is all about. The designer figured that it was a good way to get a high voltage high current diode in a compact package with enough surface area to self-cool. As it's a schools unit and probably subject to all sorts of health and safety regulations, I think that I would feel inclined to stick with the way it was designed originally, possibly uprating the specs of the bridge, if they are a regular failing point. Arfa -- Joe Leikhim K4SAT "The RFI-EMI-GUY"© "Treason doth never prosper: what's the reason? For if it prosper, none dare call it treason." "Follow The Money" ;-P C [email protected] Jan 1, 1970 0 Why do I get the idea that the designer was seeking a proprietary lamp voltage so that they could soak the school boards for$200 replacement
bulbs?

--
Joe Leikhim K4SAT

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P- Hide quoted text -

- Show quoted text -

Funny that the back EMF theory as a cause of destroyed bridges had
occurred too. Maybe I should install a small snubber, (perhaps a 1.0
ohm resistor in series with say a .10uf capacitor across the bulb. BTW
the bulb is very common and about 9.00 dollars. Lenny.

M

[email protected]

Jan 1, 1970
0
I have to replace a KBPC602 bridge rectifier. It is rated 200VRMS at
6.0 A. It is wired into the circuit using only the + and - terminals.
The AC connections are not used. If I were to build a bridge out of
four 6.0 amp 100V diodes, would I be able to directly replace this
device? Does the circuit basically require a 12.0A 200V device?
Conversely if I were to place four 3.0 amp 200V diodes in parallel
would that arrangement work also? Thanks. Lenny Stein, Barlen
Electronics.

Using devices in series parallel is an effective way to fail-safe
things. Any one of those diodes can short or go o/c and the rectifier
still works as a rectifier.

And you say its failed before - sounds like the designer was trying to
reduce the failure rate instead of getting to the bottom of the cause.

I dont know what type of bulb it uses, or why the BR is failing, but
if its a filament bulb, arc over will draw huge currents at fail time.
Fitting an mcb in the line to the bulb may save the diode sometimes,
maybe. This must be a magnetic one, not a thermal one.

Of course you could eliminate the problem entirely by using a mains
voltage bulb and losing the BR.

I'm not sure a CR across the bulb would help, as its current surge
thats killing the BR. But if you do that then 100 ohms and 0.1u in
series is typical.

Another solution would be to lose the BR and fit a capacitor dropper
with a fixed R to drop a bit of the power. Now the C&R will prevent
any monster currents when the bulb dies. Just a small R, not much
Pdiss and an X rated cap. The R helps limit peak i, though with the
lightbulb's R you should be fine with just the C alone.

NT

J

James Sweet

Jan 1, 1970
0
Using devices in series parallel is an effective way to fail-safe
things. Any one of those diodes can short or go o/c and the rectifier
still works as a rectifier.

And you say its failed before - sounds like the designer was trying to
reduce the failure rate instead of getting to the bottom of the cause.

I dont know what type of bulb it uses, or why the BR is failing, but
if its a filament bulb, arc over will draw huge currents at fail time.
Fitting an mcb in the line to the bulb may save the diode sometimes,
maybe. This must be a magnetic one, not a thermal one.

Of course you could eliminate the problem entirely by using a mains
voltage bulb and losing the BR.

I'm not sure a CR across the bulb would help, as its current surge
thats killing the BR. But if you do that then 100 ohms and 0.1u in
series is typical.

Another solution would be to lose the BR and fit a capacitor dropper
with a fixed R to drop a bit of the power. Now the C&R will prevent
any monster currents when the bulb dies. Just a small R, not much
Pdiss and an X rated cap. The R helps limit peak i, though with the
lightbulb's R you should be fine with just the C alone.

NT

For some reason a lot of projectors seem to use oddball voltage bulbs.
If the bridge is failing a lot, I'd try installing a buck transformer if
there's room. You'd probably have to series a couple of secondary
windings to get the odd 38V drop though.

S

Sofie

Jan 1, 1970
0
Lenny:
Now that you have finally given us more information I would be inclined to
suggest that you replace the bridge with a "like and kind" exact OEM part or
a possibly upgraded voltage and current version.
Since this is in a commercially designed overhead projector and used in a
school, you would be best advised NOT to CHANGE the original design or use
anything other than a "factory" part.
Bridges of this nature and rating are readily available so stop wasting time
posting to the newsgroup and get online and order the proper part.... get
the proper and safe part that was originally installed.

The one word that comes to my mind is "liability".

Daniel Sofie
Electronics Supply & Repair
- - - - - - - -

C

[email protected]

Jan 1, 1970
0
Lenny:
Now that you have finally given us more information I would be inclined to
suggest that you replace the bridge with a "like and kind" exact OEM part or
a possibly upgraded voltage and current version.
Since this is in a commercially designed overhead projector and used in a
school, you would be best advised NOT to CHANGE the original design or use
anything other than a "factory" part.
Bridges of this nature and rating are readily available so stop wasting time
posting to the newsgroup and get online and order the proper part.... get
the proper and safe part that was originally installed.

The one word that comes to my mind is "liability".

Daniel Sofie
Electronics Supply & Repair
- - - - - - - -

- Show quoted text -

I talked to a tech at Elmo this morning and asked about the use of the
bridge as opposed to using a large single diode. He said that the
engineers found that the DC when looked at with a scope from the
bridge was cleaner than the output of just a single diode. Does that
sound possible? As far as wasting anyones time, if I was I appoligize.
I thought we were having an interesting discussion. Lenny

A

Arfa Daily

Jan 1, 1970
0
Sofie said:
Lenny:
Now that you have finally given us more information I would be inclined to
suggest that you replace the bridge with a "like and kind" exact OEM part
or
a possibly upgraded voltage and current version.
Since this is in a commercially designed overhead projector and used in a
school, you would be best advised NOT to CHANGE the original design or use
anything other than a "factory" part.
Bridges of this nature and rating are readily available so stop wasting
time
posting to the newsgroup and get online and order the proper part.... get
the proper and safe part that was originally installed.

The one word that comes to my mind is "liability".

Daniel Sofie
Electronics Supply & Repair
- - - - - - - -
I absolutely agree, and already said exactly the same several posts above

Arfa

S

[email protected]

Jan 1, 1970
0
Lenny:
We were and are having an interesting discussion and thread and no,
you are NOT wasting anyone's time.
Instead of trying to find ways to jury rig a substitute for a common
and readily available bridge rectifier you should have just procured
one and installed it and be done with it.... saying that, perhaps the
only person's time "wasted" was your own.
Until your later posting that revealed it was for a commercially
manufactured overhead projector being used in a school environment you
had everyone guessing about how the bridge was being used in the
circuit, in fact, you never revealed the circuit in any kind of detail
as it related to equipment, configuration, voltage, amps, etc... even
As you know, none of us can read minds and no one has a working
crystal ball on the newsgroup so the more information an OP can give,
the better and more straight forward will be the answers.
The best answer for fixing the overhead projector is to replace the
bridge with an OEM part..... obviously other parts and configurations
will work, BUT if something goes wrong and the projector malfunctions
and causes smoke and fire damage... particuarly in a school
environment.... your LIABILITY will be much more exposed if you
DIDN'T use replacement parts that were used in the original
manufacture. Enough said.
Lenny, please feel free to start up more "interesting"
conversations... it sure beats the spammers and the trolls and their
filthy subject matter. Electronics discussions are much more
enjoyable than that crap.
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - -

snipped:
As far as wasting anyones time, if I was I appoligize.
I thought we were having an interesting discussion.
Lenny
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