Diodes in parallel

[Jack// ani]

Hi there,

Can I increase the current rating of my psu which is having 1N4007
diode bridge rectifier, to 2amps by placing similar diodes in parallel
to each diode in the bridge rectifier? Actually my pcb is not having
enough room for 1N540X series diode, but I can easily put 1N4007 diodes
in parallel!

Thanks for any help

 

[Jamie]

Jack// ani wrote:

Hi there,

Can I increase the current rating of my psu which is having 1N4007
diode bridge rectifier, to 2amps by placing similar diodes in parallel
to each diode in the bridge rectifier? Actually my pcb is not having
enough room for 1N540X series diode, but I can easily put 1N4007 diodes
in parallel!

Thanks for any help

Nope.

since paired diodes need to be match perfectly to insure both share an
equal load it's not practical.
one diode may start conducting before the other, and this happens the
other diode normally does not hardly even or at all conduct. thus one is
doing all of the work.

 

[sparky]

"Jack// ani" <nospam4u_jack@yahoo.com> wrote in message
news:1107625117.825467.147910@o13g2000cwo.googlegroups.com...

Hi there,

Can I increase the current rating of my psu which is having 1N4007
diode bridge rectifier, to 2amps by placing similar diodes in parallel
to each diode in the bridge rectifier? Actually my pcb is not having
enough room for 1N540X series diode, but I can easily put 1N4007 diodes
in parallel!

Just increasing the diodes will not increase the capacity of the psu.
You must also increase the rating of the other components.

Thanks for any help

 

[JanRwl]

No. Minute differences between the diodes will cause one to handle all or
nearly all of the current. The "parallel second diode" will not conduct much
at all.
Use 1N5402 diodes, even if you have to "stand 'em up" off the PCB. Some clever
fiddling should get 'em all-four in place!

 

[Ray]

"Jack// ani" <nospam4u_jack@yahoo.com> wrote in
news:1107625117.825467.147910@o13g2000cwo.googlegroups.com:

Hi there,

Can I increase the current rating of my psu which is having 1N4007
diode bridge rectifier, to 2amps by placing similar diodes in parallel
to each diode in the bridge rectifier? Actually my pcb is not having
enough room for 1N540X series diode, but I can easily put 1N4007 diodes
in parallel!

Thanks for any help

Listen to Nike, just do it. You "can easily put the diodes in parallel" so
do it and take current reading thru both your 1n4007 diodes at the same
time to see if one conducts more or not. Post your results, sounds
interesting.

--
-Ray

 

[John Popelish]

Jack// ani wrote:

Hi there,

Can I increase the current rating of my psu which is having 1N4007
diode bridge rectifier, to 2amps by placing similar diodes in parallel
to each diode in the bridge rectifier? Actually my pcb is not having
enough room for 1N540X series diode, but I can easily put 1N4007 diodes
in parallel!

Thanks for any help

Whether the power supply can provide more amperes is not just
dependent on the diodes. But to address the diode question,
paralleling with a similar type will allow a bit higher current
without destroying the diodes, but not twice as much. The diodes will
not share the current exactly and each will heat the ambient air near
he other, so each will get hotter for its share of the current than if
it were operating at that current without its partner near by.

Even alone, a 1 amp diode is not normally expected to deliver 1 amp
average, except under the most ideal of conditions (leads heat sunk to
25 C a short distance from the body, for example).

--
John Popelish

 

[Don Bruder]

In article <4205195E.59FC5115@rica.net>,
John Popelish <jpopelish@rica.net> wrote:

Jack// ani wrote:

Hi there,

Can I increase the current rating of my psu which is having 1N4007
diode bridge rectifier, to 2amps by placing similar diodes in parallel
to each diode in the bridge rectifier? Actually my pcb is not having
enough room for 1N540X series diode, but I can easily put 1N4007 diodes
in parallel!

Thanks for any help

Whether the power supply can provide more amperes is not just
dependent on the diodes. But to address the diode question,
paralleling with a similar type will allow a bit higher current
without destroying the diodes, but not twice as much. The diodes will
not share the current exactly and each will heat the ambient air near
he other, so each will get hotter for its share of the current than if
it were operating at that current without its partner near by.

Even alone, a 1 amp diode is not normally expected to deliver 1 amp
average, except under the most ideal of conditions (leads heat sunk to
25 C a short distance from the body, for example).

John...
This fellow's question brings to mind a similar concept I had over on an
automotive group - Alternators are fairly tough little beasties - Most
of the guts of them are all but indestructible short of physical damage.
But a very common failure mode for them is for the diode trios to barf
if/when they're asked to try to charge a mostly-dead battery.

I had the thought not too long ago that paralleling multiple diodes per
"trio position" should give at least some added "anti-fry" protection in
terms of how dead a battery the alternator can charge without burning
itself (or more specifically, its diode trios) up.

Since it's such a common failure mode, and cheap to repair (compared to
"buy a new/reman alternator and replace as a unit") the benefit would
potentially be huge to the person doing such a mod to their alternator.

Now, it sounds like you're saying that rather than improving the
situation, such a setup would likely be an actively BAD thing?

Is the "extra heating" issue still a significant problem in a forced-air
environment such as what I'd have in my particularly alternator? (diode
trios in it are heat-sinked, and are the first thing that the air, being
actively pulled in through the back of the alternator by its built-in
fan, encounters)

It would seem to me, at least at first glance, that "stacking" multiple
diode trios (let's say to three diodes per phase and polarity, for a
total of 18 discrete diodes (versus the standard 6 -- two, one for each
polarity, on each of three phases)) in this beast would be beneficial,
if only in terms of "Well, that one over there cooked, but I'm still
doing fine, and so is the one next to me" style backup - should one
fail, the remaining two for that phase pick up the slack. (Of course,
with such an arrangement, if there's an overload big enough to blow one
of the diodes, I think it unlikely that the other two would survive as
they were forced to pick up even more of the load that managed to burn
out one of the three already...)

Which doesn't even start to address the whole "Since three of them are
sharing the load (however unevenly they might be portioning it out
amongst themselves) there should be little or no reason for one to fail
in the first place" concept...

Gimme a sanity-check on this idea, would ya, John?

--
Don Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004.
Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
subject unless it comes from a "whitelisted" (pre-approved by me) address.
See <http://www.sonic.net/~dakidd/main/contact.html> for full details.

 

[John Popelish]

Don Bruder wrote:

In article <4205195E.59FC5115@rica.net>,
John Popelish <jpopelish@rica.net> wrote:

Jack// ani wrote:

Hi there,

Can I increase the current rating of my psu which is having 1N4007
diode bridge rectifier, to 2amps by placing similar diodes in parallel
to each diode in the bridge rectifier? Actually my pcb is not having
enough room for 1N540X series diode, but I can easily put 1N4007 diodes
in parallel!

Thanks for any help

Whether the power supply can provide more amperes is not just
dependent on the diodes. But to address the diode question,
paralleling with a similar type will allow a bit higher current
without destroying the diodes, but not twice as much. The diodes will
not share the current exactly and each will heat the ambient air near
he other, so each will get hotter for its share of the current than if
it were operating at that current without its partner near by.

Even alone, a 1 amp diode is not normally expected to deliver 1 amp
average, except under the most ideal of conditions (leads heat sunk to
25 C a short distance from the body, for example).

John...
This fellow's question brings to mind a similar concept I had over on an
automotive group - Alternators are fairly tough little beasties - Most
of the guts of them are all but indestructible short of physical damage.
But a very common failure mode for them is for the diode trios to barf
if/when they're asked to try to charge a mostly-dead battery.

I had the thought not too long ago that paralleling multiple diodes per
"trio position" should give at least some added "anti-fry" protection in
terms of how dead a battery the alternator can charge without burning
itself (or more specifically, its diode trios) up.

Since it's such a common failure mode, and cheap to repair (compared to
"buy a new/reman alternator and replace as a unit") the benefit would
potentially be huge to the person doing such a mod to their alternator.

Now, it sounds like you're saying that rather than improving the
situation, such a setup would likely be an actively BAD thing?

I didn't say anything about a bad thing. I said that two 1 amp diodes
in parallel and also in close proximity should not be expected to
deliver 2 amps. They will deliver somewhat more than one diode would
be capable of, just not twice as much.

Is the "extra heating" issue still a significant problem in a forced-air
environment such as what I'd have in my particularly alternator? (diode
trios in it are heat-sinked, and are the first thing that the air, being
actively pulled in through the back of the alternator by its built-in
fan, encounters)

Forced air definitely redefines close proximity.

It would seem to me, at least at first glance, that "stacking" multiple
diode trios (let's say to three diodes per phase and polarity, for a
total of 18 discrete diodes (versus the standard 6 -- two, one for each
polarity, on each of three phases)) in this beast would be beneficial,
if only in terms of "Well, that one over there cooked, but I'm still
doing fine, and so is the one next to me" style backup - should one
fail, the remaining two for that phase pick up the slack. (Of course,
with such an arrangement, if there's an overload big enough to blow one
of the diodes, I think it unlikely that the other two would survive as
they were forced to pick up even more of the load that managed to burn
out one of the three already...)

Blown diodes are normally short circuits, so they will not take turns
as you describe. A better way to protect the alternator might be to
add a resistor between the regulator and the armature winding, so that
the excitation current was limited to a value slightly less than the
design maximum. Since the alternator normally uses way less than the
maximum possible excitation, this would affect its operation only at
lowest speed and during overload situations.

I am working on a new regulator for my motorcycle that includes an
adjustable current limit for the excitation, but for a completely
different reason.

Which doesn't even start to address the whole "Since three of them are
sharing the load (however unevenly they might be portioning it out
amongst themselves) there should be little or no reason for one to fail
in the first place" concept...

There would be less heat in any one of the parallel diodes than if
only one were carrying the whole current. The problem is that the
hottest diode tends to have the lowest forward drop and hog most of
the current, making sharing worse. So all sets need similar heat
sinking.

Gimme a sanity-check on this idea, would ya, John?

--
Don Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004.
Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
subject unless it comes from a "whitelisted" (pre-approved by me) address.
See <http://www.sonic.net/~dakidd/main/contact.html> for full details.

--
John Popelish

 

[Don Bruder]

In article <4205296A.1BE5D30F@rica.net>,
John Popelish <jpopelish@rica.net> wrote:

Don Bruder wrote:

In article <4205195E.59FC5115@rica.net>,
John Popelish <jpopelish@rica.net> wrote:

Jack// ani wrote:

Hi there,

Can I increase the current rating of my psu which is having 1N4007
diode bridge rectifier, to 2amps by placing similar diodes in parallel
to each diode in the bridge rectifier? Actually my pcb is not having
enough room for 1N540X series diode, but I can easily put 1N4007 diodes
in parallel!

Thanks for any help

Whether the power supply can provide more amperes is not just
dependent on the diodes. But to address the diode question,
paralleling with a similar type will allow a bit higher current
without destroying the diodes, but not twice as much. The diodes will
not share the current exactly and each will heat the ambient air near
he other, so each will get hotter for its share of the current than if
it were operating at that current without its partner near by.

Even alone, a 1 amp diode is not normally expected to deliver 1 amp
average, except under the most ideal of conditions (leads heat sunk to
25 C a short distance from the body, for example).

John...
This fellow's question brings to mind a similar concept I had over on an
automotive group - Alternators are fairly tough little beasties - Most
of the guts of them are all but indestructible short of physical damage.
But a very common failure mode for them is for the diode trios to barf
if/when they're asked to try to charge a mostly-dead battery.

I had the thought not too long ago that paralleling multiple diodes per
"trio position" should give at least some added "anti-fry" protection in
terms of how dead a battery the alternator can charge without burning
itself (or more specifically, its diode trios) up.

Since it's such a common failure mode, and cheap to repair (compared to
"buy a new/reman alternator and replace as a unit") the benefit would
potentially be huge to the person doing such a mod to their alternator.

Now, it sounds like you're saying that rather than improving the
situation, such a setup would likely be an actively BAD thing?

I didn't say anything about a bad thing. I said that two 1 amp diodes
in parallel and also in close proximity should not be expected to
deliver 2 amps. They will deliver somewhat more than one diode would
be capable of, just not twice as much.

OK, clarification noted. So does it make sense to expect that
"unloading" any single diode by splitting the load across (as per my
previous example) two more diodes wired in parallel with it would have a
positive effect as far as "diode-death prevention" is concerned?

Basically, I'm working under the concept of "A draw that would kill a
"lone" diode should (generally speaking, and for the sake of discussion,
ignoring the possibility/effects of uneven load division/thermal runaway
that you mention later on) be insignificant when three diodes are
splitting the load."

Do I need a new concept?

Is the "extra heating" issue still a significant problem in a forced-air
environment such as what I'd have in my particularly alternator? (diode
trios in it are heat-sinked, and are the first thing that the air, being
actively pulled in through the back of the alternator by its built-in
fan, encounters)

Forced air definitely redefines close proximity.

Kinda figured it would Seems to me that heat would become (at least
for practical purposes) a non-issue in such a situation.

It would seem to me, at least at first glance, that "stacking" multiple
diode trios (let's say to three diodes per phase and polarity, for a
total of 18 discrete diodes (versus the standard 6 -- two, one for each
polarity, on each of three phases)) in this beast would be beneficial,
if only in terms of "Well, that one over there cooked, but I'm still
doing fine, and so is the one next to me" style backup - should one
fail, the remaining two for that phase pick up the slack. (Of course,
with such an arrangement, if there's an overload big enough to blow one
of the diodes, I think it unlikely that the other two would survive as
they were forced to pick up even more of the load that managed to burn
out one of the three already...)

Blown diodes are normally short circuits, so they will not take turns
as you describe.

Hmmm... not a concept that I had thought about - That would tend to
throw a bit of a wrench in the works, wouldn't it? Again, though, it
comes back to the whole "Shouldn't the load that would blow a single
diode be seen as effectively insignificant by three similarly
rated/heat-sinked/etc diodes wired in parallel?" - If the diode is
unloaded enough by paralleling multiple "copies" of itself in its
position in the circuit that even under ridiculaous loading, no single
diode of the group should fail in the first place, it's pretty much
irrelevant that a given diode "usually fails shorted" when it dies, no?

A better way to protect the alternator might be to
add a resistor between the regulator and the armature winding, so that
the excitation current was limited to a value slightly less than the
design maximum. Since the alternator normally uses way less than the
maximum possible excitation, this would affect its operation only at
lowest speed and during overload situations.

I am working on a new regulator for my motorcycle that includes an
adjustable current limit for the excitation, but for a completely
different reason.

May I be so bold as allow my curiousity to run wild long enough for me
to enquire about what this completely different reason is?

Which doesn't even start to address the whole "Since three of them are
sharing the load (however unevenly they might be portioning it out
amongst themselves) there should be little or no reason for one to fail
in the first place" concept...

There would be less heat in any one of the parallel diodes than if
only one were carrying the whole current. The problem is that the
hottest diode tends to have the lowest forward drop and hog most of
the current, making sharing worse. So all sets need similar heat
sinking.

Ahhh, yes... Good ol' thermal runaway.

Makes good sense, now that I consider it. That would seem to indicate
that one would want to carefully match the diodes being used to
construct the "trio set" - A task with the potential to be anywhere from
"trivial - I did it three times while sleeping last week" to "outright
impossible", I imagine...

--
Don Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004.
Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
subject unless it comes from a "whitelisted" (pre-approved by me) address.
See <http://www.sonic.net/~dakidd/main/contact.html> for full details.

 

[John Popelish]

Don Bruder wrote:

John Popelish <jpopelish@rica.net> wrote:
Don Bruder wrote:
John...
This fellow's question brings to mind a similar concept I had over on an
automotive group - Alternators are fairly tough little beasties - Most
of the guts of them are all but indestructible short of physical damage.
But a very common failure mode for them is for the diode trios to barf
if/when they're asked to try to charge a mostly-dead battery.

I had the thought not too long ago that paralleling multiple diodes per
"trio position" should give at least some added "anti-fry" protection in
terms of how dead a battery the alternator can charge without burning
itself (or more specifically, its diode trios) up.

Since it's such a common failure mode, and cheap to repair (compared to
"buy a new/reman alternator and replace as a unit") the benefit would
potentially be huge to the person doing such a mod to their alternator.

Now, it sounds like you're saying that rather than improving the
situation, such a setup would likely be an actively BAD thing?

I didn't say anything about a bad thing. I said that two 1 amp diodes
in parallel and also in close proximity should not be expected to
deliver 2 amps. They will deliver somewhat more than one diode would
be capable of, just not twice as much.

OK, clarification noted. So does it make sense to expect that
"unloading" any single diode by splitting the load across (as per my
previous example) two more diodes wired in parallel with it would have a
positive effect as far as "diode-death prevention" is concerned?

A positive effect, yes. A multiple of the current capability equal to
the multiple of diodes, no.

Basically, I'm working under the concept of "A draw that would kill a
"lone" diode should (generally speaking, and for the sake of discussion,
ignoring the possibility/effects of uneven load division/thermal runaway
that you mention later on) be insignificant when three diodes are
splitting the load."

Do I need a new concept?

No. Paralleling can be some use. But a bigger diode and more
effective heat sinking may do better.

Is the "extra heating" issue still a significant problem in a forced-air
environment such as what I'd have in my particularly alternator? (diode
trios in it are heat-sinked, and are the first thing that the air, being
actively pulled in through the back of the alternator by its built-in
fan, encounters)

Forced air definitely redefines close proximity.

Kinda figured it would Seems to me that heat would become (at least
for practical purposes) a non-issue in such a situation.

It would seem to me, at least at first glance, that "stacking" multiple
diode trios (let's say to three diodes per phase and polarity, for a
total of 18 discrete diodes (versus the standard 6 -- two, one for each
polarity, on each of three phases)) in this beast would be beneficial,
if only in terms of "Well, that one over there cooked, but I'm still
doing fine, and so is the one next to me" style backup - should one
fail, the remaining two for that phase pick up the slack. (Of course,
with such an arrangement, if there's an overload big enough to blow one
of the diodes, I think it unlikely that the other two would survive as
they were forced to pick up even more of the load that managed to burn
out one of the three already...)

Blown diodes are normally short circuits, so they will not take turns
as you describe.

Hmmm... not a concept that I had thought about - That would tend to
throw a bit of a wrench in the works, wouldn't it? Again, though, it
comes back to the whole "Shouldn't the load that would blow a single
diode be seen as effectively insignificant by three similarly
rated/heat-sinked/etc diodes wired in parallel?" - If the diode is
unloaded enough by paralleling multiple "copies" of itself in its
position in the circuit that even under ridiculaous loading, no single
diode of the group should fail in the first place, it's pretty much
irrelevant that a given diode "usually fails shorted" when it dies, no?

If paralleling prevents failure, then, yes, you don't have to deal
with failure.

A better way to protect the alternator might be to
add a resistor between the regulator and the armature winding, so that
the excitation current was limited to a value slightly less than the
design maximum. Since the alternator normally uses way less than the
maximum possible excitation, this would affect its operation only at
lowest speed and during overload situations.

I am working on a new regulator for my motorcycle that includes an
adjustable current limit for the excitation, but for a completely
different reason.

May I be so bold as allow my curiousity to run wild long enough for me
to enquire about what this completely different reason is?

I have a motorcycle that has its idle speed loaded variably by the
alternator. If I adjust the idle when the battery is under heavy
charge, then it races after the battery is fully charged. If I adjust
the idle when the battery is fully charged, it has trouble stalling
the next time the battery needs charge. I am going to make the
regulator a switcher for improved efficiency and include a current
limit so that the low RPM maximum torque load can be reduced. I also
expect it to keep the battery more accurately charged, compared to
what the electromechanical regulator accomplishes, now.

Which doesn't even start to address the whole "Since three of them are
sharing the load (however unevenly they might be portioning it out
amongst themselves) there should be little or no reason for one to fail
in the first place" concept...

There would be less heat in any one of the parallel diodes than if
only one were carrying the whole current. The problem is that the
hottest diode tends to have the lowest forward drop and hog most of
the current, making sharing worse. So all sets need similar heat
sinking.

Ahhh, yes... Good ol' thermal runaway.

Makes good sense, now that I consider it. That would seem to indicate
that one would want to carefully match the diodes being used to
construct the "trio set" - A task with the potential to be anywhere from
"trivial - I did it three times while sleeping last week" to "outright
impossible", I imagine...

--
John Popelish

 

[Don Bruder]

In article <42058629.64DB1171@rica.net>,
John Popelish <jpopelish@rica.net> wrote:

A positive effect, yes. A multiple of the current capability equal to
the multiple of diodes, no.

Right. Got that part. Pessimistically assuming that you'd actually LOSE
some capacity to the paralleling (For the sake of discussion, let's pull
a number out of the air and say each diode would only handle 75% of its
rated load) that would still give 125% more "head space" over that which
is available from a single diode in that position when the group is
considered as a unit. One would HOPE that an alternator rated for 55
amps is never going to be asked to supply nearly 125! Of course, should
that ever happen with the "ganged" diodes, the failure point may well
end up being the coil cooking open, rather than a diode frying...

Basically, I'm working under the concept of "A draw that would kill a
"lone" diode should (generally speaking, and for the sake of discussion,
ignoring the possibility/effects of uneven load division/thermal runaway
that you mention later on) be insignificant when three diodes are
splitting the load."

Do I need a new concept?

No. Paralleling can be some use. But a bigger diode and more
effective heat sinking may do better.

No argument there. "How much better, and for what price - in both
dollars and difficulty?" probably becomes an issue quickly. As of yet, I
haven't figured out what the price on one of the diodes from the trio
would be. (For that matter, I haven't yet figured out what the installed
diodes actually are.) I would expect that, as is usually the case when
messing about with rectifiers and regulators, moving up in current
capacity implies moving up to a bigger price tag.

May I be so bold as allow my curiousity to run wild long enough for me
to enquire about what this completely different reason is?

I have a motorcycle that has its idle speed loaded variably by the
alternator. If I adjust the idle when the battery is under heavy
charge, then it races after the battery is fully charged. If I adjust
the idle when the battery is fully charged, it has trouble stalling
the next time the battery needs charge. I am going to make the
regulator a switcher for improved efficiency and include a current
limit so that the low RPM maximum torque load can be reduced. I also
expect it to keep the battery more accurately charged, compared to
what the electromechanical regulator accomplishes, now.

Sounds like a fun mess with the idle... NOT!

Electromechanical? As in the old-style "solenoid and gap" type? Oi,
vey... those things always were a mess. I gotta give 'em credit - They
worked amazingly well. But keeping them working correctly... Wotta
headache...

--
Don Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004.
Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
subject unless it comes from a "whitelisted" (pre-approved by me) address.
See <http://www.sonic.net/~dakidd/main/contact.html> for full details.