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Default Indicator relay post-mortem.

Its a 2-terminal relay for a motorcycle, after adding an earth lead so I
could fit a car type; I then discovered that the intermittent operation was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was blameless.

The circuit could probably be adapted for 6V with a logic level MOSFET - but
would need 2 in parallel to handle twice the current (don't forget filament
cold resistance surge!).




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Default Indicator relay post-mortem.

On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead so I
could fit a car type; I then discovered that the intermittent operation was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was blameless.

The circuit could probably be adapted for 6V with a logic level MOSFET - but
would need 2 in parallel to handle twice the current (don't forget filament
cold resistance surge!).


Now *that* is an application for a 555!


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
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Default Indicator relay post-mortem.


"John Larkin" wrote in message
...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead so I
could fit a car type; I then discovered that the intermittent operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was blameless.

The circuit could probably be adapted for 6V with a logic level MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!



Whoever designed that may have had reservations about putting a 555 into the
automotive envirenment - a quick google shows the bipolar 555 as having a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to withstand
the reservoir voltage as any externally applied reverse voltage would be
clamped by the MOSFET body diode (maybe they got a better price break on
quantity 4007s).


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Default Indicator relay post-mortem.

On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
.. .
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead so I
could fit a car type; I then discovered that the intermittent operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was blameless.

The circuit could probably be adapted for 6V with a logic level MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!



Whoever designed that may have had reservations about putting a 555 into the
automotive envirenment - a quick google shows the bipolar 555 as having a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to withstand
the reservoir voltage as any externally applied reverse voltage would be
clamped by the MOSFET body diode (maybe they got a better price break on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb thing
(with a depletion mosfet?!) might be prudent.


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
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Default Indicator relay post-mortem.


"John Larkin" wrote in message
...
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
. ..
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead so I
could fit a car type; I then discovered that the intermittent operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was blameless.

The circuit could probably be adapted for 6V with a logic level MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!



Whoever designed that may have had reservations about putting a 555 into
the
automotive envirenment - a quick google shows the bipolar 555 as having a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would be
clamped by the MOSFET body diode (maybe they got a better price break on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb thing
(with a depletion mosfet?!) might be prudent.



I'm curious to see a schematic of a depletion MOSFET in that application?

At first blush I'm thinking maybe an oscillator driving a negative O/P diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!




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Default Indicator relay post-mortem.

On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
.. .
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead so I
could fit a car type; I then discovered that the intermittent operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was blameless.

The circuit could probably be adapted for 6V with a logic level MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555 into
the
automotive envirenment - a quick google shows the bipolar 555 as having a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would be
clamped by the MOSFET body diode (maybe they got a better price break on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb thing
(with a depletion mosfet?!) might be prudent.



I'm curious to see a schematic of a depletion MOSFET in that application?

At first blush I'm thinking maybe an oscillator driving a negative O/P diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG




--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
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Default Indicator relay post-mortem.


"John Larkin" wrote in message
...
On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
. ..
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
m...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead so
I
could fit a car type; I then discovered that the intermittent
operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was
blameless.

The circuit could probably be adapted for 6V with a logic level
MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555 into
the
automotive envirenment - a quick google shows the bipolar 555 as having
a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and
the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would be
clamped by the MOSFET body diode (maybe they got a better price break on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb thing
(with a depletion mosfet?!) might be prudent.



I'm curious to see a schematic of a depletion MOSFET in that application?

At first blush I'm thinking maybe an oscillator driving a negative O/P
diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG



The bean-counters at the firm that made it would freak out if the engineers
showed them that!


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Default Indicator relay post-mortem.

On Wed, 6 Jun 2012 16:37:47 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
.. .
On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
...
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
om...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead so
I
could fit a car type; I then discovered that the intermittent
operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was
blameless.

The circuit could probably be adapted for 6V with a logic level
MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555 into
the
automotive envirenment - a quick google shows the bipolar 555 as having
a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and
the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would be
clamped by the MOSFET body diode (maybe they got a better price break on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb thing
(with a depletion mosfet?!) might be prudent.


I'm curious to see a schematic of a depletion MOSFET in that application?

At first blush I'm thinking maybe an oscillator driving a negative O/P
diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG



The bean-counters at the firm that made it would freak out if the engineers
showed them that!


Yeah, it makes better financial sense to sell something that's a few
cents cheaper, and let the buyers deal with the blown fet gates.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
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Default Indicator relay post-mortem.

On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin
wrote:

On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
. ..
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
m...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead so I
could fit a car type; I then discovered that the intermittent operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was blameless.

The circuit could probably be adapted for 6V with a logic level MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555 into
the
automotive envirenment - a quick google shows the bipolar 555 as having a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would be
clamped by the MOSFET body diode (maybe they got a better price break on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb thing
(with a depletion mosfet?!) might be prudent.



I'm curious to see a schematic of a depletion MOSFET in that application?

At first blush I'm thinking maybe an oscillator driving a negative O/P diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG


Correction, the main mosfet drain has to move a notch left, before the
diode.


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
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Default Indicator relay post-mortem.


"John Larkin" wrote in message
...
On Wed, 6 Jun 2012 16:37:47 +0100, "Ian Field"
wrote:


"John Larkin" wrote in
message
. ..
On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
m...
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
news:6c7qs797vd7f771hct3n65emcf93iqaktb@4ax. com...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead
so
I
could fit a car type; I then discovered that the intermittent
operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was
blameless.

The circuit could probably be adapted for 6V with a logic level
MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555
into
the
automotive envirenment - a quick google shows the bipolar 555 as
having
a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and
the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would
be
clamped by the MOSFET body diode (maybe they got a better price break
on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb thing
(with a depletion mosfet?!) might be prudent.


I'm curious to see a schematic of a depletion MOSFET in that
application?

At first blush I'm thinking maybe an oscillator driving a negative O/P
diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG



The bean-counters at the firm that made it would freak out if the
engineers
showed them that!


Yeah, it makes better financial sense to sell something that's a few
cents cheaper, and let the buyers deal with the blown fet gates.



The relay was date stamped 98 - which is older than the bike I took it off.
So it had already been salvaged from elsewhere and fitted to the bike as
replacement for whatever went brfore it.

As I stated in my original post, I wrongly blamed the relay for intermittent
operation which turned out to be a corroded connector hidden under the tank
(in my defence; it was much easier to swap the relay than take the tank
off).

At the end of the day: the astable they've used is cheaper and more reliable
than a 555 and all the extra gubbins to keep it safe in the automotive
environment.




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Default Indicator relay post-mortem.


"John Larkin" wrote in message
...
On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin
wrote:

On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
...
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
om...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead
so I
could fit a car type; I then discovered that the intermittent
operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was
blameless.

The circuit could probably be adapted for 6V with a logic level
MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555
into
the
automotive envirenment - a quick google shows the bipolar 555 as having
a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and
the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would
be
clamped by the MOSFET body diode (maybe they got a better price break
on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb thing
(with a depletion mosfet?!) might be prudent.


I'm curious to see a schematic of a depletion MOSFET in that application?

At first blush I'm thinking maybe an oscillator driving a negative O/P
diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG


Correction, the main mosfet drain has to move a notch left, before the
diode.



Wondered how long it'd take you to notice that.


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Default Indicator relay post-mortem.

On Wed, 6 Jun 2012 18:20:19 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
.. .
On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin
wrote:

On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
m...
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
news:6c7qs797vd7f771hct3n65emcf93iqaktb@4ax. com...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead
so I
could fit a car type; I then discovered that the intermittent
operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was
blameless.

The circuit could probably be adapted for 6V with a logic level
MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555
into
the
automotive envirenment - a quick google shows the bipolar 555 as having
a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V and
the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would
be
clamped by the MOSFET body diode (maybe they got a better price break
on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb thing
(with a depletion mosfet?!) might be prudent.


I'm curious to see a schematic of a depletion MOSFET in that application?

At first blush I'm thinking maybe an oscillator driving a negative O/P
diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG


Correction, the main mosfet drain has to move a notch left, before the
diode.



Wondered how long it'd take you to notice that.


Well thanks for not pummeling me with insults in the interim.


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
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Default Indicator relay post-mortem.


"John Larkin" wrote in message
...
On Wed, 6 Jun 2012 18:20:19 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
. ..
On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin
wrote:

On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
om...
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
news:6c7qs797vd7f771hct3n65emcf93iqaktb@4ax .com...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead
so I
could fit a car type; I then discovered that the intermittent
operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was
blameless.

The circuit could probably be adapted for 6V with a logic level
MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555
into
the
automotive envirenment - a quick google shows the bipolar 555 as
having
a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V
and
the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would
be
clamped by the MOSFET body diode (maybe they got a better price break
on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb
thing
(with a depletion mosfet?!) might be prudent.


I'm curious to see a schematic of a depletion MOSFET in that
application?

At first blush I'm thinking maybe an oscillator driving a negative O/P
diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG

Correction, the main mosfet drain has to move a notch left, before the
diode.



Wondered how long it'd take you to notice that.


Well thanks for not pummeling me with insults in the interim.



That's JF's & JT's job - and most of us have to endure their schoolyard
bully act!


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Default Indicator relay post-mortem.

On Wed, 6 Jun 2012 22:46:37 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
.. .
On Wed, 6 Jun 2012 18:20:19 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
...
On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin
wrote:

On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
news:ehlss71ic567t7f63tfsrggp0upabbdfr9@4ax. com...
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
news:6c7qs797vd7f771hct3n65emcf93iqaktb@4a x.com...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth lead
so I
could fit a car type; I then discovered that the intermittent
operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was
blameless.

The circuit could probably be adapted for 6V with a logic level
MOSFET -
but
would need 2 in parallel to handle twice the current (don't forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555
into
the
automotive envirenment - a quick google shows the bipolar 555 as
having
a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V
and
the
60V MOSFET is spec'ed for the automotive environment according to the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage would
be
clamped by the MOSFET body diode (maybe they got a better price break
on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will peak
detect and store any load dump spikes. So some sort of transzorb
thing
(with a depletion mosfet?!) might be prudent.


I'm curious to see a schematic of a depletion MOSFET in that
application?

At first blush I'm thinking maybe an oscillator driving a negative O/P
diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG

Correction, the main mosfet drain has to move a notch left, before the
diode.


Wondered how long it'd take you to notice that.


Well thanks for not pummeling me with insults in the interim.



That's JF's & JT's job - and most of us have to endure their schoolyard
bully act!


So, we finally have a thread where it's possible, actually possible,
that a 555 might be useful, and JF is MIA.


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
  #15   Report Post  
Posted to alt.binaries.schematics.electronic
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Posts: 1,405
Default Indicator relay post-mortem.


"John Larkin" wrote in message
...
On Wed, 6 Jun 2012 22:46:37 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
. ..
On Wed, 6 Jun 2012 18:20:19 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
m...
On Tue, 05 Jun 2012 19:52:15 -0700, John Larkin
wrote:

On Tue, 5 Jun 2012 20:35:23 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
news:ehlss71ic567t7f63tfsrggp0upabbdfr9@4ax .com...
On Tue, 5 Jun 2012 19:00:00 +0100, "Ian Field"
wrote:


"John Larkin" wrote in message
news:6c7qs797vd7f771hct3n65emcf93iqaktb@4 ax.com...
On Mon, 4 Jun 2012 18:41:30 +0100, "Ian Field"
wrote:

Its a 2-terminal relay for a motorcycle, after adding an earth
lead
so I
could fit a car type; I then discovered that the intermittent
operation
was
due to a corroded connector block hidden under the tank.

After breaking up the epoxy potting I found the old relay was
blameless.

The circuit could probably be adapted for 6V with a logic level
MOSFET -
but
would need 2 in parallel to handle twice the current (don't
forget
filament
cold resistance surge!).


Now *that* is an application for a 555!


Whoever designed that may have had reservations about putting a 555
into
the
automotive envirenment - a quick google shows the bipolar 555 as
having
a
16V Vcc limit & 18V for the 7555, the BC547B is good for about 45V
and
the
60V MOSFET is spec'ed for the automotive environment according to
the
datasheet.

Note however the 1kV rating of the 1N4007 they've used to isolate
the
reservoir from the MOSFET is somewhat superfluous, it only has to
withstand
the reservoir voltage as any externally applied reverse voltage
would
be
clamped by the MOSFET body diode (maybe they got a better price
break
on
quantity 4007s).


The fet gate is only rated for 20 volts, and the diode/cap will
peak
detect and store any load dump spikes. So some sort of transzorb
thing
(with a depletion mosfet?!) might be prudent.


I'm curious to see a schematic of a depletion MOSFET in that
application?

At first blush I'm thinking maybe an oscillator driving a negative
O/P
diode
pump to generate the pinch off bias.

Wouldn't do much for production costs though!



No, I meant that you could use a depletion fet in the load-dump
protection part, something like this:

https://dl.dropbox.com/u/53724080/Circuits/Blinker.JPG

Correction, the main mosfet drain has to move a notch left, before the
diode.


Wondered how long it'd take you to notice that.


Well thanks for not pummeling me with insults in the interim.



That's JF's & JT's job - and most of us have to endure their schoolyard
bully act!


So, we finally have a thread where it's possible, actually possible,
that a 555 might be useful, and JF is MIA.



I'm still not convinced a 555 is the best way to go - I'd put a stopper
resistor from the 555 O/P to the gate, then I could add a 16V zener from
gate to cathode of the isolating diode. that should nip any cummulative
spikes that try to push the reservoir voltage above the limit of Vcc.

In the failsafe condition; the indicators would be on longer than they
should, but the 555 should be safe enough.


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