Not sure how to look up Diode number

Guest
I'm replacing the obsolete generator on one of my farm tractors with a
Delco Remy (Chevy) alternator. This is a 3 wire alternator with built in
regulator. One of the small wires need to connect to the ignition switch
with a diode in that wire. I found a drawing online for a much smaller
tractor and that one uses a 1N5408 Diode rated at 1000v 3A. However
someone who has wired these said that I need a 6A (minimum) diode. I
dont think the voltage needs to be 1000V on a 12V system, but I'd rather
oversize it so it dont burn out at the wrong time. So a 1000V 6A diode
would be ideal. Without just randomly choosing diode numbers and looking
them up, is there a method to find a similar diode to this 1N5408,
except get one rated at 6A (or more). I'm not sure how to look this up.
 
olds...@tubes.com wrote:

-------------------------

I'm replacing the obsolete generator on one of my farm tractors with a
Delco Remy (Chevy) alternator. This is a 3 wire alternator with built in
regulator. One of the small wires need to connect to the ignition switch
with a diode in that wire. I found a drawing online for a much smaller
tractor and that one uses a 1N5408 Diode rated at 1000v 3A. However
someone who has wired these said that I need a 6A (minimum) diode. I
dont think the voltage needs to be 1000V on a 12V system, but I'd rather
oversize it so it dont burn out at the wrong time. So a 1000V 6A diode
would be ideal. Without just randomly choosing diode numbers and looking
them up, is there a method to find a similar diode to this 1N5408,
except get one rated at 6A (or more). I'm not sure how to look this up.
Click to expand...

** Ever thought of using Google ?

" 1000V 6A diode " gets lots of hits.



..... Phil
 
On 12/18/2017 4:36 PM, Phil Allison wrote:
olds...@tubes.com wrote:

-------------------------

I'm replacing the obsolete generator on one of my farm tractors with a
Delco Remy (Chevy) alternator. This is a 3 wire alternator with built in
regulator. One of the small wires need to connect to the ignition switch
with a diode in that wire. I found a drawing online for a much smaller
tractor and that one uses a 1N5408 Diode rated at 1000v 3A. However
someone who has wired these said that I need a 6A (minimum) diode. I
dont think the voltage needs to be 1000V on a 12V system, but I'd rather
oversize it so it dont burn out at the wrong time. So a 1000V 6A diode
would be ideal. Without just randomly choosing diode numbers and looking
them up, is there a method to find a similar diode to this 1N5408,
except get one rated at 6A (or more). I'm not sure how to look this up.


** Ever thought of using Google ?

" 1000V 6A diode " gets lots of hits.



.... Phil

digikey selector guides
Click to expand...
 
On 19/12/2017 8:36 AM, Phil Allison wrote:
olds...@tubes.com wrote:

-------------------------

I'm replacing the obsolete generator on one of my farm tractors with a
Delco Remy (Chevy) alternator. This is a 3 wire alternator with built in
regulator. One of the small wires need to connect to the ignition switch
with a diode in that wire. I found a drawing online for a much smaller
tractor and that one uses a 1N5408 Diode rated at 1000v 3A. However
someone who has wired these said that I need a 6A (minimum) diode. I
dont think the voltage needs to be 1000V on a 12V system, but I'd rather
oversize it so it dont burn out at the wrong time. So a 1000V 6A diode
would be ideal. Without just randomly choosing diode numbers and looking
them up, is there a method to find a similar diode to this 1N5408,
except get one rated at 6A (or more). I'm not sure how to look this up.


** Ever thought of using Google ?

" 1000V 6A diode " gets lots of hits.



.... Phil
Click to expand...

Phil be prepared for the query "what's a google?"
 
wrote in message news:atmg3d9chhl7ah30t2fqq8kra7ganou2fq@4ax.com...

I'm replacing the obsolete generator on one of my farm tractors with a
Delco Remy (Chevy) alternator. This is a 3 wire alternator with built in
regulator. One of the small wires need to connect to the ignition switch
with a diode in that wire. I found a drawing online for a much smaller
tractor and that one uses a 1N5408 Diode rated at 1000v 3A. However
someone who has wired these said that I need a 6A (minimum) diode. I
dont think the voltage needs to be 1000V on a 12V system, but I'd rather
oversize it so it dont burn out at the wrong time. So a 1000V 6A diode
would be ideal. Without just randomly choosing diode numbers and looking
them up, is there a method to find a similar diode to this 1N5408,
except get one rated at 6A (or more). I'm not sure how to look this up.






*******************************************


http://uk.farnell.com/c/semiconductors-discretes/diodes/standard-recovery-rectifier-diodes?repetitive-reverse-voltage-vrrm-max=1kv&forward-current-if-av-=6a


Gareth.
 
On Tuesday, December 19, 2017 at 3:54:57 AM UTC-5, Gareth Magennis wrote:
> http://uk.farnell.com/c/semiconductors-discretes/diodes/standard-recovery-rectifier-diodes?repetitive-reverse-voltage-vrrm-max=1kv&forward-current-if-av-=6a

Sending such a perfect example of American Ingenuity and Creativity to a British site is pure evil! You should be ashamed of yourself!

Peter Wieck
Melrose Park, PA
 
On Tuesday, December 19, 2017 at 12:14:47 PM UTC-5, tschw...@gmail.com wrote:
> --. --- --- --. .-.. .

.... ..- .-. . --..-- / .-- .... -.-- / -. --- - ..--..

Peter Wieck
Melrose Park, PA
 
wrote in message
news:71258acc-83d1-4135-ab48-f56d318554d9@googlegroups.com...

On Tuesday, December 19, 2017 at 3:54:57 AM UTC-5, Gareth Magennis wrote:
> http://uk.farnell.com/c/semiconductors-discretes/diodes/standard-recovery-rectifier-diodes?repetitive-reverse-voltage-vrrm-max=1kv&forward-current-if-av-=6a

Sending such a perfect example of American Ingenuity and Creativity to a
British site is pure evil! You should be ashamed of yourself!

Peter Wieck
Melrose Park, PA



*********************************


I thank you, I thank you.


Gareth.
 
On Mon, 18 Dec 2017 17:04:57 -0800, mike <ham789@netzero.net> wrote:

On 12/18/2017 4:36 PM, Phil Allison wrote:
olds...@tubes.com wrote:

-------------------------

I'm replacing the obsolete generator on one of my farm tractors with a
Delco Remy (Chevy) alternator. This is a 3 wire alternator with built in
regulator. One of the small wires need to connect to the ignition switch
with a diode in that wire. I found a drawing online for a much smaller
tractor and that one uses a 1N5408 Diode rated at 1000v 3A. However
someone who has wired these said that I need a 6A (minimum) diode. I
dont think the voltage needs to be 1000V on a 12V system, but I'd rather
oversize it so it dont burn out at the wrong time. So a 1000V 6A diode
would be ideal. Without just randomly choosing diode numbers and looking
them up, is there a method to find a similar diode to this 1N5408,
except get one rated at 6A (or more). I'm not sure how to look this up.


** Ever thought of using Google ?

" 1000V 6A diode " gets lots of hits.



.... Phil

digikey selector guides
Or Mouser if he happens to be closer to Texas than Northern Minnesota.
Click to expand...
 
The 1000v rating is the PIV or Peak Inverse Voltage rating. It has nothing to do with the "12V system". That is the voltage the diode can stand up to in reverse bias mode.

Voltages like that can easily be generated in 12v systems, caused by load dumps, normal variations in switching on/off loads like motors & valves & solenoids, etc.

Generally a higher PIV rated diode will cost you more. There is no harm in using a diode with a higher than required PIV rating. But whether or not it's needed at all in your system is a question.

I can't see why you would need a 6A diode for the excite terminal. That terminal powers the field winding until the alternator is spinning fast enough to power itself. It generates the magnetic field. 6A is an awful lot of field strength. You should base your diode selection on the alternator you are using, not the tractor. Research your alternator.

Often there is no diode -- in fact typically there is just a light on the dash tied to B+ -- your "charge" light -- that provides the excite current when the key is on and the alternator is not yet turning. Once it's turning, the voltage on that alternator excite terminal rises to the B+ voltage, then you have B+ on both sides of the lamp, and the lamp turns off.

Maybe the diode is there to prevent current from flowing out of the alternator back to the ignition circuit -- but I fail to see the harm if that happens unless the voltages are very different. If you have no charge lamp, a suitable resistor will provide the same function, and limit current in that circuit.

Do a little more research before you believe everything you read or hear..... and I'm sure you can come up with a suitable solution.
 
In article <89f6d0b5-ad27-4f17-a513-f8aa66559f82@googlegroups.com>,
tschw10117@gmail.com says...
The 1000v rating is the PIV or Peak Inverse Voltage rating. It has nothing to do with the "12V system". That is the voltage the diode can stand up to in reverse bias mode.

Voltages like that can easily be generated in 12v systems, caused by load dumps, normal variations in switching on/off loads like motors & valves & solenoids, etc.

Generally a higher PIV rated diode will cost you more. There is no harm in using a diode with a higher than required PIV rating. But whether or not it's needed at all in your system is a question.

I can't see why you would need a 6A diode for the excite terminal. That terminal powers the field winding until the alternator is spinning fast enough to power itself. It generates the magnetic field. 6A is an awful lot of field strength. You should base your diode selection on the alternator you are using, not the tractor. Research your alternator.

Often there is no diode -- in fact typically there is just a light on the dash tied to B+ -- your "charge" light -- that provides the excite current when the key is on and the alternator is not yet turning. Once it's turning, the voltage on that alternator excite terminal rises to the B+ voltage, then you have B+ on both sides of the lamp, and the lamp turns off.

Maybe the diode is there to prevent current from flowing out of the alternator back to the ignition circuit -- but I fail to see the harm if that happens unless the voltages are very different. If you have no charge lamp, a suitable resistor will provide the same function, and limit current in that circuit.

Do a little more research before you believe everything you read or hear.... and I'm sure you can come up with a suitable solution.
Click to expand...

at one time for some alternators, not sure if this applies, the field
supply for the internal regualators was also used as a voltage
reference for regulation, meaning, once you had enough voltage there to
get the internal regulator working supplying the field some current, it
did so until the input voltage matched the internal Zener to reduce
current to the field.

Using a diode would make the alternator generate ~ .5 volt more output
and this worked because the input field voltage was coming from the same
source so it made it an easier place to reference final charge voltage..

I think in some EMC's it was an easier way to adjust voltage in a two
step instead of having a DAC in the system. Some systems placed a temp
sensor modual near the battery and could open the field circuit to allow
a diode drop in normal conditions, hot conditions it was by pass it to
force the output to drop .5 volts.

Just a thought..
 
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